Mechanism of pentachloroethane dehydrochlorination to tetrachloroethylene

Journal Article · Mon Dec 31 23:00:00 EST 1990 · Environmental Science and Technology; (USA)

DOI:https://doi.org/10.1021/es00013a006· OSTI ID:6102778

Roberts, A L; Gschwend, P M ^[1]

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1. Massachusetts Institute of Technology, Cambridge (USA)

The dehydrochlorination of pentachloroethane to tetrachloroethylene was investigated to gain insight into mechanisms of hexachloroethane reduction as well as structure-reactivity relationships for polyhalogenated alkanes. Although the absence of deuterium exchange excludes the possibility of an (E{sub 1CB}){sub R} mechanism, several factors suggest the transition state possesses considerable carbanion character: the reaction is insensitive to buffer catalysis, exhibits a moderately large solvent kinetic isotope effect, and only displays a neutral mechanism at low pH. Though our results cannot rule out a stepwise (E{sub 1CB}){sub I} or (E{sub 1CB}){sub ip} sequence, we believe CHCl{sub 2}CCl{sub 3} reacts via a concerted mechanism based on a comparison of its dehydrohalogenation kinetics with proton-exchange rates for CHCl{sub 3} and CHCl{sub 2}CF{sub 3}. Pentachloroethane reported in the reduction of hexachloroethane to tetrachloroethylene is unlikely to result from carbanion protonation. Rather, it may be diagnostic of free-radical reduction mechanisms. Because pentachloroethane reacts relatively rapidly, future studies of hexachloroethane reduction should consider whether pentachloroethane represents a reaction intermediate instead of dismissing it as a minor side product.

• OSTI ID: 6102778
• Journal Information: Environmental Science and Technology; (USA), Journal Name: Environmental Science and Technology; (USA) Vol. 25:1; ISSN ESTHA; ISSN 0013-936X
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
54 ENVIRONMENTAL SCIENCES
540320* -- Environment
Aquatic-- Chemicals Monitoring & Transport-- (1990-)
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
DECHLORINATION
DEHALOGENATION
EXPERIMENTAL DATA
HALOGENATED ALIPHATIC HYDROCARBONS
INFORMATION
KINETICS
MEASURING METHODS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
REACTION KINETICS
STRUCTURE-ACTIVITY RELATIONSHIPS