Thermochemical study of the 2,5-dibromonitrobenzene isomer: An approach of the energetic study for the other dibromonitrobenzene isomers

Abstract

The standard ( p ∘ = 0.1 MPa ) molar enthalpy of formation, of the 2,5-dibromonitrobenzene, in the crystalline phase, at T = 298.15 K, was derived from the standard massic energy of combustion, in oxygen, at 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 crystal as a function of the temperature and applying the Clausius–Clapeyron equation, the standard molar enthalpy of sublimation of the compound, at T = 298.15 K, was calculated. Compound - Δ c U m ∘ ( cr ) /(kJ · mol −1) Δ f H m ∘ ( cr ) /(kJ · mol −1) Δ cr g H m ∘ /(kJ · mol −1) 2,5-Dibromonitrobenzene 2792.2 ± 1.0 43.3 ± 1.3 97.0 ± 0.4 The combination of the values of the standard molar enthalpy of formation, in the crystalline phase, and the standard molar enthalpy of sublimation of the dibromonitrobenzene isomer, allowed the calculation of the standard ( p ∘ = 0.1 MPa ) molar enthalpy of formation, in the gaseous phase, at T = 298.15 K. Additionally, this value was estimated by employing two different methodologies. One based on the conventional Cox Scheme and another one, much more accurate, based on the values of the standard molar enthalpies of formation of 2- and 3-bromonitrobenzene already determined experimentally. Once the best approach was found, it was applied in the estimation of the standard molar enthalpies of formation of the other five isomers.