Secondary Reactions and Partial Rate Factors in the Sulfonation of Chlorobenzene and Toluene

Brigham Young University BYU ScholarsArchive

Theses and Dissertations

1967-08-01

Secondary reactions and partial rate factors in the sulfonation of chlorobenzene and toluene

Ernest Arthur Brown Brigham Young University - Provo

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BYU ScholarsArchive Citation Brown, Ernest Arthur, "Secondary reactions and partial rate factors in the sulfonation of chlorobenzene and toluene" (1967). Theses and Dissertations. 8178. https://scholarsarchive.byu.edu/etd/8178

This Dissertation is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. SECONDARYREACTIONS AND PARTIAL RATE FACTORS IN THESULFONATION OF CHLOROBENZENEAND TOLUENE 'Y \ I v

A Dissertation

Submitted to the

Department of Chemistry Brigham Young University

In Partial F'ulfillment

of th~ Requirements for the

Doctor of Philosophy Degree

Ernest A. Brown

August, 1967 l -~ This dissertation, by Ernest A. Brown, is accepted in its present form by the Department of Chemistry of Brigham Young University as sati.sfying the dissertation requirement for the degree of Doctor of

Philosophy"

\,. ACKNOWLEDGMENTS

I wisn to extend my appreciation to the faculty and staff of Brigham Young Unive:r.sity for the assistance given during the course

of this work~ and to the U.S. Department of Health, Education 9 and

Welfare for the N. D. E. A. fellowship which helped support me while this work was being done.

A special thanks is extended to Dr. K. L. Nelson for his encouragement and assistance and for providing an atmosphere conducive

to indepem,dent. thought and individual achievement.

My deepest gratitude is also expressed to my wife and sons who have supported me with their patience and understanding.

iii TABLEOF CONrENTS

Page ACI

LIST OF TABLES. . . "' . . Ct • • ,, • • .. • • vi LIST OF FIGURES ix ...... • ✓ INTRODUCTION•.• 1

I. MECHANISMOF ELECTROPHILICAROMATIC SUBSTITUTION. 2 II. DIRECTIVEEFFECTS AND THE REACTIVITY-SELECTIVITY RELATIO?\"SH~P. • • • • • • • • • . • • •.• , • • 11 III. ELECTROPHILICSUBSTITUTION REACTIONS INVOLVIllG CRLOROBENZENE. . . . • • . . • . . • • • 18

IV. MECHANISMOF AROMATICSULFONATION. • 25 V. PURPOSEAND PROCEDURE OF THE U~JESTIGATION. 34

VI. RESULTSAND DISCUSSION: •. O O O O •. • • o 36

Competitive. Sulfonation in the Benzene·· Chlorobenzene System Competitive Sulfonation in the Toluene- Benzene System Isomer Distribution for the Sulfonation of Chlorobenzene Isomer Distributions for the Competitive Sulfonaticm of Toluene and Benzene Partial Rate Factors for the Sulfonati.on o.f Toluene and Chlorobenze.ne

VII. CONCLUSIONSA~'!O RECOMMENDATIONS. 85

VIII. EXPERIME:~'TALPROCEDURES. • • oooe•oooo 89

Preparation of Sodium£-,~- and E- Chlorobenzene:sulfon.stes Preparation 0£ Derivatives Prepa.ra.t.ion of :Radioacti.ve, Sulfor Di.oxide

iv Page

Preparation of Radioactive Benzene Purification of Benzene, Chlorobenzene, and Toluene Sulfonation Procedure Analysis of Reaction Products of Isomer Di.stri.bution Experiments Analysis of Products of Competitive Reactions

IX. EXPERIMENTALDATA AND•CALCULATED RESULTS. 109

Isomer Distribution Data Competitive Sulfonation Data: Benzene- Chlorobenzene System Test of Thermodynamic vs, Kinetic Control Mole Fraction of BS as a Function of (Mole Fraction B1)_/ (S03) Product Composition as a Function of so3 Concentration Comparison of Actual BS and CS Values with Those Predicted for no Secondary Reactions -Sulfonation of Toluene-Benzene Mixtures Comparison of Predicted and Actual TS and BS Values in Constant Ti/Bi Experiments Relative Concentrations of Primary and Secondary Sulfonations Isomer Distribution in Competiti·11e Reactions

APPENDIX. o O O O O e • • • • • 0 • • • • 0 140

I. COMPUTERPROGRAMS 140

A, Calculation of kB/kc B. Calculation of Mole Fraction Values C. Calculation of BS,CS, and R Assuming no Secondary Reactions D. Calculation of BS,CS, and R from Constant Bi/Ci. Experiments E" Calculation of BS,TS, and R from Constant Ti/Bi Experiments Fo Calculation of Relative Contributions of Primary and Secondary Reactions G. Isomer Distribution in Competitive Reactions

II. RESEARCHPROPOSAL •• 151 LIST OF REFERENCES•••• , 157

V LIST OF TABLES

Table Page

1. Electrophilic Aromatic Substitution Reactions on Chlorobenzene ...... 19

2. Typical Magnitudes for pf in Reactions on Toluene,, • • • . . • . • • 23

-3. Relative Rates a,s a. Function of Initial Benzene- Chlorobenzene Ratio ..•.. 38

4. Test of Thermodynamic vs. Kinetic Control. . 41

5. Relati,re Rates for Experiments with Varying so3 Concentrations 43

6. Product Composition as a Function of so3 Concentration at Constant Bi/Ci· .••• 44

7. Determination of kB/kc from Extrapolated Values of BS and CS....•.•...• 54

8. Comparison of Actt:1.al Values of BS and CS with Those Predicted for Sulfonation with no Secondary Reactions . 57

9. Comparison of Actual vs. Predicted BS,CS, and BS/CS Values for B1/Ci = 0.708 Data ...• 60

10. Competitive Sulfonations in the Toluene-..,__ Benzene System . • . • • • • • • • . • • • 64

11. Relat:l've Rates Calculated from Extrapolations in the Benzene=Toluene System. • • • • • • • 68

12. Comparison of Ac:t1.1alvs. Predicted Products from Ti/Bi~ 0.858 and T1/Bi ~ 0.279 Experiments • 69

13. Rel.ati•1e Con.t'.".'ibuti•ons of Primary and Secondary Reactioos on the Toluene-Benzene System. • , • . , 71

14. Isomer Dist:eibutic,n for the Sulfonation of ChlorobenzenE!. , , . • . • . 72

vi Table Page

15. Variation in Isomer Distribution with Percent Toluene·conversion in Cerfontain's Sulfonation of Neat Toluene with so3 at 2~5o Co ., o o • • • • • • • • • • • .. • • • 73

16. Isomer Distribution and Relative Rates for Cerfontain's Competitive Sulfonation of Benzene·~Toluen.e Mixtures at 25° C. 75 17. Ortho/Para Ratios for the Sulfonation of Chlo~obenzene and Benzene .••••••• . . . . 77 18. Isomer Distribution as a Function of S03 Concentration in Toluene-Benzene Competitive Sulfonations. • . . . . • • • . • • 80

19. Partial Rate Factors .• 81

20. Melting Points of S-Benzylisothiouronium Derivatives of the Isomeric Chlorobenzene- su:lfonates ...... • . • . .. . • . . . • . 92 ,. 21., Melting Points of _E-Toluidine Derivatives of the Isomeric Chlorobenzenesulfonates. • • 92

22. Experimental Conditions for Isomer Distribution Experiments . • • . . • • • • • • . • • • • . 109

23. Conditions for Dilution of Isotopes • 109

2.4. Counting Data for Isomer Distribution Experiments • • • • • • • • • • . 110

25. Summary of Avexa.ge Values for Counting Data 0 ~ • • 113

26. Suumary of Isomer Distribution Results. 115

27. Experimental Conditions for Competitive Sulfonation of Benzene=Chlorobenzene Mixtures 116

28. Counting Data for Competitive Sulfonation l!:xperiments in Benzene-Chlorobenzene Mb:tures 118

29. Calculated Values for. Competitive Sulfonation Experiments i'r! Benzene-Chlo:robenzene Mixtures 120

30. Err.or Limits for Calculation of kB/kc . , . . 121

vii Table Page

31. Data for Thermodynamic vs. Kinetic Control Test • • 0 • • ...... 122 32. Calculations of Mole Fraction Values for

Fig. 7 . • o • • • • • • • • • o • • • 1l • • • 123

33. Data for Computer Program to Calculate BS and CS in the Absence of Secondary Reactions 127

34. Data for Comparison of BS and CS with Values Calculated on the Basis of no Secondary Reactions. . OC100000••···•··· 128

35. Experimental Conditions for the Competitive Sulfonat.ion of Benzene-Toluene Mixtures. • • 129

36. Analyti.c:al Data for Experiments 21-P and 22-P. . 130

37. Counting Data for Toluene-Benzene Competitive Sulfonation.s .. , . • . . • . . • • . . • . • 131 38. Data Points from TS/BS vs. so Concentration Curves . . • . . • • . • • . 3 . . • . • • • . 132

39. Absorbance and Absorptivity Values for Standard UV Curves. . • • • . • • • • • • • • • 138

40. Absorbance Values of Competitive Sulfon.ation

Samples 4;11 " • • • • • • • e • • " • • • • o • 139 '

viii LIST OF FIGURES

Figu:re Page

L Nelson and Brown's Mechanism for Electrophilic Aromatic Substitution • • • . • . • • • • • • • . . 6 2. Reaction Energy Profile for a Syrmnetrical Substitution Reaction in Which Formation of a ct' Complex is Rate Determining •.•. 7

3. Reaction Energy Profile for a Substitution Reaction in Which 71-Complex Formation is Rate Determining, ...••••.•..••. 9

4. The Selectivity Relationship for Toluene and Proposed E~tension to Other Monosubstituted

Benzenes Q o .. ;) • • • • • • • o • • o • 15 s. Potential Energy Profiles for Substitutions Where (?""'-Complex Formation is Rate Determin-· ing (I) and ff-Complex Formation is Rate Determining (II). . • • . • . . • . . . . 16 6. Relationship of log Pf to log pf/mf for a Series of Electrophilic Substitutions on

·chlorobenze:ne • . • . • . • • • o e O • 0

7. Apparent Relative Rates as a Function of Initial Benzene=Chlorobenzene Ratio •.• 39

8. Mole Fraction of BS as a Function of Mole Fraction Bi/(S03) .• • • • • • • • • • • 42

9. Ratio of Benzen.e-to Chlorobenzene-Sulfonates in Product at Constant Bf/Ci as a Function of Concentration. of S03. • • • • • • • • • . • . • 45

10. Moles of Product Formed as a Function of so3 Concentration ...•.••••• • • 0 • • 53 11. kT/kB as a :Pu.netion. of Bi/Ti for the Sulfonation of Benzene-Toluene Mixtures with _S03 in Liquid s02, T : -12.5° C. . • • • • • • 62

ix F.igu:re Page

12. Apparent k.r/kB as a Function of T1/B1 for the Sulfonation of Benzene-Toluene Mixtures with so3 in Liquid so2 at T : -12.5° C. • • • • • • 63 13. Variation of TS/BS as a Function of so3 Concentration •.••••••••••• . . . . 65

14. BS and TS as Functions of so3 Concentration 67 15. Ie:0t:op;e E:j{change Reactor...... 93 14 16. Vacuum Line for c Benzene Preparation •. . . . . 95

17. Sulfonatioo. Apparatus ., •• 0 • • • • • • • • • • Q 97

X INTRODUCTION

Reactions involving aromatic compounds have been studied extensively since it was first discovered th'lt benzene reacts to yield subst:itl\lltion rather than addition products. A la:rge amount of information has 'been amassed about electrophilic aromatic substit,!tion

:r:eactions which serves as a basis for many important industrial and laboratory procedures., In addition, theoretical organic chemistry owes mue;h t:o these studies since many important concepts con.ce:n:1ing indu~tive effects, resonance, linear free energy relationships, and the rea~tivity=selectivity principle - to name just a few - have been evolved or tested in aromatic systems. A number. of recent reviews are available which surrmarize the current state of knowledge concerning 5s88~90,91 t h e c h emistry o f· aromatic systems.

Despite t:he considerable work that has been done~ there still remain many questions to be answered. Although there is general agreement about the broad outline of the mechanism of electrophilic aromatic substitution, there are still many details to be resolved, particularly with regard to the nature of intermediates and transition states. There are also some specific reactions which do not fit the general patterns of reactivity and selectivity which should be investigated further"

1 MECJE!Al,1ISMOF ELECTROPHILIC AROMATIC SU:BSTITUTION

Ele,c:trophilic aromatic substitution reactions can conceivably occur by two mechanisms -a-synchronous one-step mechanism (Reaction 1) or a mul'tistep mechanism involving the formation of an intermediate which temporarily disrupts the resonance of the ring {Reaction 2).

(l)

I , \ 0. E H I

>- (2)

In the first mechanism, I is ·a- -·-----~transition state; while in the second I 83 mechanism.9 II represents a true intermediateo Melander studied the nitration of tritiated benzene~ nitrobenzene, toluene, b:r.omobenzene:1 and othei compounds and observed a negligable kinetic isotope effect"

A one-step mechanism would require a kinetic isotope effect since a

C-H bond must be broken in the rate determining step. Mechanism 2 would require a kinetic:isotope effect only if the second step, in which the proton is lost from the ring, were rate controlling. Later

2 3

69 isotope effect studies 9 ,51 •64 •86 and salt effect studies tend to substantiate Melander 1 s conclusion that Mechanism 2 is correct for the nitration of many aromatic systems. Perhaps the most dramatic evidence for the fo:nnation of an addition intermediate has been the isolation of se·\J'e:r.al intermediate complexes. At low temperatures, nitryl fluoride, benzotrifluoride~ and boron trifluoride form a 1: 1: 1 colored crysta.lline complex which has been assigned Structure III. 94

III IV

On heatingj the complex decomposes to yield benzotrifluoride, HF3 and BF • Si!\.1.::em-n.itrobenzenetrifluoride is the product of the normal 3 nitration of benzotrifluoride, it seems reasonable that the cation of complex III is the intermediate for the reaction. Similarlyj a stable complex of mesitylene, ethylfluoride, and boron trifluoride (IV) has 94 been isolated. The only difference between a reaction intermediate an.d a rea;etion product is a matter of. relative stability and so the pr«:lbable existence o.f such intermediates as II may be considered to be established., Currently~ there is general agreement that reaction 2 represents the gross features of the mechanism for electrophilic aromatic substi.tution. 4

To understand the more subtle features of the mechanism, it is necessary to understand the interactions between the electrophile and the: aromatic ring as the two species make contact and bon.d with each other. It has been known for some time that aromatic compounds can form complexes with electrophilic substances, and the inter.actions betwE:en the electrophile and aromatic ring seem to vary from vecy weak to very strong, depending on the properties of the species involved. 89 Mulliken has deyelope~ a complex system for classifying the various possible types of interactions. The types most often mentioned in

disc:uss:i.on:s of ar01natic substitution mechanisms are '71' 'complexes 9

/7'complexes and charge-transfer complexes.

The /ff complexes are considered to be loose complexes in which the electrophilic substance is weakly associated with the electron cloud of the aromatic compound and is not uniquely associated with . I any particular aromatic carbon atom. Such complexes have been indicated

0 ~ b e t ween b enzeno:i. a compoun d s an d s il ver i on, 2 u~1n\j ~ 11 r~al ogens ~ 52,76 1 and ma.ny other substances. These complexes are generally unstable 3

give little or moderate changes in TN spectra 9 are colo:rless 3 and do 5,88,90 not conduct an electric current, Another characteristi~ is 88 that no deuterium exchange is observed when deuterium chloride is involved in 1f'·-complex formation with an aromatic substance.

In contrast,crcomplexes feature much stronger interactions between the electrophile and aromatic ring. These complexes are characterized by i.ntense color in the visible region, high electrical conductivity, rapid exchari.ge wi.th deuterium chlol'ide, and a relatively high degree of stability. 88 The isolatable boron trifluoride complexes 5 pr.·eviou.sly mentioned would be considered ~complexes. The ~ complex is assumed to have a fully formed 0--- bond to one of the aromatic carboil atoms which is thought to be essentially sl hybridized.

Charge=transfer complexes might be visualized as intermediate be.tween 1f' and ercomplexes although the term is sometimes loosely used and the distinction between charge-transfer complexes and o-" c,omplexes is not always obvious. Charge=transfer complexes are usually rep:r,e~.en.ted as resonance hybrids between (7""-bonded and non-bonded 21 , , canonical forms. R, D. Brown suggests that an aromatic-electrophile charge-transfer complex involves a resonance hybrid of a series of bonds involving the electrophile and each conjugated atom in the a:romatic compound, but that one of these bonds is significantly stronger than the other.·s. Typical representations of the three types of complexes are· as follows~

E E E+, I I +Ar-B ~ A:r=H

11 Complex (J COinplex Charge·~T:rans fer Complex

. Each of the above tiypes· of complexes has been suggested as an intermediate in elect:rophilic aromatic substitution reacti(())ns.

As in many mechanistic disputes~ the same basic structural formula- tions a:re often proposed by different author.ss but agreement cannot be :reached a';, to whether a given structure represents an intermediate or a t:ra.nsition state. A generalized mechanism for elect:rophilic 88 aromatic substitution has been presented by Ne.lson and Brcrwn and ! 6

i.s presented in Figure 1. As the attacking electrophile approaches

the a:r.omatic: compound, it is first believed to become involved with

thB Ting's electron. cloud to form a '71"•complex. In Figu~e 1~ ZB

~+ OZB--,- v- Z +B· (3) 1'(ZB) y~ (4) n z Q-'

o·~ (5) z z 1r (HB)

Fig. L~=Nelson and B!'own's

is a :rQ:iei.gentwhich can contribute the electr.ophile Z.f. to the ring.

In some ca.:ses the elecetrophile z+,may e:dst .free in solution and fo:rm a 1f' complex directly. The 11'complex ZB then can rearrange to a

+ ; I to different 1T'complex (Z ) which in ,turn converts the rf.I complex.

A p:not:oi:?,m9.y tnen be eliminated through thei' subsequent formation of

7f complexes B+ and RB. Nelson and Brown postulated that the forma-

tio~ of the o--complex is the rate-determining step and hence the energy

profile for: the reacti.on would be similar to Figure 2. Figure 2 rep- 7

A B

Potential Energy

1r (H'~)

Reaction Coordinate

F'ig. 2. --Reaction Energy Profile for a Symnetrical Sub.stitution Reaction in Which Formation of a o--Complex is Rate-Determining

resents a symmetrical reaction such as hydrogen exchange. The energy

barriers A and B would not be of equal height for an unsymnetrical

reaction. If EA>EB' the formation of the a-complex would be the rate-determining step while if EB,)EA, the conversion of the er complex

to a 1T' complex would be rate determining. In the latter case~ since

the transition state must involve a partial C-H bond, a kinetic isotope

effect would be observed, Evidence for the above mechanism comes from

the correlation of relative rates of halogenation of methylbenzenes 11 with ~-complex stabilities but not with 1T -comple.x stabilities. 38,39 Dewar · has proposed that the formation of a 7( complex might be the rate-determining step. He suggests the following as

a possible mechanism for nitration: 8

+N02+ --➔) ~o/ ~ (6)

V VI

Accor:di.ng to this mechanism, the energy barrier leading to the forma= tion of V would be large and the transition state corresponding to the conversion of V to VI would probably have the same structure as the G"'""complex intermediate in the Brown and Nelson formulation. R.

D. Brown.20 criticized this work on the grounds that/// complexes are so loosely bonded that they would require little activation energy to form or disrupt. For this reason neither the first nor the third steps could be rate determining and it would not be possible to observe the kinetic isotope effects which have been found for some reactions.

R. D. Brown's alternative mechanism proposed that rate determining steps involve the formation of unsynnnetrical charge-transfer complexes which are more strongly bonded and would, therefore, involve greater activation energies. His mechanism may be formulated as follows; E H I I +B I 1 Ar=H + ~ ➔ +Ar-B ', ,j!Ar-E · -A1:'•~Ef H+ \ -B

VII VIII

Presumably, the transition state for the conversion of VII to VIII would be a syn:imetrical structure similar to a ~ complex while the structures for the transition state leading to Nelson and Brown's 9

_o-' intermediate would probably resemble R. D. Brown's charge-transfer complex. In view of the increasing number of isolated, stable benze- nonium complexes~ it appears that the 0- complex should be considered 93, 97 an intermediate rather than a transition state. "

The fact that the 0-' complex is best thought of as an interme- dfate does not rule out the formation of 11 complexes as rate-determining 96,97 steps, Olah, et al., have concluded that 11-complex formation is rate determining in the nitronium tetrafluorobor.ate nitration of alkyl- and halo-benzenes. The large amounts.of ortho isomer claimed for the nitration of t_oluene (65 .4%) were not explainable on the basis of a rate=determining er-complex formation step but were rationalized in terms of 1r'=complex formation. The relative rates of nitration were also correlated with known /Ji'-complex stabilities but could not be related to known 0--complex stabilities. The proposed energy profile for Olah's mechanism is:

Potential Energy

Reaction Coordinate

Fig. 3., --Reaction Energy Profile for a Substitution Reaction in Which 1T'-Complex Formation is Rate Determining

A small secondary kinetic isotope effect was also explained in terms of changes in bond hybridization in the -1t"'-complex transition state. 10

The distinction between 11' and (/"" complexes may be one of degree more than kind and depends essentially on the extent of penetration of the 1(-electron cloud and the degree of localization of bonds. 14 In fact, 00directed" or 00 localized" 1T' complexes have been proposed which begin to resemble charge-transfer or 0- complexes. It seems reasonable that either or both ,f- or 0-:-complex formation could be involved in rate-determining steps. The formation of a '1T'complex could require considerable activation energy, particularly if extensive rearrangement of solvent shells were involved~ while under some circumstances the energy needed for the intramolecular (and hence favored)

.shift of an electrophile to a localized carbon atom might be corres- pondingly lowered. On the other hand, relative energetics might be such that a if complex could be directly formed with little or no transient '71-complex formation. DIRECTIVEEFFECTS AND THE REACTIVITY- SELECTIVITYRELATIONSHIP

Early in the study of electrophilic aromatic substitution reactions it was noted that substituent groups on the aromatic r:i.ng had a powerful influence in directing the site of substitution of electrophiles. As additional data was accumulated, the common substit= uent groups came to be categorized as activating ortho-par~ directiri.g~ deactivating ortho-para directing, or deactivatir~ meta directing groups. With the development of theory it was realized that deactivating groups decreased the ff-electron density on the ring by induc~ tion and that activating groups had the opposite effect. Orientation could also be explained by the ability of the substituent group to delocalize - either by induction or resonance - the positive charge developed at various carbon atoms in the cr'complex.

Abnormally large amounts of !!!ili isomers were found for the 109 111 alkylation of toluene with aluminum chloride and alkyl halides. ~

The observation that anomalous~ substitution occurred under non- 34 isomerizing-conditions led H. c. Brown and K. L. Nelson to the conclusion that the nature of the attacking electrophile nmst also be considered in the prediction of isomer-product compositions. In 17 a c l assic· paper t 1iey out li ne d t h e pr i ncip. l et h at more react i ve electrophiles will oe less selective in discerning between the various

11 12

positions on a substituted ring and will produce more meta isomer product

than expected for an ortho-para directing substituent. A weakly

electrophilic reagent, such as bromine, will require a large donation

of electrons from the aromatic in the formation of the transition

state leading to the o-'-complex intermediate, and, hence~ will

selectively bond to the electron-rich ortho or para carbon atoms in

preference to the~ carbon atoms. The more reactive the incoming

electrophile is (carbonium ions formed in Friedel-Crafts alkyla- tions are very reactive), the less it will require the contribution

of electrons from the ring in the formation of the transition state and the less selective it will be in its "choice°' of positions on 117 the ring. Subsequent work has demonstrated the applicability of

this principle to a wide variety of electrophilic substitution reactions

on toluene.

The relationship between reactivity and selectivity can be understood in terms of the nature of the transition state leading to the o--complex. The less reactive the electrophile, the more the

transition state will resemble the- er-complex intermediate and the more it will be influenced by resonance interactions with the ring 6 substituent.. 41 • 116 With more reactive electro9hiles, the electron

cloud is more distorted and the transition state will occur earlier as the reaction proceeds along the reaction coordinate, The transi-

tion state will be less symmetrical and less like the O---complex and

the resonance and inductive properties characteristic of the substituent will have less influence on orientation.

The selectivity-reactivity relationship can be represented by 13 a linear free energy relationship involving partial rate factors.

A partial rate factor measures the rate of substitution at a particular position on the substituted~~,·-:. ring relative to a single position on benzene. The partial rate factors for a monosubstituted benzene compound are given by

Pf= 6(% J?,-isomer)kx (8) 5(20%)kB

6 (% _o-isomer)kv Of "' A (9) 5(40%)kB and

mf = 6(% _!!!-isomer)kx (10) 5(40%)kB where 1

Pflmf is taken as a measurement of the selectivity of the reagent while Pf is said to measure the reactivity of the reagent. A plot r of log Pf vs. log Pf/mf has been shown to give a Hnear relationship for many reactions on toluene. 116, 117

That such a linear relationship should exist has been demon- st~ated by considering equations similar to the Hammett equation. 81

The rate of substitution at the~ and para ring positions should be related to a reaction constant (f) and a constant (o-'+) represent= ing the ability of the ring substituent to donate electrons to the reaction site (Equations 11 and 12). ' . log Pf ~ prrp . (11) 14

. 4- log mf : fcr:n (12) Substracting 12 from 11 gives 13

(13)

and 11 divided by 13 gives 14

(14)

The ahove relationship was originally tested for reactions on toluene~ but Equation 14 permits an extension of the theory to other aromatic compounds. The er'+ values for chlorobenzene are crp+ = 0,114 and r+: 0.399. 116 From Equation 14 a slope of -0.4 is obtained for m the plot of log Pf vs, log Pf/mf for reactions on chlorobenzene.

Figure 4 presents a plot of the selectivity relationship for toluene and its proposed extension to chlorobenzen.e and other systems.

Substituent constants~ were chosen in preference to Hammett's constants because the latter do not account for direct resonance interaction with ring substituents, 116 Despite the general success of the selectivity relationship utilizing er'+ constants, this approac:h 90 makes faulty predictions for a number of react:i.ons • These excep~ tions have prompted the development of other relationships employing additional parameters. 78 ' 122

A large amount of ortho isomer in the product has been used as 100 102 a criterion for a 17'=complex transition state, ' but it has also been suggested that low selectivity is not a necessa~y consequence 92,103 of this type of reaction. Olah and co-workers have argued 15

4.0

O(c) 3.0 ~f/ fl \. '\)- 0 0 "o (a) (b) 2.0

·log Pf 0.0 "

-2.0

-3.0

-2.0 -LO 0.0 1.0 2.0 3.0

(a) Cerfontain's Sulfonation (not corrected for secondary reactions) (b) Guillot's Sulfonation (not corrected for secondary reaction: Guillot's ·extrapolat:'ed m value)

Fig. 4•:--The Selectivity Relationship for Toluene and P:,::oposed Extension to Other ~onosubstituted Benzenes 16 that only in the situation where the formation of the er-complex is rate controlling (case I in Fig. 5) should there be a relationship between selectivity and reactivity. In case I, both substrate reactivity and pos~tional selectivity are determined by the same transition state

(A) while in case II, the reactivity of the substrate and the final position of substitution are governed by two different transition states (Band C).

A B

Energy Energy

I II

Fig. 5.=-Potential Energy Profiles for Situations Where ~ =Complex Formation is Rate Detennining (I) and '77'-Complex Formation is Rate Determining (III)

Thus, the relative heights of transition states l~adiitg; to the formation of ortho-, ~-, and para- a-- complexes (C) wo~ld determine isomer distributions while the relative heights of t~ansition states leading to the benzene and substituted benzene ?Tcomplexes (B) would determine the ratio kx/kB.

Other reaction features which might cause deviations from the predicted selectivity relationship include complexing with the electrophilic reagent or catalysts, C-H bond breaking, and differential 17 solvation of the electron-deficient transition state. 116 Unrecognized secondary reactions or faulty data might also give apparent discrep- a.ncies with the theory. ELECTROPHILICSUBSTITUTION REACTIONS

INVOLVINGCHLOROBENZENE

Electrophilic substitution reactions involving the halobenzenes have not been investigated as extensively as those of toluene. Table

1 presents a summary of data on reactions for chlorobenzene with

·reported values for relative rates of substitution ('I

The most obvious feature of Figure 6 is the very large scatter

in the data points; however, certain types of reactions fall closer to the predicted line than others. Reactions inv,olving Friedel=

Crafts acylation or alkylation (1, 2, 8, 9, 10, 13, 14, 15v and 16) and mercuration reactions (17, 18, and 19) fit the line better than the other types of reactions - all of the points for these reactions fall within ±0.3 log units. Nitration by HN03 (20) falls on the

line but nitrations by No2+BF4- (21 and 22) deviate widely. With the exception of one stray point (6), the bromination data points

(3, 4, 5, and 7) are far removed from the line as are the chlorina~ tion (11 and 12) and sulfonation (24) data points. As a crude estimate,

18 TABLEl

ELECTROPHILICAROMATIC SUBSTITUTION REACTIONS ON CHLOROBENZENE ...... ,:-..- ~------~-

No. Reaction Conditions Isomer Ratio Partial Rate Factors Lit. _g-. m- .. . -~·- - .. .E.::- l~/kB Of Illf ... Pf Ref. I L Acetylation (~~OCl, ,.~1~1 ~ .. 3 -·. •·" C2li4Cl2, 25 . .. . 0~5 99.5 0.0209 0,0003 0.125 55 .. -- 2. ·Benzylation (PhCH2Cl, AlCl3, . MeN02, 25~) .. -~ 33,0 0.6 66.4 0.24 0.248 0.0043 0.995 98 ,, 3. Brominatiori (FeCl3, Br3(neat) , MeN02, 25°) . , 20.3 (0.2 79.7 0.35 0.21 0.021 ·1. 67 99 . ~ . . - - ~ ..' ' - ..... 4. Bromination &FeCl3, Br2-MeN02j '°

,.. MeN02,• 25 ,) .J".•1 22.l (0.2 77 .9 0.12 0.079 b.0072 0.56 99 .. 5. Bromination &FeC13-Br-MeN02, , MeN02, 25 .) .. . . 25.l 0.2 74.9 0.20 0.15 0,0012 0.90 99 - - -· ' - - . '·' - - .. 6. Bromination (Br2, HOAc-MeN02, ' 30°) . 0.0056 8 0.145a 70 ' ~ ,- 1• - 7. Bromination (Br2, CS2AlBr3, 10.7 0.1 89.2 0.264 0,0006 0.0006 1.07 54 ' ... 55°) .. '"~ .. ,. . - 8. ; t-Butylation (AlCl3, MeN02, i 5.5 0,0049 . ,, t-bu-bromi9e- ' '.,. 25°),...... 94.5 0.03 0.170 101 ; 9. ; t-Butylation (SnCl~', t-bu-bro- , mide, MeN02.~25 ) 5.0 95 .o 0.07 0.011 0.40 101 ,' TABLE1--Continued

. No. Reaction Cl.:)nditioris · .. Isrnner Rati5'· .•, Piirt ·al Rate· Factors Lit.

~o- m- kx/kB ,,tllf !lef. .. - .. ... -:... , ~-- "". ..~:- Of. Pf

,.,., 10. t-Butylation (AlCl3, !so- . "' putylene, ~N02, 25) 5.5 94.5 0.06 0.0090 0.34 101 ' ,i'" ,., 11. Chlorination (FeCl3, Clz, .. MeN02, 25°) .. _ . 42.5 3.1 54.4 0.17 0.24 0.016 0.56 ' 100 . N 0 12. Chlorination {Cl2, HOAc-H20, . 25°} " .. •".. . 32.4 67 .6 0.10 0.097 0.0023 8 0.406 115 13. Ethylation {EtBr, GaBr , 0 .3 . C2f¼Cl2, Z~ ) ... 42.2 15.9 41.9 0.214 0.271 0.102 0.588 18 .. 14 . Isopropylation (isopropyl- . bromide, AlC13 , MeNOz, 25°) 49.8 7.9 42.3 0.10 0.15 0.024 0.260 101 .. ··• 15. Isopropylation (isopropyl- . bromide, FeCl3, MeNOz~25°) 51.4 8.1 40.5 0.13 0.20 0.032 0.310 100 16. Isopropylation (propylene, . AlClj lJ MeNOz~ . 250) 53.9 5.1 41.0 0.11 0.18 0.015 0.270 101

17. Mercuration (Hg(OAc)2, . F3CCOOH,2~?) ·. 11.9 5.8 82.3 0.0470 0.0168 0,0082 0.232 19 - .., 18. Mercuration (Hg(OAc)2; .. HOAc, 25°) IJ 25 .1 25.8 69,5 0,10 0,075 0.060 0,36 12 •" TABLE1--Continued

~ No. Reaction· Coridft :fons . " ~ = ·Isom ~r Ratio :: ·Partial·Rate ·Factors Lit.

, ...... 2.:- m- ...e.- kx/kB ,,,.?£ .. mf Pf Ref.

" .. 19. M.ercuration (Hg(OAc)2, ... HOAc, 90°) _...... ,. 30. l 21.5 48.5 0.090 0.081 0.058 0.26 12 < ·,. 20. Nitratiori (HN03, ~N02, 25°) 29.6 0.9 69.5 0.0312 0.0277 0.00084 0.130 8

/"· - .~- -·. -~ ~- 21. Nitration (N02BFf, C4H8S02, 25°) ( - . . ,...... -2.2~.1. o. 7 76.6 0.14 0.093 0.0029 0.643 97 .. 22. Nitrgtion (N02BF4, C4H8S02·,.. N> I-' , 25 ) , C •• C ·••.-;,, ~ 23.8 1.0 75.2 0.14 0.096 0.0029 0,63 95

23. Sulfonation (S03 , so2~ -12.5°) 0.95 0.09 98.96 0.087 0.0025 0.00024 0,517 b

' ' aThis value was determinecroy .a.ii.indirect: llleasurement- explained· iii the literature referepce.

bThis research. 0,8

0,6

0,4

0.2

0 07 21 -0.2 11 22B 0 023 log i3 N 9 N Pf -0.4 14 o 5 1sP ------010 012 0 ~ O 16 -0.6 -017 6 -0.8 r:JJ~ 20 0 0 ol -1.0

0,2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 log pf/mf

Fig. 6.--Relationship of log Pf to log Pflmf for a Series of Electrophilic Substitutions on Chlorobenzene 23 the order in which the types of reactions tend to fit the predicted line would be acylation, alkylation, mercuration)chlorination, nitration> bromination, sulfonation. 117 Stock and Br.own record partial rate factors for a large n.urober of reactions on toluene. In general, the para rate factors for. types of reactions fall within the limits given in Table 2.

Small values of Pf indicate highly reactive electrophiles so it may

TABLE2

TYPICALMAGNITUDES FOR Pf IN REACTIONSON TOLUENE

Type of Reaction

Friedel=Craft's Alkylation 5-12 Mercuration 11~33 Nitration 46-60 Sulfonation (H2S04) 112 Chlorination (Cl2) 820=870 Bromination (Br2) 2400

be generalized that more reactive electrophiles give closer agreeme.nt to the selectivity relationship for chlorobenzene.

The chloro=group in chlorobenzene has two effects on the properties of the ring which would favor the formation of a 1T-complex transition state. The electron withdrawing power of the chloro=group decreases the 1{-electron density on the ring reducing the polariza- . 96 bility rE-Jsponse of the ring electrons needed for '1'""'-complex formation"·

The non=bonding electrons bn the chlorine atom are also available for interaction with the ir,x::oming electrophile. Inte:ract:ion with .. 24 non~bonding electrons has been postulated to rationalize lar·ge ortho/- 79 eara ratios for anisole and chlorobenzene. A transiti.on state .

in which the electrophile is strongiy in.volved with· chlorine electrons would more closely resemble a directed '77'complex and, therefore,, one would not expect close correlation with the selectivity relationship,

The more reactive electrophiles appear to be forming c,--complex transition states while the weaker electrophiles m.:1y be for.ming ;(-complex transition states. The scatter in the alkylati.on. and mercu:ration. data, however. may indicate some ff-complex character in these transi~ tion states.also. MECHANISMOF AROMATICSULFONATIO:N

Aromatic sulfonation is an important industrial process and many different sulfonating reagents have been employed including sulfur trioxide, sulfure trioxide complexes, halosulfonic acids, sulfonic acid, acyl-and alkylsulfates, o,leum, and sulfuric acid.

The literature for this reaction is extensive and a number of reviews 87 are available, among the more recent being those of Nelson and . 53 Gilbert.

Sulfonation in sulfuric acid and oleum comprise complex systems with H3S04+, S03, HS0 +, s 0 , and H s o as possible sulfonating 3 2 6 2 2 7 reagents. The reactions are complicated by side products, isomeri- zation at higher temperatures, and variations in electrophile concentrations. Reactions in concentrated sulfuric acid and olecm are first order in so3 and it is generally believed that so3 is the . . 10,35 59 73 . primary sulfcnating agent ~ ' although Gilbert advises caution 57 in interpreting such complicated systems. Spryskov and co=workers have presen~ed kinetic evidence for a third order dependence on H2S04 + - in nitrobenzene solvent systems and propose that HS03 ••• HSo4 is the . 74,75 su lf onat i ng species. 10 A proposed mechanism for sulfonation in oleum is

25 26

,f-H+ ::. __ 1_ .a+- (15) +so3 -:--7 0 ~r,-nt 5

In solutions containing basic.species (i.e., sulfuric acid) the . 73 pr,oton. elimination step may be

3 - tB (16) ) ) fBR 0. followed by

(17) .

It is also possible that.an intramolecular proton shift may eliminate the-proton. from the intermediate in aprotic or non-basic systems.

; I'

(18)

From the small kinetic isotope effect found for the reaction, Cerfontain 73 et a1.j concluded that the addition of so3 to the ring is the slow step in the reaction.

Kinetic isotope effects have b~en reported for the so3 sulfonation of benzene in nitrobenzene and nitromethane solvents (1)i/~ = 9 .l.25-1.35/ and without solvent' (kH/kn = 1.14). 23 , 27 A generalized 27

reaction mechanism may be written

(19)

For this reaction, making the steady state approximation for the kinetics,

k1kz/k_1 (20) 1 + k2/k_ 1

When k_1))k 2 a kinetic isotope effect is noticed since the expression fork b reduces to 0 S

CU)

5 and no kinetic isotope effect is found. A maximum~/~= 6.9 67 is expected at 25°. Frequently it is assumed, as Cerfontain does 9 that large kinetic isotope effects are primary effects which involve

C=R bond breaking while smaller values must be secondary effects not involving the C-H bond. From the above, however, it is seen that no such rigorous mechanistic interpretations need be made. The manner in which the intermediate partitions itself is the important deter·~ minant and primary effects can be small. This would be particularly true if the potential energy profile for the reaction were approx= imately symmetrical.

Steric effects may influence the magnitude of k=l" A bulky 28.

3 reagent has greater difficulty passing from the sp configuration 2 . of the o-'-complex intermediate to the sp configuration of the ring 123 which increases k_1 relative to kz and enhances the isotope effect. Thus, kinetic isotope effects in reactions of halo-compounds show 7 the o:rder I) Br) Cl. Sulfonation by might be expected to show an isotope. effect so3 for ster:ic reasons and also for electrostatic reasons. The intermediate for sulfonation is a neutral species in contrast to the so3 positively=charged species usually found in electrophilic substitu= tions and would be less likely to repel the proton thus decreasing 92 k2 • Olah, et al.~ state that small isotope effects are to be expected from ff-complex transition states and larger effects a:re anticipated for 0--complex transition states. If the above so3 sulfonation isotope effects are secondary effects rather than primary ones, they may constitute evidence for a rate-controlling, proton- eliminating '11'-complex transition state. The sulfonation of benzene, bromoben.zene and chlorobenzen.e in nitrobenzene solvents are second order in. so . 42 ' 121 Since Raman 3 spectra indicate that S03 exists principally as the monomer in sol= 58 ution, it is probable that s206 is not the attacking species. Cer= fontain, et al.:i 30 favor a stepwise addition of S03 to the molecule as in the following mechanism:

ArH t S03 ::===:: {23) 29

(24)

Arso oso H ArS03H 4" so (25) 2 3 :===':: 3 IX

The participation of a second so molecule acting as a base 3 to abstract the proton would give the same kinetics but in view of the much higher concentration of a stronger base (the solvent), this is not likely. 66

Pyrosulfonic acids (species IX in Equation 25) are important intermediates whose significance in sulfonation kinetics are n,ot always considered. They may arise from a mechanism like that above and would be expected to exist in equilibrium in any system containing sulfonic acids and free so . 3 Ruggeberg and associates 107 proposed in 1955 that pyrosulfonic acid intermediates provide the route through which by-product sulfones are formed in sulfonation reactions. The mechanism proposed is

ArH (26)

Certontain 30 reached a similar conclusion and the mechanism is now generally accepted. In pioneering studies, Hinshelwood and co=workers discovered that the rate of sulfonation of benzene and chlorobenzene in nit:robe:n:iene with so was reta;rded by the formation of a 1: l so -Arso H 3 3 3 . 42 121 species. •

Christensen, in a series of very extensive studies of the SO 3 30

. . h 31,32,3.3 d su lf onation o f io d ob enzene in nitromet ane, iscovered the formation of a colored 1:1 iodobenzenesulfonic acid-sulfur trioxide species which he identified as the pyrosulfonic acid. By spectrophotometry he established that the species is short-lived and v~ry reactive and that the rate of formation of the species was fast: relative to its disappearance. He discovered indications of such a species in so - 3 chlorobenzene and so3-bromobenzene mixtures but did not study these systems further. He also demonstrated the presence of another inter= mediate species, the sulfonic acid anhydride, and concluded that in aprotic systems the relative order of stability of possible sulfonated species would be

The sulfonic acid anhydride can be isolated if the so3/ArI r~tio is large enough ( 1.5 at 40° C.) so this can be considered a fairly stable intermediate. It is also believed that the anhydride is not a significant sulfonylating agent and that both the pyrosulfo~11ic acid and the acid anhydride are more important sulfonati~ agents in aprotic than in protic solvents. 33 ..,dr.. ...!., h e b as1.s· o f hi s o b serva..:t i ons, Chris · t .ense,ri,· propose~ d th e following mechanism forsulfonation by in aprotic solvents: so3 k1 (27)

(28) 31

(ArS0 ) t t H (29) 2 2o so3 2so4

k4 (30)

(31)

1be species ) 0•H is also conside,red to be a possible inter- (Ar.so2 2 2so4 mediate in the formation of the anhydride (Equation 29) ot· may be the actual sulfonating agent in Reaction 30. The attainment of equilibrium is believed to be fast in the first step and k2 is believed smaller than k . Christensen considers Reaction 29 to be fast relative 1 to Reaction 30 and the con·centration of the pyrosulfonic acid must be small compared to that of the anhydride. Reaction 31 accounts for sulfones that might be found in the reaction products.

The concentration of anhydride is small and Reaction 28 is rate determining during the initial stages of the reaction while at the end of the reaction, Equation 30 would control the rate. At the beginning of the reaction, when the so3 concentration is largest, the formation of the pyrosulfonic acid is enhanced (Equation 28) and the formation of the anhydride is suppressed (Equation 29) which leads to the accumulation of a detectable amount of pyrosulfonic acid. As the reaction proceeds, the concentration of so3 decreases leading to a reversal of relative amounts of anhydride and pyrosulfonic acid.

Christensen does not include sulfonation of the aromatic by 32 pyrosulfonic acids directly but this may be important during the early stages of reaction. Thus, Equation 32 should also be considered in the mechanism.

(32)

The effects of these secondary reactions on isomer distributions, relative rates of reaction, and the resulting partial rate factors have not always been adequately considered in previous sulfon.ation studies.

Partial rate factors for sulfonation by concentrated sul.furic acid 24 25 vary cons id era bl e wit. h t h.. e concentration' o f t h e aci 'd j a 1 t h oug h the selectivity relationship holds for these and other sulfonation.s in protic systems. Small deviations from the selectivity relationship in protic systems have been explained in terms of differential 28 26 solvation of the transition states or heterogeneity of the system.

A considerable deviation from the selectivity relationship was 30 found by Ce.:rfontain for the sulfonation of benzene and toh.lle:ne with

S03 ~ the aromatics consti.tuting the solvent. No variation in k.r/kB was found on varyi,ng the relative amounts of benzene and toluene>but the isomer distribution was shown to vary with both initial benzene to toluene ratios in competitive experiments and with the extent of toluene conversion in the sulfonation of neat toluene. The 2ara/ortho ratio was shown to increase as the benzene/toluene and toluene conversion values increased. Although he recognized the possible presence of pyrosulfonic acids in the system, Cerfontain disregarded them as sulfonating species and considered them only as transient: species which store and then release so3 • Cerfontain believed that the 33 deviations from the selectivity relationship resulted from 1T-complex format.ion in the transition state or from kinetic abnonnalities resulting from the temporary consumption of to form the pyrosulfonic acids. so3 PURPOSEAND PROCEDURE OF THE INVESTIGATION

60 Guillot, in studying the sulfonation of toluene with so3 in liquid , obtained anomalous relative rate data. He believed so3 that pyrosulfonic acids were effecting the results but did not make an extensive study of the system. The partial rate factors obtained in his work did not agree with the selectivity relationship but in the light of the anomalies in his results these values are questionable" Because of the paucity of information on so sulfonations in aprotic 3 solvents and the interesting possibilities raised by Guillot's preliminary

work 9 it was decided to extend work in the toluene-benzene system in an effort to illucidate the mechanism and to obtain better data for the calculation of partial rate factorso The general lack of such information on the sulfonation of chlorobenzene in liquid so2 prompted an extensive study of that system alsoo

Sulfur dioxide is a good aprotic solvent in which all the reactants are soluble. 56 ,lOS and gives clean reactions with little o:r no sulfone by=products. Sulfur dioxide forms congruently and 112 incongruently melting compounds with benzene and toluene.. Whether. or not this implies that unusually strong solvent-aromatic interactions exist at the reaction temperature (40 to 80 degrees above the melting point of these compounds} 'is not knowno

' Partial.rate ft.tctors can be calculated if isomer dist:ribu-

34 35 tions and relative rate values can be obtained. Consequently, the isomer distribution for the sulfonation of chlorobenzene in liquid so2 at reflux temperature (-12.5° C.) was obtained by an isotope dilution technique. Relative rates for chlorobenzene-benzene and toluene-benzene systems were obtained by sulfonating chlorobenzene and toluene in competition with c14 labeled benzene. By knowing the actual count rate for the products and the count rate for pu~e c14 labeled sodium benzenesulfonate, it was possible to calculate the amounts of benzene-and substituted benzene~sulfonic acids produced in the reaction.

The relative rates for the reactions were investigated as a function of both initial ArX/benzene ratio and concentrationo so3 Variations in isomer distributions as functions of concentration so3 were also studied by means of UV spectrophotometry. The resu.lts of these studies indicate that some of the sulfonic acids produced in the reactions are being formed by sulfonating agents other than so3 and that corrections mu.st be made for the reactions of these sulfonating agents in calcuL':tting pa.rtial rate factors. RESULTSAND DISCUSSION

The sulfonation of chlorobenzene and benzene with so3 in liquid so2 proved to be a very clean reaction. Essentially, all of the so3 consumed was recovered as titratable acid. It is believed that the amount of sulfones formed in the reaction is negligible. The comparison of weighed vs. titrated (see Experimental Procedures) so3 so3 gives no indication of sulfone formation since for every two molecules cf so consumed in sulfone formation, a molecule of n so is formed 3 2 4 which would be interpreted as two sulfonic acid molecules on titration.

Calculations comparing weights of products with titrated moles of p~oducts~ however, gave result~ in good agreement with the count-rate method which impl_ies that little or no sulfone formation took place.

An attempt to correlate amounts of product formed with sulfone formation failed when evaporation of ether extracts of the reaction mixtures produced an amount of sulfone material too small for meaningful compar= ison.

Competitive Sulfonation in the Benzene-Chlorobenzene System

Knowledge of relative rates of reaction (kx/kB) are necessary for the calculation of partial rate factors. With very fast reac= tions it is often not convenient to measure the rate constants directly and competitive methods are employed. Relative rates can be obtained from the amounts of initial and final components by the use of Ingold 1 s

36 37

71, 72 equation:

kx = log(Xi/Xf) (33) kB log (Bi/Bf)

where X. and B. are the initial molar amounts of substituted aromatic 1 1 · and benzene and Xf and Bf are the molar amounts of the respective starting materials remaining at the end of the reaction.

This equation is applicable only if both aromatic species

are substituted by the same electrophilic reagent and the reaction is

first order with respect to the aromatic, 40 The order of the reaction

with respect to the electrophile is not iIIlportant provided 9 of course,

that it is the same for both aromatic substrates. Olah, in a very care·~ 96 ful study of aromatic nitration reactions, demonstrated that when

the above conditions were met, variations in rate of stirring~ ratio

·of starting materials, and temperature did not chan.ge kx/kB. The

absence of a variation in kx/kB with changing Xi/Bi is a common criterion applied to test for the applicability of Ingold 1 s equation"

A se:ri.es of sulfonations was made of benzene-chlorobenzene

mixtures in which the relative amounts of starting material were varied,

Table 3 presents the results of the eighteen experiments in this

seriesj together with results for one experiment in which water was

added to test the effect of moisture on the kB/kc ratio (76-P). The

Bi/C1 range included a nearly 100-fold variation in relative ratios of

sta:rti~..g materials. The S03 concentration was only approximately

constant= the average value was 0.02356 moles/liter. As can be

seen from the table, kB/kc values are not constant. The variation 38

TABLE3 RELATIVERATES AS A FUNCTIONOF INITIAL BENZENE/CHLOROBENZENERATIO

Experiment S03 No. Concentration Bi/Ci KB/Kc (M./1.)

49=P 0.02177 0.02162 17.40 65-P 0.02354 0.04431 18 • .58 66=P 0.02256 0.08314 15 .43 39-P 0.02640 0.1102 12.07 43=P 0. 03253 0.1125 11.39 67=P 0. 03178 0.1269 13 .07 68=P 0.01919 0.1475 11.89 59-P 0.02519 0.1864 9.39 4l=P 0.03477 · 0.3329 6.67 38=P 0.02688 0.3515 8.67 76-pc¼ 0.01093 0.5150 ' 0.91 74=P 0.02122 0.5486 12.58 40-P 0.02307 0.6460 9.67 75-P 0.02811 1.004 6.12 36=P 0.03097 1.063 4.61 50=P 0.02385 1.150 4.41 48=P 0.02435 1.502 6.64 73=P 0.02397 1.899 3.44

awater was added to the reaction mixture.

Two features of this plot are significant: first, kB/kc is not independent of Bi/Ci, but increases with decreasing Bi/Ci - the increase being very pronounced at low B1/ci. ratios; and second, although the general trend is clearj there is considerable scatter in the data points. Traces of moisture were considered as possible causes of the scatter in the data and one experiment (76-P) was made in which water was deliberately added. This experiment gave deviant results but the kB/kc value obtained was low (0.91) rather than high so that it did not appear that moisture could ex~lain the 20

" 12 kB/kc 10 l,J '° 8 I - ~ ...... ~~~-·- - B El : t I 13 2 • 0.2 0.4 0.6 0.8 1,0 1.2 1.4 L6 1,8 Bi/Ci Fig. 7.--Apparent Relative Rates as a Fiinction of Initial Benzene-Chlorobenzene Ratio 40

particular shape of the curve.

The possibility that the results were thermodynamically rather

than kinetically controlled was also investigated since the work~·up

times for: the reactions varied. Sulfonations are known to be reve:r-

sible although reversibility usually occurs at much higher tempera-

tures and more drastic conditions than those employed in this study,

If the reversible reaction

Cl 0 + were responsible for the observed results» the equilibrium constant

for the reaction wbuld be

K = (CS)(Bi - BS) {BS)(Ci - CS) where CS and BS represent the moles of chlorobenzene- and benzene-

sulfonic acids in the final solution.

Table'4,gives the calculated K for the data in Table 3. The

· complete lack of any constancy in the calculated K values rules out

thermodynamic control of product composition in the reaction. The ,,,l high degree of selectivity shown by the isomer distribution {p. 72) , also mitigates against thermodynamic control.

The effect of S03 concentration was next investigated. It was decided to determine what effect the variation of so3 concentration would have on the amounts of BS and CS produced in the reaction.

Since neither a constant number of moles of each'component nor a 41

TABLE4 TEST OF THERMODYNAMICVS. KINETIC CONTROL

Experiment Calculated No. K

36-P 0.273 38=P 0.122 39=P 0.092 40-P 0.097 41-P 0.162 43-P 0.108 48-P 0. 156 49-P 0.105 50-P 0.141 59-P 0.110 65-P 0.070 66=P 0.073 67-P 0.086 68-P 0.098 73~P o.• 284 74-P 0.077 75=P 0.159

constant total number of moles of aromatics was used, the function had to be expressed in terms of mole fractions. Several functions were tried unsuccessfullyj but it was finally found that a plot of mole fraction of BS (XBs) versus mole fraction of Bi divided by so3 concentration (XB. / (S03)) gave. a. smooth cu~cve along "which all the l. data points fell with a ~oder8te degree of scatte,r. Figure 8 shows the data plotted in this fashion. The solid curve represents the data from this series of experiments. The dashed curve will be discussed later.

Nine additional experiments were performed using deliberately varied amounts of • The results of these experiments are given so3 -0 LO ----. ---J!) @ --if-(f"--- - ® J) @ 0.9 ®

0.7

0.6 /

.i;:.. 0.5 N

XBS 0.4

0.3

0.2

0.1

~ 2 4 6 8 10 12 14 16 18 20 22 24 26 ,fta 40 42 44

··XB / (S0 ) i 3

Fig. 8.=~Mole Fraction of BS as a Function of Mole Fraction B /(S0 ) 1 3 43

TABLE 5

RELATIVE RATES FOR EXPERIMENTS WITH VARYINGso 3 CONCENTRATIONS

Experiment so3 No. Concentration B·/C·l. l. kB/kc (M./1.) 78=P 0.01062 o.708 12.56 79=P 0.01783 3.554 4.39 80=P 0.02647 o.708 / 6.78 81-P 0.01883 o.717 7.55 82=P 0.05350 0.709 4.50 84~P 0.004087 0.129 12.33 85=P 0.03066 0.129 15 .17 86-P 0.00574 0.129 11.35 87-P 0.00142 0.902 13 .22

in Table 5. These experiments were made to test some extreme cases.

Experiment 79=P couples a very large Bi/Ci ratio with a small S03 concentr.ation 9 and 82,-P uses a very large so3 concentration with a moderate Bi/Ci ratio. The remaining experiments are designed to test the effect of varying so3 concentrations at two Bi/Ci ratiosj one ratio being moderate (0.708) and the other (0.129) being small. The kB/kc values show deviations from the curve in Figure 7 and the sensitivity of kB/kc to changes in so3 concentration is evidenced by the variation of relative rates at constant B1/Ci ratios. In spite of the extreme spread in experimental conditions and the wide range of kB/kc results, the data for all but three of the experiments fall within reasonable limits on the curV'e in Figure 8. The three points which failed to fit this curve were the three taken at the lowest so3 concentrations (84-P,

86-P 9 and 87--P). All three of these experiments employed so concent:ra- 3 44 tions of less than 0.006 M. and gave XBS values below the curve.

The three points are not plotted in Figure 8, but the data for them

is included in Table 27 in the Treatment of Data Secti.on. The general sh.ape of th~ curve is what would be expected for a series of competi~

tive sulfonations such as this, although it dif :fers i.n detail from the expected curve (dashed line). Plotting the data :i.r1.this manner reduces inconsistencies due to the variations in so3 concentrations. A plot of relative amounts of benzene= and chlorobenzene.- sulfonates (BS/CS) obtained from reactions in mixtures of constant

Bi/Ci (Figure 9) was very informative. Table 6 presents the pertinent data for this plot.

TABLE6

PRODUCTCOMPOSITION AS A FUNCTION OF so3 CONCENTRATIONAT CONSTAN'r Bi/Ci

.:>U3 Expe!.'iment Concentration BS cs BS/CS No. Bi/Ci (M./L)

78=P 0.708 0.01062 0.009394 0.001255 7.485 81=P o. 717 0.01886 0.01812 0.003430 5.282 80-P o. 708 o. 02647 0.02437 0.005295 4.602 82=P 0.709 0.05350 0.04477 0.01470 3"046 84=P 0.129 0.00409 0.002698 o.oo:wo2- 1.348 86~,P 0.129 0.00574 0,003945 o. 003231 L221 85-P 0.129 0.03066 0.01981 0.0154.5 1.282 67··P 0.127 0. 03178 0"01920 0.01445 L329 .

The data for the two different starting r-9.tios give two dif.ferent cu:t"vea. Fo:r Bi/Ci,.. 0 .129 the plot of BS/CS is a straight line with slope. zero» while. that for the larger Bi/Ci ratio gives a smooth ctrr~re with BS/CS dec:reasi!'l..g with increasing S03 concentration. 8 ·@ : B1/Ci O. 708

0 : B/Ci 0.129

BS/CS +:'- VI 4

2 ---0@------,[!JD-

0.01 0,02 0.03 0.04 · 0,05 Concentration of so3 (Moles per. Liter) Fig, 9, --Ratio of Benzene to Chlorobenzemf Sulfonates in Product at Constant B1/ci as _a Function of Con~entratio~ ~f so3 46

It is possible to explain the shape of the upp~r curve if we

assume that all of the products from the reaction are not coming from

the sulfonation of the aromatic compounds by so3 but that secondary reactions are occurring which also lead to products. A few simple

calculations show how a curve similar to that in Figure 9 can be

produced on this assumption. Assume that the direct sulfonation of the

aromatics by so3 (the primary reaction) leads to products in the ratio BS/CS• 10 and that a secondary reaction (or reactions) is producing

extra amounts of both BS and CS in approximately equal amounts, We will further assume that the amount of products from the secondary reaction(s) is proportional in some way to the so concentration so 3

that larger amounts of seco~dary products are fo:nned as the so3 concentration increases. A sequence of hypothetical values obtained as so3 increases might be:

10+1 BS =· :: 5.5 cs 1+1

10.+2 BS. = 4.0 cs 1+2 =

BS :: 10+3 :::: 3.3 cs 1+3

BS ,,.,- 10,\,4 __ 2 8 CS H4 . and so on, As the amount of secondary product increases, the BS/CS

ratio decreases but the rate of decrease becomes smaller as the secondary products become more important. Thus, a curve similar in all essential respects to that of Figure 9 is obtained. 47

It is important to emphasize that the above treatment does not require that side products contribute more to the species in the denominator than to the species in the numerator. rn the above illus- tration, equal contributions to both species are assumed and a similar cut·ve with a smaller rate of decrease in BS/CS would be obtained even if the contribution to the species in the nume:r:ato:t·were somewhat larger than the contribution to the species in the denominator. There is also no need to invoke any special properties for the secondary reaction(s) for either species. It is necessary, however, that the ratio of secondary products be·less than that of the primary products if a curve shaped like that in Figure 8 is to be obtained. If the

ratio of secondary products is identical to that of the primary products 9 a straight line with slope zero would be found, while if the secondary product ratio were larger than the primary product ratioj an upward= curving line would result.

The secondary reactions will contribute a proportionately greater amount to that species which is produced in smaller. quantities by the primary reaction. This is evident from the following considerations,

Let BSl and CSl represent the products formed in the primary reaction while BS2 and CS2 represent the products formed by the secondary reactions.

BSl)CSl and

BS2 )CS2 and 48

BSl BS2 CSl) CS2 (34) then CSl x BSl >CSl x BS2 BS2 CSl BS2 CS2 (35) and

(36) or

BS2< CS2 BSl CSl (37)

Thus CS2 is larger relative to CSl than BS2 is relative to BSl. The above derivation holds when the starting Bi/Ci ratio is chosen so that the product of the more reactive species (BS) is produced in gt·eater abundance than that of the less reactive species. It is possible~ however~ to choose a starting ratio that will yield more CS than BS.

It will be shown later that the secondary sulfonating reagents in this investigation apparently more reactive than , that are so3 This means the difference between BS2 and CS2 will be less than BSl and CSl in the same experiment. It follows that: when

BSl< CSl then

. BS2 >BSl CS2 CSl (.38) and

B.S2)CS2 BSl CSl (39) 49

Again it is seen that the secondary reactions contribute a proportionately larger amount to the total concentration of the species produced in the smal~est amounts by the primary re~ction. The lack of any change in slope for the BS/CS curve at Bi/Ci= 0.129 only further supports this interpretation since, as will be shown later, the initial B1/Ci ratio was chosen coincidentally to have a value near the ratio for which the BS/CS value is least sensitive to a change in S03 concentration.

It is proposed, then, that in the sulfonation of chlorobenzene under the conditions of this investigation, part of the recovered benzenesulfonic acid product and part of the chlorobenzenesulfonic acid product results from reactions of benzene and chlorobenzene with 31 32 33 sulfonating species other than so3 . From Christensen's studies , ~ i.n other aprotic solvents it seems that the most likely secondary sulfonating species would be sulfonic acid anhydrides and/or pyrosulfonic acids.

If we apply Christensen's mechanism to the present system 9 the following reactions are possible~

(40) B + so3 BS C + S03 ) cs (41)

BS + BSS (42) so3 cs + so css (43) 3 ' css + B 2BS (44) BSS + C BS + cs (45) css -+ B BS + cs (46) 50

css + C ) 2CS (47)

2BSS BS-0-BS + H2S04 + S03 (48) 2CSS cs-o-cs + H2S04 t S03 (49)

BSS + css BS-0-CS t H2so4 + so 3 (50)

BS=O-BS t B + HzS04 ~ 3BS (51)

BS-0-BS + C + H;2S04 ') 2BS + cs (52) CS-O=CS + B + H2S04 ) 2CS + BS (53)

CS=O=CS+ C + H2so4 3CS (54) BS-0-CS + C + HzS04 2CS t BS (55) 2BS cs (56) BS=O-CS + B .,+ H2S04 ) +

B9 BSj and BSS represent benzene, benzenesulfonic acid and benzene-

pyrosulfonic acid; C, CS, and CSS represent the comparible chloro-

benzene species and BS-0-BS, cs-o-csi and BS-0-CS represent the . respective sulfonic acid anhydrides. The amount of total benzene-

sulfonic acid produced in the reaction will be:

(57) where Bs40 , BS44, Bs46 , etc., represent the amounts of benzenesulfonic acids produced in Reactions 40j 44, 46, etc. Only those reac-

tions in which a sulfonating species attacks B will yield a net gain

in BS. Reactions like 45 merely regenerate BS that was consumed earlier in the formation of BSS. In a similar mannerj the total amount of CS produced would be:

(58)

Benzene= and chloro-benzenesulfonic acids would also be formed from 51

the hydrolysis of any anhydrides left at the end of the reactio~, but

since the ratio of so3/ArH is very low in these studies, it can be safely assumed that the concentration of anhydrides at the end of the

reaction is inconsequential. Sµlfonation might also occur by free

HzS04 but we will assume, as does Christensen, that it is complexed with the anhydride and does not enter into independent reactions.

There are six possible reactions leading to each of the reaction products.

If we assume that all of the reactions leading to sulfonating

species are reversible, the concentrations of these species will be

(BSS) :: K (BS) (S0 ) (59) 42 3

(CSS) K (CS) (S0 ) :: 43 3 (60) 2 Kaa(BSS) (BS=O~BS) (61) = (HzS04) {S03) 2 K49 (CSS} (CSQO-CS) (62} = (HzS04) (S03)

K {BSS) (CSS) (BS=O=CS) :;; 50 (63) (H2S04) (S03)

Expressed in terms of the amounts of BS and CS in solution, these concentrations become

(BSS) K (BS) (S0 ) (64) - 42 3

(CSS) (65) :: ¾3 {BS) (S03) K K 2 (BS) 2 (S0 ) 48 42 3 (BS-0-BS) = (66) HzS04 52

(CS-0-CS): (61)

(BS-0-CS) (68)

Further confirmation for the existence of secondary sulfonation reactions in the benzene-chlorobenzene system is given in Figure 10.

In this figure, the moles of product (BS and CS) obtained from sulfona= tion at constant B1/ci values are plotted as a function of S03 concentration. Straight lines are plotted through the origin and the smallest product values. The BS and CS va,lues at higher so3 concentrations are seen to curve away from the straight line indicating that somewhat more CS and less•BS is being formed than would be expected if the trends 1· at lower so3 concentrations were continued. It is also noteworthy that the deviation from the CS line in the Bi/Ci= 0.708 plot is greater and occurs earlier than that for the BS line. This is in harmony with the proposal that, at this Bi/Ci ratio, the concentration of the product from the less reactive species is influenced proportionately more than the concentration of the product from the more reactive species. No deviation from the straight line is noted for the CS data for Bi/Ci=

0.129 while the BS data differ only slightly.

Figure 10 provides a means of determining ~/kc for the. p:dmary reactions. The secondary reactions become progressively less important as so3 concentration decreases. There will be no secondary reactions at an so3 concentration of zero. Therefore, straight lines obtained by extrapolating the data to zero in Figure 10 represent the /

·0 :: Bi/Cp 0, 708

El= B1/ci• 0.129

.04

.03

Moles of Product - wVI I / BS ,02 ~---

.01

.01 .02 .03 .04 .05 .06 Concentration of so3 (Moles pe:i: Liter)

Fig, 10.--Moles of Product Formed as a Function of'so 3 Concentration 54

values anticipated for a system with no secondary reactions.

Very careful extrapolations of the data were made on a.n expanded

scale. BS and CS points were taken from the straight lines resulting from these extrapolations, a constant Bi and Ci were assumed for the

series of points, and kB/kc values were calculated from Ingcld's equation. The results of these calculations are given in Table 7.

TABLE7

DETERMINATIONOF kB/kc FROMEXTRAPOLATED VALUESOF BS ANDCS

Bi/Ci Bi Ci BS cs kB/kc

0.708 0.1975 0.2789 0.01810 0.00238 11.36 0.02170 0.00282 11.47 0.01445 0.00188 11.21 0.01629 0.00210 1L37 0.01990 0.00258 11.47 Av. ll. 27 J:.0. 22

0.129 0.04265 0.3306 0. 01330 0,01061 11.44 0.01462 0.01168 11.68 0.01598 0.01270 12.00 0.01068 0.00850 11.06 0.01867 0.01482 12.50 0.01732 0.01378 12.24 Av, ll.82j:0.30

In this table and throughout this dissertation, all deviations are expressed as one standard deviationunit unless otherwise specified. The.

average of the two sets of data gives kB/kc= 11.54 ± 0.30. The reasonable agreement in kB/kc from the two sets of data is good support

for the validity of this method. This is particularly satisfying in view of the large difference in Bi/Ci and the differences in the shapes 55 of the.curves in Figure 10.

The determination of a value fork /k for the primary reaction B C now permits a further test for the existence of secondary reactions.

According to the proposed mechanism for the formation of sulfonation products, the ratio BS/CS if given by:

+ BS ::: .BS40 + BS44 + BS46 + BS51 BS53 + BS56 (69) cs CS41 + CS45 + CS47 + CS52 + CS54 + CS55

It has been shown that secondary reactions will contribute to a greater extent to the species made in the smallest amount by the primary reac= tions, Usually this will be the sulfonic acid of the less reactive:

aromatic but if Bi/Ci for a reaction is sufficiently small 9 one would e...xpect cs to be greater than BS and seconda:ry re.actions would then 41 40 contribute more to the formation of BS than CS. At larger Bi/Ci ratios one would predict a greater.contribution of secondary reactions to the formation of CS. Since kB/kc is 11.5 we would expect the 10 c:ross= ove:'..'11 Bi/Ci value to certainly be less than on.e and possibly near

0.1, Low so3 concentrations would also favor the formation of the product formed in the smaller amount by the primaty re.action since, although both BS40 and cs41 will_ be small, the concentration of the species preaent in the smaller amount would be more sensitive to secondary reactions.

A semiquant-itative test of these predictions was made. A s~:lries of calculations was made to determine what BS/CS ratio and what quantities of BS and CS would have been obtained if there had been no secondary reactions. This was done by assuming a value of 56

kB/kc of 11.5 for all of the competitive experiments and calcula-

ting the values of BS and CS needed to produce the known total number

of moles of product from the known amounts of starting materials.

(See the section on Treatment of Data for details of the calculations.)

Table 8 presents the results of these calculations" For each

experiment, the differences between the calculated values (BSC~ CSC~

and RC) and the actual ~~lues are expressed as percentage differ-

ences (A%). The percentage differences were obtained from

6%: (actual value - calculated value)(lOO) Actual value (70)

Certain gen.eralizations can be drawn from the data in Table

8, At low Bi/Ci ratios the ~ % BS values are positive, indicating

that more BS was produced than expected. As the Bi/Ci rati.o is

increased, there is a decrease inA% BS uritil at high Bi/Ci ratios

less Bi is being produced than expected. The opposite trend is seen

for /).% CS which is in accord with the proposed mechanism. The. magni-

tude of I:::.%CS at large Bi/Ci ratios implies that at least half again

as much CS is produced as was predicted" The concentration of so3

also is important. Thus, 87-P, which couples a low so3 concentration with a relatively large B1/ci ratioj gives the largest increase

in CS and the small so3 concentration for 86-P may explains at least in part, the anomalously large apparent b. % CS value for that experiment" The computer program for Experiment 49-P would not converge

on consistent BSC and CSC values and it is probably significant that

this is the only experiment made with fewer moles of initial benzene TABLE8 COMPARISONOF ACTUALVALUES OF BS ANDCS WITHTHOSE PREDICTED FOR SULFONATIONWITH NO SECONDARYREACTIONS

S03 BSC Experiment Bi/Ci Cooc. BSC csc cSc ~ RC ~% A% A% No, BS/CS (M:/1.) BS I cs ...... - 49-P 0,0216 0,02177 a a a a a a 65-P 0.0443 0,02354 0.00798 0.02354 0.37 25.43 -14.59 34.92 66-P 0.0831 0.02256 0.01090 0.01392 0.78 13.48 -13 .88 24.02 39-P 0.1102 0.02640 0,01598 0.01570 l.02 3.07 - 3.33 6.19 43-P o. 1125 0.03253 0.01890 0.02014 0.94 2, 72 - 2. 70 5.28 67-P 0.1269 0.03178 0.02801 0.01536 1.17 5.38 - 7 .14 11.68 84-P 0.1289 0.00409 0.00277 0,00193 1.43 2.99 - 4.62 7.27 86-P 0.1289 0.00574 0,00421 0.00297 1.42 - 0.80 1.11 - 1.92 V1 85-P 0.1289 o. 03066 0.01853 0.01672 1.11 11.53 -16,88 24.30 -.J 68-P 0.1475 0.01919 0.01315 0.00892 1.48 2;21 - 3.44 .. 5.46 59-P 0.1864 0,02519 0.01798 0,00973 1.85 - 6.44 10.05 - 18.33 41-P 0.3329 0,03477 0, 03182 0.00991 3.21 -14; 70 29:16 - 61. 92 38-P, 0.3515 0,02688 0,02522 0,00703 3,59 - 6.35 17 :66 - 29.17 74-P 0.5486 0.02122 0.02149 0.00450 4. 78 l. 70 - 9.00 9.82 40-P 0.6460 o. 02307 0.02374 0,00337 7. 05 - 1:97 12~01 - 15.89 78=P 0, 7079 0.01062 0,01037 0.00131 7.91 - o. 71 5.27 - 6.31 80-P o. 7079 0.02647 0,02688 0,00356 7.54 - 7.76 35.20 - 66.30 82-P 0. 7090 0,05350 0,05374 0.00778 6.91 -17.60 50.83 -139. 15 81-P 0.7170 0.01886 0.01923 0,00246 7.82 - 5.73 29.77 - 50.55 87-P 0.9024 0,00142 0.00149 0.00014 10,33 -46.04 76.51 -521. 72 75-P 1.004 0.02811 0.02957 0.00276 10.73 - 7, 18 41.80 - 84 .14 36-P 1.063 0 .03097 0.03561 o. 00311 11,47 -11.51 54.21 -143 .51 50-P .,1.150 0.02385 0.02431 0.00193 12.62 - 4.23 33.88 - 57.65 48-P 1.502 0.02435 0.02751 0.00171 16.06 - 4.10 38.73 - 69.91 73-P 1.899 0.02:397 0.02576 0.00181 14,25 -14 .80 64, 76 -22.5.8 79-P 3.554 O. 01783 0.02087 0.00052 39.79 - 4. 19 61.53 -170.82 Not calculated. The computer pr?gra.m could not pro~uce consistent results for this experiment. 58 than so . 3 The deviation from the scheme• for 74-P probably results from minor experimental errors. Throughout the experimentation every effort was made to keep stirring rates, mixing times, and concentra= tions as constant as possible. If there were no secondary reactions, these factors would be unimportant; but since secondary reactions are present in the system~ small changes in experimental conditions could measurably influence the results. Of particular concern were stirring rates and the concentration of aromatics in the small chamber (see Experimental Sulfonation Procedure Section). The sulfonation reaction is very fast and so mixing and stirring rates are critical. The aromatic solution was added to the dilute so3 solution (which would result in a reduced sulfone product 105) and local excesses of aromatics caused either by inadequate mixing or variations in aromatic concentrations in the small chamber could cause sericus effects. It is most probable that the minor deviations found i.n the data result from such causes.

At small Bi/Ci ratios, the amount of BS formed in the main reaction causes BS to increase relative to CS while at higher ratios, the reverse is observed. At some ratio, conditions will be such that these two effects will balance each other. From Figure 7 this should occur at the point where the apparent kB/kc is 11.5. The observed Bi/Ci ratio at this point is 0.14. It is not surprising, therefore, that a variation of BS/CS with so3 concentration at

B,/C. ~ 0.129 (Figure 9) is not observed. It is also interesting J. J. to note that the point where the signs change for A% BS and A% CS 59 values in Table 8 occurs between 0.15 and 0.18.

The BS and CS values expected for reactions with no secondary effects we:re converted to mole fraction values .for comparison in

Figure 8 (dashed curve). The general shape of the dashed curve is similar to that of the curve representing the actual results but it is noted that at higher XBi/so values the actual a.mount of BS 3 produced is less than predicted and a cross-over point is obtained for this curve also. Although the actual data for 84-P, 86-P, and

87-P did not fit the curve in Figure 8, the predicted values also fail to fit the dashed curve. There is good agreement between the predicted and actual values for 84-P and 86-P (B1/ci = 0.129) while

87-P (B./C. ~ 00902) gives an actual value below the predicted one. 1. l. An approach similar to that above was foll.owed to interpret data obtained from the BS/CS vs. so3 concentration (Figure 9) for Bi/Ci"' 0.708. A series of twenty data points was taken from the curve and the values for BS and CS which would have been predicted with no side reactions were calculated. Table 9 tabulates the results of these calculations and compares the BS and CS values which fit the curve with the predicted values. A gradual i.ncrease of ~ CS with a cor~esponding decrease in l:J,,BS is noted as the so 3 concentration increases, This is also in accord with the p:remi.se that at this

B1/C1 ratioj secondary _reactions will contribute more to the formation of the product from the less reactive species, '

TABLE9

COMPARISONOF ACTUALvs. PREDICTEDBS9 cs~ ANDBS/CS ..VALUES FOR _B/~\, ~ _0~708 DATA

~·-4,.~-- -·-

so3 Concentration BSC BS csc cs RC R 6.BS 6CS AR (M.iL) Cxl93> (x~03) -,,,, 0.0100 0.01022 --0,01016-- 0,00128 0.00134 7.99 7.60 -0.06 0,06 0.39 - 0.0125 0.01277 0.01249 0,00161 0.00189 7.94 6.62 -0.28 0.28 1.32 0.0150 0. 01531 0.01479 0.00194 0.00246 7 .89- 6.02 -0.54 0,54 1.87 0.0175 0,01785 o. 01706 0.00228 0,00307 7.84 5.56 -0. 79 o.79 2.28 0.0200 0.02038 0.01929 0,00261 0.00371 7.79 5.20 -1.09 1.10 2.59 0.0225 0.02292 0,02147 0.00296 0,00441 7.74 3 .87 -1.45 1.45 2.87 0.0250 0.02544 0,02363 o. 00331 0,00512 7,69 4.6.l -1.81 1.81 3.08 ·o°' 0.0275 0,02797 0. 02572 0.00366 0.00590 7.64 4.36 -2.25 2.24 3.28 0. 0300 0.03048 0,02779 0,00402 0,00671 7.59 4.14 -2.69 2.69 3.45 0. 0325 0.03300 0.02984 0,00438 0.00754 7.54 3.96 -3 .16 3.16 3.58 0. 0350 ·0.03551 0.3183 0.00474 0.00842 7.49 3.78 -3.68 3.68 3.71 0.0375 0.03801 o. 03383 0.00511 0.00929 7.44 3~64 =4.18 4.18 3.80 0.0400 0.04052 0.03580 0.00548 0.01020 7.39 3.51 -4. 72 4. 72 3.88 0.0425 0,04301 o. 03777 0.00586 0.01111 7.34 3.40 -5.24 5.25 3 .94 0.0450 0.04550 0.03972 0,00625 0,01203 7.28 3.30 00 5.78 5.78 3.98 0.0475 0.04799 0. 04165 0.00644 0.01298 7.23 3.21 -6.34 6.34 4.02 0,0500 O. 05047 0.04358 0,00703 0.01392 7.18 3 .13 -6.89 6,89 4.05 0,0550 0.05542 0,04744 0,00783 0,01581 7 .07 3.00 -7.98 7,98 4.07 0,0575 0,5788 o. 04938 0,00824 0.01674 7.02 2.95 -8.50 8.50 4.07 61

Competitive Sulfonation in the Benzene-Toluene System

In an earlier investigation of the sulfonation of toluene by 60 so3 in liquid so2~ Guillot found a variation of kT/kB with B1/Ti. The apparent Ic.r/kB values remained reasonably constant up to a Bi/T 1 ratio of ·about eight. At hi.gher ratios, the apparent relative. rate values increased sharply. Guillot's curve is reproduced in Figure 11,

There are only eight data points on the curve and some scatter is observed at lower Bi/Ti, It is believed that the dip shown in the curve is not significant and arises from a normal point scatter for the reaction which is reminiscent of that found under similar condi= tions with chlorobenzene=benzene sulfonations.

The general shape of the curve suggests that secondary reactions are occurring. In this sytem toluene is the more reactive aromatic and a sharp increase is apparent in Ic.r/kBonly when very small amounts of the more reactive species are present, If kT/kB vs"

T1/Bi is plotted (Figure 12)~ then a curve resembling Figure 7 fo:r the chlorobenzene-benzene system is obtained.

A series of sulfonations were made in the benzene~toluene system. Two experiments (21-P and 22-P) were made using Guillot' s

UV spectrophotometric method. These are included in both Figures 11 and 12. A third experiment (47-P) was made using the count-:rate method to see if° the. two analytical schemes ga·ve comparable results,

The result of 47-P is plotted in Figure 12 (sh.a.dad ci.:rcle) and seems to agree reasonably well with the other data. The remaining experi= ments were conducted at constant ·T1/Bi ratios with varying amounts 62

2.5

4 6 12

,,,-- B./T. l. ].

Fig. 11.=-k._r/KBas a Function of B./Ti for the Sulfonation of Benzene-Toluene Mixtures with so3 in Liqui3 so2• T:: ~12.5° C. 63

·30

0 10 0 00

0.2 0.4 0.6 0.8 LO

Fig. 12.==Apparent k.r/kB as a Function of Ti/Bi ,·for the Sulfonation of Benzene=Toluene Mixtures ~ith so3 •in liqu1d so2 at T::: -12.5° c.

\ 64

of so3 . The results of these experiments are presented in Table 10. Experimental and analytical details are given in the Treatment of

Data Section.

TABLE10

COMPETITIVE SULFONATIONSIN THE TOLUENE-BENZENESYSTEM

S03 Experiment Ti/Bi BS TS Concentration TS/BS k.rlkB No. (M./1.)

2l=P 0.136 0.0158 0.0233 0. 03697 12.33 22=P 0.984 0.0020 0.0230 0.02277 10.61 47=P 0.126 0.01314 0.02801 0.03436 27 .12 88-P 0.858 0.001070 0.00512 0.006192 4. 787 89-P 0.858 0.01312 0.04221 0.08258 3 .217 9l=P 0.858 0.002957 0.01722 0.02925 5.823 93-P 0.858 0.000172 0.00311 0.004148 18.050 95=P 0.858 0.002373 0.01592 0.02613 6.707 96~P 0.279 0.003697 0.01531 0.02639 4.140 97-P 0.279 0.002582 0.00976 0.01755 3.780 98-P 0.279 0.001174 0.00669 0.01124 5.700 99-P 0.279 0.000277 0.00279 0.00439 10.079

The way TS/BS changes with so3 concentration is shown in Figure 13. The two curves in this figure exhibit the same general

features that were characterisitc of the curve for the chlorobenzene~ benzene system in Figure 9. At higher so3 concentrations, the upper curve begins to level off to a marked degree. In terms of the

secondary-reaction mechanism, this would correspond to a situation where the sulfonation by so3 is now contributing a minor - if not negligible - amount of the total product.

On the basis of the similarity of these data and of subse-

quent data to those of the benzene-chlorobenzene system~ it is postu- 20 0 T./B, : 0.858 ' . l. 1. 18 El ti/Bi :: o.279

C.' TS/BS V, 10

4 ______f _..__~. 2

0.01 0.02 0.03 0.04 0.0.5 0.08 (SO,.,) .J

Fig, 13, --Variation of TS/BS as a Function of SO".).) Concentration 66

lated that the same general mechanism of sulfonation by primary

and secondary reactions is occurring in this system. The same kinds

of secondary sulfonating species would be present, chlorobenzene-

pyrosulfonic acid and the chlorobenzenesulfonic acid anhydrides

being replaced by the corresponding toluene compounds. Equations

40=69 will have their exact counterparts in the benzene-toluene system.

The ratio of rate constants for the sulfonation of toluene

and benzene in the absence of secondary reactions was determined

in the same manner as in the chlorobenzene=benzene case. A plot

of moles of product as a function of so3 concentration was made (Figure 14). This plot again showed the product of the less reactive

aromatic (BS) increasing at the expense of the product of the more

reactive aromatic. Careful extrapolations of the data to very low concentrations gave straight lines from which the results in so3 Table 11 were obtained. Values used for Bi/Ti were 0"1667 and 0.1396

for the Ti /Bi : 0. 858 line and 0. 2386 and 0" 0666 for the T ./B. = l. l. 0.279 line. From these results a 'k.rlkB value of 27.0 ± 1.0 is obtained.

The data for one reaction (88-P, T./B. : 0.858) are not l. l. given in either Figure 13 or Figure 14. In' this experiment, a volume of 1000 ml. was used while in the remainder of the experiments

in the series, an average of about 700 ml. was used. The TS/BS value for 88=P is lower than would be anticipated. It is believed that

complete mixing did not occur as rapidly in the larger volume as it

did in the smaller volumes. This caused local excesses of aromatics 67

0.048 G) ·T. /B. : 0.858 l. l.

0.044

0.040

0.036

0,032

0.028 Moles of Product 0.024

0.020

0.016

0.012

0,008

0.004

0;01 0.02-. 0.03 0.04 0.05 0.06 0,07 0.08 0,09

..,: .· Fig, 14.--BS and TS as Functions of Concentration so3 68

TABLE11

RELATIVERATES CALCULATED FROM EXTRAPOLATIONS IN THEBENZENE-TOLUENE SYSTEM

BS TS Ti/Bi (From (From k'T/kB • Extrapolation) Extrapolation)

0.858 0.00052 0.01142 27.52 0.00069 0.01516 28.52 0.00086 0.01889 28.06 0.00060 0.01329 27 .89 Av. 27. 91.±,0.14 0.279 o. 00156 0.01052 25.32 0.00200 0.01354 26.32 0.00112 0.00750 26.05 0.00134 0,00902 26.49 Av. 26 .16.±,0.35

which in turn gave rise to additional secondary products and a

lower TS/BS ratio. Such sensitivity to mixing rates is not observed in situations with no secondary reactions.

The amounts of BS and TS which would have been formed in the

absence of any secondary reactions in the constant Ti/Bi series

(Figure 13) were calculated and.compared with the amounts actually

formed. Table 12 presents the results of these comparisons. The

expected pattern of increasing A BS and decreasing b. TS with

:Lnc:reasing is found. The data for Ti/Bi= 0.858 cover a wide so3 range of so3 concentrations. It is seen that at the largest concen= •' tration of S03. the actual amount of BS produced is more, than 4. 5

times the amount predicted. Since the calculations which lead to

the predicted BS values assume all of the is consumed in the so3 TABLE12

COMPARISONOF ACTUALVS. PREDICTEDPRODUCTS FROM T 1/Bi:: 0.858 ANDTi/Bi:: 0,279 ~ --~~~•:-<,---~- ~~-~--~ ...~ .... "9'T',-,e--. - ' -~ - -~ ~ - --- ~- Experiment BSC BS TCS TS RC BX L.\BS llTS _so _ 3 3 3 3 'T'./B·~ l. ]. No. (:d0 ) {xl0 ) (xlo3) (x~93) I§.Q, 12, (x;I.o j (x~Q3) .tl R Cone. ~SC.. {M./1.) ,, ______.._,...... _,. ~~ 0.279 2 -0.634 0.614 4.616 -4.636 ·• -7-,28-- 7.55 - 0.010-' 0,020 0.27 0.0075 3 0.854 0.975 6.146 6.025 7.20 6,18 0.121 - 0,121 - 1.02 0.0100 4 1.079 L357 7.671 · 7 .393 7 .11 5.45 0,278 - 0.278 - 1.66 0.0125 5 1.309 1. 765 9.191 8.735 7.02 4.95 0,456 - 0.456 - 2.07 0.0150 6 1.544 2.248 10.706 10,002 6.94 4.45 0.704 - O. 704 - 2.49 0. 0175 7 1.784 2.692 12.216 11.308 6.85 4.20 0.908 - o. 908 - 2.65 0.0200 8 2.030 3,088 13.720 12.662 6.76 4.10 1.058 - 1. 058 - 2.66 0.0225 9 2.282 3.500 15.218 14.000 6.67 4.00 1.218 - 1.218 - 2.67 0.0250 °'\0 10 2.539 3.850 16.711 15.400 6.58 4.00 1.311 - 1.311 - 2 •.58 0.0275 0.858 11 0.073 0.084 L677 1,666 23 .05 19.75 0.012 - 0.012 - 3.30 0.0025 12 0.146 0,188 3.354 3.312 22.92 17 .60 0,042 - 0.042 - 5.32 0.0050 13 0,221 0.317 5.029 4.933 22. 79 15.55 0.097 - 0.097 - 7 .24 0.0075 14 0,296 0.473 6.704 6.527 22.66 13.80 0.177 - 0.177 - 8.86 0.0100 15 0.449 0.882 10.051 9.618 22.40 10.90 0.434 - 0.434 -11.50 0.0150 16 0,605 1.451 l3 .395 12.549 22.14 8,65 0.846 - 0.846 -13 .49 0.0200 17 o. 765 2.188 16.735 15 .313 21.87 7.00 1.422 - 1.422 -14.87 0.0250 18 0.929 3.044 20,071 17 .967 21.61 5.90 2.115 - 2 .115 -15.71 0.0300 19 1.097 3. 952 23,403 20.548 21.34 5.20 2.855 - 2.855 -16.14 0.0350 20 1,269 4.956 26.731 23 .044 21,07 4.65 3.687 - 3.687 -16.42 0.0040 21 1.445 6.058 30.055 25.442 20.80 4.20 4.613 - 4.613 -16.60 0.0045 22 1,626 7.292 33.374 27.710 20.52 3.80 5.666 - 5,666 -16,72 o, 0050 23 1.812 8.556 36.688 29.944 20,24 3.50 6.743 - 6,743 -16.74 0. 0055 24 2.240 10,500 43.960 35.700 19.62 3.40 8.260 - 8.260 -16,22 0.0060 25 2.403 11.667 46.597 37.332 19.39 3.20 9.264 ~ 9.264 -16, 19 0.0070 26 2,827 13.333 53.173 42 .667 18,81 3.20 10.506 -10 ,506 -15.61 0.0080 27 30280 15.000 59.720 48.000 18,21 3.20 lL720 -11.720 -15.01 0.0090 70

primary te~ction, the predicted value is certainly high; and a much

larger difference must actually exist between the amounts of BS

fo:r.med in the primary and secondary reactions.

A detennination of the relative contributions of the primary

and secondary reactions to the total product would be desirable.

Because of the complexity of the system, an exact calculation of

relat.ive. contributions is not possible. The concent:ra.tions of the

various sulfonatir.,g species can be expressed in terms of the starting

reactants and several attempts were made to apply curve-fitting

methods to the curves obtained at constant Bi/Ci and Ti/Bi ratios.

The systems were too compl:i,cated and too many unknowns were present

· in the calculations for this approach to succeed.

An estimate can be made, however, if assumptions are made

about the ratios of products from the primary and secondary reac-

tions. The ratio TS/BS for reaction by so3 in. the absence of second~· a:ry reactions can be calculated. This :ratio varie.':! slightly with

the concentration of so3 involved in the primary reaction but was assumed to be constant for this estimation. The curves in Figure

13 show that TS/BS becomes essentially constant larger concen- at so3 trations. This could occur only if secondary reactions were predomi-

nent at these so3 concentrations. It was assumed that: the TS/BS ratio in the horizontal portions of the curves represented the ratio

of products from the secondary reaction. The relat:f:vely small values

of these TS/BS ratios implies that the secondary sulfonating reagents

are more reactive than S03"_ A series of calculations were per.formed

(see Treatment of Data $ection) using these assumptions and the 71 results are tabulated in Table 13. No calculations were made in the chlor.obenzene-benzene system since the BS/CS ratio had not .. reached a sufficiently constant value. The data points were taken from curves in Figure 13.

TABLE13

RELATIVE CONTRIBUTIONSOF PRIMARYAND SECONDARY REACTIONS IN THE TOLUENE-BENZENESYSTEM

S03 Fraction of Total Concentration so3 Consumed in (M. /1.) Primary Reactions

0.279 0.0100 0. 7786 0.0125 0.5863 0.0150 0.4238 0.0175 0.2232 0.0200 0.1060 0.0225 0.0551 0.0250 0.0000 0.0275 0.0000 0.858 0.0025 0.9664 0.0050 0.9391 0.0075 0.9062 0.0100 0.8708 0.0150 o. 7886 0.0200 0.6900 0.0250 0.5818 0.0300 0.4806 0.0350 0.3973 0.0400 0.3170 0.0450 0.2382 0.0500 0.1553 0.0550 · 0.0831 0.0650 0.0571 0.0700 0.0000 0.0800 0.0000

The results in Table 13 show tha:t there is a g:rndual decrease in the importance of the primary reaction as S03 concentration 72

increases. The relative unimportance of secondary reactions at

low concentrations justifies the extrapolation procedures used so3 in determining I<:.rlk:s·

Isomer Distribution for th~ Sulfonation of Chlorobenzer1e

The isomer distribution for the sulfonation of chlorobe:nzen~ with so3 i.n liquid sulfur dioxide at ..:12.5° C. is given in Table 14 together with the isomer distributions for the sulfonations of toluene and other halobenzenes under the same con.ditions. The me.t1 value for bromobenzene is questionable.

TABLE 14

ISOMER DISTRIBUTIONS FOR THE SULFONATION OF TOLUENEAND CHLORO-, BROMO-, AND IOD000 BENZENE

Arow.ati.c %.Q % .ill •. % .2 Lit . Compound ReL Toluene 10.03 .:L0.20 0.73 -+ 0.20 89.2.4 + 0.2 61 Chlo:robenzene 0.95 + 0.03 0.09 + 0.02 98.96 .± 0.12 This work Bromobenzene 0.6 + 0.2 3.6 + 0.8 95.9- + 0.6 107 Iod.o'benzene 1.40 ± 0.11 o.34 I 0.11 98.26 + 0.11 119

Counting for this determination was done on a planchet in a Geiger

Co-:i:nter while. the other values in the table resulted from a more accurate scintillation counting technique. Evaluation of the origi- na.1 data also casts doubt on the purity of the meta isomer. Redete.r= mi!'!.ation of t.he bromobenzene values are expected to b·r:i:ng them into positions intermediate between chlo:robenzene and iodobenzene,

The sulfonation of chlorobenzene by so3 in liquid sulfur 73 dioxide at -12.5° C. is seen to be a very selective reaction, t:he

E~~/~ ratio being larger than for the reaction on iodobenzene. 105 This pa:rall_els the obeervations of Roberts~ et al., for the nitration of halobenzenes. The small percentage of ortho isomer fo:r chlorobenzene as compared to iodoben:zen~ is surprising since the bulkier iodo~group might be expected to inhibit :reaction at the ortho position. This reversal of the expected trend in ortho/Qara ratio was also found by Roberts and a majority of the investigators in Table 1 (Reactions 2=5, 7-12, 14-17, 21, and 22). The steric- predicted order is found in only three instances where sufficient data are presented for comparison (Reactions 13, 18, 19). A large ortho/Qara ratio has occasionally been used as evidence for extensive ff-complex formation and it may be that the large~ polarizable iodine atom might enter more easily into such bonding than the chlo:ri.ne atom. The relatively low percentage of ortho isomer, when compared to other values found in Table 1, is attributed to the steric requirements of the comparatively bulky so3 group.

A decreasing para/meta ratio (decreasing selectivity) and decreasing reactivity are generally found for the sequence fluoroj chloro~• b:como with occasional irregularities in the iodo group.

The electron withdrawing inductive effect is known to follow the order F) Cl) BR) I, and the above order of reactivities would seem to imply tb..at the electron releasing resonance effect is in the reverse order although there is still some dispute about the relative: 53 direction. of this latter effect.

Secondary re.actions within a system would be expected to have 74 an effect on the isomer distribution. Variations in the different

steric requirements and reactivities of the different electI·ophile could effect both ortho/para and _Era/meta ratios. Not enough is known about the reactivities of the possible secondary sulfonating

:reagents to permit any predictions. Under suitable conditions 9 however, it might be possible to detect secondary reactions .~s a co~sequence of their steric effects.

In this regard a comment should be made about Cerfonta.in • s study of th.e sulfonat:ion of toluene and toluen,e-ben.zene mi:l!'.tures"

Table 15 presents his data which show that tli:e ort:ho/,eara isomer ratio decreases as perc'ent toluene conversion increases when neat toluene is sulfonated. His data also show (Table 16) that the o:rthq/para ratio decreases as the Bi/Ti ratio increases. Although

Ce:rfo:ntain discounts secondary sulfonation reactions in his :system; the data seem to confirm their presence. It should be emphasized that Cerfontain considered only pyrosulfonic acid side~reactions and not reactions of the acid anhydrides which Christensen believes to be more powerful reactants.

Equations 66~68, indicate that the concentrt:itions of anhydrides in the toluene systems would be proportional to the concentration of and to the squares of the concent:r:ati.on.s of the so3 benzene- and toluenesulfonic acids. From Equations 51-56j it can be seen that the H2S04 terms will drop out in the kinetic equation for the formation of product. Cerfontain bubbled so3 through the aromatics and so maintained a constant concen.tration. of so , The 3 co:m::entrations of anhydrides increased as product was formed which 75

TABLE15 VARIATIONSIN ISOMERDISTRIBUTION WITH PERCENT TOLUENE CONVERSION 2.5° C. IN CERFONTAIN'SSULFONATION OF NEATTOLUENE WITH so 3 AT

% Sulfonic Acid Isomer Toluene Distribution Conversion £ ~ .e. 0.03 18.0 4.6 77 .4 0.09 13 .1 5.7 81.2 0.26 13 .2 5.1 81.7 0.31 16.0 4.1 79.9 1.14 16.2 4.9 78.9 100.0 11.7 2.8 85.5

TABLE16

ISOMER DISTRIBUTIONS AND RELATIVE RATES FOR CERFONI:'AIN'S COMPEII"rIVE SULFONATIONOF BENZENE-TOLUENEMIXTURES AT 25° C.

Isomer Distribution for Toluene Bi/Ti !vr/kB Sulfonic Acids

,Q ~ .E. 1.2 9.1 18.7 2.8 78.5 2.0 13.9 16.7 2.7 80.6 10~0 9.3 17 .o 2.7 80.3 29.9 6.9 12.1 2.1 85.3 59.8 11.8 10.5 1.7 87.8 II is in keeping with Christensen's observation that: more anhydride 33 products are isolated at larger so3/ArH ratios • Since all of the postulated secondary sulfonating species are bulkier than , and so3 since stet'ic effects predominate in determining ortho/.E,era ratilDs ~ it would be expected that the ortho/para ratio should deer.ease as the reaction progressed. 76

The variation in ortho/para ratio with increasing Bi./Ti is

also understandable when secondary reactions are considered. Accord~

in.g to previous considerations, the secondary reac·::.:ions con.tribute

an i.nc:re.<1sing perce.:.1.t.~ge of. product as the amount of product made.

from the primary reaction decreases. We would predict, then~ th.at

as the Bi/Ti ratio increases and the amount of the TS produced by

the: primary :reaction' decreases, more of the product TS will be ma.de

by the secondary re.actions and the ortho/£e:t:a ·ratio will decrease.

When the isomer distribution experiments were being performed

for the toluene and chlorobenzene systems, the possibility of us:i:ng

orthQ/Qara ratios as a means of investigating secondary r~actions

had not become apparent. As a consequence, no attempt: was made to

deliberately vary the so3 concentration as isomer distributions wer~ determined. In the chlorobenzene system, the amounts of so3 and aromatic were kept quite constant, but there was a g:re.-!lte.r

variation of reaction conditions fo:r the toluene system.

Table 17 gives the experimental ~onditi.m1s and the ~/pa.t'a

ratios for the sulfonation of chlorobenzene in this work and for

Gu.ill,ot I s sulfonation of toluene. No significant var:i.atior;J is found

in the chlorobenzene data, but a small variation is noted for the

tolue·ne data. The difference between the la:rgest ort:ho/par.E!_ ratio

and the smallest is outside the error limits Guillot claims for his

data. The smallest ortho/para ratio is found for the largest so3 concentration which is what is expected and the ortho/pa:ra ratios

at lower conc::entrati.ons are larger than those at the higher so3 so3 concentrations. The data for 13-Q-B is out of order, since 9 on the 77 basis of so concent-ration alone, this experiment· should have the 3 largest ortho/l~~ra ratio. The concentrations of anhyd:r~des i.n the

system, however, would be dependent not only on the so~.;p concentration~ bu.t aiso m.~ the /ArH ratio. Whether the increased /ArH for so3 so3 13~-Q-B is sufficient to increase the an.hydride conc~ntration eirnough

TABLE17

ORTHO/PARARATIOS FOR THE SUL'F'ONATION OF CRLOROBENZENEAND TOLUENE

S03 Ml. of · System Experiment Concentration Aromatic so3 /ArH 2-IE. No. (M./1.) per Ml. of Solution

Chloro- benzene 62=P 0.0230 12 0.0019 0.0099 2.0-P 0.0292 2'7 0.0011 0.0094 71=P 0.0293 27 ! 0.0011 0.0092

64-P 0.0329 27 ! 0.0012 0.0098 70-P 0.0340 27 I 0.0013 0.0097 i Toluene 13-Q-D 0.0492 10 0.0049 0.100 13=Q-E 0.0467 8.7 0.0054 0.112 13-Q-B 0.0194 2.6 0.0015 0.115 13-Q-C 0.0254 4.2 I 0.0061 0.132

to cause the lower ortho/,Ea~ ratio is not known. Of course any conclusions about the existence of secondary reactions drawn from these data must be highly speculative, because of th~ small differences in the ratios obtained. Nevertheless, the apparent trend is in the right direction and it is not out of harmony with the other results of this study. 78

Isomer Dist·ributions in the Competitive Sulfonation of Toluene and Benzene

A much better indication that isomer dist:ributions a:re influ-

enced by secondary reactions was obtained from UV studies of the

pr.·oducts of the benzene-toluene competitive e:xperiments. Ce:dontai!ll

and co-workei·s have developed methods for analyzit.tg the L'V spectt'1U\m

of a mb:tu:re of sulfonic acids by crnnparin,g it with the UV spectra

of the component acids. By suitable computer ted:1..niques the UV cu:cve

of the mixture is matched against the UV curves of the components

and the composition of the mb:ture is determined. This method

requires great care in obtaining the absorbance values of the sulfonic

acids, pa:rticularly when the UV curves of several components are

quite similar. Cerfontain uses a modified spectrophotometer which

allows immediate comparison of the absorbance of the mi.:il',t.m:e at each wavelength with the absorban.ce of the pure component at that wave-

length.

An attempt was made to utilize the above technique in analyzing

the products of the benzene-chlorobenzene competitive sulfonations,

A Beclrnlan DK-2 recording spectrophotometer was used to obtain UV

spectra and a STAT03 multiple-correlati.on and regression analysis

program was used in conjunction with the IBM 7040 computer to analyze

the spectra. Unfortunately, the UV curves of the variol..:!s isomers were too similar for this technique to succeed,

The t:ecb.n:i.qu.ewas more successful when applied to the benzene-

toluene sulfonate mi%tures. Toluenesulfonates are present in greater.

abunda.nce than benzenesulfonates in the Till\ :.: 0,279 and T1/Bi ~ 0.858 79

series of experiments. The UV curves of the various components

are also less similar than those of the chlorobenzene-benzene-

sulfonate mi~tures.

A Carey 15 recording spectrophotometei:· was used to obtain

the UV spectra of the products of Experiments 89-P through 99-P.

'I:he results obtained by this method are not believed to be as acicu:r:;l.te

as Cerfontain 1 s results since a special spectrophotometer was not

used, Sl'llSll errors were unavoidably introduced by reading absorb-

ance values from the curve, from instrumental drift, and from

small changes ih the base lines of the curves, etc. As a re:sult

of these errors, two experiments (91-P and 97-P) did not give meani.v,g=

ful values and are not included in the table.

An analysis of the data which comps.red the UV curve of a mixture against the curve of sodium benzenesulfonate and the curves

of the three sodium toluenesulfonate isomers gave results indicating

that approximately equal amounts of ortho and ~ isomers had beeri

formed. This is undoubtably not the case. The UV curves for the ortho and -meta isomers are very. similar and with the e:r:cors mentioned above~ it is most likely that the computer was unable tc, correctly disce~n between the concentrations of the two isomers.

The UV curves of the product mixtures were analyzed using a program which considered the ortho and !!!ili isomers as one component.

The results of this analysis are given in Table 18. The amounts of

.E.,.~ isomer did not differ greatly from those of the original analysis and the UV curves obtained by mixing the component's curves matched the actual curve as well (t 1%) as did the first analysis. 80

TABLE18

ISOMERDISTRIBUTIONS AS A FUNCTIONOF S~~ CONCENTRATION IN TOLUENE-BENZENECOMPETITIVE SULFONATIONS .

so3 % % Experiment Ti/Bi Concentration .Q + !!! .E. (Q+.m)I.E. No. (M./1.)

93~P 0.858 0.00415 13 .o 87.0 0.149 95-P 0.858 0.0261 8.5 91.5 0.093 89~P 0.837 0.0826 5.7 94.3 0.060 99-P 0.279 0.00439 15 .2 84.8 0.179 98-P 0.279 0.0112 8.6 91.4 0.094 96-P 0.279 0.0264 8.8 91.2 0.096

For these reasons, it is believed that the results in Table 18 reflect the actual relative concentrations of the isomers as well as the limitations of this analysis permit.

The results in the table clearly show a decrease in the

(ortho +~)/para ratio with increasing so3 concentration. Guillot's data show that about fourteen times as much ortho isomer is produced as~ isomer and Cerfontain 1 s data do not show a very large change in the percent of~ isomer even though the ortho/para ratio does vary with experimental conditions. The change in the (ortho + ~) /J!,_ar~ratio, therefore, results"principally from changes in the rela~ tive amounts of the ortho and para isomers. It is believed that the data in Table 18 reflect the effects of the increasing contributions of secondary reactions to the reaction products.

Partial Rate Factors for the Sulfonation of Toluene and Chlorobenzene

The partial rate factors can now be calculated for the reactions investigated in this work. Table 19 gives the pertinent results, 81

TABLE19 PARTIALRATE FACTORS

Aromatic Chlorobenzene Toluene Pf 0.517 144.6 Of 0.0025 81.2 ID£ 0.00024 0.59 log Pf -0.287 2.159 log Pflmf 3.33 2.389 kx/kB 0.0870 27 .o . .i 1.0 % .Q 0. 95 .±.0. 03 10.03 .±.0.2 %!!! 0.09 .±.0.02 0.73 .±.0.2 % .2 98.96 .i 0.12 89.74 .±.0.2

The average isomer distributions and the extrapolated values for

kx/kB were utilized in the calculations. The resulting log values

are included in Figures 4 and 6. Neither sulfonation fits the

selectivity relationship predicted for it.

The deviation of the sulfonation point from the chlorobenzene

line is perhaps the more easily understood. This tendency to deviate

is shared with the other less reactive electrophiles represented in

Figure 6 and appears to result from interactions with the non-bonding

electrons on chlorine. It seems likely that the incoming electrophile

is first associated with the electron cloud around the chlorine

atom and then shifts intramolecularly to the ring. Two similar

representations might be visualized. In the first representation,

two distinct 1f complexes are formed followed by conversion to the

(7'intermediate. If the transition state energies leading to either ff (Cl) or ff (ArCl) were larger than that of the er -transition state, there would be little or no correlation between selectivity 82

6*~-6-4E•,&E•-► 0 (71) 7T(Cl) ,,r (Arel) E H

)( and reactivity. In the second representation, one might also

visualize a single 1r complex in which the electrophile is inter- acting strongly with the electrons of both the ring and the chlorine

atom.

> (j·~➔~ (72)

1( X~ X

Again, the relative heights of the energy barriers leading to the

fr_ and r-complexes would determine the extent to which the system

fits the selectivity relationship. The existence of a '11' complex

like X could also lead to unusual ortho/2ara ratios, although it is

expected that the so3 group would be so sterically hindered as to favor the para intermediate. The lack of agreement of the sulfonation data and the selec-

tivity relationship for the toluene situation is more difficult to ·": ·, explain. Considerations of secondary reactions helped to:move the

sulfonation point closer to the expected line than Guillot's point, but was insufficient to bring about exact agreement. The isomer 83

distribution values used in calculating partial rate factors were

not corrected for secondary effects and adjusted values may give a

small improvement in fitting the data to the- selectivity line. In his study, Cerfontain suggested that either a significant

amount of 'l(character was present in the transition state or that

differences in salvation existed in the transition states. In view

of the many electrophiles that fit the selectivity relationship for

toluene, there seems to be no.!, priori explanation why should so3 form an exceptional type of transition state. 112 It has recently been discovered that sulfur dioxide forms

a 1:1 incongruently melting compound (m.p. -58° c.) with benzene and a 2:1 toluene-sulfur dioxide compound of congruent m.p. -95°· C.

The formation of such compounds may indicate a stronger-than-usual

interaction between solvent and aromatic. The solvation of the

transition state will surely be different from the ground state.

Sulfur dioxide forms complexes with the aromatic electrons because

it is an electron acceptor. Inclusion of the so3 group in the transition state will greatly decrease the electron density of the ring

and, hence, the transition state will probably not be as highly

solvated as the ground state. The relative magnitudes of such effects

on the transition states leading to the different products is not known.

There is also reason to suspect the amount of~ isomer found in the toluene isomer distribution. The mf value of 0.59 is -unreasortib~~;,The~ factor should be smaller than the ortho and Qara factors but it should not have a value less than unity. No 84 position on the toluene ring should be less reactive than a position on benzene. Guillot did not canpletely purify his !!!ill isomer but had to make a slight extrapolation to obtain the final value.

Another source of error was introduced when he ..did not use .e.-toluid.ine samples for·background counting blanks. The background count rates, which were subtracted from the total count rate for calculation purposes were, therefore, not corrected for color quenching. This would introduce a small error in all of the isomer distribution values but the error would be most serlous in the case of the meta isomer. Failure to correct for color quenching of the background count rate makes the percent~ isomer too small. ;Spryskov and 113 Gredin report between 2 ana 3.8 percent !!!ill isomer for the so3 sulfonation of toluene in liquid sulfur dioxide at -80° C. If the

~ factor was 2.7 (corresponding to 3.3% ~ isomer) the sulfonation data would fit the selectivity relationship. CONCLUSIONSAND RECO?-MENDATIONS

Data have been presented for the sulfonation of two widely different aromatic compounds which suggest that secondary reactions play significant, and under certain conditions, dominant roles in sulfonations by so3 in liquid sulfur dioxide. Anomalous variations of apparent kx/kB, isomer distributions, and product ratios can be interpreted in the light of these reactions. The isomer distribution of Cerfontain 1s sulfonation of toluene in the absence of solvent can also be interpreted in this manner. , 31,32,33 By analogy with Christensen s work, these secondary reactions may be important in many aprotic solvents. The lack of a significant variation of ~/kB with changing Bi/Ti convinced

Cerfontain 30 that secondary reactions were not occurring in his system. Guillot, however, also obtained a region (up to Bi/Ti= 8) in which constant k-:r/kB values were obtained and a similar horizontal portion of the curve is also evident for the chlorobenzene system.

An important corollary to the interpretation of secondary I reactions can be'made. If the interpretation of curves in Figures

6 and 10 are correct, horizontal portions of such curves are most likely to occur when large amounts of secondary products are formed.

Thus, the classic test for the presence of such effects and for the applicability of Ingold 1 s equation (constant kz:I~ with changing

85 86

Xi/Bi) would give the same results - a constant k,r/~ ratio - when there are either B.2 secondary reaction effects or large sec- . ondary reaction effects, and it is only in intermediate situations when the expected deviations are noted. Thus, if in the present chlorobenzene sulfonation studies, a Bi/Ci range of 1 to 10 or even 1 to 100 had been selected, the apparent k;s/kc values would have been reasonably constant and it would have been decided that no secondary reactions were occurring.

These conclusions suggest that criteria for the applicability of Ingold 1s equation are more complex than usually realized. If one is to be certain that secondary reactions are not important, he must include ratios of starting materials ,.that will,. p:r.oduce an excess of product from the less reactive aromatic in testing the constancy of 1,c/kB. Plots of benzene product/substituted-benzene product vs. electrophile concentration should also be made. The electrophile concentration should cover a wide range including the smallest practical concentration values and several different ratios of starting material shouid also be employed to avoid the coincidence found for the B./C. 0.129 curve (Figure 9). Care l. l. = should also be taken in determining isomer distributions - wide ranges of electrophile/aromatic being used to insure that variations in the ortho/para ratio will be apparent if secondary effects are present. These criteria should be applicable to any electrophil- aromatic system and are not restricted to sulfonation reactions.

1 ·i~-~~~y~eresting : possibility exists if it is assumed that secondary reactions were occurring in Cerfontain's system. If it 87 is assumed that·at minimum toluene conversion minimum secondary effects are taking place, .the isomer distribution, which should be employed for the determination of partial rate factors, is

% ~ = 4.6, and%£= 77.4. Cerfontain's reported k.rl~ value was 9.2 and corresponded to the average value for the k.r/kB range studied.

The average value for Guillot's "constant" Ior/kB was 9.7. After correction for second~ry reactions, I<.r/kB becomes 27.0. If we arbitrarily use Cerfontain 1s isomer distribution and a I<.rl~= 27.0, we calculate Pf: 111, mf = 3.29, log Pf: 2.05, and log Pf/mf = 1.53. When plotted on the selectivity relationship established for toluene, these values fall exactly on the line, whereas treatment of the data with no consideration of secondary effects gives a point far removed from the line. Of course, there is no way of proving Cerfontain's

I<.r/kB value is in error, short of repeating and extending his work; and there is no real justification for predicting a k.i,/kB = 27.0 even if his value is thought to be wrong. However, if secondary reactions are occurring in Cerfontain 1s system, as the isomer distribution results imply, the true k.i,/ki3 will be larger than the reported value and the resulting partial rate factors will give better agreement with the selectivity relationship.

This investigation has established the presence of secondary relations but has not determined the nature of the secondary substituting species, nor have the relative contributions of possible species been estimated. Further studies in this area, perhaps by spectrophotometric means, are suggested. Extension of this work into sulfonations of other aromatic systems with other aprotic solvents 88 would also be of value to determine how general this phenomenon is.

It would also be desirable to ascertain whether or not the sulfonation of toluene with so3 in less complexing solvents than sulfur dioxide will fit the selectivity relationship after suitable corrections have been made for secondary reaction effects.

Future studies of the sulfonation of other halobenzenes in sulfur dioxide should include tests by the criteria outlined above.

Other criteria might also be considered. Studies of kinetic isotope effects and kinetics could also be made for halobenzene and toluene sulfonations to determine to what extent secondary reactions might influence the results. It will be of particular interest to obtain more extensive data on isomer distributions as a function of possible secondary sulfonation reactions. A careful redetermination of the isomer distribution for toluene should also be undertaken to determine if corrected values for the isomer distribution would give better agreement with the selectivity relationship. EXPERIMENTALPROCEDURES .

In order to measure isomer distributions by an isotope dilution technique, it was first necessary to prepare about 300 g. of the pure sodium salt of each isomeric chlorobenzenesulfonic acid. The salts were obtained by hydrolysis of the corresponding chlorobenzenesulfonyl chlorides which were prepared by the method of Meerwein, et at. 82 The essential steps in the synthesis are:

c~ HCl ·) Cl(/E Cl HOAC,SO~ ClqsO Cl NaOIJ) Cl¢60 Na (73) 2 NaNo2 2 Cuc12 2 H20 3 Ini.tia:lly small batches (1 mole) of each isomer were made, but the bulk of the material was prepared on a larger scale (3.3 to 5 moles).

In a. typical large scale preparation of the para isomer,-~ 430 g. (3.3 moles) of .E_-chloroaniline (Eastman Organic Chemicals, red label, lot SOS) was added. to 1150 ml. of concentrated hydrochloric acid which had been cooled in an ice bath to 8° C.- To this was added, dropwise, 400 ml. of an aqueous solution containing

250 g. (3.6 moles) of NaN02, the temperature being maintained at

0 to 10° -C. with a salt-ice bath. While the diazotization of the amine was proceding, sulfur dioxide gas (war surplus, grade unknown) was bubbled, with stirring, through 3.4 1. of glacial acetic acid.

When the acid was saturated with sulfur dioxide, 132 g. (0.77 mole) of.CuCl2•2H20 (Baker's C.P. grade) in 200 mL· of water was added

89 90 to it and bubbling of the sulfur dioxide through the solution was continued. The diazotized amine solution was slowly added to the acetic acid solution, and after addition was completed the gas flow was stopped and a yellow precipitate of the sulfonyl chloride was obtained by the addition of a three-fold excess of ice water. The precipitate was filtered, washed with ice water, and then hydrolyzed by boiling with 264 g. (6.6 moles) of NaOH in four liters of water. The resulting solution was boiled down and the sodium salt of the sulfonic acid was recovered in several crops. The salts were obtained as plate-like crystals which were dissolved in hot water, boiled with Norit, filtered and reprecipitated.

The average yield for the preparation of the para isomer salt at this point in the synthesis was about 80%. Meerwein claims a 90% yield for the sulfonyl chloride.

The ortho and meta isomers were prepared in a similar manner.

The sulfonyl chlorides of these isomers are liquids at room temperature and were isolated from the aqueous mixtures as water-insoluble oils. The aqueous solutions (about three liters) were extracted with four 800-ml. portions of ether and the ether solutions were combined with the sulfonyl chlorides. The ether was then boiled away and the sulfonyl chlorides were hydrolyzed in boiling NaOH solutions. The salt cry~tals were then collected and recrystallized once after treatment with Norit in a manner similar to that for the para isomer. The yields of the salts of the ortho and~ sulfonic acids averaged about 55%. (Meerwein reports 73% yield for the sulfonyl chlorides of both isomers.) 91

The various batches of each isomer salt were combined and recrystallized carefully three times to achieve purification. The

Eara isomer was recovered as white plate-like crystals in an overall yield (calculated from the starting amine) of 77%. The other

isomers, particularly the !!!lli isomer, were more difficult to re-

crystallize, but with successive recrystallizations the quality of

the crystals improved, giving white plate-like crystals somewhat

finer than those of the para isomer. The overall yields of the

purified salts were ortho, 34% and,~' 31%.

Preparation of Derivatives

S-Benzylisothiouronium derivatives were prepared by reacting

the salts with S-benzylisothiouronium chloride according to standard 110 procedures. The derivatives were recrystallized three times from

a SO-SO methanol-water solution. Some difficulty was encountered in

the recrystallization of the ortho and~ derivatives as they had a tendency to oil out; however, with seeding and careful cooling and after several recrystallizations, satisfactory crystals were

obtained.

The £-toluidine derivatives were also obtained by adding 16.5 ml. of a solution of . E_-toluidine hydrochloride (2 g./1O ml.) to aqueous solutions containing 5 g. of the respective chlorobenzenesulfonates. The £-toluidine salts were recrystallized twice from water and allowed to air dry.

Melting points were taken on a Hoover-Unimelt melting-point apparatus whose thermometer had been previously calibrated against 92 pure standard samples provided with the instrument. The corrected melting points c,:f the derivatives are given in Tables 20 and 21. Infrared spectra of the sodium chlorobenzenesulfonates taken on a Beckman IR 5 fectrophotometer (KBr pellet) indicated that each isomer was free of contamination by the others.

TABLE20

MELTINGPOOOS OF S-BENZYLISOTHIOURONIUMDERIVATIVES OF THE ISOMERICCHLOROBENZENESULFONATES

Isomer M.P. Lit. Ref,

ortho 160.5-161.5° C. 160.8° c. 85 ~ 137 .5-139.5° c. 138.9° c. 63 para 175 -175 .5° c. 174.4° c. 85

TABLE21 MELTINGPOINI'S OF ,e-TOLUIDINEDERIVATIVES OF THE ISOMERICCHLOROBENZENESULFONATES

Isomer M.P. Lit. Ref. ortho 260.5-263.5° c. - - ~ 198 -199° C. 199-200° c. 69 para 205 -208° C. 208-210° c. 69

Preparation of Radioactive Sulfur Trioxide The s35 used in isomer distribution experiments was obtai~ed 35 in the form of n2s o4 (New England Nuclear Corp., lot V-14-C, 10 me., 7.8 mc./ml., 99+% pure). This was washed with distilled water into a 50 ml. beaker containing 2.0 g. ~aso4 (Baker and Adamson reagent,

..·. 93

lot M 170) and 0.25 g. BaC12 (Brothers Chemical Co. reagent). The beaker was then set on a hot plate to digest for several days. The

resulting radioactive Baso4 was filtered, washed, and dried overnight at 125° C.

About 0.33 g. of the dried Baso4 (1.7 me.) was placed in chamber A of an is?tope exchange reactor (Fig. 15) together with / a Teflon coated stirring bar. A constriction was then made in

the side arm Band the reactor was dried. About 4-5 ml. of so 3 (Sulfan B, Baker and Adamson, stabilized) was added to the flask

and frozen by immersing the reactor in an ice-water bath. The reactor was evacuated to about 0.1 to 1.0 Torr. and the system was sealed off

at B. The reactor was then kept warm on a hot plate for several

Fig. 15.--Isotope Exchange Reactor days with occasional stirring to exchange radioactivity between the Baso and so • 4 3 94

Prior to use, the so3 was distilled into section C and the thin walled capsule D and then poured back into section A to rinse

the capsule and remove any traces of water or sulfuric acid. This was repeated several timeS;and finally, the capsule was filled with

so3, the so3 was frozen and the capsule was sealed off.

Capsules containing nonradioactive so3 for competitive rate experiments were prepared in a similar manner except that no

Baso4 or stirring bar was placed in the reactor.

The amount of so3 used in each experiment was determined by weighing the capsule and contents before the reaction and the

capsule fragments after the reaction. In addition, the arylsulfonic

acids produced in most of the competitive experiments w~re titrated with standardized NaOHwhich gave a cross check on the amount of

so3 recovered as product.

Preparation of Radioactive Benzene

A small vacuum line (Fig. 16) was constructed to prepare 14 the c labeled benzene-used in the competitive rate reactions. Radioactive benzene (New England Nuclear Corp., 0.10 me. in 6.4 mg., lot no. 161-295-17) was received in a glass vial (A) equipped with a break seal. This was sealed onto the line and a 50 ml. Erlenmeyer flask (B) with a 12/30 joint containing 12.967 g. of benzene was attached to the other end of the line. The benzene was frozen by iunnersing the flask in liquid nitrogen and the system was evacuated to 0.1 Torr. The stopcock D was closed to seal the system under vacuum and the break seal was broken by shaking glass 95

B A

Fig. 16.--Vacuum- Line for C14 Benzene Preparation rod c. The benzene was distilled back and forth between A and B five times by alternately warming one chamber and freezing the other with liquid nitrogen. In each case, care was taken to quanti- tatively transfer the last traces of material from chamber A. Finally, the benzene was transferred into the Erlenmeyer flask, the flask was removed from the line, a small piece of sodium was put into the benzene to dry it, and the flask was stoppered and stored for use. Portions of this material were diluted with different amounts of benzene and chlorobenzene for the various competitive rate experiments.

Purification of Benzene, Chlorobenzene, and Toluene Some of the benzene and·toluene used in this work had been 96

62 previously purified by Guillot. The remaining benzene and toluene and the chlorobenzene used in these experiments were purified by distilling reagent grade material through a 30-plate (4 ft. packed with glass helices) vacuum-jacketed column with a total-condensing, partial-take-off head. A reflux to take-off ratio of between 23:1 and 50:1 was used. Only the middle third of each distillation was kept. The purified benzene and toluene were stored over sodium while the chlorobenzene was stored over calcium hydride.

Samples of the arenes were injected into a Basic Gas Chroma- tograph (Carle Instruments Inc.) and under the conditions employed

(Be gas flow of 60 cc./min. over carbowax on firebrick, 135° C.), no evidence of any contaminants was observed even when the instrument was operated at maximum sensitivity. These reagents were considered pure enough for the reactions contemplated.

Sulfonation Procedure

The sulfonation reactions were conducted in the same apparatus for both t~e isomer distribution experiments and the competitive . . . rate experiments. In the former case, s35 labeled so was used while 3 14 in the latter case, nonradioactive so3 and C labeled benzene were employed. The apparatus, represented schematically in Fig. 17, consisted essentially of the two-liter, three-necked main reaction chamber D surmounted by a cold-finger condenser (C) and a capsule- breaking chamber (B). A three-junction copper-constantan thermocouple (G) was inserted through one neck of the main reaction chamber while a siphon ·tube connected to a smaller condensing chamber and 97

G J

Fig,.._ 17 .--S~lfonation Apparatus 98

cold-finger assembly (F and E) was inserted through another neck.

A thin-walled glass capsule containing was placed in the bowl of so3 the capsule-breaking chamber and a glass-encased magnet was inserted into a side arm in the upper part of the chamber. The magnet could be manipulated with a magnet extemal to the system and could be dropped on the capsule to crush it. A fine mesh platinum screen was placed on the bottom of the capsule-breaking chamber to prevent small fragments of the broken capsule from falling into the main chamber. Small Teflon-coated magnets were placed in chambers D and E to permit stirring of the solutions.

Gases passing through the system entered through drying tube

A (P2o5 supported on glass beads) and exitted through a small mercury bubbler (B) attached to a P2o5 drying tube (not shown). Thus, any air which might occasionally be sucked back into the system would be dry. The apparatus was carefully dried in a drying oven for at

least 12 hours. It was then assembled while warm and dry nitrogen was flushed through the set-up for 15 minutes prior to use. One experiment was made in which small amounts of water were added to the system. The results varied widely from those obtained under dry conditions indicating that the drying procedure was necessary. After drying was completed, the main chamber was surrounded with a 1:1 mixture cooled to -20° to -40° C. and the cold finger C was filled with a methanol-dry-ice mixture. Sulfur dioxide gas

(Matheson, anhydrous grade) was introduced into the system through drying tube A and chamber Band condensed into the main reaction 99 chamber. After about 300 ml. of liquid sulfur dioxide had been condensed, the gas flow was stopped, the coolant was removed from the cold finger; and the capsule-breaking chamber, the cold finger, and the upper portions of the reaction chamber were heated with a hot-air gun until warm to the touch. The capsule was then crushed and the upper portions of the system were again heated to distill the so3 into the stirred liquid sulfur dioxide. In some experiments, the so3 capsule was introduced directly into the liquid sulfur dioxide through G and broken with a glass rod. Either method of introducing the so3 was satisfactory and no variations in results could be attributed to the way in which the capsule was broken.

After the had all dissolved, the coolant was replaced in so3 the cold finger and sulfur dioxide was condensed to make the final volume from 800 to 900 ml. The direction of gas flow was then reversed and sulfur dioxide was condensed by cold finger E into the smaller chamber F. When 100-200 ml. of liquid sulfur dioxide had accumulated in this chamber, the gas flow was stopped, dry nitrogen was introduced to blanket the system, and the aromatic compounds were added to the small chamber through the side port I.

The cooling baths surrounding D and E were removed and both, solutions were allowed to warm to reflux temperatures. With the contents of both chambers being stirred as rapidly as possible, the arene solution was transferred to the main reaction chamber via the siphon tube by closing stopcock J and applying nitrogen pressure to chamber F. The time needed for combining the two solutions was usually

8 to 12 seconds. The resulting solution was stirred for about 10 100 minutes and then a stopper was removed and the sulfur dioxide was allowed to boil away.

The temperatures of the sulfonation reactions were measured by means of the thermocouple and a Leeds and Northrup model 8690 mili- volt potentiometer. The reflux temperature was not exactly the same in all cases since varying amounts of so3 were dissolved in the solvent in different experiments. The measured temperature range for the sulfonation experiments was -12° to -13° c. The reaction products were in the form of a light yellow liquid containing some solid material. This material was dissolved in diethyl ether and washed into a 250-ml. Erlenmeyer flask, the final volume being about 200 ml. This was set on a steam plate and the bulk of the ether was boiled off. This was done to remove any traces of sulfur dioxide. Ether was then added to make the solution back up to 200 ml. and this solution was extracted four times with 50-ml. portions of distilled water. The aqueous extract was extracted· in turn with two

50-ml. portions of ether. The remaining aqueous solution, containing the sulfonic acid product, was then titrated with a standardized solution of 1.0 M. Na0B to pH 7.0. A Leeds and Northrup model 7401 pH meter was used to follow the titration. The resulting salt solution was ether made up to a known volume in a volumetric flask for isomerdistribution experiments or the salts were obtained by carefully evaporating the solution to dryness for the competitive experiments.

The toluene-benzene competitive sulfonations were also conducted according to the same general procedure except that a 1-liter main reaction chamber was used to reduce the amount of reagents used. 101

In the chlorobenzene-benzene systems a total weight of arenes of between 45 and 50 g. was used in each run, while in the toluene- benzene systems a total of about 0.31 mole (ca. 25 g.) of comb,ined arenes was used. A weight of between 12 and 24 g. of chlorobenzene was employed in the isomer-distribution experiments.

Analysis of Reaction Products of Isomer-Distribution Experiments

The isomers were purified by recrystallization as the£- toluidine salts. A series of ,2-toluidine, 2-toluidine, quinoline and isoquinoline salts of the different chlorobenzenesulfonic acids was investigated and the £-toluidine salts were found to have the best crystallization properties.

Aliquot portions of the solution containing the reaction products of an isomer distribution ~periment were pipetted into three beakers - each containing about 50 g. of the pure, dry, nonradioactive sodium salt of one of the isomeric chlorobenzenesulfonates.

To each beaker 33.5 g. of £-toluidine hydrochloride was added together with enough hot distilled water to dissolve the salts. The solution was allowed to cool and the £-toluidine salts crystallized. The salts were filtered, washed once with cold methanol, and a 0.2 to 0.5 g. sample was taken' for future counting. The crystals were then redissolved in a minimum of hot water and the process was repeated.

Between 15 and 25 recrystallizations could usually be made until too little material remained to continue.

The ortho salts recrystallized as large, well-formed needles while the~ and para salts came out as fine flat plates. The 102

~ salts were the most difficult to recrystallize and seeding and refrigeration were occasionally required to produce crystals of a

satisfactory quality.

Certain selected samples which had been set aside for counting were dried overnight at 110° C. under vacuum. Tests demonstrated

that this procedure was sufficient to dry all of the salts to conBtant weight. A 50-mg. portion of each sample was dissolved in 0.5 ml.

of water and 1.0 ml. of absolute methanol. To the solution was added

15 ml. of Kinard's solution and the resulting solution was counted

in a Nuclear Chicago Unilux ambient temperature liquid scintillation

counter. The Kinard solution was composed of five parts £-xylene,

five parts peroxide-free _e-dioxene, and three parts absolute ethanol

{U.S.P.) in which were dissolved 80 g./1. reagent grade napthalene,

5 g./1. 2,5-diphenyloxazole (Packard PPO, scintillation grade, lot

No. 255421) and SO mg./1. d,~napthylphenyl-oxazole (Packard

The principal disadvantage of using _e-toluidine salts is that they slowly become colored on standing in solution. The samples were counted as quickly as possible after the counting solutions were prepared to minimize color quenching of the count rate. Attempts 103 to correct for this effect by extrapolation to a zero time or by comparison with artificially quenched standard samples were only moderately successful. Consequently, the first count rate for each sample was taken rather than an average of several countings and nonradioactive ,2-toluidine salt samples were used as blanks for the determination of the background count rate. Since relative - rather than absolute - count rates were utilized in subsequent calculations, it is felt that under these circumstances color quenching did not introduce serious errors.

Examination of the data obtained by the above procedure showed that each isomer was brought to a constant count rate and hence each isomer had been effectively purified by removal of the other isomers.

From the final count rate and initial aliquot size, it was possible to calculate the ratio of isomers in the original reaction product.

Analysis of Products of Competitive Reactions

Several methods of analyzing the products of the competitive reactions were evaluated. Two competitive experiments in the toluene= benzene system (Experiments 21-P and 22-P) were analyzed by UV spectra= photometry after the method of Guillot 63 and are reported in his dissertation. According to this method, concentrations of the component salts are determined from several selected absorbances in a UV spectrum of the mixture.

The chlorobenzene-benzene system gave UV curves that were not amenable to this simple approach. A more involved analysis of UV data was attempted similar to that employed by Cerfontain and other 104

3,22,65,114 wor k ers. In utilizing this method, a large number of

points are taken from the UV spectrum of a mixture of components.

This leads t~ a series of simultaneous equations in which the number

of equations exceeds the number of unknown quantities in the equations.

By means of a suitable computer program all of the possible simul-

ta~eous equations are solved and, in essence, the UV spectrum of

the unknown mixture is matched against the curve resulting from the

best combination of the UV spectra of the individual components. A multiple-regression and correlation analysis program (STAT03 adapted

from U.C.L.A. BIMDNo. 29) was ~sed in conjunction with an IBM 7040 computer to analyze data obtained by a Beclanan DK-2 ultraviolet

spectrophotometer. Although considerable effort was expended on

this method, it was not possible to obtain sufficiently accurate

results for the analysis of competitive sulfonations. An accuracy

of about± 10% for the concentration of the various species was

about the best that could be achieved with known mixtures. The

inaccuracies resulted in part from the great similarity in the shapes

of the UV curves of the chlorobenzenesulfonate salts and partly from

limitations in the use of the DK-2 spectrophotometer. This approach was used with some success to determine isomer distributions in the

toluene-benzene system with a Carey 15 recording spectrophotometer,

but it is probable that a specially modified spectrophotometer such

as that employed by Cerfontain would be· required to obtain more accurate

results~

The procedure which proved successful for analyzing the compet- 14 itive experiments utilized c -labeled benzene. This procedure was 105

used for both the chlorobenzene-benzene and toluene-benzene systems. The sodium salts resulting from the titration of the product sulfonic

acids were very carefully evaporated to dryness and then weighed. A 1 g. sample of the salt was then vacuum dried at 110° C. overnight

and a 50-mg. portion was counted in Kinard solution in the same

manner as the isomer distribution samples. By knowing what count rate would be expected for 50 mg. of pure c14 labeled sodium benzenesulfonate, it was possible to determine what fraction of the sample

was the benzene-sulfonation product. From this fraction the apparent

relative rate for the reaction was obtained. Details of the calcu-

lations are given in the section on experimental data and calculated

results. The count rate for pure sodium benzenesulfonate was determined ;by sulfonating a sample of the main c14 benzene supply (Experiment I f5-P) and counting the sulfonation product in the usual way. Portions l ,of the standard benzene were diluted to different degrees for various

I ;experiments and so a dilution factor had to be used to calculate the

expected count rate for a particular reaction. A standard stock I ~elution was sometimes prepared for a series of experiments and a

portion of this was sulfonated to provide the expected count rate 1 directly (Experiments 54-P and 88-P).

Several experiments were conducted to evaluate the above pro-

cedure. In one experiment (52-P) 3.6552 g. of £-toluenesulfonic

~cid (MCB,monohydrate, lot 391337) was added to 50 ml. of benzene.

The acid was wet, but titrations showed that the weight of the acid J ' corresponded to 18.69 meq. of acid. The acid-benzene mixture was added I . to 250 ml. of sulfur dioxide, the sulfur dioxide was evaporated, and I the material was extracted and titrated according to the normal procedure.

The titration indicated that 18.48 meq. of acid were present or that

99% of the original acid had been recovered.

In another experiment (54-P) a small amount of benzene stock \I solution was counted directly in Kinard solution and the remainder

of the stock solution was sulfonated, worked up, and counted in the usual way. The count rate for the product sodium salt was 43.7.±0,2

counts/min./mg. while that of the stock solution was 101.6.±0.4 counts/- min./mg. After multiplying the count rate of the stock solution by

the factor 78.11/180.16 to adjust for differences in molecular weights,

the corrected count rate was 44.1_!().2 counts/min./mg. The difference

between the two values is less than 1 percent.

Another analytical approach was also tried in some instances .

. For each experiment the total number of moles of sulfonic acids

produced was known from titration and the total weight of products

was also known. It was possible to calculate the fraction of sodium

benzenesulfonate in the product from the following equation:

(BSM;)(W'f) + (CSK;) (WT) = Total moles (74) MB MC

Where

BSMG=mg.of sodium benzenesulfonate per mg. of sample

CSMG: 1 - BSM:; =mg.of sodium chlorobenzenesulfonate per mg. of sample

WT= total weight of sample

MB= molecular weight of sodium benzenesulfonate

MC• molecular ~eight of sodium chlorobenzenesulfonate

The results of these calculations were not sufficiently accurate 107 for the calculation of kB/kc but did serve as cross checks against the results obtained from the counting procedure. On the average, the values for BS!-(; from the above approach agreed with that obtained from the counting method by about ±3 percent.

The problem of possible dechlorination during the sulfonation process was also considered. Knight 78 reported loss of the iodo- group from iodobenzene under reaction conditions similar to those of this investigation. He reached this conclusion after recrystallizing a mixture of salts of nonradioactive benzenesulfonic acid and the product from the sulfonation of iodobenzene" by S35 03. A significant count rate was observed in the purified benzenesulfonate salts and it was concluded that this came from benzenesulfonate material which was produced from iodobenzene by the loss of the iodo-group. Thompson noted, however, that iodobenzenesulfonates could not be separated from 117 toluenesulfonates by recrystallization and.preliminary tests in the present investigation indicate that chlorobenzenesulfonate salts cannot be removed from benzenesulfonate salts either.

Nitrodehalogenation occurs in the order I>Br>Cl· for aromatic halo-compounds activated by ..2.- or £-hydroxy, methoxy, or phenoxy 89. groups and bromodesulfonation is also known to occur 4 but nothing was found in the literature about sulfodehalogenation reactions or mechanisms. Small portions of reaction products from several competitive experiments were titrated with 0.1030 N. AgNo with K cro - 3 2 4 in. di cator. 104 In all cases, the amount of chloride ion detected was negligible (less than 0.3%) and it was concluded that loss of the 108 chloro-group is not a problem in this reaction. It should be noted that the isotope analysis procedure used in this investigation would not be extremely sensitive to halogen loss should it occur since the results do not depend on independently determining the amounts of benzene- and chloro-benzenesulfonates in the product. The only effect dehalogenation would have would be a small error in weight, small amounts of benzenesulfonates having been weighed as chlorobenzenesulfonate. EXPERIMENTALDATA AND CALCULATED RESULTS

Isomer Distribution Data Five isotope dilution experiments were conducted to determine the isomer distribution for the sulfonation of chlorobenzene. The conditions for these experiments are suDDDarized in Table 22.

TABLE22 EXPERIMENTALCONDITIONS FOR ISOMERDISTRIBUTION EXPERIMENTS

Experiment Vol. of Chloro- Moles Vol. S02 No. benzene Sulfonated S03 (ml.) 20-P 15.0 0.0373 1250 62-P 30.0 0.0253 1100 64-P 30.0 0.0364 1100 70-P 30.0 0.0374 1130 71-P 30.0 0.0322 1120

Aliquots of the product solutions were diluted with nonradioactive salts in the proportions given in Table 23.

TABLE23

CONDITIONSOF DILUTIONOF ISOTOPES

Experiment Aliauot Size (ml.) Weight of Inactive Salts <2.) No. 0 !B .e .Q !B .e

20-P 50.0 50.0 50.0 .. ,50:00 50.00 50.00 62-P 150.0 250.0 50.0 49.077 49.268 50.000 64-P 150.0 250.0 50.0 49.929 48. 707 49.994 70't'P 150.0 300.0 50.0 47 .980 53.694 50.137 71-P 150.0 300.0 50.0 49. 711 49.458 I 49,967 · 109 110

The counting data for the isomer distribution experiments are given in Table 24. Most samples were counted for twenty minutes or

20,000 counts.

-TABLE24 COUNTINGDATA FOR ISOMERDISTRIBUTION EXPERIMENTS

Ortho ~ Para

Exper- lle- Re- Re- ' Back- iment crystal- cts./min/mg. crystal- cts./minJmg. _crystal- cts./min/mg. grnd No. lization lization lization cts. No. No. No. min.

20-P l 57.58 1 344.7 1 722.6 44,8 2 10.21 2 123.7 4 711.l .,t0,8 6 . 6.62 4 13 .59 6 747.7 8 6.73 6 3.95 8 719.9 10 6.75 8 1.23 10 733.3 .. 12 6.73 10 0.76 12 728.1 14 6.85 11 0.87 ··•·· u-•- 14 700.5 15 6.60 12 0. 79 16 672.2 16 6.76 13 0.70 17 644.2 17 6.85 14 0.80 18 659.1 15 0.65 19 646.4 16 0.79. 20 661.8 17 0.60 21 676.9 18 0.60 22 671.4 19 1.00 23 698.8 - 20 0.89 24 723.0 25 706.3

·- -··"·· 26 670.6 27 693.8 28 713.4 29 654.6 30 682.7.

62-P 1 151.l 1 694.4 l 735.6. 75.7 3 25.3 3 142.l 3 829.5 ±3,4 5 25 .o 5 15.6 5 857.S 7 24.7 7 4.87 7 836.4 9 24.5 9 3.77 9 822.l 11 24.2 13 3.00 13 800.l 13 24.9 15 5.58 17 799.6 15 24.2 16 3.58 11 809.8 17 24.2 17 3.95 / 18 5.35 111

TABLE24--Continued

Ortho ~ ~ Exper- Re- .. Re- Re- Back- iment. crystal.;, cts,/min/mg, crystal- cts-/min/mg, crystal- cts,/min,/mg grnd No. lization lization lization cts. No. No. No. min.

64-P l 117 .2 1 166.7 l 550.1 75.7 3 20.6 3 57.4 3 674.7 i3,4 5 19.8 1 5 12.0 5 659.4 7 19.7 7 3.63 7 651.3 9 19.8 9 3.90 9 659.5 11 19.5 11 -2.57 11 688.1 13 20.5 13 3.46 13 679.2 15 19.4 16 4.23 15 671 / 70-P l 134.0 ,.i 618.4 1 556.3 75.7 13 3 19.2 / 98.7 3 628.5 _±3.4 I 5 18.6 ' 5 7.95 5 627.8 8 18.4 / 6 4.32 7 616.3 9 18.4 I 8 2.69 10 603 '.9 11 18.3 ,/ 9 2.71 11 619.7 12 18.5 / 10 2.76 12 591.5 / 13 17 .2 / 11 3.06 13 595.0 14 18.8 1 12 2.58 14 586.1 15 18,,. i() 13 2.97 15 605.2 16 1,8.3 16 615.6

17 / /i9.7 17 605.7 1/ 71-P 37.0 1 342 1 133.7 75.7 ; ,,// 5.68 3 37.1 3 206. 7 t3 .4 5 5.68 5 32.7 5 214.1 7 5.81 7 3 .31 7 207 :3 9 5.84 8 0.74 9 206.4 10 5.72 9 0. 71 11 205.8 11 5.62 10 0.68 13 205.9 13 5.75 11 0.69 14 210.8 14 5.98 12 0.93 16 198.1 16 - 5.75 13 0~82 17 207 .0 17 6:05 16 0.83 19 20L8 17 0.87 112 The purification on recrystallization of the 2-toluidine salts is quite dramatic in the case of the ortho isomer - an essentially constant count rate was a.chieved in as few as three recrystallizations. The purification of the~ isomer is also quite satisfactory. The count rate of the para isomer increases abruptly after the first recrystallization as 2-toluidine hydrochioride ~nd the less active isomers are removed and then remains fairly constant for the remainder of the recrystallizations.

The precision that would be expected for any count rate may be calculated from \ 0-. (n /min.) (75) where n = the average number of counts min.= the counting time in minutes

The standard deviation of the actual count rate for each isomer was calculated from

o; . (76) n(n-1)

r = average count rate - count rate for sample i

n = total number of samples counted The average value for the constant count rate was obtained from a small sample size (usually less than 10) and so a correction 121 had to be made by multiplying by a factor from available tables. ·

Table 25 presents a summary of the counting data. The last column in the table gives the deviation required for a 90% confidence l~vel for the particular sample size. 113

TABLE 25 SUMMARYOF AV~RAGEVALUES FOR COUNTINGDATA

average uev1ac1on Experiment Isomer Count Rate Expected Actual No. of for 90% No. (cts./min./mtz.) Deviation Deviation Samole Confidence:

20-P ortho 6.74 0.10 0.09 8 0. 17 ~ 0.77 0.05 0.04 11 0.07 para 692.7 1.2 6.5 22 11.0 62-P ortho 24.6 0.23 0.2 8 0.38 meta 4.30 0.11 0.32 7 0.62 para 822.1 4.0 7.9 7 15 .6 64-P ortho 19.9 0.2 0.2 7 0.35 meta 3.57 0.10 0.28 6 0.57 para 669.0 4.0 4.1 7 8.0 70-P ortho 18.6 0.2 0.2 11 0.36 ~ 2.85 0.28 0.15 6 0.30 para 604.3 3.5 3.9 9 7.3 71-P ortho 5.79 0.40 0.45 10 0.83 meta 0.78 0.20 0.33 8 0.63 para 206.4 2.0 1.4 10 2.6

Most of the data fall within one to two times the expected deviation and all data fall within the 90% confidence deviation limit. This is good evidence that color quenching is a relatively minor problem.

The isomer distributions were calculated from

) C0 (F0 )(W0+X0 100 {77) %£•---~---~---~------Co(Fo) CWotXo) r Cm(Fm)CWm+Xm) + Cp(Fp) CWp+Xp)

(78)

(79) 114 where

Ci= total activity of the.! isomer in the diluted! isomer

Fi• ml.~ alequot/mi. ! aliquot= a factor to correct all data to the same size aliquot

Wi = the weight of nonradioactive! isomer used in the dilution

Xi= the weight of the isomer salt from the sulfonation product Values for Xi were calculated from the size of the aliquot, the known number of moles of S03 used in the reaction and an approximate isomer

distribution obtained by disregarding Xi terms in Equations 77, 78, and 79.

The errors in the final calculated isomer distributions were determined from the general expressions 36

(80) and

= n (81)

Thus, if it is assumed that the only significant error is in the count rate, the errors in the numerators of Equations 77, 78, and

79 are gl-ven by

(82) and the errors in the denominators are

6. denominator = ~(AC1/ci} (F 1> (Wi + X1} (83) the overall error in the calculation of%! would be

11. ,: • .,, • (,Anumerator Adenominator) O Ll _! : lo _! , numerator - · Genom:inator (84} A summary of the isomer distribution results and the calculated error limits for them are given in Table 26. 115

TABLE26

Sm-MARYOF ISOMERDISTRIBtrrION RESULTS

Experiment % .£ %!!! % .e.

20-P 0.934 .!. 0.008 0 . 107 i O. 008 98. 96 ±. 1. 53 62-P 0. 977 .i O. 004 0.102 ! 0.013 98. 92 .±.1. 82 64-P 0.966 .i 0.005 0.104 ! 0.015 98.93 .±.1.19 70-P 0.957 .±.0.007 0.082 + 0.008 98.96 .±.1.18 71-P 0!-909, .±.0.117 0.061 i 0.048 99.03 .±.1.39 Average 0.95 i 0.03 0.09 .±.0.02 98.96 ±. 0.12

The errors assigned to the average values in Table 26 are standard deviations calculated at the 90 percent confidence level for the average of the five sets of numbers.

Competitive Sulfonation Data, Benzene - Chlorobenzene Systems

Twenty-eight experiments were conducted in studying factors influencing competitive sulfonations in benzene:..chlorobenzene mixtures.

The conditions under which these experiments were made are given in

Table 27.

Experiment 35-P was made to obtain a count rate value for pure sodium benzenesulfonate. It was the only exp~riment in which the product salt was recrystallized t·o purify the product; in all other experiments the product was taken to dryness and counted without purification. Experiments 36-P through 75-P were carried out to determine the effect of the initial benzene to chlorobenzene mole ratio. Because the technique used for preparing the so capsules 3 did not permit accurate predetermination of the amount used, the so3 116 I concentrations for these runs are only approximately constant. The average so3 concentration for this series of experiments was 0.02616 mole/1.

TABLE27

EXPERIMENTALCONDITIONS FOR COMPETITIVE SULFONATIONOF BENZENE-:~ID.OROBENZENEMIX.TURES

Moles Moles Moles so3 Total Weight Experiment Initial Initial Volume of Recovered No. 'Benzene Chloro- Weighed Titrated (l.) Salts benzene (g.)

35-Pa 0.3201 0.05 1.000 36-P 0.3229 0.3038 0.03871 1.200 38-P 0.1248 0.3552 0.03225 1.200 5.993c 39-P 0.0444 0.4031 0.03168 1.100 6.888c 40-P 0.1925 0.2979 0.02711 1.175 41-P 0.1160 0.3485 0.04172 0.04126 1.200 7.698c 43-P 0.04277 0.3802 0.03903 0.03837 1.200 7.424c 48-P 0.2198 0.1463 0.02922 0.02916 1.200 49-P 0.004352 0.2014 0.02503 0.02511 1.150 50-P 0.2745 0.2387 0.02624 1.100 59-P 0.06910 0 3708 0.02771 0.02448 1.100 65-P 0.01930 0.4356 0.02943 0.02997 1.250 66-P 0.03269 0.3932 0.02482 0.02513 1.100 4.818c 67-P 0.04805 0.3787 0.03337 0.03365 1.050 68-P 0.05589 0.3789 0.01969 0.02207 1.150 73-P 0.2321 0.1761 0.02757 0.02765 1.150 5.0237 74-P 0.1651 0.3677 0.02599 1.225 4. 7197 75-P 0.2244 0.2234 0.03233 0.03254 1.150 5.9203 76-Pb 0.1495 0.2902 0.01202 1.100 1.8466 78-P 0.1978 0.2794 0.01168 0.01077 1.100 1.9246 79-P 0.4330 0.1218 0.02139 0.02120 1.200 3.7393 80-P 0.1975 0.2789 0.03044 0.03070 1.150 5.5267 81-P 0.1988 0.2771 0.02167 0.02193 1.150 4.0008 82-P 0.1967 0.2773 0.06153 0.06414 1.150 11.2210 84-P 0.04265 0.3306 0.00436 0.00470 1.150 0.7750 85-P 0.04315 0.3345 0.03526 1.150 4.9283 86-P 0.04297 0.3335 0.00878 0.00718 1.250 1.2636 87-P 0.1729 0.1916 0.00223 0.00163 1.150 0.2562

asulfonated to obtain a count rate for pure sodium benzenesulfonate. bAlso contained 0.1. ml. water to test the effect of moisture on cEstimated from weight-mole relationships on small samples. 117

Water was added to the reaction flask in Experiment 76-P to determine the effect of moisture on the product composition. The results of this experiment varied widely from those of the others~ indicating that moisture was a serious problem. The careful drying process which was followed for the remaining experiments produced results more in general agreement. Since other factors sufficed to explain variations in kB/kc for most experiments, it is concluded that the usual drying procedure was adequate.

Experiments 78-.P through 87-P were undertaken to determine the effect of so3 concentration on the product composition. Most of these experiments were made at constant Bi/c 1 ratios with varying amounts of so3 used ~n each react_ion. The weigh~ of the recovered salt was obtained directly only for the later experiments in the series. Estimated weights, expected to be accurate to+ 3%, were obtained ~s a by-product of the evaluation - ' of an analytical method for some of the earlier experiments. To determine if product composition could be obtained from the known weight of a sample and the number of moles contained in the sample, small (ca. 1 g.) samples of the sodium salts from five experiments were converted to acids by passing the salt through an ion exchange column (Dowex 50 W - xl2, 100-200 mesh, hydrogen state). The resulting acids were titrated, the salts were weighed, and the compositions of the salts were then calculated. The estimated values for total weights given in Table 27 were calculated from the weight per mole and the total number of moles in the reaction product.

On the average, it was found that 98,9% of the so3 weighed at 118

TABLE28

COUNTIN3DATA FOR COMPETITIVE SULFONATION EXPERIMENTSIN BENZENE-CHI.OROBENZENEMIXTURES - Experi- Total Time Sample Count Rate Dilution Standard ment Counts (min.) Size (cts. /min. /mg.) Factor Count Rate No. (mg.) (DF) (cts. /min. /mg.) . 35-P 19,397 2.38 48.6 173 0.04055 36-P 19,397 2.64 50.8 148 0.04248 173 38-P 196,780 10.00 50.3 391 0.1225 185 39-P 198,916 5.27 55.6 692 0.3122 185 40-P 25,580 10.00 45.8 56.3 0.01464 185 41-P 37,760 10.00 40.6 93.0 0.03263 185 43-P . 19,397 2.69 51.5 140 0.06948 180 48-P . _19,445 2.82 55.0 40.3 0.009914 187 49-P 3,476 10.00 51.1 5.78 0.009914 187 50-P 8,992 10.00 48.4 17 .5 0.004416 187 59-P 19,403 6.72 50.2 58.6 0.02223 185 65-P 16,350 10.00 49.6 33.0 0.02223 185 66-P 19,177 7.84 52.0 47 .4 0.02223 185 67-P 19,599 7 .05 57.6 48.3 0.02223 167 68-P 19,582 7.44 50.7 51.9 0.02223 167 73-P 19,582 4.34 56.6 90.6 0.02223 185 74-P 19,582 3.65 64.8 95.8 0.02223 185 75-P 19,582 4.49 51.8 67. 9 0.02223 185 76-P 14,138 10.00 49.4 28.6 0.02223 185 78-P 19,354 4.41 50.2 87.4 0.02223 185 79-P 19,411 4.18 49.5 93 .8 0.02223 185 80-P 19,411 4.11 58.8 80.4 0.02223 185 81-P 19,411 6.49 52.4 82.6 0.02223 185 82-P 19,411 5.89 45.9 72.7 0.02223 185 84-P 19,516 8.62 43.8 51. 7 0.02223 167 85-P 19,562 7.72 50.2 50.5 0.02223 167 86-P 19,624 6.90 57.7 49.3 0.02223 167 87-P 19,602 7 .11 51. 7 53.3 0.02223 167

; the beginning of an experiment was recovered as titratable sulfonic acids. This value is about the same as found for the recovery of a sulfonic acid from the reaction mixture (cf. Experiment 54-P). The weight measurements are probably less accurate than the titration values since it was difficult to recover all of the fragments of the 119 broken capsules and occasionally sulfonated stopcock grease was found on the glass particles. In a few instances, more so3 was apparently recovered than was put into the reaction flask originally. Because the titrated value for concentration was considered to be so3 more accurate than the weighed value, it was used in most calcula~ tions. The values for kB/kc were calculated using both values and an average kB/kc is reported in Table 29. The difference between the relative rate constants calculated using the two so3 values is very small.

The counting data for the competitive sulfonations are given in Table 28 and the important values calculated from them are presented in Table 29. Since count rates varied as a Kinard solution age~ or as new solutions were made up, standard samples (35~P) were counted each time competitive rate samples were counted.

The count rate that would be expected if the product were pure sodium benzenesulfonate (CE) is given hy

CE• (DF)(CTSTD/0.04-055) (85)

Where DF = a dilution factor• g. of radioactive benzene per g. of nonradioactive benzene used in the reaction

CTSTD= the count rate of the standard sample 0.04-055 = dilution factor for the standard sample

The mg. of sodium benzenesulfonate per mg. of sample (BSMG)is given by I BSMG= experimental count rate/CE (86) and the mg. of sodium chlorobenzenesulfonate per mg. of sample

(CSMG)is given by 120

TABLE29 CALCULATEDVALUES FOR COMPETITIVESULFONATION EXPERIMENTSIN BENZENE-CHI.OROBENZENEMIXTURES

.l"lOles o:t .l"lOles ot Experiment Benzenesulfonate Chlorobenzene- Bi/Ci Apparent No. Product (BS) sulfonate kB/kc Product (CS) ··-36-P 0.03193 0.006783 1.063 4.61 .±.0.28 =~-~38-P 0.02372 0.008533 0.351 8.67 ±. 0.19 39-P 0.01648 0.015196 0.110 12. 07 ±. 0 .19 40-P 0.02328 0.003828 0.646 9.67 .±.0.62 41-P 0 •.02743 0.013831 0.333 6 .67 ±. o. 25 43-P 0.01909 0.019278 0.113 11.39 t 0.31 48-P 0.02642 0.002795 1.502 6.64 + 0.20 49-P 0.003744 0.02137 0.021 17 .40 + 0.20 50-P 0.02431 0.002913 1.150 4.41 I o.3o 59-P 0.01492 0.009560 0.186 9.39 ±. 0.26 65-P 0.01092 0.019046 0.044 18.58 + 0.52 66.;.P 0.01275 0.012377 0.083 15.43 ± 0.51 67-P 0.01920 0.01445 0.127 13.07 .±.0.42 68-P 0.01345 0.008621 0.147 11.87 .i 0.36 73-P 0.02251 0.005144 1.318 3.44 ±. 0.20 74-P 0.02190 0.004129 0.449 12.58 .±.0.86 75-P 0.2777 o. 004770 1.005 6.12 i 0.42 76-P 0.003834 0.008186 0.515 0.91 i 0.01 78-P 0.00949 0.00128 0.708 10.76 + 0.92 79-P 0.01985 0.00135 3.555 4.21±0,70 80-P 0.02515 0.00555 0.708 6. 78 .±.0.40 81-P 0.01839 0.00354 o. 717 7 .55 ..: 0.48 82-P 0.04764 0.01650 0.709 4.50 + 0.18 84-P 0.002853 0.001847 0.129 12.33 I o.34 85-P 0.02095 0.01431 0.129 15.17 .i 0.52 86-P 0.004175 0.003005 0.129 11.35 .±.0.32 87-P 0.001018 0.000612 0.902 1.84 .± 0.05

CSMG • 1, 0000 - BS!!;_ (87) The moles of sodium benzenesulfonate (BS) and sodium chlorobenzenesulfonate (CS) produced in the reaction are

BS= (BSMG/180.16)(S03/(BSMG/180.16 - CSMG/214.60)) (8~) and

CS= (CSMG/214.60)(S03/(BSMG/180.16 - CSMG/214.60)) (89) 121 where

so3 = moles of so3 consumed in the reaction The apparent ratio or rate constants for the reaction were then determined from Ingold 1 s equation:

(90)

In practice, a computer program was set up which calculated apparent rate constant ratios based on both the weighed and titrated

S03 values and then averaged them. The expected deviation resulting from all possible known errors were also calculated and the error in kB/kc was determined by substituting these values into the calcula= tions. Table 30 lists the error limits arbitrarily chosen for the quantities involved in the calculations.

TABLE30

ERROR LlMITS IN CALCULATIONOF kB/kc

Value Error Limits

Total counts i (counts)\ Weight of counting sample + 0.2 mg. Volume of base -1- 0.03 ml. Normality of base ± 0. 002 meq. /ml. Standard count rate ± 1.40 counts./min./mg. Weight of S03 .±.0 . 0004 g • Weight of initial benzene ~ 0.0002 g. Weight of initial chlorobenzene .±.0.0002 g.

These error limits are felt to be quite generous. When all the errors were made additive, kB/kc values varied by 1 0.40. This represents the maximum deviation that can reasonably be justified 122 on the basis of the normal errors involved in the measurements. The computer program for the above calculations is given in Appendix

1-A.

Test .Q! Thermodynamic!.!.:_ Kinetic Control

The numbers used in testing thermodynamic vs. kinetic control were taken from the computor results for the relative rate experiments. The equation used was

(CS)(Bi-BS) K = (BS)(Ci-CS) (91)

The relevant calculations are summarized in Table 31.

TABLE31 DATAFOR THERMODYNAMICVS. KINETIC CONI'ROL TEST

Experiment B1-CS Ci-CS Numerator Denominator K No. xl0 4 x104

36-P 0.3187 0.3027 3 .503 12 .841 0.273 38-P 0.1209 0.3538 1.681 13. 781 0.122 39-P 0.04173 0.4007 0.997 10.835 0.092 40-P 0.1878 0.2972 1.354 13 .945 0.097 41-P' 0.1123 0.3468 l.956 12.051 0.162 43-P 0.04025 0.3777 l.026 9.503 0.108 48-P 0.2149 0.1458 1.120 7.188 0, 156 49-P 0.00364 0.1973 0.148 1.403 0.105 50-P 0.2694 0.2381 l.626 11.505 0.141 59-P 0.06589 0.3680 1.295 11.809 0.110 65-P 0.01749 0.4325 0.550 -7.820 0.070 66-P 0.03009 0.3907 0.744 10.174 0.073 67-P 0.04506 0.3766 0.968 11.268 0.086 68-P 0.05285 0.3768 1.116 11.439 0.098 73-P 0.2277 0.1751 2.188 7 .715 0.284 74-P 0.1601 0.3669 l.295 16 .830 0.077 75-P 0.2197 0.2227 l.652 10.369 0.159 , 123

Mole Fraction of BS!!~ Function of (Mole Fraction of Bi)/(S0 3) Data for Figure 8 was obtained from a computer program written for that purpose (Appendix I-B). The input FORMATfor the program was the same as for other programs based on this series of experi= ments so that new data cards did not have to be punched. The results from this program are given in T~b}e 32. All of the data fit the curve reasonably well except Experiments 84-P, 86-P, and 87-P.

TABLE32

CALCULATIONSOF MOLEFRACTION VALUES FOR FIGURE8

XBS XB· Experiment 1 XBi/ (S03) BSC:Xa (S03) No.

36-P 0.8248 0.5152 15.97 0.920 0.03226 38-P 0.7354 0.2599 9.27 0.782 0.02804 39 ..p 0.5204 0.0993 3.45 0.504 0.02880 40-P 0.8588 0.39,67 17 .20 0.876 0.02307 41-P 0.6648 0.2498 7.18 0.763 0.03477 43-P 0.4968 0.1011 3.11 0.484 0.03253 48-P 0.9043 0.6005 24.66 0.941 0.02435 49-P 0.1488 0.02113 0.97 - 0.02178 50-P .0.8890 0.5348 22.42 0.927 0.02385 59-P 0.6094 0.1571 6.24 0.649 0,02519 65-P 0.3645 0.0424 1.80 0.272 0.02354 66-P 0.5075 0.0768 3.40 0.439 0.02256 67-P 0.5705 0.1126 3.54 0.540 0. 03178 68-P 0.6093 0.1285 6.69 0.59~ 0.01919 73-P 0.8140 0.5686 23.72 0.934 o. 02397 74-i? 0.8412 0.3099 14.60 0.827 0.02122 75-P 0.8535 0.5010 17 .82 0.915 0.02811 70-P 0.8815 0.4141 38.99 0.888 0.01062 79-P 0.9363 o.7804 43.77 0.975 0.01783 80-P 0.8194 0.4145 15.66 0.883 ' 0.02647 81-P 0.8386 0.4177 22.15 0.887 0.01886 82-P 0.7428 0.4149 7.76 0.874 0.05350 84-P 0.6070 0.1143 27.94 0.559 0.00409 85-P 0.5941 0.1142 3.73 0.526 o.. 03066 86-P 0.5815 0.1143 19.91 0.586 0.00574 87-P 0.6243 0.4743 333.98 0.912 0.00142 i:l·BSCX = mole fraction of BS calculated on the assumption that no secondary reactions are occurring. 124

These give low BS mole fraction results and are the only e..xpe:riments in which very low so3 concentrations ( 0.006M) were used.

Product Composition,!!.! Function of so3 Concentration Because the numbers developed in this series of calculations would fater be used for an extrapolation to obtain k:sl~C' it ~as necessary to make them as accurate as possible. Consequently, the average value for so3 ~oncentration obtained from weighing so3 and titrating so3 was not used. Most of the products in the experiments made in this series had been accurately weighed. Since the grams of chloro- and benzenesulfonate products per gram of product

(BSMGand CSMG)were known from the counting data, it was felt that the most accurate method of determining BS and CS was by multiplying

BSM; and CSK; by the total weight of product. The only experiment in this series for which a product weight was not obtained was

67-P and the BS and CS values for that experiment were taken from Table 29. The BSMGand CSMGdata were taken directly from the computer output and were multiplied by the weights given in Table 28.

The results of these calculations are given in the Results and Dis- cussion Section in Table 6.

Comparison of Actual Results with Those Predicted for B.Q. Secondary Reactions The proposed mechanism was tested by comparing the known amounts of products produced with the amounts that would have been produced if no secondary reactions were occurring. The amounts of BS and CS that were formed in each experiment were calculated as part of the determination of the apparent kB/kc for the reaction and are recorded with 125 those data. The amounts of BS and CS that would have been formed with no secondary reactions (BSC and CSC) were calculated by assuming kn/kc= 11.5. Ingold 1 s equation

kB/kc: 11.5 = log (Bi/(Bi - BSC))/log (Ci/ti - CSC)) (92) contains two unknowns, BSC and CSC. As a first approximation, BSC was set equal to the measured value of BS and

log (Ci/(Ci - CSC)) = (log (B1/(Bi - BS)))/11.5 (93) The right-hand term in the equation was evaluated and its antilog (ALY) was· found. CSC could then be calculated from

CSC = ((ALY)(Ci) - Ci)/ALY (94) This gave a first approximation for CSC. It was necessary that

BSC ~ CSC = moles of (95) so3 This was not generally the case with the first approximation, so a factor Z was obtained from

Z = moles S03/(BSC + CSC) (96) and a new app~oximation for BSC was obtained by

1 BSC • Z(BSC) (97) This new value was substituted back into Equation 92 and the process was repeated.

A computer program (Appendix I-C) was written which permitted eight reitterations of the above process. At the end of each re- itteration, values for (BSC) and (CSC) were recorded together with values for BSC/CSC, the differences between the actual and calculated values, and these differences expressed as percentages of the actual values. A value for ki3lkc was also calculated from BSC and CSC using Ingold's equation and it was found that before the reitterative 126 process was completed, constant values for BSC and CSC were obtained and ki3/kc equaled 11.5 in all cases but one. Experiment 49-P was the only experiment for which this procedure did not give meaningful results. Although the process was carried through 20 reitterations, the numbers failed to converge on values for BSC and CSC. This was the experiment in which the lowest Bi/Ci ratio was used and is the only one of the series in which the number of moles of Bi was less than that of so3 . This probably explains the failure of the program. The results of these calculations are given in Table 8 in the Results and

Discussion Section. The data used for the computer program are given in Table 33.

A similar process was followed to obtain comparisons of expected and actual BS and CS values for the Bi/Ci= 0.708 series. Data points taken from the curve in Figure 8 are given in Table 34.

The concentrations of S03 from the table were converted to molar quantities (S03V) by multiplying by the average volume for the series

(1.150 liters). Since

BS+ CS = S03V (98) and

RX = BS/CS (99) Then

BS: S03V - CS= (RX){CS) (100) and

cs II S03V/ (RX + 1) (101) These values were then employed in a repetitive process similar to that used for the competitive rate experiments. The computer I TABLE 33

DATA FOR COMPtlTERPROORAM TO CALCULATE..BS .AND CS IN THE ABSENCEOF SECONDARYREACTIONS

~ ·~-:iSGzT:~-~-:~ .:-:,~"!~~~~ ..-,.;~- ..-_~·:.:-:-.::r":.:..'..-~:,_~_'.._7~--'-='>'F·.=·-~½O:.:-:<- -_:·.=-~...- .. -.,~ ·:: ...· -~ _ -~:~--:-~;~£~·-..::-~~~~~i,.,. .·."--- " '--~-

S03 Experiment •,-,_B i Ci Concentration (kB/kc) BSMG csm Vol. No. '. · rn:11.) - (1.) 36-P 0.2691 0~2532__ . ,.,,, 0. .,03226. . ___3 .• 17~ . 0.7641 . 0.2359 1,.208 38-P 0.1085 0.3089 0.02806 8.76 o. 7017 0.2983 1.150 39-P 0.04040 0.3665 0.02880 12.68 0.4872 0.5128 1.100 40-P 0.1638 0.2491 0.02307 10.68 0.8453 0,1547 1.175 41-P 0.09678 0.2904 0.03477 6.93 0.6261 0,3739 1.200 43-i> 0.03564 0.3168 o. 03253 11.81 0.4533 0.5467 1.200 48-P 0.1832 0,1219 0:02435 6.64 0,8881 0 .1119 l.200 49-i> 0.00378 0.1751 0.02178 17.40 0.1280 0.8720 l.150 ,... 50-·P 0.2495 0.2170 0.02385 4.41 0.8705 0, 1295 1.100 ~ 59-P 0.06282 0,3370 0.02519 9.84 0.5781 0.4219 1.100 65-P 0.01544 0,3485 0,02354 18.66 0.3257 0.6743 ' l. 250 66-P 0.02972 0,3575 0,02256 15.81 0.4691 0.5309 1,100 67-P 0.04576 0.3607 0,03178 13 .82 0,5390 0,4610 1,050 68-P 0.04860 0.3295 0,01919 10.89 0.5470 0.4530 1.150 73-P 0.2018 0.1531 0,02397 2.46 0.7937 0.2063 l.150 74-P 0.1348 0.3002 0,02122 11.02 0.8265 O.1735 1.225 75-P 0.1951 0.1943 0,02811 6.52 0.8387 0.1613 1.150 78-P o. 1798 0.2540 0.01062 12.57 0.8794 0.1206 l.100 79 ..p 0.3608 0.1015 0.01783 4.39 0.9265 0 .0735 1.200 80-P 0.1717 0.2425 0.02647 11.17 0.7944 0.2056 1,150 81-P 0.1729 0.2410 0.01886 15.72 0,8160 0.1840 1.150 82-P 0.1710 0,2411 0,05350 21.60 o. 7188 0,2810 1.150 84-P 0.03709 0.2875 0.00409 10. 75 0,5361 . 0,4639 1.150 85-P 0.03752 0,2909 0,03066 12.02 0.5216 0.4784 1.150 86-P 0.04298 0.3332 0,00574 9,56 0.4973 0.5027 1.250 87-P 0.1729 0,1916 0,00142 13 .2.2 0.5292 0,4708 l.150 128

TABLE34

DATAFOR COMPARISONOF BS ANDCS WITHVALUES CALCULATED ON THE BASIS OF NO SECONDARYREACTIONS

.::iv3 Data Point RX : BS/CS Conce?tration (IEXPT) (m. 1.)

1 7.60 0.0100 2 6.02 0.0150 3 5.20 0.0200 4 4.61 0.0250 5 4.14 0.0300 6 3.78 0.0350 7 3.51 0.0400 8 3.30 0.0450 9 3.13 0.0500 10 3.00 0.0550 11 6.62 0.0125 12 5.56 0.0175 13 4.87 0.0225 14 4.36 0.0275 15 3.96 0.0325 16 3.64 0.0375 17 3 .40 0.0425 18 3.21 0.0475 19 3 .07 0.0525 20 2.95 0.0575 program is given in Appendix I-D.

Sulfonation of Toluene - Benzene Mixtures

The experimental conditions for the competitive sulfonation of benzene-toluene mixtures are given in Table 35. Experiments 21-P and 22-P were analyzed by means of UV spectrophotometry. The· absorbance (A) for any pure material of concentration C (at a wave length 7') is

(102) 129

TABLE35

EXPERIMENTALCONDITIONS FOR THE COMPETITIVE SULFONATIONOF BENZENE-TOLUENEMIXTURES

weight Experiment Bi Ti Ti/Bi Vol. S03 of No. (moles) (moles) {ml.) (moles) Product fo.) I 21-P I 0.6377 0.0871 0.136 1065 0.03937 22-P 0.3208 0.3182 0.984 1050 0.02391 ,, 47-P ·i 0.3364 0.0425 0.126 1200 0.04123 1000 0.00619 1.1872 88-P ,,·, 0.2539 0.2179 0.858 89-P 0.1672 0.1435 0.858 670 0.05533 10.5611 91-P \ 0.1708 0.1466 0.858 690 0.02018 3.8769 93-P 0.1667 0.1396 0.837 790 0.00328 0.6338 I i 95-P i 0.1672 0.1400 0.837 700 0.01829 3.5182 96-P 0.2386 0.0666 0.279 720 0.01900 3.6384 i 97-P I 0.2433 0.0679 0.279 700, 0.01229 2.3604 98-P 0.2385 0.0666 0.279 700 0.00787 1.5110 99-P 0.2417 0.0675 0.279 700 0.00307 0.5924

I ' ' for a mixture of two substances 1 l A7\: ~C - 0.:7\C (103) '! ·\-:,, For a mixture of sodium toluenesulfonate (T) and sodium benzenesulfonate

(B), the absorbance at three wavelengths are:

A274 = 126.l (T) + 20.4 (B) (104)

A269: 215.9 (T) + 409.8 (B) (105) A267: 301.0 (T) + 202.3 (B) (106) solving 104 and 105 gives

_ . 'tr' - 126 .1 A - 215. 9 A 269 274 (B) = ------(~07) 126. l X 409.8 - 20.4 X 215.9

A269 - 409.8 (A) (T) = (108) 215.9 130

solving 105 and 106 gives

215.9 A267 - 301.0 A269 (Jn = (109) ------2 l S. 9 X 203.2 - 301.0 X 409,8

A269 - 409.8 (B) (T) = (110) 215.9 Table 36 gives the analytical data for Experiments 21-P and 22-P.

TABLE36 ANALYTICALDATA FOR EXPERIMENTS21-P AND22-P

Experiment A274 A269 A667 No.

21-P 0.175 · 0.631 0.567 22-P 0.310 0.575 0.701 ..

The results of these calculations are given in Table 18.

The counting data for the toluene-benzene competitive sulfona-

tions are given in Table 37. Values calculated from the count rate data are presented in Table 10 in th~ Results and Discussion Section.

The data were treated in the same way as comparable experiments

in the chlorobenzene-benzene system. Values for BS and TS were obtained by multiplying BSMGand TSMGtimes the weights of the

respective samples. . Values for BSMGwere obtained from

count rate sample BSMG: ------(111) count rate standard

TSM;: 1.000 - BSMG (112) 131

TABLE37 COUNTINGDATA.FOR TOLUENE-BENZENE COMPETITIVE SULFONATIONS

Experiment Weight Average Av~rage Back- Cts • /min. /mg. No. Sample Counts Time ground Corrected for (mg.) . (min.) (cts. /min.) Background a 47-P 51.0 2,963 10.00 57.3 4.68 Standard 50.2 20,000 1.56 59.4 276.5 88-P 45.l 20,000 9.59 44.9 89-P 48.0 20,000 7.28 56.l 91-P 51.9 20,000 9.85 38.0 93-P 53.7 15,734 20.00 13.5 95-P 52.2 20,000 11.04 33.6 96-P 51.l 20,000 6.90 50.6 97-P 57.9 20,000 6.22 54.5 98-P 52.5 20,000 9.56 38.7 99-P 53.9 20,000 15 .21 23.3 8 The standard count rate for this experiment was 184.4.

The t

The number of moles of so3 used in each experiment was determined in a different manner for Experiments 88-P to 99-P. After the samples had been titrated, it was found that the NaOHsolution had gone bad and that the normality was unknown. Rather than trust the weighed values of so3 for the careful extrapolations anticipated, the total moles of so3 were obtained by adding BS and TS.

Comparison of Predicted and Actual TS and BS Values in Constant Ti/Bi Experiments------

The comparison of actual and predicted TS and BS products in the constant Ti/B 1 experiments was made b! the same process as used in the chlorobenzene-benzene system. The same computer program was 132 used with only a few minor variations (Appendix I-E). The data used with the computer program are given in Table 38 and were obtained

£ rom Figure 3 •

TABLE38

DATAPOINTS FROM TS/BS VS. so3 CONCENTRATIONCURVES

T1/Bi Number TS/BS so3 Concentration , 0.279 1 9.30 0.0050 2 7.55 0.0075 3 6.18 0.0100 4 5.45 0.0125 5 4.95 0.0150 6 4.45 0.0175 7 4.20 0.0200 8 4.10 0.0225 9 4.00 0.0250 10 4.00 0.0275

0.858 11 19.75 0.0025 12 17.60 0.0050 13 15.55 0.0075 14 - 13 .80 0.0100 15 10.90 0.0150 - 16 8.65 0.0200 17 7.00 0.0250 18 5.90 0.0300 19 5.20 0.0350 20 4.65 0.0400 21 4.20 0.0450 22 3.80 0.0500 23 3.50 0.0550 24 3 .40 0.0600 25 3.20 0.0700 26 3.20 0.0800 133

Relative Contributions of Primary and Secondary Reactions

·1n order to estimate the relative amounts of products produced from the primary and secondary reactions, it is necessary to make certain assumptions about the ratios of products for both types of reactions. The relative amounts of BS and TS expected in the absence of any secondary reactions were calculated for each S03 concentration for a series of points taken from the constant Ti/Bi curves in

Figure 12. From Table 9 it can be seen that the ratio TSC/BSC (RC) decreases slightly with increasing S03 concentration. For the purpose of these calculations, it was assumed that this ratio of primary reaction products remains constant for each S03 concentration even though the fraction of the total so3 consumed in the primary reactions was in some cases much less than the total S03 concentration.

A value also had to be assumed for the ratio of secondary products.

It can be seen from Figure 13,that at high so3 concentrations the curves become essentially horizontal. T~is should occur only if either the ratio of primary products and secondary products were the same, or if the amount of primary products were negligible with t·espect to the secondary products. The first alternative is not possible since the calculated RC values for the primary products are much too large at the higher S03 concentrations. The second alternative is the more likely of the two possibilities.

It was assumed that the ratio of the secondary products (Y} remains constant throughout the so3 concentration range. This is, of course, not completely valid since the relative concentrations of the secondary sulfonating species probably change with so3 concentraa 134 tion. Values of Y 4.0 and 3.2 were chosen for the T./B. : 0.279 = 1 1 and 0.858 data respectively.

An equation giving the fraction of the total so3 consumed by the primary reaction can be derived as follows:

TSl/BSl : RC (113) and

TS2/BS2: Y (114) where TSl, BSl, TS2, and BS2 are the amounts of toluene- and benzenesulfonic acids produced by the primary and secondary reactions respectively. Let S03P = so3 consumed in making the primary products. TSl + TS2 (RC)(BSl) + (Y) (BS2) RX • • (115) ----BSl f BS2 ------(BSl) + (BS2) where RX: the observed ratio of products. Now

(RC)(BS 1) + (BS 1) = S03P (116) and

(Y) (BS2) + (BS2) : S03 - S03P (117) . . - (BSl) = S03P/(RC + 1) (118) and

(BS2) : (S03 - S03P) / (Y t 1) (119) so

RX = RC(S03P/(RC + l)) f Y((S03 - S03P)/(Y t 1)) (120) S03P/ (RC f 1) + (SOj · - S03P) / (Y +· 1) RX(S03P/(RC-fl)) + RX((S03-S03P)/(Y+l)) : - RC(S03P/(RC+l)) + Y((S03-S03P) /(Y+l)) (121) 136 collecting terms in Y

RC(S03P) - RX(S03P) : RX(S03) - RX(S03P) - Y(S03) - Y(S03P) (RC+l) (Y+l) (122)

S03P: (RC-RX)/(RC+l) = (RX-Y)S03/(Ytl) - S03P(RX-Y)/(Y+l) (123) let

ZZ = (RC-RX)/(RCtl) (124) then, solving for S03P

so3 (RX.;.Y)/(Y+l) S03P = ------(125) ZZ + (RX~Y)/(Y.~l)

Let X = the fraction of the total so3 concentration consumed in the primary reaction. then

S03P : X(S~) (126) and

(S03)(RX-Y)/(Ytl) = ZZ + (RX-Y)/ (Y+ 1) (127) so

X : (RX-Y) (128) · ZZ(Ytl) + (RX-Y) A computer program (Appendix I-F) was written to calculate the necessary quantities in the above equations. The program was written so that the same data cards could be used that had been used in previous calculations. The results of these calculations are given in Table 13 of the text.

Isomer Distribution~:_ Function of so3 Concentration Ultraviolet absorption curves of pure sodium ortho-, ~-, and para- toluenesulfonate, sodium benzenesulfonate, and samples 137 of the products of the Experiments 89-P through 99-P were determined with a Carey 15 recording spectrophotometer. The concentrations of the samples were about 2xl0- 3 to 4x10· 3 molar and a matched set of

1 cm. path-length quartz curvets was used. Absorbances were taken between 250 and 290 m_µ,. None of the species absorbs at 290 ~ and all absorbance values were corrected to a base-line value of zero at this wavelength. The absorbance (A) at a given wavelength for a mixture of four compounds is

{129) where

C1, C2, c3 , and c4 =concentrations of the four components a.1, C½,0-J, and o..4 = absorptivities of the four components at the given wavelength The absorptivities of the various components were obtained from

(130) where

A1 = measured absorbance of pure species i The absorbance values .. of the pure standard solutions are given in Table 39 together with the calculated absorptivity values for these solutions. The concentrations of the ortho-, ~-, para- toluenesulfonate and benzene sulfonate standard solutions were . -3 . 2:204, 2.362, 4.764, and 3.407xl0 molar respectively. The measured absorbances of the competitive sulfonation samples are given in Table 40. The data for Experiments 91-P and 97-P are not given since they did not give meaningful results with the computer TABLE39

ABSORBANCEAND ABSORPTIVITY VALUES FOR STANDARDUV CURVES

7'-- A ,::to tJ., t:tB (o/--l) .2. ~ ~.2 AB !!! a...E. . ... 250.0 0.220 0.223 0.475 0.324 ~·..... 99 .8 94.4 99.7 ..95.l 251.3 0.262 0.259 0.498 0,356 118.9 109.7 104.5 104.5 2'52 .5 0.308 0.305 0.545 0.359 139.7 129.l 114.4 105.4 253.8 0.344 0.342 0.623 0.346 156 .l 144.8 130.8 101.6 255.0 0.374 0,371 0.660 0.444 169.7 157 .1 138.5 130.3 256.3 0.420 0.406 0.627 0.534 190.6 171.9 131.6 156.7 257.5 0.491 9.466 0.591 0.536 222.8 197.3 124.1 157.3 258.8 0.570 0.542 0.634 0.476 258.6 229.5 133 .1 139. 7 260.0 0.612 0.597 0.764 0.438 277 .7 252.8 160.4 128.6 c; 261.3 0.623 0.602 0.772 0.566 282.7 254.9 162."o 166.l 00 262.5 0.625 0.587 0,686 0.733 283.6 248.5 144,0 215.l 263.8 0,681 0.616 0.562 0.556 309.0 260.8 118.0 163.2 265.0 0.826 0.726 0.514 0.439 374.8 307 .4 107.9 128.8 266.3 0.920 0.866 0.552' 0.316 417.4 366.7 115.9 92.7 267.5 0.852 0.822 0.532 0.356 386.6 348.0 111.7 104.5 268.8· 0.716 0.691 0.412 0.637 325.3 292.6 86.5 187.0 270.0 0.594 0,540 0.332 0.446 269.5 228.6 69.7 130.9 271.3 0.579 0,489 0.350 0.230 260;9 207.0 73;5 67.5 272.5 o. 721 0.576 0,268 0.106 327. l 243.9 . 56:3 31. l 273.8 0.910 0.826 0.155 0.045 412.9 349;7 · 32.5 13.2 275.0 0.711 0~789 0.070 0.019 322.6 334.l 14. 7 5.6 276.3 0.401 0.452 0.049 0.010 181.9 191.4 10.3 2.9 277 .5 0.199' 0.220 0.025 0,006 90.3 93.l 5.2 l.9 139

TABLE40

ABSORBANCEVALUES OF. COMPETITIVE SULFONATIONSAMPLES

A. Absorbance 89-P 93-P 95-P 96-P 98-P 99-P (~) I 250.0 0.442 0.368 0.394 0.390 0.424 0.253 251.3 0.473 0.394 0.423 0.417 0.448 0.273 252.5 0.502 0.435 0.455 0.448 0.486 0.284 253.8 0.555 o.4aa 0 • .509 0.494 0.538 0.332 255.0 0.610 0.523 0.554 p.550 0.585 0.360 256.3 0.633 0.516 0.556 0.554 0.588 0.366 257.5 0.605 0.511 0.542 1 0.542 . 0.575 0.356 258.8 0.616 0.552 0.567 0.558 0.604 0.376 260.0 0.68f 0.639 0.649 0.630 0:685 0.432 261.3 o.750 ,0.651 0.698 0.681 0.728 0.461 262.5 o.745 0.608 0.650 0.662 0.695 0.440 263.8 0.613 0.528 0.543 0.550 0.588 0.383 265.0 0.543 0.522 0.513 0.503 0.5.53 0.364 266.3 0.543 0.562 0.532 0.507 0.574 0.387 267.5 0.549 0.544 0.530 0.514 0.570 0.382 268.8 0.539 0.442 0.476 0.533 0.458 0.327 270.0 0.413 0.358 0.367 0:375 0.392 0.261 271.3 0.350 0.354 0.346 0.324 0.365 0.246 272.5 0.280 0.323 0.273 0.262 0.306 0.222 273.8 0.206 0.291 0.227 0.203 0.254 0.200 275.0 0.141 0.208 0.156 0.135 0.176 0.150 276.3 0.080 0.122 0.088 0.078 0.098 0.090 277.5 0.044 0.060 0.044 0.040 0. 0.50 0.046

program. For these two experiments negative values for some concen- trati.ons of samples were reported.

The details of the STATO3 computer program are given in

Appendix I-G. A table of residuals, comparing the absorbance values of the mixture at each wavelength with the sum of the absorbances for the best combination of pure-component absorbances, was printed for each set of data. The average residual for each run was about

1 to 1.5%. APPENDIX I

A. Computer Program for the Calculation of k:slkc All of the programs for the calculations reported in this work are written in the FORTRANIV Language.

Definitions: IEXPT = experiment number BI= moles of initial benzene

CI= moles of initial chlorobenzene

so3w • moles of so3 consumed in the reaction determined by weighing the capsule and and capsule fragments. so3 S03T = moles of so3 consumed determined by titration VOL = total volume of solution '!WT = total weight of sulfonation products CTS = total number of counts for the counting sample MIN= counting time in minutes

AM; = weight of counting sample in mg. DF = dilution factor = g. radioactive benzene per g. of total benzene CTSTD= count rate for standard (35-P) sample CEX = experimental count rate in counts/min./mg. DEV= expected deviation of count rate in counts/min./mg.

CE= expected count rate for the sample if it were pure

sodium benzenesulfonate

140 141

BSMG: mg. benzenesulfonate/mg. sample

CSMG= mg. chlorobenzenesulfonate/mg. sample

BSW= moles of benzenesulfonate product determined from S03W CSW= moles of chlorobenzenesulfonate product determined from S03W BST = moles of benzenesulfonate product determined from S03T RKW = kB/kc determined from S03W RKT= kB/kc determined from S03T TAR = total moles used initially PCTR= percentage of so3 recovered as titratable sulfonic acids

AVK = average of RKWand RKT

TMOLE: total moles of sulfonate products as determined frau

the counting procedure

PCTWT= degree (expressed as a percentage) to which TMOLE and S03T agree

XBS • mole fraction of benzenesulfonate in the product

XBI = mole fraction of benzene in the original arene mixture XBIS = mole fraction of benzenesulfonate in the product

divided by S03T or S03W~hen S03T was not determined,

S03TC = concentration of so3 in moles per liter as determined by titration

S03WC= concentration of ·so3 in moles per liter as determined by weight 142

SOURCESTATEMENT $ IBFTC SBCDF C PROGRAMFOR DETERMINING RELATIVE RATES USING A STDSOLN AND C DF cm.oROBENZENE- BENZENE SYSTEM 1 FORMAT(I3) 2 FORMAT(2F7.4,2F8.5,F6.3,F8.4) 3 FORMAT(F9.l,F6.2,F5.l,F8.5,F6.l) DO 50 J:1,100 READ(S, 1) IEXPT READ(S,2)BI,CI,S03W,S03T,VOL/l'WT READ(5 ,3)CTS,AMIN,Am,DF, CTSTD DO 50 I•L,2 RATIO= BI/CI CEX= (CTS/AMIN)/ AID DEV: ((SQRT(CTS))/AMIN)/AMG CE• (DF*CTSTD)/0.04055 BSM:;: CEX/CE CSMG= l. - BSID BSW= (BSMG/180.16)*S03W/((BSMJ/180.16)+(CSMG/214.60)) BST: (BSMG/180.16)*S03T/((BSM.;/180.16)+(CSMG/214.60)) CSW= (CSMG/214.60)*S03W/((BSM.;/180.16)+(CSMG/214.60)) CST: (CSMG/214.60)*S03T/((BSMG/180.16)+(CSMG/214.60)) RKW: ALOO(BI/(BI-BSW))/ALOG(CI/(CI-CSW)) Rl,{T = ALOO(BI/(BI-BST))/ALOG{CI/(CI-CST)) TAR = BI+ CI . PCTR = (S03W-S03T)*l00.0/S03W AVK= (RKW+ Ricr)/2.0 TMOLE= ((BSMG'ATl-lT)/180.16)+((CSM:;~)/214.60) PCTWT= (S03T - TMOLE)*100.0/S03T XBS = BST/(BSTfCST) XBI: BI/{BI+CI) XBIS = XBI/S03T S03TC = S03T/VOL S03WC: S03W/VOL 4 FORMAT(F8.4,2F7.2,F8.3,2Fl0.7) WRITE(6, 1) IEXPT WRITE(6,4) RATIO,CE,CEX,DEV,BSMG,CSM:; 5 FORMAT(4F9.6,3F8.3) WRITE(6,5)BSW,CSW,BST,CST,RKW,IUcr,AVK 6 FORMAT(F7.4,F7.2,F8.5,F7.2) WRITE(6,6)TAR,PCTR,TMOLE,PCTWT 7 FORMAT(2Fl0.8,F7.2) 8 FORMAT(2F9.6) 9 FORMAT(lB·:lF10;7) WRITE(6,9)BSZ.C,CSMG WRITE(6,7)XBS,XBI,XBIS WRITE(6,8)S03WC,S03TC S03T • (S03T*0.004)fS03T CTSTD: CTSTD- 1.40 CTS = CTS~ (SQRT(CTS)) AM;= AMG+ 0.2 143

S03W= S03W+ 0. 0004 BI : BI+ (0.0002/180.16) 50 CI• CI - (0.0002/214.60) STOP END

JL. Calculation of Mole Fraction Values DefinitioQS of terms not previously defined:

S03 = concentration of so3 in moles per liter S03V = moles of S03 BSM=BS= moles of benzenesulfonic acid produced in the reaction BSX :: XBS

;'-J· BIX = XBI

BIXS : XBIS

SOURCESTATEMENT

$ IBF!'C XBX C PROGRAMFOR CALCULATOO MOLE FRACTION VALUES 1 FORMAT(I4,3Fl0.5,F7.2,2F7.4,F6.3) DO 50 J:1,100 READ(5,l)IEXPT,BI,CI,S03,RK,BSMG,CSMG,VOL S03V = S03-A'VOL ., BSM= (BS!C/180.16)'kS03V/((BSM;/180.16)t(CSMG/214.60)) cs= (CSM;/214.60)1cS03V/((BSMG/180.16)+(csK;/214.60)) BSX = BSM/ (BSM + CS) BIX = BI/(BI + CI) BIXS = BIX/S03 4 FORMAT(I4 ). . _,,,. . 7 FORMAT(lH·,2Fl0.6~Fl0.4) WRITE(6,4)IEKPT 50 WRITE(6,7)BSX,BIX,BIXS STOP END· 144

£.:. Calculation of Predicted BSL cs. and .RAssuming !!Q Secondary Reactions~ Present

Definitions of terms not previously defined:

Y: terms in Ingold 1 s equation involving benzene species

ALY= antilog Y

CSC = CS calculated from Ingold 1s equation BSC = second approximation of BS CSCC= second approximation of CS R • ratio of BS/CS

RC: ratio of BSC/CSCC RKC• rate constant ratio calculated for no secondary

reactions DIFB,DIFC,DIFR = difference between actual and calculated

BS,CS, and R PCTB,PCTC,PCTR= difference between actual and calculated BS,CS, and R expressed as percentages

SOURCESTATEMENT $ IBFTC RKCS C PROGRAMFOR CALCULATINGBS,CS AND R FROMRK C THE ASSUMPTIONIS MADETHAT THERE ARE NO SECONDARY C REACTIONS RK IS ASSUMEDTO BE 11. 5 1 FORMAT(I4,3Fl0.5,F7.2,3F7.4,F6.3} DO 50 J•l,100 READ(S,l}IEXP'l',BI,CI,S03,RK,BSID,CSMG,VOL S03V • S03-kVOL X = 11.5 BSM: (BSMG/180.16)1cS03V/((BSMG/180.16}+(CSID/214.60}) CS= (CSMG/214.60}1cS03V/((BSMG/180.16}t(CSMG/214.60}} DO SO K = 1,8 Y = (ALOGlO(BI/(BI-BS}}}/X ALY= (10.

··,tffsc}.·;z'1rBs.. -- cscc = Z*CSC R • BS/CS RC: BSC/CSCC DIFB = BSM- BSC DIFC: CS - CSCC DIFR: R - RC PCTB= DIFB*lOO.O/BS PCTC= DIFC*l00.0/CS PCTR= DIFR*l00.0/R RATIO= BI/CI RKC: ALOG(BI/(BI-BSC))/ALOG(CI/(CI~CSCC)) 2 FORMAT(FS.1'~2FlO.7,F7.3) 3 FORMAT(lH. ,FlO. 7yE1O.5) 4 FORMAT(I4) ' .. "'~.. _ 5 FORMAT(lH , 3FlO. 7, 2FlO. 3.) 6 FORMAT(F8.4) .. . .. WRITE(6 ,4) IEXPr WRITE( 6 , 2 )X, BSC', CSCC, RC WRITE(6,S)BSM,CS,S03,R,RATIO WRITE(6,3)DIFB,rcTBI WRITE(6,3)DIFC,PCTC WRITE(6,3)DIFR,PCTR WRITE(6,6)RKC 1 50 BS= BSC STOP END 146

!L_ Calculation of !L., BS. and CS in the Absence of Secondary Reactions for the Bi/Ci.:. 0.708 Experiments in the Chlorobenzene-Benzene System

SOURCESTATEMENT $ IBFTCCSCALC C PROGRAMFOR CALCULATINGWHAT R,BS ,AND CS ANDOTHER VALUES C WOULDBE OBTAINEDFROM THE R: 0.708 (BENZENEVS C CHLOROBENZENE)EXPERIMENTS IF NO SIDE REACTIONSWERE C TAKINGPLACE- C ASSUME KB/KC= 11.5 _ C DATAPOINTS ARE TAKENFROM THE BS/CS VS S03 CURVE 1 FORMAT(I4,FS.2,F7.4) DO 50 J=l,100 READ(S,l)IEXP!',RX,S03 BI: 0.1977 CI : 0.2778 CS= S03*1.150/(RX+l.OO) BS= S03*1.150 - CS 4 FORMAT(2Fl0.7) WRITE(6 ,4 )BS, CS DO 50 K = 1,6 Y = (ALOGlO(BI/(BI-BS)))/11.5 ALY= (10.0*Y) CSC = ((ALY'kCI)-CI)/ALY Z = (S03*1.150) / (BS+CSC) BSC .. Z*BS CSCC: Z*CSC RC : BSC/CSCC DIFR,: RK-RC PCTR= (RX-RC)*l00.0/RX 2 FORMAT(I4) WRITE( 6, 2) IEXPr 3 FORM4T(lR ,2Fl0.7 ,2F7 .2,Fl0.7,Fl0.3) WRITE(6,3)BSC,CSCC,RC,RX,DIFR,PCTR SO BS: BSC STOP END 147

!:. Calculation of·R,BS,TS, and Other Values for the Ti/Bi= 0.279 and Ti/Bi= 0.858 Experiments Assuming .!!.Q.Secondary Reactions~ Present

SOURCESTATEMENT

$ IBFTC TSCALC C PROGRAMFOR CALCULATINGWHAT R;BS,TS ANDarBER VALUES C WOULDBE OBTAINEDFROM THE R = 0.279- THE FIRST 10 C :CARDSAND THE R = 0.858 - THECARDS FROM 11 TO 26 - C DATAASSUMING THAT NO SECONDARYREACTIONS ARE TAKING C PLACE DATAPOINTS ARE TAKENFROM THE TS/BS CURVES C ASSUMEKT/KB= 27.0 1 FORMAT(I4,F6.2,F7.4) DO 50 J=l,100 READ(S,l)IEXP.r,RX,S03 i4 BI: 0.1708 15 -TI : 0.1466 BS= S03*0.700/(RX + 1.00) TS: S03*0.700 - BS BSM= BS TSM: TS 4 FORMAT(lH,2?10.7) WRITE(6,4)BS,TS DO 50 K = 1,6 Y: (ALOG10(BI/(BI-BS)))*27.0 ALY: (10. 0tty) .·• TSC • ( (ALY~I) .:.TI)/ ALY Z: (S03*0.700)/(BStTSC) BSC: Z1(-J3S TSCC : Z,\-T$C RC: TSCC/ESC DIFR: RX - RC PCTR: (RX - RC)*l00.0/RX DIFB : BSM- BSC DIFT = TSM- TSCC 2 FORMAT(I4) 8 FORMAT(lH ,4Fl0. 7, 2F7 ._-2,lF)0. 7) WRITE(6,2)IEXPT ' WRITE(6,8)BSC,BSM,TSCC,TSM,RC,RX,DIFB,DIFT,DIFR 50 BS= BSC STOP END

To convert to T1/B1 = 0.279, replace cards 14 and 15 with 14 BI= 0.2386 15 TI: 0.0666 148

!'..!. Calculation, of the Relative Contributions ,2! Primary and Secondary Reactions in the T9l~ene-Benzene System

SOURCESTATEMENT

$ IBFTC RELX C PROGRAMFOR ESTIM4\TING THE REL EFFECTSOF PRIMARYAND C SECONDARYREACTIOtf.; C DATAPOINTS TAKEN FROM THE TS/BS CURVES C TO CONVERTFROM ONE STARTING RATIO TO THEOTHER Cf!ANGE C CARDS44, 45, AND46 1 FORMAT(I4,F6.2,F7.4) DO '60 J:1,100 READ(5,l)IEXPT,RX,S03 44 BI= 0.2386 45 TI: 0.0666 BS: S03*0.700/(RX+l.OO) TS= S03*0.700 - BS DO 50 K=l,6 Y = (ALOG10(BI/(BI-BS)))*27.0 ALY: (10.0*"ky) TSC: ((ALY-ATI)-TI)/ALY Z = (S03*0.700)/(BS + TSC) BSC = Z*BS TSCC= Z-kTSC RC: TSCC/BSC 50 BS: BSC ZZ: (RC - RX)/(RC + 1.00) 46 Y: 4.00 X : (RX - Y) / (ZZ*(Y 4- 1.00) + RX - Y) 19 FORMAT(llI , 14) 17 FORMAT(lll;Fl0.6) WRITE(6,19)IEXPT 60 WRITE(6,l7)X STOP END

For the Ti/Bi: 0.858 data, use 44 BI: 0.1708 45 TI• 0.1416 46 Y = 3.20 149

G...STAT03 Analysis of Isomer Distribution UV Curves The program used is as follows:

$EXECUTESTAT03 PR890500023000000200.00 01 ABSMIXABORTBABMETAABPARAABBENZ blank card (5F6 .1) input data cards RD020100 RD020l0l03...... FINISH Preparation of the problem card is as follows:

Column 1,2 PR 3-6 problem number 7 ,8 number of. original variables 9-13 sample size 14~ 15 00 = no transgeneration cards 16, 17 00: no variables added to the original set after transgeneration 18-20 number of Replacement and Deletion cards 21-25 00.00,: no limit is placed on the significance of variables 71,72 number of variable FORMATcards

The third card in the series gives a six letter name for the coefficient of each variable. The fourth card (blank) is a scale card and the fifth card gives the input FORMAT.After the data cards are inserted, the Replacement and Deletion cards are placed in the deck. The preparation of the Replacement and Deletion cards is as follows:

Column 1,2 RD 3,4 02 calls for a table of residuals and an analysis of extreme residuals 5,6 states the variable to be treated as the dependent variable 7,8 gives the total number of variables to be deleted 9,10 first variable to be deleted 150

A new problem card, set of systems cards and data cards may be inserted after the·RD cards of the previous problem. The FINISH card ends the sequence. APPENDIXII

A Research Proposal in Organic

Chemistry in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

A STUDYOF THE SOLVOLYSISOF SELECTEDORGANIC HALIDES IN MOLTENQUATERNARY AMMoNIUM SALTS

January 5, 1966 11: 00 A.M. 242 ESC

Ernest A. Brown A STUDYOF 'I1tE SOLVOLYSISOF SELECTEDORGANIC HALIDES

IN MOLTENQUATERNARY AMMONIUM SALTS

The chemistry of fused organic salts has not been studied extensively partly because of the lack of information about melt-

ing points, thermal stability, and miscibility of such systems with organic compounds and partly because of misconceptions about the complexity and suitability of such systems as organic reaction media. Recently a series of papers have been published which . l 2 3 4 present data on a number of molten quaternary ammonLumsalts. ' , '

Many of the pure salts and their binary mixtures melt at 100° C. or less, and are thermally stable over a moderate temperature range.

They are also miscible with a wide variety of organic compounds.

Molten quaternary ammonium salts are expected to have some unique properties. Because the anions of the melt are not solvated, are probably not closely associated-with the cations in tight ion pairs, and exist in large concentrations, the salts should exhibit enhanced nucleophilic properties. Investigations of reactions of molten quaternary nitrates 1' 2 indicate that the nitrate ion, which is a weak electrophile in aqueous systems, is reactive in a molten salt system.

Although it might be expected that molten quaternary ammonium salts would be highly polar, measurements of surface tension, viscous

152 153

4 . flow and Z values of salts with large cations (tetra n-pentyl to tetra n-heptyl ammonium ions) suggest that these systems may be no more polar than acetone. It is conceivable that a solvent system with moderate polarity but with high nucleophilicity might induce solvolysis by an essentially

Sn2 mechanism. In an extreme case, even tertiary substances might show appreciable nucleophilic assistance to solvolysis.

A study of the solvolysis of some carefully chosen compounds would provide data useful for characterizing a fused salt system.

Linear free energy relationships similar to the Grunwald-Winstein correlation 5 ' 6 could be employed to provide a semi-quantitative measure of the ionizing power of mixed salt systems.

The measurement of rates of solvolysis in salt systems of comparable ionizing power but containing different nucleophiles would provide criteria for determining mechanism and data for establishing relative orders of nucleophilicity for the anions of the salt. •comparison of rates of solvolysis in fused salts with comparable reactions in more conventional solvents would provide a basis for evaluation of molten salts as solvents. This proposal consists of a study of the rates of solvolysis • of 1-chloro-and 1-bromo-bicyclo jJ..2.t..:.7 octane, tertiary butyl chloride, tertiary butyl bromide, n-hexyl chloride, n-hexyl bromide, benzyl chloride, and benzyl bromide in molten binary mixtures of tri-n-hexyl, n-heptyl ammonium iodide (Q6667I) (mp. 95.4° C.),

Q6667Br (mp. 105° C.), Q6667N03 (mp. 71.6° C.) and Q6667SCN. 154

The salts are chosen to give a constant cation with a variety of anions. All binary mixtures are expected to give linear melting or minimum melting phase diagrams and be thermally stable at the l O 4', temperature of solvolysis (110 c.). The substrates chosen offer a variety of susceptibilities toward Snl and Sn2 reactions. The substrates are all either available camnercially or have been 7>8 , previously synthesized. Data on solvolysis in aqueous solvents and for Sn2 displacements for these compounds or very similar ' 9 compounds are sunnnarized by Streitwieser.

The bicyclo compounds will be solvolyzed in the solvent mixtures to establish a Grun~ald-Winstein relationship. The remaining halides will be solvolyzed in a series of solvents having the same ionizing power but cont~ining varying amounts of different electrophiles. Differences in rates in these systems will indicate the exte~t of nucleophilic assistance to solvolysis. The ratios of the products resulting from, the solvolysis will also be indica- tive of the mechanism.

The rate of appearance of products will be determined as well as the rate of disappearance of reactants. This will give data which> under favorable circumstances, will serve as another criterion of mechanism.

The reactions will be"eonducted in suitable closed vessels in a constant temperature bath. At given ti~es the reaction will be quenched, the products extracted from the solvent and then analyzed by gas chromatography.

To convert rate data to units suitable for comparison 155 purposes, the densities of the various molten salt systems will be determined.

.. LIST OF REFERENCESFOR RESEARCHPROPOSAL

1. J. E. Gordon, 1:_ Am. Chem. Soc. , 86, 4492 (1964) .

2. J.E. Gordon, --.-ibid.,87, 1499 (1965). 3. J.E. Gordon, b Org. Chem., 30, 2760 (1965). 4. J.E. Gordon, b Am. Chem. Soc., 87, 4347 (1965). 5. E. Grunwald and S. J. Winstein, ~Am.Chem. Soc., 79, 846 (1957). 6. S. Winstein, A.H. Fainberg and E. Grunwald, ibid., 79, 4146 (1957). -- -

7. C. A. Grob, M. Ohta, E. Renk and A. Weiss, Helv. Chim. Acta., 41, 1191 (1958). 8. A. Sayigh, Diss. Abst., 14, 1552 (1954).

9. A. Streitwieser Jr., "Solvolytic Displacement Reactions,°'

McGraw-Rill, New York, N.Y., 1962, p·p. 12 3 18, 25, 30, 35-43, 46.

156 LIST OF REFERENCES

1. L. J. Andrews, Chem.~, 54, 713 (1954). 2. L. J. Andrews and R. M. Keefer, J. Am. Chem. Soc., 71, 3644 (1949); 11:.,3113 (1950). - -- 3. J.M. Arends, H. Cerfontain, I. S. Herschberg, A. J. Prinser, A. c. M. Wanders, Anal. Chem., 36, 1802 (1964). 4. B. T. Baliga and A. N. Bourns, Can. J. Chem.,!!:!!:., 363 (1966).

5. E. Berliner, "Electrophilic Aromatic Substitution Reactions /u in "Progress in Physical Organic Chemistry," S. G. Cohen, A. Streitwieser, Jr., and R. W. Taft, Ed., Interscience Publishers, New York, N.Y., )964, Vol. II, pp. 253-321. ·••:·... 6. Ibid., p. 280.

7. l!u..g_., pp. 283-293.

8. M. L. Bird and C. K. Ingold, 1-:_ Chem. Soc., 1938, 918. 9. T. G. Bonner, F. Bowyer and G. Williams,~-, 1953, 2650. 10. J. c. D. Brand, A. W. P. Jarvie. and W. C.H. Horning,~-, 1959,. 3844.

11. H. c. Brown and J. D. Brady, ;L_ Am. Chem. Soc., 74, 3570 (1952). 12. 11. c. Brown and G. Goldman, ibid., 84, 1950 (1962) •

13. H. c. Brown and F. R. Jensen, ibid., ag_l>2296 ·(1958). 14. H. c. Brown and H. Jungk, .!,lli., 77, 5579 (1955). 15. H. c. Brown and G. Marino, ibid •., ~' 1648 (1962). 16. B. C. Brown and c. W. McGary, ~, 77, 2306 (1955). 17. B. c. Brown and K. L. Nelson, ibid •., Ii, 6292 (1953). 18. B. c. Brown and N. Neyens, ibid., 84, 1655 (1962).

157 158

19. H. C. Brown and R. A. Wirkala, ibid.;' .§.a, 1456 (1966).

20. R. D. Brown, 1.:. Chem. Soc., 1959, 2224.

21. R. D. Brown, ibid., ill.2,, 2232.

22. H. Cerfontain, H. G. J. Duin and L. Vollbracht, Anal. Chem., 35, 1005 (1963) .

23. H. Cerfontain, H.J. Hofman and A. Telder, Rec. Trav. Chim., 83, 493 (1964).

24. H. Cerfontain, A. W. Kaandorp and L. Vollbracht, ibid., 82., 923 (1963).

25. H. Cerfontain, F. L. Sixma, L. Vollbracht, ibid., g 659 (1963). 26. H. Cerfontain, F. L. J. Sixma and L. Vollbracht, ibid., 83, 226 (1964).

27. H. Cerfontain and A. Telder, Proc. Chem. Soc., 1964, 14.

28. H. Cerfontain and A. Telder, Rec. Trav. Chim., 84, 545 (1965).

29. H. Cerfontain and A. Telder, ibid .., 84, 1613 (1965).

30. H. Cerfontain, A. Telder and L. Vollbracht, ibid., 83, 1103 (1964). - -

31. N. H. Christensen, Acta. Chem. Scand., 15, 1507 (1961). 32. N. R. Christensen, -- ibid., 17, 2253 (1963). 33. N. R. Christensen, ibid •., 18, 954 (1964).

34. F. E. Condon, ,L_ Am. Chem. ~' l.!, 3544 (1949). 35. w. A. Cowdrey and D. S. Davies, 1.:. Chem. ~' 1949, 1871.

36. F. Daniels, J. W. Williams, P. Bender, R. A. Alberty and C. D. Cornwell, "Experimental Physical Chemistry," McGraw- Bill Book Co., Inc., New York, N.Y., 1962, p. 400.

37. F. B. Deans and C. Eaborn, 1.:.Chem. Soc., 1959, 2299.

38. M. J. S. Dewar, "Electronic Theory of Organic Chemistry, 11 Clarendon Press, Oxford, 1949, p. 168.

39. M. J. S. Dewar, 1.:. Chem. Soc., 1946, 777.

40. M. J. S. Dewar, T. Mole and E.W. T. Warford,~-, 1956, 3576. 159

41. M. J. s. Dewar, T. Mole and E.W. T. Warford, ibid., .ill.§,, 3581. 42. E. Dresel and C. N. Hinshelwood, ~-, 1944, 649. 43. c. c. Eaborn and K. C. Pande, ibid., 1961, 297. 44. c. Eaborn and K. c. Pande, ibid., 1961, 3715. 45. c. Eaborn and K. c. Pande, ibid., 1961, 5082. 46. c. Eaborn and R. Taylor, ibid., 1960, 1480. 47. c. Eaborn and R. Taylor, ibid., 1961, 247. 48. c. Eaborn and J. A. Waters, ibid., 1961, 542. 49. c. Eaborn and D. E. Webster, ibid., 1957, 4449. ,so. Ibid., 1960, 179. 51. J. F. Eastman, J. L. Bloomer and F. M. Hudson, Tetrahedron, 18, 653 (1962).

52. F. Fairbrother, .J..:..Chem. Soc., .!fil, 1051. 53. L. N. Ferguson, "The Modern Structural Theory of Organic Chemistry," Prentice Hall, Inc., Englewoods Cliffs~ N. J.» 1963, pp. 393-401. - 54. L. N. Ferguson, A. Y. Gamer and J. L. Mack, J. Am•. Chem. 22£.:., 76, 1250 (1954). 55. E. E. Gilbert, "Sulfonation and Related Reactions~ 00 Interscience Publishers, New York, N.Y., 1965.

56. Ibid., p. 402.

57. ~-, p. 102. 58. R. J. Gillispie and E. A. Robinson, Can. L. Chem., 39, 2189 (1961).

59. V. Gold and D. P. N. Satchell, J. Chem.~' 1956, 1635. 60. D. G.. Guillot, Doctoral Dissertation, Brigham Young University, (1966) pp. 22-27.

61. Ibid., p. 37.

62. ~-, pp. 47-58. 160

63. J. A. Gurney, Doctoral Dissertation, Brigham Young University, (1963), p. 21.

64. K. Halvarson and L. Melander, Arkiv. Kemi., 11, 77 (1957).

65. J. S • Herschberg and F. L. S :f.xma, J. Koninkl. Ned. Akad. Wetenschap. Proc., Ser. lh, §1, 244, 256 (1962), JJh A •., 57 ~ 9285 b (1962'i].

66. J. L. Hine, "Physical Organic Chemistry,°' McGraw-Hill Book Company, Inc.» New York, N.Y., 2nd Ed., 1962, p. 352.

67. Ibid., p. 72.

68. c. D. Hodgeman, Ed., "Tables for Identification of Organic Compounds,'' Chemical Rubber Publishing Company, Cleveland, Ohio, 1960, p. 215.

69. E. D. Hughes, C. K. Ingold and R. I. Reed, :L.. Chem. Soc. 9 1950j 2400.

70. G. Illuminati and G. Marino, b Am. Chem. Soc., 78, 4975 (1956).

71. c. K. Ingold, A. Lapworth, E. Rothstein and ·n. Ward, ;L_ Chem. ~' 1931, 1959.

72.' C. K. Ingold and F. R. Shaw,· ibid., 1927, 2918.

73. A. W. Kaandorp, R. Cerfontain and F. L.' J. Sixma~ Rec. Trav. Chim., fil, 969 (1962).

74. o. I. Kachurin and A. A. Spryskov, ~ Vses. M.ezhvuz. Nauchn.- Tekhn. Kon£ • .22.:, Vopr. Sinteza ! Primineniva Organ. Krasitelei., 1961, 87 f!.:. ~, 61, 1723 (1964}]./ ' :·\ ·, 75. 0. I. Kachurin, A. A. Spryskov and E. V. Kovalenko, 1!,Q, Vyoshikh. Uchebn. Zavedenii. Khim.! Khim. Tekhnol., .§., 425 (1963) lJI.:..A., 59, 13781 (1963.l]. .

76. R. M. Keefer and L. J. Andrews, .J..:_Am. Chem. ~' 72, 4677 (1950).

77. J .--.K:Jiiglil:"";""'Ma°~-fer•·s.Thesis, Brigham Young University (1957), p. 29.

78. J. R. Knowles, R. 0. C. Norman and G. K. Radda, J. Chem. Soc., 1960, 4885.

79. P. Kovacic and J. J. Riller, .Jr., ,L_ Org. Chem., 30, 1581 (1965). 161

80. H. C. Kuivila and A. R. Hendrickson,~ Am. Chem.~' 74, 5068 (1962).

81. C. W. McGary, Jr., Y. Okamoto and H. C. Brown, ibid., 3037 (1955).

82. H. Meervein, G. Dittmar, R. Gollner, K. Hafner, F. Mensch and O. Steinfurt, Chem.~' .2.Q, 841 (1957) /c. A., 52, 9003 b (195817, 83. L. Melander, Arkiv Kemi, 2, 211 (1950).

84. R. S. Mulliken, J. Phys. Chem., 56, 801-22 (1952).

85. , Y. Muramoto, M. Morita and N. Hirao, Science and Industry. (Japan), 28, 347 (1954) & ~. 49, 14582 e, g (195517, 86. P. C. Myhre, Acta. Chem. Scand., 14, 219 (1960).

87. K. L. Nelson, "Sulfonation" in "Friedel-Crafts and Related Reaction," G. A. Olah, Ed., John Wiley and Sons, New York, N.Y., 1964:, Vol. III, pp. 2, Chap. 42. 88. K. L. Nelson and H. c. Brown, "Aromatic Substitution - Theory and Mechanism," in "Chemistry of the Petroleum Hydrocarbons, 00

B. T. Brooks, C. E. Board, S.S. Kurtz and L. Schmerling, Ed. 9 Reinhold Publishing Corp., New York, N.Y., 1955, Vol. III, Chap. 56. 89. D. V. Nightingale, Chem.~, 40, 117 (1947).

90. R. O. C. Norman and R. Raylor, °'Electrophilic Substitution in Benzenoid Compounds," Elsevier Publishing Company, New York, N.Y., 1965. 91. G. A. Olah, Ed., "Friedel-Crafts and Related Reactions, 00 John Wiley and Sons, New York, N.Y., 1964.

92. G. A. Olah, S. H. Flood, S. J. Kuhn, M. E. Moffatt and N. A. Overchurch, .J.:_ Am. Chem. Soc., 86, 1046 (1964).

93. G. A. Olah and S. J. Kuhn, ibid., 80, 6535 (1958).

94. G. A. Olah and S. J. Kuhn, ibid., 80, 6541 (1958).

95. G. A. Olah and S. J. Kuhn, ibid., 84, 3684 (1962).

96. G. A. Olah ands. J. Kuhn and S. R. Flood, l.:_ Am. Chem. ~s 83, 4571 (1961). 97. G. A. Olah, S. J. Kuhn and S. R. Flood, ibid., 83, 4581 (1961). 162

98. G. A. Olah, S. J. Kuhn and S. H. Flood, ibid., 84, 1695 (1962). 100. G. A. Olah, S. J. Kuhn and B. A. Hardie, ibid., 86, 1055 (1964). 101. G. A. Olah, S. H. Flood and M. E. Moffatt, ibid., 86, 1065 (1964). 102. G. A. Olah, M. E. Moffatt, S. J. Kuhn and B. A. Hardie, ibid., 86, 2198 (1964).

103. G. A. Olah and N. A. Overchuk, ibid., 87, 5786 (1965).

104. W. c. Pierce, E. L. Haenisch, "Quantitative Analysis/ 0 3rd Ed., John Wiley and Sons, New York, N.Y., 1953, p. 303. 105. J. D. Roberts, J. K. Sanford, F. J. L. Sixma, B. Cerfontain and R. Zagt, J. Am. Chem. Soc., 76, 4525 (1954). 106. J.C. Robertson, Doctoral Dissertation, Brigham Young University (1962), p. 85.

107. W ·u. Ruggeberg, T. W. Sauls ands. L. Norwood, .J:.:_Org. Chem., 20, 455 (1955).

108. L. C. Schroeter, "Sulfur Dioxide," Perganmon Press, Oxford, 1966, p. 9. 109. K. T. Serijan, H.F .. Hipsher and L. G. Gibbons, .J.:.Am. Chem. ~' 71, 873 (1949).

110. R. L. Shriner, R. c. Fuson and D. Y. Curtin, 10The Systematic Identification of Organic Compounds," 4th Ed., John Wiley and Sons, Inc., New York, N.Y., 1956, p. 269. 111. J. H. Simons and H. Hart, .J.:.Am. Chem.~, 69, 979 (1947).

112. B. C. Smith and G. H. Smith, ;L_, Chem. Soc., 1965, 5514.

113. A. A. Spryskov and B. G. Gnedin, Zh. Obshch. Khim., 33, 1082 (1963) lb.. b., 59, 9748a (196317. • 114. J.C. Sternberg, H. S. Stello and R.H. S. Schendeman, Anal. Chem., 32, 84 (1960).

115. L. M. Stock and F. W. Baker, ;L_ ~Chem.~' 84, 1661 (1963). 116. L. M. Stock and H. c. Brown in "Advances in Physical Organic Chemistry," V. Gold, Ed., Academic Press, New York, N.Y., 1963. 117. L. M. Stock and H. c. Brown,~ Am. Chem. Soc., 81, 3323=29 (1959). 163

118. E. M. Thompson, Doctoral Dissertation, Brigham Young University (1963), p. 44. 119. Ibid., p. 19.

120. K. D. Wadsworth and C. N. Hinshelwood, 1.:,. Chem. Soc., 1944.

121. E. B. Wilson, Jr., "An Introduction to Scientific Research/ 0 McGraw-Hill Book Co,, Inc., New York, N.Y., 1952, p. 240.

122. Y. Yukawa and Y. Tsuno, Bull. Chem. Soc. Japan, 32, 971 (1959).

123. H. Zollinger, "Hydrogen Isotope Effects· in Aromatic Substitu- tion Reactions" in "Advances in Physical Organic Chemistry / 0 V. Gold, Ed., Vol. 2, Academic Press, New York, N.Y., 1964, pp. 163-196: MANUSCRIPTS Criteria for the Applicability of Ingold's Equation

Competitive reactions are frequently employed in the study of electrophilic aromatic substitutions to obtain relative rate data needed for the calculation of partial rate factors. Mixtures of a substituted arene and benzene are reacted with the electrophilic species and the ratio of the relative rate constants for the reaction 1 ·(k -x /k Benzene ) is obtained from Ingold's equation ..

x. log -1:. kxlkBenzene = Xf (1)

where Xi, Xf, Bi and Bf are the initial and final concentrations of the substituted and unsubstituted benzene compound respectfully.

1. C. K. Ingold and F. R. Shaw, !L. Chem. Soc., 1927, 2918.

This equation is applicable only if both aromatic species are substituted by the same electrophilic reagent and the reaction is first 2 orde.r with respect to the aromatic.

2. M. J. S, Dewar, 'I'. Mole and E.W. T. Wa.rford, ;L_ Chem. Soc., 1956, 3576,

The order of the reac:tio::1 with respect to the elect:rophile is not

2 3 important provided, of course, that it is the same for reaction 3 with both aromatic substrates. Olah in a very careful study of

3. G. A. Olah 3 S. :J Kuhn and S. H. Flood, 1.:., Am. Chem. Soc., 83, 4571 (1961). aromatic nitration reactions, demonstrated that when the above condi-

tions were met, variations in rate of stirring 3 ratio of starting materials, and temperature did not influence the relative rate ratio.

The absence of a variation in the relative rate ratio with changes in the ratio of starting materials is a common criterion applied to determine the applicability of Ingold 1s equation. During the course of recent investigations of the sulfonation of aromatics with in solvent, have had occasion to re-evaluate this so3 so2 we criterion and have found a serious limitation to its usefulness.

The sulfonation systems we studied are believed to contain sulfonating species other than • Thus, some of the product so3 aromatic sulfonic acids recovered from the reaction are produced by these secondary sulfonating agents. Our studies hav·e shown that a constant kx/kBenzene value may be obtained over a large range of varying Xi/Bi values when a large proportion of the products result from the reaction of the secondary sulfonating agents. Therefore, although it is possible to calculate a rate constant ratio, the value is mi.sleading since it does not represent the reaction the investi- gator thinks he is studying.

Let Bl and. B:2. r.ep!:'ese.rtt the molar amounts of benzene product produced by the primary and secondary 1:·eactions and Xl and XZ repre- 4 sent the molar amounts of the substituted aromatic produced by primary and secondary reactions. Let us assume that Xis the product of the less reactive aromatic and that the ratio of products formed by the secondary reactions (B2/X2) is less than that of the primary reactions. The ratio of products recovered from the reaction will be

B Bl-+ B2 = X Xl + X2 (2) since

Bl) B2 Xl X2 (3)

~) B2 Xl Bl (4)

The secondary reactions thus contribute proportionately more to the formation of the product of the less reactive species. It can be shown that the secondary reactions will always contribute a relatively larger amount to the formation of the product of the species produced in the smaller quantity by the primary reaction.

In the absence of secondary reactions

B = Bl X Xl (5)

With the addition of secondary-reaction products (from Equations

2 and 3) it is evident that

B /; Bl x'fx1' (6)

When the &mounts of B:Z and X2 are small :relative to Bl and Xl 9 the value of X is i,:1C::".'e11.::3E:dp:topo:t·::i,on,at.ely much more thi::m the value of B, and B/X dec::rea.se.'.3rapidly with the addition of small quantities 5 of secondary reaction products. As the contribution of secondary products is increased relative to that of the primary products,

B/X continues to decrease but at a slower rate until the point is reac.hed where the primary pr1)ducts constitute a negligible fraction of the total product and B/X becomes approximately equal to B2/X2.

If the amount of products from secondary reactions increases with

:lnc1·e:asi.ng electrophile concentration, a plot of B/X against electro- phUe concentration (at constant Bi /Xi) produces curve A in Figure 1. ------B

B/X r------C

------A

Fig o L--B/X as a function of electrophile concentration

If the :r.ati.o of secondary products (B2/X2) is greater than th~ ratio of primary products, an upward curving lin,e (curve B in

F'igure 1) :results. Only when the ratios of prima:r:·y and secondary products are equal will no variation in B/X wit:h changing electrophile concentration be obse·rve.d (curve C in F:Lgu:re 1).

When k:r/kx is plotte.d against Bi/Xi (Ki is the less reactive spedes), .:i curve si:m:Uar t<'.• thE.t: i.n Fig1.1r.,:; 2 :results. At low pr.oduct w:i.11 he ..fm::med i:n smaller amounts Fig. 2.--Relative rate constants as a function of starting ratios when secondary reactions are present by the primary reaction, the secondary reactions will contribute proportionately more to the benzene products and kB/kx will be too large. At larger Bi/Xi ratios the secondary reactions will contribute relatively more to the X product than to the benzene product

0 and. kB/1,c will be too small. The ntrue ' value of ~/l

From these conside·rations, it is apparent that mis leading conclusions can be reached if a plot_ of kB/kx vs. Bi/Xi is the only criterion applied to determine if Ingold's equation can be applied to obtain relative rate for the primary reaction. The same results - consta.nt k:Blkxwith c~~-r,.ging Bi/Xi - will be obtained either when there are. no secondary re:::wt:ions occurring or large secondary effects are present. The choice of a wide Bi/Xi range is an insufficient guaran- tee that such a plot wnl detect complicating rea.ctions unless the \ 7 range includes values that will produce reasonably. large excesses of products of the less reactive as well as the more reactive species.

Plots of product ratios vs. electrophile concentrations are more sensitive tests for the presence of secondary reactions. Plots of moles of individual products formed as functions of electrophile concentrations also-indicate the presence of secondary reactions and by suitable extrapolations in such plots, corrections for secondary reactions can be made.

Examples of the application of these principles to sulfonation reactions will be prese~ted in forthcoming papers. It is believed that these ideas are of general utility and may be applied to any reaction system utilizing competitive reactions.

K. LeRoi Nelson

Ernest A. Brown

Department of Chemistry

Brigham Young University Provo, Utah THE SULFONATIONOF CHLOROBENZENE

WITH SULFURTRIOXIDE!

1. Based on the Ph.D. Dissertation of E. A. Brown1 Brigham Young University, 1967.

by K. L. Nelson and E. A. Brown

The sulfonation of chlorobenzene and chloroben-

zene-benzene mixtures with sulfur trioxide in liquid

sulfur dioxide at -12,5° was studied to obtain partial

rate factors. The apparent relative rates of sulfona-

tion vary with both the initial ratio of aromatics and

the concentration of sulfur trioxide. These observa=

tions are rationalized in terms of secondary reactions

in which the aromatics are sulfonated with re.9,gents other

than sulfur trioxide. The isomer distribution for chloro-

98. o 96 .±.0 .12%. The relative rat~ corrected for the

effects of the secondary reactions is kbenzenikchloro- b e.nzene :: lL 5 ± 0 .3. Calculated partial rate factors

are Pf :: 0 . .517 ~ OJ: ::: 0. 0025 ~, and mf ::::0. 00024.

1 2

The sulfonation of halobenzenes has not been investigated as thoroughly as other electrophilic aromatic substitution reactions.

There is a particular lack of information about partial rate factors for this reaction. This work was undertaken to determine isomer

distributi.ons, and relative rate data to permit calculation of partial rate factors for the sulfonation of chlorobenzene with sulfur trioxide in liquid sulfur dioxide. The isomer distribution was obtained by an isotope dilution

technique. Chlorobenzene was sulfonated with S-35 labeled sulfur

trioxide at reflux temperature (-12.5° C.). The reaction products were obtained as aqueous solutions of the sodium chlorobenzenesulfonate salts. Aliquot portions ' of the reaction-product solution were added to excess quantities of each of the pure, nonradioactive sodium salts of the isomeric chlorobenzensulfonates. The isomers were then purified by recrystallization as the 2-toluidine salts and the isomer distribution was calculated from the sizes of the aliquots, the weights of the nonradioactive salts, and the count rate of the purified isomer salts. Relative rate data were obtained by sulfonating chlorobenzene in competition with C-14 labeled benzene. The products were recovered as dry sodium salts of the product sulfonic acids. Knowledge of the count rate expected for a sample of pure sodiumbenzenesulfonate and the actual count rate for the mixture of sulfonate salts permitted the calculation of product compositions.

Results and Discussion The sulfonation of chlorobenzene and benzene with sulfur 3

trioxide in liquid sulfur dioxide is a very clean reaction. Essentially

all of the sulfur trioxide consumed was recovered as titratable acid

products. Attempts to correlate amounts of prod~ct formed with sulfone formation failed when evaporation of ether extracts of the

reaction mixture, after the method of Ruggeberg, 2 et al., produced

an amount of sulfone material too small for meaningful comparison.

2. W H. Ruggeberg, T. W. Sauls~ and S. L. Norwood, :J.:..Org. Chem., 20, .455 (1955) .

The relative rates of reaction were calculated from Ingold's

equation. 3

3. C. K. Ingold and F. R. Shaw, L_ Chem.~, 1927, 2918.

log initial moles of benzene final moles of benzene kB/kc = ------(1) log initial moles. of chlorobenzene final moles of chlorobenzene

Table 1 presents the results of a series of sulfonation reactions in which the initial benzene/chlorobenzene ratio was varied.

A plot of the data in Table 1 is given in Figut·e 1. Two features of

this plot are significant: first, kn/kc is not independent of B1/ci, but increases with decreasing Bi/Ci - the increase being very pronounced

at low Bi/Ci ratios; and second, although the general trend is clear,

there is conside~able scatter in the data points. Traces of moisture were considered as possible causes of the scatter in the data and

experiment (76-P) was made in which water was delibe:".'ately added. '\

" 20

12 kB/kc- -10 ~

6 B 8 4 B \ 2 8 0.2 0.4 0.6 0.8 1.0 1.2 1. 1.6 1,8

B/Ci

Fig. 1.--Apparent Relative Rates as a Function of Initial Benzene~Chlorobenzene Ratio r.: l•, • 5

TABLE1 RELATIVERATES AS A FUNCTIONOF INITIAL BENZENE/CHLOROBENZENERATIO

so3 Experiment Concentration Bi/Ci kB/kc No. (M./1.)

49-P 0.02177 0.02162 17 .40 6S~P 0.02354 0.04431 18.58 66-P 0.02256 0.08314 15.43 39-P 0.02640 0.1102 12.07 43-P 0.03253 0.1125 11.39 67-P 0.03178 0.1269 13 .07 68-P 0.01919 0.1475 11.89 59-P 0.02519 0.1864 9 .39 41-P 0.03477 0.3329 6.67 38-P 0.02688 0.3515 8.67 76-Pa 0.01093 0.5150 0.91 74-P 0.02122 0.5486 12.58 40-P 0.02307 0.6460 9.67 75-P 0.02811 1.004 6.12 36-P 0.03097 1.063 4.61 50-P 0.02385 l.150 4.41 48-P 0.02435 1.502 6.64 73-P 0.02397 1.899 3.44

8 Water was added to the reaction mixture.

This experiment gave deviant results but.the kB/kc value obtained was low (0.91) rather than high so that it did not appear that moisture could explain the particular shape of the curve.

The sulfur trioxide concentrations listed in Table 1 are not constant. The possibility that variations in sulfur trioxide concentration might1 influence product composition was investigated by conducting a series of sulfonations with different amounts of sulfur trioxide at two constant B1/ci ratio.s. Table 2 and Figure 2 present the results from these experiments. BS and CS represent 6

TABLE2 PRODUCTCOMPOSITION AS A FUNCTION OF S03 CONCENTRATIONAT CONSTANTBi/Ci

S03 Experiment B1/C1 Concentration BS cs BS/CS No~ (M. /l.)

78-P 0.708 0.01062 0.009394 0.001255 7.485 81-P o.717 0.01886 0.01812 0.003430 5.282 80-P 0.708 0.02647 0.02437 0.005295 4.602 82-P 0.709 0.05350 0.04477 0.01470 3.046 84-P 0.129 0.00409 0.002698 0.002002 1.348 86-P 0.129 0.00574' o. 003945 0.003231 1.221 85-P 0.129 0.03066 0.01981 0.01545 l.282 67-P 0.127 0.03178 0.01920 0.01445 l.329

the total moles of benzenesulfonic and chlorobenzenesulfonic acids produced in each reaction. The data for the two different starting ratios give two different curves. For Bi/Ci: 0.129 the plot of BS/CS is a straight line with slope zero, while that for the larger' B1/C1 ratio gives a smooth curve with BS/CS decreasing with increasing so3 concentration.

In an earlier communication 4 we have presented arguments to

4. K. L. Nels'on and E. A •. Brown, prior publication. show that curves similar to those in Figures land 2 can be obtained in systems in which secondary reactions are occurring.

Several species which could setve as secondary sulfonating agents have been identified as side products in sulfonations by sulfur 135 trioxide in aprotic solvents. Pyrosulfonic acids are generally considered to be responsible for sulfone formation and may act as 8 . (u :: Bi/Ci 0. 708 t) m = ~itc\ 0.129 r - 6 I .\

BS/CS J ~ -...J

2 --@mr------~

0.01 0,02 0.03 0.04 0.05 0.06 Concentration of S03 (Moles per Liter)

Fig. 2.--Ratio of Benzene to Chlorobenzene Sulfonates in Product at Constant Bi/Ci as ..a Functi9n of Coni::entration 9f so3 . '- 5. R. Cerfontain, A. Telder and L. Bollbracht, Rec. Trav. Chim., 83, 1103 (964) . sulfonating.as well as sulfonylating reagents. Christensen, in a series of studies of the sulfur trioxide sulfonation of iodobenzene 6 7 8 in· nitromet · h ane ~ , d emonstrate d t h e presence o f b ot h pyrosu lf on i c

6. N. H. Christensen, Acta. Chem. Scand., 15~ 1507 (1961).

7. N. R. Christensen, ibid., 17, 2253 (1963).

8. N. H. Christensen, ibid., 18, 954 (1964). acids and sulfonic acid anhydrides and concluded that the anhydrides were the more stable species. On the basis of his observations, Christensen proposed the following mechanism for sulfonation by

in aprotic solvents. so3

~·:A;if~§ci;_k_l____ (2) 'k-1

(3)

k3 2 Arso-o-so H ;:::;::=:::::' (4) 2 3 'k -3

(5)

(6)

The species (Arso2) 20 • n2s04 is also considered to be a possible intermediate in the formation of the anhydride (Equation 4) or may be the actual sulfonating agent in Reaction 5. The attaimnent of equilibrium is believed to be fast in the first step and k2 is believed smaller than k1. Christensen considers Reaction 4 to be fast relative to Reaction 5 and the concentration of the pyrosulfonic acid must be small compared to that of the anhydride. Reaction 6 accounts for sulfones that might be found in the reaction products.

If we apply Christensen's mechanism to the present system and include the possibility of pyrosulfonic acid sulfonation, the following reactions are possibl~:

B BS (7) + so3 ---4) C -+ S03 ) CS (8)

BS ~ so3 ==~ BSS (9) cs t S03 ;::::=~css (10) CSS + B -----+) 2BS (11) BSS + C ----,) BS + CS (12)

CSS + B -----+) BS + CS (13)

' CSS t C ---~) 2CS (14) 2BSS =====BS-0-BS + H2S04 + S03 (15) 2CSS ;=::==== CS-0-CS t H2S04 + S03 (16) BSS t CSS === BS-0-CS + H2S04 + S03 (17) BS=O-BS + B t RzS04---) 3BS (18)

BS-0-BS t Ct HzS04 ) 2BS + 2BS + BS (19)

CSmQmCSt B + HzS04 ) 2CS + BS (20)

CS=OmCSt C t !½S04 ) 3CS (21) BSmO-CS+ C + HzS04 --➔' 2CS + BS (22) l BS-0-CS + B + H2.S04-- ➔) 2BS + CS (23) I lO

B, BS, and BSS represent benzene, benzenesulfonic acid and benzenepyrosulfonic acid; c, CS, and CSS represent the comparible chlorobenzene species and BS-0-BS, cs-o-cs, and BS-0-CS represent the respective sulfonic acid anhydrides. The amount of total benzenesulfonic acid produced in the reaction will be:

(24) where BS7 , Bs11, Bs13, etc., represent the amounts of benzenesulfonic acids produced in Reactions 7, 11, 13, etc. Only those reactions in which a sulfonating species attacks B will yield a net gain in BS.

Reactions like 12 merely regenerate BS that was consumed ear.lier in the formation of BSS. In a similar manner, the total amount of CS produced would be.:

cs : csa + CS12 + CS14 ~ CS19 + CS21 + CS22 (25) There are, therefore, six different reactions leading to each of the reaction products.

Further confirmation for the existence of secondary sulfonation reactions in the benzene-chlorobenzene system is given in Figure

3. In this figure, the moles of product (BS and CS) obtained from sulfonation at constant Bi/C 1 values are plotted as a function of so3 concentration. Straight lines are. plotted through the origin and the smallest product values. The BS and CS values at higher so3 concentrations are seen to curve away from the straight line indicating that somewhat more CS and less BS is being formed than would be expected if the trends at lower so3 concentrations were continued. It is also noteworthy that the deviation from the CS line in the Bi/Ci~ 0.708 plot is greater and occurs earlier than 0 = Bi/Ci o. 708 BS

Gl =Bi/Ci, 0.129

.04

.03

Moles of Product ...... 02 cs

.01

. 01 .02 .03 .04 .05 .06 Concentration of S03 (Moles per Liter)

, ,,, , I Fig. 3. --Moles of Product Formed as a Function of S03 Concentration 12

4 that for the BS line. This is in harmony with the proposal that

the concentration of the less reactive species is influenced propor-

tionately more than the concentration of the more reactive species. No deviation from the straight line is noted for the CS data for

B /c • 0.129 while the BS data differ only slightly. 1 1 = Figure 3 provides a means of determining k:slkc for the primary reactions. The secondary reactions be~ome progressively less impor-

tant as so3 concentration decreases. In the limit there would be no secondary reactions at an so3 concentration of zero. Therefore, straight lines obtained by extrapolating the data to zero in Figure 3

represent the values anticipated for a system with no secondary

reactions. Very careful extrapolations of the data were made on an

expanded scale. BS and CS points were taken from the straight lines resulting from these extrapolations, a constant Bi and Ci were assumed

for the series of points, and kB/kc values were calculated from

Ingold's equation. The results of the calculations are given in

Table 3. The deviations are expressed as one standard deviation unit. The average of the two sets of data gives ~/kc.:= 11.54 i Oo30.

The reasonable agreement in kB/kc from the two sets of data is good support for the validity of this method. This is particularly satisfying in view of the large difference in Bi/c 1 and the differences in the shapes of the curves in Figure 3.

The determination of a value for kB/kc for the primary reaction permits a further test for the existence of secondary sulfonation reactions. It has been shown that the secondary reactions will 13

TABLE3 DETERMINATIONOF kB/kc FROMEXTRAPOLATED VALUESOF BS ANDCS

BS . cs

0.708 0.1975 0.2789 0;01810 0.00238 11.36 0.02170 0.00282 11.47 0.01445 0.00188 11.21 0.01629 0.00210 11.37 0.01990 0.00258 11.47 Av. 11.27..±.0.21

0.129 0.04265 0.3306 0 0 01330 0.01061 11.44 0.01462 0.01168 11.68 0.01598 0.01270 12.00 0.01068 0.00850 11.06 0.01867 0.01482 12.50 __ '"_>< 0.01732 0.01378 12. 24~ , :··--- Av. 11.82.!0.30

..,-coii~rip_ute to a greater extent to the species ma.de in the smallest

amount by the primary reactions. Usually this will be the sulfonic

acid of the less·reactive aromatic, but if Bi/Ci for a reaction is

sufficiently small> more CSl than BSl m~y·be:.formed. Secondary reactions

would then contribute proportionately more to i::he formation of BS

than CS. At larger B1/ci values one would expect a greater contribution to the formation of CS. There would also be some vucross-over"

Bi/Ci value where the effects of the secondary reactions will balance

each other. Since kB/kc is 11. 5, we would expect the ~'cross =ove:r'g

Bi/C1 value to certainly be less than one and possibly near 0.1.

Low so3 concentrations would also favor the formation of the product formed in the smaller amount by the primary reaction sincej although

BS and will be small, the concentration of the species present 7 cs8 14 in smaller concentration would be more sensitive to secondary reactions.

A semiquantitative test of these predictions was made. A series of calculations was made to determine what BS/CS ratio and what quantities of BS and CS would have been obtained if there had been no secondary reactions. This was done by assuming a value of

~/kc of 11.5 for all of the competitive experiments and calculating the values of BS and CS needed to produce the known total number of moles of product from the known amounts of starting materials.

Table 4 presents the results of these calculations. For each experiment, the differences between the calculated values (BSC,

CSC, and RC) and the actual values are expressed as a percentage difference 6 %• The percentage di£ ferences were obtained from

= (actual value - calculated value)(lOO) Actual value (26)

Certain generalizations can be drawn from the data in Table·

4. At low B1/Ci ratios the 6 % BS values are positive, indicating that more BS was produced than expected. As the B1/ci ratio is increased, there is a decrease in l::,.% BS until at high Bi/Ci ratios less Bi is being produced than predicted. The opposite trend is seen for .6.% CS which is in accord with the proposed mechanism. The magnitude of i:)% CS at large Bi/Ci ratios implies that at least half again as much CS is produced as was predicted. The concentration of so3 also iii'impo:rt-9:nt. Thus, 87-P, which couples a low"S03 concentration with a relatively large Bi/Ci ratioj gives the largest increase. TABLE4 COMPARISONOF ACTUALVALUES OF BS ANDCS WITHTHOSE PREDICTED FORSULFONATION WITH NO SECONDARYREACTIONS -~· -

,_ os>•

so3 Experiment B1/Ci Cone. BSC csc 1lli.£: RC 6.% 6% Li% No. ~SC:: !M./1.) - - + ~. •• BS cs - i BS/CS ,.. ,_,. 65-P 0.0443 _o.02354_ 0.00798 0.02354 0.37 25~43 -14~59 - -34; 92 66-P 0.0831 0.02256 0.01090 0.01392 0.78 13.48 -13 .88 24~02 39-P 0.1102 0.02640 0.01598 0,01570 1.02 3 .07 - 3.33 6.19 43-P 0.1125 0.03253 0.01890 0.02014 0.94 2. 72 - 2.70 5.28, 67-P 0.1269 0.03178 0.02801 0.01536 1.17 5.38 - 7 .14 11;68 84-P 0.1289 0.00409 0,00277 0.00193 l.43 2.99 - 4.62 7;27 86-P 0.1289 0,00574 t- 0,00421 0,00297 1.42 - 0.80 l.11 - 1.92 V! 85-~ 0.1289 0. 03066 0,01853 0.01672 1.11 11.53 -16 .88 - c'-'24 ,30 68-P 0.1475 0.01919 0.1315 0.00892 1.48 2.21 - 3.44 5.46 59-P 0.1864 0.02519 0.01798 0.00973 1.85 - 6.44 10.05 - 18.33 41-P 0 .3329 0.03477 0,03182 0.00991 3.21 -14.70 29 .16 - 61.92 38-P 0.3515 0.02688 0.02522 0.00703 3.59 - 6.35 17 .66 - 29.17 74..,p 0.5486 0,02122 0.02149 0.00450 4. 78 l.70 - 9.00 9.82 40=P 0.6460 o. 02307 0.02374 0.00337 7 .05 - l.97 12.01 - 15.89 78-P 0.7079 0.01062 0.01037 0.00131 7.91 - o. 71 5.27 - 6 .31 80-P 0. 7079 0.02647 0.02688 0.00356 7.54 - 7.76 35.20 - 66 .30 82-P o.7090 0.05350 0.05374 0.00778 6.91 -17 .60 50.83 -139.15 81-P 0.7170 0.01886 0.01923 0.00246 7.82 - 5.73 29.77 - 50 . .55 87-P 0.9024 0.00142 0.00149 0.00014 10.33 -46.04 76.51 -521.72 75-P 1.004 0.02811 0.02957 0.00276 10.73 - 7 .18 41.80 - 84.14 36-P 1.063 0.03097 0,03561 0.00311 11.47 -11.51 54.21 -143 .51 -- 50-P l.150 0,02385 0,02431 0.00193 12.62 - 4.23 33.88 - 57.65 48-P 1.502 0.02435 0.02751 0.00171 16,06 - 4.10 38.73 - 69.91 73-P 1.899 o. 02397 0.02576 0.00181 14.25 -14.80 64.76 -225 .8 . 79-P 3.554 0.01783 0.02087 0,00052 39.79 - 4.19 61.53 -170.82 Small deviations from the scheme probably result from minor experimental errors. Throughout the experimentation every effort was made to keep stirring rates, mixing times, and concentrations as constant as possible. If tqere were no secondary reactions these factors would be unimportant, 9 but since secondary reactions

9. G. A. Olah, S. J. Kuhn and S. H. Flood, 1.:. Am. Chem. Soc., 83, 4571 (1961). are present in the system, small changes in experimental conditions could measurably influence the results. The sulfonation reaction is very fast and so mixing and stirring rates are critical. The aromatic solution was added to the dilute so3 solution and local excesses of aromatics caused either by inadequate mixing or variations in aromatic concentrations in the small chamber could cause serious effects.

It is most probable that the minor deviations found in the data result from such causes.

At small Bi/Ci ratios, the amount of BS formed in the main reaction causes BS to increase relative to CS while at higher ratiosj the reverse is observed. At some ratio, conditions will be such that these two effects will bala~ce each other. From Figure l this should occur at the point where the apparent kB/kc is 11.5 The observed

Bi/Ci ratio at this point is 0.14. It is not surprising, therefore, that a variation of BS/CS with so3 concentration at B1/c 1 = 0.129 (Figure 2) is not observed.

An approach similar to that above was followed to interpret data obtained from the BS/CS vs. so3 concentraticn (Figure 2) for Bi/Ci= 0.708. A series of twenty data points was taken from the curve and the values for BS and CS which would have been predicted with no side reactions were calculated. !Table 5 tabulates the ,I results of these calculations and compares the BS and CS values which fit the curve with the predicted values. A gradual increase of h CS with a corresponding decrease in 4BS is noted as the so3 concentration increases. This is also in accord with the premise that at this Bi/Ci ratio, secondary reactions will contribute more to the formation of the product from the less reactive species.

Isomer Distribution Determination

Five isotope.dilution experiments were conducted to determine the isomer distribution for the sulfonation of chlorobenzene. The isomers were all recrystallized to count rates constant within the statistical counting range.:, The isomer distributions were calculated from

(27)

·Sn(Fm) CWotXo) + Cm(Fm)(Wm+Xm)+ Cp(Fp)CWp+Xp)

. Cp(Fp) CWp+Xp)100 %·2 = ------(29) co

Ci= total activity of the! isomer in the diluted! isomer

Fi= ml.~ aliquot/ml.! aliquot= a factor to correct all data to the same size aliquot

Wi = the weight of nonradioactive! isomer used in the dilution TABLE5 COMPARISONOF ACTUALVS. PREDICTEDBS, CS, ANDBS/CS _ \1ALUES FOR !h /

803 Concentration BSC BS csc cs RC R 6BS ,1CS AR (M. /1.) 3 ,. .. ~-- (x.10 ) (x;o3) _, - . - 0.0100 0.01022 0.01016 0,00128 0.00134 7.99 7.60 -0.06 0.06 0.39 · 0.0125 0.01277 0.01249 0,00161 0.00189 7.94 6.62 -0.28 0.28· 1.32 0.0150 0.01531 0.01479 0,00194 0,00246 7.89 6.02 -0.54 0.54 1.87 0.0175 0.01785 0.01706 0,00228 0.00307 7.84 5.56 -o. 79 0.79 2.28 0.0200 0.02038 0.01929 0.00261 0,00371 7.79 5.20 -1:09 1.10 2.59 0.0225 0.02292 0.02147 0.00296 0.00441 7.74 3.87 -1.45 1.45 2.87 t-'· 0,0250 0.02544 0.02363 0.00331 0.00512 7.69 4.61 -1.81 1.81 3 .08 co; 0.0275 0.02797 0.02572 0.00366 0.00590 7,64 4.36 -2.25 2.24 3.28 0.0300 0.03048 0.02779 0.00402 0.00671 7.59 4.14 -2.69 2.69 3.45 0.0325 0.03300 0.02984 0.00438 0.00754 7.54 3.96 -3.16 3 .16 3.58 0.0350 0.03551 0.03183 0.00474 0,00842 7 .49 3.78 -3.68 3.68 3.71 0.0375 0.03801 o. 03383 0.00511 0.00929 7.44 3.64 -4.18 4.18 3.80 0.0400 0.04052 0.03580 0.00548 0.01020 7,39 3.51 -4.72 4.72 3.88 0.0425 0.04301 0.03777 0,00586 o.01111 7.34 3.40 -5.24 5.25 3.94 0.0450 0.04550 0 .03972 0.00625 0,01203 7 .28 3,30 -5.78 5.78 3.98 0.0475 0.04799 0.04165 0.00644 0,01298 7 .23 3.21 -6.34 6.34 4.02 0.0500 0.05047 0.04358 0.00703 0,01392 7.18 3 .13 -6.89 6.89 4.05 0.0550 0.05542 0,04744 0.00783 0,01581 7 .07 3.00 -7.98 7.98 4.07 0.0575 0.5788 0.04938 0.00824 0.01674 7 .02 2.95 -8.50 8.50 4.07 Xi: the weight of the isomer salt from the sulfonation product

Values for Xi were calculated from the size of the aliquot, the known number of moles of so3 used in the reaction and an approximate isomer distribution obtained by disregarding Xi tenns in Equations 27, 28, and 29. The results of these experiments are given in Table 5.

TABLE5 SUMMARYOF ISOMERDISTRIBUTION RESULTS

Experiment % .2 %!!! % .e 20$P 0.934 + 0.008 0.107 i 0.008 98.96 + 1.53 62 .. p 0.9'77 i 0.004 0.102 .±.0.013 98 :92 I 1. 82 64-P 0.966 i 0.005 0.104 .±.0.015 98. 93 .±.1.19 70 .. p 0. 95 7 .±.0. 007 0.082 ± 0.008 98. 96 + l.18 71 .. p 0.909 .±.0.117 0.061 .±.0.048 99.03 i l.39 Average 0.95 i 0.03 0.09 .± 0.02 98.96 .± 0.12

The errors assigned to the average values in Table 5 are standard deviations calculated at the 90 percent confidence level for the averag- ing of the five sets of numbers, The reaction is thus seen to be very selective with a para/meta ratio of about 1000. The low ortho/para ratio is attributed to steric requirements of the comparitively bulky

S03 group. Partial rate factors of Pf= 0.517, Of= 0.0025 and mf ~ 0.0024 are calculated from the above isomer distribution data and the competitive rate value of 11.5.

Experimental Section 9

9. Melting points were determined with a Hoover Unimelt melting point apparatus·and are corrected. Materials About 300 g. of the pure sodium salt of each isomeric chlorobenzenesulfonic acid was prepared for the isomer distribution experiments. The salts were obtained by hydrolysis of the corresponding chlorobenzenesulfonyl chloride which were prepared by the method of

Meerwein et ai. 10 In a typical preparation of the para isomer, 430 g.

10. H. Meerwein, G. Dittmar, R. Gollner, K. Hafner, F. Mensch and O. Steinfurt, Chem.~, 90, 841 (1957) .ff:._~, 52, 9003 b (195817

(3:.3 moles) of .e,-chloroaniline (Eastman Organic Chemicals, red label, lot 505) was added to 1150 ml. of concentrated hydrochloric acid which had been cooled in an ice bath to 8° c. To this was added, dropwise, 400 ml. of an aqueous solution containing 250 g. (3.6 moles) of NaNo2, the temperature being maintained at Oto 10° C, with a salt- ice bath. While the diazotization of the amine was proceeding, sulfur dioxide gas (war surplus, grade unknown) was bubbled, with stirring, through 3,4 1. of glacial acetic acid. When the acid was saturated with sulfur dioxide, 132 g. (0.77 mole) of cuc1 2 .2n2o (Baker's G. P. grade) in 200 ml. of water was added to it and bubbling of the sulfur dioxide through the solution was continued. The diazotized amine solution was slowly added to the acetic acid solution and after addition was completed the gas flow was stopped and a yellow precipitate of the sulfonyl chloride·was obtained by the addition of a three~fold excess of ice water. The precipitate was filtered, washed with ice water, and then hydrolyzed by boiling with 264 g. (6.6 moles).of NaOB in four l. of water. The resulting solution was boiled down and the sodium salt of the sulfonic acid was recovered in several crops. 21

The salts were obtained as plate-like crystals which were dissolved

in hot water, boiled with Norit, filtered and reprecipitated. The

average yield for the preparation of the para isomer salt at this

point in the synthesis was about 80%.

The ortho and~ isomers were prepared in a similar manner.

The sulfonyl chlorides of these isomers are liquids at room temper-

ature and were isolated from the aqueous mixtures as water-insoluble

oils. The aqueous solutions (about three 1.) were e:ir.tracted with four 800-ml. portions of ether and the ether solutions were combined with the sulfonyl chlorides. The ether was then boiled away and the

sulfonyl chlorides were hydrolyzed in boiling Na.OHsolutions. The

salt crystals were then collected and recrystallized once after treatment with Norit in a manner similar to that for the para isomer. The yields of the salts of the ortho and~ sulfonic acids averaged about 55%.

The various batches of each isomer salt we~e combined and

recrystallized carefully three times to achieve. purification. The

overall yields (calculated from the starting amine) were para, 77%;

ortb.o~ 34%; and~» 31%. The melting points of the S~benzylisothiour-

onum derivatives of the isomer salts were or.tho, 160.5-161.5° C.; ~, 137.5=138.5° C.; and 2ara, 175.0-75.5° c. (literature values for the 0 11 ·12 respective salts are 160.8 C., 138.9° c., and 174.4 o c. 11 ).

11. Y. Muramota» M. Morina~ and N. Hirao~ Science and Industry, (Japan), 28, 347 (1954) /c. A:..,j 49, 14582 e, g (195517.

12. J. A. Gurney) Doctoral Dissertation, Brigham Young University (1963). 22

Purification of Benzene and Chlorobenzene The benzene and chlorobenzene used in these experiments were purified by distilling reagent grade material through a 30-plate (4 ft. packed with glass helices) vacuum-jacketed column with a total- condensing, partial-take-off head. A reflux to take-off ratio of between 23~1 and 50:l was used. Only the middle third of each distilla-_ tion.was kept. The purified benzene was stored over sodium while the chlorobenzene was stored over calcium hydride,

Preparation of Radioactive Sulfur Trioxide

The S-35 used in isomer distribution expe~iments was obtained in the form of sulfuric acid (New England Nuclear Corp., lot V-14=Cj

10 me., 7.8 mc./ml., 99-% pure). This was washed with distilled water into a 50 ml. beaker containing 2.0 g. BaS04 (»aker and Adamson reagent 1 lot M 170) and 0.25 g. BaCl2 (Brothers Chemical Co. reagent). The beaker was then set on a hot plate to digest for several days. The resulting radioactive Baso4 was filtered, washed~ and dried overnight at 125° C. About Oo33 g, of the dried Baso4 (lo7 mco) was placed in a small isotope exchange. reactor consisting of two connected chambers (50 ml. and 10 ml. capacity) to which a thin-walled glass capsule was sealedo About 4=5 ml. of so3 (Sulfan B, Baker and Adamson, stabilized} was added to the flask and frozen by immersing the reactor in an ice-water bath. A Teflon~coated stirring bar was inserted, the reactor was evacuated to about 0.1 to 1.0 Tor.r.~ and the system was sealed off, The rea.ctor was then kept warm on a hot plate for several days with occasional stirring to exchange radioactivity between the 23

Baso and so . After about three days, so was transferred to the 4 3 3 thin-walled glass capsule and. the capsule was sealed off from the reactor and set aside for future use. Capsules containing nonradioactive so 3 for competitive rate experiments were prepared in a similar manner except that no BaS04 or stirring bar were placed in the reactor.

The amount of so 3 used in each expe•riment was determined by weighing the capsule an.cl contents before the reaction and the capsule fragments after the reaction. In addition, the arylsulfonic acids produced in most of the competitive experiments were titrated with standardized NaOHwhich gave a cross check on the amount of so 3 recovered as product.

Preparation of Radioactive Benzene A small vacuum line was constructed to prepare the c14 labeled benzene used in the competitive rate reactions. Radioactive benzene

(New England Nuclear Corp., 0.10 me. in 6.4 mg., lot no. 161-295-17) was received in a glass vial equipped with a break seal which was sealed onto the line and a 50 ml. Erlenmeyer flask with a 12/30 joint containing 12:967 g. of benzene was attached to the other end of the line. The benzene was frozen by innnersing the flask in liquid nitrogen and the system was evacuated to 0.1 Torr. The system was sealed under vacuum and the break seal was broken.

Tbe benzene was distilled back and forth between the vial and

Erlenmeyer. flask five times by alternately warming one chamber and freezing the other with liqu:i.d nitrogen. The benzene was transferred into the Erlenmeyer fL:isk, the flask was removed from the line~ a small 24

piece of sodium was put into the benzene to dry it, and the flask was

stoppered and stored for use. Portions of this material were diluted

with different amounts of benzene and chlorobenzene for the various

competitive rate experiments (Re gas flow of 60 cc./min. over carbowax

on firebrick, 135° C.), no evidence of any contaminants were observed

even when the instrument was operated at maximum sensitivity. These reagents were considered pure enough for the reactions contemplated.

Sulfonation Procedure

The sulfonation reactions were conducted in the same apparatus

for both the isomer distribution experiments and the competitive 35 rate experiments. In the former case, labeled was used while s so3 in the latter case nonradioactive so and c14 l~bele.d benzene were . 3 employed. The apparatus consisted essenti.ally of a two-liter, three-

necked main reaction chamber surmounted by a cold~finger condenser

and a capsule-breaking chamber. A three-junction copper-constantan

thermocouple was inserted through one neck of the main reaction chamber while a siphon tube connected to·a smaller condensing chamber and

cold-finger assembly was inserted through another neck. A thin-walled

glass capsule containing so3 was placed in the bowl of the capsule- breaking chamber and a glass-encased magnet was inserted into a side

arm in the upper part of the chamber. The magnet could be manipulated with a magnet external to the system and could be dropped on the

capsule to crush it. A fine mesh platinum screen was placed on the

bottom of the capsule=breakir..g chamber to prevent small fragments of

the broken capsule from falling into the main chamber. Small Teflon- :zs coated magnets were placed in the main chamber and condensing chamber to permit stlrring bf the solutions. Gases passing through the system

,, entered and exitted through drying tubes (P2o5 supported on glass beads). The apparatus was carefully dried in a drying oven for at least 12 hours. It was then assembled while warm and dry nitrogen was flushed through the set-up lot 15 minutes prior to use. One experi-

·.. I ment was made in which small amounts of water were added to the system. The results varied widely from those obtained under dry conditions indicating that the drying procedure was necessary. After drying was C81Dpleted, the main chamber was surrounded with a 1:1 mixture cooled to -20° to -40° c. and the cold fingers were filled with a methanol-dry-ice mixture. Sulfur d:tmcide gas (Matheson, anhydrous grade) was introduced into the system and condensed into the main reaction chamber. After about 300 ml. of liquid sulfur dimcide had been condensed~ the gas flow,was stopped, the coolant was removed from the cc;,ld fingers; and the capsule-breaking chamber, the cold fingers, and the upper portions of the reaction chamber were heated with a hot-air gun until warm to the touch. The capsule was then crushed and the upper portions of the system were again heated to distiil the so, into the stirred liquid sulfur dioxide.

After the s031had all dissolved, the coolant was replaced in the cold fingers and sulfur dimcide was condensed.to make the final volume from 800 to 900 ml·. Sulfur dioxide was then condensed into the smaller condensing chamber. When 100-200 ml. of liquid sulfur dioxide had accumulated in this chamber, the gas flaw was stopped, 26 dry nitrogen was introduced to blanket the system, and the aromatic compounds were added to the small chamber,

The cooling baths were removed and both solutions were allowed to warm to reflux temperatures. With the contents of both chambers being stirred as rapidly as possible, the arene solution was transferred to the main reaction chamber via the siphon tube by applying nitrogen pressure to the smaller chamber. The time needed for combining the two solutions was usually 8 to 12 seconds. The resulting solution was stirred for about 10 minutes and then a stopper was removed and the sulfur dioxide was allowed to boil away.

The temperatures of the sulfonation reactions were measured by means of the thermocouple and a Leeds and Northrup model 8690 mill- volt potentiometer. The reflux temperature was not exactly the same in all cases since varying amounts of were dissolved ·in the solvent so3 in different experiments. The measured temperature range for the sulfonation experiments was -12° to -13° C. The reaction products were in the form of a light yellow liquid containing some solid material. This material was dissolved in diethyl ether and washed into a 250-ml. Erlenmeyer flask, the final volume being about 200 ml. This was set on a steam plate and the bulk of the ether was boiled off. This was done to remove any traces of sulfur dioxide. Ether was then added to make the solution back up to 200 ml. and this solution was extracted four times with 50-ml. portions of distilled water. The aqueous extract was extracted in tum with two

50-ml. portions of ether. The remaini:ng aqueous solution, containing the sulfonic acid product~ was then titrated with a standardized solution 27

of 1.0 M. NaOHto pH 7.0. A Leeds and Northrup model 7401 pH meter

was used to follow the titration. The resulting salt solution was

either made up to a known volume in a volumetric flask for isomerdistribution experiments or the salts were obtained by carefully evapor-

ating the solution to dryness for the competitive experiments. A

total weight of arenes of between 45 and 50 g. were used in each competi-

tive sulfonation experiment while a weight of between 12 and 24 g. of

chlorobenzene was employed in the isomer-distribution experiments.

Analysis of Reaction Products of Isomer-Distribution Experiments

The isomers were purified by recrystallization as the ,2.-

toluidine salts. Aliquot portions of the solution containing the reac-

tion products of an isomer-distribution experiment were pipetted into

three beakers - each containing about 50 g. of the pure, dry, non-

radioactive sodium salt of one of the isomeric chlorobenzenesulfonates.

To each beaker 33.5 g. of .e-toluidine hydrochloride was added together

with enough hot distilled water to dissolve the salts. The solution

was allowed to cool and the .e-toluidine salts crystallized. The salts

were filtered, washed once with cold methanol, and a 0.2 to 0.5 g.

sample was taken for future counting. The crystals were then redissolved

in a minimum of hot water and the process was repeated. Between 15

and 25 recrystallizations could usually be made until too little material \ remained to continue.

The ortho salts recrystallized as large~ well=formed needles

while the~ and para salts came out as fine flat plates. The~

salts were the most difficult to recrystallize and seeding and refriger~ 28 ation were occasionally required to prod~e crystals of a satisfactory quality.

Certain selected samples which had been set aside for counting were dried overnight at 110° c. under vacuum. A SO-mg. portion of each sample was dissolved in 0.5 ml. of water and 1.0 ml. of absolute methanol and counted in 15 ml. of Kinard 1 s solution in a Nuclear Chicago

Unilux ambient temperature liquid scintillation counter. The Kinard solution was composed of five parts ,e-xylene, five parts peroxide- free _e-dioxane, and t~ree parts absolute ethanol (U.S.P.) in which were dissolved 80 g./1. reagent grade napthalene, 5 g./1. 2,5-diphenyloxazole (Packard PPO, scintillation grade, lot No. 255421) and 50 mg./1. d..-napthylphenyloxazole {Packard d.NPO, scintillation grade). The

_e-dioxane was purified by distillation through the 30-plate distillation column and filtration through activated alumina (Alcoa) for the removal of peroxides. The ,e-xylene was also purified.by boiling overnight over sodium metal and distillation through the 30-plate colunm. The

Kinard solution was used as fresh as possible since peroxide formation causes deterioration. It was stored in a brown bottle under refrigeration until used. Examination of the data obtained by the above procedure showed that each isomer was brought to a constant count rate and hence each isomer had been effectively purified by removal of the other isomers. From the final count rate and initial aliquot size, it was possible to calculate the ratio of isomers in the original reaction product.

Analysis .2£_ Products of Competitive Reactions The procedure chosen for analyzing the competitive experiments 29

14 utilized c -labeled benzene. The sodium salts resulting from the titration of the product sulfonic acids were very carefully evaporated

to dryness and then weighed. A one g. sample of the salt was then vacuum dried at 110° c. overnight and a 50-mg. portion was counted in Kinard solution in the same manner as the isomer distribution samples. By knowing what count rate would be expected for 50 mg. of pure c14-labeled sodium benzenesulfonate, it was possible to determine what fraction of the sample was the benzene-sulfonation product. From this fraction the apparent relative rate for the

reaction was obtained. The count rate for pure sodium benzenesulfonate 14 was determined by sulfonating a sample of the main c benzene supply and counting the sulfonation product in the usual .way. Portions of the standard benzene were diluted to different degrees for various experiments and so a dilution factor had to be used to calculate the expected count rate for a particular reaction. THE SULFONATIONOF TOLUENE 1 WITH SULFURTRIOXIDE

1. Based on the Ph.D. Dissertations of E. A. Brown (1967) and D. G. Guillot (1966), Brigham Young University.

by K. L. Nelson, E. A. Brown and D. G. Guillot

The sulfonation of toluene and toluene- benzene mixtures with sulfur trioxide in liquid sulfur dioxide at -12.5° c. was studied to obtain partial rate factors. The reaction is believed to be complicated by the presence of suifonating reagents other than sulfur trioxide. The variation of i<.r/kB with changing initial aromatic ratios, changes of product ratios with electrophile concentration and with initial aromatic ratios are all explained in terms of these secondary reactions. The isomer distribution for the sulfonation is~= 10.02 ! 0.2%, m = 0.73 ± 0.2%, and~= 89.74%" The relative rate (kt/kB) corrected for the effects of secondary reactions is 27.0 i 1.0. Calculated partial rate factors are Pf= 144.6 9 mf = 0.59, Of= 81.2.

1 2

The sulfonation of toluene in concentrated sulfuric acid and 1-5 oleum has been studied by a number of workers and partial rate

l. H. Cerfontain, F. L. J. Sixma and L. Vollbracht, ~ Trav.- Chim., 83, 227 (1964).

2. H. Cerfontain, F. L. J. Sixma and L. Vollbracht, ibid., 82, 662 (1963). 3. S. W. Englund, R. S, Aries and D. F. Othner, Ind. !!!a.:. Chem., 45, 189 (1953) .

4. A. F. Holleman and P. Caland, ~' 44, 2504 (1911).

5. L. Vollbracht, H. Cerfontain and F. L. J. Sixma, ~ Trav.- Chim., 80, 11 (1961). factors have been calculated for sulfonations' utilizing a variety 2 of sulfuric acid concentrations: These data indicate that the sulfonation of toluene in these protic systems fits the selectivity relation- ship6'7 established for electrophilic substitution reactions on toluene. 8, 9

6. H. Cerfontain, A. W. Kaandorp and L. Vollbracht, ibid., 82, 923 (1963).

7. H. Cerfontain, F. L. Sixma, L. Vollbrachts ibid., 82, 659 (1963).

8. L, Stock and H. c. Brown, .::I.:.Am. Chem. Soc., 81, 3323-29 (1959). 9. H. C. Brown and K. L. Nelson, ibid., ll, 6292 (1953).

The data for the sulfonation of toluene with so3 in aprotic solvent systems is less extensive.lO,ll

10. H. Cerf:ontain, A. Telder, and L. Vollbracht, ~ Trav, Chim., 83, 1103 (1964).

11. A. A. Spryskov and B. G. Gnedin~ Zh, Obshch. Khim., 33(4), 1082 (1963). 3

A considerable deviation from the selectivity relationship was found by Cerfontain 10 for the sulfonation of benzene and toluene with so3 (the aromatics constituting the solvent). No variation in k.r/kB was found orr varying the relative amounts of benzene and toluene but the isomer distribution was shown to vary with both initial benzene/ toluene ratios in competitive experiments and with the extent of toluene conversion in the sulfonation of neat toluene. The ortho/para ratio was shown to decrease as the benzene/toluene and toluene conversion values increased. Although he recognized the possible presence of pyrosulfonic acids in the system, Cerfontain disregarded them as sulfonating species and considered them only as transient species which store and then release so3 . Cerfontain believed that the deviations from the selectivity relationship resulted from

T( -complex formation in the transition state or from kinetic abnormal- ities resulting from the temporary consumption of S03 to form the pyrosulfonic acids. 12 14 The sulfonation of iodobenzene - and chlorobenzene 15

12. N. H. Christensen, Acta. Chem. Scand., 15, 1507 (1961). 13. N. H. Christensen, ibid., .!l., 2253 (1963).

14. N. H. Christensen, ibid., 18, 954 (1964).

15. K. L. Nelson and E. A. Brown - previous paper. with so3 in apr.otic solvents are complicated by the presence of secondary sulfcnating reagents. These reagents, ,fr:ich also give rise to sulfonic acid products, are believed to be sulfonic acid 4

anhydrides and/or pyrosulfonic acids. The existence of secondary

sulfonating species makes the determination of relative rate constants

(k.rlk:a) for the so3 sulfonation reaction more difficult. It has been shown16 that under these circumstances the common criterion for the

16. K. L. Nelson and E. A. Brown - previous note.

applicability of Ingold's equation 17, 18 in competitive reactions (lack

of variation of the relative rate ratio with changing initial relative

17. M. J. S. Dewar, T. Mole and E.W. T. Warford, 1.:..Chem. Soc., 1956, 3576.

18. G. A. Olah, S. J. Kuhn and S. H. Flood, :L_ Am. Chem. Soc., 83, 4571 (1961).

. . . arene concentrations)' j:wiy not indicate the presence of secondary

reactions and that incorrect relative rate ratios may be calculated as a result.

It was considered desirable to investigate the possible presence of secondary reactions in the sulfonation of toluene in an

aprotic solvent and to determine, if possible, partial rate factors

for the reaction. Liquid sulfur dioxide was chosen as the solvent because of the small sulfone production expected. All reactions were

run at reflux temperature (-12.5° C.). The isomer distribution for

the reaction was determined by an isotope dilution technique, S-35

labeled so3 being used in the sulfonation. Relative rate experiments were conducted by sulfonating c 14 labeled benzene in competition with nonradioactive chlorobenzene and toluene and the count rate of 5 the products was used to determine product composition. Ultraviolet spectrophotometry was also used to investigate variations in isomer distributions as a function of sulfur trioxide concentration, and to determine some relative rate values.

RESULTS AND DISCUSSION SECTION Competitive Rate Experiments

The relative rate of substitution of toluene as compared to benzene (kT/kB) was determined with various amounts of benzene and toluene. Table 1 gives the results. The results are also given in

Figure l.

TABLEl RELATIVERATE RESULTS FOR THE SULFONATIONOF TOLUENE

benzene, initial mol. Apparent Experiment toluene ratio k.r/kB 22-P 1.01 10.61 14-Q-F 2.98 11.15 14-Q-C 4.93 8.45 14-Q-D 6.01 8.30 14-Q-B 6.87 11.5 21-P 7.32 12.33 14-Q-E 10.94 24.09 14-Q-G 11.27 27 .62

The existence of secondary reactions is indicated by the shape of the curve in Figure 1. Investigations of competitive reactions in the chlorobenzene-benzene system 15 indicate that when secondary reactions compete with so3 sulfonation, a plot of kB/kx (rate of more reactive species/rate of less reactive species) vs. ratio of initial 6

0 0 1 0 0

2 4 6 8 10 12

B,/T•J. J.

Fig. 1.=-I<.r/kB as a Function of Bi/Ti for the Sulfonation of Benzene-Toluene Mixtures with so3 in Liquid so2. T = -12.5° C. 7 arene concentration, produces a curve similar to that in Figure 1.

The kB/kx values are high when the concentration of the more reactive species is small relative to the less reactive species but decrease rapidly as the relative concentration of the more reactive species increases. A horizontal portion of the curve also occurs when the concentration is small relative to the concentration of the more reactive species. The scatter, in the points in Figure l are also reminiscent of the chlorobenzene-benzene data and reflect the extreme sensitivity of syste~s containing secondary sulfonati~..g species to small changes in stirring rates.

Plots of product ratios as a function of electrophile concentration also indicate the presence of secondary reactions. The data presented in Figure 2 and Table 2 were obtained by varying the S03

TABLE 2

COMPETITIVESULFONATIONS IN TRE TOLUENE-BENZENESYSTEM

S03 Experiment Ti/Bi BS TS Concentration TS/BS No. (M. /1.-)

88-P 0.858 0.001070 0.00512 0;006192 4. 787 89-P 0.858 0.01312 0.04221 0.08258 3 .217 91-P 0.858 0.002957 0.01722 0.02925 5 .823 93-P 0.858 0.000172. 0.00311 0.004148 18.050 95-P 0.858 0.002373 0.01592 0.02613 6.707 96-P 0.279 0.003697 0.01531 o. 02639 4.140 97-P 0.279 0.002582 0.00976 0.01755 3.780 98-P 0.279 0.001174 0.00669 0.01124 · 5. 700 99-P 0.279 0.000277 0.00279 0.00439 10.079

concentration of the solution at two constant arene concentration ratios. The data show (Figure 2) that the ratio of the products 20 t- . 0 Ti/Bi : 0,858 EJ T /B = 0.279 18 '- r.1 1 1

16 ,- ' ./ 14

12 TS/BS I \ '\. (,J 10

4 I.I {!•- 2 I -

0.07 0.08 0.01 0.02 q,03 0.04 o.os 0.06 (S0 ) 3

Fig. 2,--Variation of TS/BS as a Function of so3 Concentration 9

of the more reactive species to the products of the less reactive

species (TS/BS) decreases with increasing so3 concentration. This is the shape of curve that would be expect~d if secondary reactions were occurring and the ratio of the products of the primary reaction

(TSl/BSl) were greater than the ratio of the products of the secondary

reactions (TS2/BS2). Since the total product recovered from the reaction (TS/BS) is

TS = ~l + TS2 BS BSl + BS2 (1) and

TSl)TS2 BSl BS2 (2) then

Further confirmation for the existence of.secondary sulfonation reactions is given in Figure 3. In this figure, the moles of product (TS and BS) obtained from sulfonation at constant T1/B1 values are plotted as a function of so3 concentration. Straight lines are'plotted through the origin and the smallest product values.

The TS and BS, values at higher so3 concentrations are seen to curve away from the straight line indicating that somewhat more BS and less 10

l!I Ti/Bi = 0.279 0.044 TS

0.040

0.036

0.032 Moles of Product 0.028

0.024

0.020

0.016

0.012

0.008

0.004

0.01 0.02 0.03 0.04 0,05 0.06 0.07 0.08 0.09

(S03)

Fig. 3.--BS and TS as Functions of so3 Concentration

( 11

TS is being formed than would be expected if the trends at lower so3 concentrations were continued.

Figure 3 provides a means of determining k.rlkB.for the primary , reactions. The secondary reactions become progressively less important as so concentration decreases. In the limit there would be no 3 secondary reactions at an S03 concentration of zero. Therefore, straight lines obtained by extrapolating the data to zero in Figure

3 represent the values anticipated for a system with no secondary reactions. Careful extrapolations of the data to very low so3 concentrations gave straight lines from which the results in Table 3 were obtained. Values used for Bi/Ti were 0.1667 and 0.1396 for the

Ti/Bi= 0.858 line and 0.2386 and 0.0666 for the Ti/Bi= 0.279 line. From these results a k.rlki3 value of 27.0 ± 1.0 is obtained.

TABLE3 RELATIVERATES CALCULATED FROM EXTRAPOLATIONS IN THEBENZENE-TOLUENE SYSTEM

BS TS • Ti/Bi (From (From k>r/kB Extrapolation) Extrapolation)

0.858 0.00052 0.01142 27.52 0.00069 o. 01516 28.52 0.00086 0.01889 28.06 0.00060 0.01329 27.89 Av. 27.9110.14

0.279 0.00156 0.01052 25.32 0.00200 0.01354 26.32 0.00112 o. 00750 26.05 0.00134 0.00902 26.49 Av. · 26 .16i0 .35 12

A series of calculations were made to determine what TS/BS ratio and what quantities of TS and BS would have been obtained if there had been no secondary reactions. Data points were taken from the curves in Figure 2, and usirig Ingold's equation and the kf/kB value of 27.0 i 1.0, the values of BS and CS needed to produce the known number of moles of product from the known amounts of starting materials were calculated. Table 4 presents the results of these calculations; BSC, TSC, and RC represent the values calculated for the1absence of secondary reaction effects. The 6 BS, ~ TS and .6 R represent the differences between actual and calculated amounts. At the Ti/Bi ratios chosen, the less reactive spe~ies (benzene) is ·yielding less product than toluene. Secondary reactions should, therefore, cont~ibu_te relatively more to the production of BS than of TS. The expected pattern of increasing LlBS and decreasing bTS with increasing so is found. ,. 3 The data for T./B. = 0.858 cover a wide range of so concentrations. l. l. 3 It is seen that at the largest concentration of S03, the actual amount of BS produced is more than 4.5 times the amount predicted. Since the calculations which lead to the predicted BS value assume all of the so3 is consumed in the primary reaction, the predicted value is certainly high; and a much larger difference must actually exist between the amounts of BS formed in the primary and secondary reactions. An estimate of the amounts of primary and secondary products can be made if assumptions are made about the ratios of products from the primary and secondary reactions. The ratio TS/BS for reaction by so3 in the absence of secondary reactions can be calculated. This TABLE4

COMPARISONOF ACTUALVS. PREDICTEDPRODUCTS FROM_Ti/Bi =.0,858 and Ti/Bi: 0.279 .-

BSC BS TSC TS RC RX ABS ilTS S03 - . 3 3 Ti/Bi (xlQ3) (~10 ) (x193) (:itlo3) TSC I§. (xl0 ) (xl.03) AR Cone: ;""'i ,-, BSC BS ;'"j ,'. :.:. •,! r, n (M./1.) - " r: (' ' 0,279 0.854 0.975 6.146 6.025 7.20 .6.18 0.121 - 0.121 - 1.02 0:0100 l.079 1.357 7 .671 7,393 'i. ll 5.45 0.278 - 0.278 -· 1.66 0:0125 1.309 1.765 9.191 8,735 7.02 4.95 0.456 - 0.456 - 2.07 0~0150 1.544 2.248 10. 706 10,002 6.94 4.45 o. 704 - o.704 - 2.49 0:0175 1.784 2.692 12.216 11.308 6.85 4.20 0.908 - o.908 - 2.65 0:0200 2.030 3.088 13. 720 12.662 6. 76 4.10 1.058 - 1.058 - 2:66 0:0225 2.282 3.500 15.218 14,000 6.67 4.00 1.218 - 1. 218 - 2. 67 0:0250 2.539 3.850 16. 711 15 .400 6.58 4.00 1.311 - 1.311 - 2.58 0:0275 (.,)..... 0.858 0.073 0.084 1.677 1.666 23.05 19.75 0.012 - 0.012 - 3.30 0;0025 0.146 0.188 3,354 3.312 22.92 17 .60 0.042 - o.042 - 5.32 o:ooso 0.221 0.317 5.029 4.933 22.79 15.55 0,097 - 0.097 - 7 .24 0:0075 0.296 0.473 6.704 6.527 22.66 13.80 0,177 - 0 .177 .. 8.86 0:0100 o.449 0.882 10.051 9,618 22.40 10.90 0.434 - 0.434 -11.50 0.0150 0.605 1.451 13 .395 12.549 22.14 8.65 0.846 - 0.846 -13 ;49 0:0200 0. 765 2.188 16.735 15 .313 21.87 7.00 1.422 - 1.422 -14 ~87 0;0250 0.929 3,044 20.071 17.967 21.61 5.90 2.115 - 2.115 -15 .71 0:0300 1.097 3.952 23 .403 20.548 21.34 5.20 2.855 - 2.855 -16 .14 0.0350 1.269 4.956 26. 731 23 .044 21.07 4.65 3.687 - 3.687 -16 .42 0.0040 -1.445 6.058 30.055 25.442 20.80 4.20 4.613 - 4.613 -16.60 0.0045 1,626 7.292 33.374 27.710 20.52 3.80 5.666 - 5.666 -16. 72 0.0050 1.812 8.556 36 .688 29.944 20.24 3.50 6.743 - 6.743 -16.74 0:0055 2.240 10.500 43.960 · 35. 700 19.62 3.40 8.260 - 8.260 -16 .22 0~0060 2.403 11.667 46.597 37.332 19.39 3.20 9.264 - 9.264 -16 .19 0:0070 2.827 13.333 53 .173 42.667 18.81 3.20 10.506 -10.506 ··15;61 0.0080 3 .280 15. 000 59. 720 48.000 18.21 3.20 11.720 -11. 720 -15 .01 0.0090 14 ratio varies slightly with the concentration of so3 involved in the primary reaction but was assumed to be constant for this estimation. The curves in Fig~re 3 show that TS/BS becomes essentially constant at larger S03 concentrations. This could occur only if secondary reactions were predominant at these so3 concentrations. It was assumed that the TS/BS ratio in the horizontal portions of the curves represented the ratio of products from the secondary reaction. The relatively small values of these TS/BS ratios implies that the secondary sulfonating reagents are more reactive than so3. A series of calculations were performed using these assumptions and the results are tabulated in Table 5. The results in Table 5 show that there is a gradual decrease in the importance of the primary reaction as so3 concentration increases. The relative unimportance of secondary reactions at low S03 concentrations justifies the extrapolation procedures used in determining

Christensen 14 proposed a mechanism for the sulfonation of iodobenzene with so3 in aprotic solvents. This mechanism which includes the contributions of secondary sulfonating agents has been extended to the sulfonation ·.of chlorobenzene-toluene mixtures •15 Because of the great similarities between the reaction in the chlorobenzene-benzene and benzene-toluene systems, it is proposed that the same mechanism be applied to the latter system. Let B, BS', BSS, and BS-0-BS represent benzene, benzenesulfonic acid, benzenepyrosulfonic acid, and benzenesulfonic acid anhydride respectively and T, TS, TSS, etc., represent the corresponding toluene compounds. The possible reactions that 15

TABLE5

RELATIVE CONTRIBUTIONSOF PRIMARYAND SECONDARY REACTIONSIN THE TOLUENE-BENZENESYSTEM

S03 Fraction of Total Concentration S03 Consumed in (M. /1.) Primary Reactions

0.279 o.·0100 0. 7786 0.0125 0.5863 0.0150 0.4238 0.0175 0.2232 0.0200 0.1060 0.0225 0.0551 0.0250 0.0000 0.0275 0.0000 0.858 0.0025 0.9664 0.0050 0. 9391 0.0075 0.9062 0.0100 0.8708 0.0150 0.7886 0.0200 0.6900 0.0250 0.5818 0.0300 0.4806 0.0350 0.3973 0.0400 0.3170 0.0450 0.2382 0.0500 0.1553 0.0550 0. 0831 0.0650 o. 0571 0.0700 0.0000 0.0800 0.0000

may be occurring in solution are:

BS B + S03 . ) (4) T t S03 .) TS (5)

BS BSS + so3 (6)

TS+ S0 3 TSS (7)

BSS t B ) 2BS (8)

BSS + T ➔ BS+ TS (9) 16

TSS + B BS + TS (10)

TSS + T ) 2TS (11)

2BSS. BS-0-BS + H2S04 t S03 (12) 2TSS TS-0-TS -t H2S04 + S03 (13)

TSS + BSS BS-0-TS t H2S04 t S03 (14)

BS-0-BS + B + BzS04 ➔ 3BS (15) BS-0-BS + T + H2S04 ) 2BS + TS (16) TS-0-TS + B t H2S04 ) 2TS t BS (17) TS-0-TS t T + H2S04 ) 3TS (18) BS-0-TS + T + H2S04 ) 2TS + BS (19)

BS-0-TS ~ B + H2S04 ? 2BS + TS (20) The concentrations of the various sulfonating agents (expressed

.in terms of BS and TS concentrations) are:

(BSS) = K6 (BS)(S03) (21)

(TSS) = K7 (TS) (S03) (22)

2 2 K K (BS) (so ) (BS-0-BS) = 12 6 3 (23) H2S04

2 2 K13K7 (TS) (S03) (TS-0-TS) :: (24) H2S04

: K K ~ (BS) (TS) (S0 ) (BS-O..;TS) 14 6 3 (25) H2S04 There are, therefore, six possible sulfonating reactions which could

lead to the formation of each product and

TS = TS5 -+ TS9 + TS11 -+ TS16 4 TS18 + TS19 (26) BS: BS4 t BSa + BS10 + BS15 + BS17 + BS20 (27) where TS5, TS9, TS11, etc.j represent the pnoducts formed in Reactions ' 17

5, 9, 11, etc. Of these reactions, only two (4 and 5) are primary reactions involving sulfonation by so3 directly.

Isomer Distribution Results Secondary reactions within a system would be expected to have an effect on the isomer distribution. Variations in the different steric requirements and reactivities of the different electrophiles could affect both ortho/para and para/meta ratios. Not enough is known about the reactivities of the possible secondary sulfonating reagents to permit any predictions. Under suitable conditions, however, it might be possible to detect secondary reactions as a consequence of their steric effects.

In this regard a comment should be made about Cerfontain's study of the sulfonation of toluene and toluene-benzene mixtures. 10

Table 6 presents his data which show that the ortho/para isomer

TABLE6 VARIATIONSIN ISOMERDISTRIBUTION WITH PERCENT TOLUENECONVERSION IN CERFONTAIN1S SULFONATION OF NEATTOLUENE WITH so3 AT 25° C.

% ' Sulfonic Acid Isomer Toluene Distribution Conversion ':, .2 !!! £ i 0.03 ! 18.0 4.6 77 .4 0.09 13. l 5.7 81.2 0.26 13 .2 5.1 81. 7 0.31 i 16.0 4.1 79.9 1.14 16.2 4.9 78.9 100.0 ~,· 11.7 2.8 85.5 18

ratio decreases as percent toluene conversion increases when neat

toluene is sulfonated. His data also show (Table 7) that the ortho/

para ratio decreases as the Bi/Ti ratio increases. Although Cerfon- tain discounts secondary sulfonation reactions in his system, the

data seem to confirm their presence. It should be emphasized that

Cerfontain considered only pyrosulfonic acid side-reactions and not reactions of the acid anhydrides which Christensen believes to be more powerful reactants.

TABLE7 ISOMERDISTRIBUTIONS AND RELATIVE RATES FOR CERFONTAIN'S COMPETITIVESULFONATION OF BENZENE-TOLUENEMllTURES AT 25° C.

Isomer Distribution for Toluene Bi/Ti k.r/kB Sulfonic Acids .2 m .e ' L 1.2 9.1 18.7 2.8 ! 78.5 ·2.0 13. 9 16.7 2.7 80.6 10.0 9.3 17. 0 2.7 80.3 6.9 12.l ' 85.3 29.9 2.1 ! 59.8 11.8 10.5 1.7 ,, 87.8 i

Equations 23-25 indicate that the concentrations of ..anhydrides

in the toluene system would be proportional to the concentration of so3 and to the squares of the concentrations of the benzene- and toluene sulfonic acids. From Equations 15-20 it can be seen that·

the HzS04 terms will drop out in the kinetic equation for the formation

of product. Cerfontain bubbled so3 through the aromatics and so maintained a constant concentration of S03, The concentrations of anhydrides .l increased as product.was formed which is in keeping with Christensen's

,_ 19 observation that more anhydride products are isolated at larger 14 /ArH ratios. Since all of the postulated secondary sulfonating so3 species are bulkier than , and since steric effects predominate so3 in determi~ing ortho/para ratios, it would be expected that the ortho/ para ratio should decrease as the reaction progressed.

The variation in ortho/para ratio with increasing Bi/Ti is also understandable when secondary reactions are considered. According to previous considerations, the sec_ondary reactions contribute an increasing percentage of product as the amount of product made from· the primary reaction decreases. We would predict, then, that as the

B1/Ti ratio increases and the amount of the TS produced by the primary reaction decreases, more of the product TS will be made by the second~ ary reactions and the ortho/para ratio will decrease. Table 8 gives the experimental conditions and the ortho/para ratios for the sulfonation of toluene in this work. The difference between the largest ortho/pa.ra ratio and the smallest is outside the

TABLE8

ORTHO/PARARATIOS FOR THE SULFONATIONOF TOLUENE

S03 Ml. of Experiment Concentration ·Aromatic so3/ArH 2.h~. No. (M./L) per Ml~ of Solution

13-Q-D 0.0492 10 0.0049 0.100 13-Q-E 0.0467 8.7 0.0054 -0.112 13-Q-B 0.0194 2.6 0.0075 0.115 13-Q-C 0.0254 4.2 0.0061 0.132

' 20 error limits for the data. The smallest ortho/para ratio is found for the largest so3 concentration which is what is expected and the ortho/para ratios at lower so3 concentrations are larger than those at the higher so3 concentrations. The data for 13-Q-B is out of order, since, on the basis of so3 concentration alone, this experiment should have the largest ortho/para ratio. The concentrations of anhydrides in the system would be dependent not only on the concentration, but so3 also on the so3/ArH ratio~ Whether the increased S03/ArH for 13-Q-B is sufficient to increase the anhydride concentration enough to cause the lower ortho/para ratio is not known. Of course any conclusions about the existence of secondary reactions drawn from these data must be highly speculative, because of the small differences in the ratios obtained. Nevertheless, the apparent trend is in the right direction and is not out of harmony with the other results of this study.

Isomer Distributions ,1!! the Competitive Sulfonation of Toluene and Benzene A much better indication that isomer distributions are influenced by secondary, reactions was obtained from UVstudies of the products of the benzene-toluene competitive experiments. Cerfo~tain 19- 22 and co-workers have developed methods for analyzing the UV spectrum

19. J.M. Arends, H. Cerfontain, I. s. Herschberg, A. J. Prinser, A. c. M. Wanders, Anal. Chem., 36, 1802 (1964). 20. R. Cerfontainj H. G. J. Duin, and L. Vollbracht, Anal. Chem., 35, 1005 (1963). 21. J. s. Herschberg and F. L. Sixma, l.:, Koninkl. Ned. Akad. 21

Wetenschap. Proc., Ser. !.:_ .22,, 244, 256 (1962) ff· A:., 21..,9285 b (19628. 22. J.C. Sternberg, H. s. Stello, and R.H. S. Schendeman, Anal. Chem. , 32, 84 (1960).

of a mixture of sulfonic acids by comparing it with the UV spectra

of the component acids. By suitable computer techniques the UV curve

of the mixture is matched against the UV curves of the components

and the composition of the mixture is determined. The method requires

great care in obtaining the absorbance values of the sulfonic acids,

particularly wh~n the UV curves of several components are quite similar. Cerfontain uses a modified spectrophotometer which allows immediate comparison of the absorbance of the mixture at each wavelength with

the absorbance of the pure component at that wavelength.

A Carey 15 recording spectrophotometer was -used to obtain the

UV spectra of the products of Experiments 89-P through 99-P. The

results obtained by this method are not believed to be as accurate as Cerfontain's results since a special spectrophotometer was not used. Small errors were unavoidably introduced by reading absorbance values from the curve, from instrumental drift, and from small changes

in the base lines of the curves . , etc. As a result of these errors, two experiments (91-P and 97-P) did not give meaningful values and are not included in the table. An analysis of the data which compared the UV curve of the mixture against the curve of sodium benzenesulfonate and the curves of the three sodium toluenesulfonate isomers gave results indicating that approximately equal amounts of ortho and~ isomers had been 22 formed. This is undoubtably not the case·. The UV curves for the ortho and !!!ill isomers are very similar and with the errors mentioned above, it is most likely that the computer was unable to correctly discern between the concentrations of the two isomers.

The UVcurves of the product mixtures were analyzed using a program which considered the ortho and~ isomer.s as one component.

The results of this analysis are given in Table 9. The amounts of para isomer did not differ greatly from those of the o~iginal analysis and the UV curves obtained by mixing the component's curves matched the actual curve as well (i 1%) as in the first analysis. For these

TABLE 9

ISOMERDISTRIBUTIONS AS A FUNCTIONOF S03 CONCENTRATION IN TOLUENE-BENZENEC

S03 % % Experiment T1/B1 Concentration .2. +-!!! .E. (Q+~) I.E. No. (M./1.)

93-P 0.858 0.00415 13 .o 87 .o 0.149 95-P 0.858 0.0261 8.5 .91.5 0.093 89-P 0.837 0.0826 5.7 94.3 0.060 99-P 0.279 0.00439 15.2 84.8 0.179 98-P 0.279 0.0112 8.6 91.4 0.094 96-P 0.279 0.0264 8.8 91.2 0.096

reasons, it is believed that the results in Table 9 reflect the actual relative concentrations of the isomers as well as the limitations of this analysis.

The .results in the table clearly show an increase in the

(ortho + meta)/para ratio with increasing so3 concentration. Our 23 data show that about fourteen times as much ortho isomer is produced as !!!ill isomer and Cerfontain's data do not ~how a very large change in the percent of ~ isomer even though the ortho/para ratio does. vary with experimental conditions. The change in the (ortho + metal/para ratio, thereforej results principally from changes in the relative amounts of the ortho and para isomers. It is believed that the data in Table 9 reflect the effects of the increasing contributions of secondary reactions to the reaction products.

Partial Rate Factors

The partial rate factors calculated from the above isomer distribution and competitive rate data are Pf= 144.6, of= 81.2, and mf = 0.59. These data do not fit the selectivity relationship.

It is believed that the mf value is incorrect. The mf should be lower than Pf and Of, but it s.hould not be less than unity. No position on toluene should be less-reactive than a position on benzene. The percentage of~ isomer in the reaction products is believed to be low. A more reasonable value of 2=3%, which would be in agreement with most of the othe~ sulfonation reactions on toluene, would give good agreement of this data with,the selectivity relationshi~. It should also be remarked that if a correction for secondary rea~tions would make as much difference in Cerfontain's data as it does for the data p·resented here, Ce:rfontain' s sulfonation data would also agree well with the selectivity relationship.

Experimental Section

The preparation of materials 3 determination of isomer distribu- 24 tions, and measurement of competitive rates have been discussed 15 l previously. The UV anaiysis of isomer distributions parallels 19 22 the method of Cerfontain and his colleagues. ' A STAT03 (BYU) multiple-regression and correlation analysis program (adapted from

U.C.L.A. BIMD,No. 29) was used in conjunction with an IBM7040 computer for analysis of the data. SECONDARYREACTIONS AND PARTIAL

RATE FACTORSIN THE SULFONATION OF CHLOROBENZENEAND TOLUENE

An Abstract of a Dissertation Submitted to the

Department of Chemistry

Brigham Young University

• In Partial Fulfillment

of the Requirements for the Doctor of Philosophy Degree

Ernest A. Brown August, 1967 ABSTRACT

The sulfonation of chlorobenzene, chlorobenzene-benzene, and toluene-benzene mixtures by sulfur trioxide in liquid sulfur dioxide at -12.5° C. was studied to obtain isomer distribution and relative rate data. The isomer distribution for the reaction on chlorobenzene was determined by an isotope dillution technique. Relative 14 rate experiments were conducted by sulfonating C labeled benzene in competition with nonradioactive chlorobenzene and toluene and the count rate of the products was used to determine product composition. Ultraviolet spectrophotometry was also used to investigate variations in isomer distributions as a function of sulfur trioxide concentration.

The apparent relative rates of sulfonation (kx/kB) as calculated by Ingold 1s equation, vary wit~ both the initial ratio of arenes and the concentration of sulfur trioxide. The ortho/para ratio decreases with increasing sulfur trioxide concentration.

These observations are explained in terms of secondary sulfonation reactions which produce significant amounts of product sulfonic acids by reaction of the arenes with reagents other than sulfur trioxide. The secondary sulfonating agents are presumed to be sulfonic acid anhydrides and/or pyrosulfonic acids. The secondary reactions contribute proportionately more to the total product of that species formed in the smaller amounts by the primary reaction.

Criteria for the applicability of Ingold 1 s equation are discussed in connection with the possibility of secondary reactions. Relative rate constants for competitive chlorobenzene:benzene and toluene:benzene sulfonation with sulfur trioxide, corrected for secondary reaction effects, are 0.087f0.002 and 27.0±1,0 respectively.

The observed isomer distribution for the sulfonation of chloro benzene is 2 = 0.95 ± 0.03%, m = 0.09 ! 0.02%, and�= 98.96 ± 0.12%. Partial rate factors calculated for the sulfonation of chloro benzene and toluene are Pf= 0.517, of= 0.0025, mf = 0.00024 and

Pf= 144.6, of= 81.2, and mf = 0.59 respectively. Neither sul fonation fits the selectivity relationship predicted for it, although correction for secondary reaction effects greatly improves the fit for the toluene data. The deviation of the toluene data from the selectivity relationship probably results from a low percentage of

� isomer in the reported isomer distribution' for toluene.