Direct and nickel(I) salen-catalyzed reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) in dimethylformamide

Cyclic voltammetry, controlled-potential (bulk) electrolysis, gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), and high-performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC–ESI–MS) have been employed to investigate the direct reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) at a carbon cathode in dimethylformamide (DMF) containing 0.10 M tetra-n-butylammonium tetrafluoroborate (TBABF4) as well as the nickel(I) salen-mediated reduction of CFC-113 in the same medium. Cyclic voltammograms for direct reduction of CFC-113 show two irreversible cathodic peaks attributable to formation of, first, 1-chloro-1,2,2-trifluoroethene (CFC-1113) and, second, trifluoroethene (HFC-1123); bulk electrolyses of CFC-113 at potentials corresponding to each of the cathodic peaks afford CFC-1113 and HFC-1123, respectively, in essentially quantitative yield. Cyclic voltammograms for reduction of nickel(II) salen in the presence of CFC-113 provide evidence for the catalytic formation of CFC-1113 and HFC-1123, and bulk electrolyses involving electrogenerated nickel(I) salen lead to mixtures of CFC-1113 and HFC-1123, although 1,1,1,2-tetrafluoroethane (HFC-134a) has been detected as a minor product. It has been determined with the aid of HPLC–ESI–MS that the salen ligand of the nickel(I) catalyst is modified during the catalytic reduction of CFC-113. A mechanistic scheme is proposed for the direct reduction of CFC-113.

► Direct reductive dechlorination of CFC-113 occurs at a carbon cathode in DMF.
► Electrogenerated nickel(I) salen catalyzes the dechlorination of CFC-113.
► Electrochemical reduction of CFC-113 involves carbanion intermediates.
► Nickel(I) salen is deactivated upon alkylation by a fragment from CFC-113.