Measurement of Vapor Pressures and Melting Properties of Five Polybrominated Aromatic Flame Retardants

Abstract

While vapor pressure is among the most important properties used in the environmental fate assessment of organic contaminants, measured vapor pressures exist only for a few representatives of the group of novel brominated flame retardants (BFRs). To expand on this limited set of data, the vapor pressures of five BFRs1,2,4,5,-tetrabromo-dimethylbenzene (TBX), 1,2,3,4,5-pentabromo-6-methyl-benzene (PBT), 1,2,3,4,5-pentabromo-6-ethyl-benzene (PBEB), 2,3,4,5,6-pentabromo-phenol (PBP), and 1,3,5-tribromo-2­(2,3-dibromopropoxy)-benzene (TBP-DBPE)were measured in the temperature range 322.7–367.7 K with the gas saturation method. Enthalpies of sublimation or vaporization were determined from the slopes of semilogarithmic plots of measured vapor pressure against reciprocal temperature. The melting temperature and enthalpy of fusion were measured using differential scanning calorimetry. From these experimental data, the vapor pressures and subcooled liquid vapor pressures at 298.2 K, p i ° and p i °,sl, respectively, were derived and compared with values estimated using group contribution methods, polyparameter linear free energy relationships, as well as EPISuite, SPARC, and COSMOtherm. Depending on the method and compound, deviations between measured and estimated log­(p i °) or log­(p i °,sl) values ranged from 8 to 77% of the measured values. The gas/particle partitioning behavior of the five BFRs was estimated using the measured p i °,sl values and the Junge–Pankow model. This estimation could account for the observed partitioning behavior of PBT and TBP-DBPE.

Quantum chemical calculation of the vapor pressure of volatile and semi volatile organic compounds

“…The three-dimensional structure of a molecule is explicitly considered. For a number of organic compounds, vapor pressures have been estimated using density functional theory (DFT) based quantum mechanics, [16][17][18][19][20] mostly using the COSMO-RS (conductor-like screening model for realistic solvation) method, developed by Klamt and co-workers. 21 While this is straightforward for small, usually quite rigid molecules, open questions arise for larger, often conformationally rather flexible systems.…”

“…The three-dimensional structure of a molecule is explicitly considered. For several organic compounds, vapor pressures have been estimated using density functional theory (DFT) based quantum mechanics, 16–20 primarily using the COSMO-RS (conductor-like screening model for realistic solvation) method, developed by Klamt and co-workers. 21…”