Dibenzofuran, formation from

Morita, M., J. Nakagawa, and C. Rappe. 1978. Polychlorinated dibenzofuran formation from PCB mixture by heat and oxygen. Bull. Environ. Contam. Toxicol. 19 665-68. 

It has been observed that pyrolysis of polychlorodiphenyl ethers in the presence of air at 600°C produces low yields of polychlorodibenzofurans, as well as polychlorodibenzo-p-dioxins, which were identified by GC-MS methods. The major reaction pathways leading to dibenzofuran formation involve loss of hydrogen and hydrogen chloride from the o,o -positions. 

Dumler R, Thoma H, Lenoir D, et al. 1989b. Thennal formation of polybrominated dibenzodioxins (PBDD) and dibenzofurans (PBDF) from bromine containing flame retardants. Chemosphere 19(l-6) 305-308. 

Buser HR (1979b), Chemosphere 8 157-175.. .Formation of chlorinated dibenzofurans (PCDF) from the pyrolysis of individual PCB isomers"... 

Buser, H.R. and C. Rappe, Formation of Polychlorinated Dibenzofurans (PCDFs) from the Pyrolysis of Individual PCB Isomers, Chemosphere, (3), 115-124 (1979). 

In addition, the downfield shifts of the signals due to C(19 ), C(15 ), and C(20 ), in comparison with those of the corresponding carbons of peceylanine (388), are suggestive of formation of a lactone ring. These results are accommodated by formation of a bond between N(l ) and C(16 ), following cleavage of the C(7 )-C(16 ) bond of peceylanine, followed by intramolecular lactone formation from attack of the carboxy-late function on the epoxide moiety. Ceylanicine (391) was shown by the spectral data to bear a close similarity to pelankine (389), with the monomeric units linked to incorporate a similar central dibenzofuran unit. The main departures concern the cleavage of the C(3 )-N(4 ) bond, and the formation of a lactone from reaction of the C(16 )-carboxylate function with the 19, 20 -epoxide moiety. The third bisindole 392 was readily shown to be the -demethyl derivative of peceyline from the spectral data. 

H.R. Buser et al., "Formation of polychlorinated dibenzofurans (PCDF) from the pyrolysis of PCBs," Chemosphere, pp. 109-119, 1978. 

FIGURE 7.1 Formation of dioxin and dibenzofuran (from Crosby 1998). 

In contrast with the relatively facile thermal rearrangement of sulfinates to sulfones discussed in the preceding section, the reverse process is relatively, rarely encountered and is usually observed only at elevated temperatures. One of the first thermal sulfone to sulfinate isomerizations has been invoked by Fields and Meyerson to occur during the pyrolysis of dibenzothiophene S, S-dioxide (26) to dibenzofuran, through elimination of sulfur monoxide from the sultine intermediate 27 (equation 27). More recently, the flash vapor-phase pyrolysis of various 2,5-dialkyl and diaryl thiophene-S, S-dioxides has also been shown to involve SO extrusion and formation of the corresponding furans in good yields . 

C. Rappe and R. Lindahl, "Formation of Polychlorinated Dibenzofurans (PCDFs) and Polychlorinated Dibenzo-p-Dioxins (PCDDs) from the Pyrolysis of Polychlorinated Diphenyl Ethers,"Chemosphere, 2, 351 (1980). 

Chlorinated dibenzo-p-dioxins and dibenzofurans are among the most toxic substances known, especially 2,3,7,8-tetrachloro-p-dibenzodioxin (TCDD). These extremely hazardous compounds can be produced from 3,4,5- and 2,4,5-trichlorophenols by peroxidases [207]. However, the biological formation of such toxicants in nature or by microorganisms has not been described. 

The fragmentation of dibenzothiophene sulfoxide resembles that of dibenzothiophene rather than that of the sulfone. This is due to primary loss of 0 to give the dibenzothiophene ion, which is the strongest feature of the spectrum. Much of the breakdown which follows is due to that of the dibenzothiophene ion. There are, however, some aspects of sulfone behavior, notably the formation of the dibenzofuran ion (14) by the loss of sulfur from the rearranged molecular ion (13). ... 

For dibenzofuran, no diphenyl was detected in the product, but phenylcyclohexane and bicyclohexane were detected. Therefore, hydrogenation of at least one of die rings was necessary before ring opening took place. A similar conclusion was found for the analysis of the product from hydrogenation of carbazole. There was evidence for the formation of the hexahydro-derivatives of the two compounds which could make both these compounds effective hydrogen donors. 

Lewis acids zinc chloride or aluminum chloride. Heat alone is sometimes effective, and the kinetics of the formation of dibenzofuran from 2,2 -biphenyldiol have been studied in both the presence and absence of zinc chloride. The rate and the degree of conversion are both markedly increased with increasing temperature under these conditions. ... 

Watanabe I, Tatsukawa R. 1987. Formation of brominated dibenzofurans from the photolysis of flame retardant decabromobiphenyl ether in hexane by UV and sun light. Bull Environ Contam Toxicol 39 953-959. 

The formation of the substituted dibenzofuran-l,4-dione (405) from 5,5 -dimethyl-2,2 -di-p-benzoquinone (406) can be achieved thermally or by photolysis in hydroxylic solvents such as methanol or acetic acid,421 and a related cyclization has been observed in dinaphtha-quinones.422 A dibenzofuran derivative (407) is also obtained on irradiation of the conjugated dione (408) the intermediate (409) can be isolated by maintaining a temperature of 6° in the reaction flask.423 A mechanism for the photorearrangement of 2-acetyl-3-furyl-p-benzoquinones to derivatives of isobenzofuran has been proposed424 [Eq. (109)]. 

As discussed in the earlier survey (1), a biogenic source of polychlorinated dibenzo-p-dioxins and dibenzofurans is peroxidase-catalyzed transformation of chlorophenols as first reported by Oberg and Rappe (2041-2044). More recent studies confirm these observations (2045-2048). In addition to lactoperoxidase and horseradish peroxidase, human leukocyte myeloperoxidase catalyzes in vitro formation of dioxins and dibenzofurans from chlorophenols (2046, 2047). Formation rates are in the pmol/mol range (Scheme 3.6) demonstrating that a human biosynthesis of dioxins and furans is not only possible but also likely. These observations are reinforced by the reported in vivo (rats) conversion of the pre-dioxin nona-chloro-2-phenoxyphenol to octachlorodibenzo-p-dioxin (OCDD) (2049), and the production of hepta- and octachlorodibenzo-p-dioxin in the feces of cows fed pentachlorophenol-treated wood (Scheme 3.7) (2050, 2051). 

Wittsiepe J, Kullmann Y, Schrey P, Selenka F, Wilhelm M (1999) Peroxidase-Catalyzed in Vitro Formation of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans from Chlorophenols. Toxicol Lett 106 191... 

Hagenmaier H, Kraft M, Brunner H, et al. 1987. Catalytic effects of fly ash from waste incineration facilities on the formation and decomposition of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans. Environ Sci Technol 21 1080-1084. 

Briois, C., Ryan, S., Tabor, D., Touati, A. and Gullett, B.K. (2007) Formation of polychlorinated dibenzo- -dioxins and dibenzofurans from a mixture of chlorophenols over fly ash Influence of water vapor. Environ. Sci. Technol. 41, 850-856. 

Buser HR, Lindahl R, Rappe C (1980), Chemosphere 9 351-361.. .Formation of polychlorinated dibenzofurans (PCDF) and polychlorinated dibenzo-p-dioxins from the pyrolysis of polychlorinated diphenylethers"... 

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