Mechanism of benzidine and semidine rearrangements. Part XXVII. Kinetics, products, and solvent isotope effects for acid-catalysed rearrangements of some N-substituted hydrazoarenes

Abstract

The acid-catalysed rearrangements and accompanying reactions of NN′-dimethylhydrazobenzene at acidities convenient for kinetic measurements were first order in acid and had a solvent isotope effect (k_D2O/k_H2O) of 2·3. A large proportion of products (ca. 38%) comprised compounds, e.g. o-benzidine, semidines, fission amine, and tar, that are not typically found in acid-catalysed reactions of hydrazoarenes but the reaction was intramolecular and addition of scavengers provided no evidence for radical intermediates. Acid treatment of NN-dimethyl-1,1′-hydrazonaphthalene, N-methylhydrazobenzene, and N-acetylhydrazobenzene promoted reactions first, second, and second order respectively in acid with solvent isotope effects of 2·3, 4·0, and 3·1. No unusual products were now formed. The kinetic form, products, and isotope effects of these reactions are discussed on the basis of the previously suggested polar transition state mechanism.