A STUDY OP SO MIL PHYSICAL AMD CHEMICAL PROPERTIES

OP THE BINARY SYSTEM DINITROGEN TETR0XIDE-1,4-DI0XANE

DISSERTATION

Presented in partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By

Harry Wilson Ling, A.B. The Ohio State university

1954 i

ACKNOWLEDGEMENTS

The author wishes to express appreciation to

Dr. Harry H. Sisler for suggesting this research and for his continued personal interest and guidance throughout the course of the investigation. Appreciation is also extended to E. D. Loughran for his cooperation in the use of the Perkin-Elmer infrared spectrophotometer, and to Dr. William J. Taylor for contributing to the discussion of the structure of the dioxane-dinitrogen tetroxide complex. The assistance of the Ordnance corps,

U. S. Army, through a contract with The Ohio state

University Research Foundation, and of the Standard oil

Company (Indiana), through fellowship funds, are gratefully acknowledged. ii TABLE OP CONTENTS Page

ACKNOWLEDGEMENTS i LIST OP FIGURES iv

LIST OP TABLES v

I. INTRODUCTION 1

II. HISTORICAL a. physical Properties of Dinitrogen

Tetroxide 2

b. structure of Dinitrogen Tetroxide 3

c. Molecular Addition Compounds of Dinitrogen Tetroxide 11

III. VISCOSITY STUDY IN THE SYSTEM DINITROGEN TETROXIDE-1,4-DIOXANE a. Introduction 23 b. purification of Materials 30

c. Experimental Procedure 31 d. Results 36 e. Discussion and Conclusions 40

IV. CRYOSCOPIC STUDY OP SOLUTIONS OP DINITROGEN TETROXIDE IN 1,4-DIOXANE a. introduction 41

b. purification of Materials 44

c. Experimental Procedure 45 d. Results 51

e. Discussion and Conclusions 53 iii

Page

V. STUDY OF THE SYSTEM DINITROGEN TETROXIDE

1,4-DIOXANE IN THE GAS PHASE a. Introduction 56

b* Experimental Procedure 59

c. Results 65

d. Discussion and Conclusions 76

VI. SUMMARY AND DISCUSSION 78

BIBLIOGRAPHY 8 6 AUTOBIOGRAPHY 91

I iv

LIST OF FIGURES

Figure Page

1. Dinitrogen Tetroxide purification Apparatus 32

2. Dinitrogen Tetroxide Transfer Cell 33

3. viscosity Apparatus 35

4. Density-Composition Diagram of Binary System 38

5. Viscosity-composition Diagram of Binary

System 39

6 . Freezing point Apparatus 46

7. Typical Cooling Curve 50

8 . Cryoscopic Data; X-Composition Diagram 55 9. Colorimetric Apparatus for Gas phase Study 60 10. Dioxane Gas Infrared Absorption Cell 64

11. Infrared Absorption Spectrum of Gaseous

1,4-Dioxane 6 6

12. Infrared Absorption Spectrum of Gaseous

Dinitrogen Tetroxide • 67

13. Infrared Absorption Spectrum of the

Combined Gases 6 8 v LIST OF TABLES Table Page

I. Viscosity Study in the System Dinitrogen Tetroxide-1,4-Dioxane 57

II. Cryoscopic Constant of 1,4-Dioxane 52

III. Cryoscopic Measurements of Solutions of Dinitrogen Tetroxide in Excess 1,4-Dioxane 54

IV. Calibration of Electrophotometer 65 v. Colorimetric Study of the Gas phase System Dinitrogen Tetroxide-1,4-Dioxane 70

VI. Qualitative Observation of the Gas phase System Dinitrogen Tetroxide-1,4-Dioxane 71

VII. Infrared Absorption Study of the Gas phase System Dinitrogen Tetroxide-1,4-Dioxane 72 1

A STUDY OF SOME PHYSICAL AND CHEMICAL PROPERTIES OF THE BINARY SYSTEM DINITROGEN TETROXIDE-1,4-DIOXANE

I. INTRODUCTION

Recently Rubin, Sisler and Shechter^ established that dinitrogen tetroxide is capable of forming addition compounds with certain ethers. This was accomplished by making phase studies of the binary dinitrogen tetroxide- ether systems. The addition compounds formed In the systems investigated were shown to be complexes of N2 O4 molecules by magnetic and spectroscopic analysis. Of the several addition compounds observed it was noted that the 1:1 addition compound formed between 1,4-dioxane and dinitrogen tetroxide was quite different from the others in its higher stability and relatively high melting point.

A bicyclic monomer, a dimer, and a polymeric aggre­ gation were proposed as possible structures for the dinitrogen tetroxide-1 ,4-dioxane addition compound. In the case of the bicyclic structure the relatively high melting point of the compound may be explained by analogy with a number of other compounds which also have unusually high melting points, e.g. camphor. in the case of the polymeric aggregation the relatively high melting point of the compound may be explained as resulting from its high molecular weight.

With the hope of obtaining information which would

assist in resolving this question of structure the

authors proposed (1 ) to investigate the viscosity of

various 1,4-dioxane-dinitrogen tetroxide liquid mixtures,

and (2 ) to determine the molecular weight of the addition

compound using the cryoscopic method.

Since the existence of the addition compound between

1 ,4-dioxane and dinitrogen tetroxide has been established

in the solid and liquid states, it was proposed, as a

logical extension of these facts, to study gaseous mix­ tures of the two components to investigate the possibility

of association in the vapor phase.

II. HISTORICAL

a. Physical properties of Dinitrogen Tetroxide

The dinitrogen tetroxide-nitrogen dioxide equilibrium

N 2 0 4 2 n 0 2 has long been recognized. At temperatures well below the

melting point of dinitrogen tetroxide the equilibrium is shifted almost entirely to the left as indicated by the Q formation of colorless crystals. At -11.2°c. , the melting point of dinitrogen tetroxide, the slight yellow

color present indicates that some dissociation has taken place and nitrogen dioxide is present. At the boiling 2 point 21.15°C. t the vapor is dissociated to the extent of about 16 per cent2 and is deep reddish-brown in color. On heating above the boiling point the color of the vapor darkens, the color change being accompanied by a decrease in vapor density to 140°C. At 140°C. the density corres­ ponds to molecular nitrogen dioxide. As the vapor is heated above this temperature the density decreases and the color becomes paler owing to the dissociation 2N0g ^"'" — 2N0 + 02 until at 62o°C. the gas is colorless and dissociation into nitric oxide and oxygen is essentially complete'"’.

According to vapor density measurements the dissociation of dinitrogen tetroxide into nitrogen dioxide at various temperatures ( 1 atmosphere pressure) is as follows^.

Temp.°C. 21.9 26.7 6 0 . 2 100.1 135.0 140.0 % Dissoc. 15.7 20.1 52.8 89.3 99.1 '"**100.0

The equilibrium constant for the dinitrogen tetroxide-nitrogen dioxide equilibrium has been measured by Verhoek and Daniels^ at several temperatures. The idealized equilibrium constants (Kp) extrapolated to zero pressure are 0.1426 atmospheres at 25°C., 0.3183 atmos­ pheres at 35°C. and 0.6706 atmospheres at 45°C. b. The Structure of Dinitrogen Tetroxide

The structure of the dinitrogen tetroxide molecule has been the subject of much controversy. Several

structures have been proposed. A typical resonance form for each structure is shown below*

0=N-0-0-N“0 i tt I II III

la IV Ilia la and Ilia are the older representations of modern

structures I and III.

Structures I, III and their older counterparts have received considerable support whereas structure II was never considered very seriously because of the peroxide linkage. The initial approach to the determination of the structure of the dinitrogen tetroxide molecule was through chemical evidence obtained from various reactions of

Mellor5 has summarized the early chemical evidence which seems to favor structure Ilia. Mellor pointed out that

Exner® favored Ilia because of the reaction of nitryl chloride and silver, nitrite to produce dinitrogen tetroxide and silver chloride, and also because dinitrogen

tetroxide reacts with water to form nitrous and nitric acids

NOo I J D ----- >HONO ■+• HONOp i r ~ p~' j N O ______

Henryk reported the production of alkyl nitrates from alkyl halides, a fact which supports structure Ilia.

Further chemical support for this structure comes from the reaction® of potassium nitrate and nitrosyl sulfuric acid to form dinitrogen tetroxide and potassium hydrogen sulfate, and from the formation® of diazobenzene nitrate from aniline. Nitrosyl sulfuric acid also reacts® with sodium chloride or sodium bromide with production of nitrosyl chloride or nitrosyl bromide, respectively.

Houston and Johnson-**®, In their summary of evidence for structure Ilia, indicate the presence of a nitroso group from the reaction of N-methylaniline to give

N-methyl-N-nitroso-p nitroaniline. They point out that dinitrogen tetroxide reacts with water to produce nitrous and nitric acid which contain nitrogen of different oxidation state. Hence, it must be that these two atoms are of dissimilar oxidation state in the original molecule. Otherwise, It would have to be supposed that mutual oxidation and reduction have taken place between these two nitrogens. Regarding this possibility of mutual oxidation and reduction, structure la shows both nitrogens as having an oxidation state of five whereas in

structure II, both are assigned an oxidation state of three. In either of these cases one atom would have to

retain its original oxidation state and the other change

on reaction with water. The primary reaction of dimethyl or diethyl malonate

is explicable on the basis of structure Ilia. When

dinitrogen tetroxide is distilled into aniline, ortho-,

meta- or para- nitroaniline in anhydrous benzene,

diazonium nitrates are formed along with diazo-amido-

benzenes. The unusual behavior of dinitrogen tetroxide towards mercury diphenyl**"*- is easily explained by the nitrosyl nitrate structure. Pauling-*-^ suggested that

structure I should be less stable than structure III primarily on the basis of the adjacent charge rule.

Meyer**-® considered that structure II is consistent with the combination of amylene and dinitrogen tetroxide

to form a substance of formula C^H^o(NOg)2 • Reduction of

this compound gives ammonia and not the diamine indicating

carbon to oxygen attachments rather than carbon to nitrogen. However this work was later shown to be in erro Sudborough and Millar**-8 considered nitrogen dioxide as the oxide of nitrosyl, corresponding'to nitrosyl

chloride. They argued that since nitric oxide and

nitrosyl chloride show little or no tendency to

polymerize, the union which is established between two

N0£> molecules is probably due to the oxygen atoms. Hence

they favor the structure II.

Divers^ also favored structure II because of the

analogous reactions of dinitrogen tetroxide and potassium

peroxylaminesulphonate (SOsK^WOONfSO^Kjg with water. The information gained from a study of the dinitrogen

tetroxide molecule using physical methods is over­ whelmingly in favor of structure I. From x-ray

diffraction photographs of solid dinitrogen tetroxide-*-8

it was suggested that the crystal lattice is built up of

linear and symmetrical NO2 groups. Hendricks-*-® critized

this proposal and claimed that an unambiguous deter­ mination of structure was not possible from these particular photographs.

From electron diffraction data Maxwell, Moseley and

Deming^® concluded that the N-N distance is 1.6 to 1.7 S

for the model O2 N-NQ2 although no definite angular relationships between the two planes containing the NO2 groups could be determined.

Perhaps the first enlightening opinion in this controversy was that expressed by Sutherland 2 "L in inter­

preting data from infrared absorption and Raman spectra.

These data are overwhelmingly in favor of structure I

and make the r©conciliatory attempt of Schaarschmidt*^, who proposed an equilibrium among the structures la, II,

and Ilia, seem untenable. Evidence for a weak N-N bond is given by the low, very intense Raman frequency which was observed.

Giauque and Kemp2 found that the entropy for

dinitrogen tetroxide was consistent with the symmetrical

0 gN-N0 2 structure if the assumption of no free rotation

of the RC>2 groups was made. Longuet-Higgins^^ proposed the planar structure IV which has the same symmetry as the planar form of I and gives precisely the same number of fundamental fre­ quencies in both the Raman and infrared spectra. The very low intense Raman frequency, which Sutherland^^ had attributed to the weak R-H bond, was attributed to an angular deformation of the ring. There is no motion of

IV corresponding to internal rotation I, so that there is no need to explain why such a motion makes no contri­ bution to the entropy. The structure is also in accord with the adjacent charge rule. Further, it is difficult to reconcile the weakness of the N-N link In structure I with its torsional rigidity. Ingold and Ingold^ have correlated the experimental

results of workers In this field to state that "the long

debated question of the structures of the stable forms

of these oxides (meaning N2 O4 and NgOg) may be regarded as settled". They drew heavily upon the results of Levy and Scaife^ to show that some of the earlier results'^

of the action of dinitrogen tetroxide on organic compounds

have been invalidated. Commenting on the results of Levy

and Scaife^ in studying the addition of dinitrogen tetroxide to lower olefins, these authors indicated that

the addition is an electrophilic attack and adds NO2"*’ and

NOg~ successively. The NOg*” adds as would a proton in an

HCl addition and necessarily forms a nitro group, while

the nitrite can attach itself as a nitro or a nitrito

group. The polarization necessary to react in this way is shown as

‘*0 .*.+ 4~;P: ;n : n

Also Levy and Scaife^ have found that N2 O5 adds to simple olefins to form nitro-nitroso products in which the nitro group initiates the attack as an electrophilic

addendum. 10 Tills latter Tact and the auto oxidation of NgOg to NgO^. at -100°C., and the reduction back to NgO-j at -150°C» indicate that structure I represents the correct structure. Addison and Thompson2^ in studying the dinitrogen tetroxide solvent system have postulated that dinitrogen tetroxide is capable of dissociation into NO* NO3 ” as well as NOg"*" and NOg”. With respect to structure I the nitrosyl-nitrate dissociation requires that an N-0 bond be broken and an oxygen atom transferred across the weak N-N bond. Structure III while at variance with symmetry requirements is capable of both types of dissociation at positions 1 or 2 (page 4). The.:structure

IV appears to be similarly capable of dissociation into either NOg** ancl NOg”., or NO** and NOs” without atom transfer and, as has been indicated, has the correct symmetry requirements from a spectroscopic standpoint.

X-ray measurements on a single crystal of the solid

N2 O4 were made by Broadley and Robertson2^. In the final electron density maps, obtained by these authors, the atoms were fully resolved and their positions estimated. The coplanar molecule is reported as having the following dimensions• A molecular orbital treatment^® of dinitrogen tetroxide has been given which leads to interaction distances that agree within experimental with those given above.

n q Recently Bernstein and Burns have reviewed the entropy problem associated with the structure of dinitro­

gen tetroxide. using the fundamental frequencies proposed O T by Sutherland A and the following molecular dimensions; Z. 0N0 = 120°, /(, n-q = 1.15 “ 1.66 A., these authors calculated the entropy using statistical thermo­

dynamic methods. About 3 units of entropy had to be

attributed to internal rotation in order for the calcu­ lated value to agree with the experimental of Giauque and q PS Kemp . The model of Longuet-Higgins ^ (IV) has no torsional mode so that the lack of agreement of this model with entropy is strong evidence for excluding it as a possible structure. The reactions presented as evidence for structures II and III have not been discussed in terms of structure I. c. Molecular Addition Compounds of Dinitrogen Tetroxide

Spath3 3 prepared U02(NOgJqby adding a mixture 12

of dinitrogen pentoxide and dinitrogen tetroxide to partially dehydrated uranyl nitrate dissolved in fuming nitric acid* The compound is reported to be a yellow, crystalline material, stable in vacuum to 100°C. but

losing NOgj at 160°C. to form anhydrous uranyl nitrate.

WIeland and Wagner*^ passed a slow current of NO2 into a cooled solution of ethyl phenylpropiolate in dry

gasoline and obtained a ljl addition product of the ester

and NOg which separated in prisms. It is possible that

this product could be an addition compound containing two moles of the ester and molecular dinitrogen tetroxide.

The freezing points of mixtures of dinitrogen

tetroxide and camphor*^ showed the existence of two com­ pounds: 5 (dinitrogen tetroxide) • 4 (camphor) melting

at -52°c. and 2 (dinitrogen tetroxide) • 3 (camphor) melting at -45.5°C. By treating tin tetrachloride or titanium tetra­

chloride dissolved in carbon disulfide with dinitrogen tetroxide Reihlen and Hake^S obtained SsnCl^^NgO^ and

2TiCl4 *3Ng04 . Excess dinitrogen tetroxide gave the

compound 2 snCl4 *3 N 2 0 4 at -60°C.

Torres and constantinescu3 4 constructed temperature versus composition plots from melting point and compo­ sition data for the sulfur dioxide-nitrogen dioxide system and showed the formation of an unstable compound 13 at fifty per cent nitrogen dioxide, a possible addition product. This product could also be an addition compound involving two sulfur dioxide molecules and one molecule of dinitrogen tetroxide.

The first addition compound of dinitrogen tetroxide with an ether was reported by crowder3^. He isolated a white crystalline powder with the empirical formula

N2 O4 *0 (CH2 CH2 )2® ?rom a mixture of dinitrogen tetroxide and dioxane in petroleum ether.

Lukin and Dachevskaya^ have reported addition com­ pounds between nitrogen dioxide and polycyclic ketones. As an example benzanthrone is reported as forming an addition compound containing two moles of the ketone per mole of nitrogen dioxide. The benzonaphthone addition compound can be i solated. 'zty Gibson and Katz°' have investigated the reactions of several uranium oxides with liquid dinitrogen tetroxide,

U0 ^*2 H 2 0 and 1 1 0 3 *2 ^ 0 react completely with liquid dinitrogen tetroxide to give UO2 (NO3 )g • 2 H2 O; UC>3 *H2 0 gives U 0 2 (K0 3 )g*2 H 0 2 *H2 0 . The anhydrous oxides UO3 ,

U3 OQ and UO2 . 2 react partially with liquid N2 O4 . The product formed from all the anhydrous uranium oxides is U02(W03)2*2N02. Prom freezing point data Addison, conduit and

Thompson^® have shown that liquid dinitrogen tetroxide 14 and diethylnitrosoamine undergo compound formation giving

N2 0 4 *2 EtgHN0 , melting point -37.5°C. This compound was also indicated by conductivity measurements. The possible existence of another compound having a ljl mole ratio of the two components was suggested by calorimetric measurements of the heat of mixing. Crowder^^, and Levy and Scaife-^, in studying the reactions of dinitrogen tetroxide with olefins, have found that the type of products formed depends, to a significant extent, upon the nature of the solvent in which the reaction is carried out. For example in

certain solvents of the ether or ester type the oxidizing power of dinitrogen tetroxide on olefins was reduced and the addition products were obtained in good yield. a s a possible explanation of this observation, it was suggested the solvent formed a molecular addition com­ pound with the dinitrogen tetroxide. This intermediate compound might then react with the olefin forming the addition products without appreciable oxidation.

For the purpose of investigating the possibility of molecular addition compounds in systems of this type,

* Rubin, Sisler and shechter^ have constructed temperature versus composition diagrams of the solid-liquid phase equilibria of several binary systems viz., diethyl ether- dinitrogen tetroxide, tetrahydrofuran - dinitrogen 15 tetroxide, 1,4 dioxane - dinitrogen tetroxide, tetra- hydropyran - dinitrogen tetroxide and dichloro- diethyl ether - dinitrogen tetroxide. They demonstrated the existence of compounds N2 04 *2( (m.p. -74.8°),

N2 04 -2C5 Hl00 (m.p. - 56.8°), N2 0 4 *C4 Hq0 (m.p. -2q.5°), n2°4’2c4h8° incongruent melting), and N2 04 *0(CH2 CH2 )20 (m.p. 45.20c). The absence of N02, N02”, W02", NO” and

N0 3 ~ units in appreciable amounts in these addition com­ pounds was shown by magnetic and spectroscopic analysis.

Hence, it was concluded that these compounds are com­ plexes of N2 04 molecules. The fact that no compound was detected in the dichlorodiethyl ether - dinitro­ gen tetroxide system was attributed to a decrease in electron density around the oxygen atom due to the inductive effect of the chlorine atoms, or to steric interference of the chlorine atoms, or to both.

The molecular addition compound formed by 1,4-dioxane and dinitrogen tetroxide has a relatively high melting point compared to the melting point of the complexes of the other ethers. The relatively sharp maximum in the temperature versus composition curve in the N2 04 -

1,4 dioxane system when compared to those for the other ethers indicates that the 1 ,4-dioxane complex is the most stable. In considering a possible structure for these addition compounds it was suggested that the two 16 nitrogen atoms In the dinitrogen tetroxide molecule

(each having a positive formal charge) act together as a center of attraction for the ether oxygen atoms. Thus the compound N2 0 4 *2 R2 ^ ^an 130 pictured as

Assuming that this is the case 1,4-dioxane with two ethereal oxygen atoms at opposite ends of the molecule could form an addition compound with an indefinitely ex­ tended structure,.

“ TC

This concept would be of value in attempting to explain the relatively high melting point and stability of the dioxane - dinitrogen tetroxide addition compound.

A bicyclic monomeric structure was proposed as an alternative for the 1 ,4-dioxane complex: 17

0

0

Ordinarily the coordination number of nitrogen with respect to oxygen is limited to three by the radius ratio

effect. However, the fact that the N-N bond distance in 27 dinitrogen tetroxide (1.64 £ 0.03 a . ) is considerably

longer than the typical N-N covalent linkage (1.47 A.) may serve to minimize this limitation and permit an in­ crease in the coordination number of the nitrogen atoms.

This structure could also explain the high melting point

of the compound by analogy with other bicyclic compounds having relatively high melting points, e.g. camphor.

With the elucidation of the structure of the dinitrogen tetroxide - dioxane molecular addition com­ pound as one of their main objectives, Gibbins and

Sisler constructed a ternary phase diagram of the system dioxane - tetrahydropyran - dinitrogen tetroxide.

If the dinitrogen tetroxide - dioxane addition compound were polymeric, it was possible that some tetrahydro- pyran molecules might have replaced some dioxane mole­ cules and stopped the chains. Thus ternary compounds might have been formed. The results of this investigation 18 indicated that no ternary compound was formed, and that the field of primary crystallization for the compound dioxane* dinitrogen tetroxide is much larger than that for the 2

tetrahydropyran*dinitrogen tetroxide compound. The

following facts are pertinent to the structural arguments

of G-ibbins and Sisler:

1) The molecular structures of 1,4-dioxane and

tetrahydropyran differ only by the replacement of one

oxygen by a -CH2 ~ SrouP» 2) The mutual influence of the oxygen atoms in

1 ,4-dioxane is probably small as far as basicity is

concerned, 5) Both ethers have a non-planar configuration.

Considering these facts, the tendency of the two ethers

to form addition compounds with dinitrogen tetroxide should differ very little unless the two addition com­ pounds have markedly different structures.

In addition to these arguments it has been observed

that 1 ,4-dioxane forms only a 1 : 1 addition compound with dinitrogen tetroxide, whereas tetrahydropyran forms only a 2 ; 1 addition compound with dinitrogen tetroxide. This may be due to the fact that tetrahydropyran cannot act

as a bidentate group.

Whanger and Sisler^ have extended the study of dinitrogen tetroxide molecular addition compounds to 19 include other ethers using the solid-liquid phase

diagram technique. The purpose of their investigation

was (1 ) to determine the effect on compound formation of

longer and more bulky alkyl groups in the ether, (2 ) to

compare compounds formed between dinitrogen tetroxide

and other 11 dibasic" and " tribasic" ethers (i.e. ethers potentially capable of coordinating as bi- or tri­

functional molecules) with the stable 1 ,4-dioxane -

dinitrogen tetroxide compound, and (3) to show the effect

on compound formation of electronegative and electro­ positive groups placed in the ether ring. The binary

systems of dinitrogen t etroxide and the following ethers

were investigated: n-propyl ether, isopropyl ether, t- and

n-butyl ether, 1,3-dioxane, ethylene glycol diethyl

ether, perfluorotetrahydrofuran, trioxane, and 0 C-

methyltetrahydrofuran. The existence of the following

compounds has been demonstrated or suggested: NgO^.*

6cH20CH2CH2c{i2 (m.p. 2.0°), N2 04 -2 (n-CsH7 )2 0 (?, incon-

gruent melting point), N2 04 *2(iso-CgH?)20 (?, incongruent melting point), N2 0 4 *2 (n-C4 H g )2 0 (?, incongruent melting

point), N2 04 • ^H^QCH^jCHgOCgHg (m.p. approx. -58° to -59°),

N2 0 4 *2 C2 H 5 0 CH2 CH2 0 C2 H 5 (m.p. approx. -59° to -60°),

^2°4'c3h6°3 * incongruent melting point), N 2 04 *

2 C4 H 7 (CH3 ) 0 (m.p. -65.5°C). Both t -butyl ether and perfluorotetrahydrofuran failed to form addition 20 compounds.

A comparison of the phase diagrams for the binary systems dinitrogen tetroxide - n-propyl ether, dinitro­ gen tetroxide - isopropyl ether and dinitrogen tetroxide- n-butyl ether with the diagram for the ethyl ether system indicated that increasing the bulk of the hydro­ carbon radicals attached to the ether oxygens decreases the stability of the addition compounds with dinitrogen tetroxide. The failure of t-butyl ether to form an addition compound with dinitrogen tetroxide was attributed to steric factors, while the failure of per- fluorotetrahydrofuran to form an addition compound with dinitrogen tetroxide was attributed to the inductive effect of the fluorine atoms.

The 1;1 addition products formed in the systems con­ taining ethylene glycol diethyl ether, 1 ,3 -dioxane and trioxane are consistent with the ljl addition compound in the 1,4-dioxane system. Each of these ethers is potentially capable of acting as a Mdibasic" ether. The stability of the addition compound formed by 1,3-dioxane appears to be practically the same as that for the 1 , 4 isomer. The oxygen to oxygen distances in the "boat" form of these two ethers differ by only 0.1 A so that the bicyclic structure concept could be applied equally well.

In the case of the trioxane system the slope of the 21

freezing point curve approaching tlie incongruent melting point of what is probably a 1 ; 1 addition compound is

steeper than in the case of the aliphatic ethers and is about the same as for the corresponding portion of the 1,4-dioxane curve. The fact that the compounds formed by the ethylene

glycol diethyl ether, a potentially dibasic ether, are much less stable than the one formed by 1,4-dioxane is

probably due to steric factors. or* the basis of electron

density at the oxygen atoms the basic strength of the oxygen atoms in ethylene glycol .diethyl ether should be

nearly the same as the oxygen atoms in dioxane. However,

it is probable that steric factors are very important in the ethylene glycol diethyl ether system, and, regardless

of the structure of the dioxane addition compound, one

would expect that any addition compounds of ethylene

glycol diethyl ether with dinitrogen tetroxide would be less stable than that formed by dioxane. Perkins and sisler4^- have investigated the binary systems trimethylene oxide -dinitrogen tetroxide, 2,5- dimethyl tetrahydrofuran - dinitrogen tetroxide, and 1,3-dioxalane - dinitrogen tetroxide using the phase diagram technique. They have established the existence

of the following compounds: N2 O4 *031160 (m.p. -54°c),

N2 O4 -2 C3 H6 O (m.p. -54°), N2 04 (CH3)OCH(CH3 )CH2 22

(m.p. -34°), (3N2 0 4 -2c3H 60 2 )x where X *= 1 (ni»p. -35°), and an incongruently melting compound of 1,3-dioxolane* dinitrogen tetroxide in which the mole ratio of reactants is unknown. Davenport, Burkhardt and Sisler4^ have investigated addition compounds formed by tertiary amines and dinitrogen tetroxide. The technique employed in this study involved the slow addition of a cooled ethereal solution of the amine to a cooled solution of dinitrogen tetroxide in ether. The solvent was pumped off at low temperature and the addition product was hydrolyzed.

The aqueous solution obtained was analyzed for amine by making the solution alkaline and distilling the amine into an excess of standard acid followed by back titration. Devarda's alloy was added to the residue of the distillation to reduce the remaining nitrogen to ammonia, which was distilled into boric acid solution and titrated with standard acid.

In general the addition products formed were of the type where B is pyridine, quinoline, isoquino­ line, acridine, -picoline, -picoline, or trimethyl- amine. Addition compounds in which the mole per cent of dinitrogen tetroxide is greater than that required by the formula N2 C>4 *2 b were found with pyridine, PC-picoline, P -picoline, and triethylamine. These authors generally 23 conclude that the nature of the addition compounds formed between dinitrogen tetroxide and tertiary amines seems to depend on steric factors, basicity of the amines, relative concentration of reactants and the sus­ ceptibility of the amine toward oxidation. It is of interest to note that no evidence for com­ pound formation was observed when 2-methylquinoline and 2,6-lutidine were used as reactants. This is probably due to steric hindrance of the basic nitrogen atom.

III. VISCOSITY STUDY IN THE SYSTEM DINITROGEN TETROXIDE - 1,4 - DIOXANE a. Introduction

Liquids exhibit a resistance to flow known as

viscosity. In general, it is the property which opposes

the relative motion of adjacent portions of the liquid

and therefore can be regarded as a type of internal friction. The the force per unit area required to maintain unit

difference of velocity between two parallel liquid layers

separated by unit distance. For example, if two layers

of liquid dx cm. apart have a difference of velocity dy

cm. per second, then the force _f acting per square cm. must be

(1) 24 Tiie mathematical expression which relates the coef­ ficient of viscosity to other variables when a liquid flows through a capillary is given hy

-n = <2> where the symbols have the following meaning: s coefficient of viscosity (poise *» dyne sec) cm2 )

V = volume of liquid delivered (tnTl^) t a time to deliver volume V (seconds)

P » hydrostatic pressure (dyne/cm2 ) r a radius of capillary (cm.)

1 =. length of capillary (cm.)

This expression is primarily due to poiseuille^ and is frequently referred to as Poiseuille»s Law. The coef­ ficient of viscosity is usually expressed in dyn_e__sec^ and the value of unit coefficient of viscosity is called a poise in honor of poiseuille.

Couette4^ has pointed out that equation (2 ) is strictly correct if a portion of a longer tube is con­ sidered in -which the liquid has reached a constant velocity of flow. If, however, as is always the case in viscosity measurements, 1 is taken as the entire length of the capillary tube between two large reservoirs, and 25 p as the difference of pressure between them, only a portion of this pressure serves to overcome viscous re­ sistance, while the balance is used to impart kinetic energy to the liquid. The expression for the coefficient of viscosity corrected for kinetic energy is given as

Vi _ TTpr4t _ Vdm \ = — WT~ “ efTTt {) where the symbols have the same meanings as above, d is the density of the liquid and m is a numerical factor.

Couette44, and Finkener and Wilberforce4^ found m * 1.00 while other4® investigators have reported slightly different values.

Couette4 4 also suggested a second correction to allow for the non-laminar flow at the ends of the capillary tube. Equation (3) becomes

- TTpr4t _ ydm , A ^ 5 vT~ STfrrr“-“XT { } where _/j^ is the correction factor and has the dimension of length. The value of _A_ cannot be deduced theoretically but must be found experimentally.

The direct measurement of viscosity requires the determination of the rate of flow of liquid through a capillary tube of known dimensions and the application of equation (4). A few. liquids have been studied in this manner, but frequently it is much simpler to make use of a relatively simple method, whereby the viscosities or two liquids may be compared. IT the subscript (1) refers to a standard substance whose coefficient of viscosity and density are known and subscript (2 ) refers to a substance whose coefficient of viscosity is to be determined, then

(5)

and Y\ - P2^4t2TT. rl 2 - “ gyl----

Dividing (6 ) by (5) gives

*^1 2 _ P2 t 2 (7) ■V\i " Pit!

since 8 and TT are constants, r 4 and 1 are constant if the same viscometer is used for each determination, and the viscometer is loaded to the same V each time. Equation (7) may be modified further since p - hdg where h is the height of a liquid column and g is the acceleration due to gravity. Hence

"A 2 <*2 ^ 2 (8) ~V\l diti since £ is a constant and h is the same for both liquids. Thus by measuring the efflux time of liquid (1) and knowing its density and coefficient of viscosity it is 27 possible to calibrate the viscometer. It only remains to

determine the density, and efflux time of liquid (2 ) to

be able to calculate its coefficient of viscosity. This

treatment, of course, neglects the kinetic energy and

non-laminar flow corrections of Couette. However, it may be employed advantageously where highly precise deter­

minations of viscosity are not required. The comparative simplicity of viscosity determin­ ations is a natural temptation to employ them for demon­

strating association in liquid mixtures. However, the fundamental difficulty in attempting to draw any conclu­ sions from viscosity data is the fact that the law of

ideal viscous mixtures is not known. proposed

mathematical relationships defining the viscosity law for idea}, liquid mixtures range from the simple

assumption that the viscosity of an ideal mixture is merely the sum of the product of the individual viscosities and their respective fractions in the mixture, to very complicated expressions involving fractional exponents of the individual viscosities^?.

However, none is completely satisfactory. This situation renders the interpretation of the viscosity versus composition data for binary systems difficult indeed.

Accordingly numerous investigations intended to demon­ strate the relationship between viscosity maxima and 28 compound formation have been made on binary mixtures for which there is independent evidence for such combination. Tsakalatos^® studied mixtures of m-cresol with aniline and with o-toluidine. Both curves showed a very marked maximum at about 65 mole per cent of m-cresol. The freezing point curves of Kremann^® showed the existence of a 1 * 1 compound of m-cresol with each of the other com­ ponents. The displacement of the maximum in the viscosity curve was explained by the ternary character of the system, which consisted of the inactive binary mixture and the 1 ; 1 addition compound which would be present in maximum amount at the ratio 1 *1 , and shifts the maximum towards the side of the component having the higher viscosity.

Kurnakow^O considered maxima which shift with temperature as insufficient evidence of formation of definite molecular compounds. He^l investigated mixtures of ethyl formate with stannic chloride, the viscosity curves of which at 50°, 40° and 50° had very sharp maxima at almost exactly 32 mole per cent of stannic chloride, indicating an addition compound of one molecule of stannic chloride to two of the ester. Freezing point data also indicated a very marked maximum at this ratio.

Faust^, on the other hand, pointed out that the ratio at which the maximum occurs is a function of 29

temperature; with rising temperature the maximum shifts

more and more towards the viscosity of the more viscous

component, and at the same time becomes less pronounced

or disappears entirely.

The preceding brief discussion is not intended to

represent an exhaustive review of the voluminous data

appearing in the literature concerning the theory of

viscosity of binary mixtures and interpretation of

viscosity curves of binary systems. It is presented merely to point out seemingly irreconcilable opinions ex­

pressed on these subjects. Hatschek^ concluded that

viscosity studies can give some useful indication of

compound formation, stating, in effect, that maxima are held to occur whenever there Is chemical combination, but

that it is questionable whether all maxima are due to the

formation of compounds. Viscosity data, then, when used

in attempts to explain association phenomenon in binary

systems should be supplemented with data from other Inde­ pendent experiments e.g. freezing point diagrams.

Recognizing the c ontroversy set forth in the above discussion, an attempt was made to study the viscosity of

the binary system dinitrogen tetroxide - 1,4-dioxane not primarily to detect compound formation, since this has been established^ by freezing point diagrams but to relate any observable changes in viscosity to the proposed 30 structures. The existence of long chain polymers was

suggested for the 1 ; 1 addition compound between dinitrogen

tetroxide and 1,4-dioxane, and it was postulated (1) that

these polymers, if they are formed, should persist into

the liquid phase at temperatures slightly above the

melting point, and (2 ) that their existence should be

reflected in a very large increase in the viscosity of the

binary mixture.

b. Purification of Materials

The method of Fieser^ was used in purifying 1,4-

dioxane (Carbide and carbon Chemical Corporation). Two

liters of 1,4-dioxane were mixed with 200 ml. of water and 28 ml. of concentrated HCl and refluxed for twelve

hours. A stream of nitrogen was passed through the mix­ ture during reflux to entrain the acetaldehyde impurities

driven off. The solution was cooled and KOH pellets were

added slowly with stirring until they no longer dissolved

and a second layer had separated. The two phases were

allowed to separate and the dioxane was decanted. More

KOH pellets were added to the decantate to remove adhering aqueous liquor, and the dioxane was again decanted.

Metallic sodium was added to the final decantate and mix­

ture was refluxed for twelve hours with nitrogen passing

through the mixture. ■ The dioxane was then distilled from sodium under a nitrogen atmosphere and stored in a glass 31

vessel over sodium and iron wire. The middle Traction boiling at 100.2°C. (745 mm. Hg) was collected. The value reported in the literaturei5 lol.l°C. at atmospheric pressure.

The dinitrogen tetroxide (Matheson Company) was puri­ fied by a method similar to that of Qiauque and Kemp‘S in an all glass apparatus shown in Figure 1. The gaseous

dinitrogen tetroxide was condensed into the first trap by

cooling with a dry ice, carbon tetrachloride and chloro­ form bath and frozen to a pale blue solid. The blue solid was allowed to melt and was kept at 0°C. by an ice-water bath while dry oxygen was bubbled through the liquid until the dark green color had changed to orange-red. The dry ice cooling mixture was then placed around the dinitrogen tetroxide transfer cell (Figure 2) which was protected from mois.ture by a drying tube filled with phosphoric an­ hydride and sand. The product was distilled at room temperature through the drying tubes of phosphoric anhy­ dride into the transfer cell. The white, crystalline solid obtained melted to an orange-red liquid at -11.5°C. P in agreement with the literature value . The liquid WgO^ was stored under its own vapor pressure in a refrigerator at 0 ° to 5°C. c. Experimental procedure

The viscosity measurements were carried out with the NO

P4O10 and sand Impure N20,

P4O10 and sand

DINITR 06EN TETROXIDE PURIFICATION APPARATUS.

Figure 1 DINITROGEN TETROXIDE TRANSFER CELL

Figure 2 34 modified Ostwald-cannon-Fenske viscosity pipet illustrated

in Figure 3. A typical measurement on a dinitrogen

tetroxide - 1,4-dioxane mixture was carried out as follows;

The apparatus was thoroughly cleaned and dried. Dioxane was added to weighed vessel A through stopcock g from a weight buret and vessel A weighed again. The dinitrogen tetroxide cell was fitted into place and the desired amount of dinitrogen tetroxide distilled into vessel A, the vessel being cooled in a dry ice bath. The weight of dinitrogen tetroxide added was determined by the change in weight of vessel A and was checked by loss in weight of the transfer cell. The dry flask B and the viscosity pipet were then fitted into place and the system was placed in a thermostat at 48.02 0-04°, a temperature slightly above the melting point of the 1 ; 1 addition compound. After the system had been in the bath for about one hour, stopcock Id was opened and some of the mixture forced over into the flask B which had been previously calibrated and weighed. The flask B was then removed and weighed. From the volume of the flask and the weight of the mixture added, the density of the liquid was calculated. With stopcock b closed, the stop­ cock _e was opened as shown in Figure 3 and the viscosity pipet filled to mark a by nitrogen pressure exerted v. through stopcock g. The stopcock e was immediately closed. 35

Ost wald-Cannon- Fenske Viscosity Pipette / (Modified) (

Clomp

25 ml. volumetric 50 ml. Erlenmeyer flask , N20 4 Transf e r Cell

COMPOSITE VISCOSITY CELL (not drawn to scale)

Figure 5 36 The viscosity pipet _c was removed from vessel A, in­ verted and placed in the constant temperature bath. After the liquid in the pipet had been in the bath for 45 minutes it was forced up into bulb II by nitrogen pressure exerted through stopcock dl. The stopcock _e was then turned to make the inner chamber of the viscometer a com­ plete circuit isolated from the environment. The time required for the liquid meniscus to pass from c to f was then carefully measured. From the known values of Yl i and cL 1 and the the vaL ue of A 2 was calculated. in these determinations doubly distilled water was used as the calibrating liquid for the viscometer. d. Results

The results of the viscosity study in the binary system dinitrogen tetroxide - 1,4-dioxane are presented in Table I and are represented graphically in Figures 4 and 5. The data include the concentration range from zero to nearly fifty mole per cent dinitrogen tetroxide, the stochiometric composition for the 1 ; 1 addition com­ pound. Several attempts were made to extend the viscosity measurements to the dinitrogen tetroxide rich region of the system. However the pressures encountered with mixtures containing excess dinitrogen tetroxide presented TABLE I

VISCOSITY STUDY IK THE SYSTEM DINITROGEN TETROXIDE 1,4-DIOXANE AT 48.02 - 0.04°C.

MOLES MOLES MOLE FRACTION DENSITY EFFLUX TIME VISCOSITY % o 4 DIOXANE - n 2o 4 .g/ml. AVERAGE(SEC.) CENTIPOISE

CALIBRATION WITH DOUBLY DISTILLED HoO 0.98895 159.44 0.5680

0.0000 . pure 0.0000 . 1.0031 220.29 0.7964 0.0106 0.4167 0.0247 1.0162 218.48 0.8002 0.0396 0.4076 0.0886 1,0405 217.72 0.8165 0.0401 0.3335 0.1073 1.0340 220.34 0,8235 0.0628 0.4107 0.1326 1.0462 214.50 0.8088 0.0942 0.4072 0.1879 1.0764 214.08 0.8305 0.0945 0.3423 0.2163 1.0766 208.10 0.8098 0.1295 0.3941 0.2473 1.0916 207.12 0.8149 0.1648 0.3917 0.2961 1.1150 202.23 0.8127

0.2328 0.3714 0.3853 1.1368 199.20 0.8162 0.2163 0.3447 0.3855 1.1440 193.86 0.7993 0.2432 0.3316 0.4232 1.1612 0.2846 0.2865 0.4983 1.1880 181.75 0.7782 Density 9/mi 1.0600 1.0300 1.0900 I.OOOi 1.1800 1.2100 1.1200 1.1500 .9700 0 .05 .10 .15 .20 Mole Fraction Fraction Mole Figure 4 Figure .25 System: Dinitrogen Tetroxide -Dioxane Tetroxide Dinitrogen System: .30 204 0 N2 Concentration Concentration .35 Density ( Density AO 20^ ^ 0 N2 vs. / i) 9/m .45 (M ole Fraction) ole (M

.50 9900

.9100

.8300

.7500

5ystem: Dinitrogen Tetroxide - Dioxane .6700 OJ Viscosity i/S. .5900 Mole Fraction N204w

.5100

i i I I I 1 L .20 .25 .30 .35 .40 .45 .50

Mole Fraction N2 O4

Figure 5 40 insurmountable difficulties in using the apparatus in its present state of design and were abandoned. Viscosity de­ termination cannot be carried out at lower temperatures because most compositions are solid at temperatures near room temperatures. In spite of the incomplete nature of the viscosity versus composition data, sufficient data were obtained to give evidence concerning the point in question i.e. whether or not the molecular addition com­ pound formed by dinitrogen tetroxide and dioxane is polymeric. e. Discussion and conclusions

As illustrated in Figure 5 the viscosity versus com­ position curve increases to a slight maximum at about 17 mole per cent of dinitrogen tetroxide and then descends towards 50 mole per cent of dinitrogen tetroxide. The difference between the highest viscosity value determined

(.8305 centipoise) and the viscosity value of the pure dioxane (.7964) represents an increase of about 4 per cent in the viscosity. The experimental error is about i 2 ^J.

The viscosities of the mixtures containing .1326 and .2163 mole fraction of N2 O4 fall below the viscosity versus composition curve. However, on the density versus compo­ sition curve, the same points fall below the density curve also indicating that these values may be low. 41 Hence it appears that this relatively flat maximum is

real and may probably be attributed to the formation of

the 1:1 addition compound in solution. However, the

amplitude of the maximum is too small to be of signifi­

cance in terms of the formation of polymeric aggregation.

The fact that the maximum does not occur at the

stochiometric mole fraction for the addition compound is

not surprising in view of the results of other workers, and the explanation of Tsakalatos (see page 28) may be employed to explain this shift. The fact that the

viscosity maximum represents only about a 4 per cent increase over the value for pure dioxane indicates that there are no long chain polymers in the solution. Hence

it may be concluded that the postulate of polymeric

aggregates as a possible structure for the dioxane -

dinitrogen tetroxide addition compound is incompatible

with the viscosity data for the binary system.

IV. CRYOSCOPIC STUDY OP SOLUTIONS OP DINITROGEN TETROXIDE IN 1,4-DIOXANE a. introduction In order to amplify the results obtained in the pre­ ceding viscosity studies and to obtain information which can be used in resolving the question of a monomeric or dimeric structure of the 1 - 1 addition compound formed by

1,4-dioxane and dinitrogen tetroxide, a cryoscopic 42 investigation of the molecular weight of the addition compound was proposed. Since the addition compound is relatively soluble in excess 1,4-dioxane, it was decided to use 1,4-dioxane as solvent. The addition of small amounts of dinitrogen tetroxide to a large excess of 1,4-dioxane should result in the formation of the Ijl addition compound in amounts proportional to the quantity of dinitrogen tetroxide added with the excess dioxane functioning as the solvent for the cryoscopic determination. in the procedures discussed below, solute refers to the calculated quantity of the 1 ; 1 addition compound based upon the weighed quantity of dinitrogen tetroxide added.

The addition of a solute to a solvent causes the freezing point of the latter to be lowered. The extent of the freezing point depression, assuming the solute does not dissociate, depends directly on the concentration of solute. The following quantitative relation is known to hold for ideal dilute solutions^.

RT0 2 IOOOW2 1000W2 m 2 = ±0 0 0 Lf * A T f W i = Kf "ZSTpV3“ ^

In equation (1) M2 is the molecular weight of solute, A T f is the observed freezing point lowering caused by the addition of W 2 grams of solute to Wi grams of solvent.

L_f is the latent heat of fusion per gram of solvent. T0 43 is the freezing point of the pure solvent, and R is the gas constant. Kp is the freezing point depression constant or cryoscopic constant and may evidently be calculated by

% = i . (2>

However it is usually more satisfactory to obtain values of Kf for a particular solvent by experimental determination. If, when dinitrogen tetroxide is added to 1,4-dioxane, polymerized species containing more than one unit of di­ nitrogen tetroxide are formed each polymer molecule would act as a single molecule in lowering the freezing point, and the freezing point depression would be less than would be the case if only monomers were present. The number of dinitrogen tetroxide units per molecule of solute can be calculated as

X = — (3) M where M 2 is the apparent molecular weight of the.ljl addition compound calculated from the freezing point de­ pression. M is the formula weight of the addition com­ pound calculated from the sum of the atomic weights in the empirical formula, and X is the number of dinitrogen tetroxide units per molecule of the addition compound. 44

The molality m of any solution may be related to M,

W 2 and Wi by the equation

IOOOW2 m = -®r ( >

Substituting the expressions for M2 and M as given by equations (1) and (4) respectively into equation (3) results in the expression

x = TStff <5) which may be used in calculating the number of dinitrogen tetroxide units in a molecule of the addition compound in solution.

The cryoscopic constant of 1,4-dioxane is known^®*^.

However, it was decided to redetennine the value for the present investigation, with 1,4-dioxane functioning as the solvent, benzene, o-xylene, toluene, and t-butyl- benzene were used as solutes. If each solute is assumed to be a monomer in 1,4-dioxane, X in equation (5) is equal to unity and

% " 4^ . b. Purification of Materials

Dinitrogen tetroxide and 1,4-dioxane were purified according to the methods described in Chapter III, except that 1,4-dioxane was subjected to further purification by 45 slow fractional crystallization. Samples of very pure benzene, o-xylene, toluene and _t-butylbenzene used as solutes in the reevaluation of the cryoscopic constant of dioxane were obtained from the American Petroleum

Institute project. c. Experimental Procedure

A Cr-2 Mueller bridge equipped with a platinum re­ sistance thermometer was used for measuring the temperature. The freezing point cell was so constructed as to protect the sample from moisture and to provide constant stirring. The detailed construction of the cell is shown in Figure 6 .

The platinum resistance theimometer T which was calibrated at the Bureau of Standards was protected from the action of the stirrer by shield S. It entered the shield S at A through a Teflon plug P which was machined to fit snugly into the ground glass joint A. The: ther­ mometer T was sealed to plug P which was in turn sealed to joint A using DeKhotinsky cement. The stirrer was made of glass and was caused to move by intermittent activation of a solenoid which was fitted over the stirrer-guiding chamber G* M is a small metal slug hermetically sealed within the stirrer arm. The ground glass joint B accommodated a weight burette, which was used for the addition of 1,4-dioxane to the freezing Transfer Celt fitted here 47 point cell E. The ground glass joint c was fitted with, a transfer bridge p through which dinitrogen tetroxide was distilled from a transfer cell connected at ground glass joint H. The entire cell E was fitted into a double walled cooling jacket J which was immersed directly in a cooling bath. In a typical run the apparatus was cleaned and dried.

The platinum resistance thermcmeter T and the bridge p with stopcock D closed were fitted into place. A drying tube containing phosphoric anhydride and sand was con­ nected to the bridge F at H. A burette containing 1,4- dioxane was fitted into ground glass joint B, stopcock D was opened and dioxane flowed into the cell. The weight of the burette was noted before and after the addition, the difference being the weight of dioxane added. With stopcock D closed and joint B plugged, the dinitrogen tetroxide transfer cell was connected to the bridge p at ground glass joint H. Stopcock D was opened and a small amount of dinitrogen tetroxide was distilled into the freezing point cell E, after which stopcock D was closed.

The dinitrogen tetroxide transfer cell was placed in liquid nitrogen before being datached from the bridge p in order to prevent loss of dinitrogen tetroxide which might otherwise have remained in the bridge outside either cell. The weight of the transfer cell was noted 48 before and after the addition of dinitrogen tetroxide, the difference being the weight of dinitrogen tetroxide added to the freezing point cell.

The freezing point cell E in jacket J was then re­ turned to the cooling bath and the freezing point of the mixture determined. prom the known weights of dioxane and dinitrogen tetroxide, the freezing point depression, and the cryoscopic constant of dioxane, the apparent number of dinitrogen tetroxide units per molecule of addition compound was calculated.

The freezing points of the various mixtures were ob­ tained using a platinum resistance thermometer in con­ junction with a G— 2 Mueller bridge. The resistance (In absolute ohms) of the platinum resistance thermometer was measured directly on the bridge. The resistance was then converted to temperature by use of the Callendar equation:

where the symbols have the following meanings:

R 0 a ice point resistance

C = steam point calibration constant

= 0.00392557 = sulfur point calibration constant = 1.492 49 B = oxygen point calibration constant - o for

temperatures above 0 °C.

t = temperature in degrees centigrade

R^. » the resistance at temperature t

The constants Cj S, and B were supplied by the Bureau of Standards but an average value of the ice point re­ sistance R 0 must be determined by the user of the instru­ ment. This was done using pulverized ice made from dis­ tilled water and was found to be 25.5595 ohms. It may be observed that the solution of equation (7) for t above 0°C. in terms of resistance involves a quadratic equation. In order to eliminate the task of solving a quadratic equation each time a new temperature was determined, temperatures near the expected range of operation were substituted and the equation was solved for R^, By proceeding in this manner it was possible to construct a plot of resistance R^ versus temperature t and to read the temperature corresponding to a definite resistance directly from the graph.

The freezing points of the various mixtures were de­ termined by plotting cooling curves (resistance versus time) for each trial. Figure 7 shows a typical cooling curve. In every case supercooling was encountered and hence the method of Rossini et al^® applied to correct for this difficulty. The method merely requires the Resistance (abs. ohms) 26.7500 26.7500 ‘ *- 26.7300 26.7400 26.7200 26.7IOO 26.7000 t R IOO .0736g. qui oln Curve Cooling id u iq L R e s i s t a n c( e a b s . o h m s ) v s . T i m e ( s e c o n d s ) dioxane 200 Figure 7 Figure Ter.-butyl benzene in ie (Seconds) Time 50 300 / rsalzto Started S Crystallization '/ is Pit band /ifter Obtained Point First 400 Check 500 600 25.339g 700

51 extrapolation of the cooling curve, after solid has started to form, back to the portion of the curve ob­

tained before solid appeared. The resistance at the point where the extrapolated curve intersects the other was taken to be the correct resistance. This resistance reading was then converted to temperature as described

above.

d. Results The results of the reevaluation of the cryoscopic constant of dioxane using the four solutes mentioned

above are shown in Table II. The average value of the

cryoscopic constant of dioxane for the sixteen deter­

minations was 4.68 degrees per mole. This compares

favorably with the average value of 4.7 reported by

Oxford5^ and the value of 4.63 reported by Kraus and

Vingee^®. In each of the determinations it was assumed

that the solid separating when each mixture was cooled was pure dioxane. No analysis was performed. The agree­ ment with the values reported by Oxford^ indicates that no serious error was made in making this assumption. The

value of Kf - 4.68 degrees per mole was used in determining the determination of the molecular weight of

the 1 * 1 addition compound formed by dinitrogen tetroxide

and dioxane. TABLE II

CRYOSCOPIC CONSTANT OF 1,4-DIOXANE

WEIGHT OF WEIGHT OF MOLALITY, Tf Tf SOLUTE.,. GRAMS DIOXANE, GRAMS m °C. K m

BENZENE 0.5524 24.8563 0.2845 1.270 4.46 CHECK’ 24.8563 0.2845 1.271 4.47 0.0608 26.0202 0.0299 0.132 4.41 CHECK 26.0202 0.0299 0.128 4.28

ORTHO XYLENE .0.0807 25.6047 0.0297 0.144 4.87 CHECK 25.6047 0.0297 0»143 4.83 0.i845 25.6047 0.0679 0.338 4.98 CHECK 25.6047 0.0679 0.338 4,96

TOLUENE . .0.0808 27.206 0.0322 0.147 4.58 CHECK 27.206 0.0322 0.150 4.64 0.1370 27.206 0.0547 0.256 4.69 CHECK 27.206 0.0547 0.252 4.60

T-BUTYL BENZENE 0.0736 25.339 0.0216 0.108 4.99 CHECK 25.339 0.0216 0.104 4.81 0.1505 25.339 0.0443 0.205 4.63 CHECK 25.339 0.0443 0.2Q8 4.70 53 Table III shows the results of the cryoscopic measurements of solutions of dinitrogen tetroxide in excess 1,4-dioxane. The data are shown graphically in

Figure 8 . The values of X used for the graph are the average values obtained for the trial run and the check run at each molality. Extrapolation of the curve to zero molality (infinite dilution) gives a value of X equal to 0.994, which may be taken as unity within experimental error. The very slight upward trend at the two higher concentrations reflects the fact that as the concentration of dinitrogen tetroxide increases an appreciable partial pressure of dinitrogen tetroxide develops above the solution.

e. Discussion and conclusions The value of X equal to unity indicates that the 1*1 addition compound formed by dinitrogen tetroxide and 1,4-dioxane is monomeric in solution of excess 1,4- dioxane. These data confirm the conclusion derived from the viscosity data that no polymeric aggregates exist in solution at temperatures slightly above the melting point of the addition compound. Although the viscosity and cryoscopic data apply only to the liquid phase, it seems unlikely that the state of aggregation of the solid product would differ markedly from that in the liquid phase. As a result of these data the most TABLE III

CRYOSCOPIC MEASUREMENTS OP SOLUTIONS OP DINITROGEN TETROXIDE IN EXCESS 1,4-DIOXANE

CALCULATED EFFECTIVE WT OP 1;1 WEIGHT SOLVENT WT. ADDITION MOLALITY AVERAGE nTf T " ^ OF N204 (g) OP DIOXANE(g) COMPOUND(g) . m. °C X Tf .. X

0.0093 28,703 0.0182 0.00352 0.017 0.998 CHECK 28.703 0.0182 0.00352 0.017 0.998 0.998

- 0 .i002 29.116 0.1961 0.0374 0.175 1.000 CHECK 29.116 0.1961 0.0374 0.178 0.983 0.992

0.1049 27,784 0.2053 0.0410 0.199 0.965 CHECK 27.784 0.2053 0.0410 0.199 0.965 0.965

0.1216 23.521 0.2380 0.0562 0.251 1.047 CHECK 23.521 0.2380 0.0562 0.246 1.069 1.058 0.2434 28.479 0.4763 0.0946 0.408 1.087 CHECK 28.479 0.4763 0.0946 0.409 1.081 1.084 1.40

1.20

1.00

.60

.40

0 .02 .03 .04 .05.07 .08 .09 .10

Molality (Moles of I'l Addition Compound per lOOOg. Dioxane) Figure 8 56 reasonable interpretation of the structure of the 1 ; 1 addition compound is the bicyclic structure mentioned in

the original work of Rubin, Sisler and Shechter-1-. The bicyclic structure is shown on page 17.

V. STUDY OF THE SYSTEM DINITROGEN TETROXIDE-

1,4-DIOXANE IN THE GAS PHASE a. Introduction The existence of .the 1;1 addition compound has been established in the solid and liquid phases. The white

solid is stable at room temperature and may be easily isolated. The existence of the compound in the liquid phase may be inferred from the relatively sharp maximum occurring at a 1 ; 1 mole ratio of the two components from the freezing point diagram-*-. Also the observation^ that solvents of the ether type greatly reduce the oxidizing power of dinitrogen tetroxide on olefins indicates that the 1 - 1 addition exists in the liquid phase. The results of the viscosity experiments reported here may probably be interpreted as indicating association in the liquid phase.

As a logical extension of these facts a study of the gas phase system was proposed to determine if association takes place to a significant extent in the gas phase. The system was studied by colorimetric and infrared spectroscopic techniques. The colorimetric technique 57 utilized a photoelectric cell for determining the concen­

tration of NOg and observing the effect of the addition

of gaseous 1,4-dioxane to the equilibrated gaseous

dinitrogen tetroxide - nitrogen dioxide system. In this

system N 0 2 was assumed to be the only colored chemical

species.

Consider the following equilibria;

N2 04 ^ ~ - 2 N 0 2 (A)

0(CH2 CH2 )20 - N 2 04 ^ --- — 0( CH2 CH2 )2 o n 2 o4 (B) The following equations may be written;

. (1) % 2o 4

NN 2 0 4 = % 2 0 4 + »dioxane.N2 0 4 + * % 0 2 ^

oxane = ^dioxane "t* ^dioxane*N2 0 4 where N is the concentration in moles per liter of the

substance shown as a subscript, N^ioxane is the concentra­

tion in moles per liter of dioxane which would be present

if dioxane alone occupied the entire system i.e. no inter­

action with N2 04 . Similarly Wj}2 o4 is tlle concentration in moles per liter of N2 O 4 which would be present in the

entire system if H 2 0 4 alone occupied the system, i.e. no interaction with dioxane and no dissociation to N02 - Solving these three equations simultaneously gives 58

(4)

(5)

(6)

Thus, since NjjQg can he determined eolorimetrically ,

J-Idioxane an

K = Ndioxane»N2Q4 ^ x ^dioxane

can be calculated* There are two other methods which may be adapted to this study. Since NOg is the only para­ magnetic species present, a method utilizing this fact and mathematical consideration similar to those presented

above would be used. Also a tensimetric method similar to

that used by Verhoek and Daniels4 in studying the dis­ sociation constant of NgO^ could be employed. Preliminary investigations indicated that the photoelectric method was much more satisfactory from the standpoint of adequacy and availability of equipment.

The infrared absorption spectrum of the gaseous mix­ ture of dinitrogen tetroxide and 1,4-dioxane was studied 59 to confirm the results of the photoelectric experiment.

The appearance of new absorption bands in the infrared spectra of the two components would indicate that appreciable compound formation in the gaseous state is very probable; the absence of new absorption bands would indicate that such compound formation occurs to no more than a very slight extent. b. Experimental Procedure The all glass apparatus used in the colorimetric de­ termination is shown in Figure 9. Two 1000 ml Florence flasks (A and j3) were connected by 20 mm Pyrex glass tubing. This connecting section was used to accommodate four side arms, the lower two of which contained capsules of the substances to be mixed, and the upper two contained hammers made of iron filings hermetically sealed in Pyrex glass jackets. The end of this connecting section was terminated with a thin glass membrane (C) which could be broken by allowing a hammer to fall upon it. Several expansion stages were connected in this manner.

The initial stage of the system was connected to a colorimeter cell by two 12 mm Pyrex glass side arms ex­ tending from flask A- A gas pump containing a closely fitting plunger, which was similar to the hammers in design, was installed in one of the arms of the color­ imeter cell in order to mix the vapors thoroughly. The Water jacket- Water in Water out-^ Hammer

Colorimeter cell 12mm. Gas pump Hammer Hammer Plunger 20 mm: it K

Thin glass Thin glass 1000 ml. membrane membrane A \ J2O4 ‘ Dioxane Capsule] Capsule

COLORIMETRIC APPARATUS

Figure 9 61 colorimeter cell was sealed in a glass jacket so that it could be maintained at a constant temperature by pumping water through it from a constant temperature bath.

The instrument used for the colorimetric determin­

ation was a Fisher Electrophotometer (A.C. M°del) equipped

with a blue filter. It is a dual photocell, null type,

line operated colorimeter. Its operation is not affected

by line voltage variations or by fluctuations in light

source intensity since both the reference and the

measuring photocells are activated by the same light

source. The absorption indicator dial has two sets of

scales, scale B is a per cent transmission scale and

scale A is a logarithmic scale which may be used for substances which follow the Beer-Lambert Law. The electrophotometer was calibrated by shining the

blue filtered light through an evacuated colorimeter cell,

adjusting the absorption indicator dial to one hundred per cent transmission and setting the galvanometer needle

to the null position. The introduction of colored material into the colorimeter cell causes the galvanometer

to deflect. When the galvanometer is restored to the null

position using the absorption indicator dial, the

corresponding transmission may be read directly from the dial.

The procedure for calibrating the electrophotometer was as follows: The volume of each, of the Individual units constituting the assembly was determined by finding the weight of distilled water required to fill the unit at 45°C. The units were not filled completely but only to calibration marks M, N, R, S, T, U, V, W, etc. The individual units with all the hammers and the capsule containing known weight of N2 O4 were then joined together as indicated by the dashed lines and the system was examined for leaks by pumping to a good vacuum and using a Tesla coil. When the system was found to be vacuum tight it was pumped to a good vacuum, flamed, and sealed off. The system was anchored in a constant temperature • bath regulated at 45°. The N2 O4 capsule was broken and the system was allowed to reach thermal equilibrium.

When the electrometer reading was constant over a con­ siderable period of time the system was assumed to be in equilibrium and the electrometer reading was noted. Then the thin glass membrane C was broken, the system allowed to come to equilibrium and the electrometer reading noted again. Pour successive readings were taken in this manner. The system was broken apart and the volume between calibration marks M and N, R and s, T and u, etc. were determined by adding water from a burette. The ' volumes determined in this manner were added to those previously determined to give the total volume for each 65 expansion stage. The procedure Tor attempting to detect the addition of NgO^ and 1,4-dioxane was similar to that for the calibration run except that the dioxane capsule was also broken and it was only necessary to use one stage of the apparatus.

The dioxane gas absorption cell used in the study of the infrared spectrum of the gaseous mixture of the two components is shown in Figure 10. A piece of 30 mm Pyrex glass tubing was flanged on both ends and ground flat. A Teflon gasket was inserted between each salt window and the ground flange. The entire assembly was held together by means of brass face plates which fitted closely over the salt windows and which were tightened in place by long screws parallel to the longitudinal axis of the cell.

After the cell had been firmly assembled, glyptal was used to prevent the occurrence of small leaks around the windows when the cells were evacuated. A second and similar cell, used for obtaining the NgO^-NOg spectrum was constructed having an inner ball joint terminating the side arm.

In order to fill a cell to a known gas pressure, the cell and the gas source were connected to a vacuum system equipped with a mercury manometer. The gas was ■. allowed to enter the vacuum system and its pressure was measured. The gas in the absorption cell was then isolated by closing the stopcock on the cell. When filling the 64 Vii Vii it/ft U 2 1

50 mm. NaC! window

Teflon gasket

30mm. jr Ball joint

Pyrex tubing 10mm.

Reservoir Vacuum Stopcock

Dioxane Gas Absorption Cell

Figure 10 65 dinitrogen tetroxide gas absorption cell a buffer of Dow dilicone fluid No. 200 (viscosity 100 centipoise) was used between the gas source and the manometer. After the spectra of the individual gases had been obtained, the two gas absorption cells were connected together and the

N2 ° 4 was distilled into the dioxane gas absorption cell by cooling the reservoir attached to the side arm of the dioxane cell. After allowing the cell to warm to temperature the spectrum of the combined gases was determined. The Perkin-Elmer double beam recording infrared spectrophotometer (Ivlodel 21) was used to obtain the spectra shown in Figures 11, 12, and 13. c. Results The results of the calibration of the electrometer are shown in Table IV.

TABLE IV

CALIBRATION OF ELECTROPHOTOMETER

VOLUME OF ELECTROPHOTOMETER IDEALIZED SYSTEM READINGS CONC.No0a N02 CONC. (liters) LOG. SCALE A (moles/liter) (moles/liter)

2.6594 77.5 6.894 x 10“ 4 1 2 . 6 x 1 0 ” 4

3.8565 56.9 4.754 x 10“ 4 8.90 x 10 ” 4

5.0601 44.5 3.623 x 10 “ 4 6.85 x 10- 4

6.2635 37.0 2.927 x 10“ 4 5.60 x lO - 4 % TRANSMISSION 80 |\3 £ O O O O T

6 8

W 8 1 0 WAVELENGTH, MICRONS 1PreRfiurp - 3 OP m jn Blank - 11.0 mm. air Gain - 7. 0 Response ->.0 J Suppression - 3.0 Speed - 3.0 1 ntensity “4 amp S lit - 900 7.63 cm. cell 10.0 cm. cell

G

12 14 f . % TRANSMISSION (D m O O o Pre

Gai Res Suj Sp< lnt< Sli 7 6 IO.C

GASEI

WAVELENG Pressure - 157 mm. Blank — 11.0 mm. air Gain - 7.0 Response - 2.0 Suppression - 3.0 Speed - 3.0 Intensity - .4 amps Slit - 900 7 63 cm. ce 10.0 cm. cel

GASEOUS DINITROGEN TETROXIDE

8 10 WAVELENGTH, MICRONS 14 % TRANSMISSION OOI COMB

WAVELENG COMBINED DINITROGEN TETROXIDE - DIOXANE SPECTRUM I______L ______I_____ 8 10 WAVELENGTH, MICRONS

69

T^-e idealized concentration of N2 O4 refers to the amount

of N2 O4 which would be present if no dissociation

occurred. The concentration of NO2 was calculated from

the idealized equilibrium constant of Verhoek and

Daniels^. Their equilibrium constant was given in terms

of pressure and thus was converted to concentration

terms. This was done by using the expression

K c ■ — ^ f c r - (8) (RT) where Kp is the pressure equilibrium constant, Kc is the concentration equilibrium constant, R is the gas constant, T is the absolute temperature and h-d is the increase in

the number of moles of gas in the N2 0 4 " ^ 0 2 equilibrium

( * * 1 in this case). The value of Kp given by Verhoek

and Daniels^ is 0.6706 atmosphere at 45°C leading to a value of Kc equal to 2.569 x 10“^ mo*^-es/liter^ r^e con­

centration of N0 2 (N^Qg) may then be calculated by

_ - i K c + V 4 / 4 - 4 K o N h 2 0 4 %o2 —------■ a (9> where is the idealized concentration of N2 O4 in moles per liter.

The following table shows the data obtained when a 5:1 mole ratio of dioxane to dinitrogen tetroxide was allowed to mix at 45°C.

TABLE V COLORIMETRIC STUDY OF THE GAS PHASE SYSTEM DINITROGEN

TETROXIDE - 1,4-DIOXANE AT 45°C.

ELECTRO­ METER % 0 2 nk3 0 4 dioxane TIME READING ,conc. cone. conc. (MIN­ LOG (moles/ (moles/ (moles/ UTES) SCALE(A) liter) liter) liter)

0 69.0 1 1 . 2 x 1 0 “ 4 6.088 x lo“ 4 2.984 x 10~ 3 2 0 69.0 1 1 . 2 x 1 0 “ 4 155 65.9 1 0 . 6 x 1 0 “ 4 1535 64.0 10.3 x 10" 4 2585 62.2 9.94 x 10" 4

0 63.0 1 0 . 1 x 1 0 “ 4 5.447 x 10" 4 1.632 x 10~ 3 16 63.0 1 0 . 1 x 1 0 ” 4 1 2 1 60.4 9 . 6 6 x 10” 4

These data show that during the first twenty minutes

of contact of the two gases there is no detectable change

in the concentration of NOg in the system. An independent qualitative experiment was performed in which no electro­ meter data were taken but the gas phase mixture was con­ densed to a solid using liquid nitrogen. The following table indicates the results of this qualitative experiment 71

TABLE VI QUALITATIVE OBSERVATION OP THE GASEOUS SYSTEM

1,4-DIOXANE - DINITROGEN TETROXIDE AT 45°C.

TIME (MINUTES) COLOR OP CRYSTALLIZED PRODUCTS

0 WHITE SOLID 19 WHITE SOLID 444 WHITE SOLID, TRACE OP LIGHT BLUE SOLID 1556 WHITE SOLID, MORE LIGHT BLUE SOLID .. 2016 WHITE SOLID, STILL. MORE LIGHT BLUE SOLID

These qualitative observations indicate that a slow oxi-

dation-reduction reaction occurs in the gas phase system with the production of dinitrogen trioxide under the experimental conditions.

The results of the infrared investigation of the gas

phase system are shown in Table VII and Figures 11, 12

and 13. The wave lengths in Table VII are reported in microns and the relative intensities are listed in

parenthesis as very weak, weak, medium, strong and very strong. Literature values are also listed for comparison.

Some of the wave lengths reported as very weak were difficult to distinguish from the noise level and are therefore less reliable than the others.

As shown in Table VII and Figures 11, 12 and 13 there are no absorption peaks present in the spectrum of the combined gases which cannot be accounted for from the

spectra of the individual gases. Some of the absorption TABLE VII

INFRARED ABSORPTION STUDY OF THE GASEOUS SYSTEM 1,4-DIOXANE - DINITROGEN TETROXIDE

DIOXANE LITERATURE5 9 N2 O4 -NO2 LITERATURE6 0 , 6 1 COMBINED GAS MICRONS MICRONS MICRONS . MICRONS MICRONS

2.394(v.w.) 2.392(v.w. 2.468{v.w.) 2.475(v.w. 2.502(v.w.) 2.518(v.w. 2.580(v.w.) 2.577(v.w. 2.615(v.w.) 2.618(v.w. 2 ,660(v.w.) 2.667(v.w. 2.679(v.w.) 2.685(v.w. 2.905(v.w.) 3.086(v.w.) 2.905( v .w . 3.2o8(med.) 3*205(med.) 3.2o2(med. 3.365(v.st.) 3.367(v.s.) 3.370(med.) 3.361(med.);3.50 3.372(st.) 3.432(st.) 3.436(med.) 3.445(st.) 3.423(v.s.) 3.441(st.) 3.451(v.s.) 3.460(st.) 3.469(st.) 3.489(v.s.) 3.493(v.s.) 3,491{st.) 3.634(w.) 3.649(v.w. 3.710(w.) 3.725( v .w . 3.820(med.) 3.817(w.); 3.82 o (med. 3.880(v.w.) 3.870(v.w. 3.898(v.w.) 3.900(v.w. 4.058(v.w.) 4.061(v.w. 4.137(v.w.) 4.142(v.w. 4.349(v.w.) 4.323(v.w. questionable 4.368(v.w. TABLE VII (cont.)

59 DIOXANE LITERATURE N2O4-NO2 LITERATURE6 0 ' 6 1 COMBINED GAS MICRONS MICRONS MICRONS MICRONS MICRONS

questionable 4.380(v.w.) 4,42o(v.w. questionable 4.430(v.w. questionable 4.475(v.w. 4.482(v.w,) 4.532(v.w. 4.523(v.w.) 4.571(v.w. questionable 4.715(v.w. ) 4.7l6(v.w.) 4.993(w.) 4.995(v.w.) 5.051(w.) questionable 5.158(v.w.) 5.249(v.w.) 5.250(v.w.) 5.425(v.w.) 5.578(v.s.) 5.748(v.s.) 5.718(st.);5.70 5.750(v.s.) 5.763(v.w.) 5.872(v.w.) 5*899(v.s.) 5.942(v.s.) 6.195(v.s.) 6.192(v.s.);6.14 6 .2 2 o(v.s.) 6.498(v.w.) 6.498(v.w.) 6.52o(v.w.) 6.523(v.w.) 6.570(v.w.) 6.570(v.w.) 6 .597(v.w.) 6 .599(v.w.} 6.630(v.w.) 6.640{v.w.) 6.675(v.w.) 6.680(v.w.) 6.680(v.w.j TABLE VII {cont.)

DIOXANE LITERATURE5 9 Ng 0^ -NOg LITERATURE6 0 *6 1 COIffilNED GAS MICRONS MICRONS MICRONS MICRONS MICRONS

6.725(v.w.) 6.725(v .w ,) 6.790(v.w.} 6.793(v.w.) 6.830(v.w.) 6.832(v.w.) 6.856(med.) 6 .845(med.) 6.870(v.w.) 6 .8 6 8 (w.) 6.989(med.) 6.892(st.) 6 .9l0(v.w.) • 6.903(v.w.) 6.970(v.w.) 6.970(v.w.) 7.00Q(v.w.) 7 .030(v.w.) 7.030(v.w.) 7.054(v.w.) 7.058{v.w.) 7.075(v.w.) 7.082(v.w.) 7.098(v.w.) 7.102(v.w.) 7.123(v.w.) 7.125(v.w.) 7.153(v.w.) 7.150(v.w.) 7.179(v.w.) 7.170(v.w.) 7.220(v.w.) 7.285(med.) 7.315(med.) 7.315 7.329(med.) 7.350(med.) 7.390(st.) 7.407(w.);7.28 7 .384(med.) 7.470{v.w.) questionable 7.556(w.) 7.552(v.w.) 7.730(med.) 7.763(med.) 7.752(v.s.) 7.920(st.) 7.939(v.s .} 7.905(st.);7.85 7.950(v.s.) 7.949(st.) TABLE VII (cont.)

DIQXANE LITERATURE5 9 N2 04 -N02 LITERATURE6 0 '6 1 COMBINED GAS MICRONS MICRONS MICRONS MICRONS MICRONS

7:.980(st.) 7.968 -8 .0 l0 (st.) 8.838(v.s.) 8.826(v.s.) 8.830(st.) 9.221(v.w.) 9.225(st.) 9.405(w.) 9.390 9.407(v.w.) 9.442(w.)(filter) 9.432(v.w.) 9.505(med.) 9.506(st.) 9.506(w.) 11.149(v.w.) 11.175(v.w.) 11.254(st.) 11.293(v.w.) 11.3l0(v.w.) 11.358(w.) 11.330(v.s.) 11.249(v.s.) 11.360(st.) 11.364(v.s.) 11.390(v.w.) 11.605(v.v/.) 11.851(w.) 11.850(v.w.) 11.968(v.w.) 11.962(v.w.) 12.113(w.) 12,107(w.) 12.380(w.) 12.379(w.) 12.650(med.) 12.648(w.) 13.375(v.s.) 13.298(st.);13.30 13.375(v.s.) 14.046(w.) 14.040(w.) 14.568(w.) 14.561(w.) 14.640(v.w.) 14.649(v.w.) 14.8l7(w.) 14.805(v.w.) 15.Ql9(v.w.) 15.0l3(v.w.) 76 peaks occurring in the spectra of the individual gases do not appear in the combined gas spectra because of the masking effect of very strong bands. The combined gas spectrum is not quantitative since there was some condensation in the reservoir of the dioxane absorption cell after the N2 O4 had been distilled into it. However the condensate remained in the reservoir and there was no observable condensate on the windows of the absorption cell. d. Discussion and Conclusions

The qualitative observations on the gas phase system indicate that an oxidation-reduction reaction occurs with the production o f N2 O3 . However, during the first twenty minutes of both the qualitative and quantitative obser­ vations no appreciable reaction of any type was detectable. If it is assumed that the addition reaction is rapid as compared to the oxidation-reduction reaction the conclusion that no detectable addition takes place is a valid one. If, however, the rate of the addition reaction is of the same order of magnitude as the oxidation-reduction reaction, the addition reaction in this system would be obscured by the onset of the oxidation-reduction. Assuming that no detectable addition takes place it is possible to calculate a maximum equilibrium constant for the reaction 77

N204 + 0 (CH2CHg )20 ^ — 0 (CHgC^)gO»N204 (B)

The instrument cannot detect less than a 1$ change in the

NOg concentration. Using the data in Table V and as­

suming a 1% change in NC>2 concentration,

N a 4. 29.84 x 10~4 ■+- 5.6 x lo”4 dioxane 2.569xlo“2 4 - 6.088 x 1 0

= 29.85 x 10“ 4

= 2.984 x lO"-5 - 2.983 x 10“ 3 = ^dioxane «H2 0 4

1 x 1 0 " 6

(ll.lxlO- 4 )2 n _ 5 N ■ i L- = 4.796 x 10” 3 n 2°4 2.569x10

Then

^dioxane«U2 0 4 _ 1 x lo"^______

^ ^^2 ^ 4 X ^i°xane (4.796x10 3) ( 2 .983x10

~ 7.0 liters/mole

This corresponds to no more than 2.0^ association of N2 O4 with dioxane. It is, therefore, possible that some

addition could have occurred under the conditions of the

experiment without being detected.

The infrared spectrum of the combined gases shows no

new absorption bands or significant shifts of bands when

compared to the spectra of the individual components.

Thus these experiments confirm the conclusion of the 78 colorimetric determination that no significant association

occurs in the gas phase under the experimental conditions employed. It is difficult to estimate the maximum amount

of the addition compound which could be detected since

the detectability depends on the intensity of absorption

of the compound. Assuming that it is possible to detect

one part per million of the addition product, an

association corresponding to approximately one tenth of

one per cent of the W2 O4 present would have been observed.

It is possible that the addition compound, if it were

formed, would absorb at some wave length other than

those investigated in this experiment. However, Rubin,

Sisler and Shechter-*- found lines at 1678 cm-'*', 1408 cm-'*'

and 8 2 1 cm--*- in the infrared spectrum of the solid com­ pound which they believed to result from bonds formed

between dinitrogen tetroxide and dioxane. The wave

lengths corresponding to these wave numbers fall within

the range of wave lengths reported here.

VI. SUMMARY AND DISCUSSION In order to obtain information which can be used to

resolve the question of structure of the 1 ; 1 addition

compound'*' formed by 1,4-dioxane and dinitrogen tetroxide,

viscosity and cryoscopic measurements were made on the binary system. The plot of viscosity versus mole per cent

of dinitrogen tetroxide shows a slight maximum at about 79 17 mole per cent of dinitrogen tetroxide. This maximum is probably the result of association of the two com­ ponents in the liquid phase, but is not of sufficient magnitude to Indicate the existence of polymeric

aggregation in solution. The cryoscopic data presented confirm the conclusion

that the addition compound is not polymeric in solution, and are interpreted as indicating that the compound is monomeric under the experimental conditions employed in the investigation. Although the conclusions drawn from the viscosity and cryoscopic studies apply strictly to solutions, there is no apparent reason to doubt that they

may also be applied to the solid state. Any structure proposed for the compound dinitrogen

tetroxide - 1,4-dioxane must be compatible with the fact

that (1 ) the viscosity of mixtures of the two components indicates the absence of polymeric aggregates in

solution, and that (2 ) cryoscopic measurements on

solutions of dinitrogen tetroxide in 1,4-dioxane indicate only monomers are present in dilute solutions. Also the

structure must be compatible with facts established by previous research that (1) 1,4-dioxane forms a stable

1 * 1 addition compound with dinitrogen tetroxide, tetra

■i hydropyran does not form such a compound . (2) Tetra-

hydropyran forms a stable 2 ; 1 addition compound with 80 dinitrogen tetroxide, 1,4-dioxane does not form such a compound^. (3) Ho stable ternary compound was formed in the system 1,4-dioxane - tetrahydropyran - dinitrogen tetroxide^. (4) The compound formed by dinitrogen tetroxide and 1,4-dioxane melts higher and is more stable than similar compounds formed by other ethers. The most reasonable structure of those proposed which is compatible with the facts presented above is the bicyclic structure involving the "boat” form of 1,4- dioxane coordinating as a bidentate group. The compatibility of the viscosity and cryoscopic data with this structure is obvious. The fact that 1,4- dioxane forms a 1 * 1 compound and not a 2 * 1 compound may be directly related to the enhanced stability of a bi­ dentate group as compared to two monodentate groups, and to the fact that in this structure all the orbitals of the nitrogen atoms are used in forming the bidentate structure. The fact that the geometrically similar ether tetrahydropyran forms no stable 1 ; 1 addition compound is probably due to the fact that tetrahydropyran is not a

"dibasic" ether and hence cannot act as a bidentate group. That no stable ternary compound was formed in the ternary system dioxane - tetrahydropyran - dinitrogen tetroxide is probably due to the great stability of the dioxane complex and to the fact that there are no bonding 81 orbitals available on the nitrogen atoms for coordination with tetrahydropyran. The high melting point of the 1,4- dioxane - dinitrogen tetroxide compound is compatible with the observation that other bicyclic substances have high melting points e.g. camphor. The enhanced stability of the dioxane addition compound may be related to the bidentate structure using the entropy effect. Calvin has pointed out the significance of the entropy change in the formation of chelates in comparing the following reactions:

Ni(H2 0 ) ^ 2 ■+ 6 NH3 (aq) ^ ■.-->Ni(MH5 )6 * 2 + XH2 O A H = -19 kcal. A S = -22 cal/deg.

l\ri(H2 0 ) x + 2 + 3 en(aq)^. ~^ Ni(en)-J- xH20 A H ■ -25 kcal. A S = +2 cal./deg.

By combination of these two reactions a direct comparison was possible;

Ni(NH3 )6 + 2 Hr 3 en(aq)^=^Ni(en ) 3 ’+2 +- 6 NH 3 (aq)

A H s - 6 kcal. AS - +24 cal./deg.

Here 11 en" represents one molecule of ethylene diamine. The values of A H and AS indicate that heat and entropy effects contribute about equally to the free energy change for the reaction. The difference in heat content is due primarily to a difference in the Ni-N bond energy in the complex and in the chelate. The entropy increase may be 82 +2 due partly to the fact that the Ni(en)g may have a somewhat greater entropy than NiCNHgJg^ because of its greater size, but the major increase is probably due.-to the other species involved and particularly the fact that there are three more particles on the right side of the reaction than there are on the left. Thus the greater part of the entropy increase may be directly related to the formation of chelate rings.

Taylor®^ has suggested that if the 1,4-dioxane molecule exists in the "boat" form a lateral projection of the carbon-oxygen skeleton will be approximately as shown below.

^ - 2 superimposed carbon atoms

1 oxygen atom

1 nitrogen atom

© - 2 superimposed oxygen atoms The two "lone pairs" of electrons on each of the oxygen atoms in 1,4-dioxane occupy directed orbitals which make approximately tetrahedral angles with the two bonding orbitals on each oxygen. Prom the oxygen to oxygen dis­ tance in the 1,4-dioxane molecule and the_orientation of the orbitals containing "lone pairs” it seems reasonable that these orbitals can form bonds with the 11 pi" orbitals of the nitrogen atoms in the dinitrogen tetroxide molecule. Any incompatibility in the n-N and 0-0 dis­ tances can be reduced and the overlap increased if some rehybridization occurs at the nitrogen atoms*

Hybridized s p orbitals on N atom With respect to the bidentate coordinating concept for the dioxane molecule, the geometrical arrangement of the "chair" form of the molecule is much less favorable than the "boat" form. In the "chair" form the oxygen to oxygen distance is greatly increased, and the orientation of the lone pairs is very unfavorable: 84 Hence it appears that the 1,4-dioxane in the coordination

compound is in the boat configuration, even though

electron diffraction data®^*®^*®® indicate that the nchair" form is more stable in the isolated molecule.

In cyclohexane, the "boat" form probably has an

energy about 6 kcal. (twice the 5 kcal. barrier for ro­ tation about a carbon to carbon single bond) higher than

the "chair" form. It seems reasonable that in 1,4-

dioxane essentially the same factors operate with the

"boat" form approximately 6 kcal. higher in energy than

the "chair" form for the isolated molecule, making the

"chair" form the only form present to any degree. However, it seems probable that in the formation of the

addition compound the "chair" form is converted to the

"boat" form. This would require only a small bonding

energy for the coordination bonds to overcome the 6 kcal.

favoring the "chair" form in the isolated molecule. The fact that little or no association takes place in a gaseous mixture of 1,4-dioxane and dinitrogen tetroxide has been established by colorimetric and infrared spectroscopy techniques. A maximum equilibrium constant for the reaction

OCCHgCHjJgOjg, + MS°4(S)V •>0(CHsCHg )g0-Mg04(s)

has been calculated to be 7.0 liters/mole from the colori­ metric determination. This corresponds to more than two 85 per cent association of the dinitrogen tetroxide with

1,4-dioxane. The infrared absorption spectrum of the combined gas failed to reveal any new absorption bands or significant shifts in bands. Assuming that it would be possible to detect one part per million of the addition compound, if it were formed, an association corresponding to approxi­ mately one tenth of one per cent of the W2 O4 present would have been observed. This, of course, indicates that little or no association of dinitrogen tetroxide and 1,4-dioxane takes place in the vapor phase. 86

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AUTOBIOGRAPHY I, Harry Wilson Ling, was born in painesville, Ohio,

February 14, 1927. I received my secondary school education in the public school of the village of. Van

Buren, Ohio. My undergraduate training was obtained at

Bowling Green State University, Bowling Green, Ohio,

from which I received the degree Bachelor of Arts in

June, 1950. In September, 1950 I accepted a graduate assistantship in the Department of Chemistry at The Ohio

State university. I held this position until September, 1951 at which time I received an appointment of assistant instructor in the Department of Chemistry at The Ohio State University. In June, 1952 I accepted a position as a Research Fellow at The Ohio State

University until October, 1953 at which time I accepted the Standard Oil Company (Indiana) fellowship. I held this position until June, 1954 when I received an appointment as a research assistant in the Department of

Chemistry. I held this position while completing the requirements for the degree Doctor of philosophy.