Quantum Chemical Investigation on the Mechanism and Kinetics of PBDE Photooxidation by ·OH: A Case Study for BDE-15

TLDR

Computational approaches are essential for risk assessment and pollution prevention of newly synthesized compounds, and understanding the kinetics and mechanism of tropospheric reactions of semivolatile organic compounds with ·OH is a key component of that assessment. The study demonstrates that density functional theory can be used to probe the kinetics and mechanism of atmospheric photooxidation of polybrominated diphenyl ethers by ·OH, using BDE‑15 as a case. The authors employed density functional theory calculations to investigate the reaction pathways and rate constants for the photooxidation of BDE‑15 by hydroxyl radicals. The calculations predict HO‑PBDEs, brominated phenols, and Br₂ as products with a rate constant at 298 K that matches experimental data, identify two pathways—Br substitution by ·OH and H‑gem abstraction by O₂—and provide a cost‑effective approach to probe atmospheric indirect photooxidation of PBDEs.

Abstract

Computational approaches are crucial to risk assessment and pollution prevention of newly synthesized compounds prior to large-scale production and commercialization. Understanding the kinetics and mechanism of the tropospheric reaction of semivolatile organic compounds with ·OH is an indispensable component of risk assessment. In this study, we show that the density functional theory (DFT) can be successfully employed to probe the kinetics and mechanism of atmospheric photooxidation of polybrominated diphenyl ethers (PBDEs) by ·OH, taking 4,4′-dibromodiphenyl ether (BDE-15) as a case. The predicted products (HO-PBDEs, brominated phenols and Br2) and overall rate constant (kOH) at 298 K are consistent with the experimental results. Two pathways leading to formation of HO-PBDEs are identified: Br substitution by ·OH, and abstraction of H gem to ·OH in BDE-OH adducts by O2. This study offers a cost-effective way for probing the atmospheric indirect photooxidation kinetics and mechanism of PBDEs.