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

Cyclic voltammetry, controlled-potential electrolysis, GC, GC–MS, HPLC, and HPLC–ESI–MS have been employed to investigate the catalytic reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (chlorofluorocarbon 113, CFC-113, or FreonTM 113) by cobalt(I) salen electrogenerated at a carbon cathode in dimethylformamide (DMF) containing tetra-n-butylammonium tetrafluoroborate (TBABF4) as a supporting electrolyte. A cyclic voltammogram for the reduction of cobalt(II) salen in the presence of excess CFC-113 exhibits a large prewave, attributed to both the formation of a 1,1-dichloro-1,2,2-trifluoroethylcobalt(III) salen complex and its reduction to chlorotrifluoroethene and cobalt(II) salen. This prewave is followed by a smaller wave which involves the reduction of cobalt(II) salen to cobalt(I) salen; a slower catalytic reaction of chlorotrifluoroethene to form trifluoroethene takes place at this same potential, but only when CFC-113 has been completely consumed. Controlled-potential electrolyses carried out at a potential slightly more negative than this second wave also lead to other products, one confirmed to be 1,1,1,2-tetrafluoroethane and at least two other species suspected to be difluoro compounds. From results obtained by means of cyclic voltammetry and controlled-potential electrolysis, along with already published knowledge about the electrochemistry of cobalt-containing complexes, a mechanism is proposed to explain our findings. Catalyst death is also addressed in the light of data from controlled-potential electrolysis and from experiments done with the aid of HPLC and HPLC–ESI–MS.