Autoprotolysis in aqueous organic solvent mixtures. Water/dipolar protophilic solvent binary systems

The autoprotolysis of binary aqueous mixtures of dimethyl sulfoxide, acetonitrile, acetone, tetrahydrofuran and 1,4-dioxan is studied. It is demonstrated that except for solvent mixtures very rich in water, the autoprotolysis is produced by proton transfer from water to the dipolar organic solvent. Only in water rich mixtures the autoionization of water contributes appreciably to autoprotolysis. It is also suggested that the so-called autoprotolysis constant or ionic product of these pure organic solvents is in fact, produced by proton transfer from the very small amounts of water present in the medium to the organic solvent. Equations and parameters are presented that allow calculation of the autoprotolysis constant for any solvent composition at 25 °C. The variation of the autoprotolysis constant with temperature is also studied for dimethyl sulfoxide/water and acetone/water mixtures.