Gibbs energies of transfer of hydrogen ion from water to tetrahydrofuran plus water mixtures and basicity and structuredness of aquo-ethers

The thermodynamic dissociation constants for isoelectric reaction of the ty pe LH+ double left right arrow L + H+ (where L = 2,2'-bipyridine or 1,10-ph enanthroline) have been determined pH-metrically at 298 degrees K in aqueou s binary mixtures of tetrahydrofuran (0-90 wt% of organic co-solvent). The pK-values have been found to decrease continuously. The data have been util ized to calculate the Gibbs energies of transfer of H+-ion from water to te trahydrofuran-water mixtures. The results have been explained in terms of i on-solvent interactions, structural variations and basicity of aquo-organic mixtures. Attempts have been made to understand the basicity and structuredness of di fferent aquo-ethers (D + H2O, THF + H2O and DME + H2O) from a comparative s tudy of Delta G(t)(0) (H+) profiles and excess relative permittivity Delta epsilon(r)(E)(X) profiles of the aquo-ethers. The order of basicity has bee n found to be THF + H2O > DME + H2O > D + H2O. DME has been found to be structureforming and D has been found to be struct ure breaking over the whole composition range (0-87 wt% of organic solvent) . But THF is slightly structure forming initially but structure breaking ab ove 40 wt%.