Phenyl substituted ureas: Evaluation of thermochemical data with complementary experimental and computational methods

Abstract

Standard molar enthalpies of formation of 1-phenyl-3-isopropyl-urea and 1-phenyl-3-tert-butyl-urea were derived from results of high-precision combustion calorimetry. Standard molar enthalpies of sublimation of these compounds and of phenyl-urea were derived from their vapour pressure – temperature dependences measured by the transpiration method. Thermal behaviour of phenyl substituted ureas was studied by DSC. Thermochemical data on phenyl-substituted ureas available in the literature were collected, evaluated, and combined with our own experimental results. We have evaluated and recommended for further thermochemical calculations a set of sublimation, vaporization, fusion and formation enthalpies for the phenyl-substituted ureas at 298.15 K. A computational procedure was developed to support the experimental gas-phase enthalpies of formation. The theoretical gas phase molar enthalpies of formation of the phenyl-substituted ureas calculated by the high-level quantum-chemical G3MP2 method were in a good agreement with the recommended experimental data. General regularities in energetics due to introduction of phenyl substituent in the alkyl-substituted ureas have been revealed and used for validation of the experimental and theoretical data. Additivity methods were developed to estimate the thermochemical properties of organic compounds containing the carbamide moiety.