Electrophilic substitution in a basic hydrazone system: the first synthesis of N-pyridylhydrazonyl bromides

Abstract

A kinetic study of the bromination of substituted benzaldehyde 3-pyridylhydrazones in 70% acetic acid has shown that the protonated hydrazone species is brominated. In water, both protonated and free hydrazones (the latter 162-fold more rapidly) react with bromine. The products formed are the corresponding N-(3-pyridyl) substituted benzohydrazonyl bromides, rather than N-bromo-complexes, and substituent effects (ρ=–0·42 for C-aryl ring and –1·42 for N-pyridyl ring) are in accord with direct electrophilic attack at methine carbon atom. The novel hydrazonyl bromides (isolated as hydrobromides) may be readily hydrolysed to N-(3-pyridyl) substituted benzohydrazides and react with azide ion to give benzohydrazonyl azides.