title: Experimental and computational thermochemical study of 2-thiobarbituric acid: structure-energy relationship.
abstract: This paper reports an experimental and computational thermochemical study on 2-thiobarbituric acid (2-thioxodihydropyrimidine-4,6(1H,5H)-dione), [CAS 504-17-6]. The value of the standard (p(0) = 0.1 MPa) molar enthalpy of formation in the gas phase at T = 298.15 K has been determined. The energy of combustion was measured by bomb combustion calorimetry, using a rotatory bomb, and from the result obtained, the standard molar enthalpy of formation in the crystalline state at T = 298.15 K was calculated as -(396.8 ± 0.9) kJ·mol(-1). The enthalpy of sublimation was determined using a transference (transpiration) method in a saturated N(2) stream and a value of the enthalpy of sublimation at T = 298.15 K was derived as (118.3 ± 2.2) kJ·mol(-1). From these results a value of -(278.5 ± 2.4) kJ·mol(-1) for the gas-phase enthalpy of formation at T = 298.15 K was determined. Theoretical calculations at the G3 and G4 levels were performed, and a study of the molecular and electronic structure of the compound has been carried out. Calculated enthalpies of formation are in very good agreement with the experimental value.
authors.affiliation: Instituto de Química Física Rocasolano, CSIC, Serrano 119, 28006 Madrid, Spain.
authors.forename: Maria Victoria
authors.initials: MV
authors.lastname: Roux
authors.forename: Rafael
authors.initials: R
authors.lastname: Notario
authors.forename: Dzmitry H
authors.initials: DH
authors.lastname: Zaitsau
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Emel'yanenko
authors.forename: Sergey P
authors.initials: SP
authors.lastname: Verevkin