Solubility Behavior, Solvent Effect, and Data Correlation of 3,4-Dimethoxycinnamic Acid in 12 Pure Solvents at Multiple Temperatures

Abstract

3,4-Dimethoxycinnamic acid (DMCA) is a crucial pharmaceutical intermediate, and the research on the solubility behavior of DMCA in organic solvents is necessary for processes of crystallization and separation. The solid–liquid equilibrium data of DMCA in 12 pure solvents (methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, acetone, 2-butanone, acetonitrile, methyl acetate, ethyl acetate, and 1,4-dioxane) ranging from 283.15 to 323.15 K were measured by the static gravimetric method. Its solubility in all studied solvents increases with an increase of temperature. Besides, solubility behavior is primarily determined by solvent polarity [E_T(30)], hydrogen bonding, and cohesive energy density. Hirshfeld surface analysis and molecular electrostatic potential surface were applied to obtain visual analysis of the crystal structure and the overall charge distribution. What is more, five solubility fitting models were used to correlate the experimental mole fraction solubility data, including the modified Apelblat model, the λh equation, the non-random two liquid (NRTL) model, the Wilson model, and the UNIQUAC model. Furthermore, the NRTL model was utilized to calculate the mixing thermodynamic characteristics of DMCA in these solvents. The results indicated that the mixing process was entropy-driven and spontaneous.