Hydrogen bromide is the inorganic compound with the formula HBR, It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water to form hydrobromic acid , which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by mass form a steady-boiling azeotrope mixture that boils at 124.3 °C. Boiling less concentrated solutions releases H2 O until the steady-boiling mixture reaches composition.
Hydrogen bromide, and its aqueous solution, are commonly used reagents in the preparation of bromide compounds.
reactions
organic Chemistry
Hydrogen bromide and hydrobromic acid are important reagents in the production of organobromine compounds. [8] [9] [10] In a free-radical reaction, HBr adds to the alkanes:
RCH = CH 2 + HBr → R CHBr-CH 3
The resulting alkyl bromides are useful alkylating agents, for example, as precursors of fatty amine derivatives. Relaated to free radicals excess allyl chloride and styrene to give 1-bromo-3-chloropropane and phenylethylbromide, respectively.
Hydrogen bromide reaction with chlorides give bromochloromethane and dibromomethane, sequentially:HBr + CH 2 Cl 2 → HCl + CH 2 BrClHBr + CH 2 BrCl → HCl + CH 2 Br 2
These metathesis reactions reflect the consumption of strong acid (HBr) and release of weak acid (HCl).
Allyl bromide is prepared by treating allyl alcohol with HBr:
CH 2 =CHCH 2 OH + HBr → CH 2 =CHCH 2 Br + H 2 O
Adds alkynes to HBR to yield bromoalkenes. The stereochemistry of this type of joint is usually opposite :
RC≡CH + HBr → RC(Br) = CH 2
In addition, HBr adds epoxides and lactones, resulting in ring-opening.
With triphenylphosphine, HBr gives triphenylphosphonium bromide, which is a solid “source” of HBr.
P(C 6 H 5 ) 3 + HBr → [HP (C 6 H 5 ) 3 ] + Br –
inorganic Chemistry
Vanadium(III) bromide and molybdenum(IV) bromide were prepared by treatment of high chloride with HBr. These reactions proceed through redox reactions:
2 VCl 4 + 8 HBr → 2 VBr 3 + 8 HCl + Br 2
industrial preparation
Hydrogen bromide (with hydrobromic acid) is made by mixing hydrogen and bromine at temperatures between 200 and 400 °C. The reaction is usually catalyzed by platinum or asbestos.
laboratory synthesis
HBr can be prepared by distillation of sodium bromide or potassium bromide with phosphoric acid or sulfuric acid:
KBr + H 2 SO 4 → KHSO 4 + HBr
Concentrated sulfuric acid is less effective because it oxidises HBr to bromine:
2 HBr + H 2 SO 4 → Br 2 + SO 2 + 2 H 2 O
Acid can be prepared by:
- Reaction of bromine with water and sulphur:
2Br 2 + S + 2H 2 O → 4HBr + SO 2
- Bromination of Tetraline:
C 10 H 12 + 4 Br 2 → C 10 H 8 Br 4 + 4 HBr
- Reduction of bromine with phosphorous acid:
Br 2 + H 3 PO 3 + H 2 O → H 3 PO 4 + 2 HBr 2
Anhydrous hydrogen bromide can also be produced on a small scale by thermolysis refluxing of triphenylphosphonium bromide in xylene. [11 1]
Hydrogen bromide prepared by the above methods can be contaminated with Br 2 , which can be removed by passing the gas through a solution of phenol at room temperature in tetrachloromethane or other suitable solvent (producing 2,4,6-tribromophenol and generating more HBr) process) or through copper turning or copper gauze at high temperature. [13]
Security
HBr is highly corrosive and irritating to inhalation.
