Sublimation and Vaporization Enthalpies of Niclosamide: Application of Transpiration Method and Thermogravimetric Analysis

The thermodynamic functions of sublimation and vaporization of the drug niclosamide were determined by several experimental methods. The vapor pressure of niclosamide was measured at different temperatures in the crystalline phase by the transpiration method. The drug sublimation standard molar enthalpy, entropy, and Gibbs free energy were derived from these data. The vaporization enthalpy was determined by thermogravimetric analysis. The fusion temperature and enthalpy of the compound were also measured. The enthalpies of sublimation, vaporization, and fusion were adjusted to the reference temperature using the heat capacity values experimentally obtained in this work. By combining the vaporization and fusion enthalpies obtained by thermogravimetry and differential scanning calorimetry, the standard molar enthalpy of sublimation was derived (166.7 ± 4.5) kJ·mol–1, which was 4% higher than the value determined by the transpiration method (160.3 ± 1.9) kJ·mol–1.