Standard molar enthalpies of formation of 2-, 3-and 4-cyanobenzoic acids

The standard (p degrees = 0.1 MPa) molar enthalpies of formation of 2-, 3- and 4-cyanobenzoic acids were derived from their standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpies of sublimation of 2- and 3-cyanobenzoic acids. The standard molar enthalpies of formation of the three compounds, in the gaseous phase, at T = 298.15 K, have been derived from the corresponding standard molar enthalpies of formation in the condensed phase and standard molar enthalpies for phase transition. The results obtained are -(150.7 +/- 2.0) kJ . mol(-1),-(153.6 +/- 1.7) kJ . mol(-1) and -(157.1 +/- 1.4) kJ . mol(-1) for 2-cyano, 3-cyano and 4-cyanobenzoic acids. respectively. Standard molar enthalpies of formation were also estimated by employing two different methodologies: one based on the Cox scheme and the other one based on several different computational approaches. The calculated values show a good agreement with the experimental values obtained in this work. (C) 2008 Elsevier Ltd. All rights reserved.