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BEKNDT, Donald Carl, 1935- THE KINETICS AND MECHANISM OF THE REAC TION OF HYDRAZOIC ACID WITH SUBSTITUTED NAPHTHOIC ACIDS.
The Ohio State University, Ph.D., 1961 Chemistry, organic
University Microfilms, Inc., Ann Arbor, Michigan THE KINETICS AND MECHANISM OF THE REACTION' OF HYDRAZOIC
ACID WITH SUBSTITUTED NAPHTHOIC ACIDS
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University
By
Donald Carl Berndt, B. Sc.
******
The Ohio State University 1961
Approved by
idviser Department of Chemistry ' ACKNOWLEDGMENTS
The author wishes to thank Professor Harold Shechter for his suggestion of this investigation, for his encour agement and guidance during the course of this study, and for his aid in the preparation of the manuscript.
The author is grateful to the Mershon fellowship fund and the Chemistry Department of The Ohio State
University and to the National Science Foundation for fellowship funds. He is also grateful to the members of the staff and fellow graduate students for informa tion and for the use of chemicals and apparatus.
i i CONTENTS P^ge
I, Introduction ...... 1
Statement of Problem ...... 1
Historical Aspects ...... 3
II. Discussion of Results ...... 12
Kinetic Order of the Schmidt Reaction . . 12
Proximity Effects ...... 12
Electrical Effects ...... l6
In terp retatio n of Reaction Mechanism . . . 19
Relationship between Schmidt and Gurtius R eactions ...... 24-
III. Experimental ...... 27
Syntheses of Naphthoic Acids ...... 27
Reaction of Naphthoic Acids with Hydrazoic A cid ...... 35
Solvents for Kinetic Determinations . . . 42
Stability of Naphthoic Acids in Sulfuric A cid ...... 4-2
Kinetic Rrocedure ...... 44
Calculations ...... 46
Determination of DissociationConstants . . 53
IV. A ppendix ...... 55
Autobiography ...... 60
i i i Illustrations
Table Page
1. Relative Rates of Schmidt Reactions of Substituted Benzoic àcids in Excess 95.8% Sulfuric A cid ...... 6
2. Average Rate Constants for Reaction of Naphthoic Acids with Hydrazoic Acid . . 13
3. Relative Rates of Reaction at 0° of Substituted Naphthoic and Benzoic Acids with Hydrazoic Acid ...... 15
4. Dissociation Constants of Conjugate Acids, and Free Energies of Activation of 1-Naphthoic and 8-Chloro-l-naphthoic A c i d s ...... 22
5. S ta b ility Data for 1-Naphthoic and 2-M ethyl-l-naphthoic Acids in Sulfuric A cid ...... 43
6. Analytical Wave Lengths for Kinetic Determinations . 45
7. Rate Constants and Activation Para meters for Schmidt Reactions of Naphthoic Acids ...... •...... 48
8. Spectrophotometric Data for Determination of pKgH+ ...... 54
9-17. Typical Kinetic Data for the Schmidt Reaction of Naphthoic A c i d s ...... ' ...... 55-59
Figure
1. Graph of Kinetic Data for Schmidt Reaction of 1-Naphthoic Acid ...... 50
2. Graph of Kinetic Data for Schmidt Reaction of 9-Chloro-l-naphthoic A c i d ...... 51
3. Activation Energy Plots ...... 52
iv I. Introduction
Statement of Problem
Reaction of a carboxylic acid with hydrazoic acid
(the Schmidt reaction) in the presence of sulfuric acid yields the corresponding amine, nitrogen and carbon dioxide (Equation 1).
RCOOH + HN3 > RNHg + CO2 + Ng (1)
Schmidt reactions in concentrated sulfuric acid of
^-substituted phthallc acids (l), ^-substituted isophtha-
■ (1 ) H. R. Barkemeyer, M. Sc. thesis, The Ohio State University, 1952. lie acids (2 ), 2 -substituted terephthalic acids ( 2 ), and
(2 ) T. Moritsugu, Ph.D. d issertatio n . The Ohio State University, 1954.
2 , 6-disubstituted terephthalic acids ( 2 , 3 ) occur exclus-
(3 ) M. S. Newman and H. L. Gildenhorn, J. Am. Chera. 8 0 c., 10, 317 (1 9 4 8). ively at the sterically hindered carboxyl group to give the corresponding amino acids. 3-Araino-phthalic, anthra- nilic and jg-aminobenzoic acids do not react with hydrazoic acid however in concentrated sulfuric acid (l). 2
Presumably the electrical effect of the ammonium group is responsible for this result. 1,2- and 1,6-Naphthalic acids (2) yield amino acids derived from exclusive reac tion of the 1-carboxyl group (Equation 2).
HOOC—ks * « 3 HOOcJ O U * * "2
The kinetics of Schmidt reactions of substituted benzoic acids in excess 95.8% sulfuric acid are first order with respect to the benzoic acid and to hydrazoic acid (4 ). Electronegative or electropositive substitu
er) M. E. D. Hillman, Ph.D. d isse rta tio n . The Ohio State U niversity, 1958. ents (with the exception of fluoro and carboxyl) in the ortho position increase the rate of reaction.with respect to benzoic acid. & study of the Schmidt reaction of toluic acid in sulfuric acid over a concentration range of 7 4 .3 - 98% indicates that the activity of water in the rate-controlling transition state is low ( 4 ).
k kinetic study of reactions of hydrazoic acid with
1-naphthoic acid and its 2- and 8-substituted derivatives,
4-bromo-'l-naphthoic acid, and 2-naphthoic acid was undertaken in order to determine the relative electrical and steric effects of ortho and oeri substituents on the
Schmidt reaction and to provide data on the relative re activity of naphthalene and benzenoid systems. 3 The predominant form of a carboxylic acid dissolved in concentrated sulfuric acid is usually the dihydroxy- cerbonium ion (5), RCfOH)^. In order to determine the
(5) H. Stewart and K. Yates, J. Am. Chem. Soc., 8g, 4059 (I960). effect of different extents of protonation of the carboxy- lic acids on the rates of Schmidt reactions^ dissociation + constants of the species RCOgHg in sulfuric acid were de termined .
Historical aspects
The reactions of hydrazoic acid with carbonyl com
pounds in the presence of strong mineral acids as catalysts
have been named Schmidt reactions. kldehydea give nitriles
and formyl derivatives of amines, and ketones give amides.
Carboxylic acids yield amines with one less carbon atom,
carbon dioxide, and nitrogen; an isocyanate, subsequently
hydrolyzed, is presumed to be an intermediate (Equation 3).
RCOOH + HN^ ----- Hg + RHGO RNH2+ COg (3)
Caronna obtained 3 -n itro isa to ic anhydride (l) from the
Schmidt reaction of 3-nitrophthalic acid (6). 4-Pb8nan-
do )0
NOg “ I
(6) G. Caronna, Gazz. chira. i t a l . , 21, 475 (1941); C. A., 21, 118 (1943) . 4 thryl isocyanate was isolated (7) from a Schmidt reaction
(7 ) K, F. Rutherford and M. S. Newman, J. Am. Chera. Soc., 22, 213 (1957).
of 4-phenanthrenecarboxylic acid with a mixture of tri-
-ijf' fluoroacetic acid anhydride and trifluoroacetic acid as
solvent and ca ta ly st. Wolff has reviewed the scope of
the Schmidt reaction (8). Hillman has summarized in
(8) H. Wolff in Adams Organic R eactions, Vol. I l l , John Wiley & Sons, Inc., New York, N. Y., 1946, pp. 307- 336.
d e ta il the mechanisms proposed for Schmidt reactions of
carboxylic acids ( 4 )•
Perhaps the most striking aspect of the Schmidt re
action of substituted aromatic dicarboxylic acids is that
the reaction occurs exclusively at the more "sterically
hindered" carboxyl group (1-4) • Newman and Gildenhorn
(3 ) found that 2,6-dimethylterephthalic acid reacted with
one equivalent of hydrazoic acid exclusively at the hin
dered carboxyl group (Equation 4 ). On the basis of the GOGH IÜI2
^3°|rS^^3 + HN 3 ^3°|fj~^^3 + Ng + GO2 ( 4 )
GOOH COOH
similarity of this reaction to the estérification of mesi-
toic acid in sulfuric acid they proposed the following
mechanism for the Schmidt reaction of hindered acids (Equations 5-7):
RCOOH RC(0H)2 hC = 0 + HgO (5)
jj) R&=0 + HN------> EGN-N5N (6 ) 3 H 0 RGN-NSN ------> RNC=0 + ----RHH^ + GOg (7)
The function of the sulfuric acid is to convert the
hindered carboxyl group to an oxocarbonium ion. Loss
of nitrogen from the protonated acyl azide produces an
unstable imino derivative which undergoes rearrangement
and subsequent hydrolysis. The authors also pointed out
that dihydroxycarbonium ions may react in a similar
manner (Equations 8,9): OH HgSOv . HN-3 ' + RCOOH RC(0H)2 — HO-y-y-H=M (8 ) R H
HO-Ç-]jI-N=N ------> RNh5(0H) + N2 KNH3 + GO2 (9) R H Because of the accelerative influences of proximal
groups in Schmidt reactions, Hillman ( 4 ) studied the
rates of Schmidt reactions of ortho- . meta-, and oara-
substituted benzoic acids. Table 1 contains the relative
rates determined in excess 95.8% sulfuric acid. The
kinetics are second order, first order in the substituted
benzoic acid and first order in hydrazoic acid (the de
composition of hydrazoic acid in sulfuric acid was first Table 1
Relative Rates of Schmidt Reactions of Substituted Benzoic Acids in Excess 95.8^ Sulfuric Acid
Substituent Relative Rate,^ Q°
None 1 û-methyl 300 ethyl 753 2 -isopropyl 2,260 o-tert-butvl 15,900
2 ,5-dimethyl 388 2,A-dimethyl 358 2 ,3-dimethyl 2,310 2,6-dimethyl 28,900 2,A,6-trimethyl 117,000
.2-f luoro 0.659 o-chloro 28.8 _o-br omo 60.2 2 -iodo 295 a -n itro 5.94
a-carboxyl 0.222 a-methyl 1.73 £ - methyl 1.53 m-tert-butvl 2.17 p-tert-butvl 1.60
a-fluoro 0.220 j2-f luoro 0.399 a-chloro 0.220 j2-chloro . 0.407 a-bromo 0.197
a-raethoxy 0.252
® For compounds not studied at 0°, rate constants were calculated from the equation;. -AH* -RT- 7 order and slow enough not to interfere with the kinetic measurements of the substituted benzoic acids).
The dramatic effect of proximal groups is readily apparent from Table 1. Electronegative and electroposi tive groups in the ortho position with the exception of fluorine and carboxyl (minor deceleration) increase the rates of reaction with respect to benzoic acid. The im portance of proximity effects can be seen from the fact that the maximum relative rate ratio in meta and nara compounds studied is only 11 (m-t e r t -b u tv l- and jji-bromo- benzoic acids), whereas the maximum relative rate ratio for the ortho compounds is 71,600 (o-tert-butvl- and
^-carboxybenzoic acids); di-ortho-substituted compounds show even greater e ffe c ts . These proximity e ffe c ts were interpreted as being primarily steric effects (4): There appears to be a qualitative correlation between the rate constants and the effective sizes of the groups in the ortho-halo and ortho-alkvl derivatives, respectively; the greater reactivity of 2,3-dimethylbenzoic acid than of 2,5-dimethylbenzoic acid is indicative of steric in fluences arising from buttressing effects,
k Hammett plot for the meta- and para-substituted benzoic acids ( 4 .) (jn-methoxybenzoic acid was not included because it deviated considerably from the linear relation ship) gave a value of -1,538 i 0,094 for ^ ; the correlation coefficient was 0 , 9 6 4. In the meta- and para-su b stitu ted 8 benzoic acids, electron-donating groups accelerate and electron-withdrawing groups decelerate the Schmidt re action relative to benzoic acid. It is to be noted that
the steric effects of the substituent groups are much larger than their electrical effects (see Table l).
A c rite rio n for uniform ity of mechanism of a series
of compounds is the existence of a linear relationship between the enthalpy and entropy of activation for the
series (9). In the study of substituted benzoic acids,
(9) J. E. L effler, J. Org. Ghem., 20, 1202 (1955).
no simple correlation resulted, rather three or four
separate "straight lines" were discernible (4). The
obtainment of these several correlations was interpreted
on the basis th a t the overall mechanism for a ll the com
pounds is the same and th a t the requirements for the
in i tia l and tra n sitio n sta te s of each series of compounds,
ie., those compounds correlated by one of the straight
lines of the enthalpy-entropy plot, are slightly differ
ent from the requirements of the initial and transition
states for the other series.
In order to learn the effect of sulfuric acid upon
the Schmidt reaction of carboxylic acids, the kinetics
of ü-toluic acid were studied at 2 4 .3 ° over a concentra
tion range of 71.6 - 97^ sulfuric acid ( 4 ). A satisfactory 9
Cq (sometimes named ) correlation (lO) was obtained
(lO) Cg is a measure of the ability of the solvent to convert an alcohol to its corresponding carbonium ion. See N. G. Deno, J. Jaruzelski, and à. Schreisheim, J. &m. Chem. Soc., 21, 3044 (1955). when the extent of mono- and di-protonation of hydrazoic acid and the extent of protonation of jo-toluic acid were considered (11) . The correlation was derived on the basis
(ll) (a) An assumed value of -7.6 for pKgy+ for &- toluic acid gave the best correlation. Subsequently Stewart and Yates (5) reported a value of -7.4. (b) A determ ination by a somewhat d ifferen t method by H. Stewart et al.. private communication, gave a value of -7.12. The Gg correlation is essentially unchanged if the ex perimental values are substituted for the assumed value of -7.6. that unprotonated hydrazoic acid reacts with oxocarbonium ion and decomposition of the resulting protonated acyl- azide is the rate-determining step.
h'illraan gives two mechanisms which are consistent with the observed kinetic order and 0^ correlation; they
involve rate-determ ining (l) reaction of oxocarbomium
ion with hydrazoic acid or (2) decomposition of protonated
benzazide (Equations 10 - 14):
lOOHg fa st ( 10) •fast
GOOHj'^ G^o
(11) 10
slow. + HN, products (1 2 )
0£
:0NH-N2
+ HN^ fa st (13) ^ f a s t + ONH-Ng G slow products (14)
The second mechanism (rate-determ ining decomposition of protonated benzazide) was preferred for several reasons:
(l) If reaction of oxocarbonium ion with hydrazoic acid were the rate-determining step, the transition state (II) could (a) involve minimal interaction with hydrazoic acid
0=C— NH,
II or (b) involve fairly complete bond formation between hydrazoic acid and oxocarbonium ion. In case (a) resonance effects are expected to be more important in the transition state than in the initial state (dihydroxycarbonium ion) and therefore positive deviations from a Hammett ^plot for (]■+ substituents would be expected - negative deviations were observed, however. In case (b) the electrical demand from a ja- or ^-substituent in the transition state should exhibit a positive value for - the observed value is negative; furthermore, the observed steric acceleration of proximal groups would not be expected. (2) The 11 entropies of activation are quite favorable (-6.0 to
+2.8 e. u.). A bimolecular reaction between dihydroxy carbonium ion and hydrazoic acid would be expected to show an unfavorable entropy of activation. The loss of water in the formation of oxocarbonium ion and the loss of nitrogen in a rate-determining decomposition of pro tonated azide are favorable entropy steps; thus the pro posed mechanism is consistent with the observed entropies of activ atio n . (3) Addition of a chloroform solution of benzazide to concentrated sulfuric acid gave fair yields of benzoic acid. The mechanism is proved by application of the principle of microscopic reversibility if it is assumed th a t protonated benzazide is an interm ediate in the Schmidt reaction and that direct protonation of benz azide leads to a species identical with that occurring as a Schmidt reaction interm ediate.
Newman and Gildenhorn (3) pointed out the similarity between the Schmidt and Gurtius reactions and predicted that the Gurtius reaction should be acid catalyzed if the same or a similar intermediate, RG0^HN2 , is involved in both reactions. Subsequent to Hillman's study, an investigation of the Gurtius rearrangement of ortho- substituted benzazides was made. A discussion of these resu lts and th e ir bearing on the mechanism of the Schmidt reaction w ill be deferred to part II of th is th e sis. II. Discussion of Results
Kinetic Order of the Schmidt Reaction
The rates of the Schmidt reactions of the naphthoic
acids were determined in excess 93.4# sulfuric acid and
in excess sulfuric-phosphoric acid. It was necessary to
use su lfu ric acid diluted with phosphoric acid as the
solvent for the kinetic measurements of certain naphthoic
acids which are not stable in concentrated sulfuric acid.
The composition of the sulfuric-phosphoric acid solvent
mixture and the stability of the various naphthoic acids
in concentrated sulfuric acid are described in part III.
The kinetic order in excess solvent for the Schmidt re
action of the naphthoic acids was second order, first
order with respect to the naphthoic acid and first order
with respect to hydrazoic acid. The same kinetic order
was obtained for substituted benzoic acids ( 4 ). The re
sults are accomodated by and will be discussed in terms
of the mechanism proposed for the Schmidt reaction of
substituted benzoic acids (see part I). In th is mechan
ism decomposition of protonated acylazide is rate-
.determining.
Proximity Effects
The rate constants obtained for the naphthoic acids
are summarized in Table 2. (A complete list of the ex
perimentally determined rate constants is found in
12 Table 2 Average Rate Constants (liters mole“^in.~^) for Reciction of ilaphthoic Acids with Hydrazoic Acid
Solvent : 93 »h% Sulf uric Acid
Temperature Reli tiv e k c a l. c a l . Acid - 10. 7* 0° 10° 25° Rates, 0° mole deg.-m ole 1-naphthoic 0.737 1.96 8 .U9 1.00 15.3 - 1 1 .1 2-chloro—1- naphthoic O.I3I 0.195 1.76 0.672 17.9 - 2.28 8-chloro-l- naphthoic 3.66 9.29 LL .L L .97 15. L - 7.60 8-bromo-l- naphthoic it .12 5.59 8—iodo—1— naphthoic 6.38 8.66 h-bromo—1— naphthoic L .90
Solvent: Sulfuric-Phosphoric Acid
Acid Temperature Relative Rates 0° 30° 0° .
1-naphthoic 0 ,306 11.0 1.00 2-naphthoic 0.0557 (0 .00506)2 2-methyl-l-naphthoic 9.18 30.0 8-methyl-l-naphthoic 2 .Sit. 9.28 8 -c h lo ro -l-n a p h th o ic 1 ,2ii it .05 a At 3 0 0. H Vo 14 Table 7, part III.) All substituents studied (12)
(l2) The study of the Schmidt reaction of 2-sub stitute d-l-na phthoic acids was limited because of the relative instability of 2-substituted-l-naphthoic acids in concentrated sulfuric acid. Kinetic measurements of the reaction of 8-nitro-l-naphthoic acid with hydrazoic acid in concentrated sulfuric acid showed that 8-nitro- 1-naphthoic acid reacts several times slower than does 1-naphthoic acid. Since little or no product could be isolated from several attempted Schmidt reactions of 8-nitro-l-naphthoic acid (details are in part III), it is not certain that the rates determined for this com pound are the rates of the Schmidt reaction.
(with the exception of 2-chloro which gives slight de celeration) in the 2- or 8-positions of 1-naphthoic acid accelerate the rate with respect to 1-naphthoic acid.
1-Naphthoic acid reacts 197 times faster than does 2- naphthoic acid in excess sulfuric-phosphoric acid at 30°,
This indicates the marked effect of a fused ring when adjacent to a carboxyl group. In Table 3 relative rates of reaction of substituted naphthoic and benzoic acids are compared, 1-Naphthoic, 2-methyl-l-naphthoic, and 8-methyl- l-naphthoic acids react faster than do 2-methylbenzoic,
2,6-dimethylbenzoic and 2-tert-butvlbenzoic acids, respec tively, Qualitatively, the steric effect of a fused aromatic ring ortho to a function is considered to be similar to that of an ortho methyl group and the steric effect of a fused aromatic ring containing a methyl group in the adjacent oeri position similar to the effect of an ortho-tert-butvl group (13), The effect of the fused 15
Table 3
Relative Rates of Reaction at 0° of Substituted Naphthoic and Benzoic Acids with Hydrazoic Acid
Acid Relative Rates benzoic 1.00®
2-methylbenzoic 300®
2-tert-butvlbenzoic 15,900®
2,6-dimethylbenzoic 28,900®
1-naphthoic 1,750^
2-naphthoic (8.89)°*^
2-methyl-l-naphthoic 52,500®
8-m ethyl-l-naphthoic 16,300®
(a) From re f. 4. (b) Calculated assuming th a t the difference between 95.8;A and 93 «4/^ sulfuric acid on the rates of reaction is negligible. 2-Methyl- benzoic acid reacts 1 . 64 - times faster in 95.8$6 than in 89.2jo sulfuric acid at 24.3°, ref. 4. (c ) Calcu lated from the value for 1-naphthoic acid and the values in Table 2 assuming that the relative rates of reaction are the same with concentrated sulfuric acid and sulfuric-phosphoric acid serving as solvents and catalysts. (d) Calculated by assuming that the temperature dependence of the rate of reaction of 2-naphthoic acid is the same as that of 1-naphthoic ac id . 16
(13) M. S. Newman and W. H. Powell, J. Org. Chem., 26, 812 (1961). ring of 1-naphthoic acids on the reactivity of these com pounds in the Schmidt reaction is not entirely a s teric effect however (see E lectrical Effects below).
Proximity effects in the 1-naphthoic acid system are thus quite large and appear to be the combined effect of the adjacent fused ring and the ortho or peri substituent.
The proximity effect is considered to be primarily a steric effect. The kinetic effect of a substituent in the peri position (except methyl) is greater than that in the ortho position. All the 8-halo substituted com pounds react faster than does 1-naphthoic acid and the rates of these compounds increase in'the order of the size of the 8-halo substituents.
Electrical Effects
By referring to Table 2, it is seen that chlorine
in the 2-position decreases the rate of reaction with respect to this substituent in the 8-position; the re verse is true for a methyl group. Furthermore 8-methyl- l-naphthoic acid reacts faster than any of the 8-halo-
1-naphthoic acids (it is assumed that the relative rates
are the same in 93.4$ sulfuric acid and sulfuric-phosphoric
acid). The entropies and enthalpies of activation for 17
1-naphtholc, 2-chloro- and 8-chloro-l-naphthoic acids are contained in Table 2, These resu lts are consistent with the operation of an electrical effect, the effect being less in the peri position than in the ortho posi tion. It appears, then, that in addition to their proximity effects, election-donating groups accelerate and electron-withdrawing groups decelerate Schmidt re actions. Thus in the Schmidt reaction 2-methyl-l-naph thoic acid reacts faster than does 8-methyl-l-naphthoic acid and 2-chloro-l-naphthoic acid reacts slightly slower than does 1-naphthoic acid.
The relative importance of electrical and steric ef fects upon the Schmidt reactio n of 8 -s u b stitu te d -l- naphthoic acids may be estimated in the following manner:
Taft (14 ) has derived a parameter which measures the
(14 ) R. W. Taft, Jr., in Newman, Steric Effects in Organic Chemistry. John Wiley & Sons, Inc., New York, N. Y ., 1956, p. 597. steric effect of substituent groups. ortho-Methvl and bromo groups have the same steric effect in acidic hy drolysis of ortho-substituted benzoates. If this result is applicable to the Schmidt reaction of 8-substituted-
1-naphthoic acids, the steric effects of the 8-methyl and 8-bromo groups may be taken as the same. Any d iffe r ences in rates, then, between 8-methyl-l-naphthoic and
8-bromo-l-naphthoic acids can be attributed to non-steric 18 effects (polar effects). 8-Methyl-l-naphthoic acid reacts
1.66 times faster than does 8-bromo-l-naphthoic acid at
0°. The difference in polar effects between methyl and bromo groups is ordinarily considerable, yet in the 8-
substituted-l-naphthole acids undergoing the Schmidt reaction, the difference in the effects of the 8-methyl and 8-bromo groups is small compared to the to ta l effe c t
of the substituent upon the rate relative to unsubstituted
1-naphthoic acid. It may be concluded, therefore, that
the e ffe c t of the 8-substituents upon the Schmidt reac
tion of 8-substituted-l-naphthoic acids is primarily
steric although the polar effect is not negligible.
In order to ascertain the importance of electrical
effects in the absence of steric influences, the rate of
reaction of 4-bromo-l-naphthoic acid was determined. U-
Bromo-l-naphthoic acid reacts 0.577 times as fast as 1-
naphthoic acid at 25° in 93.4% sulfuric acid as solvent
and catalyst. The effect is neither large nor negligible.
2-Naphthoic acid reacts faster than does benzoic acid
(Table 3). It is believed that this difference in rates
is observed primarily because the contributions of the
electronic systems of the benzene and naphthalene nuclei
are not identical in the rate-determining step. The
sigma constant for a 3,4-benzo substituent based on the
ionization constants of 2-naphthoic and benzoic acids (15) 19
(15) D. H, McDaniel and H. C. Brown, J. Org. Chem., Zl, 42 0 (1958). is 0 . 04.2 . Thus relative to phenyl, a 3,4-benzo substituent is electron-withdrawing on the basis of its sigma value.
The 3,4-benzo group increases the rate of reaction of the Schmidt reaction relative to benzoic acid, however.
Consequently the 3, 4 -benzo group is behaving as an electron- donor in the Schmidt reaction. k naphthyl group can ac comodate a positive charge better than a phenyl group.
The effect of steric inhibition of resonance will be discussed below.
Interpretation of Reaction Mechanism
The re s u lts of the present study of reaction of sub
stituted naphthoic acids and hydrazoic acid are accomodated by the mechanism proposed for the Schmidt reaction of sub
stituted benzoic acids (see part I). The step-wise
sequence is represented by Equations 15 - 18,
fa 81 + RCOOH + H+ " RC(OH). (15) ^ fa s t 2
R^(OH)^ RGO + HoO (16) 2 "^fast 0 RGO + HN- RCNHNg (17) ^ fa st
9 + RGNHN2 > products (18) 20
It is suggested that the rate-determining transi
tion state for the Schmidt reaction (decomposition of
protonated azide) be represented by III (Equation 19)
♦ 0=C—NH—N2 N2 NO OH + N. % <
o — > (19) III where the plane of the aryl nucleus (benzene or naph thalene) is out of the plane defined by the triangle in
III, The accelerative influences of electropositive and decelerative influences of electronegative substituents arise from the interaction of the aryl nucleus with the electron d e fic ie n t nitrogen atom - i t is assumed th at the electrical demand of the transition state is greater than that of the initial state (dihydroxycarbonium ion).
Two possible explanations, applicable separately or jointly, for the large accelerative proximity effects other than electrical effects are (l) relief of steric compression as the system passes from the initial state to the transition state and (2) steric inhibition of re sonance between the aryl nucleus and the carboxyl group in the initial state. The latter point will be expanded.
In meta- and para-substituted benzoic acids, benzoic acid, and in 2-naphthoic acid, the dihydroxycarbonium ion (the initial state) can attain coplanarity with the aryl nucleus and resonance between it and the aryl nucleus 21 is possible. In the transition state III (Equation 19), coplanarity is diminished and little or no resonance be tween the carbonyl and aryl groups is possible. Thus the initial state for non-hindered molecules is relatively resonance stabilized whereas the transition state is not
(in the sence of carbonyl-aryl interaction). In ortho- substituted benzoic acids and in all 1-naphthoic acids, this particular resonance interaction is diminished in the initial state by steric effects; therefore, there is less resonance stabilization of the type described in the initial state of sterically hindered acids than in non hindered acids, and little stabilization by this type of resonance in the transition state for either hindered or non-hindered acids.
Relative rates reflect differences between rate- controlling transition states and between initial states.
In order to investigate the difference between initial states in the Schmidt reaction of naphthoic acids, the pK's for reaction 20 for 1-naphthoic acid and 8-chloro-
1-naphthoic acid were determined in sulfuric acid. These values are reported in Table 4, along with other values to be used in the subsequent discussion,
R&(OH)p ... ^ RCOOH + (20) 22
Table 4
Dissociation Constants of Conjugate Acids, and Free Energies of Activation of 1-Naphthoic and 8-Chloro-l-naphthoic Acids
Acid pK, 2 5° Alt 2 5° #R&(0H)2
1-naphthoic -7.06® 18.6^ 97.5
8 -chior 0- 1- naphthoic -7.28 17.6^ 92.8
® Since these values were determined, another value for 1-naphthoic acid has been reported, -7.1 (lib).
In 93.4# sulfuric acid, 1-naphthoic acid and 8-chloro-
1-naphthoic acid exist predominantly in the form of dihydroxycarboniiim ion. The percentages of Table 4 were calculated by use of Equation 21. The difference between
log - pK (21) the standard free energy change for the two compounds, ahF°, for the reaction according to Equation 20 is 0.30 kcal./mole. The difference in free energies of activa
tion, is 0.9g kcal./mole. Thus if the pK's are
accurate measures of the difference between the initial
states with respect to electrical factors, it can be
concluded that this difference accounts for about one-
third of the observed difference in free energies of
activ atio n for these two compounds. An electro p o sitiv e
substituent supposedly would decrease K and consequently
lower the energy of the initial state with respect to 23 the unsubstituted acid. This would bring about a decrease in the rate; electropositive substituents increase the rate however. Hence the contribution of differences in the initial states to the differences in observed rates must be minor with respect to electrical effects (relief of steric strain in the hindered acids can be viewed as primarily a difference in energy between initial states).
It should be mentioned however that the conversion of a neutral compound to its conjugate acid is not the only factor effecting the solubility of that compound in sul furic acid although it is an important factor in the case of carboxylic acids (16). It is possible, then, that
(16) L. P. Hammett and R. P. Chapman, J. km. Chem. Soc., ii, 1282 (1934). the relative energies of the initial states reflect fac tors other than steric effects and extents of protonation; these factors are expected to be small however.
Finally attention should be drawn to the fact that the observed rate constants and entropies and enthalpies of activation are functions of all the processes outlined in Equations 15 - 18, and that the initial and transition states for a series of compounds undergoing a given re action are expected to be similar but not identical from compound to compound. 24 R elationship Between Schmidt and Curtlua Reactions
Newman and Glldenhorn (3) on the basis of th e ir proposed mechanism (see part I) for the Schmidt reaction pointed out that the Curtlus rearrangement should be acid catalyzed. This has been verified (17). The kinetics
(17) R. k. Coleman, M. S, Newman, and k. B. Garrett, J. Am. Chem. Soc., 2Â, 4534 (1954). of the thermal rearrangement of meta- and para-substituted benzazidas,in toluene have been reported (18a) Subsequent
(18) (a) Y. Yukawa and Y. Tsuno, J. Am. Chem. Soc., Z2, 5530 (1957); (b) ibid.. 80, 6346 (1958). to Hillman's ( 4 ) study of the Schmidt reactions of sub stituted benzoic acids, an investigation of the Curtlus rearrangement of ortho-substituted benzazides in toluene has been reported (l8b). The orthe-substituted benza zides reacted much faster than the me ta and para deriv atives. In the me ta position electropositive groups accelerated and electronegative groups decelerated the reaction. All para substituents, including para-methoxv and para-hvdroxy. decreased the rate of reaction. The acceleration observed with ja-substituents was attributed partially to relief of steric compression but primarily to steric inhibition of resonance, in the initial state, of the aryl residue with the carbonyl group. 25
Resonance forms for the azide are:
0 0 ^ 0" n ,, + .T M N + I + RG-N=N=N If R Is an aryl group, cross conjugation of the carbonyl group with the aryl nucleus leads to an increase in the double bond character of the N-N bond which must be broken (Equation 22) in order that the nitrogen may be lost. Thus the contribution of V to the structure of 0 _ GH30-^^-G-N=^= î( GHjS«=^^ =G-N=N=N (22) IV V meta- and para-substituted benzazides lowers the energy of the initial state. Steric inhibition of this resonance in the ortho derivatives prevents this de crease in energy of the initial state, i.e., the acti vation energy for the ortho derivatives is lower than that for the other derivatives. The rates of the Curtius reaction of several meta- and para-substituted benzazides in several solvent systems (acetic-sulfuric (20# vol.) acid, aqueous (20# vol.) acetic acid, acetic acid containing lithium chlor ide (0 .25M); acetic acid, acetic anhydride, toluene) have been determined (17,19). The order of substituent (19) Y. Yukawa and Y. Tsuno, J. &m. Ghem. Soc., Ü , 2007 (1959). 26 effects was not the same in all of the solvent systems. With acetic-sulfuric acid as solvent, the order of sub stituent effects in the Curtius reaction is the same as that found for the Schmidt reaction of meta- and para- substituted benzoic acids ( 4.), although the number of compounds available for comparison is not large. Yukawa and Tsuno consider decomposition of protonated azide as the rate-determining step in the Schmidt reaction and conclude that substituent effects in the Curtius reac tion with acetic-sulfuric acid as solvent should be similar to substituent effects in the Schmidt reaction; the polar effect of substituents predominates over that of the resonance contribution to the bond energy of the breaking N-N bond, i.e., the effect pictured in Equa tion 22 is less important in reactions catalyzed by sulfuric acid than in non-catalyzed Curtius reactions. If the acid catalyzed Curtius reaction and the Schmidt reaction can indeed be compared, then perhaps, in view of the above discussion, a different order of substituent effects (non-proximal) would appear in the Schmidt reaction if a non-sulfuric acid system were used. The studies of the Schmidt reaction of benzoic acids in sulfuric acid and naphthoic acids in su lfu ric acid and in su lfu ric- phosphoric acid indicate that the electrical effect of substituent groups in general follows the inductive order. III. Experimental Syntheses of Naphthoic acids Synthesis of 8-methyl-l-naphtholc acid (20); A steel bomb was charged with 1,8-naphthallc anhydride (20) J. Cason and J. D. Wordle, J. Org. Chem., 15^ 608 (1950). (78 g., 0.39 moles, m.p. 273.3 - 274.0°, corr.), thlo- phene free benzene (260 m l.), and copper chromite c a ta ly s t - T| (l6.0 g.). Hydrogen was introduced at room temperature at a pressure of 1475 psl. The mixture was heated to 220° and maintained at 220° with shaking for about 16 hours. Maximum pressure at 220° was 2390 p sl. The bomb was cooled and rinsed with benzene. The mixture was fil tered and the f i l t r a t e washed with aqueous sodium car bonate. Removal of the 'benzene yielded a yellow solid which was added to aqueous potassium hydroxide (10 g. in 100 ml. of water). After the mixture had been heated and stirred for two hours the alkali Insoluble material was filtered. 1,8-Haphthalido (11.7 g., 16.1# yield, m.p. 140 - 149° uncorr.) was precipitated from the alkaline filtrate by titrating (while heating) to pH 10 until no more acid was consumed. A steel bomb was charged with 1,8-naphthallde (11.7 g., 0.0634 moles), copper chromite catalyst (2.4 g.), 67 ml. 27 28 of 1.24 N sodium hydroxide, and hydrogen (1750 p sl, at room temperature). The mixture was shaken and heated to 250° and maintained at 250° with shaking for 5-1/2 hours. Maximum pressure at 250° was 284 O psl. The reaction mixture from the cooled bomb was filtered. The two phase system produced upon acidification of the filtrate with hydrochloric acid was baslfled with sodium carbonate and filtered. Acidification of the filtrate with hydro chloric acid gave a precipitate. The solid was extracted with boiling water. 8-Methyl-l-naphtholc acid was crystal lized from the aqueous phase; 2.22 g., m.p. 149.6 - 151.6° corr. (lit. ( 20) 152.2 - 153.2°), neutralization equiva le n t 189.6 (th eo re tic al 186.2), yield 18.8%. Synthesis of 2-chloro-l-naphtholc acid: Phosphorous pentachlorlde (181,5 g.) was added.to 2-hydroxy-l-naph- tholc acid ( 54.3 g.). Upon cessation of evolution of gases, the mixture was placed In a glass-lined bomb which was then flushed with nitrogen leaving a residual pres sure of 80 psl. The temperature was maintained at 135 - 150° for 5-1/3 hours. After cooling the mixture was re moved from the bomb and exposed to the atmosphere over night. The remainder of the hydrolysis was effected by cautiously adding water. The resulting solid was treated with aqueous sodium hydroxide (43 g . In 6OO ml. of w ater). Ether e x tra ctio n removed the Insoluble oily phase. The precipitate formed upon acidification of the aqueous 29 phase with hydrochloric acid was extracted with warm absolute ethanol. The residue resulting from removal of the ethanol was treated with aqueous sodium bicar bonate and the mixture filtered. Crystallization from water followed by recrystallization from aqueous ethanol of the solid formed by acidification of the filtrate yielded 2-chloro-l-naphthoic acid, 2.79 g., m.p. 151.3 - 152.6° corr. (lit. (21) 151 - 152°), neutralization equivalent 205.6 (theoretical 206.6), yield 4-.7/b. (21) E. Bergmann and J. Hirshberg, J. Chem. Soc., 331 (1936). Synthesis of 8-chloro-l-naphthoio acid; 1,8-naph- thalic anhydride (43 g., 0,20 moles) was mercurated (22) (22) G. J. Leuck, R. P. Perkins, and F. C. Whitmore, J. km. Chem. Soc., 1831 (1929). by treating its alkaline solution (1,03 1. of water, 26.5g. of sodium hydroxide) with mercuric acetate (47 g . mer curic oxide dissolved in 130 ml. of water and 90 ml. of glacial acetic acid) and refluxing the resulting mixture for four days. The solid was filtered and dissolved in aqueous sodium hydroxide. Sodium chloride (13 g.) was added and the mixture boiled for a few minutes. The solu tion was barely acidified with hydrochloric acid and f ilte r e d . Chlorine (14 g.) dissolved in 700 ml. of 30 glacial acetic acid was added to the filtered solid mixed with 500 ml. of glacial acetic acid and the mixture was heated to boiling ( 23). A solid (l) was (23) F. 0. Whitmore and &. L. Fox, J . àm. Chem. Soc., ii, 3363 (1929). filtered from the cooled mixture. The filtrate was con centrated and cooled; water was added and the resulting solid (II, 5.2 g.) filtered. I was mixed with 250 ml. of glacial acetic acid and chlorine was bubbled through the mixture for a few minutes. The mixture was heated to boiling and chlorine bubbled through the mixture for a few minutes. Glacial acetic acid (250 ml.) was added and the hot mixture filtered. Water was added to the cooled, concentrated filtrate and the resulting solid (5.4 g.) filtered. Crystallization of this solid and II from ethanol-water gave 8-chloro-l-naphthoic acid, 3.64 g., m.p. 166 - 167° corr. (lit. ( 24 ) 168 - 169°), neutralization equivalent (24 ) H. G. Rule and A. J. G. Barnett, J. Chem. Soc., 175 (1932). 208.2 (theoretical 206,6); @.8% yield. 31 Synthesis of 8-bromo- and 8-iodo-l-naphthoic acids ; (25) A solution of mercuric acetate (mercuric (25) A. Gorbellini and V, Fossati, Rend. ist. lombarde sci., [2] 264 , 265 (1936). oxide, 49 g ., dissolved in 133 ml. of water plus 87 ml. of g la c ia l acetic acid) was added to a warm mixture of 1,8-naphthalic anhydride (44.9 g., 0.227 moles), sodium hydroxide (27.6 g.) and water (1070 ml.). After glacial acetic acid (60 ml.) was added to the mixture, it was re fluxed for 96 hours (22). The cooled mixture was fil tered yielding solid I. One-half of I was treated with aqueous sodium hydrox ide (9 g. in 450 ml. of water) and filtered while hot. A solution of sodium hypobromite (l6.3 g. of bromine, 8 g. of sodium hydroxide, 20 ml. of water) was added to the cooled filtrate, and the mixture heated to boiling. The precipitate resulting from addition of concentrated hydrochloric acid (50 ml.) to the cooled mixture was filtered and then treated with aqueous sodium carbonate and filtered. Acidification of the filtrate with hydro chloric acid produced a precipitate which was then ex tracted with hot benzene. The material recovered from the benzene extraction appeared to contain 1,8-naphthalic anhydride; therefore, the treatment with aqueous sodium carbonate followed by acidification was repeated. 32 8-Bromo-l-naphthoic acid was crystallized from toluene; 12.2 g., m.p. 176.4 - 178.2° corr. (lit. ( 26) 177 - 178°), neutralization equivalent 253.1 (theoretical (26) H. G. Rule, V. P ursell, and R. R. H. Brown, J. Ghem. Soc., 168 (1934). 251.1), yield 43.0# based on 0.113 moles of 1 , 8-naph thalic anhydride. One-half of I was trea ted with aqueous sodium hy droxide (9 g. in 450 ml. of water) and filte re d while hot. A solution of sodium hypoiodite (28.6 g . of iodine, 9.6 g. of sodium hydroxide, 250 ml. of water) was added to the cooled filtrate, and the mixture heated to boiling. The precipitate resulting from addition of concentrated hydrochloric acid (53 ml.) to the cooled mixture was filtered and then treated with aqueous sodium carbonate and filtered. Acidification of the filtrate with hydrochloric acid gave a solid which was then extracted with boiling water. The material which cry sta lliz e d from the water was treated with aqueous sodium carbonate followed by a c id ific a tio n as before. Two crystallizations from toluene yielded 8-io d o -l- naphthoic acid, 9.5 g., m.p. I 64.6 - 166.6° corr. (lit. (25) 164 - 165°), neutralization equivalent 300.7 (th eo re tic al 298.1), yield 28.2# based on 0.113 moles of 1,8-naphthalic anhydride. 33 Synthesis of Ô-nltro-1-naphtholc acid; The crude produce from alkaline permanganate oxidation of 1-naph- thaldehyde (O.64. mole) was heated gently with excess concentrated nitric acid until brown-red fumes were evolved (27). After the mixture had cooled, the pro- (2 7) A, G. Eckstrand, J. prakt. Ghem., [2] 38. 139 (1888). cedure was repeated. The cooled mixture was diluted with water and filtered. The precipitate was washed with water and then dissolved in excess absolute ethanol, Concentrated su lfu ric acid (2 ml.) was added and the mixture refluxed 47 hours. After most of the ethanol was removed by d i s ti lla tio n , the mixture was treated with aqueous sodium hydroxide and extracted with ether. Acidification of the aqueous layer with hydrochloric acid precipitated 8-nitro-l-naphthoic acid; crystal lized twice from aqueous ethanol, 8.6 g. (6^ yield based on 1-naphthaldehyde), m.p. 212 - 214 ° corr. ( l i t . (28) (28) E. Berliner and E. H. Winicov, J. Am. Chem. Soc., 81, 1630 (1959). 215.2 - 217.2°), neutralization equivalent 216.5 (theoretical 217.2), 34 I Synthesis of ^-bromo-l-naphtholc a c id ; Bromine (5.4 ml.) in 25 ml. of carbon tetrachloride was added dropwise over a 45 minute period to a stirred mixture of 1-methylnaphthalene ( 14.2 g.), carbon tetrachloride (35 ml.), and a little iron powder and iodine at -5 to -10°. The mixture was stirred at that temperature for one hour and then warmed to room temperature during a two hour period. The mixture was washed with aqueous sodium hydroxide and water and the carbon tetrachloride removed. Distillation of the residue yielded 4-bromo- 1-methylnaphthalene (29), fra c tio n b.p. 110 - 112° (29) h. D. Topsom and J. Vaughan, J. Chem. Soc., 2842 (1957). at 1-2 mm., 19.4 g ., 87.7% yield. 4-Üromo-l-methyl- naphthalene (19.4 g.) and 304 aqueous sodium dichromats (50% excess) were placed in a bomb and shaken and heated at 240 - 250° for 18 hours (30). The cooled bomb was (30) L. Friedman, Ph.D. dissertation. The Ohio State U niversity, 1959, and D. L. F ishel, Ph.D. dis sertation, The Ohio State University, 1959. washed out with water and the alkaline mixture filtered. The filtrate was extracted with ether and then acidified with hydrochloric acid yielding a solid. Two crystal lizations of the solid from toluene gave 4-bromo-l- naphthoic acid, 5.5 g., 25^ yield, m.p. 215.6 - 217.4° 35 corr, (lit. (31) 220°), neutralization equivalent 248,2 (theoretical 251,1), (31) J. Salkind, Chem, Ber,, 1031 (1934). 1-NaphthoiCf 2-methvl-l~naDhthoic and 2-naphthoic acids: Oxidation of 1-naphthaldehyde gave 1-naphthoic acid, crystallized from water, .m.p, 162,0 - 163.0 corr. (lit. (32) 161,4 - 161,6°) , 2-Methyl-l-naphthoic acid, synthe- (32) u. F. Fieser and n. L. Holmes, J. Am. Chem. Soc 2319 (1936), sized by R. G. Hahn, was recrystallized from benzene, m.p. 12 5, 2 - 126,00 corr. (lit, (33) 126 - 127°), 2-Naphthoic (33) R. Adams and L. 0, Binder, J, Am, Ghem, Soc,, 2773 (1941). acid (Eastman) was treated with aqueous sodium carbonate and filtered. The filtrate was extracted with ether and then acidified with hydrochloric acid. The resultant pre cipitate was crystallized from toluene, m,p. 183,6 - 184,2° corr, ( l i t , (34) I 84 - 185), (34 ) N. S. Newman and H. L. Holmes, Org, Synth, Coll, Vol. II, 428, Reactions of Naphthoic Acids with Hydrazoic Acid Reaction of 1-naphthoic acid with hydrazoic acid: Sodium azide (0,20 g , ) was added to a s tirre d solution of 1-naphthoic acid (0,50 g, in 60 ml, of concentrated sulfuric acid) at 45°, The theoretical amount of gas 36 was evolved in 45 minutes. The cooled reaction mixture was basified by dropwise addition of aqueous sodium hy droxide and extracted with ether. Hydrogen chloride was bubbled through the ether solution giving a pre c ip ita te ( 0.40 g., 77% yield based on naphthylamine hydrochloride). The precipitate was dissolved in aque ous sodium hydroxide and the alkaline solution extracted with ether. Addition of ethereal picric acid to the ether extract yielded a precipitate which was crystal lized from alcohol, pale green, m.p. 186.4 - 190. 4 ° corr. 1-Naphthylamine picrate ( 35) (greenish-yellow) (35) J. van rtlphen and G. Drost, Rec. trav . chim., èl, 625 (1948). melts at 181 - 182° (dec.). Reaction of 2-methyl-l-naphthoic acid with hydrazoic acid; 2-Methyl-l-naphthoic acid (l.OO g.) was dissolved in 25 ml. of concentrated su lfu ric acid and cooled to 0° (2-methyl-l-naphthoic acid reacts with sulfuric acid). Sodium azide (0.52 g.) was added in portions during a five minute period. The theoretical amount of gas was evolved in 25 minutes. The mixture was basified by dropwise addition of aqueous sodium hydroxide, and extracted twice with ether. Hydrogen chloride was bubbled through the ether solution producing 37 a precipitate, 0.56 g. The precipitate was crystallized from methanol, 0,27 g. (26# yield), m.p. 224.6 - 227.1° corr. (dec.). 2-Methyl-l-naphthylamine hydrochloride (from methanol) melts at 228 - 231° (dec.) ( 36). (36) B. K. Baker and G. H. Carlson, J. Am. Ghem. Soc., 6A, 2657 (1942). Reaction of 8-methl-l-naphthoic acid with hydrazoic acid ; 8-Methyl-l-naphthoic acid (0.093 g.) was dissolved (4 -I /4 hours) in 25 ml. of solvent (three volumes of concentrated sulfuric acid plus two volumes of 85# phosphoric acid) at 0°. After about two hours sodium azide (0,05 g.) was added and the mixture stored over night at room temperature. (Becausë of the removal of aliquots, the effective weight of the carboxylic acid at this point was 0.082 g.). The reaction mixture was poured onto crushed ice and basified with aqueous po tassium hydroxide. The ether layer resultihg from two extractions was f ilte r e d through anhydrous magnesium sulfate. Acetic anhydride (0.2 ml.) and glacial acetic acid (0.5 ml.) were added to the e th e r.la y e r. The solid arising from the removal of the ether by warming was crystallized from absolute alcohol, 0.011 g. (13# yield), m.p. 183.6 - 185.1° corr. N-Acetyl-8-methyl-l-naph- thylamine melts (37) at 183 - 184°. 38 (37) V. Vesely, F. Stursa, H. Ülejniçek, and F. Rein, Coll. Czech. Chem. Comm., 493 (1929). Reaction of 2-chloro-l-naphthoic acid with hydrazoic acid: 2-Chloro-l-naphthoic acid (0.50 g.) was added to 15 ml, of concentrated sulfuric acid containing sodium azide (l.OO g .). The th e o re tic al amount of gas was evolved in three minutes. The mixture was poured onto ice and basified with aqueous sodium hydroxide. The basic solution was extracted twice with ether and the ether filte re d through anhydrous magnesium su lfate. Acetic anhydride (0.5 ml.) and glacial acetic acid (l ml.) were added to the ether solution. Removal of the ether by warming produced an o il which s o lid ifie d on shaking with petroleum ether (b.p.,30 - 60°). The solid was crystallized from aqueous alcohol, then from absolute alcohol, 0.11 g. (21% yield), m.p. 189.2 - 192.3° corr. h-Acetyl-2-chloro-l-naphthylamine (38) melts at 192°. (38) H. H. Hodgson and D. E. Hathway, J. Ghem. Soc., 538 (1944). Reaction of 8-chloro-l-nanhthoic acid with hydrazoic a c id : Sodium azide (0.50 g .) was added to a solution of 8-chloro-l-naphthoic acid (0.50 g.) in 10 ml. of con centrated sulfuric acid. The theoretical amount of gas was evolved in two minutes. The mixture was poured 39 onto ice and basified with aqueous sodium hydroxide. The ether layer resulting from two extractions of the basic mixture was filte re d through anhydrous magnesium su lfa te . Acetic anhydride (0.5 ml.) and glacial acetic acid (1 ml.) were added and the ether was removed by warming. The residue was crystallized twice from aqueous alcohol and then from petroleum ether (b.p, 65 - 110°), 0.23 g. (43# yield), m.p. 136.4 - 138.7° corr. N-&cetyl-8- chloro-l-naphthylamine melts (39) at 137°. (39) F . Ullraann and F . Consonne, Chem. Ber., 3 5, 2802 (1902). Reaction of 8-bromo-l-naphthoic acid with hydrazoic a c id ; Sodium azide (0.50 g.) was added to a solution of 8-bromo-l-naphthoic acid (0.50 g.) in 10 ml. of concen trated sulfuric acid. The theoretical amount of gas was evolved in one minute. The mixture was poured onto ice and basified with aqueous sodium hydroxide . The ether layer resulting from two extractions was filtered through anhydrous magnesium su lfate. Acetic anhydride (0.5 ml.) and glacial acetic acid (l ml.) were added and the ether was removed by warming. The residue was cry stalliz ed from petroleum ether (b.p. 65 - 110°), 0.39 g. (74# yield), m.p. 136.2 - 137.2° corr. N-Acetyl-8-bromo-1- naphthylamine melts (40 ) at 138 - 139°. 40 (40) K. Meldola and F, W. S tre a tfe ild , J. Chem. Soc., â2, 1054 (1893). Reaction of S-lodo-l-naphtholc acid with hydrazoic acid ! 8-Iodo-l-naphthoic acid (0.50 g.) was dissolved in concentrated sulfuric acid (10 ml.) at 0°. Sodium azide (O.ll g.) was added over a five minute period. After three more minutes the mixture was poured onto ice (the reaction product appears to decompose if it is le f t in concentrated sulfuric acid). The mixture was basi- . fied with aqueous sodium hydroxide and then extracted twice with ether. The precipitate produced by bubbling hydrogen chloride through the ether layer was crystal lized from ether-ethanol, 0.13 g. (25# yield), m.p. 188.5 - 189.9° (dec.) corr. 8-Iodo-l-naphthylamine hydrochloride melts (41) at 186 - 189° (dec.). (41 ) R. Scholl. G. Seer, and R. Weitzenbock, Chem. Ber., A2, 2206 (1910). Reaction of 8-nitro-l-naphthoic acid with hydrazoic acid ; In concentrated sulfuric acid 8-nitro-l-naphthoic acid forms a red solution which fades to yellow after about a day. 1-Kitronaphthalene exhibits similar be havior. In sulfuric-phosphoric acid, however, 8-nitro- 1-naphthoic acid forms a yellow solution. Very little 41 or no product could be Isolated from six attempted Schmidt reactions of 8-nitro-l-naphthoic acid although gases were evolved as expected (gas chromatographic analysis of the gases, collected over water, from a reaction showed the presence of nitrogen and carbon dioxide). The general procedure for all the reactions was the same as for the other naphthoic acids, i.e, the reaction mixture was basified (in two reactions, neutral- lized with sodium bicarbonate rather than made definitely basic - no improvement resulted however) after it had been poured onto ice, and then ether extracted; (l) Very l i t t l e material was recovered upon removal of the ether in one reaction. (2) Hydrogen chloride was bub bled through the ether layer from one reaction and gave a precipitate corresponding, by weight, to a 22>% yield of 8-nitro-l-naphthylamine hydrochloride. Treatment of this material by aqueous base followed by ether extrac tion and addition of the ether layer to ethereal picric acid gave a very small amount of m aterial id e n tifia b le as 8-nitro-l-naphthylamine picrate, ( 3) The acétylation procedure used to iso la te N -acetyl- 8-bromo-l-naphthylamine was used in four reactions. In only one (sulfuric- phosphoric acid as solvent) was any material correspond ing to N-acetyl- 8-n itro-l-naphthyla mine isolated (7.2% yield). Two of these reactions were run in sulfuric- phosphoric acid; all the other reactions were run in concentrated sulfuric acid. 42 Solvents for Kinetic Determinations The sulfuric acid used throughout the kinetic de terminations was pre-mixed and stored in bottles (2-1/2 quart) until used. Titration with standard base estab lished the composition as 93.4# sulfuric acid by weight, A special solvent mixture was prepared for use with compounds too unstable in concentrated sulfuric acid to permit kinetic measurements. Sulfuric acid (3750 ml., assay 95.0 - 98.0#) and phosphoric acid (2500 ml., assay 85.0 - 87,0#) were mixed and stored in bottles (2-1/2 quart) until used. S ta b ility of Naphthoic Acids in Sulfuric Acid The stability of the naphthoic acids in sulfuric acid was checked by ultraviolet spectrophotometrie measurements. The compound was dissolved in sulfuric acid and aliquots were taken at different times, diluted with water (95# ethanol with 4-bromo-l-naphthoic acid) and the absorbance of the aqueous solutions determined. The absorbance at a given wave length should remain constant with time if the compound is stabrle in concen trated sulfuric acid. Typical data are in Table 5. 1-Naphthoic, 8-chloro-l-naphthoic, 8-bromo-1-naphthoic and 4-bromo-l-naphthoic acids are stable at room tem perature for the period of time required to execute a kinetic determination (42). The absorbance of 43 (42) J. P. B attersh all, Ann. Chem. Liebigs, 168, 114 (1873), reported that 1-naphthoic acid was sulfo- nated when a solution of it in fuming sulfuric acid was allowed to stand about 24 hours. 2-chloro-l-naphthoic and 8-iodo-l-naphthoic acids drifts with time at room temperature but not at lower tempera tures. 2-Methyl-l-naphthoic and 2-naphthoic acids are unstable in concentrated sulfuric acid at 0°. 8-L itro - 1-naphthoic acid forms a red solution in concentrated su lfu ric acid which fades to yellow over a period of a day; the same behavior is exhibited by 1-nitronaphthalene, The compounds which are unstable in concentrated sulfuric acid are stable in the sulfuric-phosphoric acid mixture (constant absorbance used as c rite rio n ). 8-N itro -l- naphthoic acid is yellow in the latter solvent. The error in the Beckman DU ultraviolet spectrophotometer is estimated at 2%', maximum error in pipeting is esti mated at 2%, Table 5 Stability Data for 1-Naphthoic and 2-Methyl-l-naphthoic Acids in Sulfuric Acid 1-Naphthoic acid, 31° 2-Methyl-l-naphthoic acid,® 0° Absorbance Absorbance Minutes 2 37mu 260mu Minutes 234mu 3 0.402 0.046 9 0.288 30 0.420 0.052 32 0.305 60 0.430 0.052 121 0.368 90 0.433 0.052 185 0.400 (a) Timing begun after a 10 minute dissolution period. 44 Kinetic Procedure A solution of the carboxylic acid and a solution of hydrazoic acid in the solvent were prepared for each kinetic run. The hydrazoic acid solution was prepared by addition of sodium azide (recrystallized Fisher chemi cal) to the cooled solvent (stirred) in a partially filled 100 ml. volumetric flask (recalibrated to con tain a Teflon magnetic stirring bar) followed by dilution to the mark. After thorough mixing the solu tions were equilibrated at the temperature of the run for 30 minutes. A 25 ml. aliquot (using the same pipet) of each solution was added to the reaction vessel (Pyrex test tube, 20-1/2 x 2-1/2 cm.), a polyethylene stopper inserted and the vessel inverted a few times. Zero time was taken as the point when the second solu tion had been completely added to the reaction vessel. Aliquots (l.OO ml.) were withdrawn, using the same pipet throughout a run, and drained into volumetric flasks partially filled with distilled water (95% ethanol with 4-bromo-l-naphthoic acid) . The time of the aliquot was taken at the point of complete drainage of the pipet. The flasks were diluted to the mark and stored for later determination of the ultraviolet absorbance at a wave length which gave the larg est difference in absorbance between reactants and products. Water was used as the solvent blank in the absorbance determinations except 45 for 4-bromo-l-naphthoic acid in which case 95% ethanol was used. The analytical wave lengths used are in Table 6. Hydrazoic acid does not absorb at these fre quencies , The temperature of -10.7° was obtained by use of a potassium chloride, ice, and saturated potassium chlor ide mixture (43). Temperatures 0.00°, 10.00°, 25.00°, and 30.00® 1 0.02° were determined with a thermometer calibrated by the National Bureau of Standards. (43) 4. S eid e ll. S o lu b ilitie s of Inorganic and Metal Organic Comoounds, 1. 747. D. Van Nostrand Co., Inc., New York, N. Y. (1940). Table 6 Analytical Wave Lengths for Kinetic Determinations Acid Wave length, mu 1-naphthoic 237 2-methyl-1-naphthoic 229 8-methyl-l-naphtholc 2 34 2-chioro-l-naphthoic 232 8-chloro-l-naphthoic 236 8-bromo-l-naphthoic 240 8-1odo-l-naphthoic 242 4-bromo-l-naphthoic 238 2-naphthoic 238 46 Calculations The rate laws for second order reactions, first order with respect to each of two reactants, are = akt + 1 , a = b (23) t Ss- - -iriw ’ <”> where x = amount reacted in time t a,b = initial concentrations of the two reactants, respectively k = second order rate constant k' = bk = pseudo first order rate constant When the concentration is proportional to a physical property (such as the absorbance, ft, at a given wave length) these equations may be converted (44) to (44) &. ft. Frost and R. G. Pearson, K inetics and Mechanism, John Wiley & Sons, Inc., New York, N. Y., 1953, p. 28. ..ip.... = akt + 1 (23a) 4qo “ 4 10, ?(&*-&.) + A. - A _ (b-a)kt , , t (2 ft0 0 - ft 2,303 ^ a log(i-tJ . , log(&o - &c) (25a) The rate constant may be calculated from the slope of the graph of the time versus the function on the left 47 hand side of the appropriate equation. Figures 1 and 2 are typical examples. Typical data for each compound are in the Appendix. In Table 7 is found a list of the experimentally determined rate constants. According to transition-state theory of reaction rates, the rate constant k may be represented as (45) (45) Kef. 44, p. 96 , kpT . ^ (26) h R RT where kg = Boltzmann constant T = absolute temperature h = Planck's constant R = gas constant S = entropy of activation H = enthalpy of activation Equation 26 may be transformed to log Ï = . log ï i - (27) T 2.303RT 2.303R h Thus may be determined from the slope of the graph of log Y 98. Y ' may then be calculated from equa tion 5. The experimentally determined entropies and enthalpies of activation are listed in Table 7. The graphs are given in Figure 3. Table 7 Rate Constants (liters mole“^niin,''^) and Activation Parameters for Schmidt Reactions ______of Naphthoic Acids ______Solvent; 93. Sulfuric Acid Substituent on 1-naphthoic acid none 2-chloro 8-chloro 8-bromo 8—iodo 4-bromo 0.125 -10.7° 0.142 a v .0.134 0.731 0.492 4.13 4.44 6.33 0.742 0.497 3.17 4.11 6.38 0.000 av.0.737 av.0.495 3.65 3.80 6.44 3.70 av.4.12 av .6.38 av.3.66 1.77 1.49 9.23 o 1.93 1.76 8.64 10.00 2.19 2.02 10.0 av;1.96 av.1.76 av.9.29 ; 9.14 41.2 7.89 47.2 25.000 8.00 44.7 0.93 av.44,4 4.57 av.8.49 5.20 4.94 av.4.90 OÏ Table 7 (contd. ) Substituent none 2-chloro 8-chloro- 8-bromo 8-iodo 4—brorao kcal./mole 15.3 17.9 15.4 cal./deg. -11.1 -2.28 -7.60 Relative t Rate,0° 1.00 0.672 4.97 5.59 8.66 Solvent : Sulfuric Acid-Rhosphoric àcid Substituent on 1-naphthoie acid none 2-methyl 8-methyl 8-chloro 2-naphthoic acid 0.302 9.74 2.84 1.24 0.310 9.08 3.07 1.23 0.00°C. av .0.306 8.72 2 .62 av.1.24 av.9.18 av.2.84 %2 10.1 0.0546 30.00°C. 11.8 0.0567 av. 11.0 a v .0.0557 Relative Rate,0° 1.00 30.0 9.28 4.05 vO 3 . 0 0 2 6 0 - i-N opW W e Acid T e m p . : 2 5 " Am~A* S o l v e n t : 9 3 . 4 % HgSq* Am-A Initial Cone.; 0 .0 0 2 5 0 M. 2 .201 - 8.93 l./m.-min. 1 . 8 0 - 1 . 4 0 VJl O 1.00 _L _L 10 20 30 40 50 6 0 7 0 8 0 9 0 100 M i n u t e s F I G U R E I 0 . 7 0 0 0 . 6 2 0 l o g X 0 . 5 4 0 0 . 4 6 0 Initial Cone. 8 - Chloro-1-naphthoic Acid 0 .0 0 2 5 0 M HN 3 : 0 0 0 5 0 0 M 0 . 3 8 0 T e m p ; 0 ® S o l v e n t H 2 SO 4 -H 3 PO 4 0 . 3 0 0 4 0 120 1 6 0 200 2 4 0 2 8 0 M i n u t e s \ji FIGURE 52 3 . 1 0 8 - Cl-l-naphthoic acid 2 . 7 0 2 . 3 0 L o g 1 0 % nophthoic cold 1 . 9 0 1 . 5 0 2 - Cl-I-naphthoic acid I.IO 0 . 7 0 0 3 . 2 0 3 . 3 0 3 . 4 0 3 . 5 0 3 . 6 0 3 . 7 0 3 . 8 0 3 . 9 0 I O ’ / ' T FIGURE 3 ACTIVATION ENERGY PLOTS 53 Determination of Dissociation Constants The spectrophotometric method of David and Geiss- raan (4-6) was used to determine pKgjj+ in su lfu ric acid, (46 ) C. T. Davis and T. L, Geissraan, J. àm. Ghera. Soc., 3507 (1945). Kgjj+ is the thermodynamic dissociation constant of a protonated carboxylic acid. Solutions of the compound in sulfuric acid of different strengths were prepared by diluting an aliquot of a sulfuric acid solution of the compound with each of the previously prepared sul furic acid-water mixtures. (^i“ was then determined for each solution at 25 - 0,5° using a Beckman DU ultraviolet spectrophotometer with thermal jackets. is the observed extinction coefficient at the wave length at which the ionized form of the compound has a greater absorbance than the unionized form. is the observed extinction coefficient at a wave length, at which the unionized form has a greater absorbance than the ionized form. kt the inflection point (determined graphically) of the curve obtained by plotting (^ -^ ) versus Hq , pKg%+ = Hq . The data are in Table 8, 54 Table 8® Spectrophotoraetric Data for Determination of P&BH+ Hq 8-chloro- •1-naphthoic acid 1-naphthoic acid (^2 55 ” <%30)10-3 (^250 - <23o)lO"^ —8 « 42 —6.64 +0.16 —8 .16 -7.88 -0.12 -7.87 -8.88 - 0.52 - 7.69 -10.6 -1.68 -7.38 -12.8 -3.08 -7.21 -14.7 -4.32 - 6.90 —16.2 -7.48 —6.63 -18.2 -9.96 -6.33 -19.3 -11.8 — 5 » 68 -22.0 -15.0 pKbh+> 25° - 7.28 - 7.06 (a) The values for the acidity function, Hq , of the sulfuric acid-water mixtures were read from a graph of acid composition versus Hq values given by M. A. Paul and F. A. Long, Chem. Revs., 1 (1957) for given su l furic acid-water mixtures. IV, Appendix The following tables contain typical rate data for each compound studied. The analytical wave lengths used are listed in Table 6. The heading on the right hand side column, f(n), refers to the function on the left hand side of equation n, page Table 9 Initial concentration; 1-Naphthoic acid 0.00250 molar Hydrazoic acid 0.00250 molar Solvent: 93.4# HgSO^ kg = 6,38 liters mole”^min.“^ Temperature: 0.00° Dilution Factor; l/lOO Minutes Absorbance f(23a) 0.0 0,406 1.00 5.5 0.372 1.13 13 0.331 1.33 20 0.315 1.43 31 0.273 1.79 44 0.261 1.93 57 , 0.238 2 .26 68 0.226 2.48 81 0.210 2.86 " go " 0.104 55 56 Table 10 Initial concentration: 2-Naphthoic acid 0,000750 molar Hydrazoic acid 0,1000 molar Solvent : Temperature: 30,00 = 0,00546 min,”^ Dilution Factor: l/50 kg = 0.0546 l i t e r s mole“lm in,“l Minutes Absorbance f (25a) 0,0 0,790 0,777 18,5 0,719 0.722 49,0 0,629 0,640 71,0 0,578 0,587 95.0 0,528 0,526 132,0 0,478 0,456 181,0 0,410 0,338 227,0 0,360 0,225 259,0 0,329 0,137 «bo M 0,192 Table 11 Initial concentration: 2-raethyl-l-naphthoic acid 0,000500 molar Hydrazoic acid 0,00100 molar Solvent : . Temperature: 0,00° k = 9,08 liters mole“^min,“^ Dilution Factor: 1/50 Minute s Absorbance f(24a) 0,0 0,338 0,301 14.5 0,313 0,334 33.0 0,277 0,397 54.0 0,272 0,408 85.5 0,251 0,462 96.0 0,239 0,500 115.0 0,229 0,538 132.5 0,223 0,5 6 4 153.0 0,218 0,588 165.0 0,218 0,588 "00 " 0,154 57 Table 12 I n it ia l concentration: 8-methyl-l- naphthoic acid O.OOO 5OO molar Hydrazoic acid 0.00100 molar Solvent : HgSO^ .- H3PO/ %2 = 2.134 l i te r s mole-lmin.-l Temperature; 0.00° D ilution factor : 1/50 Minutes Absorbance f( 24 a) 0.0 0.254 0.301 11.0 0.249 0.308 26.0 0.247 0.310 87.5 0.221 0.351 157.5 0.198 0.398 221.5 0.178 0.451 295.0 0.166 0.491 412.5 0.149 0.564 653.0 0.128 0.699 "œ " 0.086 Table 13 I n i t i a l concentration: 2-chloro-l- naphthoic acid 0.00125 molar Hydrazoic acid 0.00375 molar Solvent : 93.4% H2^°4 k2 = 1. 49 l i te r s moie~^min.“l Temperature : 10.00° D ilution facto r : 1/100 Minute s Absorbance f (24 a) 0.0 0.442 0.477 17.5 0.430 0.498 46.0 0.406 0.545 76.5 0.380 0.610 121.5 0.356 0.689 160.5 0.345 0.734 216.5 0.323 0.851 2 56.0 0.317 0.893 306.5 0.307 0.974 319*0 0.307 0.974 "oo" 0.265 58 Table 14 Initial concentration: 8-chloro-l- naphthoic acid 0,002500 molar Hydrazoic acid 0,00500 molar Solvent: H^SO^- HgPO^ ^2 - 1*24 l i t e r s mole”^rain,”^ Temperature; 0,00° Dilution factor; 1/50 Minutes Absorbance f (24 a) 0,0 0.714 0.301 18,0 0,662 0.324 38,5 0,618 0,346 60,5 0.553 0,385 84.0 0,512 0,415 109.5 0,470 0.452 141.0 0,433 0.490 181,0 0,396 0,537 210,5 0,366 0,583 231,0 0,347 O.6I 8 "oo " 0.178 Table 15 Initial concentration: 8-bromo-1- naphthoic acid 0,00400 molar Hydrazoic acid 0,00400 molar Solvent: 93.4% ^2^^4 = 4.11 l i te r s mole" ^min,"-*- Temperature: 0.00° ' Dilution factor : 1/50 Minutes Absorbance f (23a) 0,0 0,701 1.00 20,0 0.563 1.39 35.0 0,508 1.64 51.5 0.479 1,82 68.0 0.438 2.14 90,5 0,420 2,32 109.0 0.390 2,70 123.5 0,372 2,99 139.5 0,358 3.27 153.5 0.343 3.63 «00 " 0,207 59 Table 16 Initial concentration: 8—iodo—1— naphthoic acid 0.00400 molar Hydrazoic acid 0.00400 molar Solvent: 93.4% HgSO^ kg = 6.38 l i te r s mole“^min,"^ Temperature: 0.00° Dilution factor: l/lOO Minutes Absorbance f (23a) 0.0 0.588 1.00 12.5 0.524 1.37 29.0 0.490 1.71 46.5 0.462 2.14 . 62.0 0.443 2.58 77.5 0.436 2.79 96.5 0.417 3.59 119.5 0.410 4.02 130.0 0.405 4.39 "oo " 0.351 Table 17 Initial concentration: 4“6romo—1— naphthoic acid 0.00100 molar Hydrazoic acid 0.00200 molar Solvent: 93.4% HgSO^ kg = 4.94 l i te r s mole”^m in.-l Temperature: 25.' 00° D ilution factor : 1/50 Minutes Absorbance f (24 a) 0.0 0.587 0.301 18.0 0.510 0.339 42.5 0.427 0.392 74.5 0.352 0.459 93.0 0.318 0.499 113.5 0.286 0.544 144.5 0.245 0.617 165.0 0.228 0.654 "oo " 0.085 Autobiography I, Donald Carl Berndt, was born in Toledo, Ohio, April 11, 1935. I received ray secondary education at DeVilbiss High School, Toledo, Ohio. In 1957 I was granted the Bachelor of Science degree by The Ohio State University. I served as a teaching assistant in the Chemistry Department of The Ohio State Uni versity during the academic year 1957-1958. I was- appointed to a Mershon graduate fellowship for the academic year 1958-1959, to a National Science Foundation fellowship from June 1959 to June 1961, and to a Chemistry Department fellowship from July 1961 to December 1 9 6 1 , 60