Solubility products of calcium isosaccharinate and calcium gluconate

The solubility products of the calcium salts of two polyhydroxy ligands (PB L), isosaccharinate (ISA) and gluconate (GLUC), were measured. Solubility p roducts of log K-delta,K-O = -6.22+/-0.03 at I = 0 and T = 20+/-1 degrees C for Ca(alpha-ISA)(2), and log K-S,K-O = -3.54+/-0.06 at I = 0 and T = 20+/ -1 degrees C for Ca(GLUC)(2) were calculated ignoring the complexation equi librium: Ca2+ + PHL- reversible arrow CaPHL+. If this complexation reaction is taken into account with log K-1(0) = 1.7, the values of the solubility products are log K-S,K-O = -6.53+/-0.02 at I = 0 For Ca(alpha-ISA)(2) and l og K-S,K-O = -4.19+/-0.05 at I = 0 for Ca(GLUC)(2). Both dissolution reacti ons are endothermic. The standard free enthalpy change (Delta H degrees) fo r Ca(alpha-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 degrees C. The calculated standard entropy change (Delta S degrees) is 17+/-5 J mol(-1) K-1 for Ca(alpha-ISA)(2) and 60+/-14 J mol(-1) K-1 for Ca (GLUC)(2).