Solubility measurement and thermodynamic correlation of (2,4-dichlorophenoxy)acetic acid in fifteen pure solvents

Abstract The solid-liquid equilibrium behavior of (2,4-dichlorophenoxy)acetic acid (2,4-D) was investigated. The solubility of 2,4-D in fifteen pure solvents were measured using the gravimetric method from 278.15 K to 323.15 K. The Hirshfeld surface analysis provided quantitative information about intermolecular interactions in 2,4-D crystal structure. The MEPs analysis showed that the carboxyl group of 2,4-D molecule was the main site for hydrogen bond formation. Besides, four thermodynamic models including the modified Apelblat equation, van’t Hoff equation, λh equation, and NRTL model were used to correlate the solubility data, and the results showed that the modified Apelblat equation has the best fitting. The calculation results of thermodynamic properties such as mixing enthalpy, mixing entropy and mixing Gibbs free energy showed that the dissolution process of 2,4-D was spontaneous. KAT-LSER model was used to investigate the solvent effect. The results revealed that solvent-solvent interaction had a significant unfavorable effect to the solubility of 2,4-D. Finally, solvation free energy analysis was performed to quantitatively explain the differences in solubility of 2,4-D in different solvents.