Document Type : Research Paper
A series of nine Schiff bases were prepared by condensation of vanillin aldehyde and substituted anilines. The ionization constants of 3-methoxy-4-hydroxybenzaldeneaniline and its nitro, methyl and chlorine substitutions have been determined in a buffer solution medium by spectrometric titration method at 20 ̊C. The values of the ionization constants pKa1 and pKa2 were calculated for the protonation and deprotonation of the prepared Schiff bases, respectively. A Hammett relation was applied to show the effect of the substance group on the values of extracted ionization constants.