Bromine reaction with hydrogen

Bromine, like chlorine, also undergoes a photochemical chain reaction with hydrogen. The reaction with bromine, however, evolves less energy and is not explosive. 

Bromination of methane is exothermic but less exothermic than chlorination The value calculated from bond dissociation energies is AH° = -30 kJ Al though bromination of methane is energetically fa vorable economic considerations cause most of the methyl bromide prepared commercially to be made from methanol by reaction with hydrogen bromide... 

Conjugated Double Bonds. Sorbic acid is brominated faster than other olefinic acids (7). Reaction with hydrogen chloride gives predominately 5-chloro-3-hexenoic acid (8). 

Reaction with Hydrogen and Metals. Bromine combines directiy with hydrogen at elevated temperatures and this is the basis for the commercial production of hydrogen bromide [10036-10-6]. Heated charcoal and finely divided platinum metals are catalysts for the reaction (17). 

At 225—275°C, bromination of the vapor yields bromochloromethanes CCl Br, CCl2Br2, and CClBr. Chloroform reacts with aluminum bromide to form bromoform, CHBr. Chloroform cannot be direcdy fluorinated with elementary flourine fluoroform, CHF, is produced from chloroform by reaction with hydrogen fluoride in the presence of a metallic fluoride catalyst (8). It is also a coproduct of monochlorodifluoromethane from the HF—CHCl reaction over antimony chlorofluoride. Iodine gives a characteristic purple solution in chloroform but does not react even at the boiling point. Iodoform, CHI, may be produced from chloroform by reaction with ethyl iodide in the presence of aluminum chloride however, this is not the route normally used for its preparation. 

As in the case of the steroids, introduction of additional nuclear substituents yields morphine analogs of increased potency. The more important of these are derived from one of the minor alkaloids that occur in opium. Thebaine (14), present in crude opium in about one-tenth the amount of morphine, exhibits a reactive internal diene system that is well known to undergo various addition reactions in a 1,4 manner (e.g., bromination). Thus, reaction with hydrogen peroxide in acid may be visualized to afford first the 14-hydroxy-6-hemiketal (15). Hydrolysis yields the isolated unsaturated ketone (16). Catalytic reduction... 

The 2,5-dibromo-2,5-dideoxy-D-xylono-1,4-lactone (6) (Scheme 2) can also be selectively reduced to give 5-bromo-2,5-dideoxy-D-fhreo-pentonolactone (7) by reaction with either aqueous hydrazine as mentioned above, or by consumption of 1 mole of hydrogen [ 14]. Further reaction with hydrogen and Pd/C leads to 3-hydroxypentanoic acid by an initial reductive elimination [15]. Reduction of the primary bromine in these cases can be obtained by means of tributyltin hydride [25] to give 8. 

SAFETY PROFILE Poison by subcutaneous, intravenous, and intramuscular routes. Moderately toxic by other routes. A severe eye irritant. Mutation data reported. Explosive reaction with potassium chlorate or bromine trifluoride. Violent reaction (ignition) with bromine pentafluoride, NH4, NO3, and IF7. Reaction with hydrogen cyanide may give the explosive nitrogen trichloride. When heated... 

OSHA PEL TWA 2 mg(Sn)/m3 ACGIH TLV IW A 2 mg(SnVm3 SAFETY PROFILE Poison by ingestion, intraperitoneal, intravenous, and subcutaneous routes. Experimental reproductive effects. Human mutation data reported. Potentially explosive reaction with metal nitrates. Violent reactions with hydrogen peroxide, ethylene oxide, hydra2ine hydrate, nitrates, K, Na. Ignition on contact with bromine trifluoride. A vigorous reaction with calcium acetylide is initiated by flame. When heated to decomposition it emits toxic fumes of Cl. See also TIN COMPOUNDS. 

When 3,4-disubstituted 4-aminoisoxazolin-5(4Af)-ones (9) are hydrogenated, and then subsequently recyclized, high yields of imidazoles (10) are obtained (Scheme 6.1.4). The starting materials can be readily made from isoxazolin-5(4Af)-ones by sequential bromination, reaction with sodium azide and conversion of azide into amino by reaction with hydrobromic acid in acetic acid. The amines are then converted into formamidine or acetamidine derivatives with DMF or dimethylacetamide under reflux in phosphoryl chloride-chloroform. Yields at this stage are 50-93%. Catalytic... 

The chemical properties of bromine are similar to those of chlorine, but it is less active. Thus, for example, in order to bring about the reaction with hydrogen it is not sufficient to expose the mixture to light, but it is also necessary to heat it. 

The alk)mes contain two pi bonds, both of which are sources of electrons, and they are more reactive than the alkenes. The most common reaction of the alkynes is addition across the triple bond. The reactions with hydrogen and with bromine are typical. 

The reactions of alkylcyclopropanes with bromine and with hydrogen bromide have been investigated in detail. Methylcyclopropane (4, R = Me) scarcely underwent addition of bromine in the cold when light and catalysts were excluded. Similar observations were made with other alkyl-substituted cyclopropanes 4 such as ethylcyclopropane, butylcyclopropane, cis-and trans-1,2-dimethylcyclopropane. ... 

The 1,2,3-trihydroxypropyl side chain of pyrazol-3-ones 92a,b was efficiently brominated at positions 2 and 3 by reaction with hydrogen bromide acetic acid. The products, 2,3-dibromopropyl acetates 93a,b were obtained in 71% and 70% yield, respectively (88PHA77) (Scheme 25). 

---