Using gas-phase molecular descriptors to predict dechlorination rates of chloroalkanes by zerovalent iron

Sathaporn Onanong, Steve D. Comfort, Paul D. Burrow, Patrick J. Shea

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

Reductive dehalogenation of chlorinated compounds is the most important process occurring within the zerovalent iron (Fe0) barrier. The relative reaction rates of individual halocarbons with Fe0 can vary considerably. This variability has been the stimulus for using various chemical descriptors for a priori predictions of transformation rates via linear free-energy relationships (LFERs). Our objective was to determine the efficacy of four molecular descriptors to describe the transformation rates of three chloromethanes, three chloroethanes, and six chloropropanes by Fe0. This was accomplished by generating an internally consistent set of rate constants under controlled environmental conditions (16 °C, anaerobic) and regressing the surface-area normalized rate constants (kSA) against (i) energy of the lowest unoccupied molecular orbital (ELUMO); (ii) vertical attachment energies (VAE); (iii) thermal electron attachment rate constants; and (iv) the molar response from a commercial electron capture detector (ECD). Results showed good correlations between kSA'S and all four descriptors (r2: 0.72-1.0), but a separate trend line was required for the chloromethanes and the chloroethanes/propanes. Given the availability and ease with which ECD response can be obtained, this physical measurement may provide a practical means of determining relative rates of reactivity of various halocarbons in permeable reactive iron barriers.

Original languageEnglish (US)
Pages (from-to)1200-1205
Number of pages6
JournalEnvironmental Science and Technology
Volume41
Issue number4
DOIs
StatePublished - Feb 15 2007

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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