Preparation and solvolysis of N-arylbenzohydrazonyl bromides

Abstract

Two series of p-substituted N′-arylbenzohydrazonyl bromides were prepared. On solvolysis in aqueous dioxan these compounds yielded the equivalent aroylhydrazides in good yields. The solvolysis of p-substituted N′-p-nitrophenylbenzohydrazonyl bromides in 80% dioxan–20% water proved suitable for kinetic studies, and a ρ of –0·92 was obtained when the results were subjected to a Hammett ρσ plot. These results were interpreted in terms of an intermediate azo-carbonium ion stabilised by resonance into both aryl rings. The aroylhydrazides were cleaved by hydrochloric acid in ethanol to the aroic acids and arylhydrazines. This proved an effective method for the synthesis of 2-bromo-4-nitrophenylhydrazine and a series of arylidene-2-bromo-4-nitrophenylhydrazones were prepared from this hydrazine.