Evaluation of acidity constants and preferential solvation in tetrahydrofuran-water mixtures

Dissociation constant values for reference materials were determined in tet rahydrofuran-water (THF-water) mixtures containing 0, 10, 20, 30, 40, 50, 6 0, 70 and 100% (w/w) THF. The values obtained were: pK(1) and pK(2) for pht halic acid; pK(1), pK(2) and pK(3) for citric acid; pK(a) for acetic and bo ric acids. In order to explain the variation of the pK values obtained over the whole composition range studied, the quasi-lattice quasi chemical (QLQ C) theory of preferential solvation was applied. The results are discussed in terms of average macroscopic properties of the mixed solvent and in term s of the solvation shells around the solute in order to identify the solven t characteristics affecting the pK(a) values. Thus, the methodology of line ar solvation energy relationships (LSER) was used to relate pK(a) values wi th solvatochromic parameters of THF-water mixtures. The equations obtained allow calculation of the pK(a) values of substances in the widely used THF- water mixtures. (C) 1999 Elsevier Science Ltd. All rights reserved.