Determination and correlation of solubility of spironolactone form II in pure solvents and binary solvent mixtures

• The solubility data of spironolactone form II in pure solvents and binary solvent mixtures were determined.
• The experimental solubility data in pure solvents were correlated by three models.
• The experimental solubility data in binary solvent mixtures were correlated by two models.
• The dissolution thermodynamic properties of spironolactone form II were obtained.

The solubility data of spironolactone form II in six pure solvents and binary solvent mixtures of ethyl acetate and methanol were measured over the temperature range from (278.85 to 317.75) K by using a dynamic method under atmospheric pressure. The results show that the solubility of spironolactone form II in pure solvents increases with increasing temperature while the solubility in binary solvent mixtures increases with the increasing of the fraction of ethyl acetate. This phenomenon is well explained by using relative dielectric constants of the solvents. The solubility data of spironolactone form II in pure solvents were well correlated by the modified Apelblat equation, the Wilson model and the NRTL model while the solubility of spironolactone form II in binary solvent mixtures were correlated by the modified Apelblat equation and the CNIBS/R-K model. Furthermore, the thermodynamic properties of the dissolution process of spironolactone form II were also determined by using the van’t Hoff equation.

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