Diphenyl ether bromination

Marsh et al. [36] examined analogous p-hydroxybromodiphenyl ethers and their binding to TR. The diphenyl ethers (brominated or not) bind much less avidly than T3 or T4, probably owing to the absence of the 4-carboxyl group. 4-Hydroxydiphenyl ether had the lowest affinity for THR. Within the brominated diphenyl ethers, the lowest binding was observed with the unsubstituted 4-hydroxydiphenyl ether, followed by bromine substitution in the 3 - and 5-positions, and followed by substitution by iodine. 

Brominated Diphenyl Oxides. Brominated diphenyl oxides are prepared by the bromination of diphenyl oxide. They are often referred to as diphenyl ethers. Taken together, the class constitutes the largest volume of brominated flame retardants. They range ia properties from high melting sohds to hquids. They are used, as additives, ia virtually every polymer system. 

Bromine compounds are often used as flame retardant additives but 15-20ptsphr may be required. This is not only expensive but such large levels lead to a serious loss of toughness. Of the bromine compounds, octabromo-diphenyl ether has been particularly widely used. However, recent concern about the possibility of toxic decomposition products and the difficulty of finding alternative flame retarders for ABS has led to the loss of ABS in some markets where fire retardance is important. Some of this market has been taken up by ABS/PVC and ASA/PVC blends and some by systems based on ABS or ASA (see Section 16.9) with polycarbonates. Better levels of toughness may be achieved by the use of ABS/PVC blends but the presence of the PVC lowers the processing stability. 

It should, however, be noted that good flame retardancy is only achieved with the use of flame retardant additives and that some of the best of these, such as the brominated diphenyls and brominated diphenyl ethers, are restricted in their use in some countries. 

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. 

Commercially available poiybrominated aromatic ethers have been analyzed by reversed phase high performance liquid chromatography. NMR spectra of material isolated by preparative methods served to identify the observed peaks as congeners of tetrabromo to nonabromo diphenyl ether. A bromination pathway was clearly indicated. 

In 1979, it was stated that poiybrominated aromatic ethers have received little attention (ref. 1). That statement is still applicable. Analyses to characterize this class of commercial flame retardants have been performed using UV (refs. 1-2), GC (refs. 1-6), and GC-MS (refs. 1-4). The bromine content of observed peaks was measured by GC-MS, but no identification could be made. The composition of poiybrominated (PB) diphenyl ether (DPE) was predicted from the expected relationship with polyhalogenated biphenyl, a class which has received extensive attention. NMR (refs. 3-6) was successfully used to identify relatively pure material which had six, or fewer, bromine atoms per molecule. A high performance liquid chromatography (HPLC) method described (ref. 1) was not as successful as GC. A reversed phase (RP) HPLC method was mentioned, but no further work was published. 

The reaction of brominated diphenyl ethers with methoxide in dimethyl formamide has been examined, and suggested as a ranking of their susceptibility to hydrolytic reactions under natural conditions (Rahm et al. 2005). The nature of the products was not apparently systematically examined. 

Voinov VG, YuN ETkin, TA Kuznetsova, II Mal tsev, VV Mikhailov, VA Sasunkevich (1991) Use of mass spectrometry for the detection and identification of bromine-containing diphenyl ethers. J Chromatogr 586 360-362. 

The structural range of industrially important representatives of these groups is enormous, and includes chlorobenzenes (solvents), polychlorinated biphenyls (PCBs) (hydraulic and insulating fluids), and polybrominated biphenyls and diphenyl ethers (flame retardants). There is widespread concern over both the persistence and the potential toxicity of all these compounds, and sites that have become contaminated during their production represent a threat both to the environment and to human health. Pathways for the aerobic bacterial degradation of chlorobenzenes and chlorobiphe-nyls, and their brominated analogs have been discussed in Chapter 9, Part 1. 

Shi T, Chen SJ, Luo XJ, Zhang XL, Tang CM, Luo Y, Ma YJ, Wu JP, Peng XZ, Mai BX (2009) Occurrence of brominated flame retardants other than polybrominated diphenyl ethers in environmental and biota samples from southern China Chemosphere 74(7) 910-916. doi 10.1016/j. chemosphere.2008.10.047... 

Sakai S-i, Hirai Y, Aizawa H, Ota S, Muroishi Y (2006) Emission inventory of deca-brominated diphenyl ether (DBDE) in Japan. J Mater Cycles Waste Manag 8(1 ) 56—62... 

EPA (1984) Health and environmental effects profile for brominated diphenyl ethers. Environ criteria and assessment office, Cincinnati. US Environmental Protection Agency, (see also... 

BFRs are one of the last classes of halogenated compounds that are still being produced worldwide and used in high quantities in many applications. In order to meet fire safety regulations, flame retardants (FRs) are applied to combustible materials such as polymers, plastics, wood, paper, and textiles. Approximately 25% of all FRs contain bromine as the active ingredient. More than 80 different aliphatic, cyclo-aliphatic, aromatic, and polymeric compounds are used as BFRs. BFRs, such as polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), have been used in different consumer products in large quantities, and consequently they were detected in the environment, biota, and even in human samples [26, 27]. 

There is a huge variety of PBDEs considering that there might be from one to ten bromine atoms bound to the diphenyl ether molecule. Among all the PBDEs, the commercial mixtures of decabromodiphenyl ether (deca-BDE), octabromodiphenyl ether (octa-BDE) and pentabromodiphenyl ether (penta-BDE) are the products that are most found in the environment. Related to octa-BDE and penta-BDE mixtures, their commercial use was banned in the European Union in 2004 and that year their leading manufacturers in North America stopped producing them on a voluntary basis [2], Regarding the deca-BDE mixture, since July 2008, its use has been... 

Keywords Bioaccumulation, Bioavailability, Brominated flame retardants, Hexabromocyclododecane, Polybrominated diphenyl ether... 

The replacement of established chemistries with newer ones is one of the classic drivers of change in the chemical industry. One of the current hotbeds of this kind of change is the replacement of brominated flame retardants in polymer formulations. The brominated flame retardants under the most scrutiny have been polybrominated diphenyl ethers, particularly penta- and octabromodiphenyl ether, which have been shown to be persistent in the environment and to bioaccumulate. Great Lakes Chemical is voluntarily phasing out penta- and octa-BDEs by the end of next year. The phaseout is made possible by the clean bill of health granted by EPA for Firemaster 550, a replacement for penta-BDE in flexible PU applications. BRG Townsend claims the phaseout of penta-BDE and octa-BDE is not as earth shattering as would be an exit from deca-BDE, a styrenics additive that is produced in the highest volume of the PBDEs. 

Proposals to ban two types of brominated flame retardants in electrical and electronic goods are raising controversy in Bmssels. The EU DG XI (Environment) is circulating a draft proposed directive on waste electrical and electronic equipment under which polybrominated biphenyls and polybrominated diphenyl ethers would be banned by 1 January 2004. The proposal is circulating despite risk assessments which show that there is no particular cause for concern and no need for further risk assessment. 

Ikonomou, M.G. Rayne, S. Addison, R.F. 2002a, Exponential increases of the brominated flame retardants, polybrominated diphenyl ethers, in the Canadian Arctic from 1981 to 2000. Environ. Sci. Technol. 36 1886—1892. 

Due to their adverse health effects, several restrictions and bans have been imposed on the usage of polybrominated diphenyl ethers (PBDEs), namely the penta-, octa-, and deca-BDE formulations, in Europe, China, North America, and Japan (http //www. bsef.com). The restricted usage of these PBDEs increased the market demand for substitute brominated flame retardants (BERs) including hexabromocyclododecanes... 

Sjodin A, Bergman A, Pattersson DG Jr (2009) A review on human exposure to brominated flame retardants - particularly polybrominated diphenyl ethers. Environ Int 29 829-839... 

The term brominated flame retardant (BFR) incorporates more than 175 different types of substances, which form the largest class of flame retardants other classes are phosphorus-containing, nitrogen-containing, and inorganic flame retardants (Bimbaum and Sttaskal 2004). The major BFR substances in use today (depicted in Fig. 4.6) are tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and mixtures of polybrominated diphenyl ethers (PBDEs) (namely, deca-bromodiphenyl ether (DBDE), octabromodiphenyl ether (OBDE), and pentabro-modiphenyl ether (pentaBDE)). 

EPA (2000c) Environmental Protection Agency. Integrated risk information system (IRIS) data for brominated diphenyl ethers. Available at http //www.epa.gov/iris EPA (2005a) http //www.epa.gov/OGWDW/dwh/t-ioc/cadmium.html... 

---