Theoretical Investigation on Mechanistic and Kinetic Transformation of 2,2′,4,4′,5-Pentabromodiphenyl Ether

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-p-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 ortho-hydroxylated PBDEs. HO2 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(-14) and 5.24 × 10(-14) cm(3) molecule(-1) s(-1) at 298.15 K, respectively.

Atmospheric chemical reaction mechanism and kinetics of 1,2-bis(2,4,6-tribromophenoxy)ethane initiated by OH radical: a computational study

“…We noted that previous study found that $OH additions to CBr site tend to have a higher E a value than those of addition to CH sites of bromophenoxy group in the reaction of PBDEs with $OH. 33,34,51,52 This agrees with our ndings. The C-H of 2,4,6tribromophenoxy group has lower H-abstraction reactivity than that of -O-CH 2 -CH 2 -Ogroup.…”

“…The overall rate constant was calculated to be 1.0 Â 10 À12 cm 3 per molecule per s at 298 K and 101 kPa, which is about 20 times higher than that of (5.2 Â 10 À14 cm 3 per molecule per s) of 2,2 0 ,4,4 0 ,5-pentabrominated diphenyl ether (BDE99). 52 The calculated branching ratio G value for the addition products IM3 + IM3 0 + IM5 + IM5 0 is 73.5% and H-abstraction products IM7-1 + IM7-2 + IM7 0 -1 + IM7 0 -2 is 24.9% at 298 K, which are much higher than those for other addition and H-abstraction pathways. Therefore, CH site addition of 2,4,6-tribromophenoxy group and H-abstraction from -O-CH 2 -CH 2 -Ogroup are the most favorable pathways for the reaction BTBPE + $OH.…”

“…Thus, Habstraction mainly contributes to nal products for the further transformation of IM3 in the presence of O 2 , analogous to the reaction of OH adduct of PBDEs with O 2 to form OH-PBDEs. 52 Since high abundance of atmospheric O 2 , the favorable H-abstraction pathway of IM3 with O 2 should have atmospheric importance even though its reaction energy barrier is relatively high. This also can be supported by the fact that pseudo-rst order rate constant ($10 À2 s À1 ) of the Habstraction is much higher than that ($10 À4 s À1 ) of collision controlled $OH-molecule reactions that are of signicance for the transformation of atmospheric pollutants.…”

“…Although the lifetime of BTBPE is much lower than that (around hundreds days) of the banned PBDEs (pentaBDE, octaBDE and decaBDE), the substitute of PBDEs by BTBPE still has atmospheric persistence. 52,[63][64][65] In addition, it deserves mentioning that heterogeneous reactions of BTBPE on atmospheric particles will affect its overall atmospheric lifetime since BTBPE is a semivolatile compound. Therefore, the effect of other particles such as black carbon, mineral dust on the lifetime of BTBPE deserves future investigation.…”

Efficient eradication of organotin utilizing K2FeO4 augmented by nZVI: revelations on influential factors, kinetic dynamics, and mechanistic insights

“…Calculations based on Frontier Molecular Orbital theory help identify the most reactive sites in the target compounds. Cao et al (2015) explored the reactivity of pollutants through Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) values. Calculation of transition state theory and reaction barriers can determine preferred reaction pathways, crucial for a deeper understanding of the reaction mechanism (Wu et al, 2023).…”