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

Abstract

The standard (p°=0.1MPa) molar enthalpy of formation, in the crystalline phase, of N-acetyl-l-cysteine, NAC, at T=298.15K, 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=298.15K, 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.