Reductive Transformation of Trichloroethene by Cobalamin:  Reactivities of the Intermediates Acetylene, Chloroacetylene, and the DCE Isomers

The transformations of acetylene, chloroacetylene, 1,1-dichloroethene (DCE), and cis- and trans- DCE mediated by cobalamin in the presence of titanium(III) citrate were investigated at pH 8 and 22 °C. Acetylene quantitatively reacted to ethene via vinylcobalamin as the proposed intermediate. Chloroacetylene reacted to acetylene and vinyl chloride. Proposed intermediates are ethynylcobalamin and vinylcobalamin, respectively. The principal initial reaction of chloroacetylene formed ethynylcobalamin which decomposed to acetylene. The proposition for ethynyl- and vinylcobalamin formation is based on fitting reaction models to kinetic data. Kinetic modeling sug gests half-lives for ethynyl- and vinylcobalamin of 1.4 and 251 h, respectively. 1,1-Dichloroethene reacted to ap proximately 20% volatiles (ethene, ethane, vinyl chloride, and acetylene) and 80% unidentified nonvolatile products. cis- and trans- DCE transformed slowly and produced small yields of vinyl chloride, ethene, and ethane.