Phase equilibrium of the ternary system cadmium chloride + L-threonine + water at 298.15 K and standard molar enthalpy of formation of Cd(C 4H9NO3)Cl2·H2O

The equilibrium solubility of the ternary system cadmium chloride + L-threonine + water was determined at 298.15 K, and the corresponding equilibrium diagram was constructed. The ternary system is complicated with four equilibrium solid phases, CdCl2 center dot 2.5H(2)O, CdCl2 center dot H2O, Cd(C4H9NO3)Cl-2 center dot H2O, and C4H9NO3, of which a new compound of Cd(C4H9NO3)Cl-2 center dot H2O was found to be incongruently soluble in the system. The new compound obtained was identified and characterized by the methods of FT-IR, elementary analysis, powder X-ray diffraction, single X-ray diffraction, and thermogravimetric and differential thermal analysis. It belongs to the monoclinic system, space group P2(1)/, with a = 0.7672(4) nm, b = 0.9166(5) nm, c = 1.3787(7) nm, beta = 96.453(7)degrees, V = 0.9634(8) nm(3), Dc = 2.188 g.cm(-3), and Z = 2. The dissolution enthalpies of CdCl2, C4H9NO3, and Cd(C4H9NO3)Cl-2 center dot H2O in 2 mol.dm(-3) hydrochloric acid were measured by heat conduction microcalorimetry. By designing an appropriate thermochemical cycle according to Hess's law and through calculation, the reaction enthalpies of formation were found to be -(9.28 +/- 0.30) kJ.mol(-1) for L-threonine with cadmium chloride, and the standard molar enthalpies of formation were found to be -(1493.8 +/- 0.4) kJ.mol(-1) for Cd(C4H9NO3)Cl-2 center dot H2O.