Mechanistic aspects of the thermal formation of halogenated organic compounds including polychlorinated dibenzo‐p‐dioxins

Polychlorinated dibenzofurans (PCDFs) are thermally formed from polychlorinated biphenyls (PCBs) via general reaction routes. The pyrolysis of 3H and 14C labelled phenol and o‐ and p‐cresols at 665°‐865°C indicates that the mechanism of the thermal production of dibenzofuran is temperature dependent. The thermolysis of chlorinated phenols, ‐phenoxyacetic acids, and their salts and ‐phenoxy‐2‐phenols yield polychlorinated dibenzo‐p‐dioxins (PCDDs). On thermodegradation of polychlorinated diphenyl ethers, ester of 2,4,5‐T and chlorinated benzenes, a mixture of PCDFs and PCDDs is obtained. 1,2‐Ketocarbene species are involved in the thermal formation of dibenzo‐p‐dioxin from the salt of o‐halophenol.