Ana L. R. Silva, Á. Cimas, M. D. R. D. Silva
Feb 1, 2013
Citations
0
Influential Citations
18
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Journal
The Journal of Chemical Thermodynamics
Abstract
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.