Dibenzofuran structure

Dibenzofuran has also been incorporated into PAE using a unique synthetic approach that requires only the activated dihalo monomer [46]. As an example, 2,8-bis(4-fluorobenzoyl)dibenzofuran (structure 10) was reacted with potassium carbonate in the presence of silica catalyst in diphenyl sulfone at temperatures... 

FIGURE 15.5 General chemical structures of dibenzodioxin and dibenzofuran structures chlorinated at any numbered position (taken from Reference 13.)... 

Isomerization and dechlorination reactions have been implicated in the metabolism of HCBPs (McKinney, 1976 Hutzinger a/., 1974). However, identification of potentially toxic dibenzofuran structures in some metabolites, and lower ratios of PCBs to polychlorinated dibenzofiirans in liver compared to adipose tissue, have caused concern regarding the metabolic formation and accumulation of PCDFs in the liver (Kuratsune etal, 1976). Further work in this area is essential. Figure 9.5 lists the various metabolites identified in mammalian metabolism involving different species. 

Naturally occurring oxaarenes based on polycyclic pyrans encompass a plethora of structures including the plant polyphenols such as anthocyanins and a-tocopherol (vitamin E). Halogenated dibenzo-p-dioxins and dibenzofurans are formed both as by-products during the manufacture of chlorophenols, and from the incineration of organic matter in the presence of inorganic halides. 

Cheney, B. V. 1982. Structural Factors Affecting Aryl Hydrocarbon Hydroxylase Induction of Dibenzo-p-Dioxins and Dibenzofurans. Int. J. Quant. Chem. 21,445. 

Toxic and other interaction effects of PCDDs with other groups of polychlorinated chemicals having similar structure and properties, such as biphenyls, dibenzofurans, and biphenylenes. 

Loonen, H., M. Tonkes, J.R. Parsons, and H.A.J. Govers. 1994b. Bioconcentration of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in guppies after aqueous exposure to a complex PCDD/PCDF mixture relationship with molecular structure. Aquai. Toxicol. 30 153-169. 

Fig. 7 Generic chemical structures of polyhalogenated compounds. X=C1, Br. (I) Polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs) (II) chlorophenols (CPs), bromophenols (BPs) (III) polychlorinated diphenyl ethers (PCDE), polybrominated diphenyl ethers (PBDE) (IV) polychlorinated dibenzo-p-dioxin (PCDD), polybrominated dibenzo-p-dioxin (PBDD) (V) polychlorinated dibenzofuran (PCDF), polybrominated dibenzofuran (PBDF) (VI) tetrabromobisphenol A (TBBPA)...

Dioxins are a particular group of chlorinated organic molecules which have been associated with pulp and paper production and are a concern because of their extreme toxicity. There are two groups of molecular types which fall into the general category referred to as dioxins. These are the polychlorinated dibenzodioxins (PCDDs) and the polychlorinated dibenzofurans (PCDFs). The structures of these molecules are shown in Figure 10.4. 

Figure 10.4 The structures of polychlorinated dibenzodioxins and polychlorinated dibenzofurans...

Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and ortho-unsubstituted polychlorinated biphenyls (non-ortho polychlorobiphenyls) are three structurally and toxicologically related families of anthropogenic chemical compounds that have in recent years been shown to have the potential to cause serious environmental contamination due to their extreme toxicity [77-82], These substances are trace-level components or byproducts in several large-volume and widely used synthetic chemicals, principally polychlorobiphenyls and... 

Beger, R.D., Buzatu, D.A. and Wilkes, J.G. (2002) Combining NMR spectral and structural data to form models of polychlorinated dibenzodioxins, dibenzofurans, and biphenyls binding to the AhR. Journal of Computer-Aided Molecular Design, 16, 727-740. 

When PCBs burn, polychlorinated dibenzofurans (PCDFs) are among the products that may form. Examine the structure shown below, and circle and name the functional groups. 

For halogenated aromatic hydrocarbons like polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and polychlorinated dibenzo-p-dioxins (PCDDs) the binding to the aryl hydrocarbon (Ah) receptor regulates their toxicity [89]. The Ah receptor controls the induction of one of the cytochrome P450 enzymes in the liver. Toxic responses such as thymic atrophy, iveight loss, immu-notoxicity and acute lethality are associated ivith the relative affinity of PCBs, PCDFs and PCDDs for the Ah receptor [89]. The quantitative structure-activity relationship (QSAR) models predicting the affinity of the halogenated aromatic hydrocarbons ivith the Ah receptor describe the electron acceptor capability as well as the hydrophobicity and polarizability of the chemicals [89[. 

The Birch reduction of dibenzofuran is reported to give 1,4-dihydro-dibenzofuran. The electrochemical reduction of dibenzofuran by solvated electrons is reported to produce a dihydrodibenzofuran and a tetrahydro-dibenzofuran, both of unspecified structure. Treatment of dibenzofuran with W-7 Raney nickel in boiling methanol gave a moderate yield of trans-2-phenylcyclohexanol, whereas treatment of dibenzofuran with Raney nickel alloy and aqueous sodium hydroxide gave a low yield of 2-biphenylol. ... 

There are few examples of dibenzofurans occurring in the higher plants. Cannabifuran (110) and dehydrocannabifuran (268) have been isolated from cannabis in trace amounts. Cannabifuran has been synthesized. Rusco-dibenzofuran (8) occurs in the roots of Ruscus aculeatus L. and its structure was determined by the X-ray method. Three syntheses have been recorded. - - Gnidicoumarin (269) occurs in the roots of Gnidia... 

Two closely related dibenzofurans have been isolated from separate collections of the fruit of the Australian finger cherry, Rhodomyrtus mac-rocarpa Benth. Whether these are genuine metabolities or the result of fungal infection is a matter for speeulation. Structures 270 and 271 appear to be the most tenable. ... 

The naming of endocyclic O-atom heterocycles is based on the same principles as for N-PACs e.g., the structures of furan (XVII) and dibenzofuran (XVIII) are... 

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are two series of tricyclic aromatic compounds which exhibit similar physical and chemical properties. Some of these compounds have extraordinary toxic properties and were the subject of much concern. They have been involved in accidents like the Yusho accident in Japan 1968 l 9 the intoxication at horse arenas in Missouri, USA in 1971 (2.) and the accident near Seveso, Italy in 1976 (3.). The chemical structures and the numbering of these hazardous compounds are given below. 

The product distribution in the zeolite-catalysed alkylation of polynuclear aromatics depends on the structure of zeolite pores. High regioselectivities were observed in the HM catalysed isopropylation of polynuclear aromatics, such as biphenyl, naphthalene, p-terphenyl, and dibenzofuran, to yield predominantly the least bulky products e.g., 4,4 -DIPB for biphenyl, and 2,6-DIPN for naphthalene. These reactions are controlled by steric restriction at the transition state inside the pores and by the entrance of intermediate products molecules into the pores. On the other hand, the catalysts with large-pore HY and HL zeolite are controlled at low temperature by the electron density of the reactant molecule and at higher temperature by the stability of the product molecules because their pores have enough space for a transition state, which allow the formation of all corresponding isomers. 

In the USA, this plan was directed from 1929-1939 by the Committee on Drug Addiction of the National Research Council (NRC) with financial support from the Rockefeller Foundation. The program consisted of modification of the morphine molecule at all accessible points and also targeted (modified) partial structures of the morphine molecule, such as phenanthrene, hydrogenated phenanthrene, isoquinoline, dibenzofuran, and carbazole. More than 150 derivatives of morphine and more than 300... 

The only notable fragments derived from the very stable molecular ions of carbazole (64JA3729), dibenzofuran (64AJC975) and dibenzothiophene (68T3255) are at m/e 140 (CnH8) and 139 (C,H7) corresponding to loss of CX and HCX respectively structure (t) has been suggested. 

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