The solubility of ethionamide and structural analogues in buffer solutions, octanol and hexane at several temperatures

• Solubility of compounds in buffers, octanol and hexane was measured.
• Solubility in octanol is higher than in buffer solutions and hexane.
• Dissolution thermodynamic functions were calculated using the van’t Hoff equation.
• Solubilities are well predicted using partitioning coefficients and descriptors.

The solubility of antituberculosis drug ethionamide and structural analogues in buffer solutions, octanol and hexane within the temperature range from (293.15–313.15) K was measured using the shake-flack method. All the compounds studied appeared to have the solubility neither more than 10−3 mol fraction in aqueous solutions. At that the solubility in buffer pH 7.4 is lower than that in pH 2.0 which is determined by the ionization state. The solubility in octanol was estimated to be essentially higher than in hexane that is explained by the specific interactions of the compounds with the solvent. Thermodynamic solubility and solvation functions for the substances in the solvents studied were calculated. The partition coefficients of the compounds were measured in the octanol – buffer pH 7.4 system. The solubility values of the unionized molecular species of the investigated compounds using the partition coefficients and HYBOT descriptors for the biologically active substances were calculated. Comparison of the experimental and calculated solubility values showed the acceptability of the proposed approach for predicting the solubility of the compounds of aromatic thioamide series.

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