Electrolytic Model System for Reductive Dehalogenation in Aqueous Environments

Tetrachloromethane (CT) is transformed in biological systems via two major pathways: hydrogenolysis to trichloromethane (CF) and hydrolysis to carbon dioxide. The mechanism of hydrolysis is poorly understood. One possibility is a hydrolytic reduction of CT to formate or carbon monoxide followed by oxidation to carbon dioxide. In biological systems, formate and carbon monoxide are readily oxidized to carbon dioxide, making their identification difficult, but in an electrolysis cell, reduction is physically separated from oxidation, and the production of formate and carbon monoxide a t a cathode can be observed. Measurements of current, chloride, CF, dichloromethane, formate, and CO upon electrolysis of CT in aqueous solution supported the conclusion that hydrogenolysis to CF and hydrolytic reduction to CO and formate are significant and competitive reductive processes. Similar findings were obtained for the reduction of l,l,ltrichloroethane via hydrogenolysis to 1,l-dichloroethane and to an unidentified dechlorinated product via a twoelectron parallel pathway. It is suggested that electrolysis in aqueous environments may have value as a useful tool for the understanding and control of reductive dehalogenation and as a novel treatment technology.