The electrochemical reduction of a series of bromo-, chloro-, and iodobenzonitriles in N,/V-dimethylformamide has been shown to be an overall two-electron process which gives benzonitrile as the principal product.Since reduction of one of these halogenated benzonitriles (4-chlorobenzonitrile) in the presence of cyanide ion gives rise to a small amount of terephthalonitrile anion radical, the intermediacy of cyanophenyl radicals is suggested. A reaction pathway consistent with these data involves the initial one-electron reduction of the halogenated benzonitrile, rapid loss of halide ion from the anion radical to give the corresponding cyanophenyl radical, and subsequent reduction of the cyanophenyl radical at the electrode surface to cyanophenyl anion. Abstraction of a proton from the solvent system by the cyanophenyl anion yields benzonitrile and completes the reaction pathway. The results obtained here are contrasted with previously reported decomposition pathways of the anion radicals of 4-fluoroand 4-aminobenzonitrile. Electrochemical and electron spin resonance studies of numerous substituted aromatic nitrile radicals in AfA-dimethylformamide (DMF) have been reported by Rieger, et al.1 Although reduction of the cyano andnitro derivatives of benzonitrile gave very stable anion radicals, the anion radicals of 4-amino-and 4-(1) P.
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