Physico-chemical studies of the complexes of Hippuric acid with Cu(II), Ni(II), Zn(II), and Pb(II) ions in ethanol-water mixed solvent system

Potentiometric titrations have been used to calculate the dissociation constants of Hippuric acid and its stability constants with Cu(II), Ni(II), Zn(II), and Pb(II) ions in ethanol-water mixed solvent system at different temperatures, and constant ionic strength of 0.1M solution sodium nitrate. The order of the stability constants of metal complexes at 298 K with respect to ligand was found to be Cu(II) > Pb(II) > Zn(II) > Ni(II). Effect of temperature on stability of hippuric acid complexes with Cu(II) and Pb(II) has been studied in order to calculate the Gibb`s free energy and enthalpy of the complex formation reaction, the results showed that coordination process is spontanous and exothermic. Effect of solvent ratio has been studied only for Cu(II) complex and the dissociation of hippuric acid at given added different ratios decreases on the following order 75% > 50%.