Nucleophilic aliphatic substitution reactions of propachlor, alachlor and metolachlor with bisulfide (HS-) and polysulfides (Sn2-)

Reactions of bisulfide and polysulfides with alachlor, propachlor, and metolachlor were examined in aqueous solution to investigate,the role reduced sulfur species could play in effecting abiotic transformations of chloroacetanilide herbicides. Experiments at 25 degreesC, demonstrated that reactions were approximately first-order in HS- concentration and revealed that polysulfides are considerably more reactive than HS-. DeltaH(not equal)values for reactions of the three chloroacetanilides with HS- are statistically indistinguishable at the 95% confidence level, as are DeltaS(not equal) values, despite significant,differences in second-order rate constants (k(HS)-). Transformation products were characterized,by GC/MS (in some cases following methylation) and were found to be consistent with substitution of chlorine by the sulfur nucleophile. Products containing multiple sulfur atoms were observed for the reactions of chloroacetanilides with polysulfides while products resulting from reaction, with HS- only possessed a single sulfur atom. When second-order rate constants at 25 degreesC are multiplied by HS- and polysulfide concentrations reported in salt March porewaters, predicted half-lives range from minutes to hours. HS- and espeqially polysulfides could thus exert a substantial influence on the fate of chloroacetanilide herbicides in aquatic environments. Oxidation of the resulting sulfur-substituted products could generate ethane sulfonic acid derivatives, previously reported as prevalent chloroacetanilide degradates.