HBr can be prepared by distillation of a solution of sodium bromide or potassium bromide with phosphoric acid or sulfuric acid:
: KBr + HSO → KHSO + HBr
Concentrated sulfuric acid is less effective because it oxidizes HBr to bromine:
: 2 HBr + HSO → Br + SO + 2 HO
The acid may be prepared by:
* reaction of bromine with water and sulfur:
*: 2 Br + S + 2 HO → 4 HBr + SO
* bromination of tetralin:
*: CH + 4 Br → CHBr + 4 HBr
* reduction of bromine with phosphorous acid:
*: Br + HPO + HO → HPO + 2 HBr
Anhydrous hydrogen bromide can also be produced on a small scale by thermolysis of triphenylphosphonium bromide in refluxing xylene.
Hydrogen bromide prepared by the above methods can be contaminated with Br, 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 in the process) or through copper turnings or copper gauze at high temperature.