Thermochemical study of the monobromonitrobenzene isomers

Abstract

The standard ( p° = 0.1 MPa) molar enthalpies of formation, of the 2-, 3-, and 4-monobromonitrobenzene isomers, in the crystalline phase, at T = 298.15 K, were derived from the standard massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. From the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen effusion technique, their standard molar enthalpies of sublimation, at T = 298.15 K, were derived using the Clausius-Clapeyron equation. - 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-Bromonitrobenzene 2939.5 ± 1.0 26.9 ± 1.3 85.2 ± 0.3 3-Bromonitrobenzene 2919.7 ± 1.1 7.1 ± 1.3 86.8 ± 0.5 4-Bromonitrobenzene 2913.1 ± 0.9 0.5 ± 1.2 86.6 ± 0.6 The combination of the values of the standard molar enthalpies of formation in the crystalline phase, and of the standard molar enthalpies of sublimation, yielded the standard molar enthalpies of formation in the gaseous phase. The results were interpreted in terms of enthalpic increments, and compared with estimated values applying the empirical scheme developed by Cox.