CORRINOID-MEDIATED REDUCTION OF TETRACHLOROETHENE, TRICHLOROETHENE, AND TRICHLOROFLUOROETHENE IN HOMOGENEOUS AQUEOUS-SOLUTION - REACTION-KINETICS AND REACTION-MECHANISMS

It is shown that in homogeneous aqueous solution containing titanium(I II) citrate or titanium(III)-NTA as bulk electron donor, cobalamin, co binamide, and cobamide are effective electron transfer mediators for t he reduction of tetrachloroethene (PCE), trichloroethene (TCE), and tr ichlorofluoroethene (TCFE). Far a given chlorinated ethene, the reacti on rate varied only slightly with pH and type of corrinoid present and was about 5 and 50 times faster for PCE as compared to TCFE and TCE, respectively. Evidence is presented that the first and rate-limiting s tep of the reduction of PCE, TCE, and TCFE by super-reduced corrinoids is a dissociative one-electron transfer yielding the corresponding vi nyl radicals. Furthermore, the elimination of a chloride radical from the 1,1-dichlorovinyl radical yielding chloroacetylene and subsequentl y acetylene is proposed to account for the direct formation of acetyle ne out of TCE. Finally, it is demonstrated that at higher reduction po tentials the corrinoid mediators may be blocked by the formation of ad dition products.