Hydrogen bromide is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the formula . It is a

hydrogen halide In chemistry, hydrogen halides (hydrohalic acids when in the aqueous phase) are diatomic, inorganic compounds that function as Arrhenius acids. The formula is HX where X is one of the halogens: fluorine, chlorine, bromine, iodine, or astatine. ...

consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming

hydrobromic acid Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide (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. H ...

, which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by mass form a constant-boiling

azeotrope An azeotrope () or a constant heating point mixture is a mixture of two or more liquids whose proportions cannot be altered or changed by simple distillation.Moore, Walter J. ''Physical Chemistry'', 3rd e Prentice-Hall 1962, pp. 140–142 This ...

mixture that boils at 124.3 °C. Boiling less concentrated solutions releases H₂O until the constant-boiling mixture composition is reached. Hydrogen bromide, and its aqueous solution, are commonly used reagents in the preparation of bromide compounds.

Reactions

Organic chemistry

Hydrogen bromide and hydrobromic acid are important reagents in the production of

organobromine compound Organobromine compounds, also called organobromides, are organic compounds that contain carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons avai ...

s.Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809–812.Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003. In a

free-radical reaction A free-radical reaction is any chemical reaction involving free radicals. This reaction type is abundant in organic reactions. Two pioneering studies into free radical reactions have been the discovery of the triphenylmethyl radical by Moses Gomb ...

, HBr adds to alkenes: : The resulting alkyl bromides are useful

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, e.g., as precursors to

fatty amine In chemistry, a fatty amine is loosely defined as any amine possessing a mostly linear hydrocarbon chain of eight or more carbon atoms. They are typically prepared from the more abundant fatty acids, with vegetable or seed-oils being the ultimate ...

derivatives. Related free radical additions to

allyl chloride Allyl chloride is the organic compound with the formula C H2=CHCH2 Cl. This colorless liquid is insoluble in water but soluble in common organic solvents. It is mainly converted to epichlorohydrin, used in the production of plastics. It is a ch ...

and

styrene Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...

give 1-bromo-3-chloropropane and phenylethylbromide, respectively. Hydrogen bromide reacts with

dichloromethane Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible with ...

to give

bromochloromethane Bromochloromethane or methylene bromochloride and Halon 1011 is a mixed halomethane. It is a heavy low-viscosity liquid with refractive index 1.4808. Halon 1011 was invented for use in fire extinguishers in Germany during the mid-1940s, in an att ...

and

dibromomethane Preparation Dibromomethane is prepared commercially from dichloromethane via bromochloromethane: :6 CH2Cl2 + 3 Br2 + 2 Al → 6 CH2BrCl + 2 AlCl3 :CH2Cl2 + HBr → CH2BrCl + HCl The latter route requires aluminium trichloride as a catal ...

, sequentially: : : These metathesis reactions illustrate the consumption of the stronger acid (HBr) and release of the weaker acid (HCl).

Allyl bromide Allyl bromide (3-bromopropene) is an organic halide. It is an alkylating agent used in synthesis of polymers, pharmaceuticals, synthetic perfumes and other organic compounds. Physically, allyl bromide is a colorless liquid with an irritating and p ...

is prepared by treating

allyl alcohol Allyl alcohol ( IUPAC name: prop-2-en-1-ol) is an organic compound with the structural formula . Like many alcohols, it is a water-soluble, colourless liquid. It is more toxic than typical small alcohols. Allyl alcohol is used as a raw material ...

with HBr: : HBr adds to

alkynes \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and no ...

to yield bromoalkenes. The

stereochemistry Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereois ...

of this type of addition is usually ''anti'': : RC≡CH + HBr → RC(Br)=CH₂ Also, HBr adds

epoxide In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale for ...

s and

lactone Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

s, resulting in ring-opening. With

triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists a ...

, HBr gives triphenylphosphonium bromide, a solid "source" of HBr.Hercouet, A.; LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157–158. :

Inorganic chemistry

Vanadium(III) bromide Vanadium(III) bromide, also known as vanadium tribromide, is the inorganic compound with the formula VBr3. It is a green-black solid. In terms of its structure, the compound is polymeric with octahedral vanadium(III) surrounded by six bromide l ...

and

molybdenum(IV) bromide Molybdenum(IV) bromide, also known as molybdenum tetrabromide, is the inorganic compound with the formula MoBr4. It is a black solid. MoBr4 has been prepared by treatment of molybdenum(V) chloride with hydrogen bromide: ::2 MoCl5 + 10 HBr → ...

were prepared by treatment of the higher chlorides with HBr. These reactions proceed via redox reactions: :

Industrial preparation

Hydrogen bromide (along with hydrobromic acid) is produced by combining

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

and

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simila ...

at temperatures between 200 and 400 °C. The reaction is typically catalyzed by

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...

asbestos Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...

Laboratory synthesis

HBr can be prepared by distillation of a solution of

sodium bromide Sodium bromide is an inorganic compound with the formula Na Br. It is a high-melting white, crystalline solid that resembles sodium chloride. It is a widely used source of the bromide ion and has many applications.Michael J. Dagani, Henry J. Ba ...

or potassium bromide with

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...

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 formu ...

:M. Schmeisser "Chlorine, Bromine, Iodine" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 282. : KBr + H₂SO₄ → KHSO₄ + HBr Concentrated sulfuric acid is less effective because it oxidizes HBr to

: : 2 HBr + H₂SO₄ → Br₂ + SO₂ + 2 H₂O The acid may be prepared by: * reaction of bromine with water and

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 formula ...

: *: 2 Br₂ + S + 2 H₂O → 4 HBr + SO₂ * bromination of

tetralin Tetralin (1,2,3,4-tetrahydronaphthalene) is a hydrocarbon having the chemical formula C10H12. It is a partially hydrogenated derivative of naphthalene. It is a colorless liquid that is used as a hydrogen-donor solvent. Production Tetralin is pro ...

: *: C₁₀H₁₂ + 4 Br₂ → C₁₀H₈Br₄ + 4 HBr * reduction of bromine with phosphorous acid: *: Br₂ + H₃PO₃ + H₂O → H₃PO₄ + 2 HBr Anhydrous hydrogen bromide can also be produced on a small scale by

thermolysis Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...

of triphenylphosphonium bromide in refluxing

xylene In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are sub ...

. Hydrogen bromide prepared by the above methods can be contaminated with Br₂, which can be removed by passing the gas through a solution of

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...

at room temperature in

tetrachloromethane Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVACR) is an organic compound with the chemica ...

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.Ruhoff, J. R.; Burnett, R. E.; Reid, E. E
"Hydrogen Bromide (Anhydrous)"
Organic Syntheses, Vol. 15, p. 35 (Coll. Vol. 2, p. 338).

Safety

HBr is highly corrosive and irritating to inhalation.

References

{{Authority control Inorganic compounds Hydrogen compounds Bromides Nonmetal halides