Kinetics and mechanism of the reaction of substituted phenylhydrazones with thallium(III) acetate. Reactions of mercury(II) acetate with nitrogen compounds. Part 8

Abstract

The reaction of substituted phenylhydrazones with thallium(III) acetate in acetic acid involved an electrophilic attack at the hydrazone amino-NH moiety giving an intermediate which is attacked by solvent at the methine carbon. The Hammett ρ values for substituents in the methine and the N-phenyl rings were –1.05 and –3.6, respectively. Activation thermodynamic parameters ΔE_a 17.9, ΔH_a 17.2 kcal mol^–1, and ΔS_a–14.65 cal K^–1 mol^–1 were measured for p-chlorobenzaldehyde p-nitrophenylhydrazone. The main products from aromatic aldehyde arylhydrazones were N′-acetyl-N-aroyl-N′-arylhydrazines (5). The main products from ketone arylhydrazones were α-acetoxy-α-phenylazo-derivatives of the ketone (4). The unexpected divergence of reactivity of phenylhydrazones with the acetates of Hg^II, TI^III, and Pb^IV is discussed.