Experimental and computational thermochemical study of benzofuran, benzothiophene and indole derivatives

The standard enthalpies of formation of benzofuran-, indole-, and benzothiophene-2-carboxylic acids, and 2-acetylbenzofuran in the condensed phase were measured at T = 298.15 K from experimental determinations of their energies of combustion by isoperibolic calorimetry. The enthalpies, temperatures of melting, purities and heat capacities of the compounds were determined using differential scanning calorimetry. Using thermogravimetry the enthalpies of sublimation were obtained and subsequently, the standard enthalpies of formation in the gas-phase and at T = 298.15 K for the four compounds were derived. The results of this analysis were compared with the values obtained by the Gaussian-4 procedure using the atomization method. The computational results are in good agreement with the experimental values. The influence of the heteroatom (oxygen, nitrogen and sulfur) and acetyl or carboxyl groups on the standard enthalpy of formation is also discussed.