The environmental literature has extensively examined the influence of adsorption on rates of mineral-mediated reactions of ionizable organic compounds.  Far less is known about the role of adsorption in mineral-mediated reactions of neutral compounds.  We investigated the reactivity of 15 neutral dichloroacetamides (Cl2CHC(=O)NRR') in suspensions of FeII-amended hematite and goethite, as well as solutions of Cr(H2O)62+.  R-groups included alkyl, allyl, and cyclic moieties.  Three of the dichloroacetamides are commercial �safeners�, which are used to protect crops from herbicide-related injury.      All dichloroacetamides underwent reductive dechlorination in each reductant system.  Mineral-mediated transformation rates increased 100-fold as the length of n-alkyl R-groups increased (ethyl to n-hexyl).  In solutions of Cr(H2O)62+, reactivity decreased as n-alkyl R-group length increased.  Branching of alkyl groups decreased reactivity in homogeneous and heterogeneous systems.  Our findings indicate that structural groups separated from redox-active sites by several bonds can influence heterogeneous reactions of neutral compounds via adsorption and/or steric effects.

Influence of adsorption and steric effects on mineral-mediated redox transformation rates of neutral dichloroacetamide safeners

245th National Meeting (2013)

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