Ab Initio Electronic Structure Study of One-Electron Reduction Of Polychlorinated Ethylenes

Journal Article · Thu Jul 21 04:00:00 EDT 2005 · Journal of Physical Chemistry A, 109(26):5905-5916

DOI:https://doi.org/10.1021/jp0407526· OSTI ID:15020648

Bylaska, Eric J; Dupuis, Michel; Tratnyek, Paul G

Polychlorethylene radicals, anions, and radical anions are potential intermediates in the reduction of polychlorinated ethylenes (C₂Cl₄, C₂HCl₃, trans-C₂H₂Cl₂, cis-C₂H₂Cl₂, 1,1-C₂H₂Cl₂, C₂H₃Cl). Ab initio electronic structure methods were used to calculate the thermochemical properties, ΔΗ_f°(298.15K), S°(298.15K,1 bar), ΔG_s(298.15K, 1 bar) of 37 different polychloroethyleneyl radicals, anions, and radical anion complexes: C₂H_yCl_3-y^•, C₂HyCl_3-y⁻, and C₂HyCl_4-y^•- for y = 0 - 3 for the purpose of characterizing reduction mechanisms of polychlorinated ethylenes. In this study 8 radicals, 7 anions, and 22 radical anions were found to have stable structures, i.e minima on the potential energy surfaces. This multitude of isomers for C₂H_yCl_4-y^•- radical anion complexes are π*, σ*, and -H…Cl⁻ structures. Several stable π* radical anionic structures were obtained for the first time through the use of restricted open-shell theories. On the basis of the calculated thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the polychlorinated ethylenes were determined. In almost all of the gas-phase reactions, the thermodynamically most favorable pathways involve ₋H...Cl⁻ complexes of the C₂H_yCl_4-y^•- radical anion, in which a chloride ion is loosely bound to a hydrogen of a C₂H_xCl_2-x• radical. The exception is for C₂Cl₄, in which the most favorable anionic structure is a loose σ* radical anion complex, with a nearly iso-energetic π* radical anion. Solvation significantly changes the product energetics with the thermodynamically most favorable pathway leads to C₂H_yCl_3-y• + Cl⁻. The results suggest that a higher degree of chlorination favors reduction, and that reduction pathways involving the C₂H_yCl_3-y⁻ anions are high energy pathways.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 15020648
• Report Number(s): PNNL-SA-44752; 2403a; 2492; 2628; 3687; 5119; 2573; KC0302020
• Journal Information: Journal of Physical Chemistry A, 109(26):5905-5916, Journal Name: Journal of Physical Chemistry A, 109(26):5905-5916
• Country of Publication: United States
• Language: English

Related Subjects

Environmental Molecular Sciences Laboratory