Mechanistic study of electrochemical oxidation of 2,5-diethoxy-4-morpholinoaniline in aqueous solutions: hydrolysis, trimerization, and hydroxylation processes

Abstract

The electrochemical oxidation of 2,5-diethoxy-4-morpholinoaniline has been studied in various pHs using cyclic voltammetry and controlled potential coulometry. The results indicate that the electrochemically generated p-quinonediimine participates in different types of reactions (hydrolysis, hydroxylation, and trimerization). Instability of the produced p-quinonediimine depends on its structure, higher nucleophilicity of 2,5-diethoxy-4-morpholinoaniline, and pH of solution. In lower pH range, rate of hydrolysis is faster than hydroxylation and dimerization. In intermediate pHs rate of the dimerization is faster than hydrolysis and hydroxylation, and in the strongly alkaline solution, rate of the hydroxylation is faster than hydrolysis and dimerization. The effect of the charge of reaction site (C1) and N1=C1 bond order (Wiberg bond indices) on the hydrolysis rate were studied. Calculations were performed using density functional theory B3LYP level of theory and 6−311+G(p,d) basis set.