Dissociation constants of 1,10-phenanthroline and 2,2 '-bipyridine in propan-1-ol plus water mixtures and the Gibbs energy of transfer of H+ ion fromwater to binary mixtures

The thermodynamic dissociation constants for the isoelectric reactions LH= L + H+ (where L = 1,10-phenanthroline and 2,2'-bipyridine) have been dete rmined pH-metrically in propan-1-ol + water mixtures (0-87 wt% of organic c osolvent). The data have been utilized to calculate the Gibbs energies of t ransfer of H+ ion from water to propan-1-ol + water mixtures. The limitatio ns of the method have been discussed. The results have been explained in te rms of ion-solvent interactions, structural variations and basicity of the solvent mixtures. The basicity of the aquo-organic mixtures increases, beco mes maximum near about 43-53 wt% of organic cosolvent, then decreases and s ubsequently becomes less basic when the mole-fraction of organic cosolvent x(2), exceeds 0.5. The results suggest propan-1-ol to be less basic than wa ter.