Hydrobromic acid

Hydrobromic acid is a strong acid that is formed by dissolving the diatomic molecule hydrogen bromide (HBr) in water. “Constant boiling” hydrobromic acids is an aqueous solution that is distilled at 124.3 °C and contains 47.6% HBr by mass, which is 8.77 mol/L. Hydrobromic acid has a p k of -9, making it a stronger acids than hydrochloric acid , but not as strong as hydroiodic acid . Hydrobromic acids is one of the strongest mineral acids known .


Hydrobromic acid is mainly used for the production of inorganic bromides, especially bromides of zinc, calcium and sodium. It is a useful reagent for generating organobromine compounds. Some ethers are associated with HBr. It also catalyzes alkalinization reactions and extraction of some ores. Industrially important organic compounds prepared from hydrobromic acid include allyl bromide, tetrabromobis (phenol), and bromoacetic acid. HBr participates almost exclusively in the Markovnikov hydrohalogen antagonism of alkanes. The resulting 1-bromoalkanes are versatile alkylating agents, giving rise to fatty amines and quaternary ammonium salts. [2]


Hydrobromic acid can be prepared in the laboratory through the reaction of Br 2 , SO 2 and water. [3]Br 2 + SO 2 + 2 H 2 O → H 2 SO 4 + 2 HBr

More generally laboratory preparation involves the production of anhydrous HBr, which is then dissolved in water.

Hydrobromic acid is usually prepared industrially by reacting bromine with sulfur or phosphorus and water. However, it can also be produced electrolytically. [3] It can also be prepared by treating the bromide with a non-oxidizing acid such as phosphoric or acetic acid.

Alternatively the acid can be prepared with dilute (5.8 M) sulfuric acid and potassium bromide: [4]2 SO 4 + KBr → KHSO 4 + HBr

Using more concentrated sulfuric acid or allowing the reaction solution to exceed 75 °C oxidizes HBr to bromine gas. The acid is further purified by filtration of KHSO 4 and by distillation off water until the solution reaches an azeotrope (≈ 126 °C at 760 torr ). The yield is about 85%. [4]

Hydrobromic acid is available commercially in various concentrations and purities.