Potentiometric and Thermodynamic Studies of Vanillin and Its Metal Complexes

Abstract

The proton−ligand dissociation constant of vanillin (4-hydroxy-3-methoxy benzaldehyde) and metal−ligand stability constants of its complexes with metal ions (Mn2+, Co2+, Ni2+, Cu2+, and Zn2+) have been determined potentiometrically in 0.1 mol·dm−3 KCl and 10 % (by volume) ethanol−water mixture and at (298, 308, and 318) K. The stability constants of the formed complexes increase in the order Mn2+, Co2+, Ni2+, Zn2+, and Cu2+. The effect of temperature was studied, and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were derived and discussed. The dissociation process is nonspontaneous, endothermic, and entropically unfavorable. The formation of the metal complexes has been found to be spontaneous, endothermic, and entropically favorable.