Physicochemical properties of selected polybrominated diphenyl ethers and extension of the UNIFAC model to brominated aromatic compounds

The aqueous solubilities (Sw) at various temperatures from 283 K to 308 K and 1-octanol/water partition coefficients (Kow) for four polybrominated diphenyl ethers (PBDEs: 4,4′-dibromodiphenyl ether (BDE-15), 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), 2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99), and 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE-153)) were measured by the generator column method. The Sw and Kow data revealed the effect of bromine substitution and basic structure on Sw and Kow. To estimate the infinite dilution activity coefficients (γiw,∞) of the PBDEs in water from the Sw data, enthalpies of fusion and melting points for those compounds were measured with a differential scanning calorimeter. Henry’s Law constants (Hw) of the PBDEs were derived from the determined γiw,∞ and literature vapor pressure data. Some physicochemical characteristics of PBDEs were also suggested by comparing the present property data with that of polychlorinated dibenzo-p-dioxins, brominated phenols and brominated benzenes in past studies.Furthermore, in order to represent different phase equilibria including solubility and partition equilibrium for other brominated aromatic compounds using the UNIFAC model, a pair of UNIFAC group interaction parameters between the bromine and water group were determined from the Sw and Kow data of PBDEs and brominated benzenes. The ability of the determined parameters to represent both properties of brominated aromatics was evaluated.