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 binary mixtures of water and Various organic cosolvents spanning a wide range in solvent properties, for all solvents investigated, the addition to an aqueous solution resulted in an increase in solubility and an alkaline shift in the conditional ionization constant (pK(a)(c)) of benzoic acid. Sorption data were assessed using a cosolvency model that 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 model similar to what was previously observed for the sorption of carboxylic acids from methanol/water solutions. The relative importance of cosolvent properties and Various solvent-specific mechanisms is discussed. Hydrogen bonding along with preferential solvation are hypothesized as the primary mechanisms responsible for the observed deviations from the model.