ELECTROCHEMICAL REACTIONS OF SOME DIMETHYL DIALKYLAMINOMALEATES

Five dimethyl dialkylaminomaleates (1-5) have been studied by cyclic v oltammetry and controlled potential coulometry in acetonitrile solvent . For dimethyl di-isopropylaminomaleate (1), it is proposed that the e lectrochemical reduction at mercury electrodes proceeds by a rapid ECE scheme that comprises initial reduction to a radical anion, rapid pro tonation by residual water, subsequent reduction to an anion, followed by protonation that results in hydrogenation of the C=C double bond. The lifetime of the radical anion is very short. An oxidation peak for this species could not be detected on the return sweep in cyclic volt ammetry, even at scan rates up to 10(4) V s(-1) and temperatures as lo w as -40 degrees C. Controlled potential coulometry indicated an overa ll two-electron reduction, and analysis of the electrolyzed solution s howed that the principal products were the two half-esters formed by h ydrogenation of the C=C double bond and hydrolysis of one of the two n on-equivalent ester groups. The hydrolysis is induced by hydroxide for med by protonation of the intermediate anions by residual water. The o xidation of 1-5 was studied at a platinum electrode. The reaction is s uggested to proceed by the initial formation of the radical cation, fo llowed by rapid tail-to-tail dimerization of the cation radical to for m a dimeric dication that deprotonates during work-up to give, in the case of 1, the dimethyl ester of icarbomethoxy-2,5-bis(diisopropylamin o)hexadienoic acid (11).