Hydrogen bromide

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Hydrogen bromide
Skeletal formula of hydrogen bromide with the explicit hydrogen and a measurement added
Ball-and-stick model of hydrogen bromide
Preferred IUPAC name
Hydrogen bromide[citation needed]
Systematic IUPAC name
10035-10-6 YesY
ChEBI CHEBI:47266 YesY
ChEMBL ChEMBL1231461 N
ChemSpider 255 YesY
EC Number 233-113-0
Jmol interactive 3D Image
KEGG C13645 N
MeSH Hydrobromic+Acid
PubChem 260
RTECS number MW3850000
UN number 1048
Molar mass 80.91 g·mol−1
Appearance Colorless gas
Odor Acrid
Density 3.6452 kg/m3 (0 °C, 1013 mbar)[2]
Melting point −86.9 °C (−124.4 °F; 186.2 K)
Boiling point −66.8 °C (−88.2 °F; 206.3 K)
221 g/100 mL (0 °C)
204 g/100 mL (15 °C)
193 g/100 mL (20 °C)
130 g/100 mL (100 °C)
Solubility soluble in alcohol, organic solvents
Vapor pressure 2.308 MPa (at 21 °C)
Acidity (pKa) ~–9[3]
Basicity (pKb) ~23
820 mD
350.7 mJ K−1 g−1
198.696-198.704 J K−1 mol−1[4]
-36.45--36.13 kJ mol−1[4]
Safety data sheet hazard.com


GHS pictograms The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
H314, H335
P261, P280, P305+351+338, P310
Corrosive C
R-phrases R35, R37
S-phrases (S1/2), S7/9, S26, S45
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Lethal dose or concentration (LD, LC):
2858 ppm (rat, 1 hr)
814 ppm (mouse, 1 hr)[6]
US health exposure limits (NIOSH):
TWA 3 ppm (10 mg/m3)[5]
TWA 3 ppm (10 mg/m3)[5]
30 ppm[5]
Related compounds
Related compounds
Hydrogen fluoride
Hydrogen chloride
Hydrogen iodide
Hydrogen astatide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Hydrogen bromide is the diatomic molecule with the formula HBr. HBr is a colorless gas that condenses to a colorless liquid. Hydrobromic acid is a solution of HBr in water.

Solubility in water[edit]

HBr is very soluble in water, forming hydrobromic acid solution, which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by weight form a constant-boiling azeotrope mixture that boils at 124.3 °C. Boiling less concentrated solutions releases H2O until the constant boiling mixture composition is reached.

Uses of HBr[edit]

Hydrogen bromide and hydrobromic acid are important reagents in the production of inorganic and organic bromine compounds.[7] The free-radical addition of HBr to alkenes gives terminal alkyl bromides:

RCH=CH2 + HBr → RCH2–CH2Br

These alkylating agents are precursors to fatty amine derivatives. Similar free radical addition to allyl chloride and styrene gives 1-bromo-3-chloropropane and phenylethylbromide, respectively.

Hydrogen bromide reacts with dichloromethane to give bromochloromethane and dibromomethane, sequentially:

HBr + CH2Cl2 → HCl + CH2BrCl
HBr + CH2BrCl → HCl + CH2Br2

Allyl bromide is prepared by treating allyl alcohol with HBr:


Other reactions[edit]

Although not widely used industrially, HBr adds to alkenes to give bromoalkanes, an important family of organobromine compounds. Similarly, HBr adds to haloalkene to form a geminal dihaloalkane. (This type of addition follows Markovnikov's rule):

RC(Br)=CH2 + HBr → RC(Br2)–CH3

HBr also adds to alkynes to yield bromoalkenes. The stereochemistry of this type of addition is usually anti:

RC≡CH + HBr → RC(Br)=CH2

Also, HBr is used to open epoxides and lactones and in the synthesis of bromoacetals. Additionally, HBr catalyzes many organic reactions.[8][9][10][11]

Potential applications[edit]

HBr has been proposed for use in a utility-scale flow-type battery.[12]

Industrial preparation[edit]

Hydrogen bromide (along with hydrobromic acid) is produced by combining hydrogen and bromine at temperatures between 200-400 °C. The reaction is typically catalyzed by platinum or asbestos.[9][13]

Laboratory synthesis[edit]

HBr can be synthesized by a variety of methods. It may be prepared in the laboratory by distillation of a solution of sodium bromide or potassium bromide with phosphoric acid or diluted sulfuric acid:[14]

2 KBr + H2SO4 → K2SO4 + 2HBr

Concentrated sulfuric acid is ineffective because HBr formed will be oxidized to bromine gas:

2 HBr + H2SO4 → Br2 + SO2 + 2H2O

The acid may be prepared by several other methods, as well, including reaction of bromine either with phosphorus and water, or with sulfur and water:[14]

2 Br2 + S + 2 H2O → 4 HBr + SO2

Alternatively, it can be prepared by the bromination of tetraline:[14]

C10H12 + 4 Br2 → C10H8Br4 + 4 HBr

Alternatively bromine can be reduced with phosphorous acid:[9]

Br2 + H3PO3 + H2O → H3PO4 + 2 HBr

Anhydrous hydrogen bromide can also be produced on a small scale by thermolysis of triphenylphosphonium bromide in refluxing xylene.[8]

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 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 at high temperature.[13]


HBr is highly corrosive and irritating to inhalation.


  1. ^ "Hydrobromic Acid - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 10 November 2011. 
  2. ^ Record in the GESTIS Substance Database of the IFA
  3. ^ Perrin, D. D. Dissociation constants of inorganic acids and bases in aqueous solution. Butterworths, London, 1969.
  4. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. ISBN 0-618-94690-X. 
  5. ^ a b c "NIOSH Pocket Guide to Chemical Hazards #0331". National Institute for Occupational Safety and Health (NIOSH). 
  6. ^ "Hydrogen bromide". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH). 
  7. ^ Dagani, M. J.; Barda, H. J.; Benya, T. J.; Sanders, D. C. (2005), "Bromine Compounds", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a04_405 
  8. ^ a b Hercouet, A.;LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157-158.
  9. ^ a b c Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809-812.
  10. ^ Carlin, William W. U.S. Patent 4,147,601, April 3, 1979
  11. ^ Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003.
  12. ^ http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535ag.pdf
  13. ^ a b Ruhoff, J. R.; Burnett, R. E.; Reid, E. E. "Hydrogen Bromide (Anhydrous)" Organic Syntheses, Vol. 15, p.35 (Coll. Vol. 2, p.338). (http://www.orgsyn.org/demo.aspx?prep=CV2P0338)
  14. ^ a b c 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.