Catalytic reduction of 4,4′-(2,2,2-trichloroethane-1,1-diyl)bis(chlorobenzene) (DDT) with nickel(I) salen electrogenerated at vitreous carbon cathodes in dimethylformamide

Abstract

Cyclic voltammetry, controlled-potential (bulk) electrolysis, gas chromatography, gas chromatography–mass spectrometry, and high-performance liquid chromatography–electrospray ionization–mass spectrometry have been utilized to investigate the catalytic reduction of 4,4′-(2,2,2-trichloroethane-1,1-diyl)bis(chlorobenzene) (DDT) by nickel(I) salen electrogenerated at a carbon cathode in dimethylformamide (DMF) containing 0.050M tetramethylammonium tetrafluoroborate (TMABF4). Cyclic voltammograms for reduction of nickel(II) salen in the presence of DDT provide evidence for catalytic reduction such as enhanced cathodic current for the nickel(II) salen–nickel(I) salen redox couple and a decrease in the anodic current associated with oxidation of nickel(I) salen. Bulk electrolysis of nickel(II) salen–DDT solutions at reticulated vitreous carbon cathodes leads to a mixture of products that includes 1,1-diphenylethene, 1-chloro-4-(1-phenylvinyl)benzene, 4,4′-(ethene-1,1-diyl)bis(chlorobenzene) (DDNU), 4,4′-(2-chloroethene-1,1-diyl)bis(chlorobenzene) (DDMU), 4,4′-(2-chloroethane-1,1-diyl)bis(chlorobenzene) (DDMS), 4,4′-(2,2-dichloroethane-1,1-diyl)bis(chlorobenzene) (DDD), and 4,4′-(2,2-dichloroethene-1,1-diyl)bis(chlorobenzene) (DDE). In addition, we have detected adducts formed from a fragment of DMF and radical intermediates arising from reduction of DDT, along with nickel salen species for which the imino (CN) bond of the ligand is modified with different intermediates derived from catalytic reduction of DDT. A mechanistic scheme is proposed to account for the formation of products.