Investigation on solid–liquid equilibrium behavior of 4-cyanobenzoic acid in fourteen mono-solvents: Determination, correlation, molecular simulation and thermodynamic analysis

Abstract

4-Cyanobenzoic acid (4-CyBZA) is an important pharmaceutical intermediate, and the research on solubility behavior of 4-CyBZA in organic solvents is very necessary for its crystallization and separation processes. Therefore, this study aimed at exploring dissolution behavior of 4-CyBZA in several pure solvents via experiment, calculation, and simulation process. In this study, mole-fraction solubility values of 4-CyBZA in fourteen common solvents including four low alcohols (methanol (MeOH), ethanol (EtOH), n-propanol (NPOH), n-butanol (NBOH)), four acetates (methyl acetate (MeAC), ethyl acetate (EtAC), n-propyl acetate (NPAC), n-butyl acetate (NBAC)), two alcohol ethers (2-ethoxyethanol (EGEE), 2-methoxyethanol (EGME)) as well as four common heteroatom/heterocyclic solvents (acetonitrile (MeCN), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), 1,4-dioxane (Diox)) were critically measured by using laser monitoring method from 278.15/288.15 K to 323.15 K under 100 kPa. Interestingly, experimental results indicated that an increase in temperature facilitated the dissolution of 4-CyBZA in selected 14 solvents. At the same time, the solubility curve underwent a crossover phenomenon. At 298.15 K, the common order of 4-CyBZA solubility was: DMF > EGME > EGEE > NMP > Diox > MeOH > MeAC > EtOH > EtAC > NPAC > NPOH > NBOH > NBAC > MeCN. The Hansen solubility parameter (HSP) was introduced to analyze solubility behavior via molecular similarity between 4-CyBZA and chosen solvents. Molecular modeling including Hirshfeld surface (HS) analysis and molecular electrostatic potential surface (MEPS) were employed to understand internal interactions within 4-CyBZA crystals. Moreover, solubility was fitted by Margules model, NRTL model, NRTL-SAC model, UNIQUAC model as well as a combined model (Jouyban model). Results showed that NRTL and NRTL-SAC model were more suitable for correlating 4-CyBZA solubility with absolute temperature. Furthermore, given the high accuracy of the NRTL model, dissolution thermodynamic characteristics of 4-CyBZA in chosen solvents were analyzed by NRTL model, which revealed that the dissolving process and mixing process were spontaneous and entropy-driven.