Prediction of vapor pressures, boiling points and enthalpies of fusion for twenty-nine halogenated dibenzo-p-dioxins and fifty-five dibenzofurans by a vapor pressure correlation method

Abstract

A vapor pressure correlation method was used to predict vapor pressures for 15 polychloro-, 8 polybromo-, 2-iodo-, 2,3-difluoro-, 4 mixed halogenated dibenzo-p-dioxins and fifty-five polychlorodibenzofurans. Experimental vapor pressures, obtained for 10 chlorinated dibenzo-p-dioxins were used as a data base for these predictions. The correlation method uses the liquids as reference states. The boiling points and enthalpies of fusion were deduced for the measured compounds and were correlated with the degree of halogenation. The calculated boiling points and enthalpies of fusion were in good agreement with observed values. The two correlations were used to predict boiling points and enthalpies of fusion for related dioxins and dibenzofurans of known melting points and these values served as a starting point for the prediction of the vapor pressures. Predictions for four dibenzofurans of known vapor pressures were in good agreement with the experimental data and a common correlation can be used for polychloro -dibenzo-dioxins and -dibenzofurans. Molar heat capacities of the gaseous and the liquid phase, enthalpies and entropies of evaporation, of sublimation and fusion were also estimated for the investigated compounds. The correlation method permitted the testing of the experimental vapor pressure data set for self-consistency. The present work stresses the importance of reporting melting points and enthalpies of fusion when reporting on the synthesis of halogenated dibenzo-p-dioxins and dibenzofurans.