Reactions of lead tetra-acetate. Part IX. The mechanism of reaction with ketone arylhydrazones

Abstract

Benzophenone phenylhydrazone and p-nitrophenylhydrazone are oxidised by lead tetra-acetate in the presence of alcohols to mixtures of the azoacetate and an azoether; the latter product does not arise by alcoholysis of the former. The rates of oxidation of aromatic ketone arylhydrazones are dependent on the polar effects of substituents both in the ketone and (more markedly) in the arylhydrazine moieties. For one series of compounds, the effects of substituents in the arylhydrzine are correlated by the Hammett equation (ρ=–1·95), the derived σ-value for p-NO₂ being an “exalted” one (1·17). These and related facts lead to the view that the rate-determining step of the oxidation involves the displacement of an acetate anion from the lead tetra-acetate by the NH-nitrogen; this is followed by the uptake of an acetoxy or alkoxy group at the ketonic carbon which, at least for the acetoxylation, probably occurs intramolecularly within an intermediate lead derivative.