THE INFLUENCE of SUBSTITUENTS on the Cis-Trans ISOMERIZATION of AZOBENZENE

THE INFLUENCE OF SUBSTITUENTS ON THE cis-trans ISOMERIZATION OF AZOBENZENE

DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University

By ERACH RUSTOMJI TALATY, B. Sc. (Hons.), M. So.

******

The Ohio State University 1957

Approved by:

Adviser Department of Chemistrj ACKNOWLEDGMENTS

The author wishes to express his deep sense of grati tude to Dr. Earl W. Malmberg for invaluable help and guid ance throughout this investigation. It was mainly through his kind efforts that it was possible for the author to come to the United States of America and study at this univer sity, and for his kindness in this and in many other ways, the author is permanently indebted to him. The author also wishes to thank the Research Corpora tion very much for a Research Fellowship that was awarded to him for two years, namely, from October, 1954, through September, 1956. Without this timely help, it would have been well-nigh impossible for the author to maintain himself in this country. Sincere thanks of the author are due to E. I. du Pont de Nemours and Company, too, for the grant of a Research Fellowship during the Summer Quarter of 1957*

Finally, the author would like to express his indebted ness to Mr. S. Ramachandran and to Mr. Paul Anthony for the spontaneous assistance that they gave so generously in cal culations and proof-reading, respectively; to Mrs. Rosalie

Kishler, Mrs. Diane Uhler, Mrs. Jane Scott, Mrs. Esther Salisbury and Miss Mary Morley, without whose voluntary and

ii Ill valuable help, this dissertation would not have been typed in the required time; and to his fellow graduate students and other friends for help at various times in manifold ways. TABLE OP CONTENTS

Page

I . INTRODUCTION...... 1 II. STATEMENT OF THE PROBLEM...... 15

III. RESULTS AND DISCUSSION...... 15 A. Synthesis of the Necessary Compounds 15

1. Preparation of trans forms 15 2. Preparation of cis forms 21 B. Absorption Spectra of the Azo Compounds...... 25 C . Measurement of the Rates of Isomerization...... 29

IV. EXPERIMENTAL A. Materials 1. Adsorbent...... 50 2. Solvents...... 50 B. Synthesis of trans Forms of Sub stituted Azobenzenes 1. Preparation of nitrosobenzene.... 52 2. Preparation of 4-chloroazobenzene

(a) From 4-aminoazobenzene 54-

(b) By condensation of nitroso- f benzene with 4-chloroaniline 55 5. Preparation of 4-iodoazobenzene... 56

iv Page 4. Preparation of 4-cyanoazobenzene

(a) From 4-arainoazobenzene...... 57 (b) By condensation of nitroso benzene with 4-aminobenzonitrile...... 58 5 . Preparation of 5-chloroazobenzene. 59 6. Preparation of 5-iodoazobenzene... 59 7. Synthesis of 5-cyanoazobenzene (a) Preparation of 5-aminobenzonitrile

(i) Attempted catalytic re duction of 5-nitrobenzonitrile...... 6l

(ii) Reduction of 5-nitrobenzonitrile with stannous chloride...... 6l (b) Condensation of nitrosobenzene with 5-arainobenzonitrile.... 62

8. Preparation of 4-bromoazobenzene.. 6^ 9. Preparation of 5-bromoazobenzene.. 64

10. Preparation of 4-fluoroazobenzene. 65 11. Preparation of 5-fluoroazobenzene. 65

12. Preparation of 4-methoxyazobenzene 67 1 5 . Synthesis of 5-niethoxyazobenzene (a) By condensation of nitroso benzene with m-anisidine 67

(b) Prom o-anisidine (i) Preparation of 5-methoxy- 4-aminoazobenzene...... 68

(ii) Deamination of 5-methoxy- 4-aminoazobenzene 70

V Page l4. Preparation of 4-nitroazobenzene.... 71

15» Preparation of 2-nltroazoLenzene.... 71 16 . Preparation of (4-phenylazophen'yl) trlmethylammonlum nitrate (a) In nitrobenzene as solvent 72

(b) In dlmethylformamlde as solvent 72 1 7. Synthesis of (2-phenylazophenyl) trlmethylammonlum nitrate

(a) Preparation of 3-amlnoazobenzene 75 (b) Méthylation of 5-amlnoazobenzene 74

1 8. Preparation of potassium azobenzene- 5 -sulfonate 76

19- Preparation of potassium azobenzene- 4-sulfonate...... 77 20. Preparation of azobenzene-5-carboxyllc acid...... 77 21. Preparation of potassium azobenzene- 4-carboxylate...... 78 22. Preparation of 5-phenylazoacetophenone 78

2 5 . Preparation of 4-phenylazoaoetophenone 79 C. Preparation of els Isomers...... 00 D. Measurement of the Rate of Isomerization... 84 E. Calculation of Rate Constants...... 84 P. Calculation of the Activation Energies and Frequency Factors...... 86

V. SUMMARY...... 87

APPENDIX...... 90 AUTOBIOGRAPHY...... 195 vl LIST OP TABLES Page I Synthesis of Substituted Azobenzenes..... l8

II Molecular Extinction Coefficients for Maximum Absorption for Various Azobenzenes...... 2? III Rates of Isomerization of Substituted cis Azobenzenes...... 34 IV Activation Energies and Frequency ' Factors for Substituted Azobenzenes.... 39 V Melting Points of cis and trans Isomers of Substituted Azobenzenes....,...... 88 VI Isomerization of 3-Cyanoazobenzene in Ethanol...... 121

VII Isomerization of 3-Cyanoazobenzene in Dioxane...... 122 VIII Isomerization of 3-Cyanoazobenzene in Benzene...... 123 IX Isomerization of 3-Cyanoazobenzene in Heptane...... 124

X Isomerization of 4-Cyanoazobenzene in . 95 per cent Ethanol...... 125 XI Isomerization of 4-Cyanoazobenzene in . Absolute Ethanol...... 125 XII Isomerization of 4-Cyanoazobenzene in Dioxane...... 127

XIII Isomerization of 4-Cyanoazobenzene in Benzene ...... 128 XIV Isomerization of 4-Cyanoazobenzene in Heptane...... 130 XV Isomerization of 3-Fluoroazobenzene in . Ethanol...... 132

XVI Isomerization of 3-Fluoroazobenzene in Dioxane...... 153

vll Page XVII Isomerization of 5-Pluoroazobenzene In Benzene...... 154

XVIII Isomerization of 5-Fluoroazobenzene in Heptane...... 155 XIX Isomerization of 4-Pluoroazobenzene in Ethanol...... 156 XX Isomerization of 4-Pluoroazobenzene in . Dioxane...... 157 XXI Isomerization of 4-Pluoroazobenzene in . Benzene...... 159 XXII Isomerization of 4-Pluoroazobenzene in Heptane...... 140

XXIII Isomerization of 5-Chloroazobenzene in Ethanol...... 142 XXIV Isomerization of 5-Chloroazobenzene in . Dioxane...... 145

XXV Isomerization of 5-Chloroazobenzene in . Benzene...... 144

XXVI Isomerization of 5-Ghloroazobenzene in , Heptane...... 145

XXVII Isomerization of 4-Chloroazobenzene in Ethanol...... 146

XXVIII Isomerization of 4-Chloroazobenzene in Dioxane...... 147

XXIX Isomerization of 4-Chloroazobenzene in . Benzene...... 149 XXX Isomerization of 4-Chloroazobenzene in . Heptane...... 150

XXXI Isomerization of 5-Bromoazobenzene in Ethanol . ■ 151

viii Page XXXII Isomerization of 3-Bromoazobenzene in Dioxane...... 152 XXXIII Isomerization of 5-Bromoazobenzene in Benzene...... 155 XXXIV Isomerization of 5-Bromoazobenzene in Heptane...... 154 XXXV Isomerization of 4-Bromoazobenzene in Ethanol...... 155 XXXVI Isomerization of 4-Bromoazobenzene in Dioxane...... 156 XXXVII Isomerization of 4-Bromoazobenzene in Benzene...... 158 XXXVIII Isomerization of 4-Bromoazobenzene in Heptane...... 159 XXXIX Isomerization of 5-Iodoazobenzene in Ethanol...... l6l

XL Isomerization of 5-Iodoazobenzene in Dioxane...... 162

XLI Isomerization of 5-Iodoazobenzene in Benzene...... I65 XLII Isomerization of 5-Iodoazobenzene in Heptane...... 164 XLIII Isomerization of 4-Iodoazobenzene in Ethanol...... 165 XLIV Isomerization of 4-Iodoazobenzene in Dioxane...... I66 XLV Isomerization of 4-Iodoazobenzene in Benzene...... 168

XLVI Isomerization of 4-Iodoazobenzene in Heptane...... I69

XLVII Isomerization of 5-Methoxyazobenzene in Ethanol...... I7I ix Page XLVIII Isomerization of 5-Methoxyazobenzene in Dioxane...... 172 XLIX Isomerization of 5-Methoxyazobenzene in Benzene...... I?p L Isomerization of 5-Methoxyazobenzene in . Heptane...... 174- LI Isomerization of 4-Methoxyazobenzene in Ethanol...... 175 LIX Isomerization of 4-Methoxyazobenzene in Dioxane...... 176 LIII Isomerization of 4—Methoxyazobenzene in Benzene...... 178 LIV Isomerization of 4-Methoxyazobenzene in Heptane...... 179 LV Isomerization of 5-Nitroazobenzene in Ethanol...... l8o LVI Isomerization of 5-Nitroazobenzene in Dioxane...... I8l LVII Isomerization of 4—Nitroazobenzene in Ethanol...... 182

LVIII Isomerization of 4-Nitroazobenzene in , Dioxane...... 185 LIX Isomerization of (5-Phenylazophenyl)- trimethylammonium Chloride in Ethanol...... I85 LX Isomerization of (5-Phenylazophenyl)- trimethylammonium Chloride in Dimethyl Sulfoxide...... I86

LXI Isomerization of (5 -Phenylazophenyl)- . trimethylammonium Chloride in Water...... I87

X Page LXII Isomerization of (4-Phenylazophenyl)- trimethylammonium Chloride in Ethanol...... 188 LXIII Isomerization of (4-Phenylazophenyl)- trimethylaramonium Chloride in Dimethyl Sulfoxide...... 190 LXIV Isomerization of (4-Phenylazophenyl)- . trimethylammonium Chloride in Water...... I9I

xi LIST OF ILLUSTRATIONS Figure Page 1 Absorption Spectrum of 3-Cyanoazobenzene In 95 per cent Ethanol 91 2 Absorption Spectrum of 4-Cyanoazobenzene In 95 per cent Ethanol 92 3 Absorption Spectrum of 3-Fluoroazobenzene In Absolute Ethanol 95 4 Absorption Spectrum of 4-Fluoroazobenzene In Absolute Ethanol 94 5 Absorption Spectrum of 3-Chloroazobenzene In Absolute Ethanol 95 6 Absorption Spectrum of 4-Chloroazobenzene In Absolute Ethanol 96 7 Absorption Spectrum of 3-Bromoazobenzene In Absolute Ethanol 97 8 Absorption Spectrum of 4-Bromoazobenzene In Absolute Ethanol 98

9 Absorption Spectrum of 3-Iodoazobenzene In Absolute Ethanol 99 10 Absorption Spectrum of 4-Iodoazobenzene In Absolute Ethanol 100 11 Absorption Spectrum of 3-Methoxyazobenzene In Absolute Ethanol 101 12 Absorption Spectrum of 4-Methoxyazobenzene In Absolute Ethanol 102 13 Absorption Spectrum of Trlmethyl(3-phenylazophenyl)ammonlum Salt In Water 103 14 Absorption Spectrum of Trlmethyl(4-phenylazophenyl)ammonlum Salt In Water 104 15 Absorption Spectra of: I trans-Potassium Azobenzene-3-sulfonate (Anhydrous) In Water. II trans - Potassium Azobenzene- 4-sulfonate Dlhydrate In Water, 105 xll Figure Page

16 Absorption Spectra of; I trans-Potassium Azobenzene-5-carboxylate in Water, II trans-Potassium azobenzene-4-carboxylate in water. I06 17 Rate of Isomerization of 4-Pluoroazobenzene at 2 5 .2 0 c. in Various Solvents I07 18 Rate of Isomerization of 4-Pluoroazobenzene at 54 .8 0c. in Various Solvents I08 19 Rate of Isomerization of 4-Pluoroazobenzene at 44.5°C. in Various Solvents 109 20 Arrhenius Plot for the Rate of Isomerization of Gyanoazobenzenes 110 21 Arrhenius Plot for the Rate of Isomerization of 5-Pluoroazobenzene 111 22 Arrhenius Plot for the Rate of Isomerization of 4-Pluoroazobenzene 112 25 Arrhenius Plot for the Rate of Isomerization of Chloroazobenzenes 115 24 Arrhenius Plot for the Rate of Isomerization of 5-Bromoazobenzene 114

25 Arrhenius Plot for the Rate of Isomerization of 4-Bromoazobenzene II5 26 Arrhenius Plot for the Rate of Isomerization of 5-Iodoazobenzene 116 27 Arrhenius Plot for the Rate of Isomerization of 4-Iodoazobenzene 117 28 Arrhenius Plot for the Rate of Isomerization of Methoxyazobenzenes 118

29 Arrhenius Plot for the Rate of Isomerization of Nitrobehzenes II9 50 Arrhenius Plot for the Rate of Isomerization of (Phenylazophenyl)trimethylammonium chlorides 120

xiii I . INTRODUCTION

Geometric isomerism was encountered fairly early in the history of organic chemistry. The first few examples of this phenomenon involved double bonds be tween carbon atoms, and the presence of two isomers was attributed by van't Hoff^ to restricted rotation

^ J. H. van't Hoff, " Voorstel tot Uitbreiding der Structuur-Pormules in de Ruimte, " Utrecht (1874) about the double bond. The same explanation was in voked by Hantssch and Wemer^ to account for a similar

^ A. Hants8ch and A. Werner, Ber., H (I890) . isomerism known to occur in compounds containing a nitrogen atom linked to a carbon atom by a double bond, such as the oximes. A logical extension of the Hantzsch-Wemer theory leads to the prediction that other compounds containing C=N or N=^ bonds should be 2 capable of existing in geometrically isomeric forms. As a matter of fact, isomers have actually been obtained in a number of cases; for example, phenyl c hydrazones, semicarbazones, diazocyanides, diazotates and azoxy compounds.®

® J. Meisenheimer and W. Theilacker, " Stereo- chemie des Stickstoffs, " pp. 965-II65 of Vol. Ill of K. Preudenberg, Stereochemie, Pranz Deuticke, Leipzig and Vienna (1935) •

Although azobenzene and its derivatives were known to contain nitrogen atoms linked to each other by a double bond, no unequivocal demonstration of the exist ence of a cis isomer in these cases was given until Hartley,^ in 1927, first isolated the cis form of

4 G. 8 . Hartley, Nature, 140, 28l (1927) . azobenzene by crystallization from solutions of the ordinary form after exposure to sunlight. He followed up this communication by another one® in which he made

® G. S. Hartley, J. Chem. Soc., 633 (1938) . a further study of the new compound and established definitely its identity as the cis form of azobenzene. 5 It was found to revert completely to the trans form on heating. Dilute solutions of the same concentration of either form quickly became Identical on exposure to light. This behavior can be represented as follows;

N II N light

cls-Azobenzene trans-Azobenzene

The thermal rate of Isomerization of cis-azobenzene to trans-azobenzene was measured In several polar and non-polar solvents and the reaction kinetics were found to be first-order. The speed of the reaction was re ported to be not greatly dependent on the solvent. By measurement of the rate at various temperatures, an activation energy of 25 kcal. per mole was calculated for this reaction. The addition of base or salt In aqueous medium was found not to have any effect on the rate of Isomerization; acids, however, accelerated the reaction. Several para-substituted azobenzenes were also studied with a view to seeing whether these com pounds could exist In geometrically Isomeric forms 4 - like the parent compound. It was found that 4,4»-dimethylazobenzene behaved similarly to azo benzene in that the light absorption of an acetone solution of the ordinary form increased on insolation, and the compound became in part more resistant to precipitation by water. Isolation of the cis form, however, was not attempted. 4-Methoxyazobenzene exhibited an analogous behavior, and attempts to isolate the cis form by the same procedure as for azobenzene, namely, fractional precipitation of the trans form from an acetic acid solution by water, yielded a viscous, red oil. 4-Hydroxy-, 4-amino-, and 4-dimethylamino-azobenzenes all showed appreciable darkening on exposure to light; however, their rates of reversion to the trans form in hydroxylie solvents were too rapid to allow isolation of the cis form by the method described above. (4-Phenylazophenyl)tric: méthylammonium nitrate, in aqueous solution, also exhibited increased light absorption after insolation. Although its speed of isomerization to the trans form in water was much less than that of the other azo compounds studied, no attempt was made to isolate the cis form. In all cases, except in that of the hydroxy compound, the velocity of the isomerization was found to decrease with increasing polarity of the solvent. 5

Acid catalysis was noted in the case of 4-amino- and 4-dimethylamino-azobenzenes, and base catalysis in the case of 4-hydroxyazobenzene. The molecular structures of both the cis and the trans forms of azobenzene have been determined by means of crystal x-ray diffraction by Robertson and co-workers.^'7'° The trans form is nearly coplanar,

®J. J. de Lange, J. M. Robertson, and I. Wood ward, Proc. Roy, Soc., A, 171, 398 (1939). *^J. M. Robertson, J. Chem. Soc,, 232 (1939). ®G. C. Hampson and J. M. Robertson, ibid., 409 (1941). whereas the cis form is not because of steric hind rance between the ortho-hydrogen atoms of the two rings; as a result, each benzene ring is twisted approximately 50° from the planar position. The N=N bonds were found o to be of the same length, namely, 1.23±0.03 A, in both o forms; the C—N bonds, however, were found to be 1.46 A and 1.4l A in the cis and trans forms, respectively. The shortening of the C_N bond-length in the trans form is a good evidence of resonance in the coplanar trans configuration. 6 Cook and co-workers®^Isolated the cis forms

^ A. H. Cook, J. Chem. Soc., 876 (19^8). A. H. Cook and D. G. Jones, ibid., 1309 (1939). of azobenzene and several substituted azobenzenes by means of chromatography on a column of alumina. Thus were obtained the cis isomers of 4-methyl-, 4,4*-dio methyl-, 4-methoxy-, 4-ethoxy-, 4-chloro-, 3 -methyl-, 3-nitro-, 4-nitro-, 4-chloro-, 4-bromo-, 4-iodo-, 3 ,3 ’-dinitro-, 2 ,4-dimethoxy- and 2 ,6-dimethoxy-azo = benzenes. They also obtained the cis forms of 1-(phenyl c; azonaphthyl)- and substituted 2- (phenylazonaphthyl)- methyl ethers. However, in the following cases, no stable cis isomer could be isolated: 2 -methyl-, 2 ,2 *-dimethyl-, 3 ,3 ’-dimethyl-, 4-hydroxy-, 4-acetoxy-, 4-amino-, 4-acetamido-, 4-cyano-, 2-nitro-, 2 ,2 '-di nitro-, and 4,4*-dinitro-azobenzenes. It was noted that the stability of the cis isomer increased in the series: 4-chloro-<4-bromo-^4-iodoazobenzene. In general, no correlation between the stability of the cis isomer and the nature of the substituent in the azobenzene molecule was apparent. 7 They^^ also measured the absorption spectra of

n A. H. Cook, D. G. Jones, and J. B. Polya, J. Chem. Soc., 1516 (1939).

some cis and trans azo compounds in the visible and near ultraviolet regions. It was found that in the visible region, the two forms usually showed a maxi mum in absorption at about the same wave-length, but the extinction co-efficients of the cis isomers were approximately twice those of the corresponding trans isomers. There was no such definite correlation in the near ultraviolet region of the spectrum. Halpern, Brady and Winklerstudied the kinetics

J. Halpem, G. W. Brady and C. A. Winkler, Can. J.Research ^ B, 14-0 (1950) . of cis-to trans-isomerization of azobenzene in a variety of solvents. The kinetics were consistently first order. The rate increased with decreasing pol arity of the solvent. The Arrhenius activation energy plots gave good straight lines. The activation energies ranged from about 22.8 to 24.75 kcals. per mole. 8 13 Badger and Lewis investigated the oxidation of

13 G. M. Badger and G. E. Lewis, J. Chem. Soc., 2148 (1955). substituted trans-azobenzenes with perbenzoic acid. Their results seemed to indicate a linear relationship between the rate constants and Hammett's sigma-constants for the substituents.

Birnbaum, Linford and Style^"* have measured the

P. Birnbaum, J. H. Linford, and D. ¥. Style, Trans. Faraday Soc., 755 (1955). absorption spectra in ethanol of azobenzene and ten para-substituted derivatives in the trans forms, and in the cis forms, when sufficiently stable. The cis isomers prepared were those of 4-chloro-, 4-bromo-, 4-iodo-, 4-fluoro-, 4-ethoxy-, 4-methyl-, 4-carboxyo methyl- and 4,4'-diraethyl-azobenzene. They failed to isolate by chromatography on alumina the cis forms of 4-nitro-, 4-dimethylamino-, 4-cyano-azobenzene and azobenzene-4-(carboxylic acid). Le Pevre and Northcott^^ determined the rates of

15 R. J. W. Le Pevre and (Miss) J. Northcott, J. Chem. Soc., 867 (1955)• 9 cis to trans isomerization of azobenzene in seven different solvents, and of five para-substituted azobenzenes in benzene by dielectric capacity-time

measurements. The substituents studied were CH3O,

CH3, Cl, Br, and NOg. The rate constants decreased in the following order: CH30>CH3>C1 'r Br>H>NOs. The pure cis forms of the methyl- and nitro-azoz: benzenes however, were not isolated: a mixture of cis and trans forms, produced on exposure to light, was used. The activation energies ranged from 22,1 to 24,5 kcal, per mole. No direct correlation be tween the activation energies and the known properties of the groups studied was apparent, although there was a rough parallelism between the rates of cis-trans

isomerization for azobenzenes and those for diazocyancz ides containing the same substituents,

In 1951, Le Pevre and Worth^® reported that

i®R, J. W, Le Pevre and C, V, Worth, J, Chem, Soc,, I8l4 (1 9 5 1).

solutions of the trans form of 2,2*-azopyridine under went a change in dielectric constant and in light absorption after illumination by sunlight. This was taken as evidence for a partial conversion to the cis 10 form. Two years later, Campbell, Henderson, and Taylor actually isolated the els Isomer of

N. Campbell, A. W. Henderson, and D. Taylor, J. Chem. Soc., 1281 (1953).

2,2*-azopyridine by chromatography on silica gel. They also obtained cis-3 , 3 *-azopyridine in the same manner, and reported that this compound reverted to the trans form faster than cis-2 .2'-azopyridine. The cis isomers were characterized by their melting points, dipole mo ments, and absorption spectra, and x-ray powder photo graphs. Attempts to obtain the cis forms of 4,4'-azo= pyridine, 4,^ ’-dimethyl-2,2 '-azopyridine, 3-pbenyl= azopyridine and some other phenylazopyridines, however, were unsuccessful. Magee, Shand and Eyring^® have treated the cis-trang

18 J. L. Magee, W. Shand,Jr., and H.Eyring, J, Am. Chem. Soc., 6^, 677 (1941). isomerization reaction from the standpoint of the theory of absolute reaction rates. According to them, the experimental results on cis-trans conversions in ethylene ic compounds allow of two distinct mechanisms: (1) The 11 first one constitutes a rotation which involves only a singlet electronic state of the molecule and takes place against the torsion of the ir -bond with no un coupling of the electrons. This mechanism has a characteristically high frequency factor of the or der of 10^^ sec."^ and a high activation energy (55-^5 kcal. per mole). (2) The second mechanism comprises a rotation which occurs through uncoupling of the TT-electrons to give an intermediate triplet state. A characteristic of this mechanism is a relatively low frequency factor (ca. 10^ sec.“^) and a low activation energy of about 15-20 kcal. per mole. Prom these considerations, they concluded that azoo benzene probably isomerizes by the singlet state mechanism. Kaplan^^ undertook an extended investigation of

19 M. Kaplan, Ph.D. Dissertation, this University (1954). the effect of electron-withdrawing substituents on the rate of cis-trans isomerization of azobenzene. He found no general correlation between the rate of isomer ization of a substituted azobenzene and Hammett's sigma constant for "Dhe substituent under investigation. 12

Out of the series of compounds studied, 4-nitroazoc benzene stood out prominently, as this compound had an unusually high rate of isomerization. Furthermore, the effect of solvent polarity was reversed in this case: the rate constant increased on increasing the polarity of the solvent. Experimental results were obtained in some cases for which no explanation could be offered. 13

II. STATEMENT OF THE PROBLEM

The review of literature given in the preceding part shows the lack of correlation between the stability of the cis forms of substituted azobenzenes and the electrical nature of the substituents. The work of Kaplan,more than anything else, emphasizes the need for further quantitative information with more substituents, both electron-donating and electron-with drawing, on the cis to trans conversion of azobenzene. The further study of the influence of substituents on this reaction is the subject matter of the present dissertation.

The cis-trans isomerization of meta- and para-substituted azobenzenes was originally selected for investigation, because it allows an exeunination of the

electrical effects of the substituents without inter ference from steric effects. These two effects play

a very large part in the reactions of organic compounds, and, in many cases, such a study of one effect divorced from the other is not possible. Furthermore, the present, monomolecular isomerization does not depend 14 in any critical way on interaction with a second mole cule in attaining the transition state, as a bimole- cular reaction would. It was proposed to study monosubstituted cis azobenzenes with the following groups in the meta- or para-positions ; -P, -Cl, -Br, -I, -ON, -NO2 , -OCH3, CHs)3, 8O3 . The rate of cis to trans conversion is a direct method of evaluating their relative stabilities and the electrical effects of these groups on the isomerization reaction. At the same time, the first order character of the reaction under various conditions could be verified. The problem consisted of three parts: first, the synthesis and isolation of the required azo compounds in the cis and trans forms; second, the measurement of the rate of cis to trans isomerization under differ ent conditions with regard to temperature and solvent; and third, evaluation and interpretation of the results obtained. 15

III. RESULTS AND DISCUSSION

The investigation in hand required the synthesis of the desired monosubstituted azobenzenes in the trans and cis forms, the measurement of the spectra of both forms, and the determination of the rates of cis-trans isomerization to evaluate the stability of the cis isomers. These three parts are treated in that order in the following discussion.

A. Synthesis of the Necessary Compounds 1. Preparation of trans forms.-A conventional method of introducing substituents into an aromatic ring involves the replacement of an amino group by other groups through the reactions of the diazonium salt. It was originally proposed to prepare most of the re quired para-substituted azo compounds in this manner from the readily available 4—amlnoazobenzene. While the Sandmeyer reaction of diazotized 4-aminoazobenzene with potassium iodide worked fairly well, the same re action gave poor yields and a very impure product when used for the preparation of 4-chloroazobenzene; and 16 when applied to the preparation of 4-cyanoazobenzene, the product was even more impure, so much so that chrom atographic purification, despite a preliminary sublima tion, was rendered difficult. Hence, it was decided to abandon this route for the preparation of para-substituted azobenzenes. The next general method that was tried was the condensation of nitrosobenzene with the appropriately substituted aniline. Usually, the glacial acetic acid used in the condensation to remove the water formed also served as a solvent. When applied to the prepara-

-NO+H2N—^ ^ ^ ^ -h H2O

tion of azobenzenesulfonic acids, pyridine mixed with glacial acetic acid proved to be a better solvent. Ueno and Akiyoshi^° have studied the condensation of

K. Ueno and S. Akiyoshi, J. Am. Chem. Soc., 76, 3670 (1954). aniline, with nitro- and chloro-nitrosobenzenes. They found that the nitro substituents in the nitrosobenzene 17 molecule facilitated the reaction In comparison with the chloro group. The method was found satisfactory for the preparation of the meta- and para-substituted azobenzenes listed In Table I (see p. 18). This method either failed or gave extremely poor yields when tried for the preparation of the following compounds: ^-methoxyazobenzene, ^-dlmeuhylamlnoazobenc zene, ( 4-phenylazophenyl)trlmethylararaonlum nitrate, and 5-acetylamlnoazobenzene. In the case of the last- mentioned compound, the yields were somewhat better when a mixture of ethanol and glacial acetic acid was used as the solvent; however, this Improvement was not great enough to show much promise and so the reaction was not pursued further. The yield of 5-dlmethylamlnoazobenzene by the above-mentioned method was extremely low, and hence, another method was tried for this compound. The method Involved the condensation of nitrobenzene with N,N-dlmethyl-m-phenylenedlamlne In presence of solid potassium hydroxide at about 200° but even this

21 M. Martynoff, Bull, soc.chlm. Prance, l8,214 ( I951)

method did not prove satisfactory as no pure product could be Isolated. 18

TABLE I

SYNTHESIS OP SUBSTITUTED AZOBENZENES

Compound reacted Product with Nitrosobenzene

1. 2-Pluoroanlllne 5-Pluoroazobenzene 2. 4-Pluoroaniline 4-Pluoroazobenzene 5. 5-Chloroaniline 5-Chloroazobenzene 4. 4-Chloroaniline 4-Chloroazobenzene 5. 3-Bromoanillne 3-Bromoazobenzene 6. 4-Bromoaniline 4-Bromoazobenzene 7* 5-Iodoaniline 3-Iodoazobenzene*

8. 4-Methoxyanillne 4-Methoxyazobenzene 9. 5-Aminobenzonitrlle 5-Cyanoazobenzene* 10. 4-Amlnobenzonitrile 4-Cyanoazobenzene 11. 5-Nltroaniline 5-Nitroazobenzene 12. 4-Nitroanillne 4-Nitroazobenzene

15 . Sulfanilic acid Azobenzene-4-sulfonic acid 14. Metanilic acid Azobenzene-5-sulfonic acid*

15 . 5-Aminobenzoic acid 5-Phenylazobenzoic acid 16. 5-Aminoacetophenone 5-Phenylazoacetophenone 17. 4-Aminoacetophenone 4-Phenylazoacetophenone

* New compound. 19 It must be mentioned here that the preparation of 5-acetylamlno- and 5-dimethylamino-azobenzene was undertaken with the object of obtaining ultimately the (5-phenylazophenyl)trimethylammonium salt. How ever, since the above-mentioned experiments proved abortive, still another route to prepare this quat ernary salt was considered: a direct condensation of nitrosobenzene with a ( 5-aminophenyl)trimethylammonium salt. To test the feasibility of this method, the synthesis of ( 4-phenylazophenyl)trimethylammonium nitrate, a known compound, by the same route was first attempted as a model experiment. A 4:1 glacial acetic acid-water mixture, as well as a 7:4 dimethyl sulfoxide-acetic acid mixture, was employed as the solvent; but in neither case could the azo compound be salted out of the reaction mixture. Therefore, no attempts were made to try the same condensation with (3-aminophenyl)trimethylammonivm salt. Finally, another route for the preparation of the (3-phenylazophenyl)c: trimethylammonium salt was studied and found to be satisfactory. It consisted of three steps: (1) syn thesis of 5-nitroazobenzene; (2) reduction of the nitro compound to 5-aminoazobenzene by alcoholic-c: aqueous sodium sulfide; and (5) méthylation of the amine with methyl iodide in methanol at 70° in the 20 presence of solid calcium carbonate to neutralize the hydriodic acid formed. A low temperature and the presence of calcium carbonate were found to be essential conditions for obtaining high yields and a pure product. (4-Phenylazophenyl)trimethylammonium nitrate was prepared by méthylation of 4-dimethylaminoazobenzene with dimethyl sulfate, and conversion of the methoc sulfate to the nitrate by means of a saturated solution of ammonium nitrate. Nitro-benzene is mentioned by Hartley^ as a solvent for this reaction; but a much better product was obtained by the use of dimethyl formamide as the solvent. 22 3-Methoxyazobenzene was obtained by a method

P. Jacobson and P. Honigsberger, Ber., $6, 4096 (1905) . involving two steps; (1) coupling of benzene diazonium chloride with ortho-anisidine in the presence of sodium acetate to yield 3-methoxy-4-aminoazobenzene;

( 2) deamination of the product obtained in the first step by diazotization in sulfuric acid solution, followed by treatment with 30 per cent hypophosphorous acid. Out of the azo compounds prepared, the 3- and 4-phenylazophenyl methyl ketones were not employed 21 for rate studies*

2. Preparation of cis forms.-On exposure of the trans forms of azobenzenes to ultraviolet light, a photostationary steady state with the cis form is at tained. In the case of the non-ionic azo compounds, the two forms were easily separated by chromatography on a silicic acid-celite mixture on which the cis form was adsorbed more strongly than the trans form and formed a separate band at the top of the column. The same procedure failed to effect a separation of the two forms of (para-phenylazophenyl)trimethylc ammonium nitrate. Fractional crystallization from warm water was tried, since the work of Hartley^ indicated that the cis form is fairly stable in this solvent; but these experiments proved to be of no avail. Dowex 50, a cation exchange resin of high porosity, with sulfonic acid groups, supplied by The Dow Chemical Company, Midland, Michigan, was next tried in the form of the ammonium salt. It held the compound fairly strongly, for it required the use of a developer as strong as a 0.6 M barium chloride solu tion, and, even then, not all the compound was eluted. The value of the ratio, maximum optical density to minimum optical density in the visible region 22

of the spectrum, was used for detecting the cis form. The value of this ratio for the trans form is 2.11. A value higher than this number would indicate the presence of the cis form, since the cis isomer absorbs much more than an equivalent amount of the trans form in the region of the maximum. Although the first por tions of the eluent from the resin had a maximum to minimum ratio as high as 4 in some cases, yet no clear-cut separation of the two forms could be achieved.

Variation of the mesh size of the resin did not lead to any improvement. Pentasodium tripolyphosphate and ammonium chloride solutions were also tried as develop ers, but they failed to elute the azo compound. Finally, a weakly acidic resin, namely, Araberlite

XE-97j supplied by the Rohm and Haas Company, Phila delphia, Pennsylvania, was tried. It is a resin of fine particle size having carboxylic acid groups. With this resin, a successful separation of the two forms of the azo compound was effected. The equili brium mixture of the cis and trans forms of the nitrate in water, as obtained by exposure to light, was put on a column of the resin, which was used in the form of the sodium salt. The column was washed with water to remove the sodium nitrate formed by exchange, and then developed with 0.025 M sodium chloride solution. 25 Two distinct zones were thus formed and could easily be seen against the white background of the resin. The one to be eluted first had an optical density ratio of maximum to minimum as high as 15 .0, and, consequently, was recognized as the cis form. The solution of the cis form obtained in this manner was freeze-dried under reduced pressure in the dark, and the resulting solid extracted with acetone, which dissolved the cis compound, but not the sodium chlor ide. Evaporation of the acetone under reduced pressure afforded the pure cis form of (para-phenylazophenyl)o trimethylammonium chloride. Exactly the same procedure was used for obtaining the cis form of the correspond ing meta- quaternary ammonium salt. The success achieved with the quaternary ammonium salts encouraged attempts at a similar separation of the cis and trans forms of azobenzenesulfonic and azobenzenecarboxylic acids. Winkel and Siebert^^ made

A. Winkel and K. Siebert, Ber., %4, 670 (1941). a polarographic study of azobenzene-5,5'-disulfonic acid, and found that the cis form of the potassium salt of the acid is fairly stable; however, they could not separate the two isomers by fractional crystallization 24 or chromatography. In the present study, it was found that solutions of the potassium salts of azoc benzene-3- and azobenzene-4-sulfonic acids in water showed increased light absorption on exposure to light, and that these solutions reverted to the trans form fairly slowly. These experiments indicated that the cis forms of these salts are fairly stable. The separation of the two forms of the free acids by chromatography on silicic acid-celite was first attempted. Various organic solvents, both alone and mixed with water, were used as developers, but no separation into two zones occurred. Several anion exchange resins were tried next.

Amberlite XE-75 and Amberlite XE-98, both containing quaternary ammonium groups, and supplied by the Rohm and Haas Company, proved to be so strong that the azo compound could not be eluted from the resin, even with a 4 M solution of ammonium sulfate, or with a saturat ed solution of potassium sulfate. Amberlite lR-45

(Rohm and Haas Company), Dowex 3 (Dow Chemical Company), and Biorad AG 3-X4 (Bio Rad Laboratories, Berkeley, California) were then used in the form of the sulfate since they are weakly basic; however, even these resins held the azo compounds so strongly that they could not 25

be eluted with the same developers. The separation of azobenzenecarboxylic acids was now attempted in the hope that these acids, being weaker than the sulfonic acids, would not be held so strongly and would lend themselves to an easy separa tion. The potassium salt of the 4-carboxylic acid was not very soluble in water and hence attention was concentrated on the separation of the potassium salt of the 5-carboxylic acid. Spectroscopic evidence obtained showed that the cis form of this salt, like that of the sulfonic acids, is fairly stable in water. However, surprisingly enough, this compound, too, was held very strongly on the anion exchange resins men tioned above, and strong solutions of sodium chloride, potassium sulfate, ammonium sulfate, sodium phosphate and pentasodium tripolyphosphate, as well as a phosphate buffer of pH 7*0, failed to move the compound down the column. Variation in particle size was also tried, but to no avail. Hence, no further attempts at the

separation of the cis and trans forms of these acids were made.

B. Absorption Spectra of the Azo Compounds All the visible and ultraviolet absorption spectra were determined with a Beckman Model D. U. Quartz 2 6

Spectrophotometer. The solvent was absolute ethanol in most cases, although 95 per cent ethanol and water were used in some cases. The spectra of the trans formaj as well as of the cis forms, wherever prepared, are shown in Figures I-I6. It must be mentioned that for these spectral measurements freshly prepared sam ples of both the isomers were used. Extreme precau- tions were taken to exclude light during the isolation of the cis forms, since, in some cases, the cis forms were found to have isomerized somewhat, even though they had melting-points several degrees higher than the values recorded in the literature. The molecular extinction coefficient (molar absorptivity),^ , is given by the equation:

(z = (l/c.l) O.D., where c = concentration in moles per litre, 1 = length in cm. of the solution through which light passes, and O.D. = optical density (absorbance) at the wave-length in question. The values of (z at the maximum in the visible region of the spectrum for the azobenzenes studied are given in Table II (see p.27). It will be seen that in all cases, the cis iso mer has a higher absorption at the maximum in the region 415-490 mu than the trans isomer. The strong absorption band in this region is ascribed to the TABLE II

MOLECULAR EXTINCTION COEFFICIENTS AND WAVE-LENGTH OF MAXIMUM ABSORPTION FOR VARIOUS AZOBENZENES IN THE REGION 400-500 mu

Substituent Solvent t cis (mu) t trans (mu)

3-CN 95 % ethanol 1051 (429) 456 (445)

4-CN II II 1430 (430) 583.(453) 3-F Absolute ethanol 1311 (428) 483 (439) 4-F II II 1441 (429) 494 (439) 5-Cl II II 1292 (430) 469 (443)

4-Cl II II 1623 (432 ) 574 (443) 3-Br II II 1255 (432) 483 (445 ) 4-Br II II 1797 (432) 602 (444)

5-1 II II 1278 (433) 509 (444) 4-1 II II 1793 (434) 696 (444) 5 -OCH3 II II 1429 (430) 541 (444) ro -q 4 -OCH3 II II 2258 (437) 985 (430)

5-N(CH3)3 Water 1243 (420) 700 (428) TABIiE II (contd.)

Substituent Solvent cis (mi) trans (mu)

4 ^ CHs) 3 Water ll4o (419) 772 (430) 3-SO3K 11 796 (428) 4 -SO3K 11 - 965 (430) 5 -CO2K 1 t - 953 (425) 4 -CO2K 11 1050 (426)

ro 00 29 N=N linkage. In all cases except that of 4-methoxyc: azobenzene, the absorption maximum of the cis isomer with respect to the trans isomer is shifted slightly toward the side of lower wave-length; for 4-methoxyc: azobenzenethe shift is in the opposite direction. In the near ultraviolet region (220-350 mu), the spectra vary from compound to compound; however, in general, the trans isomers have an absorption maximum in the region of about 310-3^0 mu. This absorption has been attributed to conjugation between the N=N bond and the aromatic rings. In the cis forms, this resonance is inhibited due to non-coplanarity of the molecule as a result of steric interference of the ortho-hydrogen atoms of adjacent rings. Hence, this absorption is very weak and is shifted tremendously to the shorter wave-lengths.

C . Measurement of the Rates of Isomerization The rates of cis to trans isomerization reactions in various polar and non-polar solvents were measured spectrophotometrically at two temperatures in all cases and more than two temperatures in some cases. Both the cis and trans forms have absorption maxima in the region of 4-20-430 mu; however, the former has a higher absorption in this part of the spectrum (see Figures 30

1-14). The fall in optical density at a given wave-length thus constitutes a convenient method of following the rate of conversion of the cis to the trans form. The reaction vessel used was of the same type as that described by Kaplan.^® Duplicate rate measurements, made for 4-cyanoazobenzene at different concentrations in benzene and in n-heptane at 35.0°, are shown in Tables XIII and XIV, respectively; the rate constants were 1.95 % 10~^ and 1.93 x 10~^ min.~^ for heptane, and 1.35 % 10~^ and 1.6l x 10~^ min."^ for benzene. To check further the reliability of the rate constants, a trial run was made at 35.0° with azobenzene in benzene and in absolute ethanol. The rate constants thus obtained were 3.57 x 10 , and 2.02 X 10 * min. respectively; the corresponding values obtained by extrapolation from the data of

Halpem, Brady and Winklerare 3*51 x 10"^ and

2.00 X lO"^ min."^. A typical set of data obtained for the isomeriza tion reaction of 4-fluoroazobenzene in n-heptane, benzene, dioxane, and absolute ethanol at three differ ent temperatures is shown graphically in Figures 17-19. The linearity of the plots of log per cent cis versus time throughout the reaction bears out the first order nature of this isomerization reaction. With the excep tion of the quaternary ammonium salts, all other 31 compounds studied gave a similar linear plot through out the reaction, and the slope of this line was used to calculate the rate constant. Since a large number of rate studies were made, it is not possible to show all the plots; therefore the data are given in Tables VI-LXIV in the Appendix. The possibility of second order kinetics is eliminated because a variation in concentration tried in some cases did not produce any appreciable change in the rate constant. To ascer tain whether only the isomerization reaction was occurring in each case, the final optical density of the solution at infinite time was compared with that calculated for an equivalent concentration of the trans form. In all cases, except that of the cyanoazobenzenes in ethanol at a higher temperature, and of the quaternary ammonium salts, especially in water, the agreement between the two values was within the limits of experimental error. In the two cases mentioned above where the two values for the final optical density differed, the calculated value was used for computing the rate constant. The cyano compounds probably react with ethanol at a higher temperature, thus causing a difference be tween the experimental and calculated values for the optical density at infinite time. 52 In the case of the quaternary ammonium salts, the plots of log per cent cis versus time remained

linear up to about JO per cent completion of the re action, after which stage deviations from linearity were observed. In these cases, the initial slope of the line was used to calculate the rate constant. The deviation from linearity towards the later stages of the reaction, coupled with the fact that the value of the optical density at infinite time does not check with that calculated for an equivalent concentration of the trans form, indicates the occur rence of other reactions. This is in agreement with an earlier observation that prolonged heating of the para-quaternary salt with water led to the formation of 4-dimethylaminoazobenzene, which was isolated chromatographically and indentified by comparison of its melting-point and spectrum with that of an authen tic sample of the same compound. The first order rate constants (k) obtained for all the cases studied are given in Table III (see p. 54) . Plots of log k against the reciprocal of the absolute temperature for all solvent-compound combina tions investigated are shown in Figures 20-30. It is seen that the plots give good straight lines in all 33 cases where the rate studies were conducted at more than two temperatures, including those of the quaternary ammonium salts. The activation energies, E, and the fre quency factors. A, shown in Table IV (see p. 39), were calculated from the slopes of these lines on the basis of the Arrhenius equation. TABLE III 54

THE RATES OP ISOMERIZATION OP SUBSTITUTED cis-AZOBENZENES

Substituent Pirst order rate constant X 104 25 .2° 55 .0° 44 .5 ° 54 .6°

In Absolute Ethanol

4 -NO2 45.74 155.6

4-CN 4.56 15.55 47.24

4-P 0.72 2.59 8.20 4-01 1.09 5.52

4-Br 0.88 5.14 10.57 4-1 0.85 5.11 10.40 4 -OCH3 2.46 7.62

4-N(CH3)3 4.42* 12.58 56.59 H 2.02

5 -NO2 1.59 5.55 5-CN 1.75 16.33 3-P 2 .82* 8.43 25.89 5-ci 2.25 21.32

5-Br 2.17 20.75 5-1 2.52 22.15

5 -OCH3 2.22 22.58

5"^( CH3 ) 3 5 .20* 9.51 27.10 55

TABLE III (contd.) Substituent Pirst order rate constant X lO'^

25 .2° 55 .0° 44 .5 ° 54 .6°

In Benzene

4-NOa 95.5 ** 4-CN 4.37 15.80 55.26 4-P 1.17 5.82 15.51 4-Cl 1.67 5.56

4-Br 1.41 5.27 17.99 4-1 1.52 5.14 15.86

4 -OCH3 5.27 10.25 4 -CH3 10.2 ****

H 5.57 5 -NO2 3 .16**

5-CN 2.79 27.85 5-P 4 .79* 12.96 34.66

5 -ci 3.48 55.43 5-Br 5.43 54.63

5-1 5.70 55.19 5 -OCH3 3.81 59.16 56

TABLE III Ccontd.)

Substituent First order rate constant X 104

25.2° 55.0° 44.5° 54.6°

In Dioxane

4-NO2 17.75 62.95

4-CN 5.01 10.99 28.44 4-P 0.81 2.96 9.90 4-Cl 1.28 2.88

4-Br 1.01 5.74 12.12

4-1 0.97 5.70 11.91 4 -OCH3 2.65 8.24 H 2.75***

5 -NO2 1.56 5.85 5-CN 2.00 21.28

5-P 2 .29* 9.21 26.22 5-ci 2.51 24.56

5-Br 2.25 22.99 5-1 2.48 24.24 5 -OCH3 2.84 28.02 57

TABLE III (contd.)______

Substituent First order rate constant x 10"*

25 .2° 55 -0° 44 .5 ° 54 .6°

In n-Heptane

4 -N02 67.6 ** 4-CN 5.24 19.40 62.22

4-F 1.58 5.16 17.25

4-Cl 2.55 7.90 4-Br 2.12 7.50 22.84

4-1 1.89 7.09 21.79 4 -OCH3 5.79 11.62

H 5 .15 *** 5 -NO2 4.57** 5-CN 4.82 41.87

5-P 6.76* 17.64 46.80 5 -ci 5.18 46.06 5-Br 5.02 46.62

5-1 4.74 45.45 5 -OCH3 4.78 46.90 In 95 per cent Ethanol

4 -NO2 162.2 **

4-CN 1 5 . 4 5 58 TABLE III (contd.)

Substituent First order rate constant X 10"^

% . 8° 44.5° 5 0 .0° 54.6°

In Water

4-Mea 1 .56 2 .58 4.74 7.14 © 5-NMe3 0.82 1.50 2.51 5.99 In Dimethyl Sulfoxide © 4-NMea 6 .74 19.52 © 5-NMes 5.77 15.56

* Extrapolated value.

** By extrapolation or interpolation from the data of Kaplan^®. *** Extrapolated from the data of Halpern, Brady and Winkler^^. **** Interpolated from the data of Le Pevre and Northcott^®. TABLE IV

ACTIVATION ENERGIES AND FREQUENCY FACTORS FOR SUBSTITUTED AZOBENZENES

E ( kcal. per mole) Log A Normal Absolute Normal Absolute Substituent Heptane Benzene Dioxane Ethanol Heptane Benzene Dioxane Ethanol

4-NOa 22.4 * 22.1 * 23.44 22.74 13.51 * 13.51 * 14.43 14.32

4-CN 24.08 24.74 24.87 23.17 14.37 14.75 14.69 13.62 4-F 23.08 24.60 24.39 24.02 13.10 14.07 13.77 13.44 4-Cl 22.39 21.74 20.80 21.45 12.79 12.16 11.33 11.74 4-Br 23.24 24.54 24.06 23.87 13.34 14.13 13.63 13.43 4-1 23.31 23.90 24.57 24.54 13.38 13.64 13.99 13.89

4 -OCH3 20.91 21.05 21.72 21.68 11.89 11.95 , 12.34 12.27 4 -CH3 24.5 ** 12.70**

H 22.8"^ 23.3^" 23.6^ 24.3^ 12.88^ 13.lot 13.15^ 13.57*

3-NO2 23.2 * 23.6 * 23.90 24.87 12.98* 13.08 * 13.15 13.84

2-CN 22.06 23.59 24.34 23.27 12.32 13.17 13.56 12.74 ^

5-F 19.97 20.06 21.24 22.62 10.98 10.92 11.59 12.50 TABLE IV (cond.)

E (kcal, per mole) Log A

Normal Absolute Normal Absolute Substituent Heptane Benzene Dioxane Ethanol Heptane Benzene Dioxane Ethanol

5-Cl 22.28 22.88 25.10 25.55 12.52 12.79 12.79 12.91 3-Br 25.89 25.47 25.54 25.24 15.65 15.18 15.08 12.82

5-1 25.09 22.45 25.58 22.21 15.04 12.49 15.11 12.15

5 -OCH3 25.29 25.79 25.50 25.47 15.20 15.46 12.98 12.99 Dimethyl Absolute Dimethyl Absolute Water Sulfoxide Ethanol Water Sulfoxide Ethanol

, © 4-NMes 21.57 21.71 21.70 11.12 11.77 12.05 0 5 -NM63 21.26 20.52 20.40 10.78 10.90 11.07

* Values obtained by Kaplan^®.

^ Values reported by Halpern, Brady and Winkler^^.

** Value reported by Le Pevre and Northcott 15 41 An Inspection of the data shows that all the para- substltuents, both electron-withdrawing and electron-donat ing, increase the rate of cis to trans isomerization as com pared to that of the parent compound. The rate is also en hanced, though not generally to the same extent, by the meta-substituents, with the exception of cyano and nitro groups which cause a slight decrease. It is at once appar ent that there is no correlation between the effect of a substituent on the rate of cis to trans isomerization of azobenzene and Hammett’s sigma-constant for the same substi tuent . Furthermore, it will be noted that the effect of solvent polarity on these reactions is small : a change in medium from ethanol to n-heptane usually produces only about a twofold increase in rate. However, there is one case, and possibly two cases, in which the rate decreases as the medi um is changed from a polar to a non-polar one. These are the cases of 4-nitro- and 4-cyano-azobenzene. The former shows a definite decrease in rate in n-heptane, in benzene, and in dioxane, as compared to that in ethanol; the latter, however, shows a reversal of the solvent effects as compared to azobenzene only for ethanol, dioxane and benzene. It is worth noting that out of all the groups studied, the nitro and cyano groups are unique in that they allow resonance structures like the following, 42

In which the IT-electron density is decreased at the azo linkage. The valence bond formulation was used above since it is easy to represent the charge separation by this for mula; however, the molecular orbital treatment unequivocally

shows that it is not the unshared pair of electrons on the azo nitrogen atom that is withdrawn but rather the electrons constituting the TT-bond. In the latter treatment, the resistance to torsion shown by a double bond is attributed to the decrease in energy content resulting from a large amount of p-orbital overlap and formation of the TT-bond. If, then, the 7f -electron density were to be reduced at the azo linkage as would be the case for 4-cyano- and 4-nitroazobenzene, the resistance to torsion would diminish, and isomerization from the cis to the trans form would be facil itated. The nitro group, being more powerfully electron- withdrawing than the cyano group, causes the isomerization to be the faster of the two; in fact, it is the fastest in the series of azobenzenes studied. For the other substitu ted azobenzenes studied, a withdrawal of electrons by 43 resonance with the substituent Is not possible, but only an Inductive withdrawal Is possible. The -9(CHs)3 group, how ever, Is a very powerful Inductive wlthdrawer of electrons because of the positive charge that It carries, although resonance forms of the type that are possible with a para- nltro substituent cannot be written In this case. Both the meta- and the para-quaternary ammonium derivatives of azo benzene studied Isomerlzed faster than the parent compound, the para-compound being the faster of the two. The solvent effects mentioned before support the pre mise used above. If the Isomerization In 4-cyano- and 4- nltro-azobenzene occurs as a result of Increased charge separation In the transition state, then a solvent with a high dielectric constant would promote the Isomerization. This Is precisely the case for 4-nltroazobenzene. In the case of 4-cyanoazobenzene, the rate of the reaction In ethanol Is comparable to that In benzene, although In the case of the remaining azobenzenes, the rate Is always great er In benzene than In ethanol. Furthermore, the activation energy for 4-nltro- and 4-cyano-azobenzene In ethanol Is less than that In the other solvents. The fact that the effect of solvent polarity on the rate of Isomerization for the remaining azobenzenes studied Is In the other direction (an Increase In rate being pro duced by a decrease In the dielectric constant of the 44 medium) shows that these compounds probably isomerize by a different mechanism. The Influence of solvent on the re action, however. Is not as great as that In reactions In volving Ions: as stated before, the effect of changing the medium from ethanol to n-heptane Is to Increase the rate about twofold. This fact, coupled with the observation that the rate of Isomerization Is Increased by all substituents studied, except meta-cyano and meta-nltro groups, leads one to believe that the Isomerization reaction may Involve radi cals produced by uncoupling of the '%-electrons of the azo linkage. In this connection. It Is Interesting to examine the data on free radical phénylation of monosubstituted ben zenes tabulated by Rondestvedt and Blanchard.They point

C. S. Rondestvedt, Jr., and H. S. Blanchard, J. Org. Chem., 21, 229 (1956). out that all compounds with meta- and para-substltuents, ex cept the one having the meta-methoxy group, undergo phényla tion at a rate greater than that for benzene Itself. They suggest resonance stabilization of the unpaired electron by all the para-substituents to be the underlying reason for an Increase In rate with these substituents. If a similar line of reasoning Is adopted in the case under discussion, then the Increase In the rate of cls-trans Isomerization of azo benzene produced by Introducing as para-substituents the 45 groups -OCH3, -CHs, -Pj -01, -Br, and -I, can be explained as due to resonance stabilization of the unpaired electron by forms such as the following:

It will be noted that in writing these formulae, an electronic motion away from the substituent is involved. The methoxy group is known to be a better ortho-para elec tron donator than the methyl group, and the latter in turn is better than the halogens. It is, therefore, not surpris ing that the rate of isomerization of para-substituted azo benzenes decreases in this order. Amongst the halogens, the para-fluoro group slows down the isomerization in comparison with the other halogens. A similar effect is recorded by Rondestvedt and Blanchard,who attribute it to the greater electronegativity of fluorine militating against withdrawal of electrons from it. The rate, however, increases slightly in the series, 4-iodo-, 4-bromo- and 4-chloro-azobenzene. 46

This indicates that inductive withdrawal of the TT-electrons with the resulting ease of isomerization may also be playing a part, since the inductive withdrawal would be greatest in the case of chlorine and least in that of iodine. The halo gen atoms in the meta-position increase the rate of isomeri zation of azobenzene to a slight extent. This activation is in accordance with the results tabulated by Rondestvedt and Blanchard.The meta-cyano and meta-nitro groups both slow down the cis-trans isomerization, although they accelerate slightly the phénylation reaction. On the other hand, the meta-methoxy group accelerates somewhat the isomerization, but decelerates the phénylation. However, these effects in both cases are not very great. The evidence that can be cited against the uncoupling of tT-electrons in the azobenzenes is that the frequency fac tors in this isomerization reaction range between 10^^ and 10^^ sec."i, whereas from the Eyring theory^® these factors should be of the order of 10^ sec. ^ or less, if the reac tion proceeds by a triplet mechanism. Nevertheless, reson ance forms of the type discussed above would still be im portant if the electrons were not promoted to a triplet level but were merely present in separate orbitals in the singlet level in the transition state; they would then be able to resonate with the aromatic ring and the energy of the singlet transition state would thus be lowered. The 47 frequency factors in the present case are comparable to those in ethylenic compounds having an aromatic ring at tached to the doubly bonded carbon atom, where Eyring con siders the singlet mechanism of isomerization to be in volved. The activation energies for the isomerization of azobenzenes range between 20 and 25 kcal. per mole, as com pared to about 55-45 kcal. per mole for the singlet mechan ism in ethylenic compounds; but Eyring himself postulates a singlet mechanism for the cis-trans isomerization of azo benzene .

The effect of changing the solvent polarity on the rate of isomerization of azobenzene and substituted azobenzenes studied, except 4-cyano- and 4-nitro-azobenzene, can be ex plained by a consideration of the dipole moments of the cis and trans forms. cis-Azobenzene has a dipole moment of

5'0 D, whereas the trans form has a dipole moment of zero due to the symmetry of the molecule.In the cis form.

G. S. Hartley and R. J. W. L e 'Pevre, J. Chem. Soc., 531 (1939). there are two permanent dipoles with their negative ends located at the nitrogen atoms^® so as to reinforce each

23 K. E. Calderbank and R. J. W. Le Pevre, J. Chem. Soc., 1949 (1948). 48

other as follows:

The evidence for the direction of the dipoles as shown above Is based on the dipole moments of 4-substltuted cls-azobenzenes.^5 4-Nltro, 4-chloro, 4-bromo, and 4-methoxy groups cause a decrease In dipole moment as compared to cls- azobenzene, whereas the 4-methyl group Increases It. In going from the Initial to the final state during the Iso merization, there Is a decrease In dipole moment. A polar solvent like ethanol would be expected to stabilize the cis form much more than a non-polar solvent like n-heptane. If It Is assumed that a partial rotation around the N=N linkage occurs In the transition state, then this state would be less solvated than the ground state of the molecule and a decrease In rate would result In a polar solvent as compared to a non-polar solvent. This Inference Is Indeed borne out by the data for all the azobenzenes studied, except 4-nltro- and 4-cyano-azobenzene which have already been discussed. On the basis of the above discussion. It Is concluded that the Isomerization of 4-nltro- and 4-cyano-azobenzene probably proceeds through an Intermediate polar form. In volving a resonance withdrawal of TT -electrons from the azo 49 linkage. In the case of the other azobenzenes studied, the isomerization could occur by either a singlet or a triplet mechanism. The frequency factors favor the former mechanism, whereas the activation energies are more in line with the latter mechanism. 50

IV. EXPERIMENTAL A. Materials 1. Adsorbent.-The adsorbent used in the chromato graphic work was an intimate mixture of approximately two parts by weight of silicic acid and one part of Celite 5^5» a product of Johns-Manvilie Corporation. The silicic acid was a product of Mallinckrodt Chemical Works (prepared for chromatographic purposes by the method of Ramsey and Patter son) and was ground for 6-8 hours in a ball mill to obtain an adsorbent of suitable particle size. The silicic acid- celite mixture was activated according to Trueblood and MalmbergZT by heating in an oven at l80-200°C. for at least

K. N. Trueblood and E. W. Malmberg, Anal. Chem., 21, 1055 (1949); J. Am. Chem. Soc., %2, 4112 (1950). two hours, and, usually, about 15 hours.

2. Solvents.-The benzene, 95 per cent ethanol and and absolute ethanol used in the rate studies and spectral measurements were reagent grade. The n-heptane (Phillips Petroleum Company) used initial ly was freed from peroxides by passage through a column of silica gel, followed by distillation through a column packed with glass helices. The boiling point was 98.4°C. at 760 mm. 51

In later work, the distillation step was omitted as it was found that the rate constant was not changed by this modifi cation. The dioxane used for rate studies was obtained by puri fication^® of a commercial sample. A mixture of 2 1.

L. P. Pieser, ««Experiments in Organic Chemistry, «« D. C. Heath and Company, Boston (1955), p. 285. of the commercial dioxane, 27 ml. of concentrated hydro chloric acid, and 200 ml. of water was refluxed for 12 hours, during which time a slow stream of nitrogen was bubbled through the solution to carry away acetaldehyde. The solution was cooled, and potassium hydroxide pellets were added gradually with shaking until they no longer dis solved, and two layers had separated. After being allowed to stand for three hours, the upper layer of dioxane was decanted, and the treatment with potassium hydroxide pellets repeated three times, the dioxane being allowed to stand finally over potassium hydroxide for a day. Now it was de canted into a clean flask, refluxed with sodium for 12 hours and then fractionally distilled from the sodium through a column packed with glass helices. The fraction having a boiling point of 101.5° at j6o mm. pressure was collected separately and stored in a brown glass bottle over nitrogen. 52 The dimethyl sulfoxide used in rate studies with the quaternary ammonium azo compounds was obtained from Stepan Chemical Company and was fractionally distilled. The frac tion boiling at 56.0°/4.5 mm. was stored in an amber-colored glass bottle over dry nitrogen. The water employed for all purposes was distilled water.

All other reagents were obtained from the sources men tioned in the experimental section.

B. Synthesis of the trans Forms of the Desired Substi tuted Azobenzenes

1. Preparation of nitrosobenzene.^^-A mixture of

G. H. Coleman, C. M. McCloskey and P. A. Stuart in ''Organic Syntheses,'' Collective Volume III, John Wiley and Sons, Inc., New York (1955), P . 668. ,

125 ml. (1.22 moles) of nitrobenzene and a solution of 75 g. of ammonium chloride in 2.5 1. of water was stirred vigor ously, and treated slowly with l86 g. (2.58 moles) of high- grade zinc dust over a period of 5 minutes. About 5 minutes after the addition of zinc, the temperature rose to 65°C., at which stage enough ice was added to bring the temperature down to 50-55°C. Twenty minutes after the addition of zinc was started, the mixture was filtered, and the zinc oxide 55 residues were washed with 1,5 1. of boiling water. The fil trate and washings were combined and cooled immediately by the addition of ice to 0°C. to -2°C. To this cold solution of phenylhydroxylamine, a cold solution of 375 ml. of con centrated sulfuric acid was added and the temperature was brought down to -5°C. An ice-cold solution of 85 g. of sodium dichromate dihydrate in 350 ml. of water was now very rapidly poured into the reaction mixture with constant agi tation. The brown solution containing a straw-colored pre cipitate of nitrosobenzene was filtered and washed with 500 ml. of water. The crude product was rapidly steam- distilled in an all-glass apparatus and the distillate was collected in a receiver cooled by ice. The nitrosobenzene was ground in a mortar, washed with water, filtered and dried between layers of filter-paper. The yield of nitroso benzene was 70.0 g. (54^^, m.p. 64.1-67.2° (lit.^° 67.5 -68°).

°° E. Bamberger and L. Storch, Ber., 26, 473 (1893).

(The melting points reported throughout this dissertation are in degrees Centigrade and were taken on a thermometer which was calibrated against one supplied by the National

Bureau of Standards.) 54 2. Preparation of 4-Chloroazobenzene

a. From 4-amlnoazobenzene.^^-A mixture of

31 K, Heumann and E. Mentha, Ber,, 19, 1687 (1886).

55.8 g, (0,17 mole) of 4-aminozobenzene (Eastman Kodak Com pany, White Label) with IO6 ml. of concentrated hydrochloric acid (56 ^) and 800 ml. of water was cooled to 0-2° and diazotized slowly with 11.8 g. (0.17 mole) of sodium nitrite

in 25 ml. of water with constant stirring. The resulting solution of the diazonium salt was filtered and poured slow ly into a boiling solution of I6 g. (O.08I mole) cuprous chloride in 144 ml. of concentrated hydrochloric acid. After the addition of the diazonium salt was complete, the mixture was boiled for one hour. The precipitated 4-chloroazobenzene was filtered, washed first with concen trated hydrochloric acid, then with a 5 per cent solution of sodium hydroxide, and finally with water, and dried. The dark brown product weighed 16.2 g. (45.7^). Crystallization from alcohol did not yield a lighter-colored product. Hence the cmide product was dissolved in a mixture of 50 ml. of benzene and 10 ml. of Skellysolve B and filtered through a mat of silicic acid-celite. On evaporation of the solvent, 8.0 g. (21.6^) of orange crystals of 4-chloroazobenzene, m.p. 55

85.5-84.8° 92°), were obtained.

J. Burns, H. McCombie and H. A. Scarborough, J. Chem. Soc., 2928 (1928).

b . By condensation of nitrosobenzene with 4-chloroanlllne.33, ^^-A warm solution of 11.9 g. (0.095

E. Bamberger, Ber., 105 (I896).

P. Jacobson and A. Loeb, ibid., 5 6 , 4090 (1 9 0 5 ). mole) of 4-chloroanlllne (Eastman Kodak Company, White Label) in 20 ml. of glacial acetic acid was mixed with a solution, of 10.2 g. (0.095 mole) of nitrosobenzene In 15 ml. of glacial acetic acid, and the mixture was allowed to stand at room temperature for I9 hours. The product began to crystallize after about 15 minutes. The mixture was diluted with 100 ml. of cold water, and the dark brown solid col lected on a Buchner funnel and washed with water. The yield of dry product was 16.7 g. The compound was purified In the manner described In method (a) to yield 14-.7 g. (72.8^) of orange crystals of 4-chloroazobenzene, m.p. 85.5r-86.4°

(lit. 92°). A chromatographlcally purified sample melted at 8 9.8-9 0.2°. 56

5. Preparation of 4-lodoazobenzene^ ^^-To

E. Noelting and P. Werner, Ber., 23^ 5252 (I89 0). P. K. Pertsch and P. Heubach, Ann., 303, 330 (I89 8). C. Willgerodt and G. M. Smith, Ber., ^7, 1311 (1904). a suspension of 6O.O g. (0.35 mole) of powdered 4-aminoazobenzene in 800 ml. of water was added 24.0 g. (o.35 mole) of sodium nitrite, and the mixture was cooled to 0-5°. It was then slowly treated with l48 ml. of ice-cold 18 per cent hydrochloric acid so as to keep the temperature below 5 °. The resulting solution of the diazonium chloride was fil tered and added gradually to an ice-cold solution of 170.O g. (1.02 moles) of potassium iodide in 300 ml. of water. The mixture was allowed to stand for 3 hours, then warmed gently until the evolution of nitrogen was complete, and allowed to cool. The solution was made strongly alkaline with potassium hydroxide to remove free iodine, and the precipitated, dark brown 4-iodoazobenzene was filtered and washed with cold water. On being dried, it weighed 7 0.O g. (64.9^). Three grams of the crude product were dissolved in a mixture of

30 ml. of Skellysolve B and 15 ml. of benzene, and chromato graphed on a column of silicic acid-celite, 17.0 cm. long and 5.3 cm. in diameter, pre-washed with I50 ml. Skellysolve B. Development of the column, first with 150 ml. of 20 per 57 cent benzene in Skellysolve B, and then with 40 ml. of 1.5 per cent ether in Skellysolve B gave the following zones:

Zone (cm. ) Color Color with cone . H3SO4, 0- 0.2 Black Black 0.2- 0.8 Reddish-orange Violet-pink 6.0-15.5 Orange Orange The lowest zone was eluted with c.p. ether, and, on evaporation of the solvent, 2 .6 g. (overall yield, 56.5 per cent) of orange crystals of 4-iodoazobenzene, m.p. 105.5- 106.5 ° ( l i t . 105 O), were left behind. After recrystal lization from Skellysolve B, 2.2 g. of yellow-orange crys tals, m.p. 106.4-106.7°, were obtained.

4. Preparation of 4-Cyanoazobenzene a. From 4-aminoazobenzene.^^^ se-To a solution

E. Mentha and K. Heumann, Ber., 3^, 3022 (I886). E. Noelting and P. Werner, ibid., 23, 3256, (I890). of 16.9 g. (0.086 mole) of 4-aminoazobenzene in a mixture of

53 ml. of concentrated hydrochloric acid and 400 ml. of water, kept at about 3°, was added very slowly an ice-cold solution of 5 .9 g . (0.086 mole) of sodium nitrite in 20 ml. of water. The solution of the diazonium salt thus obtained was filtered and poured gradually into a mixture of 50 g. 58

(0.20 mole) of oupric sulfate pentahydrate and 57*7 g . (0.77 mole) of sodium cyanide dissolved in 500 ml. of warm water. The temperature was regulated at 60-70° during the addition. After the addition of the diazonium salt was completed, the temperature was maintained at 60-70° for two more hours, by which time the evolution of nitrogen had stopped. The dark brown precipitate was filtered, washed with water, and dried. The yield of the crude product was 28.5 g . (Theoret ical yield, 17.8 g.) On sublimation, 0.8 g. of the crude compound gave 0.2 g. (overall yield, 59*9 per cent) of orange crystals, m.p. 9 8.1-110.0° (lit. 120.5°^^ 120-125 °^^). Since this method of purification failed to yield a pure product, the crude material was extracted with Skellysolve B in a Soxhlet apparatus. A chromatographic examination of the product thus obtained showed it to be very impure. Crystal lization from Skellysolve B, benzene or ethanol did not afford a pure product, and hence this method of preparation of 4-cyanoazobenzene was abandoned. b. By condensation of nitrosobenzene with

4-aminobenzonitrile .-To a solution of 5-5 g* (0.047 mole) of 4-aminobenzonitrile (Eastman Kodak Company, Yellow Label) in 6.5 ml. of glacial acetic acid was added 5*1 g « (0.048 mole) of nitrosobenzene, and the solution was kept at 6o° for 6 hours and then at room temperature for 48 hours. The mix ture was diluted with 55 nil. of cold water and the black-red 59 solid that had separated was filtered, washed with cold water, and dried. It weighed 8.6 g. (8 9.0 per cent). On chromatographic purification and subsequent crystallization from benzene-Skellysolve B, 5*5 g* of the crude product gave 1 .5 g. (overall yield, 55*5 per cent) of red crystals of 4-cyanoazobenzene, m.p. 119.5-120.0°.

5.» Preparation of 5-Chloroazobenzene .^^-A solution of 10.2 g . (0.095 mole) of nitrosobenzene in 15 ml. of glacial acetic acid was added to 11.9 g . (0.095 mole) of 5-chloroaniline (Eastman Kodak Company, Yellow Label), and the solution was heated at 6o° for 1 hour and then allowed to Stand at room temperature for 12 days. The reaction- mixture was diluted with 100 ml. of cold water, filtered, and the dark brown solid washed and dried. It weighed 15-5 g . It was purified by dissolving it in 120 ml. of a 2:1 mixture of benzene and Skellysolve B and passing it through a mat of silicic acid-celite. In this way, 10.4 g . (51.6 per cent) of red crystals of 5-chloroazobenzene m.p. 6 5 .5 -6 4 .5 ° (lit.

6 7*5 °^^ were obtained. A sample after purification and crystallization from Skellysolve B melted at 6 7.4 -67.5 °.

6. Preparation of 5-Iodoazobenzene-A solution of

5.1 g. (0.025 mole) of 5-iodoaniline in 2.5 ml. of glacial 60

acetic acid was treated with 2.6 g. (0.024 mole) of nitroso benzene. The resulting mixture was heated at about 60° for 3 hours and allowed to stand at room temperature for 7 days. The black solid obtained after filtration weighed 7.3 g. Chromatographic purification of a 10 mg. test-sample in

0.5 ml. benzene was effected on a column (15 cm. x 1.5 cm.) of silicic acid-celite, pre-washed with 15 ml. Skellysolve B. Development with 12.5 ml. of 2:1 Skellysolve B-benzene mix ture, followed by 7.5 ml. of 5 per cent ether in Skellysolve B gave the following zones:

Zone (cm.) Color Cone. HgSO^ streak reagent 0- 0.5 Brown Violet 1.0- 2.8 Yellow Brown with violet edges 10.5-14.0 Yellow Orange (required compound) A large-scale chromatographic purification, followed by recrystallization from a 2:1 mixture of Skellysolve B-benzene, yielded 4.3 g. (60.1 per cent) of deep orange crystals of

3-iodoazobenzene, m.p. 7 0.3-7 0.5 °.

Anal.

Calcd. for C 12H9N2I: C, 46.77; H, 2.94; N, 9.09; I, 41 .19. Pound : C, 46.82; H, 3.06; N, 8.91; I, 40.95.

7. Synthesis of 3-Cyanoazobenzene a. Preparation of 3-aminobenzonitrile 61

(1) Attempted catalytic reduction of

3-nltrobenzonltrlle.-A suspension of 3*0 g. (0.020 mole) of 3-nitrobenzonitrile (Eastman Kodak Company, White Label) in 135 ml. of absolute ethanol was treated with hydrogen under a pressure of 52.5 Ibs./sq. in. in presence of Raney nickel as a catalyst until 0.06 mole of hydrogen was used up. After filtration of the catalyst, the solution was saturated with hydrogen chloride gas, but no precipitate was obtained. On standing for a week, a white precipitate was slowly formed, but it did not have the required melting point. The reduction was repeated in tetrahydrofuran as sol vent, but this modification did not yield the required amine, (ii) Reduction of 3-nitrobenzonitrile with stannous chloride and hydrochloric acid.^°-To a solution of

T. Bogert and H. T. Beans, J. Am. Chem. Soc., 26, 469 (1904).

50.0 g. (0.22 mole) of stannous chloride dihydrate in 150 ml. of concentrated hydrochloric acid was added very gradu ally 10.0 g. (0.068 mole) of 3-nitrobenzonitrile over a per iod of 30 minutes so as to keep the temperature of the mix- o ture at 30-35 • During this time, silky white needles had separated from solution. Now the mixture was warmed gently to effect solution of the crystals and then cooled in an ice- 62 salt bath for 4 hours. The yellowish-white precipitate of the stannichloride was filtered and washed with 15 ml. of concentrated hydrochloric acid previously cooled in an ice- salt bath. To liberate the free amine, the solid was dis solved in 20 ml. of water in a separatory funnel, and to this solution was added some ice, followed by 50 ml . ether, and, finally, a 10 per cent solution of sodium hydroxide, a little at a time, until the solution was alkaline. The aqueous layer was then extracted with four 20-ml. portions of ether, the ethereal extracts combined, washed ivith water, and dried over anhydrous magnesium sulfate. Evaporation of the ether gave 4.2 g . (52.7 per cent) of yellow needles. On recrystallization from carbon tetrachloride, 5*7 g. (46.4 per cent) of yellowish-white 5-aminobenzonitrile, m.p.

5 1 .6-5 2 .5 ° (lit.^^ 5 3 .0-5 3 .5 °), were obtained. b. Condensation of nitrosobenzene with

5-aminobenzonitrile.-A solution of 3-7 g . (O.051 mole) of 5-aminobenzonitrile in 4.0 ml. of warm glacial acetic acid was allowed to react with 5*4 g. (0.032 mole) of nitroso benzene at 60° for 8 hours and then left at room tempera ture for 15 hours. The reaction mixture was diluted with 20 m l . of cold water, and the black solid obtained after filtration, washing with water, and drying, weighed 6.8 g.

A small sample (5 mg.) dissolved in 1 m l . of benzene, was 63 chromatographed on a column of silicic acid-celite, 15 cm. x

1 .5 cm., pre-washed with 15 ml. of a 3:1 mixture of Skelly- solve B-benzene. On development with 20 ml. of a 5 per cent solution of ether in a 3:1 mixture of Skellysolve B-benzene, the following results were obtained: Zone (cm.) Color Color with conc. H28O4 0-0.1 Brownish-Black Black 0.1-0.5 Yellow Pink 6 .8-7.2 Yellowish-orange Orange

The zone corresponding to 6.8-7.2 cm. on a large-scale chromatogram was eluted with A;R; ether. Evaporation of the ether afforded 3«4 g. (55*4 per cent) of orange crystals of

3-cyanoazobenzene, m.p. 8 2.5 -8 5 .2°. Three recrystalliza tions from a 1:1 mixture of benzene-Skellysolve B yielded a product with m.p. 90.7-91.1°* Anal.

Calcd. for C13H9N3: C, 75-54; H, 4.38; N, 20.28.

Pound : C, 75*55; H, 4.23; N, 20.19*

33 8. Preparation of 4-bromoazobenzene.- -A warm solu tion of 16.0 g . (0.095 mole) of 4-bromoaniline in 20 ml. of glacial acetic acid was added to 10.2 g . (0.095 mole) of nitrosobenzene dissolved in 15 ml. of glacial acetic acid, and the condensation allowed to proceed at room temperature 64

for 16 hours. The reaction mixture was then worked up in exactly the same manner as that described previously under the preparation of 4-chloroazobenzene, method (b). The yield of orange 4-bromoazobenzene was 18.2 g. (75.1 per cent); m.p. 86.0-87.0° (lit. 89°,^^ 86°^^). A chromatographically purified sample, after recrystallization from a 5:1 mixture of Skellysolve B and benzene, furnished a product of m.p. 89.8-9 0.0°.

9. Preparation of ^-bromoazobenzene.^^-To a solu tion of 8.0 g. (0.047 mole) of 5“bromoaniline (Eastman Kodak Company, Mhite Label) in 4.5 ml. of glacial acetic

acid were added 5>1 g . (0.047 mole) of nitrosobenzene. The resulting solution was heated at about 6o*^ for 7 hours and

then allowed to stand at room temperature for 8 days. After addition of 55 ml. of cold water to the mixture, the black solid formed was filtered, washed and dried. It weighed 10.1 g. Part of this crude product, weighing 4.8 g ., was purified chromatographically to furnish 2.5 g. (overall yield, 45.5 percent) of red crystals of 5-bromoazobenzene, m.p. 68.0-6 8.5 ° (lit. ^^69°). After recrystallization from Skellysolve B, the m.p. was unchanged. 65 10. Preparation of 4-fluoroazobenzene solution

Lichtenberger and R. Thermet, Bull, soc. chim. France, 318 (1951).

of 5.2 g. (0,047 mole) of 4-fluoroanillne in 4.5 ml. of glacial acetic acid was reacted with 5.2 g. (0.048 mole) of nitrosobenzene. The solution began to get warm and was cooled in ice-water for 15 minutes, by which time a consid erable amount of brown-black solid had separated out. The mixture was left at room temperature for 24 hours, then di luted with 25 ml, of water and filtered to furnish 9.2 g. of crude product. On chromatographic purification, 5.0 g. (55.2 per cent) of orange crystals of 4-fluoroazobenzene,

m.p. 8 1.9-8 2.8° (lit. 8 2.5 °^^), were obtained.

11. Preparation of 3-fluoroazobenzene.^3_To a

solution of 5 .8 g. (0.052 mole) of 3-fluoroaniline in 5 ml. of glacial acetic acid were added very gradually 5 .8 g . (0,054 mole) of nitrosobenzene with cooling in ice. After the addition of nitrosobenzene was completed, the mixture was heated at about 75° for 12 hours and then allowed to stand at room temperature for 44 hours. The resulting dark purple solution was made alkaline by the addition of 50 ml. of 12 per cent potassium hydroxide solution, extracted with 66 five 30-ml. portions of ether, the ethereal extracts combined, washed with water, and dried over anhydrous magnesium sulfate. On evaporation of the ether, a dark red liquid, weighing 11.4 g. (100 per cent), was obtained. Chromatographic purification of 2 mg. of this red liquid, dissolved in 0.5 ml. of benzene, was effected on a column of silicic acid-celite

(15 cm. X 1.5 cm.), pre-washed with 15 ml. of Skellysolve B. The column was developed with 25 ml. of a 5 per cent solution of ether in Skellysolve B, giving the following zones:

25 per cent NaOH Conc. H2SO4 Zone (cm.) Color Streak Reagent Streak Reagent

0-0.1 Deep blue Deep blue Deep blue 1 .5 -2 .6 Light yellow Yellow Pink 7.O- 7 .5 Orange Orange Pinkish-orange

A large-scale purification of 2.5 g- of the crude product was then accomplished. The zone corresponding to 7*0-7*5 cm. was eluted with A.R. ether, and, on evaporation of the ether, it yielded I .9 g. (overall yield, 7 6.0 per cent) of red crystals, m.p. 41.8 - 4 5 .0°. A small amount was recrystallized twice from C-P. petroleum ether (b.p. 50-60°) to afford red crystals, m.p. 42.0-45*2° (lit.^^ 44°). 67

12. Preparation of 4-methoxyazobenzenesolu tion of 11.4 g. (0.095 mole) of p^-anlsidlne (Eastman Kodak Company, White Label) was reacted with 10.2 g. (0.095 mole) of nitrosobenzene dissolved In 15 ml. of glacial acetic acid at about 65 ° for 5 hours and subsequently at room tempera ture for 12 days. The reaction mixture was worked up In exactly the same manner as that described under 4-chloro-

azobenzene, method (b), to yield 15-1 S- (76.5 per cent) of

deep-orange crystals, m.p. 52.9-54.0° (lit. 55.5°,^^ 54 °,^^

42 R. p. Zellnskl and W. A. Bonner, J. Am. Chem. Soc., 2 1 , 1792 (1949). E. Bergmann and A. Welzmann, Trans. Faraday Soc., 52, 1521 (1956).

56 °^^). A small sample, after chromatographic purification

A. Burawoy and I. Markowltsch-Burawoy, J. Chem. Soc., 59 (1956). and recrystalllzatlon from Skellysolve B, had â m.p. of

54.2-54.7°.

1 5 • Synthesis of 5-Methoxyazobenzene a. By condensation of nitrosobenzene with meta-anlsldlne.-To a solution of 5-4 g . (0.028 mole) of 68 meta-anlsldlne In 4.5 ml. of glacial acetic acid were added gradually 5.1 g . (0.029 mole) of nitrosobenzene. The result ing dark red mixture was allowed to stand for 24 hours at room temperature. The solution was then made alkaline with sodium carbonate and extracted with three 5 0 -ml.-portions of benzene. The benzene extracts were combined, washed with water, and dried over anhydrous sodium sulfate. A 1 ml.- sample of this solution was chromatographed on a column of alumina (14.0 cm. x 1.5 cm.), pre-washed with 25 ml. of Skellysolve B. On development of the column with 25 m l . of a 10 per cent solution of ether In Skellysolve B, the fol lowing zones were obtained:

Zone (cm.) Color Color with conc. H2SO4 0-02 Dark brown Black 0.2-0.6 Orange Pink 5 .5-5*5 Yellow Orange A large-scale chromatographic purification was effected, and the lowest zone was eluted with ether. Evaporation of the ether yielded 0.9 g . (15-5 per cent) of 5-methoxyazobenzene as an orange-red, oily solid, m.p. 25-27.5° (llt.^^ 52.5-55.5°). b. Prom ortho-anlsldlne (1) Preparation of 5-methoxy-4-amlnoazobenzene.22- A solution of 7 6.0 g. (0.82 mole) of aniline In a mixture of 184 ml. of concentrated hydrochloric acid and

150 ml. of water was cooled to 0° and dlazotlzed slowly with 69

58.0 g. (0.84 mole) of sodium nitrite so as to maintain the temperature between 0-5°• The cold diazonium salt solution was added to an ice-cold solution of 101.0 g. (0.82 mole) of ortho-anisidine in 128 m l . of I8 per cent hydrochloric acid, followed immediately by 5 8 .0 g. of crystalline sodium acetate dissolved in 100 ml. of water. The mixture was then kept in a refrigerator. A saturated solution of sodium acetate was added to the mixture from time to time (every two hours during the first six hours) so that the solution just remained violet. After the mixture was cooled for a total period of 24 hours, the dark violet, crystalline precipitate of the hydrochloride was filtered and sucked dry. Addition of 50 ml. of saturated sodium acetate solu tion to the mother-liquor yielded some more precipitate, which was combined with the one obtained above. The combined solids were dissolved in hot 95 per cent ethanol, the solu tion made alkaline with a strong solution of ammonia, and the mixture diluted with 200 ml. of water. The resulting brownish-black precipitate of 5-methoxy-4-aminoazobenzene, after being filtered and dried, weighed 8 5 .0 g . Charcoal

treatment and recrystallization of 8.5 g* of the crude mate rial from 95 per cent ethanol afforded 7*6 g . (41.0 per cent) of brownish-red crystals, m.p. 9 8.0-102.2° (lit.^^

104-107°). 70

(il) Deamination of 3-methoxy-4-amlnoazobenzene.-A solution of 5.0 g. (0.022 mole) of 5-methoxy- 4-amlnoazobenzene In a mixture of 25*0 ml. of water and 4 ml. of concentrated sulfuric acid was dlazotlzed with 1.7 g. (0.024 mole) of sodium nitrite at 0°. The diazonium salt solution thus obtained was poured all at once Into 57*8 ml.

(0.55 mole) of Ice-cold 50 per cent hypophosphbrous acid. The mixture was stirred at 0° for 50 minutes and then left overnight In the refrigerator In a loosely stoppered flask. The deep orange-red solution was allowed to warm to room temperature and extracted with three 20 ml.-portions of ether. The ethereal layers were combined, dried over an hydrous magnesium sulfate, and the ether removed under re duced pressure to leave behind 4.2 g . of a reddish-brown liquid. A small sample (10.0 mg.) dissolved In 0.5 ml. of benzene was chromatographed on a column of silicic acld- cellte (15.0 cm. x 1.5 cm.), pre-wetted with 25.0 ml. Skellysolve B. The column was developed with 20 ml. of a

10 per cent solution of ether In Skellysolve B with the fol lowing results;

Zofie (cm.) Color Color with conc. H2SO4 0-0.2 Reddish-brown Brown 2.0-4.5 Orange Pink 9.2-9*8 Orange-red Greyish-orange 71

A large-scale purification was now effected, and the

zone corresponding to 9.2-9.8 cm. was eluted with ether. Evaporation of the ether yielded 2.9 g. of an orange-red solid, m.p. about 24°. It was further purified by chroma

tography on alumina as described under part (a) to give 2.7 g.(58.2 per cent) of orange-red crystals, m.p. 28-29°.

14. Preparation of 4-nitroazobenzene.-This compound was prepared from 2.8 g. (0.020 mole) of 4-nitroaniline and 2.4 g. (0.021 mole) of nitrosobenzene by the method des cribed by Kaplan.^® The chromatographically purified prod uct weighed 1.8 g. (39.1 per cent), and had a m.p. of 133.8-134 .4 ° (lit.^° 133.7-154 .6°).

15 . Preparation of 3-nitroazobenzene.-This com pound , too, was prepared by the method described by Kaplan : condensation of 8.4 g. (O.060 mole) of 3-nitroaniline with 7 .3 g. (0.064 mole) of nitrosobenzene yielded 10.1 g. (73.2 per cent) of chromatographically purified 3-nitroazobenzene, m.p. 9 4.7-9 5.2° (lit.^G 9 5.5 -9 6.7°). A sample purified by crystallization without chromatography had a m.p. of 80-83°

(purity, ca. 66 per cent). 72

l6. Preparation of (4-Phenylazaphenyl)trlmethyl-

ammonlum Nitrate a. In nitrobenzene as solvent.^-A solution of 1 5 .0 g. (0.066 mole) of 4-dlmethylamlnoazobenzene (Eastman Kodak Company, White Label) In 40 ml. of nitrobenzene was mixed with 1 6.8 g. (0.152 mole) of dimethyl sulfate, and the mixture heated at 150-l6o° for 50 mln. It was cooled and treated with a 10 per cent solution of sodium carbonate until alkaline. The dark red mixture was diluted with 500 m l . of cold water and extracted thoroughly with benzene to remove all non-lonlc organic compounds. The aqueous layer was then concentrated to a volume of 250 ml., and saturated

with ammonium nitrate to yield 7*6 g . (74.5 per cent) of orange-brown crystals, m.p. 206.2-210.5 ° (llt.^^ m.p. ca.

D. Vorlander, A. Logothetls and A. J. Perold, Ann., 545 , 505 (1906).

216°). b. In dimethylformamlde as solvent.- To a

solution of 2 .5 g . (0.011 mole) of 4-dlmethylamlnoazobenzene In 6 .5 ml. of warm dimethylformamlde was added 5*4 g . (0.022 mole) of dimethyl sulfate, and the resulting mixture heated

at 85° for 5 hours. It was cooled, treated with 50 ml. of 75

cold water and made alkaline with sodium carbonate. After a thorough extraction of the mixture with benzene, the quater nary nitrate was precipitated as described in part (a) in the form of beautiful orange-red plates, m.p. 219•8-220.6° (decompn.) (lit.^^ m.p. ca. 2l6°). The yield was 5*0 g.

(89.6 per cent). The compound was recrystallized twice from water and then from absolute ethanol to give 2.3 g • (68.7 per cent) of a product melting at 223.4-223.6° (decompn).

1 7• Synthesis of (3-Phenylazopheny^trimethylammonium Nitrate a. Preparation of 3-aminoazobenzene.^^-To a

G. Charrier and A. Beretta, Gazz. chim. ital., 54, 981 (1924).

solution of 10.083 g . (0.0444 mole) of crude 3-nitroazo benzene (m.p. 80-83°) in a mixture of 320 ml. of 95 per cent ethanol and 25 ml. of water were added 31*98 g. (0.133 mole) of crystalline sodium sulfide (Na2S.9H20), and the mixture was refluxed for 136 hours in a flask fitted with a conden ser closed at the top. The volume of the solution was now reduced to about 50 ml., and then 300 ml. of water were add ed. This dilution caused the separation of a black oil, which on standing overnight solidified to a yellowish-brown 74 mass, weighing 6 .500 g. A small sample (5 mg.) dissolved in 1 ml. of benzene was chromatographed on a column of silicic acid-celite (15 cm. x 1 .5 cm.), pre-wetted with 15 ml. of Skellysolve B. The column was developed with 25 ml. of a 5 per cent solution of ether in 5:1 Skellysolve B-benzene mixture with the following results: Zone (cm.) Color Color with conc. H2SO4 0-0.1 Black Black 0 .1-0 .4 Violet Black 0.8-1.0 Orange Pink 1.6-5 .0 Yellow Orange-Pink 1 2 .9-15.2 Orange Orange A large-scale chromatographic purification was accom plished, and the zone corresponding to I.6-5 .O cm. was eluted with ether. Evaporation of the ether yielded 4.560 g . (52.2 per cent) of orange flakes of 5-aminoazobenzene, m.p.

66.4-66.7° (lit.4° 62°). b . Méthylation of 5-aminoazobenzene.-To 4.56 g, (0.0252 mole) of 5-aminoazobenzene dissolved in a warm mix ture of 12 ml. of absolute methanol and 1 ml. of water were added 12.0 g . of calcium carbonate (0.12 mole), followed by 15 ml. (0.241 mole) of methyl iodide, and the mixture was heated at 68-72° for 96 hours. At the end of this period, the mixture was evaporated to dryness, then heated with 100 ml. of water and filtered hot to remove the calcium carbon ate. The filtrate deposited dark brown crystals. These 75

crystals were dissolved in about 800 ml. of cold water, and the solution was extracted with benzene until the benzene layer remained colorless. The aqueous solution was concen trated to a volume of 75 ml., and saturated with ammonium nitrate, whereupon 6.875 g* (80.74 per cent) of orange-brown crystals, m.p. 175*6-174.9° (decompn.) were obtained. The compound was purified by charcoal-treatment and recrystal llzatlon from water, followed by two more crystallizations from absolute ethanol, to yield 5*980 g. (70.25 per cent) of orange crystals, m.p. 176.8-177.2° (decompn.).

Anal.

Calcd. for C15 H18N4 O3 (nitrate); C, 59*59; H, 6.00; N, 1 8.55 ; 0, 1 5 *8 8. Found : C, 48.99; H, 4.85; N, 11.59; balance, 5 4 .7 7* As will be seen from the above analysis, the product obtained was not the nitrate. The only other possibility was that the salt may have been the Iodide, which was Indeed the case. Calcd. for C15 H3.8IN3 : C, 4 9 . 05 ; H, 4.94; i, 5 4 .56 ; N, 11.44.

The addition of silver nitrate to an aqueous solution of the salt produced a precipitate of silver Iodide; but with brucine and concentrated sulfuric acid, no red color characteristic of a nitrate was produced. 76

l8. Preparation of potassium azobenzene-3~sulfonate.-A solution of 7*55 S* (0.042 mole) of anhydrous meta- nlllc acid (Eastman Kodak Company, VJhlte Label) In a hot mixture of 11 ml . of pyridine and 2 ml. of water was mixed with a solution of 4.51 g. (0.042 mole) of nitrosobenzene In 14 ml. of glacial acetic acid. The mixture was maintained at 75° for 5 minutes. At the end of this period, 22.0 g . of potassium hydroxide pellets were added, and the solution was boiled for 20 minutes to convert the pyrldlnlum salt to the potassium salt, which crystallized out as a dark red solid on cooling. The crude product was dissolved In 50 m l . of warm water, and the aqueous solution extracted thoroughly with benzene until the benzene layer remained colorless. On concentration of the aqueous layer, 5*972 g . of the salt separated out as an orange solid. It was purified by three recrystalllzatlons from hot water to yield bright orange crystals, which, after being dried overnight In a vacuum desiccator containing calcium chloride, weighed 4.810 g . An analytical sample was prepared by drying 75*589 mg . of the product over phosphorus pentoxlde at the temperature of boiling xylene (157-140°) and at a pressure of 2 mm. The sample had a constant weight of 69.829 mg. after a period of 5 hours. Hence the estimated yield of the anhydrous salt

Is 55*91 per cent. 77 Anal.

Calcd. for C12H9N28O3K: C, 47*99; H, 3.02; N, 9.33; S, 10.68; K, 1 2 .9 9. Pound : C, 4?.90; H, 2.94; N, 9.23; 8, 1 0 .65 ; K, 1 2 .9 8.

1 9. Preparation of potassium azobenzene-4-8ulfon- ate.^^-Thl8 salt was obtained as the dlhydrate In 52.5 per

P. Ruggll and M. Stauble, Helv. Chim. Acta, 24, 1080 (1941). cent yield by the same procedure as was used above to obtain potassium azobenzene-3-sulfonate.

20. Preparation of azobenzene-3-oarboxyllc acld.-

To a solution of 2.74 g. (0.020 mole) of 3-amlnobenzolc acid In 10 ml. of warm glacial acetic acid were added 2.14 g .

(0.020 mole) of nitrosobenzene, and the mixture was heated at 100° for 25 mln. On cooling, brownish-orange crystals separated out. The crude product was dissolved In 120 ml. of benzene, and the solution, after being passed through a short column (5 cm. x 3.2 cm.) of silicic acld-cellte and concentrated, yielded 2.33 g . (51.4 per cent) of orange crystals, m.p. 16 7.0-16 8.5 ° (lit., 166-167°^°, 170-171°^°). 78

P. Jacobson, Ann., 267, 529 (1909). P. Freund 1er, Bull. soc. chim. France, 3^, 216 (1907)

The acid was converted into the potassium salt by the addition of the calculated amount of potassium carbonate solution and evaporation to dryness.

21. Preparation of potassium azobenzene-4-carboxylate.-A solution of 1.465 g. (O.OO60 mole) of 4-phenylazo- benzoyl chloride (Eastman Kodak Company, White Label) in 50 ml. of absolute ethanol was mixed with a solution of 20 g. (0.056 mole) of potassium hydroxide in 10 ml. of water, and the mixture was refluxed for 72 hours. On cooling, 1.4600 g. (92.4 per cent) of orange crystals of the potassium salt were obtained. The product was recrystallized twice from hot water.

22. Preparation of 5-phenylazoacetophenone.^°-To a

J. McIntyre and J. C. E. Simpson, J. Chem. Soc., 2606 (1952). warm solution of 12.56 g. (0.095 mole) of 5-aminoacetophenone (Eastman Kodak Company, Yellow Label) in 20 ml. of 79

glacial acetic acid was added a solution of 10.2 g. (0.095 mole) of nitrosobenzene in 15 ml. of glacial acetic acid. The resulting mixture was heated at about 6o° for 8 hours and then left at room temperature for 11 days. The solution was diluted with 100 ml. of water, made alkaline with sodium carbonate, and extracted with three 50 -ml. portions of ben zene. The benzene extracts were combined, dried over anhydrous sodium sulfate, and filtered through a mat of silicic acid-celite. Evaporation of the benzene gave 10.0 g . of orange-red crystals, m.p. 84.5-86.2° (lit.^° 88-90°). The product was purified further by chromatography on

silicic acid-celite to yield 9*5 g • (44.6 per cent) of orange-red crystals, m.p. 85.5 -8 7.0°.

2 5 . Preparation of 4-phenylazoacetophenone.^^-A

51 A. Angeli, Atti accad. Lincei, 24, II85 (1915).

warm solution of 7*0 g . (0.055 mole) of 4-aminoacetophenone (Eastman Kodak Company, White Label) in 25 ml. of glacial acetic acid was treated with 5*8 g . (O.056 mole) of nitroso benzene. The reaction was allowed to proceed at room temper ature for 21 hours. The light brown solid that had separa ted out was filtered, dissolved in benzene, and purified as described under the preparation of 5 -phenylazoacetophenone. 80

Thus were obtained 6.4 g. (55•! per cent) of red crystals of 4-phenylazoacetophenone, m.p. 115 .1-115 .6° (lit.^^115°)■

C . Preparation of cis Isomers

The cis forms of the azobenzenes were prepar ed from the corresponding trans forms by the following basic procedure, which was applicable to all the compounds reported in this dissertation, except the ionic azo com pounds . A solution of the chromatographically pure trans compound in a suitable amount of chloroform was placed in a quartz flask, cooled in an ice-salt bath, and irrad iated with a Hanovia ultraviolet lamp at a distance of approximately 15 cm. for about 3-4 hours, by which time the trans form had attained the photochemical steady state with the cis form. The solution was then chromatographed. The cis form was always more strongly adsorbed than the trans form, and, hence, separation was easily affected. A solution of 2 to 8 per cent of ether in Skellysolve B proved satisfactory as a developer in most cases. In some cases, insolation produced another, although minor, change, because there was present at the extreme top of the column a thin red or purple band which was cut away. The cis isomer was then immediately eluted with cold A.R. ether and the solvent was rapidly evaporated under 81 reduced pressure. The residue was crystallized from cold Skellysolve P, whenever possible; otherwise, it was washed with cold Skellysolve P to remove any trans isomer and dried under reduced pressure. All the operations other than the irradiation were performed in the dark as much as possible. In each case, the identity of the new product produced on irradiation as the cis isomer was confirmed by dissolu tion of the purified cis form in benzene and refluxing the solution overnight, A chromatographic examination showed complete conversion to the trans form. This conclusion was further supported by the fact that the spectrum of the solu tion after being boiled in benzene was identical with that of the trans form at the same concentration. In the case of the azobenzenes having a trimethylammonium group as a substituent, the method described above for isolation of the cis isomer was not applicable. To sep arate the cis forms of these compounds, a solution of the trans compound in water was irradiated as described above

and chromatographed on a column of Amberlite XE-97» a weakly acidic cation-exchange resin having carboxylic acid groups, supplied by the Rohm and Haas Company, Philadelphia, Pennsylvania, The resin was used in the form of the sodium salt. After the azo compound was put on the column, the resin was- washed with some water to move down the inorganic salt form ed by exchange, and then developed with a 0.025 M solution of 82

sodium chloride. The cis form, in this case, was less strongly held than the trans form and, consequently, was eluted first as a separate zone. The solution of the cis form of the chloride thus obtained was freeze-dried under reduced pressure in the dark. The residue was extracted with acetone in which only the organic compound dissolved. Evaporation of the acetone under reduced pressure yielded the cis isomer, which was washed with cold acetone to remove any trans isomer and dried. The identity of the new product as the cis isomer was confirmed in the same manner as for the non-ionic compounds, except that the compound was dissolved in ethanol. The solid cis isomers were characterized by their melt ing points, although the importance of this measurement■is not too great because of the inherent difficulty in making accurate measurements. The melting points were determined by rapid introduction of the capillary tube containing the cis compound in a bath in the temperature-range at which a preceding sample had melted. The best melting points for the various solid cis isomers by this method of successive approximations are shown in Table V, 85 TABLE V MELTING POINTS OF AND trans ISOMERS OF SUBSTITUTED AZOBENZENES*

m.p. m.p. Substituent trans Isomer cis Isomer

5-CN 90.7 - 91.1 80 4-ON 119.5 - 120.0 (120-125^4) 52

5-F 42.0 - 45.2 (4413) 55 4-P 81.9 - 82.8 (8 2.5^1) 75 (6514 )

5-01 67.4 - 67.5 (67.5=3) oil 4-01 89.8 - 90.2 (923=) 46 (58^4)

5-Br 68.0 - 68.5 (69=3) oil 4-Br 89.8 - 90.0 (89=3) 54 (47^4)

5-1 70.5 - 70.5 57 4-1 106.4 - 106.7 (10535 ) 75 (6514 )

5-OCH3 28.0 - 29.0 (5 2 .5 -55.533 ) oil

4-OCH3 54.2 - 54.7 (5644) oil (ca. 2513 )

5-N(GH3)3 176.8 - 177.2 129 (iodide) (chloride)

4-N(CH3)3 225.4 - 225.6 (ca. 21645) oil (nitrate) (chloride)

* The values In parentheses are the highest values given in the literature. 84 D. Measurement of the Rate of Isomerization, A sample of the cis azo compound was weighed very accurately on a semi-micro balance (about 10-15 mg.) In the absence of light as far as possible and dissolved In the solvent contained In a volumetric flask (100 ml.) In the dark. This solution was poured Into the reaction-vessel and Introduced Into a constant-temperature bath. To exclude light, the reactlon-vessel was painted black* furthermore, all the rate-measurements were done In a dark room. At known Intervals of time, a stream of dry air was admitted Into the top of the reactlon-vessel and the stop-cock opened. The first few ml. of solution were discarded; the solution follow ing was collected directly In a Beckman cell and cooled Immed iately In Ice-water. The optical density was then determined by a Beckman DU Quartz Spectrophotometer.

E. Calculation of Rate Constants. As the conversion from the cis to the trans form proceeds, the optical density, D, at a given wave-length In the vicinity of the maximum for the cis Isomer decreases In the visible region of the spectrum. After the Isomerization to the trans form Is completed, the value of D remains con stant. Since Beer's Law Is obeyed, all Intermediate D-values enable one to calculate the cis;trans ratio. The wave-length at which the optical density readings were taken was In 85 that region of the maximum where the difference between the D-values for the two forms was greatest. In order to deter mine the composition of the mixture of cis and trans azo

compounds^ the optical density of the solution of unlonown composition was subtracted from the optical density of the pure cis compound ;

Dpure cis - Dunknown composition D% (directly proportional to the amount of cis which has been isomerized). The resulting value, D^, was then divided by the diff erence in optical density between that of the pure cis and the final reading at infinite time for the trans compound. The value obtained was equal to the fraction trans in the unknown sample.

D^l(D cis - D trans) = Fraction trans.

The fraction trans when subtracted from unity gave frac

tion cis. This value, when multiplied by 100, gave the per centage of cis form in the mixture. A plot of log per cent of cis versus the time, t (min.), at which the sample was with drawn, gave a straight line with a negative slope, the numer ical value of which, after multiplication by 2 .505 , gave the first order rate constant, k (min.**^). 1 . Oo • k - 2,505 X - log ^ , where Co is the concentration of cis at the beginning of the isomerization (t=0) and C is the concentration of cis after 86 P. Calculation of the Activation Energies and Frequency Factors The values of these constants were obtained by means of the Arrhenius equation,

k = A«e"® ^

log k = ------§--- * —^-f- C. 2.505 R T ^ ' where A = frequency factor, E = heat of activation, k = rate constant, T = absolute temperature, R «= gas constant, and C = constant = log A, When the log of the rate constant was plotted against the reciprocal of the absolute temperature In the case of the compounds where rate constants were measured at three temperatures, a straight line was obtained. In other cases, the two points on a similar plot were joined by a straight line. The numerical value of the slope of this line, when multiplied by 2.505 R, Is equal to the activation energy. The value of the log of the frequency factor was obtained from the Intercept of the Arrhenius plot on the ordinate. 87

V. SUMMARY

A series of monosubstituted azobenzenes, with the substituent in the meta and para-positions, was prepared by established methods. These compounds are listed below. The ones marked with an asterisk are new compounds. 1. 5-Cyanoazobenzene* 2. 4-Cyanoazob enz ene

3. 5-Pluoroazobenzene 4. 4-Pluoroazobenzene

5. 5-Chloroazobenzene 6. 4-Chloroazobenzene 7. 5-Bromoazobenzene 8. 4-Bromoazobenzene

9* 5-Iodoazobenzene* 10. 4-Iodoazobenzene 11. 3-Methoxyazobenzene 12. 4-Methoxyazobenzene 13» (3-Phenylazophenyl)trimethylamraoniura iodide* 14. (4-Phenylazophenyl)trimethylammonium nitrate

15. 3-Nitroazobenzene

16 . 4-Nitroazobenzene 1 7. 3-Acetylaminoazobenzene 1 8. 3-Aminoazobenzene

1 9. 3-Pbenylazoacetophenone 88

20. 4-Phenylazoacetophenone

21. Potassium azobenzene-5-sulfonate* 22. Potassium azobenzene-4-sulfonate

25 . Potassium azobenzene-3-carboxylate 24. Potassium azobenzene-4-carboxylate

The cis isomers of compounds 1-2, 5 , 7, 9, 11, and 14 were prepared for the first time, and their absorption spectra measured. The rate of cis to trans isomerization for compounds 2 , 4, 8 and 10 was measured at three different temperatures and in different polar and non-polar solvents. The rates for compounds 1 , 5 , 6, 7, 9 and II-16 were measured at two temperatures in different solvents.

The rates varied considerably with the nature of the substituent: the isomerization was fastest with the

4-NOg group and slowest with the 2-NOa group. In com parison with azobenzene, the isomerization of all the substituted azobenzenes studied was faster, with the ex ception of 3-cyano- and 5 -nitro-azobenzenes which isomerized somewhat slower. The effect of solvent polarity on the rates was not very pronounced. The rate was generally enhanced by a decrease in the dielectric constant of the solvent, except in the case of 4-nitro- and 4-cyano-azoc benzenes where the isomerization was promoted by polar 89 solvents. The activation energies varied from about 20-25 kcal. per mole, and the frequency factors from about 10^^-10^® sec."i.

Prom this study, it is concluded that the isomerization of 4-nitro- and of 4-cyano-azobenzene probably occurs through an intermediate polar form involving a resonance withdrawal . of TÎ -electrons from the azo linkage. In the case of the other azobenzenes studies it is postulated that the isomer ization could occur equally well by either a singlet or a triplet mechanism. The experimental results do not allow a definite decision to be made in favor of one or the other mechanism. APPENDIX

90 LOO

0.80

c 0.60

0.40

0.20

0.00 200 300 400 500 600 Wave length (m/ii)

FIG. ABSORPTION SPECTRUM OF 3 - CYANOAZOBENZENE IN 95 PER CENT ETHANOL

Cone, (mg./ lOOmI) Isomer A B — cis 0.66 10.96 — Irons 0.55 25.0 1.00

0.80

0.60

o u 0.40 & O

0.20

0.00 200 300 400 500 600 Wave length (m/t)

FIG. 2. ABSORPTION SPECTRUM OF 4 - CYANOAZOBENZENE IN 95 PERCENT ETHANOL

Cone, (mg/ 100 ml) Isomer A B — cis 0.97 9.73 VO — Irons 0.45 25.00 ro 1.00

« c 0.60 » T5 o u a. 0 .4 0 O

0.20

0.00 200 3 0 0 4 0 0 5 0 0 6 0 0 Wave length (mfi)

FIG. 3. ABSORPTION SPECTRUM OF 3 - FLUOROAZOBENZENE IN ABSOLUTE ETHANOL

Cone, (mg/100ml.) Isomer A B — cis 1.12 10.25 VO trons 0.77 32.15 1.00

0.80

« c 0.60 o T3 o u 0.40 Q. O

020

0.00 200 3 0 0 4 0 0 5 0 0 Wave length (m;i)

Fia 4. ABSORPTION SPECTRUM OF 4 - FLUOROAZOBENZENE IN ABSOLUTE ETHANOL

Cone. (mg/lOOml.) Isomer A B

cis 1.69 10.98 VO trans 0.53 26.38 4=- 1.00

OBO

0.60 A \

Q. 0.40

0.20

0 .00^ 200 3 0 0 4 0 0 5 0 0 6 0 0 Wave length (m|x)

FIG. 5. ABSORPTION SPECTRUM OF 3 - CHLOROAZOBENZENE IN ABSOLUTE ETHANOL

Cone, (mg/ 100 ml) Isomer A B__ cis 1.23 12.28 VO ui trans 0.60 29.94 .00

OBO

.t: 0.60

0.40

0.20

O.OOl 200 3 0 04 0 0 5 0 0 6 0 0 Wave length (m/t) FIG. 6. ABSORPTION SPECTRUM OF 4 - CHLOROAZOBENZENE IN ABSOLUTE ETHANOL

Cone, (mg/100 ml) Isomer A R - — cis 1.18 9.23 MD — Irons 0 6 4 21.38 (J\' 1.00

oao -

c 0.60

o o k 0.40 O

0.20

0.00 200 300 400 500 600 Wave length (m/j.)

FIG. 7. ABSORPTION SPECTRUM OF 3“ BROMOAZOBENZENE IN ABSOLUTE ETHANOL

Cone, (m g /100 ml) Isomer A B cis 1.63 11.79 trons 0.96 47.86 VO 1.00

0.80

0.60 A (0 C o T3 O U 0.40 o. O

0.20

000 200 3 0 0 4 0 0 500 600 Wave length (m/i)

FIG. 8. ABSORPTION SPECTRUM OF 4 - BROMOAZOBENZENE IN ABSOLUTE ETHANOL

Cone, (mg/100 ml) Isomer A B 1.24 12.44 cis VO — trons 053 26.39 05 1.00

OBO

0.60 T3

a 0.40

0.20

0.00 " 1— 200 3 0 0 4 0 0 500 6 0 0 Wave length (m^)

FIG. 9. ABSORPTION SPECTRUM OF 3 - lODOAZOBENZENE IN ABSOLUTE ETHANOL

Cone, (m g/100ml.) Isomer A B cis 1.15 19.13 MD — —trons 0.89 44.34 VD 1.00

0.80

E 0.60

0.40

0.20 A\

0.00 200 3 0 0 4 0 0 5 0 0 600 Wave length (m^)

FIG. 10. ABSORPTION SPECTRUM OF 4 - lODOAZOBENZENE IN ABSOLUTE ETHANOL

Cone. (mg./IOO ml) Isomer A B - - c is 1.78 11.10 0.94 31.34 o — trons o 1.0 0

0.80

t 0.60 c a> T3

.? 0.40 a O

0.20

0.00 200 3 0 0 4 0 0 0 6 0 050 Wave length (nyi)

FIG. ABSORPTION SPECTRUM OF 3 - METHOXYAZOBENZENE IN ABSOLUTE ETHANOL

Cone, (mg / 100ml) Isomer A B — cis I.4B 12.30 — trons 0.5 B 19.48 2 LOO

0.80

■9 0.60 01C T3 o u 0.40 Q. O

020

0.00 200 3 0 0 4 0 0 5 0 0 6 0 0 Wave length (mja)

FIG. 12. ABSORPTION SPECTRUM OF 4 - METHOXYAZOBENZENE IN ABSOLUTE ETHANOL

Cone. ( mg/ 100 ml ) Isomer A B cis 1.46 7.34 trons 0.61 15.31 1.00

0.80

0 6 0 Xî

% 0.40

0.20

0.00 200 300 400 5 0 0 6 0 0 Wave length (mju.) FIG. 13. ABSORPTION SPECTRUM OF TRIMETHYL (3-PHENYLAZOPHENYL)AMMONIUM SALT IN WATER

Cone, (m g /100 ml) Isomer A 8 cis-chloride 1.30 18.89 )*■» ■trons-iodide 1.18 29.44 a 1.00

0.80 /\

<0c 0.60 a> ■o o u 0.40 Q. O

0.2 0 -

O.OOl 200 3 00 500400 6 0 0 Wave length (m/ii)

FIGi 14. ABSORPTION SPECTRUM OF TRIMETHYL(4-PHENYLAZ0PHENYL)AMM0NIUM SALT IN WATER Cone, (mg/lOO ml) Isomer A B cis-chloride 1.82 18.17 o trons - nitrote 1.02 25.51 1.00

0.80 IB

0.60 o u lA lA // •i 0.40 o

0.20

0.00 200 30 04 0 0 50 0 6 0 0 Wave length (m^)

FIG. 15. ABSORPTION SPECTRA OF ' 1 trons - POTASSIUM AZOBENZENE-3-SULFONATE (ANHYDROUS) IN WATER. H trons - POTASSIUM AZOBENZENE - 4 - SULFONATE DIHYDRATE IN WATER. Cone. (mq/lOO ml) A B I 0.82 27.24 IE 0.96 24.06 1.00

0.80

« c 0.60 « ■o o o 0.40 - 3IA MA O

0.20

0.00 200 300 400 500 600 Wdve length (m/u.)

FIG. 16. ABSORPTION SPECTRA OF: I trons-POTASSIUM AZOBENZENE-3-CARBOXYLATE IN WATER. IE trons-POTASSIUM AZOBENZENE- 4 - CARBOXYLATE IN WATER.

Cone, (mo/100ml) A B 0.78 25.92 0.55 I 1.04 2.00 ,

1.80

1.60

o» L40 o _l

.20

1.00 10,000 20,000 30,000 Time (min.)

FIG. 17. RATE OF ISOMERIZATION OF 4 - FLUOROAZOBENZENE AT 25.2<»C. IN VARIOUS SOLVENTS

O Absolute ethanol Zl Benzene □ Oioxone • n,-Heptane 1.80

1.60 ■g I 6" O* O _l .40

.20

1.00 2000 4 0 0 0 6 0 0 0 8 0 0 0 Time (min.)

FIG. 18. RATE OF ISOMERIZATION OF 4 - FLUOROAZOBENZENE AT 34.8®C. IN VARIOUS SOLVENTS

O Absolute ethanol ^ Benzene □ Oioxone • n - Heptane 2.00

1.80

(o| -1.60

o 1.40

.20

1.00 1000 2000 3000 Ti me (mi n.)

FIG. 19. RATE OF ISOMERIZATION OF 4 - FLUOROAZOBENZENE AT 4 4 .5 X . IN VARIOUS SOLVENTS

O Absolute ethanol A Benzene □ Dioxone • n.-Heptane 110

8.2

7 8

7.4

o> \ \ o 7 0

O 6.6

6.2

5.8 L- 2 .9 2 3.00 3 0 8 3.16 3.32 3.40 ^ X 10*

FIG. 20. ARRHENIUS PLOT FOR THE RATE OF ISOMERIZATION OF CYANOAZOBENZENES

3 -Cyanoazobenzene 4 “Cyanoazobenzene

O Absolute ethanol □ Oioxone A Benzene • ji-Heptane Ill

8.2

o> o 70 + o 6.6

6.2

5 .8 '— 2.92 3 .0 0 3 0 8 3.16 3.24 3 .3 2 3.40

X 10'

FIG. 21. ARRHENIUS PLOT FOR THE RATE OF ISOMERI- ZATION OF 3 - FLUOROAZOBENZENE

O Absoluteethanol □ Dioxone A Benzene • n-Heptone 112

7.8

7.4

^ 7 0 o»

6.6

6.2

5.8

2.92 3.00 3.08 3.16 3.24 3.32 3.40

T X 10^

FIG. 22. ARRHENIUS PLOT FOR THE RATE OF ISOMERI ZATION OF 4 -FLUOROAZOBENZENE

O Absolute ethanol □ Dioxone A Benzene • n-Heptone .119

8.2

7.8

74 o> o

7.0 O \\ W 6.6 \\

6.2

5.8*— 2.92 3 .0 0 3.08 3.16 3 .3 23.24 3 .4 0 Ÿ X 10^

FIG. 23. ARRHENIUS PLOT FOR THE RATE OF ISOMERIZATION OF CHLOROAZOBENZENES

— 3-Chloroozobenzene — 4 - Chloroazobenzene

O Absolute ethanol □ Dioxane A Benzene e a-Heptone 114

8.2

7.8

7.4

o» o 70 4- O 6.6

6.2

5.8 3 0 0 3 0 82.92 3.16 3.24 3.32 3.40 _L ^3

FIG. 24. ARRHENIUS PLOT FOR THE RATE OF ISOMERIZATION OF 3-BROMOAZOBENZENE

O Absolute ethanol □ Dioxane A Benzene e n - Heptane 115

8.2

7.8

o> 2 7.0 + O 6.6

6.2

5 .8 L _ 2.92 3.00 3.08 316 3 .2 4 3 3 2 3.40

-jr X 10

FIG. 2 5 . ARRHENIUS PLOT FOR THE RATE OF ISOMERIZATION OF 4-BROMOAZOBENZENE

O Absolute ethanol □ Dioxane A Benzene • n-Heptone 116

8.2

7.8

7.4

+ 70

6.6

6.2

5.81— 2 .9 2 3.00 3.163.08 3 .2 4 3.40

Y" X 10

FIG. 26. ARRHENIUS PLOT FOR THE RATE OF ISOMERIZATION OF 3-IODOAZOBENZENE

o Absolute ethanol □ Dioxane A Benzene • n - Heptane ].17

8.2

^ 7.4 o> o

+ 70 o

6.6

62.

5.8 . 8.23 .0 0 3.082.92 3.16 3 .2 4 3.32 3.40

■f X lo"

FIG. 27. ARRHENIUS PLOT FOR THE RATE OF ISOMERIZATION OF 4 - lODOAZOBENZENE

O Absolute ethanol □ Dioxane A Benzene # n - Heptane 1:8

8.2

o» o

+ 7.0 O \ \\ 6.6

6.2

3.08 3.16 3.24 3.323.00 3.40 10 T *

FIG. 28. ARRHENIUS PLOT OF THE RATE OF ISOMERIZATION OF METHOXYAZOBENZENES

— 3-Methoxyozobenzene — 4 - Methoxyazobenzene O Absolute ethanol □ Dioxane A Benzene • n - Heptane 119

8.2

7.8

7.4

O' o 7.0 + O 6.6

6.2

3 0 0 3.16 3 . 2 4 3i32 3.40

f X 10^

F I G 29. ARRHENIUS PLOT FOR THE RATE OF ISOMERIZATION OF NITROAZOBENZENES

3 “ N i troazobenzene 4 -N'ltroazobenzene O Absolute ethonol □ Dioxane 120

8.2

7.8

O' o + o

6.6

6 2

3 0 0 3.08 3.16 3.24 3.32 3.40

■jr X 10

FIG. 30. ARRHENIUS PLOT FOR THE RATE OF ISOMERIZA TION OF (PHENYLAZOPHENYL)TRIMETHYLAMMONIUM CHLORIDES

( 3 - Phenylazophenyl)trimethylammonium chloride (4-Phenylazophenyl)trimethylammonium chloride

O Water □ Absolute ethanol A Dimethyl sulfoxide 121 TABLE VI

RATE OP ISOMERIZATION OP 5-CYANOAZOBENZENE IN ABSOLUTE ______ETHANOL AT 35.0° AND 54.6°______

Time (mln.) O.P. (436 mu)______Practlon els Temp., 35.0° i 0 .03°; conc.. 0.575 millimolar 0 0.608 0.961 99 0.594 0.926 267 0.581 0.892 1451 0.512 0.715 1779 0.505 0.697 2901 0.459 0.579 3097 0.451 0.559 4297 0.410 0.454 4602 0.395 0.415 5650 0.374 0.362 6078 0.365 0.339 7619 0.332 0.254 9978 0.301 0.174 12858 0.274 0.105 CX] 0.233 0.000 Graphically determined k = 1.73 X 10”4 *

Temp.^ 54.6 i 0 .04 °; conc.. 0.552 millimolar

0 0.598 1.000 151 0.520 0.791 233 0.480 0.684 323 0.441 0.580 442 0.403 0.479 580 0.366 0.380 655 0.351 0.340 1199 0.279 0.147 1266 0.271 0.126 0 0 0.234 - Graphically determined k = I.65 x 10”®**

*A11 rate constants in this dissertation are given in min.“^ . **Calculated value of O.D.oo (0 .224 ) was used for calculations. 12a TABLE VII

RATE OP ISOMERIZATION OP 5 -CYANOAZOBENZENE IN DIOXANE AT 35.00 and 54 .6°

Time (min.) O.D. (438 mu) Praction cis Temp., 35.0 d: 0 .03°; conc.. 0.565 millimolar 0 0.571 0.927 93 0.561 0.900 302 0.550 0.869 1172 0.500 0.730 1555 0.480 0.674 2577 0.439 0.560 2965 0.419 0.504 4019 0.386 0.412 4358 0.376 0.384 5537 0.344 0.295 6975 0.319 0.226 8672 0.298 0.167 10303 0.281 0.120 ÛO 0.238 0.000 Graphically determined k = 2.00 X 10"*

Temp., 54.6 — 0 .04 °; conc.. 0.612 millimolar

0 0.647 1.000 141 0.549 0.741 224 0.501 0.614 313 0.460 0.505 432 0.419 0.397 568 0.384 0.304 642 0.373 0.275 1189 0.299 0.079 1253 0.293 0.063 Oo 0.269 0.000 -3 Graphically determined k = 2.15 x 10 123

TABLE VIII

RATE OP ISOMERIZATION OP 3-CYANOAZOBENZENE IN BENZENE .______AT 35.0° m P 54.6°______

Time (mln.)_____O.D. (4^8 mu)______Practlon els

Temp., 3 5 .0 i 0 .03°; conc.. 0.577 millimolar 0 0.590 0.906 84 0.575 0.868 229 0.569 0.852 1305 0.482 0.631 1622 0.460 0.575 2572 0.407 0.440 2729 0.402 0.428 2958 0.386 0.387 3982 0.351 0.298 4427 0.337 0.262 5425 0.315 0.206 5843 0.302 0.173 6932 0.285 0.130 Oo 0.234 0.000 Graphically determined k = 2.79 X 10~4

Temp., 54.6 Cb 0 .04 °; conc.. 0.532 millimolar

0 0.578 1.000 37 0.538 0.888 81 0.501 0.785 145 0.455 0.656 201 0.422 0.564 251 0.398 0.497 336 0.363 0.399 4 o8 0.336 0.324 456 0.321 0.282 943 0.247 0.075 994 0.242 0.061 6o 0.220 0.000 Graphically determined k = 2.79 x 10“^ 124 TABLE IX

RATE OP ISOMERIZATION OP 3-CYANOAZOBENZENE IN n-HEPTANE ______AT 35.0° AND 5 4 . 6 0 ______

Time (min.) O.D. (444 mu) Praction ci:

Temp., 35.0 t 0 .03°; conc.. 0.459 millimolar 0 0.444 0.908 118 0.421 0.831 234 0.415 0.810 1103 0.335 0.539 1291 0.323 0.485 1472 0.311 0.444 2511 0.257 0.275 2713 0.248 0.244 2880 0.243 0.227 3928 0.216 0.136 4160 0.212 0.122 00 0.176 0.000 Graphically determined k - 4.82 X 10-4

Temp., 54.6 - 0 .04 °; conc.. 0.436 millimolar 0 0.450 1.000 28 0.418 0.889 52 0.397 0.816 96 0.356 0.674 160 0.310 0.514 218 0.281 0.413 240 0.266 0.361 266 0.260 0.340 353 0.228 0.229 379 0.221 0.205 423 0.211 0.170 471 0.202 0.139 Oo 0.162 0.000 -3 Graphically determined k = 4.19 x 10 125

TABLE X

RATE OF ISOMERIZATION OF 4-CYANOAZOBENZENE _____ IN 95-PER CENT ETHANOL______

Time (mln.) O.D. (442 mu) Fraction els Temp., 55.0 0.05°; conc.. 0.488 millimolar

0 0 .6 7 6 1.000 39 0.642 0.918 74 0 .6 2 4 0.870 156 0.588 0.780 227 0 .5 5 3 0.692 305 0.523 0.618 4 18 0.488 0 .5 3 0 519 0 .4 5 3 0 .4 4 3 992 0.362 0.215 1139 0 .3 4 4 0.170 1326 0.326 Oa 0.125 OQ 0 .2 7 6 0.000 Graphically determined k = 1.54 x 10-3

TABLE XI

RATE OF ISOMERIZATION OF 4-CYANOAZOBENZENE IN ABSOLUTE

Time (mln.) O.D. (444 mu) Fraction els Temp., 25.2+0.07°; conc.. 0.659 millimolar 0 0.752 0.735 127 0.737 0.709 223 0.718 0.676 291 0.709 0.661 387 0.693 0 .6 3 3 1025 0 .6o4 0.480 1231 0.570 0.422 1332 0 .5 6 8 0.418 1462 0.557 0.399 1602 0.542 0.374 2515 0 .4 6 7 0.244 2801 0.444 0.205 TABLE XI (contd.)

Time (min.) O.D. ( 444 mu) Praction cis 3082 0.434 0.188 3957 0.401 0.131 0 0 0.325 0.000 Graphically determined k = 4.36 X 10"*

Temp., 35.0 ± 0 .03°; conc.. 0.347 millimolar 0 0.437 0.869 71 0.402 0.751 157 0.373 0.653 250 0.351 0.579 331 0.330 0.508 400 0.316 0.461 478 0.300 0.407 554 0.286 0.360 610 . 0.279 0.337 1165 0.222 0.145 1265 0.216 0.125 1328 0.213 0.115 Oo 0.179 0.000

Graphically determined k = 1.53 X 10"®

Temp., 44.5 0.07°; conc.. 0.467 millimolar 0 0.612 0.929 80 0.488 0.627 104 0.458 0.554 144 0.418 0.456 171 0.391 0.390 201 0.371 0.341 233 0.355 0.302 315 0.314 0.202 361 0.301 0.171 425 0.285 0.132 486 0.273 0.102 ÛQ 0.256 •• 00 0.267 Graphically determined k = 4.72 X 10~^*

*O.D.oo calculated (0.231) was used for calculations. 127 TABLE XII

RATE OF ISOMERIZATION OP 4 -CYANOAZOBENZENE IN DIOXANE ______AT 25 .2°. 3 5 .0° AND 4 4 .5 °______

Time (mln.) O.D. (446 mu) Fraction cis Temp., 25.2 ± 0.07°; conc.. 0.677 millimolar

0 0.744 0.793 106 0.736 0.772 198 0.705 0.726 272 0.701 0.709 564 0.693 0.693 • 1004 0.633 0.575 1205 0.617 0.543 1302 0.612 0.533 1576 0.590 0.490 2490 0.531 0.374 2779 0.513 0.339 3061 0.499 0.311 3933 0.457 0.228 4452 0.445 0.205 5401 0.420 0.156 60 0.341 0.000

Graphically determined k = 3.01 X 10"^

Temp., 35.0 0.03°; conc.. 0.490 millimolar 0 0.615 0.923 51 0.558 0.874 98 0.571 0.800 194 0.545 0.702 313 0.511 0.590 475 0.472 0.530 557 0.451 0.493 723 0.438 0.467 830 0.405 0.399 958 0.388 0.350 1520 0.332 0.189 1676 0.322 0.159 o>o 0.266 0.000 -3 Graphically determined k = 1.10 x 10 128 TABLE XII (contd.)

Temp., 44.5 — 0 .07°; conc., 0.624 millimolar 0 0.518 0.880 97 0.423 0.596 122 0.408 0.551 164 0.376 0.455 191 0.363 0.416 221 0.346 0.365 251 0.333 0.326 325 0.306 0.246 379 0.292 0.204 445 0.277 0.159 506 0.269 0.135 568 0.258 0.102 Oo 0.224 0.000 Graphically determined k = 5.84 x 10-3

TABLE XIII

RATE OP ISOMERIZATION OP 4 -OYANOAZOBENZENE IN BENZENE ______AT.25 .2°, 3 5 .0° AND 4 4 .5 °______

Time (min.) 0.0.(444 mu) Praction cis Temp., 25.2 t 0 .07°; conc., 0.564 millimolar

0 0.671 0.843 78 0.652 0.801 150 0.641 0.777 250 0.623 0.738 874 0.547 0.572 1081 0.527 0.528 1185 0.519 0.511 1298 0.508 0.487 1455 0.491 0.450 2330 0.429 0.315 2655 0.412 0.277 2938 0.395 0.240 3768 0.356 0.155 4294 0.342 0.125 0.285 0.000

Graphically determined k = 4.37 x 10~* 129 TABLE XIII (contd.)

Time (min.) O.D. (446 mu) Fraction cis Temp., 35.0 i 0.03°; conc.. 0.558 millimolar

0 0.752 1.000 21 0.708 0.945 54 0.694 0.915 94 0.672 0.862 179 0.628 0.761 503 0.567 0.622 769 0.428 0.303 919 0.400 0.239 1102 0.375 0.181 1267 0.357 0.140 O o 0.296 0.000 Graphically determined k = 1.55 X 10"3

Duplicate; conc., 0.472 millimolar 0 0.585 0.952 50 0.551 0.857 209 0.482 0.664 272 0.460 0.602 555 0.438 0.541 414 0.419 0.487 487 0.401 0.436 555 0.385 0.392 632 0.367 0.342 1055 0.307 0.172 1117 0.302 0.160 1199 0.296 0.142 O o 0.245 0.000

Graphically determined k = 1.61 X 10-3

Temp., 44.5 — 0.07°; conc.. 0.483 millimolar; wave1 length, 444 mu 0 0.629 0.976 59 0.559 0.792 70 0.504 0.647 103 0.464 0.541 134 0.432 0.456 139

TABLE XIII (contd.)

Time (min.) O.D. (444 mu) Fraction cis 161 0.411 0.401 193 0.387 0.338 281 0.336 0.203 320 0.322 0.166 386 0.304 0.119 454 0.290 0.082 Cx> 0.259 0.000 Graphically determined k = 5.53 X 10-3

TABLE XIV

RATE OF ISOMERIZATION OF 4 -CYANOAZOBENZENE IN n-HEPTANE AT 25 ..2°, 3 5 .0° AND 44 .5 °

Time (min.) O.D. ( 446 mu) Fraction cis

Temp., 25.2 i 0 .07°; conc.. 0.388 millimolar 0 0.453 0.779 44 0.448 0.765 116 0.438 0.737 220 0.427 0.706 844 0.354 0.501 1048 0.337 0.454 1150 0.327 0.426 1226 0.321 0.409 1327 0.314 0.389 1421 0.308 0.373 2330 0.258 0.233 2622 0.243 0.190 2904 0.234 0.165 3740 0.214 0.109 0.175 0.000 Graphically determined k = 5.24 X 10-4

Temp.^ 35.0 ± 0 .03°; conc.. 0.389 millimolar 0 0.468 0.814 54 0.436 0.723 131

TABLE XIV (contd.)

Time (min.) O.D. (446 mu) Praction cis 164 0.389 0.590 274 0 .351 0.483 360 0.322 0.401 475 0.295 0.325 915 0.216 0.102 1065 0.207 0.076 00 0.180 0.000 Graphically determined k = 1.95 x lO"^

Duplicate; conc., 0.325 millimolar 0 0.387 0.803 111 0.356 0.6 3 2 179 0 .3 1 6 0.5 6 5 265 0 .2 9 0 0 .4 7 8 324 0.275 0.428 348 0 .257 0.368 472 0.241 0 .3 1 4 1028 0.178 0.104 1108 0.173 0.087 Co 0.147 0.000 Graphically determined k - I.93 x 10“®

Tèmp.j 44.5 d: 0 .07°; conc., O.26I millimolar

0 0.341 0 .9 2 7 23 0.319 0.833 0.283 0.680 0 .254 0.556 118 0.232 0.462 143 0.210 0.368 155 0.204 0.342 177 0 .196 0.308 263 0.163 0.167 305 0.155 0 .1 3 3 368 0.147 0.098 435 0.140 0.068 0 0 0.124 0.000 Graphically determined k = 6.22 x 10"® 13.2

TABLE XV

RATE OF ISOMERIZATION OP 3-PLUOROAZOBENZENE IN ABSOLUTE

Time (min.) O.D. (428 mu) Praction cis Temp., 44.5 ± 0 .07°; conc.. 0.513 millimolar 0 0.672 1.000 60 0.658 0.922 169 0.601 0.838 285 0.572 0.772 779 0.462 0.521 854 0.448 0.489 955 0.431 0.450 1215 0.393 0.363 1527 0.379 0.331 1453 0.363 0.295 1554 0.353 0.272 2437 0.291 0.130 Oo 0.234 0.000 Graphically determined k = 8.43 X 10-4

Temp., 54.6 i 0 .04 °; conc.. 0.550 millimolar 0 0.708 0.970 75 0.631 0.806 153 0.556 0.646 235 0.503 0.533 304 0.461 0.444 375 0.429 0.375 486 0.382 0.275 567 0.356 0.220 629 0.341 0.188 720 0.323 0.149 302 0.302 0.105 Oo 0.253 0.000 -3 Graphically determined k = 2.59 x 10 133 TABLE XVI

RATE OP ISOMERIZATION OP 3-PLUOROAZOBENZENE IN DIOXANE

Time (min.) O.D. (428 mu) Praction cis

Temp., 44.5 — 0.07°; conc.. 0.350 millimolar

0 0.407 1.000 98 0.377 0.881 206 0.356 0.799 308 0.341 0.739 8l6 0.274 0.474 891 0.265 0.439 992 0.254 0.395 1252 0.236 0.324 1565 0.229 ' 0.297 1491 0.219 * 0.257 1592 0.212 0.229 2472 0.179 0.099 0.154 0.000 Graphically determined k = 9.21 X 10"^

Temp., 54 .6 "i- 0 .04 °; conc.. 0.507 millimolar 0 0.592 1.000 94 0.510 0.778 169 0.460 0.642 251 0.416 0.523 520 0.385 0.439 391 0.357 0.363 505 0.321 0.266 647 0.291 0.184 735 0.276 0.144 0.225 0.000 Graphically determined k = 2.63 X 10"° m

TABLE XVII

RATE OP ISOMERIZATION OF 5-FLUOROAZOBENZENE IN BENZENE

Time (mln.) O.D. (428 mu) Praction cis

Temp., 44.5 ± 0 .07°; conc.. 0.401 millimolar 0 0.450 0.959 80 0.425 0.875 141 0.402 0.795 255 0.571 0.688 545 0.549 0.615 444 0.524 0.527 884 0.264 0.522 999 0.246 0.260 1084 0.259 0.256 1520 0.221 0.175 1525 0.208 0.150 1688 0.202 0.110 Oo 0.170 0.000 Graphically determined k - 1.50 X 10-3

Temp., 54.6 0 .04 °; conc.. 0.584 millimolar 0 0.445 1.000 41 0.409 0.878 78 0.578 0.768 111 0.556 0.689 155 0.529 0.595 206 0.501 0.495 295 0.266 0.568 540 0.249 0.507 441 0.225 0.214 Oo 0.165 0.000 Graphically determined k - 5.47 X 10“^ 135

TABLE XVIII

RATE OP ISOMERIZATION OP 3-PLUOROAZOBENZENE IN n-HEPTANE

Time (mln.) O.D. (428 mu) Practlon cis

Temp., 44.5 i 0 .07°; conc.. 0.530 millimolar 0 0.481 0.935 85 0.434 0.797 146 0.408 0.721 240 0.368 0.603 548 0.330 0.491 438 0.308 0.427 888 0.232 0.203 1003 0.219 0.165 1086 0.209 0.135 1324 0.194 0.091 1525 0.184 0.062 00 0.163 0.000

Graphically determined k = 1.76 X 10-3

Temp., 54.6 i 0 .04 °; conc.. 0.530 millimolar 0 0.589 1.000 40 0.522 0.832 78 0.469 0.698 111 0.428 0.595 154 0.386 0.490 206 0.346 0.389 293 0.293 0.256 340 0.271 0.201 578 0.256 0.163 ÛO 0.191 0.000

Graphically determined k = 4.68 X 10-3 135

TABLE XIX RATE OP ISOMERIZATION OF 4-FLUOROAZOBENZENE IN ABSOLUTE ETHANOL AT 25.2°. 34.8° AND 44.5°______

Time (mln.)_____O.D. (436 mu)______Fraction cis Temp., 25.2 ± 0 .07°] conc.. 0.436 millimolar 0 0.602 0.974 955 0.570 0.891 1376 0.565 0.878 2787 0.535 0.800 4037 0.507 0.727 5759 0.472 0.636 7118 0.451 0.582 9686 0.415 0.488 12613 0.376 0.387 16791 0.338 0.288 20077 0.318 0.236 22610 0.303 0.197 25915 0.284 0.148 28682 0.273 0.120 31451 0.264 0.096 34260 0.256 0.075 Oo 0.227 0.000 Graphically determined k = 7.20 X lO'S

Temp., 34.8 i 0.03°; conc.. 0.524 millimolar 0 0.718 0.959 85 0.707 0.936 312 0.692 0.904 1079 0.623 0.755 1258 0.607 0.721 1463 0.591 0.687 l64o 0.575 0.652 2619 0.511 0.515 3085 0.487 0.464 3G53 0.442 0.367 4326 0.432 0.345 5651 0.384 0.243 6970 0.352 0.174 8587 0.329 0.125 9760 0.314 0.092 0.271 0.000 ÛO 157 TABLE XIX (contd.)

Time ( min.) O.D. (436 mu) Praction cis Graphically determined k = 2.39 X 10"^

Temp.^ 44.5 — 0 .07°; concp.. 0.460 millimolar 0 0.644 0.995 55 0.632 0.963 176 0.592 0.866 283 0.563 0.795 986 0.418 0.442 1151 0.396 0.388 1555 0.372 0.329 1590 0.346 0.266 1729 0.354 0.237 1803 0.350 0.227 2582 0.285 0.117 5107 0.269 0.078 0.257 0.000 Graphically determined k = 8.20 X 10"*

TABLE XX

RATE OP ISOMERIZATION OP 4 -PLUOROAZOBENZENE IN DIOXANE AT 2 5 .2°, 34 .8° AND 4 4 .5 °

Time (min.) O.D. (436 mu) Praction cis Temp., 25.2 t 0 .07°; cone., 0.470 millimolar 0 0.592 0.955 959 0.562 0.870 1558 0.556 0.854 2775 0.519 0.752 4020 0.491 0.674 5745 0.462 0.594 7105 0.441 0.556 9671 0.401 0.425 12598 0.566 0.529 16777 0.354 0.240 1^8

TABLE XX (contd.)

Time (mln.) O.D. (436 mu) Fraction els

20064 0.314 0.185 22592 0.304 0.158 25901 0.290 0.119 6 0 0.247 0.000 Graphically determined k = 8.11 X 10-5

Temp.3 34.8 i 0.03°; conc.j 0.398 mllllmolar

0 0.498 0.941 115 0.488 0.908 3:)8 0.468 0.842 1105 0.420 0.683 1285 0.411 0.654 1490 0.398 0.611 1667 0.388 0.578 2645 0.345 0.436 2881 0.358 0.413 3111 0.328 0.380 5979 0.301 0.287 4352 0.290 0.254 5677 0.264 0.168 6999 0.249 0.119 Oo 0.213 0.000 Graphically determined k = 2.96 X 10"^

Temp., 44.5 i 0 .07°; cone.. 0.519 mllllmolar

0 0.663 0.973 40 0.647 0.955 160 0.611 0.844 269 0.570 0.742 972 0.421 0.372 1138 0.398 0.315 1319 0.375 0.258 1574 0.555 0.203 1717 0.343 0.179 1787 0.359 0.169 2568 0.301 0.074 0 0 0.271 0.000

Graphically determined k = 9.90 X 10-4 139

TABLE XXI RATE OP ISOMERIZATION OP 4-PLUOROAZOBENZENE IN BENZENE ______AT 25.2°, 34.8° AND 44.5°______

Time (mln.) O.P. (436 mu) Practlon els Temp., 25.2 i 0 .07°; cone., 0.504 mllllmolar 0 0.639 0.955 1016 0.594 0.823 1499 0.579 0.786 2484 0.542 0.694 2915 0.551 0.667 5721 0.501 0.592 4574 0.490 0.565 '5404 0.462 0.495 7014 0.428 0.411 8372 0.408 0.361 9869 0.378 0.286 11503 0.364 0.251 12965 0.345 0.204 14348 0.355 0.174 16852 0.314 0.127 CO 0.263 0.000 Graphically determined k = 1.17 x 10 -4

Temp., 3^.8 cL 0 .03°; cone., 0.509 mllllmolar 0 0.638 0.922 62 0.630 0.905 168 0.616 0.869 856 0.541 0.686 967 0.527 0.652 1068 0.515 0.618 1232 0.496 0.577 1409 0.482 0.543 2311 0.422 0.397 2483 0.408 0.363 2717 0.592 0.324 2920 0.385 0.307 3682 0.352 0.226 4087 0.359 0.195 5428 0.306 0.114 1#0

TABLE XXI (contd.)______

Time (mln.)_____O.P. (436 mu)______Fraction els 6782 0.287 0.068 oo 0.259 0.000

Graphically determined k = 5.82 X 10-4

Temp.3 44.5 0.07°; conc.. 0.595 mllllmolar 0 0.784 1.000 93 0.727 0.881 196 0.675 0.773 274 0.658 0.695 506 0.628 0.674 548 , 0.601 0.618 1026 0.429 0.259 1180 0.405 0.209 1267 0.594 0.186 1370 0.581 0.159 1655 0.559 0.115 Oo 0.505 0.000 Graphically determined k = 1.35 X 10-3

TABLE XXII RATE OP ISOMERIZATION OF 4 -FLUOROAZOBENZENE IN n-HEPTANE .______AT 2 5 .2°, 3 4 .8° AND 4 4 .5 °______.

Time (mln.) O.P. (456 mu) Fraction els Temp., 24.2 i 0.07°; conc., 0.585 mllllmolar 0 0.725 0.947 1040 0.640 0.778 1197 0.655 0.768 1524 0.619 0.756 2505 0.569 0.654 2939 0.548 0.591 3742 0.508 0.510 4393 0.485 0.465 5188 0.460 0.415 l4,ï

TABLE XXII (contd.)

Time (mln.) O.D. (k36 mu) Practlon cls

5891 0.452 0.556 66^5 0.422 0.555 8 3 9 6 0.579 0.248 9894 0.554 0.197 11525 0.537 0.165 12987 0.519 0.126 14570 0.505 0.098 0 0 0.257 0.000 Graphically determined k = I.58 x 10"*

Temp.j 54.8 i 0.05°; conc.. 0.486 mllllmolar 0 0.582 0.897 55 0.575 0.880 156 0.558 0.859 846 0.458 0.595 957 0.442 0.556 1058 0.428 0.522 1220 0.411 0.481 1596 0.595 0.442 1466 0.586 0.420 2299 0.525 0.271 2471 0.518 0.254 2708 , 0.504 0.220 2908 0.296 0.200 5672 0.267 0.129 4074 0.260 0.112 0.214 0.000

Graphically determined k = 5.16 X lor*

Temp., 44.5 i 0 .07°; conc., 0.605 mllllmolar 0 0.777 1.000 29 0.759 0.925 110 0.681 0.810 215 0.617 0.685 295 0.575 0.600 527 0.557 0.564 570 0.557 0.525 1045 0.554 0.162 142

TABLE XXII (contd.)______

Time (mln.) O.D. (4-^6 mu) Fraction cls

1199 0.336 0.127 1286 0.326 0.107 1392 0.318 0.091 00 0.272 0.000 Graphically determined k = 1.73 x 10“®

TABLE XXIII

RATE OP ISOMERIZATION OF 3-CHLOROAZOBENZENE IN ABSOLUTE ______ETHANOL AT 34 .80 AND 5 4 .6°______

Time (mln.) O.D. (438 mu) Fraction cls Temp., 34.8 ^ 0 .03°; conc.. 0.676 mllllmolar 0 0.792 0.892 174 0.770 0.849 976 0.702 0.718 1142 0.683 0.681 1438 0.662 0.640 2400 0.600 0.520 2618 0.588 0.497 2895 0.571 0.464 3800 0.528 0.381 4240 0.508 0.342 5250 0.469 0.286 5643 0.460 0.250 6683 0.434 0.199 8384 0.400 0.134 11104 0.369 0.073 Go 0.331 0.000 Graphically determined k = 2.25 x lo"*

Temp., 54.6 i 0 .04 °; cohc., O.567 mllllmolar 0 0.712 1.000 114 0.618 0.783 166 0.590 0.719 145

TABLE XXIII (contd.)______

Time (min.) O.D. (458 mu) Fraction cis 248 0.558 0.599 552 0.494 0.498 415 0.458 0.415 449 0.442 0.578 494 0.429 0.548 554 0.409 0.502 654 0.586 0.249 829 0.555 0.175 985 0.525 0.108 Oo 0.278 0.000 Graphically determined k = 2.15 X 10-3

TABLE XXIV

RATE OF ISOMERIZATION OF 5 -CHLOROAZOBENZENE IN DIOXANE ______AT 5 4 .8° AND 5 4 .6°______

Time (min.) O.D. (458 mu) Fraction cis Temp.3 54.8 i 0.05°; conc.. 0.781 millimolar 0 0.879 0.958 192 0.840 0.865 994 0.762 0.712 1160 0.748 0.685 1456 0.722 0.655 2418 0.652 0.499 2657 0.640 0.487 2915 0.625 0.445 5819 0.579 0.558 4249 0.561 0.525 5272 0.522 0.248 5664 0.512 0.228 6702 0.487 0.180 8402 0.455 0.118 11122 0.428 0.066 ûo 0.594 0.000 Graphically determined k = 2.51 x 10“4 144

TABLE XXIV (contd,)______

Time (mln.)_____O.D. ( 438 mu) Fraction cls Temp., 54.6 ^ 0 .04 °; conc., 0.662 mllllmolar

0 0.771 1.000 154 0.648 0.726 187 0.604 0.628 268 0.558 0.526 550 0.511 0.421 450 0.478 0.547 512 0.449 0.285 572 0.452 0.245 671 0.409 0.194 847 0.576 0.120 c>o 0.522 0.000 Graphically determined k = 2.46 x 10 -3

TABLE XXV

RATE OP ISOMERIZATION OP 5 -CHLOROAZOBENZENE IN BENZENE ______AT 54 .8° AND 54 .6°______

Time (mln.) O.D. (458 mu) Practlon cls Temp., 54.8 ^ 0.05°; conc.. 0.507 mllllmolar 0 0.580 0.928 91 0.571 0.902 812 0.500 0.697 968 0.485 0.654 1118 0.475 0.626 1258 0.462 0.588 1585 0.454 0.565 2258 0.405 0.418 2400 0.596 0.598 2672 0.585 0.560 2810 0.578 0.546 5672 0.548 0.259 5959 0.559 0.255 5146 0.511 0.155 6577 0.294 0.104 145 TABLE XXV (contd.)

Time (mln.) O.D. (458 mu) Practlon cis 8296 0.277 0.055 Oo 0.258 0.000 Graphically determined k = ,5.48 X 10"4

Temp.j 54.6 0 .04 °; conc.. 0.552 millimolar 0 0.655 1.000 69 0.560 0.800 122 0.507 0.658 144 0.487 0 .6o4 201 0.449 0.505 249 0.419 0.425 280 0.598 0.566 520 0.582 0.524 565 0.565 0.275 415 0.545 0.225 445 0.558 0.206 508 0.522 0.165 607 0.501 0.107 Oo 0.261 0.000 Graphically determined k = 5.54 X 10"®

TABLE XXVI RATE OP ISOMERIZATION OP 5 -CHLOROAZOBENZENE IN n-HEPTANE AT 5 4 .8° AND 5 4 .6°

Time (min.) O.D. (458 mu) Practlon cis Temp., 54.8 "i- 0 .05 °; conc.. 0.629 millimolar 0 0.680 0.912 108 0.655 0.852 852 0.540 0.605 985 0.515 0.545 1156 0.498 0.510 1278 0.482 0.475 146

TABLE XXVI (contd.) ■ ■ '1 ■' g

Time (min.) O.D. (438 mu) Fraction cls

1403 0.469 0.446 2276 0.397 0.287 2417 0.385 0.261 2534 • 0.378 0.245 2690 0.367 0.221 2828 0.359 0.203 3692 0.328 0.135 3956 0.322 0.121 5166 0.296 0.064 (3o 0.267 0.000 -4 Graphically determined k = 5.18 X 10

Temp., 54.6 — 0 .04 °; conc.. 0.596 mllllmolar 0 0.682 1.000 51 0.598 0.804 105 0.518 0.619 127 0.498 0.573 184 0.438 0.434 232 0.401 0.348 267 0.377 0.292 302 0.356 0.244 348 0.335 0.195 427 0.310 0.137 Go 0.251 0.000 -3 Graphically determined k = 4 .6l x 10

TABLE XXVII

RATE OF ISOMERIZATION OF 4 -CHLOROAZOBENZENE IN ABSOLUTE ______ETHANOL AT 2 5 .2° AND 3 5 .0°______

Time (mln.) O.D. (438 mu) Fraction cls Temp., 25.2 t 0 .07°; conc., 0.333 mllllmolar

0 0.427 0.709 225 0.422 0.693 962 0.402 0.632 1298 0.397 0.616 147 TABLE XXVII (contd.)

Time (min.) O.D. (458 mu) Praction cis 2520 0.379 0.560 2856 0.565 0.517 3759 0.549 0.468 5458 0.526 0.596 6705 0.514 0.559 8155 0.293 0.294 9542 0.280 0.254 11505 0.264 0.204 14007 0.249 0.158 16941 0.253 0.108 19641 0.225 0.077 0 0 0.198 0.000 Graphically determined k = 1.09 X 10"^

Temp., 55.0 - 0.05°; conc.. 0.678 millimolar 0 0.880 0.752 71 0.870 0.717 226 0.841 0.674 351 0.815 0.656 490 0.797 . 0.609 1133 0.722 0.499 1306 0.698 0.465 1595 0.666 0.416 1871 0.644 0.584 2541 0.598 0.516 3071 0.552 0.248 4021 0.501 0.175 4509 0.493 0.161 5452 0.456 0.106 Oo 0.584 0.000 Graphically determined k = 5.52 X 10"^

TABLE XXVIII

RATE OP ISOMERIZATION OP 4 -CHLOROAZOBENZENE IN DIOXANE AT 25.2° AND 55.0°

Time (min.) O.D. (458 mu) Praction cis 146 TABLE XXVIII (contd.)

Time (min.) O.D. (428 mu) Fraction cis Temp., 25.2 0.07°; conc.. 0.246 millimolar 0 0.415 0.712 209 0.409 0.692 940 0.291 0.622 1277 0.282 0.601 2202 0.261 0.520 2814 0.251 0.497 2742 0.226 0.446 5415 0.212 0.265 6682 0.294 0.204 7186 0.290 0.291 8125 0.277 0.247 9525 0.267 0.212 11289 0.252 0.166 12990 0.229 0.118 16919 0.228 0.081 Oo 0.204 ' 0.000 Graphically determined k = 1.28 X 10"*

Temp.j 25.0 0 .02°; conc.. 0.521 millimolar

0 0.641 0.722 111 0.628 0.704 262 0.610 0.665 291 0.599 0.642 521 0.580 0.601 1169 0.518 0.468 1242 0.502 0.426 1621 0.479 0.284 1910 0.465 0.254 2581 0.425 0.268 2789 0.410 0.226 2100 0.401 0.217 4058 0.266 0.142 4249 0.262 0.125 Oo 0.200 0.000 Graphically determined k = 2.88 X 10"* 149

TABLE XXIX

RATE OF ISOMERIZATION OP 4 -CHLOROAZOBENZENE IN BENZENE Am op^ oO AT>m nO

Time (min.) O.D. (440 mu) Fraction cis Temp., 25.2 — 0 .07°; conc.. 0.265 millimolar

0 0.425 0.715 198 0.428 0.692 951 0.402 0.611 1269 0.292 0.580 2202 0.262 0.489 2555 0.255 0.467 2864 0.248 0.442 5770 0.228 0.279 4192 0.219 0.251 5504 0.202 0.201 5658 0.298 0.285 6667 0.280 0.229 8108 0.268 0.191 9511 0.250 0.125 C^o 0.207 0.000 Graphically determined k = 1.67 X 10"^

Temp,., 25.0 i 0.02°; conc.. 0.279 millimolar 0 0^490 0.828 180 0.468 0.760 266 0.456 0.722 886 0.285 0.505 969 0.277 0.480 1025 0.272 0.465 1159 0.261 0.421 1229 0.256 0.415 1575 0.249 0.294 1697 0.226 0.222 2211 0.298 0.227 2540 0.285 0.197 2896 0.275 0.160 2804 0.249 0.086 CX3 0.221 0.000 Graphically determined k = 5.56 X 10-4 15P

TABLE XXX

RATE OP ISOMERIZATION OP 4-CHLOROAZOBENZENE IN n-HEPTANE

Time (min.) O.D. (440 mu) Praction cis Temp.3 25.2 ± 0.07°; conc.3 0.377 millimolar 0 0.428 0.734 184 0.423 0.719 957 0.385 0.605 1257 0.570 0.557 2288 0.327 0.425 2476 0.326 0.422 2661 0.317 0.595 2856 0.311 0.376 5752 0.286 0.500 3952 0.281 0.284 4180 0.276 0.269 5287 0.254 0.202 5652 0.253 0.199 6650 0.259 0.156 8092 0.225 0.115 9498 0.212 0.075 D o 0.188 0.000

Graphically determined k = 2.35 X 10"4

Temp.3 35.0 ± 0.03°; conc.3 0.370 millimolar 0 0.450 0.829 162 0.422 0.742 250 0.405 0.682 868 0.321 0.427 950 0.316 0.411 1019 0.307 0.585 1140 0.294 0 .5%3 1224 0.284 0.512 1355 0.275 0.285 1678 0.250 0.206 2295 0.227 0.154 2522 0.217 0.105 0.184 0.000

Graphically determined k = 7.90 X 10“^ 151 TABLE XXXI

RATE OF ISOMERIZATION OP 3-BROMOAZOBENZENE IN ABSOLUTE

Time ( mln. ) O.D. (440 mu) Fraction cis

Temp., 34.8 ± 0 .05 °; conc.. 0.606 millimolar 0 0.672 0.856 104 0.661 0.851 217 0.650 0.807 855 0.609 0.716 1095 0.595 0.680 1519 0.572 0.655 2449 0.514 0.504 2627 0.505 0.485 2791 0.496 0.464 5752 0.458 0.580 4099 0.445 0.551 5159 0.412 0.278 6612 0.576 0.198 8051 0.554 0.149 9469 0.556 0.109 0.287 0.000 Graphically determined k = 2.17 X 10“^

Temp., 54.6 ± 0 .04 °; conc.. 0.452 millimolar 0 0.549 1.000 129 0.471 0.767 205 0.454 0.657 277 0.401 0.558 540 0.578 0.490 459 0.551 0.409 519 0.527 0.557 606 0.510 0.287 685 0.296 0.245 809 0.279 0.194 ÛO 0.214 0.000 Graphically determined k = 2.08 X 10"° 152 TABLE XXXII

RATE OP ISOMERIZATION OP 5-BROMOAZOBENZENE IN DIOXANE

Time (min.) O.D. (440 mu) Praction cis

Temp.j 5^•8 ± 0.03°; conc.. 0.491 millimolar 0 0.523 0.886 197 0.509 0.842 502 0.503 0.823 947 0.468 0.713 1200 0.452 0.662 1424 0.443 0.634 2554 0.395 0.483 2732 0.389 0.464 2898 0.383 0.445 3857 0.353 0.350 4204 0.348 0.334 5264 0.323 0.256 6717 0.300 0.183 8135 0.281 0.123 9576 0.271 0.091 Cvo 0.242 0.000 Graphically determined k = 2.35 X 10"4

Temp., 54.6 0 .04 °; conc.. 0.543 millimolar 0 0.619 1.000 91 0.548 0.798 157 O.5II 0.692 238 0.463 0.556 301 0.438 0.484 398 0.403 0.385 481 0.378 0.313 565 0.358 0.256 644 0.344 0.217 770 0.324 0.160 1504 0.279 0.031 ÛO 0.268 0.000 Graphically determined k = 2.40 X 10"® 155

TABLE XXXIII

RATE OP ISOMERIZATION OP 3-BROMOAZOBENZENE IN BENZENE

Time (mln) O.D. (440 mu) Praction cis Temp., 34.8 i 0.03°; conc.3 0.437 millimolar 0 0.481 0.895 134 0.465 0.841 247 0.458 0.817 885 0.413 0.692 1029 0.401 0.624 1199 0.392 0.593 1400 0.378 0.546 2461 0.329 0.380 2559 0.327 0.373 2682 0.322 0.356 2868 0.314 0.329 3740 0.291 0.251 4229 0.278 0.207 5211 0.261 0.149 6675 0.242 0.085 Oo 0.217 0.000 Graphically determined k = 3.43 X 10-4

Temp.3 54.6 'i- 0 .04 °; conc., 0.357 millimolar 0 0.418 1.000 87 0.355 0.739 128 0.330 0.635 271 0.270 0.386 294 0.264 0.361 554 0.248 0.295 434 0.231 0.224 444 0.228 0.212 500 0.220 0.178 608 0.204 0.112 0.177 0.000 Graphically determined k = 3.46 X 10-3 154.

TABLE XXXIV

RATE OP ISOMERIZATION OP 5-BROMOAZOBENZENE IN n-HEPTANE

Time (rain.) O.D. (440 mu) Praction cis Terap.j 34.8 i 0 .03°; conc.. 0.517 millimolar

0 0.559 0.886 175 0.502 0.842 279 0.490 0.823 924 0.419 0.713 1025 0.408 0.662 1152 0.595 0.634 1250 0.384 0.483 1452 0.565 0.464 2515 0.505 0.445 2613 0.299 0.350 2754 0.295 0.554 2920 0.286 0.256 5794 0.261 0.183 5980 0.258 0.123 4283 0.251 0.091 Co 0.214 0.000

Graphically determined k = 5.02 X 10-4

Terap., 54.6 i 0 .04 °j conc.. 0.615 millimolar 0 0.688 1.000 76 0.568 0.717 114 0.518 0.599 157 0.488 0.528 188 0.439 0.413 229 0.412 0.349 258 0.592 0.302 284 0.577 0.267 341 0.552 0.208 421 0.321 0.135 487 0.306 0.099 Co 0.264 0.000 Graphically determined k = 4.66 X 10-3 155

TABLE XXXV

RATE OF ISOMERIZATION OP 4 -BROMOAZOBENZENE IN ABSOLUTE ______ETHANOL AT 25.2°, 35.0° AND 44.5°______

Time (mln.) O.D. (440 mu) Practlon cis

Temp.^ 25.2 ± 0 .07°; conc.. 0.392 mllllmolar 0 0.564 0.746 217 0.559 0.725 1006 0.529 0.690 1492 0.522 0.651 2468 0.500 0.610 2894 0.491 0.581 3884 0.469 0.521 5427 0.439 0.463 6752 0.420 0.420 8323 0.391 0.354 9792 0.372 0.312 12504 0.348 0.256 16883 0.309 0.168 21223 0.286 0.116 Oo 0.235 0.000 Graphically determined k = 8.76 X 10"5

Temp., 35.0 ±. 0 .03°; conc.. 0.479 mllllmolar 0 0.558 0.497 99 0.547 0.476 1030 0.480 0.349 1161 0.472 0.326 1488 0.460 0.311 1741 0.447 0.287 2465 0.412 0.220 2717 0.407 0.211 2978 0.402 0.201 3840 0.372 0.144 4261 0.368 0.137 5558 0.329 0.081 6855 0.318 0.042 Go 0.296 0.000 Graphically determined k = 3.14 x 10"* 156

TABLE XXXV (contd.)

Time (min.) O.D. (440 mu) Praction cis

Temp., 44.5 ± 0.07°; conc.. 0.413 millimolar

0 0.653 0.875 115 0.613 0.787 200 0.580 0.715 275 0.559 0.669 412 0.519 0.581 531 0.487 - 0.511 633 0.458 0.447 755 0.436 0.399 1231 0.366 0.246 1412 0.344 0.197 1687 0.324 0.154 1928 0.309 0.121 2293 0.291 0.081 0.254 0.000

Graphically determined k = 1.04 X 10"®

TABLE XXXVI

RATE OP ISOMERIZATION OP 4 -BROMOAZOBENZENE IN DIOXANE AT 2 5 .2°, 35.0° AND 4 4 .5 °

Time (min.) O.D. (440 mu) Praction cis Temp., 25.2 i. 0.07°; conc., 0.466 mllllmolar 0 0.617 0.760 200 0.612 0.749 984 0.588 0.694 1471 0.571 0.654 2450 0.547 0.597 2877 0.537 0.576 3862 0.509 0.512 5406 0.477 0.438 6736 0.452 0.380 8306 0.428 0.325 9776 0.411 0.286 12487 0.382 0.219 TABLE XXXVI (contd.)

Time (mln.) O.D. (440 mu) Fraction cis 15400 0.558 0.164 18405 0.556 0.115 0.000 • OQ 0.287 Graphically determined k = 1.01 X 10“^

Temp., 55.0 "t 0.05°; conc.. 0.517 millimolar

0 0.547 0.502 95 0.545 0.481 219 0.559 0.467 1071 0.506 0.551 1205 0.501 0.555 1550 0.290 0.295 1786 0.285 0.270 2510 0.260 0.190 2758 0.258 0.185 5025 0.254 0.169 5886 0.258 0.112 4502 0.255 0.095 5599 0.219 0.046 0.206 ÛO 0.000 Graphically determined k = 5.74 X 10-4

Temp., 44.5 i 0 .07°; conc.. 0.400 millimolar

0 0.574 0.875 95 0.559 0.780 182 0.508 0.696 257 0.489 0.644 592 0.454 0.549 510 0.425 0.465 615 0.401 0.405 757 0.581 0.551 1215 0.525 0.198 1592 0.515 0.166 1669 0.294 0.114 1910 0.284 0.087 . 0.252 0.000

Graphically determined k = 1.21 X 10-3 158

TABLE XXXVII

RATE OP ISOMERIZATION OP 4-BROMOAZOBENZENE IN BENZENE ______AT 25.2°3 55.0° AND 44.5°______

Time (mln.y O.P. (442 mu) Practlon cls Temp., 25.2 d: 0.07°; conc.. 0.439 mllllmolar 0 0.619 0.860 171 0.611 0.840 951 0.382 0.764 1168 0.570 0.735 1573 0.556 0.700 2414 0.525 0.621 2595 0.521 0.611 3786 0.479 0.504 4104 0.470 0.481 5225 0.442 0.410 6707 0.415 0.341 8252 0.388 0.272 9697 0.366 0.216 11228 0.351 0.178 15275 0.319 0.097 Co 0.281 0.000 Graphically determined k = 1.41 X 10-4

Temp., 35_.0 t 0 .03°; conc., 0.299 mllllmolar 0 0.378 0.700 79 0.374 0.686 191 0.361 0.637 388 0.344 0.573 1057 0.299 0 .4 o4 1208 0.291 0.375 1331 0.287 0.360 1448 0.281 0.337 1585 0.276 0.318 2276 0.248 0.214 2604 0.238 0.176 2898 0.232 0.154 3918 0.214 0.086 5331 0.203 0.045 Oo 0.191 0.000 Graphically determined k = 5.27 x 10-4 15'9

■^3 /

Time (min.) O.D. (442 mu) Praction cis

Temp.3 # . 5 ^ 0.07°; conc. 3 0.413 millimolar

0 0.587 0.875 51 0.555 0.785 111 0.525 0.707 14? 0.510 0.667 249 0.470 0.558 529 0.446 0.495 585 0.429 0.447 469 0.405 0.582 555 0.586 0.551 595 0.576 0.504 712 0.559 0.257 1057 0.518 0.146 1246 0.298 0.092 0.264 0.000 Oo Graphically determined k = 1.80 X 10"^

TABLE XXXVIII

RATE OP ISOMERIZATION OP 4-BROMOAZOBENZENE IN n-HEPTANE AT 25.£2°3 55.0° AND 44 .5 "

Time (min.) O.D. (442 mu) Praction cis Temp.^ 25.2 t 0.07°; conc., 0.4l8 mllllmolar 0 0.543 0.853 146 0.555 0.807 952 0.489 0.692 1144 0.474 0.655 1355 0.458 0.611 2394 0.420 0.512 2572 0.410 0.486 2818 0.403 0.467 5765 0.370 0.581 4 o86 0.565 0.565 5201 0.329 0.274 5534 0.324 0.261 l 6 o

TABLE XXXVIII (contd.)

Time (mln.) O.D. ( # 2 mu) Practlon cis 6687 0.300 0.199 8210 0.279 0.144 9672 0.264 0.104 0

Temp., 35.0 i 0.03°j conc.. 0.268 mllllmolar 0 0.500 0.642 66 0.294 0.618 175 0.280 0.561 372 0.257 0.468 104-4 0.214 0.293 1192 0.210 0.277 1315 0.206 0.260 1434 - 0.202 0.244 1568 0.197 0.224 2262 0.170 0.114 2491 0.167 0.102 2882 0.161 0.077 Oo 0.142 0.000 Graphically determined k = 7.50 X 10“^

Temp., 44 .5 ^ 0 .07°j conc.. 0.463 mllllmolar 0 0.618 0.875 38 0.591 0.812 98 0.543 0.699 128 0.520 0.645 234 0.462 0.508 314 0.428 0.428 368 0.402 0.367 454 0.374 0.301 522 0.356 0.259 582 0.346 0.235 697 0.321 0.177 1016 0.284 0.089 C o 0.246 0.000

Graphically determined k = 2.28 x 10-3 161 TABLE XXXIX

RATE OP ISOMERIZATION OF ^-lODOAZOBENZENE IN ABSOLUTE

Time (niin.) O.D. (440 mu) Fraction cis

Temp.3 35.0 ± 0 .03°; conc.3 0.614 millimolar 0 0.616 0.670 68 0.601 0.635 186 0.586 0.601 409 0.575 0.576 106o 0.539 0.493 1355 0.523 0.456 1735 0.499 0.401 2685 0.470 0.335 3023 0.449 0.287 4049 0.417 0.213 4638 0.416 0.211 5914 0.390 0.151 7249 0.370 0.106 8641 0.352 0.073 Po 0.324 0.000

Graphically determined k = 2.52 X 10-4

Temp.3 54.6 •+ 0 .04 °; conc.3 0.621 millimolar 0 0.769 1.000 69 0.709 0.865 133 0.661 0.757 169 0.638 0.706 242 0.589 0.595 354 0.529 0.461 500 0.471 0.330 663 0.428 0.234 834 0.387 0.142 0.324 0.000

Graphically determined k = 2.22 X 10-3 l 6 2 TABLE XL

RATE OP ISOMERIZATION^OP 5-IODO^ZOBENZENE IN DIOXANE

Time (mln.) O.D. Practlon cls

Temp.j 55•0 ± 0.05°; conc., 0.649 mllllmolar^ wave length, 442 mu 0 0.659 0.726 59 0.629 0.705 117 0.627 0.698 780 0.587 0.604 1069 0.575 0.575 1455 0.549 0.514 2599 0.512 0.427 2741 0.500 0.599 5765 0.456 0.295 4555 0.437 0.250 5627 0.404 0.172 6967 . 0.384 0.125 8559 0.364 0.078 cx> 0.551 0.000 Graphically determined k = 2.48 X 10-4

Temp.j 54.6 rt 0 .04 °; conc., 0 . 682 mllllmolar/ wave length, 44 o mu 0 0.789 1.000 104 0.688 0.772 169 0.659 0.662 208 0.617 0.612 285 0.571 0.508 574 0.530 0.415 556 0.462 0.262 699 0.427 0.185 875 0.597 0.115 Go 0.546 0.000 Graphically determined k = 2.42 X 10-3 163 TABLE XLI

RATE OP ISOMERIZATION OF 3-IODOAZOBENZENE IN BENZENE

Time (min.) O.D. Fraction cis Temp., 35*0 ± 0.03°; conc.. 0.367 millimolarj wave-lenffth, 442 mu 0 0.372 0.787 72 0.368 0.771 2&4 0.357 0.727 1119 0.309 0.534 1293 0.296 0.482 1457 0.291 0.462 1590 0.284 . 0.434 2568 0.250 0.297 2795 0.245 0.277 2985 0.242 0.265 4043 0.221 0.181 4450 0.212 0.145 5380 0.202 0.104 7026 0.189 0.052 00 0.176 0.000 Graphically determined k =: 3.70 X 10-4

Temp., 54.6 i 0 .04 °; conc.. 0.399 millimolar. wave-length, 440 mu 0 0.448 0.927 39 0.414 0.802 121 0.364 0.619 184 0.334 0.509 249 0.307 0.410 322 0.286 0.333 420 0.258 0.231 552 0.236 0.150 o* 0.195 0.000 Graphically determined k =: 3.32 X 10-3 164 TABLE XLII

RATE OP ISOMERIZATION OF 5-IODOAZOBENZENE IN n-HEPTANE n m -xc: r^O n-K-m c)i i:0 —

Time (min.) O.D. Fraction cls T e m p 35 • 0 ± 0.03°; conc.. 0.291 millimolarj wave-lengthj 444 mu 0 0.296 0.813 108 0.283 0.752 186 0.277 0.724 251 0.275 0.715 1066 0.229 0.500 1243 0.217 0.444 1403 0.208 0.402 1540 0.204 0.383 2515 0.175 0.248 2745 0.170 0.224 3989 0.148 0.122 4400 0.145 0.108 5327 0.137 0.070 Go 0.122 0.000 Graphically determined k -: 4.74 X 1CT4

Temp., 54.6 i 0 .04 °; conc.. 0.746 millimolarj wave-length, 44 o mu 0 0.613 1.000 46 0.556 0.848 92 0.496 0.689 181 0 .4 o8 0.455 245 0.365 0.340 % 0.334 0.258 386 0.306 0.184 463 0.287 0.133 613 0.261 0.064 Oo 0.237 0.000 Graphically determined k = 4.35 X 10-3 16 5 TABLE XLIII

RATE OP ISOMERIZATION OF 4-IODOAZOBENZENE IN ABSOLUTE ETHANOL AT 25.2°, 35.0° AND 44.5°______

Time (mln.) O.D. ( 440 mu)______Fraction cls Temp.j 25.2 ^ 0 .07°; conc., 0.423 mllllmolar 0 0.714 0.938 133 0.701 0.909 880 0.686 0.876 1091 0.680 0.862 2391 0.633 0.758 2831 0.623 0.736 4130 0.597 0.678 5631 ' 0.557 0.590 7277 0.525 0.519 8613 0.499 0.461 10033 0.477 0.412 12654 0.438 0.326 15535 0.410 0.264 18366 0.384 0.206 21057 0.360 0.153 25553 0.341 0.111 00 0.291 0.000 Graphically determined k = 8.31 x 10“^

Temp.j 35.0 t 0 .03°; conc.j 0.458 mllllmolar 0 0.782 0.959 107 0.767 0.929 263 0.743 0.879 4 i6 0.730 0.853 602 0.701 0.793 806 0.675 0.740 1703 0.587 0.560 2163 0.554 0.493 3077 0.487 0.356 3376 0.476 0.333 3539 0.467 0.315 4717 0.428 0.235 6292 0.375 0.127 00 0.313 0.000 Graphically determined k = 3.11 x lO"^ 1 6 6 TABIÆ XLIII (contd.)______

Time (min.)____ O.P. ( 440 mu)______Fraction cls

Temp.,. 44.5 ± 0 .07°; conc.. 0.295 mllllmolar 0 0.505 0.955 96 0.476 0.869 188 0.451 0.789 265 0.428 0.716 575 0.411 0 .,662 555 0.579 0.559 719 0.346 0.454 847 0.525 0.387 945 0.320 0.371 1640 0.259 0.176 1810 0.248 0.141 1989 0.242 0..121 2517 0.230 0.083 Oo 0.204 0.000

Graphically determined k = 1.04 X 10-3

TABLE XLIV

RATE OP ISOMERIZATION[■ION OP 4 -IC-IODOAZQBENZENE IN DIOXANE ATA m 2ni- 5 .2 n O°, "3 Z 5C .0n O° AND A T1 T \ 4Il 4II .5 irO'

Time (min.) O.D. ( 4-4-0 mu)______Fraction cls Temp., 25.2 t 0 .07°; conc., 0.295 mllllmolar 0 0.469 0.948 162 0.462 0.922 924 0.445 0.859 1137 0.439 0.837 2434 0.414 0.744 2875 0.407 0.719 4175 0.384 0.633 5677 0.359 0.541 7520 0.357 0.459 8657 0.322 0.404 10080 0.309 0.356 12697 0.286 0.270 167 TABLE XLIV (contd.)

Time (min.) O.D. 440 mu) Fraction cis

15584 0.269 0.207 18413 0.257 0.163 00 0.213 0.000 Graphically determined k = 9.67 X 10“^

Temp c i 35•0 i- 0 .03°; conc.3 0.436 millimolar 0 0.693 0.949 54 0.682 0.920 143 0.671 0.892 303 0.651 0.841 453 0.628 0.782 639 0.607 0.728 847 0.597 0.703 1743 0.521 0.508 2204 0.487 0.421 3118 0.441 0.303 3414 0.430 0.274 3580 0.424 0.259 4758 0.384 0.156 4962 0.377 0.139 00 0.323 0.000 Graphically determined k = 3.70 X 10"4

Temp., 44.5 + OJOÔ mllllmolar 0 0.468 0.920 82 0.445 0.837 174 0.424 0.761 251 0.401 0.678 361 0.378 0.594 521 0.353 0.504 688 0.326 0.406 832 0.304 0.326 929 0.298 0.304 1623 0.251 0.134 1796 0.244 0.109 1971 0.238 0.087 Oo 0.214 0.000 Graphically determined k = I.I9 x 10"® l6 8

TABLE XLV

RATE OP ISOMERIZATION OP 4-lODOAZOBENZENE IN BENZENE .______AT 25.2°. 35.0° AND 44.5°______

Time (mln.) O.D. (442 mu) Praction cis

Temp.^ 25.2 i 0 .07°; conc.. 0.541 millimolar 0 0.540 0.968 147 0.550 0.955 878 0.505 0.854 970 0.498 0.852 1119 0.496 0.825 2584 0.459 0.706 2558 0.452 0.685 2811 0.448 0.670 5795 0.429 0.608 4175 0.415 0.565 5678 0.578 0.445 7245 0.556 0.572 8596 0.559 0.517 11252 0.509 0.220 15581 0.280 0.126 00 0.241 0.000 Graphically determined k = 1.52 X 10"4

Temp.., 55.0 ± 0 .05 °; conc.. 0.450 millimolar 0 0.689 1.000 125 0.656 0.914 255 0.655 0.855 525 0.615 0.808 486 0.606 0.784 605 0.588 0.758 1471 0.497 0.501 1654 0.475 0.459 1759 0.464 0.416 1966 0.454 0.590 2905 0.595 0.250 5006 0.587 0.216 5527 0.569 0.169 4269 0.545 0.107 CO 0.504 0.000 Graphically determined k = 5.14 x ICr* l69

TABLE XLV (contd.)

Time (mln.) O.D. (442 mu) Fraction cls Temp., 44.5 t 0.07°j conc.,___ 0.^70 mllllmolar

0 0.559 0.889 44 0.540 0.834 99 0.519 0.775 180 0.484 0.671 347 0.433 0.522 458 0.404 0.437 545 0.387 0.388 650 0.363 0.318 762 0.346 0.268 862 0.350 0.222 1636 0.280 0.076 O o 0.254 0.000 Graphically determined k = I.58 x 10”®

TABLE XLVI

RATE OP ISOMERIZATION OP 4 -IODOAZOBENZENE IN n-HEPTANE .______AT 25.2°, 35.0° AND 44.5 ______

Time (mln.) O.D. (444 mu) Fraction cls

Temp.3 25.2 i 0.07°; conc.3 0.411 mllllmolar 0 0.618 0.966 150 0.608 0.940 895 0.562 0.819 989 0.558 0.809 1137 0.552 0.795 2399 0.481 0.606 2577 0.472 0.585 282^ 0.461 0.554 3809 0.429 0.470 4190 0.418 0.441 5584 0.585 0.349 5695 0.573 0.323 7258 0.342 0.242 8612 0.321 0.186 10122 0.306 0.147 1 70

TABLE XLVI (contd.) Time (mln.) O.D. (444 mu) Fraction cis

Oo 0.250 0.000 Graphically determined k = I.89 x 10-4

Tfimo. IS.O — 0 .03°; conc. 3 0.399 millimolar 0 0.608 1.000 1K6 0.571 0.897 258 0.548 0.837 343 0.558 0.810 510 0.494 0.690 626 0.472 0.631 1491 0.375 0.367 1677 0.561 0.529 1760 0.355 0.311 1990 0.340 0.270 2710 0.303 0.170 Co 0.240 0.000 Graphically determined k = 7.09 x 10-4

Temp., 44 .5 — 0 .07°; conc.3 .402 millimolar 0 0.588 0.925 54 0.555 0.830 112 0.515 0.729 151 0.489 0.660 190 0.468 0.604 232 0.451 0.558 361 0 .4 o4 0.434 437 0.374 0.354 512 0.355 0.303 558 0.342 0.269 642 0.327 0.229 775 0.306 0.173 872 0.291 0.133 °o 0.241 0.000 Graphically determined k i 2.18 x 10"° 171

TABLE XLVII

RATE OF ISOMERIZATION OP 5-METHOXYAZOBENZENE IN ABSOLUTE TnnTTTn-KTrxT m m -zli D O m urr^ c l , 0 . 0

Time (mln.) O.D. (438 mu) Fraction cis Temp., 34.8 0.03°; conc.. 0.329 millimolar 0 0.394 0.770 107 0.389 0.753 331 0.384 0.735 882 0.352 0.629 1148 0.341 0.588 1484 0.329 0.546 2303 0.303 0.457 2524 0.300 0.447 2798 0.291 0.416 3697 0.270 0.344 4113 0.259 0.306 5155 0.243 0.251 5657 0.233 0.217 6619 0.222 0.179 9715 0.198 0.096 Oo 0.170 0.000 Graphically determined k = 2.22 X 10-4

Temp.j 54.6 ± 0 .04 °; conc.. 0.586 millimolar

0 0.778 1.000 54 0.734 0.902 148 0.558 0.733 282 0.571 0.538 358 0.533 0^454 434. 0.497 0.374 0.462 0.296 6l4 0.442 0.252 744 0.412 0.185 894 0.389 0.134 Oo 0.329 0.000 Graphically determined k = 2.26 X 10"^ 172 TABLE XLVIII

RATE OP ISOMERIZATION OP 3-METHOXYAZOBENZENE IN DIOXANE

Time (min.) O.D. (438 mu) Praction cis Temp., 34.8 ± 0.03°; conc., 0 .251 millimolar 0 0.276 0.771 129 0.268 0.729 364 0.257 0.670 914 0.238 0.569 1177 0.232 0.537 1514 0.223 0.489 232% 0.205 0.394 2553 0.201 0.372 2828 0.197 0.351 3727 0.182 0.271 4142 0.177 0.245 5185 0.165 0.181 5686 0.159 0.149 6652 0.155 0.128 e>o 0.131 0.000 Graphically determined k = 2.84 X 10“4 Temp., 54.6 ± 0 .04 °; conc., 0.570 millimolar

0 0.691 1.000 100' 0.602 0.761 194 0.541 0.598 327 0.470 0.408 4o6 0.441 0.330 479 0.418 0.268 578 0.392 0.198 662 0.378 0.161 790 0.358 0.107 919 0.344 0.070 Oo 0.318 0.000 Graphically determined k = 2 .80 X 10-3 175

TABLE XLIX

RATE OP ISOMERIZATION OP 3-METHOXYAZQBENZENE IN BENZENE ______AT 34.8° AND 54.6°

Time (min.) O.D. (438 mu) Praction 1 Temp.. 34.8 ± 0 .03°; conc.. 0.303 millimolar 0 0.552 0.769 182 0.318 0.706 722 0.291 0.584 877 0.282 0.543 995 0.277 0.520 1527 0.265 0.466 2143 0.237 0.340 2242 0.234 0.326 2524 0.227 0.294 2641 0.225 0.285 5555 0.207 0.204 5750 0.203 0.186 3960 0.199 0.167 4956 0.186 0.109 Go 0.162 0.000 Graphically determined k = 3.81 X 10"4

Temp.. 54.6 ± 0 .04 °; conc.. 0.564 millimolar 0.691 1,000 0.605 0.761 â 0.568 0.658 160 0.529 0.550 195 0.502 0.475 256 0.467 0.378 557 0.429 0.272 415 0.401 0.195 495 0.381 0.139 605 0.358 0.075 17 4

TABLE XLIX (contd.)

Time (mln.)______O.D. (438 mu) Fraction cls

Oo 0.351 0.000 Graphically determined k « 3.92 x 10"3

TABLE L

RATE OP ISOMERIZATION OP 3-METHOXYAZOBENZENE IN n- HBPTANE AT 34 .8° AND 54 .6°

Time (mln.) O.D. (438 mu) Fraction cls

Temp., 34.8 ± 0 .03oi conc., 0.357 mllllmolar

0 0.375 0.770 194 0.354 0.697 733 0.308 0.537 891 0.296 0.495 1005 0.288 0.467 1220 0.275 0.422 1339 0.266 0.390 2155 0.233 0.275 17 5 TABLE L (contd.)

Time {mln.) O.D. (458 mu) Fraction cls

2256 0.228 0.258 2526 0.219 0.227 2655 0.215 0.212 2549 0.194 0.159 Oo 0.154 0.000 Graphically determined k = 4.78 x 10-4

Temp., 54.6 ± 0.04°; conc., 0.584 mllllmolar

0 0.679 1.000 70 0.578 0.749 106 0.527 0.622 146 0.485 0.515 182 0.455 0.458 246 0.407 0.222 269 0.589 0.279 526 0.565 0.219 4 o4 0.529 0.154 485 0.518 0.102 co 0.277 0.000 Graphically determined k ■ 4.69 % 10“^

TABLE LI

RATE OP ISOMERIZATION OF 4-METHOXYAZOBENZENE IN ABSOLUTE ______ETHANOL AT 25.2° AND 54.9°______

Time ( mln.) O.D. (426 mu) Fraction cls

Temp.j 25.2 i 0 .07°; conc., 0.228 mllllmolar 0 0.479 1.000 256 0.466 0.947 1059 0.428 0.792 1196 0.418 0.751 1415 0.409 0.714 1595 0.401 0.682 2472 0.569 0.551 176 TABLE LI. (contd.)

Time ( min.) O.D. (426 mu) Praction cis

2747 0.361 0.518 3022 0.355 0.492 3992 0.326 0.374 4535 0.312 0.318 5435 0.299 0.265 7000 0.276 0.171 8446 0.262 0.114 9641 0.257 0.094 ' oo 0.234 0.000 Graphically determined k = 2.46 X 10-4

Temp., 34.9 i- 0.03°; conc.. 0.342 millimolar

0 0.683 0.879 54 0.667 0.839 159 0.638 0.766 231 0.624 0.731 328 0.606 0 .686 735 0.532 0.500 799 0.521 0.472 900 0.512 0.450 1246 0.472 0.349 1323 0.459 0.317 2390 0.387 0.136 Oo 0.333 0.000 Graphically determined k = 7.62 x 10-4

TABLE LII

RATE OP ISOMERIZATION OP ^-METHOXYAZOBENZENE IN DIOXANE ______AT 25 .2° AND 3^.9°______

Time (mln.) O.D. (426 mu) Praction cis Temp., 25.2 d: 0 .07°; conc., 0.182 millimolar

0 0.311 1 .0 0 0 250 0.299 0.914 177 TABLE LII (contd.)

Time (min.) O.D. (426 mu) Praction cis 310 0.297 0.896 1047 0.275 0.743 1213 0.271 0.714 1432 0.267 0.675 1609 0.261 0.643 2486 0 .2 4 4 0.521 2764 0 .2 4 1 0.500 304 o 0.235 0.457 4006 0.223 0.372 4549 0 .2 1 4 0.307 5451 0.205 0 .2 4 3 7013 0.192 0.150 8463 0.189 0.129 CO 0.171 0 .0 0 0 Graphically determined k = 2.63 X 10-4

Temp., 34.9 ±- 0.03°; conc.. 0.15 o6 millimolar 0 0.916 0.758 82 0.884 0.694 190 0.848 0.622 323 0.813 0.552 380 0.798 0.522 478 0.788 0.502 884 0.717 0.360 1049 0.690 0.306 1164 0.673 0.272 1396 0.655 0.236 1472 0 .6 4 6 0.218 2539 0.586 0.098 exD 0.537 0.000 Graphically determined k = 8.34 X IQ-4 l?8 TABLE LIII

RATE OP ISOMERIZATION OP 4-METHOXYAZOBENZENE IN BENZENE

Time (min.) O.D. (426 mu) Praction cis

Temp .5 25.2 ± 0 .07°; conc., 0.207 millimolar 0 0.222 0.905 io6 0.226 0.858 809 0.205 0.709 966 0.298 0.669 1225 0.290 0.615 1407 0.286 0.588 2247 0.264 0.429 2520 0.258 0.299 2801 0.254 0.272 2768 0.241 0.284 4215 0.222 0.222 5214 0.224 0.169 5727 0.219 0.125 6766 0.212 0.095 Oo 0.199 0.000 Graphically determined k = 2*27 x 10"*

Temp., 24.9 ± 0 .02°; conc., 0.564 millimolar 0 0.886 0.866 85 0.829 0.758 190 0.801 0.670 246 0.788 0.640 207 0.776 0.612 242 0.767 0.591 281 0.756 0.566 744 0.691 0.416 851 0.661 0.246 1025 0.629 0.296 1295 0.608 0.224 1268 0.601 0.208 2490 0.542 0.072 Go 0.511 0.000 Graphically determined k = 1.02 x 10“^ 179 TABLE LIV

RATE OP ISOMERIZATION OP 4-METHOXYAZOBENZENE IN n-HEPTANE

Time (mln.) O.D. (426 mu) Praction cis

Temp., 25.2 ± 0 .07°; conc., 0 .226 millimolar 0 0.327 1.000 78 0.321 0.964 795 0.286 0.750 955 0.278 0.705 1065 0.275 0.675 1225 ( 0.266 0.635 1594 0.259 0.590 2251 0.237 0.458 2512 0.227 0.398 2788 0.220 0.555 5755 0.201 0.241 4298 0.194 0.196 5201 0.183 0.155 5725 0.179 0.108 6748 0.175 0.081 (30 0.161 0.000 Graphically determined k = 3.79 X 10'-4

Temp., 34.9 ± 0.03°; conc., 0.747 millimolar 0 0.995 0.850 56 0.955 0.781 161 0.890 0.685 297 0.836 0.574 555 0.816 0.559 4 oo 0.796 0.504 431 0.785 0.485 473 0.769 0.457 855 0.682 0.306 909 0.660 0.268 1585 0.603 0.169 l46 o 0.589 0.144 2580 0.552 0.045 Co 0.506 0.000 Graphically determined k = I.16 X 10--3 180 TABLE LV

RATE OP ISOMERIZATION OF 3-NITROAZOBENZENE IN ABSOLUTE ______ETKANOL AT 34.8° AND 44.5°______

Time (min.) O.D. (420 mu) Praction cis Temp., 34.8 i 0 .02°; conc.. 0.186 millimolar 0 0.209 1.000 96 0.206 0.978 966 0.189 0.851 1222 0.187 0.826 1682 0.174 0.739 2542 0.164 0.664 2983 0.155 0.593 2842 0.145 0.522 4244 0 .140 0.485 5220 0.123 0.429 5854 0.126 0.281 7115 0.118 0.217 8625 0.106 0.221 10046 0.101 0.194 14246 0.091 0.119 Oo 0.075 0.000 Graphically determined k = 1.59 X 10-4

Temp., 44.5 ± 0 .07°; conc.. 0.466 millimolar 0 0.501 0.932 66 0.490 0.899 204 0.468 0.824 220 0.449 0.777 441 0.422 0.726 1089 0.254 0.496

0* 0.239 0.449 121 0.231 0.426 362 0.312 0.269 539 0.202 0.239 1260 0.266 0.222 1728 0.249 0.182 1996 0.242 0.164 l8 l

TABLE LVI (contd) Time ( mln.) O.D. (430 mu) Fraction cls 2807 0.228 0.169 0 0 0.188 0.000 Graphically determined k (average) = 5*55 x 10

*The break In the experiment Is due to electricity being turned off.

TABLE LVI

RATE OP ISOMERIZATION OF 5 -NITROAZOBENZENE IN DIOXANE ______AT 34 .8° AND 4 4 .5 ______

Time (mln.) O.D. (430 mu) Fraction cls

Temp., 34.8 ± 0.03°; conc.. 0.240 mllllmolar 0 0.259 1.000 115 0.252 0.956 988 0.232 0.828 1240 0.228 0.803 1705 0.218 0.744 2560 0.204 0.656 5005 0.196 0.606 3862 0.184 0.551 4365 0.177 0.484 5249 0.167 0.425 5875 0.162 0.394 7154 0.151 0.325 8644 0.139 0.255 10065 0.135 0.222 14265 0.118 0.119 00 0.099 0.000 Graphically determined k = 1.56 X 10-4

Temp., 44.5 + 0 .07°; conc.. 0.611 mllllmolar 0 0.624 0.911 49 0.620 0.901 ' - 182 TABLE LVI (contd.) ______

Time (mln.)____ P.P. (430 _mu)______Fraction cls 185 0.591 0.829 505 . 0.570 0.777 422 0.547 0.720 1073 0.449 0.478 0* 0.428 ' 0.456 119 0.418 0.401 363 0.394 0.342 537 0.382 0.312 1260 0.334 0.193 1726 0.316 ■ ' 0.149 1996 0.308 ' ■ 0.129 28O5 . 0.284 0.069 ÛO 0:256 0.000 Graphically determined k (average) = 5.85 x 10“^

*The break In the experiment Is due to electricity being turned off. TABLE LVII I RATE OP ISOMERIZATION OF 4 -NITROAZOBENZENE IN ABSOLUTE ETHANOL AT 25 .2° AND 34 .8°

Time (mln.) O.D. (450 muT Fraction cls X' " / Temp.5 25.2 ± 0.07 ; conc.j Cu521 mllllmolar \ / 0 0.700 , 0.965

18 0.672 , 0.892 25 0.659 0.860 35 0.644 0.822 50 0.622 0.767 67 0.603 0.720 . 96 0.564 0.622

120 0.542 0.567 - - 148 0.513 0.495 ' 212 0.459 0.360 243 0.441 0.315 ' 283 0.422 0.268 1 8 5 TABLE LVII (contd.)

Time ( mln.) O.D. (450 mu) Fraction cis

220 0.299 0.210 281 0.287 0.180 446 0.264 0.122 Oo 0.515 0.000 Graphically determined k = 4 .57 X 10-3

Temp., 24.8 i 0.02°; conc.. 0.277 millimolar 0 0.517 1.000 11 0.469 0.822 17.5 0.448 24 0.422 0.668 20 0.409 0.622 25 0.292 0.566 41 0.282 0.528 52 0.257 0.441 57 0.250 0.416 65.5 0.526 0.567 79.5 0.216 0.297 92 0.501 0.248 104 0.292 0.212 124 0.275 0.154 0.000 0 0 0.221 Graphically determined k = 1.526 x 10“^

TABLE LVIII

RATE OF ISOMERIZATION OF 4 -NITROAZOBENZENE IN DIOXANE AT.25 .2° AND 24 .8°

Time (min.) O.D. (450 mu) Fraction cis Temp., 25.2 ± 0.07°; conc., 0.^42 mllllmolar

0 0.424 0.762 21 0.428 0.742 0.410 0.681 ii 0.402 0.654 184 TABLELVIII (contd.)

Time (mln.) O.D. (450 mu) Fraction cls

125 0.387 0.603 170 0.372 0.553 268 0.348 0.471 341 0.331 0.414 415 0.316 0.363 502 0.300 0.308 549 0.298 0.302 674 0.279 0.237 Oo 0.209 0.000 Graphically determined k = 1.78 X 10-2

Temp., 34.8 "à: 0 .03°; conc., 0.390 mllllmolar 0 0.575 1.000 3 0.568 0.979 13.5 0.547 0.915 24.5 0.521 0.835 31 0.513 0.810 43 0.497 0.762 57 0.477 0.700 73 0.456 0.636 97 0.424 0.538 119 0.404 0.477 160 0.366 0.361 189 0.350 0.312 233.5 0.323 .0.229 273.5 0.306 0.177 Oo 0.248 0.000

Graphically determined k = 6.30 X 10-3 185 TABLE LIX

RATE OP ISOMERIZATION OP (5-PHENYLAZ0PHENYL)TRIMETHYLAMM0NIUM CHLORIDE IN ABSOLUTE

Time (min.) O.D. (424 mu) Praction cis

Temp., 44.5 i 0.07°; conc.. 0.436 millimolar 0 0.401 1.000 0.378 0.901 274 0.350 0.780 477 0.321 0.655 703 0.296 0.547 969 0.270 0.435 1237 0.244 0.323 1790 0.211 0.181 2303 0.190 0.090 Oo 0.151 - O o 0.169* 0.000 Graphically determined k = 9.31 X 10-4

Temp., 54.6 ± 0 .04 °; conc.. 0.436 millimolar 0 0.401 1.000 65 0.367 0.854 125 0.338 0.729 214 0.302 0.573 281 0.281 0.483 379 0.254 0.366 475 0.234 0.280 570 0.215 0.198 685 0.199 0.129 8o4 '0.184 0.065 O o 0.154 - 00 0.169* 0.000 Graphically determined k = 2.71 X 10-3

*In this and the following tables, the calcu lated value of O.D.CO was used. This value is marked with an asterisk. 1 8 6

TABLE LX

RATE OP ISOMERIZATION OF (3-PHENYLAZOPHENYL)TRIMETHYLAMMONIUM CHLORIDE

Time (min.) O.D. (424 mu) Praction cis

Temp., 44.5 i 0 .07°; conc.3 0.675 millimolar 0 0.672 1.000 172 0.639 0.809 241 0.618 0.850 311 0.611 0.831 439 0.592 0.778 995 ..0,521 0.582 1389 0.482 0.463 1505 0.466 0.429 2214 0.411 0.277 2630 0.387 0.211 3021 0.369 0.161 00 0.295 — Oo 0.311* 0.000 Graphically determined k = 5.77 X 10"4

Temp., 54.6 - 0 .04 °; conc.3 0.368 millimolar 0 0.366 1.000 67 0.347 0.904 165 0.323 0.782 261 0.303 0.680 358 0.282 0.574 , . 471 0.265 0.487 592 0.259 0.457 770 0.251 0.416 1034 0.215 0.234 1586 0.189 0.102 Co 0.218 - CO 0.169* Graphically determined k = 1.54 X 10'®

^calculated value. 187 TABLE LXI

RATE OP ISOMERIZATION OF (5 -PHENYLAZOPHENYL)TRIMETHYLAMMONIUM CHLORIDE IN WATER AT 59.8°,44.5°, 50 .0° AND 54 .6°

Time ( mln.) O.D. (424 mu) Fraction cls Temp., 59.8 ± 0 .01°; conc.. 0.489 mllllmolar 0 0.615 1.000 508 0.604 0.960 1089 0.592 0.920 1957 0.572 0.845 2965 0.560 0.802 4501 0.524 0.715 6188 0.500 0.585 8559 0.471 0.480 e>o 0.548 — 00 0.558* Graphically determined k - 8.22 x 10“^

Temp., 44.5 + 0.07°; conc.. 0.499 mllllmolar 0 0.627 1.000 550 0.599 0.901 1474 0.568 0.791 2547 0.558 0.685 5542 0.501 0.555 5626 0.459 0.404 7177 0.458 0.405 Cxj 0.545* 0.000 Graphically determined k = I.50 x lO"^

Temp., 50.0 + 0 .04 °; conc.; 0.489 mllllmolar 0 0.615 1.000 540 0.589 0.906 1069 0.551 0.769 1261 0.542 0.756 1942 0.501 0.588 2680 0.475 0.495 5175 0.451 0.408 1 8 8

TABLE LXI (contd.) Time (min.) O.D. (424 mu) Praction cis 4151 0.421 0.500 4825 0.401 0.227 5455 0.586 0.175 6182 0.575 0.126 0 0 0.502 - 0.000 00 0.558* Graphically determined k = 2.51 x 10"*

Temp.,54.6 ih 0 .04 °; conc., 0.470 millimolar

0 0.580 1.000 204 0.571 0.965 1095 0.489 0.645 1576 0.462 0.557 1567 0.447 0.479 1759 0.455 0.451 2508 0.592 0.265 2650 0.587 0.245 2824 0.582 0.224 5976 0.571 0.180 6556 0.514 - 00 0.504 0.525* 0.000 Graphically determined k = 5»99 x 10-4

♦calculated value

TABLE LXII RATE OP ISOMERIZATION OP ( 4 -PHENYLAZ0PHENYL) TRIMETHYLAMMONIUM CHLORIDE IN ETHANOL AT 44 .5 ° AND 54 .6°______

Time (min.) O.D. ( 424 mu) Praction cis

Temp., 44.5 0 .07°; conc.,____0.690 millimolar 0 0.709 1.000 66 0.671 0.914 189 TABLE LXII (cont.)

Time ( min.) O.D. (424 mu) Fraction cis 145 0.639 '0.841 225 0.600 0.755 346 0.555 0.646 418 0.558 0.612 578 0.492 0.508 1151 0.376 0.245 1208 0.366 0.222 1362 0.349 0.184 1501 0.551 0.143 1711 0.318 0.113 1999 0.302 0.077 00 0.268* 0.000 Graphically determined k = 1 .2b x 10-3

Temp., 54.6 ± 0 .04 °; conc., 0.690 millimolar

0 0.709 1.000 46 0.649 0.864 69 0.621 0.801 159 0.541 0.619 180 0.504 0.555 216 0.477 0.474 255 0.449 0.411 286 0.429 0.565 559 0.400 0.299 412 0.565 0.220 488 0.342 0.168 565 0.326 0.132 00 0.258 — 00 0.268* 0.000 -3 Graphically determined k = 5*64 x 10

♦calculated value. TABLE LXIIII 190

RATE OP ISOMERIZATION OP ( ^-PHENYLAZOPHENYL)TRIMETHYLAMMONIUM CHLORIDE

Time (min.) O.D. (424 mu) Praction cis Temp.3 44.5 ± 0.07°; conc.3 0.4o4 millimolar 0 0.590 1.000 96 0.578 0.943 174 0.367 0.891 341 0.349 0.806 556 0.328 0.706 976 0.290 0.526 1801 0.241 0.294 1998 0.232 0.251 0.248 - Oo 0.179* 0.000 Graphically determined k = 6.74 X 10"4

Temp.3 54.6 + 0 .04 °; conc.3 0 .4 o4 millimolar 0 0.390 1.000 89 0.556 0.839 126 0.545 0.787 171 0.531 0.720 2% 0.515 0.635 0.291 0.531 421 0.274 0.450 5:50 0.257 0.370 757 0.236 0.270 968 0.220 0.194 1795 0.206 0.128 00 0.278 - 00 0 .179* 0.000 Graphically determined k = 1.95 X 10"®

*calculated value. 191 TABLE LXrV

RATE OF ISOMERIZATION OF ( 4-PHENYLAZOPHENYL)TRIMETHYLAMMONIUM CHLORIDE IN WATER AT 39.8°, 44.5°, 50.0° AND 54.6°

Time ( min.) O.D. (424 mu) Fraction cis Temp., 59.8 i 0.01°j conc.. 0.652 millimolar 0 0.715 1.000 755 0.689 0.885 1657 0.669 0.795 2649 0.640 0.662 4 l66 0.611 0.552 5865 0.580 0.592 8017 0.547 0.245 c>o 0.405 - CO 0.495* 0.000 -4 Graphically determined k = I.56 x 10

Temp., 44.5 — 0.07°; cone.,____O.660 millimolar 0 0.750 1.000 119 0.741 0.964 700 0.711 0.845 1044 0.699 0.798 1545 0.681 0.726 2178 0.641 0.567 5085 0.612 0.452 5970 0.588 0.557 5142 0.556 0.250 03 0.509 - 00 0.498* 0.000 Graphically determined k = 2.58 X 10-4

Temp., 50.0 ± 0 .04 °; conc.. 0.652 millimolar

0 0.715 1.000 176 0.692 0.896 750 0.659 0.658 942 0.629 0.615 1 6 2 5 0.585 0.405 TABLE LXIV (contd.) 192

Time (min.)_____O.D. (k2h mu) Fraction ois 2270 0.548 0.248 2859 0.527 0.155 2835 0.481 Oo 0.259 Oo 0 .492* 0.000 Graphically determined k = 4.74 x 10\"4"

Temp., 54.6 ï 0 .04 °; conc., O.660 millimolar 0 0.750 1.000 116 0.721 0.925 688 0.660 0.642 914 0.622 0.552 1062 0.618 0.476 1262 0.599 0.401 1564 0.578 0.218 2178 0.529 0.122 2078 0.484 - 2671 0.461 - 2960 0.450 - 4287 0.442 - 5159 0.422 - 8822 0.441 - 00 0.498* 0.000 Graphically determined k = 7 •14 x 10“^

*calculated value. AUTOBIOGRAPHY

I, Erach Rustomji Talaty, was b o m In Nagpur, India, on 20th October, 1926. I received ray secondary school education in St. Francis de Sales' High School, Nagpur. I attended the College of Science, Nagpur, and received the degree of Bachelor of Science with Honours from Nagpur

University in 1948, and the Master of Science degree frora the sarae University in 194-9. Frora 1948 to 1954, I held the position of Lecturer in Chemistry at the College of Science, Nagpur. In September, 1954, I was admitted to the Graduate School of The Ohio State University, where I held successively the positions. Research Corporation Fellow (October, 1954-Septeraber, 1956), Teaching Assistant

(October, 1956-June, 1957), and Research Fellow under du Pont Company Grants (summer, 1957), while completing the requirements for the degree of Doctor of Philosophy.

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