| Abstract
| - The degradation of two oxime carbamate pesticides,oxamyl and methomyl, was investigated in anoxic solutionscontaining various metal ions and reducing agents. Inreagent-free solutions, these carbamates degrade slowlyvia base-catalyzed elimination. Rates of carbamatedegradation are accelerated by FeII, CuI, and CuII, but notby several other metal ions and reducing agents. In thepresence of FeII, carbamates undergo a net two-electronreduction that is coupled to the sequential one-electronoxidation of two FeII ions. The observed products are asubstituted nitrile, methanethiol, and methylamine. A radicalintermediate is inferred by polymerization of the radicalscavenger acrylonitrile. Redox kinetics (i) vary with carbamateidentity, (ii) exhibit first-order dependence on both FeIIand carbamate concentration, (iii) are relatively independentof pH, (iv) follow Arrhenius temperature dependence,and (v) are only indirectly influenced by the presence ofO2. Coordinatively saturated FeII complexes (FeIIEDTA2- andFeII(CN)64-) react with oxamyl at rates equal to andgreater than hexaquo FeII, respectively, indicating that aninner-sphere FeII-carbamate coordination complex isnot required for electron transfer. Experimental resultsindicate that CuI reduces the carbamates by the samemechanism as FeII but at much higher rates. In contrast, CuIIacts as a catalyst for both elimination and reductionreactions.
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