Phase Chemistry and Thermochemistry on Coordination Behavior of Zinc Chloride with Leucine

AbstractThe solubility property of the ZnCl2‐Leu‐H2O (Leu= L‐α‐leucine) system at 298.15 K in the whole concentration range was investigated by the semimicro‐phase equilibrium method. The corresponding solubility diagram and refractive index diagram were constructed. The results indicated that there was one complex formed in this system, namely, Zn(Leu)Cl2. The complex is congruently soluble in water. Based on phase equilibrium data, the complex was prepared. Its composition and properties were characterized by chemical analysis, elemental analysis, IR spectra, and TG‐DTG. The thermochemical properties of coordination reaction of zinc chloride with L‐α‐leucine were investigated by a microcalorimeter. The enthalpies of solution of L‐α‐leucine in water and its zinc complex at infinite dilution and the enthalpy change of solid‐liquid reaction were determined at 298.15 K. The enthalpy change of solid phase reaction and the standard enthalpy of formation of zinc complex were calculated. On the basis of experimental and calculated results, three thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), the rate constant and three kinetic parameters (the activation energy, the pre‐exponential constant and the reaction order) of the reaction, and the standard enthalpy of formation of Zn(Leu)2+ (aq) were obtained. The results showed that the title reaction took place easily at studied temperature.