Thermochemical studies of phthalimide and two N-alkylsubstituted phthalimides (ALKYL=ETHYL AND n-PROPYL)

Abstract

The standard (p 0=0.1 MPa) molar enthalpies of formation, Δf H m 0, for crystalline phthalimides: phthalimide, N-ethylphthalimide and N-propylphthalimide were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as, respectively, – (318.0±1.7), – (350.1±2.7) and – (377.3±2.2) kJ mol–1. The standard molar enthalpies of sublimation, Δcr g H m 0, at T=298.15 K were derived by the Clausius-Clapeyron equation, from the temperature dependence of the vapour pressures for phthalimide, as (106.9±1.2) kJ mol–1 and from high temperature Calvet microcalorimetry for phthalimide, N-ethylphthalimide and N-propylphthalimide as, respectively, (106.3±1.3), (91.0±1.2) and (98.2±1.4) kJ mol–1. The derived standard molar enthalpies of formation, in the gaseous state, are analysed in terms of enthalpic increments and interpreted in terms of molecular structure.