Linear Free Energy Relationship Analysis of Chlorinated Hydrocarbons in Cement Slurries

Abstract

The present study is to study linear free energy relationships (LFERs) for dechlorination rates in cement/Fe(II) slurries of eight chlorinated hydrocarbons including carbon tetrachloride, chloroform produced from carbon tetrachloride, 1,1,1-trichloroethane, trichloroethylene produced from 1,1,2,2-tetrachloroethane, tetrachloroethylene, trichloroethylene, 1,1-dichloroethylene, and vinyl chloride, with six descriptor variables in pursuit of finding a reasonable descriptor showing the highest coefficient of determination (R-2). Seventeen descriptors by various computational methods were screened into six descriptors. In addition, this study correlated logarithms of rate constants (log k) with multiple descriptors. The results have shown that the bond dissociation energy, overall free energy change of the one-electron transfer step, and lowest unoccupied molecular orbital energies calculated by ab initio methods with 6-31G* parameters were strongly correlated with the log k values of eight compounds by Fe(II) in cement slurries. The combinations of descriptors that had the highest correlation coefficient in multiple regression were one-electron reduction potential and gas-phase homolytic-dissociation energy (E-1 and DR-X), which two variables are commonly based on that a dissociative one-electron transfer is the initial and rate-limiting step in the reaction.