Catalytic reduction of 1,1,1-trichloro-2,2,2-trifluoroethane (CFC-113a) by cobalt(I) salen electrogenerated at vitreous carbon cathodes in dimethylformamide

Catalytic reduction of 1,1,1-trichloro-2,2,2-trifluoroethane (CFC-113a or Freon 113a) by cobalt (I) salen electrogenerated at a carbon cathode in dimethylformamide (DMF) containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF(4)) has been investigated with the aid of cyclic voltammetry, controlled-potential electrolysis, gas chromatography-mass spectrometry, and high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS ). Cyclic voltammetry reveals that CFC-113a and two of its degradation products, 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) and 2-chloro-1,1,1trifluoroethane (HCFC-133a), can all undergo catalytic reduction by cobalt (I) salen. Controlled-potential (bulk) electrolyses of cobalt (II) salen in the presence of CFC-113a lead to the production of HCFC-123, HCFC-133a, 2-chloro-1,1-difluoroethene (HCFC-1122), and 1,1-difluoroethene (HFC-1132a). HPLC-ESI-MS has been employed to demonstrate that, during the bulk catalytic reduction of CFC-113a, the salen ligand of the catalyst is modified through addition of a CF3CCl2- or CF3CHCl-moiety to an imino (C = N ) bond. On the basis of documented knowledge about the electrochemistry of cobalt-containing complexes, together with the results of our cyclic voltammetry and bulk electrolysis experiments, a mechanistic scheme is proposed for the cobalt (I) salen-catalyzed reduction of CFC-113a. (c) 2007 The Electrochemical Society.