Research Information System
Journal of Chemical and Engineering Data, vol.56, no.5, pp.2084-2089, 2011 (SCI-Expanded)
In this study the acidity constants of a series of biologically active pyridyl Schiff bases were calculated from UV-visible spectrophotometric data at (25 ± 0.1) °C. The first acidity constants (pKa1) of the 2-[2-aza-2-(4-methyl(2-pyridly))vinyl]phenol (1), 2-[2-aza-2-(4-methyl(2- pyridly))vinyl]-6-nitrophenol (2), 2-[2-aza-2-(4-methyl(2-pyridly))vinyl]-4- nitrophenol (3), 2-[2-aza-2-(4-methyl(2-pyridly))vinyl]-4,6-dinitrophenol (4), 2-[2-aza-2-(6-methyl(2-pyridly))vinyl]phenol (5), 2-[2-aza-2-(6-methyl(2- pyridly))vinyl]-6-nitrophenol (6), 2-[2-aza-2-(6-methyl(2-pyridly))vinyl]-4- nitrophenol (7), and 2-[2-aza-2-(6-methyl(2-pyridly))vinyl]-4,6-dinitrophenol (8) are found to be associated with the protonation of the phenolate oxygen. The second acidity constants (pKa2) are found to correspond to protonation of a pyridine nitrogen for molecules 5, 6, and 7 and oxoprotonation for molecules 1, 2, 3, 4, and 8. The third acidity constants (pKa3) are found to be associated with the protonation of a pyridine nitrogen for molecules 1, 3, 7, and 8 and amino protonation for molecules 2 and 5. For molecules 4 and 6, it is associated with oxo protonation. The contribution of the keto-amino tautomeric form was found to be considerably important. © 2011 American Chemical Society.