Determination of acid dissociation constants of some substituted salicylideneanilines by spectroscopy. Application of the Hammett relation

AbstractA series of ten Schiff bases were synthesized by condensation of salicylaldehyde and substituted anilines. The acid dissociation constants (Ka) of salicylideneaniline and methyl- , chloro- and nitro-substituted salicylideneanilines have been determined in ethanol–water and dioxan–water binary mixtures (60% (v/v)) by a spectrophotometric (UV–Vis) method at constant ionic strength and at 25°C. The calculated acidity constants, pKa values were evaluated in protonation–deprotonation mechanism. In order to investigate the effects of substituent on the acidity of hydroxy Schiff bases; the applicability of the Hammett equation to the results in two systems of solvent was discussed