title: Direct photolysis of MeO-PBDEs in water and methanol: focusing on cyclization product MeO-PBDFs.
abstract: Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs can transform into polybrominated dibenzofurans (PBDFs) via photocyclization. However, it is unclear whether methoxylated PBDEs (MeO-PBDEs) can photocyclize to form MeO-PBDFs. In this study, 5-MeO-BDE-47, 5'-MeO-BDE-99 and 6-MeO-BDE-85 were selected as models to investigate their direct photolysis, especially photocyclization in two solvent environments (water and methanol) using simulated photochemical experiments and density functional theory (DFT) calculations. The experimental results showed that MeO-PBDEs had faster direct photolysis reactions and higher quantum yields in methanol, and MeO-PBDFs could only be formed in a methanol solution of 5-MeO-BDE-47. The DFT results indicated that the lowest excited triplet state MeO-PBDEs can form dibenzofurans via direct cyclization pathways. Intra-annular H-elimination was found to be the rate-determining step for most cyclization pathways with high reaction barriers (⩾19.7kcal/mol), while 5-MeO-BDE-47 was found to have a distinct pathway for which the rate-determining step is ring closure with a low barrier (13.8kcal/mol) in a methanol environment. For this pathway, H-elimination assisted by Br cleaved from an ortho-C-Br bond was observed with a 2.0kcal/mol barrier. Thus, the DFT results reasonably explained the experimental findings, and the photocyclization of MeO-PBDEs depended on the specific Br-substitution patterns and specific effects of the environmental media.
authors: Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
authors: Weifeng
authors: W
authors: Xue
authors: Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China. Electronic address: jwchen@dlut.edu.cn.
authors: Jingwen
authors: J
authors: Chen
authors: Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
authors: Qing
authors: Q
authors: Xie
authors: Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
authors: Hongxia
authors: H
authors: Zhao
mesh_terms: D003500:Cyclization; D055768:Halogenated Diphenyl Ethers / Q000032:analysis / Q000737:chemistry*; D006900:Hydroxylation; D000432:Methanol / Q000737:chemistry*; D008962:Models, Theoretical; D015394:Molecular Structure; D010782:Photolysis; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*
chemical_list: C000607486:5'-MeO-BDE-99; C000607487:6-MeO-BDE-85; D055768:Halogenated Diphenyl Ethers; D014874:Water Pollutants, Chemical; D014867:Water; D000432:Methanol
keywords: Density functional theory; Direct photolysis; Methoxylated polybrominated dibenzofurans; Methoxylated polybrominated diphenyl ethers; Photocyclization