Sublimation and vaporisation processes of S(−) efaroxan hydrochloride

Thermogravimetric analysis was used to study the sublimation and vaporisation processes of S(−) efaroxan hydrochloride, a potent and highly selective α-2-adrenoreceptor antagonist. The kinetic parameters of the sublimation were investigated by conventional, isothermal thermogravimetric analysis (TGA) and modulated TGA (MTGA). The physico-chemical characterisation of the sublimate was determined by HPLC, elemental analysis, and DSC FTIR spectroscopy. Sublimation followed a zero-order mechanism and the activation energy and pre-exponential factor were calculated. The sublimation and vaporisation enthalpies were evaluated and used to determine the melting enthalpy, which was seen to be consistent with DSC data. The solubility parameter, which can be used to predict the miscibility of a drug in a polymer, was calculated from vaporisation enthalpy and crystallographic data. Finally, the Langmuir equation was used to construct the diagram of the sublimation process, p=f(T). The data were fitted using the Antoine equation by a least squares method.