Temperature-Dependent Solubility of Cholic Acid and Deoxycholic Acid in Ten Pure Solvents at Temperatures from 283.15 to 333.15 K: Experimental Measurement, Model Correlation, and Thermodynamic Analysis

Abstract

Cholic acid (CA) and deoxycholic acid (DCA) are natural bioactive compounds found in animal bile. In this study, the equilibrium solubility of CA and DCA was measured in ten organic solvents (esters, alcohols, ketones, and furfural), using a static method from 283.15 to 333.15 K. The results demonstrated that the solubility of both CA and DCA increased with rising temperature. At a given temperature, CA exhibited a solubility lower than that of DCA in esters; conversely, CA was more soluble than DCA in the other solvents studied. Experimental data were correlated with four models: the modified Apelblat equation, the Buchowski–Ksiazaczak λh equation, the Wilson model, and the nonrandom two-liquid (NRTL) model. The influence of solvent properties on solubility was further examined using the Kamlet–Abboud–Taft Linear Solvation Energy Relationship (KAT–LSER) equation, revealing that solvent hydrogen-bond basicity (β) and polarizability/dipolarity (π*) significantly affect solubility. Additionally, thermodynamic parameters (Δ_disH⁰, Δ_disS⁰, Δ_disG⁰, %ζ_H, and %ζ_TS) for the dissolution of both compounds were determined. Positive values for Δ_disH⁰ and Δ_disG⁰ confirm that the dissolution processes are endothermic and nonspontaneous. Overall, this study provides valuable guidance for solvent selection in the separation and purification of bile acids and enriches the solubility database.