Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule

hydrogen bromide Hydrogen bromide is the inorganic compound with the formula . It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming hydrobromic acid, which is saturated at 68.85% HBr by weight at room tem ...

(HBr) in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at and contains 47.6% HBr by mass, which is 8.77 mol/L. Hydrobromic acid has a p''K''_a of −9, making it a stronger acid than

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...

, but not as strong as hydroiodic acid. Hydrobromic acid is one of the strongest mineral acids known.

Uses

Hydrobromic acid is mainly used for the production of inorganic bromides, especially the bromides of zinc, calcium, and sodium. It is a useful reagent for generating organobromine compounds. Certain ethers are cleaved with HBr. It also catalyzes alkylation reactions and the extraction of certain ores. Industrially significant organic compounds prepared from hydrobromic acid include allyl bromide, tetrabromobis(phenol), and

bromoacetic acid Bromoacetic acid is the chemical compound with the formula CH2BrCO2H. This colorless solid is a relatively strong alkylating agent. Bromoacetic acid and its esters are widely used building blocks in organic synthesis, for example, in pharmaceuti ...

. HBr almost uniquely participates in anti-Markovnikov

hydrohalogenation A hydrohalogenation reaction is the electrophilic addition of hydrohalic acids like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes. : If the two carbon atoms at the double bond are linked to a different ...

of alkenes. The resulting 1-bromoalkanes are versatile

alkylating agent Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effectin ...

s, giving rise to fatty amines and quaternary ammonium salts.

Synthesis

Hydrobromic acid can be prepared in the laboratory via the reaction of Br₂, SO₂, and water. :Br₂ + SO₂ + 2 H₂O → H₂SO₄ + 2 HBr More typically laboratory preparations involve the production of anhydrous HBr, which is then dissolved in water. Hydrobromic acid has commonly been prepared industrially by reacting bromine with either

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...

and water. However, it can also be produced electrolytically. It can also be prepared by treating bromides with non-oxidising acids like phosphoric or acetic acids. Alternatively the acid can be prepared with dilute (5.8 M)

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...

and

potassium bromide Potassium bromide ( K Br) is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the US. Its action is due to the bromide ion ( sodium bromide is equa ...

: :H₂SO₄ + KBr → KHSO₄ + HBr Using more concentrated sulfuric acid or allowing the reaction solution to exceed 75 °C further

oxidizes Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

HBr to bromine gas. The acid is further purified by filtering out the KHSO₄ and by distilling off the water until the solution reaches an azeotrope (≈ 126 °C at 760

torr The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one " millimeter of merc ...

). The yield is approximately 85%. Hydrobromic acid is available commercially in various concentrations and purities.

References

External links

International Chemical Safety Card 0282

*Carlin, W. W. Bromides Nonmetal halides Mineral acids {{DEFAULTSORT:Hydrobromic Acid pl:Bromowodór#Kwas bromowodorowy