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

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 (k_OH) 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.