Overview: Hydrogen bromide is a simple inorganic compound with the formula HBr. As a hydrogen halide it is closely related to hydrogen chloride and hydrogen iodide. In its pure form it is a colorless gas with a sharp odor; when dissolved in water it produces hydrobromic acid, the aqueous solution commonly used in chemistry and industry. See general compound information here and the aqueous acid form here.

Physical and chemical characteristics

HBr is a covalent molecule that ionizes readily on contact with water to yield hydronium and bromide ions. It is reactive and corrosive, and its vapors can irritate the respiratory system and eyes. Chemically it behaves as a strong acid in aqueous solution and as a source of bromide for synthesis and salt formation. Bromine, a common reactant in its manufacture, is described here.

Methods of production

Industrial and laboratory routes to hydrogen bromide include several well-established methods:

  • Direct synthesis from the elements: hydrogen reacts with bromine in the gas phase, often with heat and a catalyst, to form HBr. Reference for elemental reagents: hydrogen and bromine.
  • Acidification of bromide salts: non-oxidizing acids are used to liberate HBr from inorganic bromides; an example of such an acid is phosphoric acid (H3PO4), and the general concept of non-oxidizing acids is noted here. This route is common in laboratories because it avoids strong oxidants.
  • Reductive methods: bromine can be reduced by reagents such as phosphorous acid to produce hydrogen bromide; see the reduction concept here and the reducing reagent phosphorous acid.
  • Conversion from other bromine-containing compounds is also practiced when specific purity or concentration is required; many of these begin from inorganic or organic bromide sources.

Uses and importance

Hydrogen bromide is principally used as an intermediate in the manufacture of bromide salts and organobromine compounds. Hydrobromic acid derived from HBr is a reagent in organic synthesis, for example in substitutions that introduce bromine into molecules, and as a catalyst or proton source in various reactions. Bromide derivatives produced from HBr have applications in pharmaceuticals, agrochemicals and flame retardants.

Safety, handling and notable distinctions

HBr and its aqueous solutions are corrosive and can cause burns on contact; inhalation of vapors is harmful. Laboratories and industry use appropriate ventilation, corrosion-resistant materials and personal protective equipment when handling HBr or hydrobromic acid. As a member of the hydrogen halides family it shares many behaviors with HCl and HI but differs in reactivity and strength in nonaqueous media. For further reading on related bromide chemistry see bromides.

Practical references and safety data are important when working with hydrogen bromide; additional resources can be consulted through general chemical information links such as compound overviews and specific reagent pages like hydrobromic acid and bromine.