Bromine, elemental reactions with

Elemental bromine is a diatomic molecule (Bt2). Bromine will combine with most other elements. Reaction with metallic elements leads to salts such as silver bromide (AgBr), in which the bromine atom has a — 1 charge and oxidation number. Bromine forms many interesting covalent compounds as well, including two oxides bromine (TV) oxide (Br02) and bromine... 

Halobutyls. Chloro- and bromobutyls are commercially the most important butyl mbber derivatives. The halogenation reaction is carried out in hydrocarbon solution using elemental chlorine or bromine (equimolar ratio with enchained isoprene). The halogenation is fast, and proceeds mainly by an ionic mechanism. The stmctures that may form include the following ... 

The low concentration of elemental bromine required for the chain propagation step is generated from NBS 4 by reaction with the hydrogen bromide that has been formed in the first step ... 

By this reaction a constantly low concentration of elemental bromine is supplied. With higher concentrations of free bromine, an addition to the carbon-carbon double bond is to be expected. 

In its reactions SsO shows properties typical for both sulfur homocycles and sulfoxides. With elemental chlorine SOCI2 and S2CI2 are formed, with bromine SOBr2 and S2Br2 are obtained. Water decomposes SsO to H2S and SO2 besides elemental sulfur while cyanide ions expectedly produce thiocyanate. The reaction with iodide in the presence of formic acid is used for the iodometric determination of the oxygen content [70] ... 

One Au-C bond in bis(thiazol-2-ylidene)gold cations is cleaved in the reaction with elemental iodine to give the corresponding (carbene)AuI complex and a 2-iodo-thiazolium salt, while chlorine and bromine oxidize the gold center to the gold(m) state.267... 

Undoubtedly, the best method for the production of pure anhydrous lanthanide trihalides involves direct reaction of the elements. However, suitable reaction vessels, of molybdenum, tungsten, or tantalum, have to be employed silica containers result in oxohalides (27). Trichlorides have been produced by reacting metal with chlorine (28), methyl chloride (28), or hydrogen chloride (28-31). Of the tribromides, only that of scandium has been prepared by direct reaction with bromine (32). The triiodides have been prepared by reacting the metal with iodine (27, 29, 31, 33-41) or with ammonium iodide (42). 

The starting diol was transformed into the dibromide by elemental bromine with triphenyl phosphine adduct which undergoes the Arbuzov-Michaelis reaction under somewhat drastic conditions at 150 °C (step a). Catalytic removal of the benzyl group was performed by a Pd/C catalyst (step b) and the alcohol formed was allowed to react with dichloropurine in the presence of triphenylphosphine and diethylazodicarboxylate (Mit-sunobu reaction) (step c). Finally the desired product was obtained by reaction with methylamine (step d) and the removal of ethyl groups at the phosphorus centre was performed by transilylation using trimethyliodosilane (step e). 

Very recently, Hu et al. claimed to have discovered a convenient procedure for the aerobic oxidation of primary and secondary alcohols utilizing a TEMPO based catalyst system free of any transition metal co-catalyst (21). These authors employed a mixture of TEMPO (1 mol%), sodium nitrite (4-8 mol%) and bromine (4 mol%) as an active catalyst system. The oxidation took place at temperatures between 80-100 °C and at air pressure of 4 bars. However, this process was only successful with activated alcohols. With benzyl alcohol, quantitative conversion to benzaldehyde was achieved after a 1-2 hour reaction. With non-activated aliphatic alcohols (such as 1-octanol) or cyclic alcohols (cyclohexanol), the air pressure needed to be raised to 9 bar and a 4-5 hour of reaction was necessary to reach complete conversion. Unfortunately, this new oxidation procedure also depends on the use of dichloromethane as a solvent. In addition, the elemental bromine used as a cocatalyst is rather difficult to handle on a technical scale because of its high vapor pressure, toxicity and severe corrosion problems. Other disadvantages of this system are the rather low substrate concentration in the solvent and the observed formation of bromination by-products. 

Recently, however, Tokitoh and co-workers " °° reported a versatile reactivity of Tbt-substituted plumbylenes 182a-d, that is, insertion reactions with alkyl halides, diphenyl dichalcogenides, bromine abstraction from carbon tetrabro-mide, and sulfurization with elemental sulfur as shown in Scheme 14.83. 

Two of these different isomers, 2,4-DMA and 2,5-DMA, have already been discussed in their own separate recipes. And the remaining three of the six possible DMA s that are different have been made and studied pharmacologically in animals but not in man. These are the 2,3-DMA, 2,6-DMA and the 3,5-DMA isomers. The products of their reaction with elemental bromine are discussed under META-DOB. 

SYNTHESIS (from protocateehualdehyde) A solution of 18 g commercial protocatechualdehyde (3,4-dihydroxybenzaldehyde) in 200 mL warm acetic acid was filtered free of any insolubles, to provide a very dark but clear solution. With good stirring there was then added 20 g elemental bromine. The reaction spontaneously heated to about 30 °C and solids appeared in about 5 min. Stirring was continued for 1 h, and then the light gray solids that had formed were removed by filtration and lightly washed with acetic acid. 

Reaction with bromine. Unsaturated hydrocarbons react rapidly with bromine in a solution of carbon tetrachloride or cyclohexane. The reaction is the addition of the elements of bromine to the carbons of the multiple bonds. 

Dibromoselenuranes 196 can be prepared from the corresponding selenides by reaction with elemental bromine. The a,/ -unsaturated ester 196 is converted into the a-bromo-/ ,7-unsaturated ester 197 by elimination of phenyl-selenenyl bromide (Scheme 58).338 Dibromoselenuranes from propargylic selenides undergo similar reactions leading to either allenes or propargylic bromides.339... 

Diorgano tellurium compounds are easily converted to diorgano tellurium diiodides upon treatment with elemental iodine. The reactions are carried out with solvents such as benzene, chloroform, carbon tetrachloride, and 1,2-dichloroethane. Because iodine is much less reactive than chlorine or bromine, the reactions can be performed at 20 . The diorganyl tellurium diiodides generally precipitate upon mixing the reagents. 

Bromine monofluoride is much less stable than C1F, although it has been prepared by reaction of the elements diluted with nitrogen ... 

Bromine trifluoride is produced on a commercial scale by the reaction of elemental fluorine with bromine in a continuous gas-phase process. The ratio of bromine to fluorine is maintained close to 1 3. It can also be produced on a batch scale... 

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