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KINETICS OF THE TRANSFORMATION OF TRICHLOROETHYLENE AND TETRACHLOROETHYLENE BY IRON SULFIDE. (R825958)
Citation:
Butler, E. C. AND K. F. Hayes. KINETICS OF THE TRANSFORMATION OF TRICHLOROETHYLENE AND TETRACHLOROETHYLENE BY IRON SULFIDE. (R825958). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 33:2021-2027, (1999).
Description:
The transformation of nine halogenated aliphatic compounds
by 10 g/L (0.5 m2/L) FeS at pH 8.3 was studied in batch
experiments. These compounds were as follows:
pentachloroethane (PCA), 1,1,2,2- and 1,1,1,2-tetrachloroethanes (1122-TeCA and 1112-TeCA), 1,1,1- and 1,1,2-trichloroethanes (111-TCA and 112-TCA), 1,1- and 1,2-dichloroethanes (11-DCA and 12-DCA), carbon tetrachloride
(CT), and tribromomethane (TBM). 11-DCA, 12-DCA, and 112-TCA showed no appreciable transformation by FeS
over approximately 120 days, but the other compounds
were transformed with half-lives of hours to days. PCA and
1122-TeCA underwent dehydrohalogenation faster than FeS-mediated reductive dehalogenation reactions under the
conditions of these experiments. The remaining compounds
for which significant transformation was observed
underwent FeS-mediated reactions more rapidly than
hydrolysis or dehydrohalogenation. For 1112-TeCA, the
dihaloelimination product (1,1-dichloroethylene) was the
only reaction product detected. For 111-TCA, CT, and TBM,
hydrogenolysis products were the only products detected,
although their mass recoveries were considerably less
than 100%. Two simple log-linear correlations between rate
constants and either one-electron reduction potentials
or homolytic bond dissociation enthalpies were developed,
with coefficients of determination (R 2 values) of 0.48
and 0.82, respectively. These findings are consistent with
a rate-limiting step involving homolytic bond dissociation.
However, neither correlation accurately described the
reactivity of all the compounds that were studied, suggesting
distinctions among the mechanisms for reductive
dehalogenation of these compounds by FeS or the
influence of additional molecular or thermodynamic
parameters on rate constants.