Solubility determination, model evaluation and solution thermodynamics of isovanillin in 15 pure solvents and 4 binary solvents

Abstract

Researches on the basic solubility data and the physicochemical parameters of isovanillin are scarce in literature. In this paper, the solubility data, dissolution thermodynamic properties of isovanillin in 15 organic pure solvents (methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, methyl acetate, ethyl acetate, isobutyl acetate, formic acid, acetic acid, propionic acid, acetone, xylene and diethyl ether) and 4 binary solvents (ethanol + water, iso-propanol + water acetic acid + water, propionic acid + water) were determined at T = 278.15 to 318.15 K and T = 283.15 to 315.15 K, respectively, and reported for the first time. Three classic models were employed to correlate the experimental solubility, including an empirical equation and two thermodynamics-based models of Apelblat model and λh model. The models used were further evaluated by root mean square deviation (RMSD). Results show that the solubility of isovanillin presents a strong dependency on solution temperature and the polarity of solvents used. It shows high solubility in strong polar solvents such as formic acid, methanol and acetone, while low in less polar solvents such as xylene, diethyl ether. In the investigated binary solvents, a significant co-solvency phenomenon is observed, and the increase in solubility is found to do with the polarity of good solvent used in this study. RMSD value suggests that all the models used perform good correlation. Furthermore, the single crystal structure of isovanillin was solved and reported for the first time. Besides, the melting point and the fusion entropy of isovanillin were determined by DSC, and the thermodynamic properties of isovanillin dissolution process including ΔsolG, ΔsolH and ΔsolS were calculated by Van’t Hoff equation. Results indicate that the dissolution process of isovanillin is an endothermic, nonspontaneous entropy-driven process.