Thermochemical study of some dichloroacetophenone isomers

Abstract

The standard ( p ∘ = 0.1 MPa ) molar enthalpies of formation in the condensed phase, Δ f H m ∘ ( cr,l ) , for 2′,4′-, 2′,5′-, and 3′,4′-dichloroacetophenones were derived from the standard molar energies of combustion, Δ c U m ∘ in oxygen, to yield CO 2(g) and HCl · 600H 2O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of vapourization or sublimation, Δ cr,l g H m ∘ , of these compounds, at T = 298.15 K were determined by Calvet microcalorimetry. For the 3′,4′-dichoroacetophenone, the standard molar enthalpy of sublimation, at T = 298.15 K, was derived by the Clausius–Clapeyron equation, from the temperature dependence of the vapour pressures of this compound, measured by the Knudsen effusion technique. From the values of Δ f H m ∘ ( cr,l ) and Δ cr,l g H m ∘ the standard molar enthalpies of formation of the three isomers, in the gaseous phase, Δ f H m ∘ (g) , at T = 298.15 K were derived and compared with the same parameters estimated by the Cox Scheme. Compound Δ c u ∘ / ( J · g - 1 ) Δ f H m ∘ ( g ) / ( kJ · mol - 1 ) 2′,4′-Dichloroacetophenone(l) −20437.3 ± 2.5 −124.5 ± 2.2 2′,5′-Dichloroacetophenone(l) −20415.3 ± 3.9 −126.0 ± 2.6 3′,4′-Dichloroacetophenone(cr) −20232.0 ± 2.6 −134.8 ± 1.6