ELECTROREDUCTION OF HEXACHLOROBENZENE IN PROTIC SOLVENT AT HG CATHODES

The electrochemical reduction of hexachlorobenzene (HCB) to lower chlo rinated benzenes has been studied in methanol solution. Differential p ulse voltammetry at a sessile mercury drop cathode showed four reducti on waves at E = -1.13, -1.33, -1.57 and -1.84 V vs the standard hydrog en electrode, corresponding to sequential reduction to penta-, tetra-, tri-and dichlorobenzenes, respectively. The formation of these produc ts was followed with time using a recirculating flow-through cell; the isomer distributions of the lower chlorinated benzenes were as predic ted from a mechanism involving chloride elimination from radical anion intermediates. A maximum current efficiency of 60% was achieved in si ngle-pass experiments in which the potential was controlled near the p eak of the first reduction peak (-1.2 V) and the initial concentration of HCB was 1 mM.