Trends in bond dissociation energies of brominated flame retardants from density functional theory

Bond dissociation enthalpies (BDEs) are computed using the Density Functional Theory (DFT) for a selected set of C–Br, C–O, and C–Br bonds susceptible to homolysis in the thermal degradation of four brominated flame retardants (BFRs): decabromo-diphenyl, decabromo-diphenylethane, 1,2-bis(2,4,6-tribromophenoxy)-ethane, and 3,4,5,6-tetrabromo-1,2-diethyl-phtalate. Based on BDEs computed at M06/cc-pVTZ level, choice based on a previous benchmark, we find debromination as the dominant decomposition pathway of brominated diphenyls and brominated phtalates, whereas scission to form brominated phenoxyls and benzyl radicals is preferred in aromatic BFRs containing ether and alkyl bridges, respectively. Trends in computed BDEs are rationalized in terms of (de)localization of spin density in the electronic structure of the resulting radicals.