Electrochemical Reduction of Cinnamyl Bromide at Carbon Cathodes in Acetonitrile: A Further Mechanistic Study

Cyclic voltammetry and controlled-potential electrolysis have been employed to examine the electrochemical reduction of cinnamyl bromide at glassy carbon cathodes in acetonitrile containing tetramethylammonium tetrafluoroborate. A cyclic voltammogram for the reduction of cinnamyl bromide exhibits one irreversible wave, which is due to the cleavage of the carbon-bromine bond. Bulk electrolyses of the substrates have been carried out at two different potentials (-1.35 and -1.85 V vs saturated calomel electrode) in the absence and in the presence of diethyl malonate as a proton donor. Coulometric 11 values and product distributions indicate that the reduction of cinnamyl bromide at -1.35 V mainly gives radical intermediates, whereas that at -1.85 V forms cinnamyl anions. A direct reduction of cinnamyl bromide in the presence of nitric oxide (NO) at -1.35 V reveals that the cinnamyl radical can couple with NO to generate cinnamaldehyde oxime and cinnamonitrile. More interestingly, both 5-phenylisoxazoline and 5-phenylisoxazole, arising from the cyclization of cinnamaldehyde oxime, have been found among the products. Detailed mechanisms for the reductions are proposed and discussed. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3176891] All rights reserved.