Brominated dibenzofuran

Incineration of a collection of polymers with 10 different kinds of brominated flame retardants has been studied under standardized laboratory conditions using varying parameters including temperature and air flow. Polybrominated diphenyl ethers like the deca-, octa-, and pentabromo compounds yield a mixture of brominated dibenzofurans while burning in polymeric matrices. Besides cyclization, debromination/hydrogenation is observed. Influence of matrix effects and burning conditions on product pattern has been studied the relevant mechanisms have been proposed and the toxicological relevance is discussed. 

Thermochemistry in the polymeric matrix follows a different pattern. Decabromobiphenyl ether 1 does cyclize according to the following reaction yielding brominated dibenzofurans (PBDF). The optimal yield for PBDF depends on the applied burning temperature (refs. 14,15) this itself depends on the kind of polymeric matrix, which is shown below for incineration at the DIN-oven (Fig. 5). 

Fig. 5. Yields of Brominated Dibenzofurans from Decabromobiphenyl Ether as Dependent on Temperature and Amount of Sb203 (Synergist) in the Polymeric Matrix (Polybutylene-terephtalate).

Photolysis of all brominated dibenzodioxins investigated occurs very fast in n-hexane. The rate of degradation of all compounds follows a good first-order kinetic scheme. In Table 4 the calculated first order rate constants k are summarised along with the quantum-yields. The corresponding results for three brominated dibenzofurans are also included. 

The same trend is observed in the series of brominated dibenzofurans. But the rate for OctafirDD does not follow this general pattern since its rate is decreased compared to the penta- and hexabrominated compounds. 

Brominated diphenyl oxides i Brominated dibenzofurans Glass Beads... 

O Keefe PW. 1978. Fonnation of brominated dibenzofurans from pyrolysis of the polybrominated biphenyl fire retardant, Firemaster FF-1. Environ Health Perspect 23 347-350. 

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. 

Donnelly JR, Grange AH, Nunn NJ, Sovocool GW, Brumley WC, Mitchum RK (1989), Biomed. Environ. Mass. Spectrom. 18 884-896.. .Analysis of thermoplastic resins for brominated dibenzofurans"... 

Both 4,6- and 3,4-dimethoxydibenzofurans were brominated at C-l [84AHC(35)2]. Iodination of 3 follows the same trends as other halogena-tions (65MI1). Dibenzofuran is lithiated at the 4- and thallated at the 2-position, providing access to 2- and 4-iodo derivatives (57IZV1391). 

During incineration of 1 in the polymeric matrix debromination/hydrogenation occur in addition to cyclization process. Tetrabrominated dibenzofuran isomers are the most abundant products formed in the temperature range between 300° or 400° (Figure 6 shows Br-composition at 300° - 800°C). Incineration at 400°C gives tetrabromo-benzofurans in yields up to 13 % (Fig. 6). Besides of PBDF, brominated dibenzodioxins are also formed, but to a much lesser extent (30-90 ppm) (ref. 11). 

Besides these main products, formed in incineration of 1 in polymeric matrices complex isomeric mixtures of brominated methyl-dibenzofurans and brominated condensed systems like benzo[b]naphto[2,3-d]furan have been identified by GC/MS (ref. 11). 

M. Freiberg, D.L. McAllister, C.J. Mazac, P. Ranken Analysis of Trace Levels of Polybrominated Dibenzo-p-dioxins and Dibenzofurans in Brominated Flame Retardants Presented on June 30, 1993 at Orgabrom 93 in Jerusalem. 

The use of aromatic brominated compounds as flame retardants has been a potential source of environmental contamination. Incomplete incineration of these compounds and wastes (plastics, textiles, oils etc...) containing brominated flame retardants caused formation of brominated/chlorinated dibenzodioxines (PBDDs/ PCDDs) and dibenzofurans (PCDFs/PBDFs) (refs. 1 - 4). 

In addition, the concern about e-waste not only focuses on its vast quantity generated daily, but also more on the need to handle the toxic chemicals embedded in it. It is well known that e-waste contains lead, beryllium, mercury, cadmium (Cd), and brominated flame retardants (BFRs) among other chemical materials [3]. Furthermore, highly toxic chemicals such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polybrominated dibenzo-p-dioxins and dibenzo-furans (PBDD/Fs) can be formed during the recycling process [4]. 

In order to confirm the relative retention times established for DBDPO using only CGC, additional sets of partially brominated diphenyl oxides and dibenzofurans were synthesized using the Fe°/ Br2 procedure. The course of these reactions was followed by both CGC and CGC/MS. As a result, it was possible to simultaneously confirm the previous relative retention time peak assignments as well as to correlate the retention times between the two instruments. Some of the pertinent comparative retention time data obtained from these experiments is summarized in Table I. Upon completion of the individual reactions, a cocktail containing both partially brominated furans and diphenyl oxides was mixed. A typical CGC chromatogram and a CGC/MS total ion chromatogram for this cocktail are shown in Figures 1 and 2, respectively. 

Figure 1. CGC Chromatogram of Diphenyl Oxide and Dibenzofuran Bromination Reaction Product s Cocktail...

H. Thoma, G. Hauschulz, E. Knorr and O. Hutzinger, "Polybrominated Dibenzofurans (PBDF) and Dibenzodioxins (PBDD) from the Pyrolysis of Neat Brominated Diphenylethers, Biphenyls and Plastic Mixtures of these Compounds,"Chemosphere, JJi, 277(1987). 

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), Pentachlorophenol m(PCP, mercury and organic mercury compounds, cadmium, lead and organic lead compounds, brominated flame retardants), nonylphenol/ethoxylates (NP, NPEs) amongst others in the OSPAR Strategy with regard to Hazardous Substances... 

Buser, H.R. Rapid photol34ic decomposition of brominated and brominated/chlorinated dibenzodioxins and dibenzofurans, Chemosphere, 17(5) 899-903, 1988. 

Halogenation of dibenzofuran produces the 2-halo compounds. Bromina-tion can be achieved in good yield with bromine in acetic acid " or with N-bromosuccinimide in boiling carbon tetrachloride. The 2,8-dibromo compound has been made, using dioxane dibromide. Chlorination of dibenzofuran in acetic acid in the presence of iron powder can be controlled to yield the 2-chloro or the 2,8-dichloro compounds. 2-Chlorodi-benzofuran is best prepared by reaction of dibenzofuran with phosphorus pentachloride. 2-Iododibenzofuran (45%) results from treatment of dibenzofuran with iodine in boiling chloroform in the presence of nitric acid. 2,8-Diododibenzofuran is best prepared by reaction of dibenzofuran with iodine and iodic acid in aqueous acetic acid. ... 

When there is an electron-releasing substituent in the 4-position, the electrophile attacks the 1-position. This has been used as a convenient way of preparing 1-substituted dibenzofurans by removal of an amino group at the 4-position. Bromination, chlorination, and diazo coupling of 4-dibenzofuranol occur at the 1-position. Bromination and Vilsmeier-Haack formylation of 4-methoxydibenzofuran provide the 1-substituted derivatives. Nitration and bromination of 4-acetylaminodibenzofuran take a similar course. ... 

Few data are available on the electrophilic substitution of dibenzofurans containing more than one substituent. 1,4-Dimethyldibenzofuran affords, as expected, the 2-aldehyde on reaction with dichloromethyl methyl ether and tin(IV) chloride. " The nitration of 2,4-dimethyldibenzofuran has also been studied. Acetylation of 4-methoxy-7-nitro- and 8-nitrodibenzofuran occurs exclusively at the 1-position. Similarly, both 4,6- and 3,4-dimethoxydi-benzofuran undergo bromination and acetylation at the 1-position. The acetylation of 1,3-dimethyl-, 1,4-dimethyl-, and 2,4-dimethyl-7-methoxydibenzofuran have been studied the acetyl group enters the 8-position. The chlorination of 3,7-dichlorodibenzofuran has also been studied. ... 

The 4-sodio and 4-potassio derivatives are known but are less convenient to obtain than the 4-lithio derivative, which is readily available by metallation of dibenzofuran with butyllithium. Metallation can also be achieved with cross-linked poly(p-lithiosytrene) but offers no advantage in yield. The 4,6-dimetallo derivatives of dibenzofuran can be made by treatment of dibenzofuran with butyllithium or butylsodium. Lithiodiben-zofurans and dilithiodibenzofurans are also available by bromine-lithium exchange with butyllithium. " ... 

Pyrolysis of FireMaster BP-6 in the temperature range of 600 900 °C in the absence of oxygen produced bromobenzenes and brominated biphenyls as key products, but no brominated dioxins and dibenzofurans (Thoma and Hutzinger 1987 Thoma et al. 1987). Thermolysis of Hi re Mast a- BP-6 between 400 and 600 °C in the presence of air produced 23,7,8-tetrabromodibenzofuran in the percent ( 1 %10 g/kg) range (Rappe and Buser 1980). Pyrolysis of FireMaster BP-6 in an open quartz tube at 800 °C produced 0.48 1.49 gZkg2,3,7,8-TCDD equivalent levels of polybrominated dibenzofurans (Zacharewski et al. 

---