KINETICS AND MECHANICS OF THE REACTION OF HYDRAZOIC ACID WITH SUBSTITUTED BENZOIC ACIDS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State U n iversity B y MELVILLE ERNEST DOUGLAS HILLMAN, B .A ., M.Sc, ++++++ The Ohio State University 1958 Approved by Department of Chemistry ACKNOWIÆDGMENTS The author wishes to express his appreciation to Dr, Harold Shechter for his suggestion of this problem, for his guidance and encouragement during the course of the investigation, and for his assistance in the preparation of the manuscript. The author is grateful to the Lubrizol Corporation the Socony- Mobile Company and to the Chemistry Department of The Ohio State University for fellowship funds. He also wishes to thank fellow graduate students and members of the staff for their cooperation in innumerable ways. The author is deeply grateful to his wife, Freda, for per­ forming some of the analyses and for taking over the difficult task of organizing and typing the various drafts of the dissertation. 11 CONTENTS Page I. INTRODUCTION................................................................................................ 1 II. HISTORICAL........................................................................................................ 4 The Schmidt Reaction ........................................................................... 4 The Curtins Reaction .........................................................................23 The Hammett Equation .................................................................. 28 Acidity Functions ................... 33 in. DISCUSSION OF RESULTS.................................................................... 41 Kinetic Order of the Schmidt Reaction. ............................41 Leveling of Solvent ................... 42 Decomposition of Hydrazoic Acid............................................ 43 Effect of Acidity on tlie Schmidt Reaction. .......... 48 Proximity Effects. ................... 67 Electrical Effects ................... 72 Activation Param eters. ............ 84 IV. EXPERIMENTAL. ................................................................................... 97 Preparation and Purification of Aromatic A cids,..... 97 o-Isopropylbenzoic Acid............................. 97 o-tert-Butylbenzoic Acid. .................................. 101 2, 6 -Dimethylbenzoic A cid. .......................... 106 2, 3-Dimethylbenzoic Acid. ............ 108 Purification of Substituted Benzoic Acids..................... 109 Determination of the Kinetic Constants................... I l l Constant Temperature Baths .......................................... I l l K in etic P ro ced u re........................................................ 112 Spectrophotometric Techniques................................... 112 Sulfuric Acid Solutions ................................ 115 Sodium Azide and Hydrazoic Acid Solutions 115 Execution of Kinetic Experiments 117 T reatment of Kinetic Data. ..................................... 121 Rate Constants..................................................................... 122 Activation Parameters ................ 125 APPENDIX .................................................................................................. 127 AUT OBIOGRAPH Y................................................................................. 319 iii LIST OF FIGURES Figure Page 1 -2„ Decomposition of Hydrazoic Acid .................. 45-46 3-6, Acidity Correlations for Reaction of £-Toluic A cid ................... 54-57 7. Hammett Plot for Reactions of m- and p- Substituted Benzoic Acids................................................ 76 8 . Enthalpy - Entropy Plot for Reactions of Substituted Benzoic Acids................................................................91 9-12, Activation Energy Plots for Reactions of Substituted Benzoic A cids. ....................... 128-131 13-18. Representative Plots of l/c versus time for Reactions of Substituted Benzoic Acids.................... 132-137 19-36. UV Absorption Spectra of Substituted Benzoic Acids and Substituted Anilines, ............... 138-146 37. Acidity Correlation for Reaction of ^-Toluic A cid .............................................................................. .. 147 IV LIST OF TABLES TEXT Table Page 1. The Schmidt Réaction of Substituted Benzoic Acids .... 9 2. The Schmidt Reaction of QuinolinecaxboxyXic Acids ... 19 3. Acidity Functions and Rate Constants for the Schmidt Reaction of o^-Toluic Acid at 24, 3®............................. 62 4. Rate Constants for Reaction of Hydrazoic Acid with Substituted Benzoic Acids ................................68-69 5. Activation Parameters for Reaction of Hydrazoic Acid with Substituted Benzoic Acids. ................... 74 6 . Physical Constants for the Substituted Benzoic Acids .110 APPENDIX 1-28. Collected Velocity Constants for the Schmidt Reactions of Substituted Benzoic A cids....................... 148-161 ' 29-159. Kinetic Data for the Schmidt Reactions of (O-Substituted Benzoic A cid s........................ 162-231 160-282. Kinetic Data for the Schmidt Reactions of m - and p-Substituted Benzoic A cids ........................ 232-295 283-284. Kinetic Data for the Decomposition of Hydrazoic Acid. ........................296 285-310. Kinetic Data for the Effect of Acidity on the Rate of the Schmidt Reaction of o-Toluic Acid,....... 297-318 I. INTRODUCTION Reaction of hydrazoic acid with a carboxylic acid (the Schmidt reaction) results in formation of the corresponding amine, carbon dioxide, and nitrogen (Equation 1). In order to R-COgH + HNs H2SO4 ^ R-NHz + COg + Ng (l) effect this important general reaction it is necessary to use strong mineral acids as catalysts. Mono-substituted benzenedicarboxylic acids in which the substituent is proximal to one of the carboxylic groups react selectively with one equivalent of hydrazoic acid to give only single mono-substituted amino acids. The novelty and utility of this reaction is that the more #sterically-hindered= carboxyl group is converted to the cor re spending amine. For example, 3-sub stituted phthalic acids or anhydrides in sulfuric acid react at the internal, more hindered, carboxyl group (Equation 2) to OgH CPzH CO2H + HN3 H2SO4 [I I + CO2 + N^ (2) yield exclusively the corresponding 3-substituted anthranilic acids. Upon reaction of 2- or 2,6 -disubstituted terephthalic acids (Equation 3) the more hindered carboxyl group is also 1 COzH m Î 2 (3) G (G) + HNî H2SO4 _ I I + CO2 + Nz COgH CO 2H selectively replaced. Similarly, the sole products obtained from Schmidt reactions of isophthalic acids which contain sub­ stituents in the 4-position (Equation 4) are the corresponding COgH COgH (4) + HNg HgS 0 4 ^ + COg + Ng 4-sub stituted, 3-aminoben.zoic acids. Because of the dramatic accelerative influences associated with proximal groups in Schmidt reactions, a study was initiated of the possible mechanisms of these processes. It was decided to determine the influence of structure on the kinetic order, rates, and kinetic parameters of reaction of hydrazoic acid in sulfuric acid with substituted benzoic acids in the following series: (1 ) ortho-sub stituted benzoic acids, to measure proximity effects on the Schmidt reaction (2 ) meta- and para-substituted benzoic acids, to determine the electrical requirements of the Schmidt reaction (3) di- and trimethyl/benzoic acids, to determine possible buttressing and accumulative electrical and proximity factors in the Schmidt reaction To gain additional insight into fundamental details of the mechanism, a study of the effects of sulfuric acid con­ centration on the rate of the Schmidt reaction of ortho-toluic acid was made. The kinetics of decomposition of hydrazoic acid in concentrated sulfuric acid were also investigated. n. HISTORICAL The Schmidt Reaction Reactions of carbonyl compounds with hydrazoic acid in strong acids have become known as Schmidt reactions. These reactions were first discovered by Schmidt on studying the decom­ position of hydrazoic acid by sulfuric acid (1), Acting on the (1) K, F, Schmidt, Z, angew Chem., 36, 511 (1923). hypothesis that one of the primary decomposition products of hydrazoic acid is imine, NH, which is capable of reacting with an unsaturated group, Schmidt added benzophenone to the reaction mixture. A rapid reaction occurred, and a quantitative yield of benzanilide was obtained (2) (Equation 5). O C> CfiHg-C-C^Hs + HN 3 ------> C6H5-C-NH-C 6H5 + Nz (5) (2) K, F, Schmidt, Acta Acad, Aboensis, Math. etPhys,, 2, 38 1924, C. A ., 19 , 3248 (1925). The Schmidt reaction of carboxylic acids in strong mineral acid (Equation 6 and 7) yields amines having one less carbon atom, carbon dioxide and nitrogen; a presumed 4 R-COzH + HNs > RNCO + Ng ( 6 ) R-NCO + HzO — --------- > RNHz + COg (7) intermediate is the isocyanate which is subsequently hydrolyzed in the aqueous medium. Aldehydes give nitriies and formyl derivatives of amines, and ketones yield amides, AJdehydes and ketones with excess hydrazoic acid (two or more equiva­ lents) form substituted tetrazoles (Equation 8 ), RCOR + 2 HN3 H2SO4 RC = N + H2O + Nz (8 ) A more complete description of the scope of the Schmidt reaction has been given by Wolff (3), (3) H. Wolff in Adams “Organic Reactions, * Vol, III, John Wiley and Sons, Inc,, New York, N, Y ,, 1946, pp, 307-336, The mechanisms of Schmidt reactions of carbonyl com­ pounds have attracted the attention of certain investigators, Schmidt