Electrochemical Reduction of 4-Iodo- and 4-Bromoanisole at Mercury and Carbon Cathodes in Dimethylformamide

Article abstract of DOI:10.1021/jo00290a047

In dimethylformamide containing tetramethylammonium perchlorate, cyclic voltammograms for reduction of 4-iodo- and 4-bromoanisole at mercury and carbon electrodes exhibit single irreversible waves corresponding formally to two-electron cleavage of the carbon-halogen bond.In preparative-scale controlled-potential electrolyses of 4-iodoanisol at mercury pool cathodes, a two-to-one mixture of anisole and bis(p-anisyl)mercury is obtained at potentials close to the peak potential, whereas anisole is the only species formed at more negative potentials.Reduction of 4-iodoanisole at mercury appears to proceed via p-anisyl radicals that (i) yields adsorbed p-anisylmercury radicals which disproportionate to give bis(p-anisyl)mercury or (ii) undergo further reduction, followed by protonation, to afford anisole.Electrolyses of 4-iodoanisole at carbon electrodes, as well as reduction of 4-bromoanisole at both mercury and carbon, result solely in the production of anisole; presumably, even if p-anisyl radicals are generated transiently, they undergo facile reduction to p-anisyl carbanions, which are protonated immediately to yield anisole.