Kinetics and mechanism of the oxidation of substituted benzylamines by hexamethylenetetramine‐bromine

Abstract

AbstractThe oxidation of substituted benzylamines by hexamethylenetetramine‐bromine (HABR) to the corresponding aldimines is first order with respect to each the amine and HABR. It is proposed that HABR itself is the reactive oxidizing species. The oxidation of deuterated benzylamine (PhCD2NH2) indicated a substantial kinetic isotope effect (kH/kD = 5.60 at 293 K). This confirmed the cleavage of an α‐C—H bond in the rate‐determining step. Correlation analyses of the rates of oxidation of 20 monosubstituted benzylamines were performed with various single‐ and multi‐parametric equations. The rates of the oxidation showed excellent correlations in terms of the Yukawa–Tsuno and Brown equations. The polar reaction constants were negative. The oxidation exhibited extensive cross‐conjugation, in the transition state, between the electron‐donating substituents and the reaction centre. A mechanism involving a hydride ion transfer from the amine to HABR, in the rate‐determining step, is proposed. Copyright © 2001 John Wiley & Sons, Ltd.