Structural studies of cyclic ureas: 3. Enthalpy of formation of barbital

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

Authors

Maria das Dores C R Ribeiro da Silva (Author) FCUP; Manuel A V R Ribeiro da Silva (Author) FCUP; Vera L S Freitas (Author) Other; Maria Victoria Roux (Author) Other; Pilar Jimenez (Author) Other; Manuel Temprado (Author) Other; Juan Z Davalos (Author) Other; Pilar Cabildo (Author) Other; Rosa M Claramunt (Author) Other; Jose Elguero (Author) Other

Journal

Title: Journal of Chemical Thermodynamics

Vol. 41

Pages: 1400-1407

ISSN: 0021-9614

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 19 Citations

Scopus - 20 Citations

Scientific classification

FOS: Engineering and technology > Mechanical engineering

Other information

Authenticus ID: P-003-E0H

DOI: 10.1016/j.jct.2009.06.018

Abstract (EN): A thermochemical and thermophysical study has been carried out for crystalline barbital [5,5'-diethyl-barbituric acid]. The thermochemical study was made by static bomb combustion calorimetry, from which the standard (p degrees = 0.1 MPa) molar enthalpy of formation of the crystalline barbital, at T = 298.15 K, was derived as -(753.0 +/- 1.8) kJ . mol(-1). The thermophysical study was made by differential scanning calorimetry over the temperature interval (265 to 470) K. A solid-solid phase transition was found at T = 413.3 K. The vapour pressures of the crystalline barbital were measured at several temperatures between T = (355 and 377) K, by the Knudsen mass-loss effusion technique, from which the standard molar enthalpy of sublimation, at T = 298.15 K was derived as (117.3 +/- 0.6) kJ . mol(-1). The combination of the experimental results yielded the standard molar enthalpy of formation of barbital in the gaseous phase, at T = 298.15 K, as -(635.8 +/- 1.9) kJ . mol(-1). This value is compared and discussed with our theoretical calculations by several methods (Gaussian-n theories G2 and G3, complete basis set CBS-QB3, density functional B3P86 and B3LYP) by means of atomization and isodesmic reaction schemes.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 8