Physico-chemical characterization antituberculosis thioacetazone: Vapor pressure, solubility and lipophilicity

- Vapor pressures of antituberculosis thioacetazone were determined by transpiration method.
- Solubilities of the TAZ in four modeling solvents were measured at different temperatures.
- Temperature dependence of octanol/buffer pH 7.4 partition coefficients was obtained.
- Thermodynamics parameters of solubility, sublimation, solvation and transfer were calculated.

Vapor pressure of thioacetazone (TAZ) has been determined in the temperature range of 404.15-429.15 K by the transpiration method. The obtained data were used to calculate the standard molar enthalpy of sublimation that was found to be 164.1 kJ/mol at T = 298.15 K. The drug solubility was measured at seven temperatures from 288.15 to 318.15 K in modeling solvents: octanol, hexane and aqueous buffers pH 2.0 and 7.4 by the saturation shake-flask method by using spectrophotometric analysis. It has been found that TAZ has poor solubility in hexane and buffer solutions and limited solubility in octanol. The experimental data were well correlated by van't Hoff and modified Apelblat equations. A temperature dependence of TAZ partition coefficient in the octanol/buffer pH 7.4 system has been derived. The partition coefficient value in this system (logP = 1.82) refers to the optimal interval for oral absorption drugs. The thermodynamic parameters of sublimation, solubility, solvation and transfer have been determined based on experimental data. The dominant effect of enthalpy and entropy contributions to the Gibbs energy of the investigated processes has been revealed.