Benzidine rearrangements. 17. The concerted nature of the one-proton p-semidine rearrangement of 4-methoxyhydrazobenzene

The nitrogen kinetic isotope effects (KIE) for the acid-catalyzed rearrangement of 4-methoxyhydrazobenzene (1b) into the p-semidine (4-methoxy-4'-aminodiphenylamine, 2b) and o-semidine(2-amino-5-methoxydiphenylamine, 3b) have been measured and are 1.0296 (av) and 1.074 (av), respectively. The carbon KIE for formation of 2b was found to be 1.039 (av). The results show that p-semidine formation is a concerted process. Rearrangements were carried out in 60% aqueous dioxane under conditions of earlier kinetic work. Mixtures of 1b and [15N, 15N']1b were used for the nitrogen KIE, measured mass spectrometrically with isolated N-benzoyl-2b, and mixtures of 1b and [4'-14C]1b for the carbon KIE, measured with scintillation counting on isolated N-benzoyl-2b. The method of carbon labeling did not allow for a measurement of the KIE for formation of 3b