Solution thermodynamics of S-ibuprofen n-octyl-d-glucamine salt in ethanol + water cosolvent mixtures

The solubility of S-ibuprofen n-octyl-d-glucamine salt (SIOGS) in ethanol + water cosolvent mixtures were determined from 293.15 to 323.15 K at atmospheric pressure. The thermodynamics functions of solution and mixing of SIOGS, such as the Gibbs energy, enthalpy, and entropy were calculated from the solubility data using Gibbs and van’t Hoff equations. The solubility reached maximum when the mole faction of ethanol was 0.6 to 0.8 at different temperatures and was very low in pure water at the whole range of the temperatures studied. This behavior showed that the cosolvent effect existed in this system. By enthalpy–entropy compensation analysis, a nonlinear plot between Δ H soln o and Δ G soln o was obtained, whose slope was negative when in the mole fraction of ethanol was from 0.00 to 0.35, positive from 0.35 up to 0.7 and negative when higher than 0.7.