BROMONITRILES REDUCTION - THE EFFECT OF THE ELECTRODE MATERIAL ON THE STRUCTURE OF THE REACTION INTERMEDIATES AND THE ELECTROLYSIS PRODUCTS

The electrochemical reduction has been studied on BrCR2(CH2)nCN bromonitriles [(I) R = CH3, n = 0; (II) R = H, n = 1; (III) R = H, n = 2; (IV) R = H, n = 3] in N,N?-dimethylformamide solution with Et4NClO4 as supporting electrolyte, at the Hg electrode or the vitreous carbon one. With both electrodes all the investigated bromonitriles undergo a one-electron transfer reduction, which shifts towards a two-electron one in the presence of protonating agents. The reduction potentials, the nature, and the yield of products depend on the electrode material. The reduction of (I) and (II) (EView the MathML source >EpC) on Hg pool yields debrominated nitriles, dimeric, and polymeric compounds. In contrast, the reduction at the vitreous carbon electrode yields debrominated and unsaturated nitriles, but does not yield dimeric and polymeric material. Three- and four-membered ring nitriles have been obtained in comparable yields upon reduction of (III) and (IV) (EView the MathML source ? EpC) at both electrodes. The reduction of (II) at vitreous carbon has been described as an example of "mixed" electron exchange occurring both directly at the electrode and indirectly in solution via (CH2 = CHCN)- (homogeneous redox catalysis).