PROTONATION CONSTANTS OF SOME PYRIDINE-DERIVATIVES IN ETHANOL-WATER MIXTURES

Protonation constants of a number of mono- and disubstituted pyridines were determined potentiometrically in 0, 10, 20, 30, 40, 50, 60, 70, 80% (v/v) ethanol-water mixtures at 25 degrees C with an ionic strengt h of 0.1 M. Data were calculated by a computer programme. The logarith m of the protonation constants of pyridines linearly decreased with in crease of ethanol contents but the values determined in water and 80% ethanol did not follow this linear trend. Furthermore, the effects of the substituents on the basicity of pyridine, the additivities of thes e effects and the applicability of the Hammett equation to the behavio ur of substituents are discussed.