Electrochemical reduction of benzyl iodide, benzal bromide, and benzal chlorobromide at carbon cathodes in the presence of nitric oxide in acetonitrile

Cyclic voltammetry (CV) and controlled-potential electrolysis have been employed to investigate the electrochemical reductions of benzyl iodide, benzal bromide, and benzal chlorobromide at glassy carbon cathodes in the presence of nitric oxide (NO) in acetonitrile containing tetramethylammonium tetrafluoroborate. One irreversible cyclic voltammetric wave, due to cleavage of the carboniodine bond, is observed for the reduction of benzyl iodide, whereas cyclic voltammograms for the reductions of benzal bromide and benzal chlorobromide exhibit two cathodic waves, arising from sequential cleavage of carbonhalogen bonds. At appropriate potentials, bulk electrolyses of the three starting compounds involve, respectively, the generation of benzyl, bromophenylmethyl, and chlorophenylmethyl radicals which can couple with NO, and the products include benzaldehyde oxime, benzonitrile, and O-benzyl benzaldehyde oxime, as well as toluene, bibenzyl, and cis- and trans-stilbene. Mechanisms for the formation of the various products are discussed and, using CV, we have estimated the concentration of NO in acetonitrile under the extant experimental conditions.