Solubility measurement and thermodynamic modelling of curcumin in twelve pure solvents and three binary solvents at different temperature (T = 278.15–323.15 K)

In the research, the solubility of curcumin was studied by static equilibrium method combined with HPLC. The solubility data of curcumin was measured in twelve pure solvents (dimethyl sulfoxide, tetrahydrofuran, acetone, ethyl acetate, isopropanol, acetonitrile, 1-butanol, ethanol, methanol, xylenes, n-hexane and n-heptane) and three binary solvent mixtures (acetone + tetrahydrofuran, acetonitrile + tetrahydrofuran and n-hexane + tetrahydrofuran) at different temperature (T = 278.15–323.15 K) under atmospheric pressure. The solubility values demonstrate that the solubility increased with the increase of temperature in all solvents. The modified Apelblat model and the Buchowski-Ksiazczak λh model were used to fitted the solubility data in pure solvents, the combined nearly ideal binary solvent/ Redlich-Kister (CNIBS/R-K) model and the Jouyban-Acree model were employed to adopt the solubility data in binary solvent mixtures. The RAD_max of the modified Apelblat model and the λh model are 2.621% and 5.831%, the RMSD_max are 6.9 × 10^-4 and 1.62 × 10^-3, respectively. The RAD_max of the CNIBS/R-K model and the Jouyban-Acree model are 2.249% and 4.901%, the RMSD_max are 9.33 × 10^-3 and 3.67 × 10^-3. Meanwhile, the KAT-LSER model was used to explore the effect of the solvation of curcumin. The fitting results of all equations prove the accuracy of the experimental data, these solubility data are very important for optimizing the extraction process and recrystallization of curcumin.