Electroreduction mechanism of N-arylhydroxylamines in aprotic solvents: N-(4-nitrophenyl)hydroxylamine

Using N-(4-nitrophenyl)hydroxylamine as an example, cyclic voltammetry, chronoamperometry, coulometry, electrolysis, digital simulation and quantum chemical calculations were used to show that the electroreduction of N-aryl hydroxylamine derivatives in 0.1 M Bu4NClO4/DMF proceeds via the ECE mechanism (including the stages of radical anion formation and the N–OH bond cleavage in the radical anion) complicated by the reactions of the products with the depolarizer. Among these reactions are the deprotonation of the substrate by aniline and hydroxide anions as well as the nucleophilic substitution of the hydroxylic group of the substrate by aniline and phenylhydroxylamine anions. The thermodynamic and kinetic parameters of the reactions were measured. It was shown that the formation of azobenzene derivative via OH− substitution by the phenylhydroxylamine anion contributed negligibly to the overall process in the time window of the electroanalytical methods but has a dominant influence in case of electrolysis.