Thermochemical study of some dichloroacetophenone isomers

The standard (p∘=0.1MPa) molar enthalpies of formation in the condensed phase, ΔfHm∘(cr,l), for 2′,4′-, 2′,5′-, and 3′,4′-dichloroacetophenones were derived from the standard molar energies of combustion, ΔcUm∘ in oxygen, to yield CO2(g) and HCl · 600H2O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of vapourization or sublimation, Δcr,lgHm∘, 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 ΔfHm∘(cr,l) and Δcr,lgHm∘ the standard molar enthalpies of formation of the three isomers, in the gaseous phase, ΔfHm∘(g), at T = 298.15 K were derived and compared with the same parameters estimated by the Cox Scheme.CompoundΔcu∘/(J·g-1)Δcu∘/(J·g-1)ΔfHm∘(g)/(kJ·mol-1)2′,4′-Dichloroacetophenone(l)−20437.3 ± 2.5−124.5 ± 2.22′,5′-Dichloroacetophenone(l)−20415.3 ± 3.9−126.0 ± 2.63′,4′-Dichloroacetophenone(cr)−20232.0 ± 2.6−134.8 ± 1.6Full-size tableTable optionsView in workspaceDownload as CSV