Experimental study on the energetics of two indole derivatives: Standard molar enthalpies of formation of indole-2-carboxylic acid and indole-3-carboxaldehyde

The standard (p o = 0.1 MPa) molar energies of combustion, Δ c H m o, for indole-2-carboxylic acid and indole-3-carboxaldehyde, in the crystalline state, were determined, at T = 298.15 K, using a static bomb combustion calorimeter. For both compounds, the vapour pressures as function of temperature were measured, by the Knudsen effusion technique, and the standard molar enthalpies of sublimation, Δ cr g H m o, at T = 298.15 K, were derived by the Clausius-Clapeyron equation. From the experimental results, the standard (p o = 0.1 MPa) molar enthalpies of formation in the condensed and gaseous phases, at T = 298.15 K, of indole-2-carboxylic acid and indole-3-carboxaldehyde were derived. The results are analysed in terms of structural enthalpic increments. © 2013 Akadémiai Kiadó, Budapest, Hungary.