Energetic Studies and Phase Diagram of Thioxanthene

• Type: Article in International Scientific Journal
• Date: 2009

Authors

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

Journal

Title: Journal of Physical Chemistry A

Vol. 113

Pages: 12988-12994

ISSN: 1089-5639

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 36 Citations

Scopus - 37 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: 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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 7