Using a static analytical model, experimental solubility data were obtained for capsaicin in n-hexane, cyclohexane, carbon disulfide, butyl ether, and isopropyl ether at temperatures ranging from 278.15 to 323.15 K. The melting temperature and fusion enthalpy of capsaicin were measured using differential scanning calorimetry. The measured solubility data were well correlated by the van’t Hoff, modified Apelblat, λh (Buchowski), Wilson, and NRTL models, with the Wilson model showing the best agreement. The activity coefficients of capsaicin and the mixing Gibbs free energies, enthalpies, and entropies of the resulting solutions were predicted on the basis of the Wilson model parameters at measured solubility points. In addition, the infinite-dilution activity coefficients and excess enthalpies of capsaicin were estimated. Finally, the effects of solute–solvent intermolecular repulsive interactions on the solubility behavior and the values of mixing Gibbs free energy were discussed.

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The solubilities of ginsenoside compound K in pure solvents and binary mixture solvents were determined at several temperatures from 278.15 K to 318.15 K by a static analytical method. The experimental solubility data in pure solvents were correlated by the van’t Hoff plot, the modified Apelblat equation, the λh (Buchowski) equation, the Wilson model, and the NRTL model, with the Wilson model giving the best correlation results. Based on the Wilson model and experimental data, the mixing Gibbs free energies, enthalpies, and entropies of solutions and activity coefficients in pure solvents were predicted, and other thermodynamic properties (infinite-dilution activity coefficients and excess enthalpies) were calculated as well. In addition, the solubility was maximal at a certain water mole fraction in acetone + water mixture and acetonitrile + water mixture, whereas in a methanol + water system, the solubility decreases as the water concentration increases monotonically. The solubilities in mixture solvents were correlated by the solvent components using the Wilson model. The partial molar Gibbs free energies with negative values were obtained, which indicates the changing of the solubility.

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