Studies on the Coordination Reactions of Polyphenols and Vanadium (IV) Using pH-Potentiometry

Protonation constants of pyrocatechol, pyrogallol and gallic acid, and stability constants, thermodynamic properties of their complexes with tetravalent vanadium VO2+ have been calculated by using pH-potentiometry at different temperatures and ionic strength of 0.1mol•L-1NaCl. The results indicated protonation constants and stability constants decrease with increasing temperature. Higher temperature is unfavorable to the complexation reactions. This kind of reaction is exothermic reaction that was spontaneous. Compared with all thermodynamic properties, the enthalpy change is the driving force for the reaction.