Experimental and computational study on the energetics of N-acetyl-L-cysteine

The standard (p(degrees) = 0.1 MPa) molar enthalpy of formation, in the crystalline phase, of N-acetyl-L-cysteine, NAC, at T = 298.15 K, was derived from the standard molar energy of combustion in oxygen, measured by static bomb combustion calorimetry. A value of -(737.8 +/- 1.9) kJ . mol (1) was obtained. For this compound, the standard molar enthalpy of sublimation, at T = 298.15 K, could not be determined due to the decomposition of the compound during the corresponding experiments. A theoretical study at the G3 and G4 levels has been carried out, and a value of -(610.7 +/- 4.0) kJ . mol (1) is recommend for the enthalpy of formation in the gas phase. Using this theoretical value and the experimental enthalpy of formation in the crystalline phase, it is possible to estimate a value of (127.1 +/- 4.4) kJ . mol (1) for the enthalpy of sublimation of this compound. (C) 2013 Elsevier Ltd. All rights reserved.