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

A series of ten Schiff bases were synthesized by condensation of salicylaldehyde and substituted anilines. The acid dissociation constants (K-a) 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 degrees C. The calculated acidity constants, pK(a) 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. (C) 2014 King Saud University. Production and hosting by Elsevier B.V.