3-formylchromones: Vapor pressures and standard molar enthalpies, entropies and Gibbs energy of sublimation

Abstract

In present work, the estimation of vapor pressures of 3-formylchromone and 3-formyl-6-methylchromone by the isothermal thermogravimetry method is presented. Briefly, this method consists of measuring the rate of mass loss as a function of temperature in a cylindrical cell and with a flow of nitrogen. To derive the vapor pressure, the Langmuir equation was used, from which the vaporization constant was calculated using anthracene as a calibrating compound. Subsequently, the vapor pressures 3-fromylchromone and 3-formyl-6-methylchromone were estimated. From the vapor pressure, the enthalpy of sublimation was calculated using the Clausius-Clapeyron equation for each compound at its mean sublimation temperature. Finally, the enthalpy of sublimation was calculated at T = 298.15 K. The entropy and Gibbs energy of sublimation at the same temperature were determined. In order to test the validity of the method, the vapor pressures of phenanthrene and pyrene were calculated. The values obtained by isothermal thermogravimetry agree with those reported by other techniques.