Thermochemistry of 6-propyl-2-thiouracil: An experimental and computational study

• Thermochemistry of 6-propyl-2-thiouracil – experimental and computational study.
• Vapor pressure study of the 6-propyl-2-thiouracil by Knudsen effusion technique.
• Enthalpies of formation of 6-propyl-2-thiouracil by rotating combustion calorimetry.
• Accurate computational calculations (G3 and G4 composite methods) were performed.

The standard (po = 0.1 MPa) molar enthalpy of formation of 6-propyl-2-thiouracil was derived from its standard molar energy of combustion, in oxygen, to yield CO2 (g), N2 (g) and H2SO4·115H2O (l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The vapor pressures as function of temperature were measured by the Knudsen effusion technique and the standard molar enthalpy of sublimation, ΔcrgHmo, at T = 298.15 K, was derived by the Clausius–Clapeyron equation. These two thermodynamic parameters yielded the standard molar enthalpy of formation, in the gaseous phase, at T = 298.15 K: −(142.5 ± 1.9) kJ mol−1. This value was compared with estimates obtained from very accurate computational calculations using the G3 and G4 composite methods.