Aqueous-Phase Dechlorination of Toxic Chloroethylenes by Vitamin B ₁₂ Cobalt Center: Conventional and Polypyrrole Film-Based Electrochemical Studies

This paper is focused on the dechlorination of trichloroethylene (TCE) and cis-dichloroethylene (cis-DCE) by the cobalt-centered molecule vitamin B ₁₂. The natural oxidation state of cobalt in vitamin B₁₂ is +3, and +1 is the active form, which carries out the reduction; hence, transformation to the +1 state is essential to carrying out the reduction of chlorinated organics. With respect to achieving this transformation, two different sets of studies were undertaken: (i) conventional chemical reductions in the presence of a bulk reductant, namely, titanium(III) citrate, and (ii) a novel electrochemical reduction involving constant application of an appropriate potential. The conventional chemical reduction reactions were performed at varying concentrations of titanium(III) citrate. The electrochemical reduction reactions comprised (a) electrochemical polymerization of a pyrrole monomer, involving simultaneous entrapment of vitamin B₁₂ in the film with subsequent use of the film for dechlorination, and (b) aqueous-phase electrochemical dechlorination at various solution-phase concentrations of vitamin B₁₂ in the presence of the polypyrrole film on the surface of the electrode.