IMPACT OF SEVERAL WATER-MISCIBLE ORGANIC-SOLVENTS ON SORPTION OF BENZOIC-ACID BY SOIL

Sorption of benzoic acid by a surface soil was measured from several b inary mixtures of water and Various organic cosolvents spanning a wide range in solvent properties, for all solvents investigated, the addit ion to an aqueous solution resulted in an increase in solubility and a n alkaline shift in the conditional ionization constant (pK(a)(c)) of benzoic acid. Sorption data were assessed using a cosolvency model tha t incorporated speciation of the organic acid as determined by the pK( a)(c) and soil-solution pH. The model provided reasonable predictions of the sorption trends observed from acetone/water, acetonitrile/water , and 1,4-dioxane/water solutions. However, enhanced sorption observed from DMSO/water solutions was not well described by the cosolvency mo del similar to what was previously observed for the sorption of carbox ylic acids from methanol/water solutions. The relative importance of c osolvent properties and Various solvent-specific mechanisms is discuss ed. Hydrogen bonding along with preferential solvation are hypothesize d as the primary mechanisms responsible for the observed deviations fr om the model.