This work presents a method for the preparation of imine compounds including Schiff bases derived from vanillin with aniline, o-nitroaniline, o-tolidene and o-chloroaniline. Compounds' structures of the prepared compounds were confirmed by physical methods like melting point, infrared spectroscopy (IR), electronic spectroscopy (U.V), and nuclear magnetic resonance spectroscopy (NMR). The ionization constants of the imine nitrogen proton Ka1 and the phenol hydroxyl group proton Ka2 were determined using the spectrometric titration method at five temperatures including 293,298,303,308 and 313K in a buffer solution medium. The thermodynamic of ionization for imines confirm that ionization reactions in these imines are accompanied by an increase of parameters ∆Gº and ∆Hº. These mean that ionization reactions in these imines are non-spontaneous and endothermic respectively. ∆Sº values of ionization reactions estimated have a negative and a positive signs.