Bromine-containing compounds

In spite of the fact that biotechnology rather than chemical processing will probably provide the future greatly needed chirally pure compounds (ref. 1), we believe that simple chemical reactions starting from chiral natural compounds and proceeding under stereochemical control will eventually retain full importance. On the above grounds, we report on simple reactions which start from a-aminoacids, as an example of utilization of natural compounds, and move to related bromine containing compounds (Fig. 1). 

Thus, this first example of stereoselective radical reaction, initiated with the system based on Fe(CO)5, shows opportunities and prospects of using the metal complex initiators for obtaining the stereomerically pure adducts of bromine-containing compounds to vinyl monomers with chiral substituents. 

In the present study, a new way of introducing a non-reactive bromine-containing compound, ammonium bromide, is discussed. The treatment, which can be carried out for many thermoplastic polymers 17,8] in the solid state, is performed in two consecutive stages ... 

Commercially available flame retardants include chlorine- and bromine-containing compounds, phosphate esters, and chloroalkyl phosphates. Recent entry into the market place is a blend of an aromatic bromine compound and a phosphate ester (DE-60F Special) for use in flexible polyurethane foam (8). This paper describes the use of a brominated aromatic phosphate ester, where the bromine and phosphorus are in the same molecule, in high temperature thermoplastic applications. 

Generally, flame retardants for engineering PET compositions are based on bromine-containing compounds (such as brominated polycarbonate, decabro-modiphenyl oxide, brominated acrylic, brominated polystyrene, etc.). Such compounds are available commercially (such as from the Ethyl Chemical Corporation, Great Lakes Chemical Corporation, Dead Sea Bromine Company, etc.) In addition, the flame-retardant package generally contains a synergist, typically sodium antimonate. PET may also be flame-retarded with diarylphosphonate, melamine cyanurate or red phosphorus. 

The mass spectra of chlorine- and bromine-containing compounds clearly show the abundance ratios of the stable isotopes 35C1 37C1 = 3 1 and 79Br 81Br = 1 1 in the molecular ions and those ionic fragments which contain halogens (see Section 9-11). 

The uptake coefficients for reactions involving other bromine containing compounds are generally high. The y-values for reactions (13), (16) to (18) on sulfate aerosol and water-ice substrates are in the order of 0.1 to 0.3. Reactions involving BrONO, on sulfuric acid solutions occur with near unity efficiency, except at concentrations >70 wt %, where ydrops to 0.1 at 85 wt % [99-101]. 

Ozone depletion Destruction of the stratospheric ozone layer that protects the Earth from harmful effects of ultraviolet radiation. Depletion of the ozone layer is due to the breakdown of certain chlorine- or bromine-containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules. 

Oxidizer Chemical substance that causes oxygen to combine with another chemical substance examples include oxygen and hydrogen peroxide Ozone depletion Destruction of the stratospheric ozone layer that protects the Earth from harmful effects of ultraviolet radiation. Depletion of ozone layer is due to the breakdown of certain chlorine- and/or bromine-containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules Ozone layer Protective layer in the atmosphere, about 15 miles above the ground. The ozone layer absorbs some of the sun s ultraviolet rays, thereby reducing the amount of potentially harmful radiation that reaches the Earth s surface PAHs Polycyclic aromatic hydrocarbons... 

Bromine-containing compounds have the potential to released Br atoms upon degradation in the atmosphere. Once in the stratosphere, Br atoms are about 45 times more effective than chlorine in destroying stratospheric ozone [22]. An important example of Br-containing compounds is 1-bromopropane, which is currently utilized as a industrial solvent and have been proposed as a replacement for CFCs, controlled under the agreements of fhe Montreal Protocol. 

Bromine is used in silver bromide—based photographic films. It is also used to make NaBr and KBr, two chemicals used in sedatives and soporifics (sleeping aids). Bromine-containing compounds are also used as flame retardants for cloth (see Section 22.5). 

Flame-retardant styrenic polymers find utility in applications such as building insulation (expanded polystyrene foam) and electronic enclosures (flame-retardant HIPS, ABS and styrenic blends). The most effective flame retardants are halogen-(particularly bromine)-containing compounds these flame retardants act by inhibiting the radical combustion reactions occurring in the vapor phase. Flame-retardant plastics are in a state of flux, due to influences of... 

The three possible approaches to flame-retardant polyester - additives to the polymer melt, flame-retardant copolymers and topical finishes - have all been used commercially to produce flame-retardant polyester textiles. All the methods employ phosphorous- or bromine-containing compounds as the active flame retardant. 

Ethoxyethyl)-5-hydroxy-2-methylpyrazine heated in acetic acid saturated with hydrogen bromide formed a crystalline bromine-containing compound which with 5% sodium carbonate gave 5-hydroxy-2-methyl-3-vinylpyrazine (248). Heteromacrocyclic ethers have been quaternized (989). 

An electron-transfer mechanism from the photosensitizer excited state to triazines has been proposed, which has permitted a satisfactory interpretation of the observed fluorescence quenching. The steps of the photosensitization mechanism of PAGs with bromine-containing compounds by BPHTs are summarized below ... 

Bromine compounds are much more expensive than chlorine compounds and, since the atomic weight of bromine is about twice that of chlorine, the halogen cost incurred in the use of bromine compounds as intermediates is likely to be at least an order of magnitude greater than the cost of the corresponding chlorine compound. Not least for this reason, the synthesis of phosgene from bromine-containing compounds is unlikely to be economically practical and are probably not worthy of development on a purely commercial basis. However, C-Br bonds are more readily cleaved than C-CI bonds, and bromide is readily oxidized back to bromine. 

Numerous chlorine, fluorine, and bromine-containing compounds (halocarbons) are produced at the Earth s surface, both by natural and... 

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