ACID-BASE EQUILIBRIA OF SOME PYRIDINOL DERIVATIVES IN BINARY WATER-ORGANIC SOLVENT SYSTEMS

pK(a) values of 2-hydroxy 3-pyridinol (HHP), 2-mercapto 3-pyridinol (M HP), and 2-carboxy-3-pyridinol (CHP) were determined by potentiometric titration in water/organic solvent mixtures containing 20 mole% of or ganic solvent at 25 +/- 0.1 degrees C and 0.1 M ionic strength (KNO3) applying an empirical pH correction for mixed aqueous solvents. The in fluence of the organic solvents on the dissociation constants and taut omeric equilibria of the pyridinol derivatives is discussed. The effec t of the molecular structure of the compounds on pK(a) is also explain ed. Titrations of a mixture of two weak diprotic acids (HHP and CHP) i n a water/dimethylsulphoxide medium containing 20 mole% organic solven t at constant ionic strength were evaluated using the Gran method.