Temperature dependence of the aqueous solubilities of highly chlorinated dibenzo-p-dioxins

Abstract

The aqueous solubilities of a series of highly chlorinated dibenzo-p-dioxins (PCDDs) are reported over an environmentally significant temperature range of 7-41{degree}C. The authors have demonstrated that aqueous solubilities may be determined by the dynamic coupled-column liquid chromatography or generator column method with a column loading as low as 0.0002% by weight. The enthalpies of solution of the solid solutes (1,2,3,7-tetra-, 1,2,3,4,7-penta-, 1,2,3,4,7,8-hexa-, and 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin) ranged from 39.8 to 47.5 kJ/mol, in good agreement with literature data for lower chlorinated dioxins. A brief thermodynamic analysis of the results indicated that entropy changes may be more important than enthalpy changes in limiting the aqueous solubilities of these solutes over the temperature range under consideration. The total surface areas (TSAs) and total molecular volumes (TMVs) of these solutes show a linear relationship with the logarithm of the aqueous activity coefficients.