Solubility Measurement, Data Correlation, and Solvent Effect of 4-Methoxycinnamic Acid in Pure Solvents and in Three Binary Solvent Mixtures from 293.15 to 333.15 K

4-Methoxycinnamic acid (P-MAC) is an important pharmaceutical intermediate. Investigating the solubility of P-MAC in organic solvents is crucial to understanding its crystallization and separation processes. This study employed the gravimetric method to determine the solubility of P-MAC in ten pure solvents (methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, methyl acetate, ethyl acetate, propyl acetate, and dimethylformamide (DMF)) and three binary solvent mixtures (ethanol and ethyl acetate, ethanol and n-propanol, and ethyl acetate and propyl acetate) at temperatures ranging from 293.15 to 333.15 K under atmospheric pressure. The solubility of P-MAC was found to increase with the temperature in all pure and binary solvent systems investigated. P-MAC was observed to be more soluble in aprotic solvents than in protic ones. Furthermore, a correlation analysis of solubility data using various thermodynamic models revealed that the Yaws equation exhibited the best correlation with the experimental data in pure solvent systems. In binary solvent mixtures, the Jouyban-Acree-Van’t Hoff equation had the best correlation with experimental data. Analysis based on the KAT-LSER model indicated that π* and δH significantly influence the dissolution process. The thermodynamic properties of the mixture (ΔGmix, ΔHmix, and ΔSmix) indicate that the mixing process of P-MAC is endothermic, spontaneous, and driven by entropy.