Energetic Studies and Phase Diagram of Thioxanthene

• Tipo: Artigo em Revista Científica Internacional
• Data: 2009

Autores

Vera L S Freitas (Autor) Outra; Manuel J S Monte (Autor) FCUP; Luis M N B F Santos (Autor) FCUP; Jose R B Gomes (Autor) Outra; Maria D M C R Ribeiro da Silva (Autor) FCUP

Revista

Título: Journal of Physical Chemistry A

Vol. 113

Páginas: 12988-12994

ISSN: 1089-5639

Editora: American Chemical Society

Indexação

ISI Web of Knowledge - 36 Citações

Scopus - 37 Citações

Classificação Científica

FOS: Ciências exactas e naturais > Química

Outras Informações

ID Authenticus: P-003-EB2

DOI: 10.1021/jp906413y

Abstract (EN): The molecular stability of thioxanthene, a key species from which very important compounds with industrial relevance are derived, has been studied by a combination of several experimental techniques and computational approaches, The standard (p(o) = 0.1 MPa) molar enthalpy of formation of crystalline thioxanthene (117.4 +/- 4.1 kJ . mol(-1)) was determined from the experimental standard molar energy of combustion, in oxygen, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The enthalpy of sublimation was determined by a direct method, using the vacuum drop microcalorimetric technique, and also by an indirect method, using a static apparatus, where the vapor pressures at different temperatures were measured. The latter technique was used for both crystalline and undercooled liquid samples, and the phase diagram of thioxanthene near the triple point was obtained (triple point coordinates T = 402.71 K and p = 144.7 Pa). From the two methods, a mean value for the standard (p(o) = 0.1 MPa) molar enthalpy of sublimation, at T = 298.15 K (101.3 +/- 0.8 kJ . mol(-1)), was derived. From the latter value and from the enthalpy of formation of the solid, the standard (p(o) = 0.1 MPa) enthalpy of formation of gaseous thioxanthene was calculated as 218.7 +/- 4.2 kJ . mol(-1). Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several homodesmotic reactions in order to derive the standard molar enthalpy of formation of thioxanthene. The ab initio results are in excellent agreement with the experimental data.

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 7