Kinetics and mechanism of propachlor reductive transformation through nucleophilic substitution by dithionite

C. S. Liu, K. Shih, L. Wei, F. Wang, F. B. Li

Research output: Journal article publicationJournal articleAcademic researchpeer-review

12 Citations (Scopus)

Abstract

Chloroacetanilide herbicides are extensively used in the control of weeds and have widely resulted in nonpoint contamination of groundwater and soil resources. In the attempt to achieve better remediation for herbicide-contaminated resources, we investigated the reductive transformation of propachlor through nucleophilic substitution by dithionite (S2O42-). Results showed that propachlor underwent rapid dechlorination in the presence of dithionite. The reaction was of second-order kinetics and strongly influenced by pH and temperature. At pH 7.0 and temperature 308K, the rate constant of propachlor dechlorination was estimated at 123.4±0.7M-1h-1. Within the pH range tested (3.0-9.5), higher pH promoted the ionization of dithionite, resulting in a more active nucleophilic reagent of S2O42- to enhance the propachlor transformation rate. Similarly, higher reaction temperature overcame the activation barrier of steric hindrance in propachlor structure and accelerated the excitation of dithionite, in which higher rate constants of propachlor reductive dechlorination were obtained. Dechlorination was found to be the first and necessary step of propachlor nucleophilic substitution by dithionite. Sulfur nucleophile substituted compounds, including propachlor dithionite, propachlor ethanesulfonic acid (ESA), and hydroxyl propachlor, were identified as the dechlorination products of propachlor, indicating bimolecular nucleophilic substitution (SN2) as the mechanism for propachlor transformation initiated by dithionite.

Original languageEnglish
Pages (from-to)1438-1443
Number of pages6
JournalChemosphere
Volume85
Issue number9
DOIs
Publication statusPublished - Nov 2011

Keywords

  • Chloroacetanilide herbicides
  • Dechlorination
  • Nucleophilic reagent
  • Nucleophilic substitution
  • Second-order kinetics

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • General Chemistry
  • Pollution
  • Public Health, Environmental and Occupational Health
  • Health, Toxicology and Mutagenesis

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