De novo synthesis of polychlorinated dibenzo-p-dioxins and dibenzofurans Proposal of a mechanistic scheme

This paper presents a chemical reaction scheme for de novo synthesis of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) from carbon in fly ash. The reaction scheme consists of the following mechanistic steps: (1) gaseous O2 chemisorbs upon metallic sites: O2 + 2Cu → 2CuO; (2) the oxygen is transferred to a free site in the carbon structure and the carbon is oxidized to a gaseous product: Cf + CuO → CO + Cu; (3) in the course of carbon gasification, the decomposition of the carbon structure also produces some small aromatic compounds: C (graphitic layer) + aO2 → bCO2 + cCO + dAr. These aromatic compounds include PCBz, PCPh and PCB which then undergo the Ullmann coupling reactions leading to View the MathML source formation. Alternatively, View the MathML source could be formed directly from the decomposition of the carbon structure as a consequence of the in-plane oxygen complexes: C (graphitic layer) + aO2 → bCO2 + cCO + dAr + e View the MathML source; (4) halogenation/dehalogenation on carbon structure, aromatic compounds and View the MathML source structure may occur concurrently in the above chemical transformations; and (5) decomposition of View the MathML source. Major experimental observations in de novo synthesis can be rationalized using the reaction scheme. Experimental techniques for further investigations are discussed.