Brominated compounds phenols

Bromination can be conveniently effected by transfer of bromine from one nucleus to another. As the Friedel-Crafts isomerization of bromoaromatic compounds generally takes place through an intermolecular mechanism, the migrating bromine atom serves as a source of positive bromine, thus effecting ring brominations (161,162). 2,4,6-Tribromophenol, for example, has been prepared by bromination of phenol with dibromobenzene. 

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

Evidence for molecular chlorine or bromine as the attacking species in these cases is that acids, bases, and other ions, especially chloride ion, accelerate the rate about equally, though if chlorine dissociated into Cl" and Cl , the addition of chloride should decrease the rate and the addition of acids should increase it. Compound 27 has been detected spectrally in the aqueous bromination of phenol. ... 

Selecting from scientific literature and reviews, Riskcycle researchers have defined a preliminary list of 16 additives of interest which will be analyzed and evaluated for a waste-related risk assessment chosen compounds include perfluorinated and brominated compounds, phthalates, phenols, and some heavy metals (Table 6). 

Chemical/Physical. Hypochlorous acid reacted with p bromophenol forming dichlorophenol, 4-chlorophenol, bromochlorophenol, dibromophenol, bromodichlorophenol, and dibromochloro-phenol. The displacement of bromine atom by chlorine yields hypobromous acid which then displaces a hydrogen atom from another brominated compound forming brominated substances, e.g., bromochlorophenol, dibromophenol, etc. (Hwang et al., 1988). 

Other fire retardants used include aluminum hydrate, antimony oxide, and molybdenum compound. Halogenated phosphate esters used in polyurethane foams and bromine compounds used in polyolefin foams are not used in phenolic foams. Flame retardants are used mostly in powder form, and accordingly, their distribution conditions are dependent on their particle size and shape. 

There are numerous procedures for the bromination of phenolic compounds and the regioselectivity in these reactions has been frequently achieved by varying the nature of the solvent system. Controlled monobromination of phenols can be achieved using N-bromosuccinimide (MBS) on silica gel . ... 

On p. 479 of the textbook we explain the formation of 2,4,6-tribromophenol by bromination of phenol in water. It looks as though we can go no further as all the ortho and para positions are brominated. But we can if we treat the tribromo-compound with bromine in an organic solvent. Account for the formation of the tetrabromo-compound. 

For quality control reasons, rapid screening methods are needed to identify the volatiles in polymeric materials collected for recycling. HS-SPME-GC-MS was shown to be a fast and sensitive method to screen for brominated flame retardants in recycled polyamide materials [78]. HS-SPME effectively extracted several brominated compounds, all possible degradation products from the common flame-retardant Tetrabromobisphenol A from recycled polyamide 6.6. Furthermore, the high extraction capacity of the PDMS/DVB stationary phase towards aromatic compounds was demonstrated, as the HS-SPME-GC-MS method allowed the extraction and iden-tiflcation of brominated benzenes, from a complex matrix only containing trace amounts of analytes. In addition, degradation products from an antioxidant, a hindered phenol, were extracted. Figure 14 shows a typical chro-... 

The simplest method for the synthesis of m-brominated phenolics is the bromination of o- and p-substituted phenolics. As shown in the following equations, mesitol was brominated to give 3-5 dibromomesitol (8). The o-substituted tetramethyl bisphenol gave tri- and tetra-brominated compounds (9). Similar substitution occurs with the o-substituted tetramethyl bisphenol ethane (10). 

Brominated compounds, where the bromine is in the meta position to the phenolic hydroxyl, have been shown to be more hydrolytically and thermally stable than ortho-brominated compounds such as TBBA (4). These stable bromine compounds can be incorporated in the CEN molecule and formulated into a molding compound. These molding compounds provide increased device reliability without sacrificing any of the beneficial properties of present molding compounds. 

Halogenated compounds were detected in higher concentrations in all Rhine water samples investigated. Surprisingly, the halogenated aromatics were highly dominated by brominated compounds comprising brominated phenols, (methoxyphenyl)propionic acids and... 

Chlorinated and brominated materials are burned or thermally treated in a variety of combustion sources including hazardous and municipal waste incinerators, industrial processes, backyard trash burning, and accidental fires. Chlorinated materials are used in a wide range of applications and brominated compounds are fire retardants used in many devices including electronic circuits. Although there has been some research on the reactions of CHCs and BHCs in the past 20 years, too little is known about their reactions considering the magnitude of the environmental impact. Elementary reaction studies of gas-phase reactions of Cj and C2, CHCs, and BHCs are needed to understand their most fundamental reaction properties. Reactions of the chlorinated and brominated benzenes and phenols are important intermediate steps in the formation of PCDD/F. Recent kinetic models indicate that the gas-phase reactions may be quite important and elementary gas-phase reaction studies have been overlooked by researchers. 

Bromination of Aromatic Compounds. Phenols, anilines, and other electron-rich aromatic corrqiounds can be monobromi-nated using NBS in DMF with higher yields and higher levels of para selectivity than with Br2 iV-TrimethyIsilylanilines and aromatic ethers are also selectively brominated by NBS in CHCI3 or ecu. A-Substituted pyrroles are brominated with NBS in THF to afford 2-bromopyrroles (1 equiv) or 2,5-dibromopyrroles (2 equiv) with high selectivity, whereas bromination with Br2 affords the thermodynamically more stable 3-bromopyrroles. The use of NBS in DMF also achieves the controlled bromination of imidazole and nitroimidazole. Thiophenes are also selectively brominated in the 2-position using NBS in acetic acid-chloroform. ... 

Bromination of Aromatic Compounds. Studies on the bromination of monocyclic and polycyclic aromatic compounds with NBS have continued and in particular the bromination of phenols and naphthols has received attention, e.g., the conversion of 6 into 7 (eq 35). 

Bromine compounds with exclusively aromatic-bound bromine are produced in large quantities. Occupying the first place is tetrabromobios-phenol-A, which is employed as a reactive flame retardant in polycarbonates and epoxy resins. Similarly, tetrabromophthalic anhydride has been used in the production of flame-retarded unsaturated polyester resins. 

Hydrofluoric acid Phosphorous Bromine, iodine Phenolic compounds... 

Phenols are so reactive toward electrophilic aromatic substitution that all unsubstituted positions ortho and para to the hydroxy group are brominated. The brominated compounds so formed are often solids and may be used as derivatives (Sec. 25.12E). Aniline and substituted anilines are also very reactive toward bromine and react analogously however, solubility tests are normally used to distinguish between anilines and phenols. 

The Hazards Substance Ordinance in Germany specifies the maximum level of chlorinated dibenzo-dioxins and furans that can be present in materials marketed in Germany. This has been extended to the brominated compounds. The two largest volume flame retardants decabromodiphenyl oxide and tetrabromo his-phenol A - are said to meet these requirements [1,2]. 

Effective use can sometimes be made of removable blocking groups on the ring. Suppose you are set the task of making pure < -bromophenol. Simple bromination of phenol will fail because of the dominant formation of the para isomer or of poly-brominated compounds (Fig. 14.90). A solution to this problem is first to sulfonate... 

Most material on bromine compounds is discussed under oscillating reactions. Pulse radiolysis of aqueous solutions of bromate gives the dioxide Br02. This is reduced by hexacyanoferrate(II) and phenoxide in clean, fast reactions. Reductions by manganese(II) and phenol are slower and more complex as complications arise from dimerization of BrOi to give Br204,... 

Polyamide 6 and polyamide 66 are not resistant to halogens (fluorine, chlorine, bromine, iodine), phenols, mineral acids, and certain organic and inorganic acids, sometimes even at low concentrations, neither are they resistant to strong oxidants, such as ozone, hypochlorite, and per -compounds, such as potassium permanganate and oxidizing acids. 

Bromine compounds which are particularly efficient are brominated phenol respectively bisphenol A ether, hexabromocyclododecane, and bromine containing Diels Alder reaction products based on hexachlorocyclopentadiene [29]. 

Bromination of Aromatic Compounds. Phenols, anilines, and other electron-rich aromatic compounds can be monobromi-nated using NBS in DMF with higher yields and higher levels of para selectivity than with Br2 M-Trimethylsilylanilines and aro-... 

---