Formation Of Brominated Phenolic Compounds Via Chloroperoxidase-catalyzed Oxidation Of Phenol In The Presence Of Bromide

The bromophenols（BPs）,hydroxylated polybrominated diphenyl ethers（OH-PBDEs）and brominated dibenzo-p-dioxins/dibenzofurans（PBDD/Fs）are common persistent organic compounds in the environment.They have been ubiquitously detected in many environmental media.Their origins have been attracted increasing attentions.Many studies have shown that the origin of OH-PBDEs has been attributed to biological metabolism of polybrominated diphenyl ethers（PBDEs）.PBDD/Fs are to ubiquitous and persistent toxic environmental contaminants possessing great potential harm to human health in the world.They released from the application,manufacturing of bromine flame retardants and waste incineration.Some studies have reported that phenol could generate BPs viahalogen hydrogen peroxide enzyme catalyzed oxidation at the presence of bromine ions and peroxide.Other studies have showed that BPs could generate OH-PBDEs and PBDD/Fs via reactions under sunlight or biological enzyme conditions in the aquatic environment.However,it is still unclear phenol can be directly generate OH-PBDEs and PBDD/Fs via halogen hydrogen peroxide enzymecatalyzed oxidation in the presence of bromine ions and peroxide.Therefore,we explored the formation process and mechanism of OH-PBDE/PBBs and PBDD/Fs via chloroperoxidase-catalyzed oxidation of phenols（such as phenol and BPs）in the presence of bromine ions and peroxide.The main research results include:（1）The products produced were identified and quantified by GC-MS.Results showed that BPs（such as 2-BP,4-BP,2,4-DBP,2,6-DBP,2,4,6-TBP）were readily produced via chloroperoxidase-catalyzed oxidation of bromide and phenol.In addition,21 different OH-PBDE/PBBs and PBDD/Fs,such as 2′-OH-BDE-68,6′-OH-BDE-25,2,2′-OH-BB-80,1,3,8-TrBDD,2,4,6,8-TeBDF were also detectedas main products.BPs（2,4-DBP,2,6-DBP,2,4,6-TBP）were readily produced via chloroperoxidase catalyzed oxidation of bromide and 2-BP.Moreover,2′-OH-BDE-68,2’-OH-BDE-121and 4’-OH-BDE-121 were also detected.2,4-BP and 2,4,6-TBP were produced via chloroperoxidase-catalyzed oxidation of bromide and 4-BP.At the same time,9different OH-PBDE/PBBs and PBDD/Fs,such as 6′-OH-BDE-25,2′-OH-BDE-68,2,2′-OH-BB-80,2,4,6,8-TeBDF were detected.2,4,6-TBP,1,3,6,8-TeBDD,1,3,7,9-TeBDD,2’-OH-BDE-121 and 4’-OH-BDE-121 were produced via chloroperoxidase-catalyzed oxidation of bromide,2,4-DBP and 2,6-DBP.2,2′-OH-BB-80 were produced via chloroperoxidase-catalyzed oxidation of 2,4-DBP.（2）The possible pathways for the formation of reaction products were proposed.Firstly,CPO catalyzes the oxidation of bromide by H₂O₂ producing a two electron oxidized bromine intermediate（e.g.HOBr,Br₂,Br₃）.The oxidized bromine intermediate may brominate an appropriate organic substrate（e.g.phenol,2-BP,4-BP,2,4-DBP,2,6-DBP）or further react with another equivalent ofH₂O₂,releasing dioxygen and H2O.Subsequently,a part of BPs（4-BP,2,4-DBP,2,6-DBP,2,4,6-DBP）are oxidized by the oxidative species,forming bromophenoxy radicals.OH-PBDE/PBBs were likely generated from the oxidative coupling of bromophenoxy radicals,which were formed from the oxidation of the BPs by chloroperoxidase,and then PBDD/Fs likely resulted from the cyclization reaction of OH-PBDE/PBBs.Given the abundance of bromide,phenol,H₂O₂ and chloroperoxidase in the environment,catalytic oxidation of phenol in the presence of bromide and H₂O₂ by chloroperoxidase is likely a potentially significant route for the naturalformation of BPs,OH-PBDE/PBBs and PBDD/Fs in the environment.