Thermochemical and Theoretical Studies of 2-Hydroxyquinoxaline,2,3-Dihydroxyquinoxaline,and 2-Hydroxy-3-methylquinoxaline

摘要

The standard (p deg = 0.1 MPa) molar enthalpies of formation for crystalline 2-hydroxyquinoxaline,2,3-dihydroxyquinoxaline,and 2-hydroxy-3-methylquinoxaline were derived from the standard molar enthalpies of combustion,in oxygen,at T = 298.15 K,measured by static bomb combustion calorimetry.The standard molar enthalpies of sublimation,at T = 298.15 K,of the three compounds were measured by Calvet microcalorimetry.The derived standard molar enthalpies of formation in the gaseous phase are 45.9 +- 4.3 kJ centre dot mol~(-1) for 2-hydroxyquinoxaline, -(179.2 +- 5.3) kJ centre dot mol~(-1) for 2,3-dihydroxyquinoxaline,and -(8.8 +- 4.9) kJ centre dot mol~(-1) for 2-hydroxy-3-methylquinoxaline.In addition,theoretical calculations using the density functional theory and the B3LYP/6-311G~(**) hydrid exchange-correlation energy functional were performed for these molecules in order to most stable geometries and to access their relative stability.The theoretical results are in general good agreement with experimental findings.