REDUCTIVE DECHLORINATION OF CARBON-TETRACHLORIDE BY COBALAMIN(II) IN THE PRESENCE OF DITHIOTHREITOL - MECHANISTIC STUDY, EFFECT OF REDOX POTENTIAL AND PH

A mechanistic study of the reductive dechlorination of carbon tetrachloride by vitamin B-12 (cyanocobalamin) in the presence of dithiothreitol was conducted as a function of redox potential and pH. The solution redox potential decreased both with an increase in the total concentration of dithiothreitol present and with an increase in pH. The pseudo-first-order rate constant of carbon tetrachloride disappearance increased with decreasing redox potential. The predominant cobalt species present under the reaction conditions was cobalamin(II) (vitamin B-12r), as confirmed by spectrophotometric analysis, suggesting a one-electron reduction of vitamin B-12 and the involvement of two vitamin B-12 molecules per reacting carbon tetrachloride molecule. This study illustrates the role of Co(II) in reductive dechlorination by vitamin B-12.