Catalytic reduction of ethyl chloroacetate by cobalt(I) salen electrogenerated at vitreous carbon cathodes

Cyclic voltammetry, controlled-potential electrolysis, and spectroelectroch emistry have been employed to investigate and characterize the catalytic re duction of ethyl chloroacetate by cobalt(I) salen electrogenerated at a car bon cathode in dimethylformamide containing tetraalkylammonium salts as sup porting electrolytes. A cyclic voltammogram for the reduction of cobalt(II) salen in the presence of excess ethyl chloroacetate exhibits a prewave, wh ich is attributed to the formation of an ethoxycarbonyl-methylcobalt(III) s alen complex. This prewave is followed by a large catalytic wave which invo lves the formation of both ethoxycarbonylmethyl and ethoxide anions; the fi rst anion then undergoes a series of chemical reactions with the remaining starting material (ethyl chloroacetate) to yield ethyl acetate and 1,2,3-cy clopropane tricarboxylic acid triethyl eater, whereas ethoxide is protonate d to afford ethanol. From the results obtained by means of cyclic voltammet ry and controlled-potential electrolysis, a mechanism is proposed to explai n our findings, and the validity of this mechanism has been probed with the aid of experiments involving the liquid chromatographic separation and mas s spectrometric identification of the ethoxycarbonylmethylcobalt(III) salen complex. (C) 2000 Elsevier Science S.A. All rights reserved.