Experimental thermochemical study of aryl nitriles: A structural energetic approach

The present work comprised a study of the thermochemical properties of three aryl nitriles: Methyl p-cyanobenzoate, p-Acetylbenzonitrile, and p-Methoxybenzonitrile. This study was carried out using calorimetric and thermal analysis techniques. Through differential scanning calorimetry, we obtained the temperatures and enthalpies of fusion, as well as the heat capacities in the crystal phase. Specific combustion energies were determined through static bomb combustion calorimetry, from which, the enthalpies of formation in the condensed phase were derived. Additionally, isothermal thermogravimetry was used to measure the mass loss rate as a function of temperature. Using the Langmuir equation in conjunction with benzoic acid as a calibration material, vapor pressures were determined as a function of temperature. With the obtained vapor pressures and the Clausius-Clapeyron equation, enthalpies of sublimation were calculated. Moreover, entropies and Gibbs sublimation energies were determined at T = 298.15 K. Finally, using these properties, enthalpies of formation in the gaseous phase at T = 298.15 K were calculated for the three mentioned compounds. With these data, an analysis of the energetic effect of different substituents in benzonitrile is presented.