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

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-chloro2-(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 I at glassy carbon electrodes in dimethylformamide (DMF) containing 0.050 M tetramethylammonium tetrafluoroborate (TMABF(4)). 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 -2.35 V (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. (C) 2014 Elsevier B.V. All rights reserved.