Hydrogen Bromide - Laboratory Synthesis

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.