Formation of mixed halogenated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs)

•We investigated mechanistic and kinetic parameters for PXDD/F generation.•The keto-ether adducts act as direct intermediate to form dioxin species.•The di-keto structures initiate the production of furan compounds.•PXDD/F formation mechanism is only sensitive to halogen substituent at ortho site.

This contribution investigates mechanistic and kinetic parameters pertinent to formation of mixed dibenzo-p-dioxins and dibenzofurans (PXDD/Fs) from the condensation reactions involving 2-chlorophenoxy (2-CPxy) and 2-bromophenoxy (2-BPxy) radicals. Keto-ether structures act as direct intermediates for the formation of DD, 1-MCDD, 1-MBDD, 1-B,6-CDD and 1-B,9-CDD molecules. Likewise, diketo adducts initiate the formation of 4-MCDF, 4-MBDF and 4-B,6-CDF compounds through interconversion and rearrangement reactions. As formation mechanisms of halogenated dibenzo-p-dioxins and dibenzofurans from precursors of brominated and chlorinated phenols are insensitive to substitution at meta and para sites, our mechanistic and kinetic analysis of reactions involving 2-BPxy and 2-CPxy should also apply to higher halogenated phenoxy radicals.

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