ANALYTICA CHIMICA ACTA, cilt.294, sa.2, ss.215-220, 1994 (SCI-Expanded)
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 strength of 0.1 M. Data were calculated by a computer programme. The logarithm of the protonation constants of pyridines linearly decreased with increase 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 these effects and the applicability of the Hammett equation to the behaviour of substituents are discussed.