Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The energetic study of benzoxazole, 5-chloro-2-methylbenzoxazole, and 2-chlorobenzoxazole, in condensed and gaseous states, has been developed using experimental techniques and computational approaches. The values of the standard (p = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, of crystalline benzoxazole (36.0 +- 2.0) kJ mol 1 and 5-chloro-2-methylbenzoxazole (145.6 +- 2.2) kJ mol 1 and liquid 2-chlorobenzoxazole (52.5 +- 3.0) kJ mol 1 were determined from the corresponding experimental standard molar energy of combustion in oxygen, (3432.1 +- 1.7) kJ mol 1, (3883.0 2.0) kJ mol 1, and (3298.0 +- 2.8) kJ mol 1, respectively , measured by static or rotating-bomb combustion calorimetry. At T = 298.15 K, the standard (p = 0.1 MPa) molar enthalpy of sublimation of benzoxazole and 5-chloro-2-methylbenzoxazole and of vaporization of 2-chlorobenzoxazole, (69.2 +- 0.8) kJ mol 1, (82.4 +- 2.2) kJ mol 1, and (56.3 +- 1.6) kJ mol 1 respectively, were determined by a direct method, using the vacuum drop microcalorimetric technique. From the latter values and from the enthalpies of formation of the condensed compounds, the standard (p = 0.1 MPa) enthalpies of formation of the gaseous compounds have been calculated. Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several working reactions in order to derive the standard molar enthalpy of formation of the three compounds. There exists a good agreement between the experimental and the computational data.