Isothermal Thermogravimetric Study for Determining Sublimation Enthalpies of Some Hydroxyflavones

Abstract

The sublimation enthalpies of some hydroxyflavones and one amineflavone were determined with a thermogravimetric device under isothermal conditions. These enthalpies were obtained by measuring the rate of mass loss as a function of temperature. In this methodology, the Clausius–Clapeyron and Langmuir equations were used. The diffusional effect of the gas phase was included in the Langmuir equation. In order to test and validate the experimental methodology, the sublimation enthalpy of three standard materials, anthracene, pyrene, and benzoic acid, were determined. The values obtained are in agreement with the data reported and recommended in the literature. Low uncertainties were obtained in all thermogravimetric measurements. Additionally, by differential scanning calorimetry, the molar fraction, temperature and enthalpy of fusion, and heat capacity of the solid phase were determined for all of the compounds studied. The heat capacities of the gas phase were estimated using computational methods. Isothermal thermogravimetry was applied to study a family of flavones.