CORRELATION-ANALYSIS OF RATE CONSTANTS FOR DECHLORINATION BY ZERO-VALENT IRON

Dehalogenation is among the most important processes involved in conta minant fate, but despite all the work that has been done on the kineti cs of dehalogenation, there are few linear free energy relationships ( LFERs) that can be used to explain or predict rates of dehalogenation by environmental reductants. Previously, we summarized kinetic data fo r dehalogenation of chlorinated alkanes and alkenes by zero-valent iro n (Fe-0) and showed that correlation analysis of these data with publi shed two-electron reduction potentials did not give a simple relations hip. In this study, we report successful LFERs based on estimated lowe st unoccupied molecular orbital (LUMO) energies calculated from semiem pirical(AM1 and PM3) and ab initio methods (6-31G) and one-electron r eduction potentials. Solvation effects can be modeled with COSMO and i ncorporated into semiempirical estimates of E-LUMO, but this did not i mprove the correlation with k. The best LFER (log k = -5.7-1.5 E-LUMO) explains 83% of the variability in surface area-normalized rate const ants (k) with ab initio LUMO energies. The LFER is improved by correct ing for statistical bias introduced by back transformation from log-li near regression models. New kinetic data for six compounds are compare d with rate constants predicted using the unbiased LFER.