De Novo Synthesis Mechanism of Polychlorinated Dibenzofurans from Polycyclic Aromatic Hydrocarbons and the Characteristic Isomers of Polychlorinated Naphthalenes

Abstract

Polychlorinated dibenzofurans (PCDFs) and polychlorinated naphthalenes (PCNs) are known to be emitted from municipal waste incinerators (MWIs) with polychlorinated dibenzo-p-dioxins (PCDDs). Two formation paths for PCDD/ Fs could mainly work, which are condensation of the precursors such as chlorophenols and "de novo" formation from carbon. However the correlation between the chemical structure of carbon and the resulting PCDD/Fs still remains unknown. In this study, the PCDD/Fs formation from polycyclic aromatic hydrocarbons (PAHs) and CuCl was examined at 400 under 10% O 2 . Coronene among the PAHs characteristically gave 1,2,8,9-T4CDF and the derivatives. These isomers clearly indicate that chlorination causes the cleavage of the C-C bonds in a coronene molecule and also that oxygen is easily incorporated from its outside to form 1,2,8,9-T4CDF. The symmetrical preformed structures in the coronene molecule enabled to amplify the de novo formation of the isomer. PCNs are also formed directly from these PAHs. Since there have been few reports on the formation mechanism of PCNs, this study will be a first step to know the whole formation paths. We also define the de novo synthesis as the breakdown reaction of a carbon matrix, since the word has been used without the precise definition.

Fly ash-mediated formation of polychlorinated naphthalenes during secondary copper smelting and mechanistic aspects

“…6. Despite the results of this study suggesting that the chlorination reaction may be important in the formation of PCNs, the contribution of de novo synthesis cannot be neglected because, as mentioned above, the de novo synthesis of PCNs was found to be possible in previous studies (Benfenati et al, 1991;Iino et al, 1999;Imagawa and Lee, 2001;Weber et al, 2001). It seems likely that the large amounts of PCNs formed in thermal treatments are not formed through a single pathway but rather through a combination of chlorination reactions and de novo synthesis (Oh et al, 2007;Jansson et al, 2008;Liu et al, 2014).…”

“…It has been suggested in several studies that the de novo synthesis of PCNs occurs in MSWIs, from the degradation of polycyclic aromatic hydrocarbons followed by their repeated chlorination (Iino et al, 1999;Weber et al, 2001). A considerable amount of carbonaceous material was found in the fly ash used in this study, so a similar PCN formation pathway may have been feasible.…”

“…In municipal incineration processes, PCNs may be formed from polycyclic aromatic hydrocarbons through similar de novo pathways to those that produce PCDFs (Iino et al, 1999;Imagawa and Lee, 2001;Weber et al, 2001;Oh et al, 2007). Kim and coworkers found that PCNs could be formed by the coupling of chlorinated phenoxy radicals (formed from chlorophenol) at high temperatures (Kim et al, 2005(Kim et al, , 2007.…”

Formation and emission of large furans and oxygenated hydrocarbons from flames

“…The polychlorinated dibenzofurans (PCDFs) are among the most notorious environmental pollutants, and the main source of PCDFs is biomass burning (6)(7)(8)(9)16). Nonchlorinated furans and PCDFs have been shown to be kinetically linked (17,18). Furans released during combustion are often partitioned into particles and are found in ash from peat (9) and wood (6) burning, in primary organic aerosols from meat cooking (19), and in secondary organic aerosols from hydrocarbon oxidation (20,21).…”

Unintentionally produced dioxin-like polychlorinated biphenyls during cooking

“…PAHs also are detected in oil fumes released during the cooking process (Chiang, Wu, & Ko, 1999). The formation of PCBs may take place by the reaction of PAHs with chlorine at presence of catalysts during the cooking process under certain thermal conditions (Iino, Imagawa, Takeuchi, & Sadakata, 1999;Weber et al, 2001). Indeed, many cooking processes are conducted at high temperature, and the resulting complex foodstuff matrices can provide carbon sources, which form PCBs.…”