Solvent effects on the dissociation of benzoic acid in aqueous mixtures of 2-methoxyethanol and 1,2-dimethoxyethane at 25 °C

Abstract

The thermodynamic dissociation constants (pK_T) of benzoic acid (HBz) have been determined at 25 °C in aqueous binary mixtures of 2-methoxyethanol (ME) and 1,2-dimethoxyethane (DME), at 10 wt% interval of organic co-solvent, by solubility and spectrophotometric measurements. The pK_T values have been found to increase with an increase in the proportion of organic component in the solvent mixture, the effect being more pronounced in DME–H₂O mixtures. The results have been discussed in terms of the standard Gibbs energies of transfer of H⁺ from water to the mixed solvent [ΔG^⊖_t(H⁺)] and the relative values of the standard Gibbs energies of transfer of Bz^–[ΔG^⊖_t(Bz^–)] and of HBz [ΔG^⊖_t(HBz)] in all the solvent systems. The overall dissociation of benzoic acid is found to be governed by the specific ion-solvent interactions in the solvent media besides the relative solvent basicities.