THERMODYNAMICS OF TRANSFER OF HYDROGEN-ION FROM WATER TO DIOXANE-WATER MIXTURES

The thermodynamic dissociation constants for the isoelectric reaction LH+ half arrow right over half arrow left L + H+ (where L = 1,10-phena nthroline) have been determined pH-metrically and spectrophotometrical ly in dioxane + water (D + H2O) mixtures (0-90 wt% of dioxane). The da ta were utilised to calculate the free energies of transfer of H+ ion from water to dioxane+ water mixtures. Enthalpies and entropies of tra nsfer of H+ ion (in 0-60 wt% of D) have also been determined using the calorimetric data of earlier experiments in a similar way. The change s in the pK values and the thermodynamics of transfer of H+ ion have b een interpreted in terms of solvent basicity and ion-solvent interacti ons. The thermodynamics of transfer of H+ ion suggests that D + H2O mi xtures are more basic than water. The basicity increases and passes th rough a maximum in the region 45-50 wt% of D and ultimately above 80 w t% of D (D : H2O approximately : 1); the binary mixtures are less basi c than water. It appears that D is less basic than water in the liquid state. The results are consistent with the structural changes associa ted with the addition of a solvent D to water.