Determination of the solubility and thermodynamic properties of wedelolactone in a binary solvent of ethanol and water

Experimental solubility data of wedelolactone in a binary system of ethanol and water from 278.15 K to 323.15 K were measured using a thermostatted reactor by static method and HPLC analysis. The effects of binary solvents composition and temperature on the solubility were discussed and it was found that wedelolactone solubility in (water + ethanol) mixed solvents presented a monotonic effect in the studied region. The measured data were regressed by the modified Apelblat equation, Wilson model, nonrandom two-liquid (NRTL) model and the binary solvent (CNIBS)/Redlich–Kister model, and the maximum ∑(%D) values were 0.75, 1.90, 4.34 and 0.38, respectively. The correlation results showed that calculated values by the four models agree well with the experimental data. Using the experimentally measured solubility values, the thermodynamic properties of dissolution of the wedelolactone, including Gibbs energy change (ΔGd), molar enthalpy change (ΔHd) and molar entropy change (ΔSd) of dissolution, were calculated. The values of the standard molar Gibbs energy change and standard enthalpy molar change of solution were both positive, which indicated that the dissolution of wedelolactone in the binary system of ethanol and water was endothermic and no-spontaneous process.