Kinetics of the transformation of halogenated aliphatic compounds by iron sulfide

Journal Article · Tue Feb 01 04:00:00 EST 2000 · Environmental Science and Technology

DOI:https://doi.org/10.1021/es980946x· OSTI ID:20026682

Butler, E C; Hayes, K F

The objectives of the experiments described here were 2-fold: first, to assess the relative rates and products of transformation of a variety of halogenated aliphatics by the soil mineral FeS under a uniform set of experimental conditions and, second, to establish whether there exists a relationship between rate constants for these transformations and free energy or molecular parameters. The transformation of nine halogenated aliphatic compounds by 10 g/L (0.5 m{sup 2}/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{sup 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.

• Research Organization: Univ. of Michigan, Ann Arbor, MI (US)
• Sponsoring Organization: US Department of Energy
• OSTI ID: 20026682
• Journal Information: Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 3 Vol. 34; ISSN ESTHAG; ISSN 0013-936X
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CHEMICAL REACTION KINETICS
DEHALOGENATION
GROUND WATER
IRON SULFIDES
ORGANIC HALOGEN COMPOUNDS
REMEDIAL ACTION