ELECTROCHEMICAL REACTIONS OF SOME DIMETHYL DIALKYLAMINOMALEATES

Five dimethyl dialkylaminomaleates (1-5) have been studied by cyclic voltammetry and controlled potential coulometry in acetonitrile solvent. For dimethyl di-isopropylaminomaleate (1), it is proposed that the electrochemical reduction at mercury electrodes proceeds by a rapid ECE scheme that comprises initial reduction to a radical anion, rapid protonation 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 voltammetry, even at scan rates up to 10(4) V s(-1) and temperatures as low as -40 degrees C. Controlled potential coulometry indicated an overall two-electron reduction, and analysis of the electrolyzed solution showed that the principal products were the two half-esters formed by hydrogenation of the C=C double bond and hydrolysis of one of the two non-equivalent ester groups. The hydrolysis is induced by hydroxide formed by protonation of the intermediate anions by residual water. The oxidation of 1-5 was studied at a platinum electrode. The reaction is suggested to proceed by the initial formation of the radical cation, followed by rapid tail-to-tail dimerization of the cation radical to form a dimeric dication that deprotonates during work-up to give, in the case of 1, the dimethyl ester of 3,3-dicarbomethoxy-2,5-bis(diisopropylamino)hexadienoic acid (11).