Laboratory Synthesis
HBr can be synthesized by a variety of methods. It may be prepared in the laboratory by distillation of a solution of sodium or potassium bromide with phosphoric acid or diluted sulfuric acid:
- 2 KBr + H2SO4 → K2SO4 + 2HBr
Concentrated sulfuric acid is ineffective because HBr formed will be oxidized to bromine gas:
- 2 HBr + H2SO4 → Br2 + SO2 + 2H2O
The acid may be prepared by several other methods, as well, including reaction of bromine either with phosphorus and water, or with sulfur and water:
- 2 Br2 + S + 2 H2O → 4 HBr + SO2
Alternatively, it can be prepared by the bromination of tetraline (1,2,3,4-tetrahydronaphthalene):
- C10H12 + 4 Br2 → C10H8Br4 + 4 HBr
Alternatively bromine can be reduced with phosphorous acid:
- Br2 + H3PO3 + H2O → H3PO4 + 2 HBr
Anhydrous hydrogen bromide can also be produced on a small scale by thermolysis of triphenylphosphonium bromide in refluxing xylene.
HBr prepared by the above methods can be contaminated with Br2, which can be removed by passing the gas through Cu turnings or through phenol.
Read more about this topic: Hydrogen Bromide
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