Spectrophotometric determination of the acidity dissociation constants of symmetric Schiff base derivatives

Abstract

In this study, the acidity constants of series symmetric Schiff base derivatives have been determined using the UV-visible spectrophotometric method at a temperature of 25(±0.1) °C. The deprotonated acidity constants (pKa) have been found to be associated with the deprotonation of phenolate oxygen. The first and the second protonated acidity constants (pKa1 and pKa2) have been found to cause the protonation of the imine nitrogen atom for all molecules. The deprotonated acidity constants (pKa) were found for molecules 5 (9.088), 8 (9.848), 6 (10.243), 2 (10.2569), 3 (10.297), 1 (10.587), 7 (10.692) and 4 (10.804). The first protonation (pKa1) was found for molecules 2 (3.432), 5 (4.207), 8 (4.612), 7 (4.758), 4 (4.995), 1 (5.288), 6 (5.606) and 3 (6.452). The second protonation (pKa2) was found for molecules 2 (-5.384), 8 (-5.165), 5 (-5.028), 7 (-4.775), 4 (-4.518), 1 (-4.111), 6 (-3.866) and 3 (-3.212).