Catalytic Reduction of 1,1,1-Trichloro-2,2,2-trifluoroethane (CFC-113a) by Cobalt(I) Salen Electrogenerated at Vitreous Carbon Cathodes in Dimethylformamide

Abstract

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 tetramethylammonium tetrafluoroborate 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-1,1,1-trifluoroethane (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 or moiety to an imino 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.