Solubility determination and thermodynamic characterization of orotic acid in twelve pure solvents and four binary mixed solvents

This research reports the solubility and thermodynamic characterization of orotic acid (OA) when it reaches solid–liquid equilibrium in twelve pure solvents and four binary solvents. Solubility determinations were determined by HPLC in the temperature range of T = 278.15–323.15 K (DMSO at 293.15–323.15 K). The results exhibit that in pure solvents, the solubility order of OA is DMSO > DMF > THF > methanol > water > n-propanol > isopropanol > n-butanol > ethanol > acetone > methyl acetate > ethyl acetate. The solubility order in four binary solvents is DMF + ethyl acetate > THF + ethyl acetate > methanol + ethyl acetate > n-propanol + ethyl acetate. According to the solubility data, it can be found that the solubility of OA in the selected pure solvents is positively correlated with temperature. As the temperature gradually rises to 323.15 K, the mole fraction solubility of OA also reaches the maximum. In binary solvents, in addition to the influence of temperature, the increase in the mole fraction of DMF, THF, methanol and n-propanol also promote the dissolution of OA. The properties of the solute and the solvent were combined, the KAT-LSER model was used to investigate the solvation effect of OA in the dissolution process. According to the results, the solubility of OA mainly depends on the ability to accept the hydrogen bond of investigated solvents, and the proportion of the total solvent effect of it is 21.99%. Through the fitting analysis of five thermodynamic models (λh model, modified Apelblat model, CNIBS/R-K model, Jouyban-Acree model and SUN model), the maximum RAD and RMSD are 0.3082 and 0.2272, respectively, indicating that the experimental data is highly correlated with five models.