Electrochemical reduction of 2,4-dichloro-1-(4-chloro-2-methoxyphenoxy)benzene (methyl triclosan) at glassy carbon cathodes in dimethylformamide

Abstract

Methyl triclosan [2,4-dichloro-1-(4-chloro-2-methoxyphenoxy)benzene, 1], which is now considered an environmental pollutant, has been shown to be formed via microbial methylation of triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol, 2]. In the present work, cyclic voltammetry and controlled-potential (bulk) electrolysis have been employed to investigate the direct reduction of 1 at glassy carbon electrodes in dimethylformamide (DMF) containing 0.050M tetramethylammonium tetrafluoroborate (TMABF4). Cyclic voltammograms for the reduction of 1 at a glassy carbon electrode exhibit three irreversible cathodic peaks with peak potentials of −1.72, −2.07, and −2.35V (versus a cadmium-saturated mercury amalgam reference electrode). These three peaks correspond, respectively, to (a) scission of the ortho C–Cl bond, (b) cleavage of the two para C–Cl bonds, and (c) rupture of the C–O bond. Controlled-potential (bulk) electrolyses of 1 at reticulated vitreous carbon electrodes result in the formation of mixtures of 4-chloro-1-(4-chlorophenoxy)-2-methoxybenzene (3), 4-chloro-2-methoxy-1-phenoxybenzene (4a), 1-(4-chlorophenoxy)-2-methoxybenzene (4b), 1-methoxy-2-phenoxybenzene (5), anisole (6), and phenol.