Sublimation enthalpies of organic compounds by isothermal thermogravimetry

Abstract

AbstractAn improved method has been developed to determine the sublimation enthalpies of solid organic compounds using thermogravimetric analysis and applying an isothermal methodology with a TA Instruments® SDTQ600 equipment. This was achieved by measuring the rate of mass loss as a function of the temperature from isothermal experiments in an interval of temperature of 10 to 20 K below the melting temperature of the sample. The resulting rates of mass loss were used by applying the Pieterse and Focke equation, then combined with the integrated Clausius–Clapeyron equation to calculate the heat of sublimation at the experimental temperature and it was corrected to T = 298.15 K. In order to demonstrate the reliability of this methodology, the results for benzoic acid, pyrene and phenanthrene are presented, which are respectively primary, secondary, and tertiary reference compounds in the measurement of enthalpies of sublimation, along with the sublimation enthalpies of picolinic acid, nicotinic acid and isonicotinic acid which are three pyridinecarboxylic acids isomers with the carboxyl group in the ortho, meta and para position, respectively, to the nitrogen of the pyridine.