Standard molar enthalpies of formation, vapour pressures, and enthalpies of sublimation of 2-chloro-4-nitroaniline and 2-chloro-5-nitroaniline

Abstract

The standard ( p o=0.1 MPa) molar enthalpies of formation for crystalline 2-chloro-4-nitroaniline and 2-chloro-5-nitroaniline were derived from the standard molar enthalpies of combustion, in oxygen, at the T=298.15 K, measured by rotating bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the vapour pressures of the crystals as function of temperature, and the standard molar enthalpies of sublimation, at T=298.15 K, were derived by the Clausius–Clapeyron equation. Direct measurements of the standard molar enthalpies of sublimation, using Calvet microcalorimetry, for 2-chloro-4-nitroaniline and 2-chloro-5-nitroaniline confirmed the values derived from the Knudsen technique. Δ f H m 0 (cr) Δ cr g H m 0 (kJ · mol −1) (kJ · mol −1) Calvet Knudsen 2-Chloro-4-nitroaniline (2-Cl-4-NO 2-C 6H 3NH 2) −74.9 ± 1.4 101.8 ± 1.8 102.6 ± 1.5 2-Chloro-5-nitroaniline (2-Cl-5-NO 2-C 6H 3NH 2) −71.0 ± 1.5 100.3 ± 2.2 101.0 ± 1.6 Additionally, standard enthalpies of formation were estimated by employing two different methodologies. One is based on the Cox scheme and the other one, much more accurate, is based on first-principles calculations. The theoretical calculations were performed at the AM1, B3LYP/6-31+G** and BP86/6-31+G** levels of theory. Estimated values are in good agreement with the reported experimental numbers.