Thermochemistry of 1,3-diethylbarbituric and 1,3-diethyl-2-thiobarbituric acids: Experimental and computational study
Notario, R.[Rafael], Roux, M. V.[MarIa Victoria], Ros, F.[Francisco], Emel'yanenko, V. N.[Vladimir N.], Zaitsau, D. H.[Dzmitry H.], Verevkin, S. P.[Sergey P.]
This paper reports an experimental and computational thermochemical study on two barbituric acid derivatives, viz. 1,3-diethylbarbituric acid and 1,3-diethyl-2-thiobarbituric acid. Values of standard molar enthalpies of formation in the gas phase at T = 298.15 K have been derived from experiment. Energies of combustion were measured by the static bomb combustion calorimetry in the case of 1,3-diethylbarbituric acid, and the rotating-bomb combustion calorimetry in the case of 1,3-diethyl-2-thiobarbituric acid. From the combustion energies, standard molar enthalpies of formation in the crystalline state at T = 298.15 K were calculated. The enthalpy of vaporization of 1,3-diethylbarbituric acid and enthalpy of sublimation of 1,3-diethyl-2-thiobarbituric acid were determined using the transpiration method. Combining calorimetric and transpiration results, values of -(611.9 +- 2.0) kJ mol 1 and -(343.8 +- 2.2) kJ mol 1 for the gas-phase enthalpies of formation at T = 298.15 K of 1,3-diethylbarbituric and 1,3-diethyl-2-thiobarbituric acids, respectively, were derived. Theoretical calculations at the G3 and G4 levels were performed, and a study of the molecular structure of the compounds has been carried out. Calculated enthalpies of formation were in very good agreement with the experimental values.
Compounds
#
Formula
Name
1
CO2
carbon dioxide
2
N2
nitrogen
3
H2O
water
4
O2
oxygen
5
H2O4S
sulfuric acid
6
C8H12N2O3
1,3-diethylbarbituric acid
7
C8H12N2O2S
1,3-diethyl-2-thiobarbituric acid
Datasets
The table above is generated from the ThermoML associated json file (link above).
POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied;
the numbers refer to the table of compounds on the left.
Type
Compound-#
Property
Variable
Constraint
Phase
Method
#Points
POMD
6
Mass density, kg/m3 ; Crystal
Temperature, K; Crystal
Pressure, kPa; Crystal
Crystal
Pycnometric method
1
POMD
6
Vapor or sublimation pressure, kPa ; Liquid
Temperature, K; Liquid
Liquid
Gas
Transpiration method
11
POMD
7
Mass density, kg/m3 ; Crystal
Temperature, K; Crystal
Pressure, kPa; Crystal
Crystal
Pycnometric method
1
POMD
7
Vapor or sublimation pressure, kPa ; Crystal
Temperature, K; Crystal
Crystal
Gas
Transpiration method
19
RXND
6
1
2
3
4
Specific internal energy of reaction at constant volume, J/g
Static bomb calorimetry
1
RXND
7
5
1
2
3
4
Specific internal energy of reaction at constant volume, J/g