Thermal decomposition of 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), a novel brominated flame retardant.

Abstract

1,2-Bis(2,4,6-tribromophenoxy)ethane (BTBPE) is currently one of the most commonly applied novel brominated flame retardants. In this contribution, we analyze in detail the mechanisms pertinent to its thermal decomposition in view of analogous experimental findings. We demonstrate that a 1,3-hydrogen shift, leading to 2,4,6-tribromophenol (M9) and 1,3,5-tribromo-2-(vinyloxy)benzene (M10) molecules, dominates direct scission of O-CH2 bonds up to a temperature of ∼ 680 K. H atom abstraction from CH2 sites, followed by a fission of a C-C bond, produce a 2,4,6-tribromophenoxy radical (M2) and a M10 molecule. Bimolecular condensation reactions involving M2, M9, and M10 generate several congeners of brominated diphenyl ethers and their OH/OCHCH2 substituents, which serve as direct precursors for the formation of polybrominated dibenzo-p-dioxins. Reaction of M9 with a model compound of a hydrocarbon chain preferentially yields M2. Strong adsorption energy of the latter on a radical site of a hydrocarbon chain suggests that mechanisms such as Langmuir-Hinshelwood, Eley-Rideal, and Diels-Alder might be operating during the formation of PBDD/Fs from brominated flame retardants (BFRs). Reactions of alkyl primary/secondary radicals and diradical with the BTBPE molecule proceed via H abstraction from a -CH2- moiety.