Mm. Scherer et al., CORRELATION-ANALYSIS OF RATE CONSTANTS FOR DECHLORINATION BY ZERO-VALENT IRON, Environmental science & technology, 32(19), 1998, pp. 3026-3033
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.