Catalytic reduction of 4,4′-(2,2,2-trichloroethane-1,1-diyl)bis(methoxybenzene) (methoxychlor) with nickel(I) salen electrogenerated at reticulated vitreous carbon cathodes

Abstract

Methoxychlor [or 4,4′-(2,2,2-trichloroethane-1,1-diyl)bis(methoxybenzene)], a common environmental pollutant, has been catalytically reduced with nickel(I) salen electrogenerated in situ at carbon cathodes in dimethylformamide (DMF) containing 0.050M tetra-n-butylammonium tetrafluoroborate (TBABF4). Cyclic voltammograms for reduction of nickel(II) salen in the presence of various concentrations of methoxychlor provide evidence for catalytic reduction. Cathodic peak currents for the nickel(II) salen–nickel(I) salen redox couple increase in proportion to the concentration of methoxychlor, whereas the anodic peak current associated with reoxidation of nickel(I) salen diminishes; in addition, a cathodic prepeak appears at higher concentrations of methoxychlor. Controlled-potential (bulk) electrolyses of nickel(II) salen at reticulated vitreous carbon cathodes in the presence of methoxychlor allowed the n value for reduction of methoxychlor to be determined. With the aid of gas chromatography–mass spectrometry, major electrolysis products have been identified as 4,4′-(2-chloroethene-1,1-diyl)bis(methoxybenzene) and 4,4′-(ethene-1,1-diyl)bis(methoxybenzene), and the product distribution was determined by means of gas chromatography. Adducts arising from the combination of fragments derived from methoxychlor and DMF have also been detected and confirmed, and a mechanistic scheme is proposed to account for the various products.