Solubility Measurement, Correlation, and Thermodynamic Study of trans-3-Hydroxycinnamic Acid in Nine Pure Solvents and (Ethanol + Ethyl Acetate) Cosolvent Mixtures at Temperatures from 293.15 to 333.15 K

The solubility of trans-3-hydroxycinnamic acid in pure solvents (methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, methyl acetate, ethyl acetate, and n-propyl acetate) and (ethanol + ethyl acetate) cosolvent mixtures was measured by the gravimetric method from 293.15 to 333.15 K in normal pressure. The experimental results show that the solubility of 3-HCA(E) in alcohol solvents is greater than in ester solvents, which conforms to “like dissolves like”. On this basis, the experimental result was correlated with semiempirical models (the modified Apelblat, van’t Hoff, λh, Jouyban–Acree–van’t Hoff equation, and combined model) and activity coefficient models (Wilson, NRTL, and UNIQUAC equation). The modified Apelblat model has the best correlation of the experimental data, with an ARD of less than 0.5% for pure solvents and cosolvent mixtures. The solvent effect was calculated by the KAT-LSER equation, showing that the hydrogen bond alkalinity of solvents–solutes (β) and the solvent self-association (δH) significantly influence the solubility of 3-HCA(E), accounting for 32.46 and 55.02%, respectively. Finally, the thermodynamic parameters (ΔHmix, ΔSmix, ΔGmix,%ξH, and %ξTS) were calculated. Negative values of both ΔHmix and ΔGmix indicate that the mixing process of 3-HCA(E) is exothermic and spontaneous. The Gibbs energy of the mixing process is jointly contributed by enthalpy and entropy.