Electrochemical reduction of benzyl bromide in the presence of carbon dioxide

The electrochemical reduction of benzyl bromide has been investigated in acetonitrile and CO2-saturated acetonitrile by cyclic voltammetry and controlled-potential electrolysis. Electroreduction of the halide in the absence of CO2 leads to a variety of products, the distribution of which depends on the electrode material, applied potential and proton availability in the medium. The electrocarboxylation processes have been carried out at Hg and graphite cathodes using both a two-compartment cell and an undivided cell with a sacrificial Al anode. The best results (87% phenylacetic acid yield) were obtained at Hg in the undivided cell. Catalysis by Co(salen) allows the process to be performed at potentials more positive than those required by direct reduction but gives only poor to moderate yields of acid. Results obtained from experiments carried out with benzyl chloride have been compared with those obtained in the case of benzyl bromide.