Influence of organic ligands on the reduction of polyhalogenated alkanes by iron(II)

Adam L. Bussan, Timothy Strathmann

Research output: Contribution to journalArticlepeer-review

Abstract

Experimental work demonstrates that polyhalogenated alkanes (PHAs) are rapidly reduced in aqueous solutions containing FeII complexes with organic ligands that possess either catechol or organothiol Lewis base groups in their structure and are representative of extracellular ligands and metal-complexing moieties within humic substances (tiron, 2,3-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 2,3,4-trihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, thioglycolic acid, and 2,3-dimercaptosuccinic acid). In solutions containing FeII-tiron complexes, 1,1,1-trichloroethane (1,1,1-TCA) is reduced quantitatively to acetaldehyde, a product previously reported for reactions with CrII, but not with Fe-based reductants. Observed pseudo-first-order rate constants for 1,1,1-TCA reduction by FeII-organic complexes (k′obs) generally increase with increasing pH and ligand concentration when Fe II concentration is fixed. For the FeII-tiron system, k′obS is linearly correlated with the concentration of the 1:2 FeII-tiron complex (FeL2 6-), and kinetic trends can be described by k′obs = kFeL2 6- [FeL2 6-], where kFel2 6- is the bimolecular rate constant for PHA reaction with the 1:2 FeII-tiron complex. Comparing reaction rates for 14 polyhalogenated ethanes and methanes reveals linear free energy relationships (LFERs) with molecular descriptors for PHA reduction (DR-X′, ΔG0′, and E LUMO), with the strongest correlation being obtained using carbon-halogen bond dissociation energies, DR-X′. The collective experimental results are consistent with a dissociative one-electron transfer process occurring during the rate-limiting step.

Original languageEnglish (US)
Pages (from-to)6740-6747
Number of pages8
JournalEnvironmental Science and Technology
Volume41
Issue number19
DOIs
StatePublished - Oct 1 2007

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Science(all)
  • Environmental Chemistry

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