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Indexed by:Journal Papers

Date of Publication:2015-11-01

Journal:CHEMOSPHERE

Included Journals:SCIE、EI、PubMed

Volume:139

Page Number:518-524

ISSN No.:0045-6535

Key Words:Methoxylated polybrominated diphenyl ethers; Direct photolysis; Photocyclization; Methoxylated polybrominated dibenzofurans; Density functional theory

Abstract:Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs can transform into polybrominated dibenzofurans (PBDFs) via photocyclization. However, it is unclear whether methoxylated PBDEs (MeO-PBDE5) 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-PBDE5 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 DFr 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 ( >19.7 kcal/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 (13.8 kcal/mol) in a methanol environment. For this pathway, H-elimination assisted by Br cleaved from an ortho-C-Br bond was observed with a 2.0 kcal/mol barrier. Thus, the OFT 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. (C) 2015 Elsevier Ltd. All rights reserved.