3,4,5-Trimethoxycinnamic acid in aqueous co-solvent solutions of isopropanol/acetone/methanol/ethanol: Solubility, preferential solvation and intermolecular interactions

Abstract

Quantitative analysis of molecular surface was applied at the microscopic level to emphasize the electrostatic characteristics of acidity/basicity of 3,4,5-trimethoxycinnamic acid (TMCA). The primary sites of electrophilic and nucleophilic assault are the –C=O and >OH groups owing to global maximum and lowest electrostatic potentials of −155.5 kJmol−1 and +185.8 kJmol−1, respectively. Using the independent gradient model based on Hirshfeld partition analysis, the weak interactions between TMCA and solvent were visually inspected. The solubility of TMCA in four co-solvent blends, namely isopropanol + water, methanol + water, acetone + water and ethanol + water, was determined under 101.2 kPa by the isothermal shake-flask technique. As the temperature increased from 278.15 to 323.15 K, the TMCA solubility in neat methanol increased from 66.20 × 10−4 to 942.9 × 10−4; while in neat acetone, it increased from 175.1 × 10−4 to 555.1 × 10−4. Two solubility curves intersect at about 305.8 K. According to the research based on KAT- linear solvation energy relationships, the solvent–solvent interactions are mostly responsible for the solubility fluctuation. The relationship between solubility and experimental conditions was established using three models: the Jouyban–Acree model, the modified Wilson model, and the modified Jouyban–Acree-van't Hoff model, yielding the highest relative average deviation of 9.56 %. A technique based on inverse Kirkwood–Buff integrals was used to investigate the preferential solvation of TMCA at 298.15 K. The preferential solvation parameters of TMCA showed positive values in isopropanol/acetone/methanol/ethanol -medium and -rich compositions, indicating that isopropanol/acetone/methanol/ethanol preferentially solvated TMCA. Dissolution of TMCA in these aqueous cosolvent solutions was an endothermic process.