Theoretical Investigation on Mechanistic and Kinetic
Transformation of 2,2′,4,4′,5-Pentabromodiphenyl Ether
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Abstract
This
study investigates the decomposition of 2,2′,4,4′,5-pentabrominated
diphenyl ether (BDE99), a commonly detected pollutant in the environment.
Debromination channels yielding tetrabrominated diphenyl ethers and
hydrogen abstracting aromatic bromine atom formations play significant
roles in the reaction of BDE99 + H, in which the former absolutely
predominates bimolecular reactions. Polybrominated dibenzo-<i>p</i>-dioxins (PBDDs) and polybrominated dibenzofurans (PBDFs)
can be produced during BDE99 pyrolysis, especially for PBDFs under
inert conditions. The expected dominant pathways in a closed system
are debromination products and PBDF formations. The bimolecular reaction
with hydroxyl radical mainly leads to hydroxylated BDE99s rather than
hydroxylated tetrabrominated diphenyl ethers. PBDDs are then generated
from <i>ortho</i>-hydroxylated PBDEs. HO<sub>2</sub> radical
reactions rarely proceed. The total rate constants for the BDE99 reaction
with hydrogen atoms and hydroxyl radicals exhibit positive dependence
on temperature with values of 1.86 × 10<sup>–14</sup> and
5.24 × 10<sup>–14</sup> cm<sup>3</sup> molecule<sup>–1</sup> s<sup>–1</sup> at 298.15 K, respectively