Bromine vapor, bromination with

Furan can be catalyticaHy oxidized in the vapor phase with oxygen-containing gases to maleic anhydride (93). Oxidation with bromine or in an electrochemical process using bromide ion gives 2,5-dimethoxy-2,5-dihydrofuran [332-77-4] (19) which is a cycHc acetal of maleic dialdehyde (94—96). 

BeryUium bromide [7787-46-4], BeBr2, and beryUium iodide [7787-53-3], Bel2, are prepared by the reaction of bromine or iodine vapors, respectively, with metallic beryUium at 500—700°C. They cannot be prepared by wet methods. Neither compound is of commercial importance and special uses are unknown. 

Fig. 44. An optical resonance spectrum from Tallin and Davis (1990) for the chemical reaction between an octadecene droplet and bromine vapor. Reprinted with permission from J. Aerosol Sci. 21, 73-86, Tallin, D. C., and Davis, E. J., <3opyr t 1990, Pergamon Press pic.

Similarly, arsenic tribromide AsBrs forms when the trioxide reacts with bromine vapors. Reaction with concentrated HCI under heating produces arsenic trichloride. 

Molybdenum (II) bromide was prepared first by Blomstrand8 by passing bromine vapor over heated molybdenum. Lindner et al.9 then improved the method by using bromine vapor diluted with nitrogen. More recently Sheldon10 converted molybdenum(II) chloride to the bromide by fusion with lithium bromide. Like the chloride, molybdenum(II) bromide is usually an amorphous powder however, crystalline samples have been prepared by disproportionation of molybdenum (III) bromide under vacuum at 600°C.1 Our method is substantially that of Sheldon and consists of heating an intimate mixture of molybdenum (II) chloride and a large excess of lithium bromide under vacuum. The crude product that results is dissolved in dilute sodium hydroxide and precipitated in pure form with concentrated hydrobromic acid. 

Bromobenzoyl. This compound is formed directly by mixing bromine with hydrobenzoyl (bitter almond oil). The mixture becomes heated and throws forth thick vapors of hydrobromic acid. By heating still farther, this acid as well as the excess of bromine is expelled. 

The bromination of poly-DCH is of interest because the degree of bromine uptake can be controlled, by choice of experimental conditions, between 3 and 8 Br atoms per polymer repeat unit and because a crystal-to-crystal transformation is observed. Scheme 1 summarizes the reactions of liquid bromine with poly-DCH. Interaction of poly-DCH crystals with dense vapors of bromine or cyanogen bromide for months did not lead to detectable weight gain. By contrast, DCH monomer (2a), which has a crystal structure similar to the polymer (6), readily reacts with bromine vapor to give an eunor-phous material which has gainbd ca 12 Br atoms per molecule. 

B4C reacts with CO2 to yield B2O3 and CO or free carbon [96]. Boron carbide neither interacts with sulfur and phosphorus vapors, nor with nitrogen up to 1200°C. BN can be formed upon reaction with nitrogen at higher temperatures, or when ammonia is added. With chlorine it reacts above 1000°C to form BCI3 and graphite. Bromine and iodine do not react with B4C [98],... 

The BrCl tends to decompose more to the elements as vaporization continues. It is therefore possible to recover elemental bromine. With most salts, the quantity available is too small to be attractive, and any attempt at bromine recovery will also aggravate the problems of the presence of nitrogen trichloride. 

Bromine is a dark red-brown liquid (BP = 59 °C) with a vapor pressure of 175 mm Hg at 20 °C. It is highly corrosive to the skin and either liquid or vapor contact with eyes is painful and destructive. Lachrymation, or tearing, begins at around 1 ppm, which functions as a good warning sign of exposure. Like chlorine, bromine can be fatal at 1000 ppm for short exposures. 

At elevated temperatures (250-400°C) bromine reacts with thiazole in the vapor phase on pumice to afford 2-bromothiazole when equimolecu-lar quantities of reactants are mixed, and a low yield of a dibromothiazole (the 2,5-isomer) when 2 moles of bromine are used (388-390). This preferential orientation to the 2-position has been interpreted as an indication of the free-radical nature of the reaction (343), a conclusion that is in agreement with the free-valence distribution calculated in the early application of the HMO method to thiazole (Scheme 67) (6,117). 

Loaded Adsorbents. Where highly efficient removal of a trace impurity is required it is sometimes effective to use an adsorbent preloaded with a reactant rather than rely on the forces of adsorption. Examples include the use of 2eohtes preloaded with bromine to trap traces of olefins as their more easily condensible bromides 2eohtes preloaded with iodine to trap mercury vapor, and activated carbon loaded with cupric chloride for removal of mercaptans. 

The iodides of the alkaU metals and those of the heavier alkaline earths are resistant to oxygen on heating, but most others can be roasted to oxide in air and oxygen. The vapors of the most volatile iodides, such as those of aluminum and titanium(II) actually bum in air. The iodides resemble the sulfides in this respect, with the important difference that the iodine is volatilized, not as an oxide, but as the free element, which can be recovered as such. Chlorine and bromine readily displace iodine from the iodides, converting them to the corresponding chlorides and bromides. 

Eigure 3 is a flow diagram which gives an example of the commercial practice of the Dynamit Nobel process (73). -Xylene, air, and catalyst are fed continuously to the oxidation reactor where they are joined with recycle methyl -toluate. Typically, the catalyst is a cobalt salt, but cobalt and manganese are also used in combination. Titanium or other expensive metallurgy is not required because bromine and acetic acid are not used. The oxidation reactor is maintained at 140—180°C and 500—800 kPa (5—8 atm). The heat of reaction is removed by vaporization of water and excess -xylene these are condensed, water is separated, and -xylene is returned continuously (72,74). Cooling coils can also be used (70). 

Flame Retardants. Flame retardants are added to nylon to eliminate burning drips and to obtain short self-extinguishing times. Halogenated organics, together with catalysts such as antimony trioxide, are commonly used to give free-radical suppression in the vapor phase, thus inhibiting the combustion process. Some common additives are decabromodiphenyl oxide, brominated polystyrene, and chlorinated... 

Nitrogen and sodium do not react at any temperature under ordinary circumstances, but are reported to form the nitride or azide under the influence of an electric discharge (14,35). Sodium siHcide, NaSi, has been synthesized from the elements (36,37). When heated together, sodium and phosphoms form sodium phosphide, but in the presence of air with ignition sodium phosphate is formed. Sulfur, selenium, and tellurium form the sulfide, selenide, and teUuride, respectively. In vapor phase, sodium forms haHdes with all halogens (14). At room temperature, chlorine and bromine react rapidly with thin films of sodium (38), whereas fluorine and sodium ignite. Molten sodium ignites in chlorine and bums to sodium chloride (see Sodium COMPOUNDS, SODIUM HALIDES). 

Introduction of a 3-bromosubstituent onto thiophene is accompHshed by initial tribromination, followed by reduction of the a-bromines by treatment with zinc/acetic acid, thereby utilizing only one of three bromines introduced. The so-called halogen dance sequence of reactions, whereby bromothiophenes are treated with base, causing proton abstraction and rearrangement of bromine to the produce the most-stable anion, has also been used to introduce a bromine atom at position 3. The formation of 3-bromotbiopbene [872-31-1] from this sequence of reactions (17) is an efficient use of bromine. Vapor-phase techniques have also been proposed to achieve this halogen migration (18), but with less specificity. Table 3 summarizes properties of some brominated thiophenes. 

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