Occurrence and formation pathways analysis of PBDD/Fs from 2,4,6-tribromophenol under thermal reaction conditions

Polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) are highly toxic and persistent compounds that provoke a wave of publicity. Bromophenols are important precursors for forming PBDD/Fs, and their reaction path has always been a research hotspot. In this study, the formation characteristic of PBDD/Fs from 2,4,6-TBP were studied. The yields of 2,3,7,8-substituted PBDD/Fs and 2,4,6,8-TBDF for the different thermal products ranged from 0.067 to 10.3 ng/g and 0.207–9.68 ng/g, respectively. The effects of adding Cu, Fe, and Sb2O3 were investigated and found to be more inclined to accelerate the formation of ortho-substituted PBDD/Fs than 2,3,7,8-PBDD/Fs. The formation pathways of 2,3,7,8-substituted PBDD/Fs and 2,4,6,8-TBDF were also proposed. 2,4,6,8-TBDF is generated in the C-C coupling reactions of some radical intermediates from the debromination of 2,4,6-TBP. The 2,3,7,8-PBDD/Fs are produced through more complex debromination, bromine substitution, and bromine rearrangement reactions. In addition, various catalytic effects on PBDD/F formation pathways were found, and the catalytic effect of Cu by the Ullmann reaction was the highest, while bromophenol oxidation by Fe was the highest. These results proved that both 2,3,7,8-substituted and non-2,3,7,8-substituted PBDD/Fs would be generated from 2,4,6-TBP, and the effects of the catalyst on the Br substituted position of 2,3,7,8-substituted PBDD/Fs were much lower than the Br-substituted position on bromophenol.