Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

This paper describes the application of thermogravimetry including conventional thermobalance and standard sample holders for the estimation of vapor pressure and related thermodynamic properties of a potent narcotic analgesic, fentanyl (CAS No. 437-38-7). For this study, benzoic acid was used as a reference material to calibrate the thermogravimetric analysis (TGA) instrument and experimental conditions used. The relationship between the isothermal sublimation rates of benzoic acid determined at different temperatures and the corresponding literature vapor pressure values was established, and the correlation equation thus obtained was used for the estimation of vapor pressure of fentanyl. By adopting this procedure, the vapor pressure of fentanyl was estimated at different temperatures from T ) (423.15 to 493.15) K. Extrapolation of the measured data to T ) 298.15 K gave the vapor pressure of subcooled fentanyl and estimated it to be (4.6 ( 2.7) * 10-6 Pa. The corresponding solid phase vapor pressure of fentanyl was calculated to be (5.9 ( 4.7) * 10-7 Pa after taking the enthalpy of fusion into consideration. Related thermodynamic properties, viz., enthaply of vaporization and normal boiling points, were also estimated from the vapor pressure-temperature curve.