Solubility of 2-Hydroxybenzoic Acid in Pseudo-Binary Mixtures of Choline Chloride/Propylene Glycol Deep Eutectic Solvent + Water at 293.15–313.15 K

Abstract

The equilibrium molar solubility of 2-hydroxybenzoic acid (salicylic acid, SA) in pseudo-binary mixed solvents of choline chloride/propylene glycol deep eutectic solvent (ChCl/PG DES, 1:3 molar ratio) and water was determined by a shake flask method at 293.15-313.15 K and ambient pressure (85 kPa). Based on the results, the maximum solubility of SA was observed in neat DES at 313.15 K (0.7604 mol·L⁻¹) whereas it was minimum in neat water at 293.15 K (0.0112 mol·L⁻¹). X-Ray power diffraction analysis of solid phase presented no polymorphic transformation or solvate formation in the experiments. Moreover, the molar solubility of SA was modeled mathematically with various cosolvency models attaining the average percentage deviations smaller than 6.1%, except for the modified Wilson-van’t Hoff (12.6%). Further, more favorable and entropy-driven of SA dissolution in ChCl/PG DES-rich mixtures was achieved from the apparent thermodynamic analysis.