Cobalamin-Mediated Reduction of cis- and trans-Dichloroethene, 1,1-Dichloroethene, and Vinyl Chloride in Homogeneous Aqueous Solution: Reaction Kinetics and Mechanistic Considerations

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• 作者：Guy Glod ; Urs Brodmann ; Werner Angst ; Christof Holliger ; and René ; P. Schwarzenbach
• 刊名：Environmental Science & Technology
• 出版年：1997
• 出版时间：November 1997
• 年：1997
• 卷：31
• 期：11
• 页码：3154 - 3160
• 全文大小：222K
• 年卷期：v.31,no.11(November 1997)
• ISSN：1520-5851

文摘

Since cobalamin is involved in the enzymatic reductionof halogenated ethenes by a variety of anaerobic bacteriaand since cobalamin has been suggested as electrontransfer mediator for the treatment of halogenatedsolvents,its reactions with such compounds are presently of greatinterest. In this paper, it is shown that, inhomogeneousaqueous solution containing titanium(III) citrate asthebulk electron donor, superreduced cobalamin reductivelydechlorinated cis- and trans-dichloroethene(cis-DCE andtrans-DCE), 1,1-dichloroethene (1,1-DCE), and vinylchloride(VC) in pH-dependent reactions to ethene and ethane.Evidence is given that the initial step was the additionofcob(I)alamin to the chlorinated ethenes (CEs) withsimultaneous protonation. Only for 1,1-DCE at high pH,adissociative electron transfer mechanism as suggestedfor tetrachloroethene (PCE) and trichloroethene (TCE) inearlier work was important. 1,1-DCE reacted about 30times faster than VC, 600 times faster than trans-DCE,and3000 times faster than cis-DCE. Acetylene andethenewere found to react at similar rates as 1,1-DCE and VC,respectively. However, at more positive redox potentials,thereductive cleavage of the addition products, particularlyof the adducts of acetylene, ethene, and VC withcob(I)alamin,may become very slow, thus preventing the regenerationof cob(I)alamin. The results of this study demonstratethat,at more negative potentials and at low pH, cobalamin isa potent electron transfer mediator for the complete dehalogenation of PCE and TCE without significant accumulationof VC.