Isotopic, steric, and reagent variation effects in the bromination of hydrazones

Abstract

The bromination of benzylidene-p-nitrophenylhydrazine in 70% acetic acid at 20° has been measured by an electrometric method. Kinetic measurements at various bromide ion concentrations have shown that molecular bromine is the only brominating species of importance, and also that the rate-determining step in the brominations studied involved bromine attack followed by rapid deprotonation. The rate of bromination of [α-²H]benzylidene-p-nitrophenylhydrazine afforded a k_H/k_D of 0·97, indicating no methine C–H stretching in the transition state. The kinetics of bromination of a variety of 2- and 2,6-substituted benzylidene-p-nitrophenylhydrazines have shown that the bromination process was insensitive to steric factors.