Solubility products of calcium isosaccharinate and calcium gloconate

The solubility products of the calcium salts of two polyhydroxy ligands (PHL), isosaccharinate (ISA) and gluconate (GLUC), were measured. Solubility products of log Ks.o=-6.22±0.03 at I=O and T=20±1 deg. C for Ca(α-ISA)2, and log Ks.o=-3.54±0.06 at I=0 and T=20±1 deg. C for Ca(GLUC)2 were calculated ignoring the complexation equilibrium: Ca2+ + PHL-↔CaPHL+. If this complexation reaction is taken into account with log K1 deg. = 1.7, the values of the solubility products are log Ks.o = -6.53±0.02 at I=0 for CA(α-ISA)2 and log Ks.o = -4.19±0.05 at I=0 for Ca(GLUC)2. Both dissolution reactions are endothermic. The standard free enthalpy change (ΔΗ deg.) for Ca(α-ISA)2 is 40±1 kJ mol-1 and 37±4 kJ mol-1 for Ca(GLUC)2. The enthalpy was assumed to be constant in the temperature range 7<T<90 deg. C. The calculated standard entropy change (ΔS deg.) is 17±5 J mol-1 for CA(α-ISA)2 and 60±14 J mol-1 K-1 for Ca(GLUC)2. (au)