Application of Electrochemistry to Determination of Transfer Gibbs Energies and Autoprotolysis Constants for Aqueous Mixtures of Dimethyl Sulfoxide

Abstract

A practical potentiometric method was applied successfully to experimental electrochemical data in order to determine the autoprotolysis constants (pKap) of water + dimethyl sulfoxide mixtures containing 0-90 % of DMSO by volume at 25° C and 0.1 M ionic strength was maintained in each mixture by NaClO4 solution. The results indicated that water-DMSO mixtures are more basic media than pure water and the pKap value of media increases with addition of DMSO. The variation of pKap value over the media composition range was explained by a linear solvation energy relationship. Thus the correlations between pKap values and the Kamlet- Taft parameters were analyzed by means of multiple linear regressions. The equations obtained can be used to estimate the autoprotolysis constants in a water-DMSO solvent from the relationship between the pK ap values and the Kamlet- Taft parameters of the solvent. The literature values of transfer Gibbs free energies of H+ , ∆t G0 (H+ ), have been applied successfully to quantify the activity of hydroxide ion (∆t G0 (H- )) from the pure water solvent to any binary mixtures which is critical in understanding the organic reactivity in solution.