| Cyclic voltammetry and controlled-potential electrolysis have been employed to examine the electrochemical reduction of 2-bromothiazole at glassy carbon cathodes and halopyrimidines at mercury cathodes in acetonitrile containing tetramethylammonium tetrafluoroborate. A cyclic voltammogram for the reduction of 2-bromothiazole exhibits two irreversible waves; the first wave is due to the cleavage of the carbon-bromine bond, and the second wave is attributed to the reduction of thiazole. Bulk electrolyses of 2-bromothiazole at a potential corresponding to its first voltammetric wave afford thiazole quantitatively. Cyclic voltammograms for halopyrimidines exhibit cathodic waves arising from cleavage of carbon-halogen bonds as well as the reduction of pyrimidine. Controlled-potential electrolyses of halopyrimidines at potentials for different stages of reduction lead to products that are consistent with expectations based upon cyclic voltammetry.; An investigation of the direct and cobalt(I) salen-catalyzed reduction of 2,6-bis(chloromethyl)pyridine has been undertaken. A large cathodic cyclic voltammetric wave with a shoulder is observed for the direct reduction of 2,6-bis(chloromethyl)pyridine, corresponding to the consecutive cleavage of carbon-chlorine bonds of the starting material. Cyclic voltammograms for reduction of cobalt(II) salen in the presence of excess 2,6-bis(chloromethyl)pyridine exhibit three waves: (a) a prewave attributed to formation of cobalt(I) salen and its follow-up reaction with 2,6-bis(chloromethyl)pyridine to give, most likely, a 2,6-bis[(salen)cobalt(III)methyl]pyridine complex; (b) a large catalytic wave which involves reduction of the complex; and (c) another wave due to direct reduction of 2,6-bis(chloromethyl)pyridine. Controlled-potential electrolyses of 2,6-bis(chloromethyl)pyridine give 2,6-lutidine, 3-(6methylpyridin-2-yl)propionitrile, and bis(6-methyl-2-pyridylmethyl) ether as major products.; Finally, the electrochemical reduction of benzyl iodide, benzal bromide, and benzal chlorobromide in the presence of nitric oxide (NO) has been studied. 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. Mechanistic aspects of the reduction of all these halogenated aromatic compounds are discussed in detail. |
