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Ab initio study of carbon-chlorine bond cleavage in carbon tetrachloride

机译：从头开始研究四氯化碳中碳-氯键的裂解

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Chlorinated solvents in groundwater are known to undergo reductive dechlorination reactions with Fe(II)containing minerals and with corroding metals in permeable-barrier treatment systems. This research investigated the effect of the reaction energy on the reaction pathway for C-Cl bond cleavage in carbon tetrachloride (CCl4). Hartree-Fock, density functional theory, and modified complete basis set ab initio methods were used to study adiabatic electron transfer to aqueous-phase CCl4. The potential energies associated with fragmentation of the carbon tetrachloride anion radical (.CCl4-) into a trichloromethyl radical (.CCl3) and a chloride ion (Cl-) were explored as a function of the carbon-chlorine bond distance during cleavage. The effect of aqueous solvation was investigated using a continuum conductor-like screening model. Solvation significantly lowered the energies of the reaction products, suggesting that dissociative electron transfer was enhanced by solvation. The potential energy curves in an aqueous medium indicate that reductive cleavage undergoes a change from an innersphere to an outer-sphere mechanism as the overall energy change for the reaction is increased. The activation energy for the reaction was found to be a linear function of the overall energy change, and the Marcus-Hush model was used to relate experimentally measured activation energies for CCl4 reduction to overall reaction energies. Experimentally measured activation energies for CCl4 reduction by corroding iron correspond to reaction energies that are insufficiently exergonic for promoting the outer-sphere mechanism. This suggests that the different reaction pathways that have been observed for CCl4 reduction by corroding iron arise from different catalytic interactions with the surface, and not from differences in energy of the transferred electrons.
机译：已知地下水中的氯化溶剂会与渗透性屏障处理系统中的含Fe（II）矿物和腐蚀性金属进行还原性脱氯反应。这项研究调查了反应能量对四氯化碳（CCl4）中C-Cl键断裂的反应途径的影响。 Hartree-Fock，密度泛函理论和改进的完整基础集从头算方法用于研究绝热电子向水相CCl4的转移。探索了与四氯化碳阴离子自由基（.CCl4-）裂解为三氯甲基自由基（.CCl3）和氯离子（Cl-）相关的势能，该能量是裂解过程中碳-氯键距离的函数。使用连续导体样筛选模型研究了水溶剂化的效果。溶剂化显着降低了反应产物的能量，表明通过溶剂化可增强离解性电子转移。水性介质中的势能曲线表明，随着反应的总能量变化增加，还原性裂解经历了从内球到外球的变化。发现该反应的活化能是总能量变化的线性函数，并且使用Marcus-Hush模型将实验测量的CCl4还原活化能与总反应能联系起来。在实验中测得的通过腐蚀铁还原CCl4的活化能对应于不足以促进外球机理发挥作用的反应能。这表明已观察到的通过腐蚀铁还原CCl4的不同反应途径是由于与表面的催化相互作用不同而引起的，而不是由转移电子的能量差异引起的。

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