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

AuthorsRibeiro da Silva, M. D. M. C.; Ribeiro da Silva, M. A. V.; Freitas, V. L. S.; Roux, María Victoria ; Jiménez, P.; Temprado, Manuel ; Dávalos, J.Z. ; Cabildo, Pilar; Claramunt, Rosa M.; Elguero, José
Issue Date2009
PublisherAcademic Press
CitationJournal of Chemical Thermodynamics 41: 1400- 1407 (2009)
AbstractA thermochemical and thermophysical study has been carried out for crystalline barbital [5,5′-diethylbarbituric acid]. The thermochemical study was made by static bomb combustion calorimetry, from which the standard (p{ring operator} = 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. © 2009 Elsevier Ltd. All rights reserved.
Identifiersdoi: 10.1016/j.jct.2009.06.018
issn: 0021-9614
Appears in Collections:(IQM) Artículos
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