“De novo”-synthesis of chlorinated biphenyls, dibenzofurans and dibenzo-p-dioxins in the fly ash catalyzed reaction of toluene with hydrochloric acid

Toluene is converted into benzaldehyde and halogenated aromatic oxidation products in an air atmosphere at 425 °C with fly ash from a municipal waste incineration plant as the catalyst. Several halogenated products such as chlorinated and brominated benzenes, biphenyls and traces of PCDDs/PCDFs could be detected under these conditions, resulting from the reaction of metal chlorides and bromides present on the surface of the fly ash. The addition of a “chlorine” source to the reaction gases in the form of trichloroethylene or hydrogen chloride dramatically increased the production of PCBs, PCDDs/PCDFs and other chlorinated aromatic compounds, giving evidence for a “ de novo ” synthesis of PCBs and PCDDs/PCDFs. A reaction pathway, based on the initial oxidation of toluene to benzaldehyde as the key intermediate, followed by chlorination and condensation reactions is proposed.