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
3D model (JSmol)
ECHA InfoCard 100.030.090 Edit this at Wikidata
EC Number
  • 233-113-0
MeSH Hydrobromic+Acid
RTECS number
  • MW3850000
UN number 1048
  • InChI=1S/BrH/h1H checkY
  • Br
Molar mass 80.91 g/mol
Appearance Colorless gas
Odor Acrid
Density 3.307 g/L (25 °C)[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) −8.8 (±0.8);[3] ~−9[4]
Basicity (pKb) ~23
Conjugate acid Bromonium
Conjugate base Bromide
1.325[citation needed]
820 mD
350.7 mJ/(K·g)
198.696–198.704 J/(K·mol)[5]
−36.45...−36.13 kJ/mol[5]
Safety data sheet hazard.com


GHS pictograms GHS05: Corrosive GHS07: Harmful
GHS Signal word Danger
H314, H335
P261, P280, P305+351+338, P310
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
2858 ppm (rat, 1 h)
814 ppm (mouse, 1 h)[7]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 3 ppm (10 mg/m3)[6]
REL (Recommended)
TWA 3 ppm (10 mg/m3)[6]
IDLH (Immediate danger)
30 ppm[6]
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).
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Infobox references

Hydrogen bromide is the inorganic compound with the formula HBr. 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 temperature. Aqueous solutions that are 47.6% HBr by mass 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.

Hydrogen bromide, and its aqueous solution, are commonly used reagents in the preparation of bromide compounds.

Uses of HBr[edit]

Hydrogen bromide and hydrobromic acid are important reagents in the production of inorganic and organic bromine compounds.[8] The free-radical addition of HBr to alkenes gives alkyl bromides:

RCH=CH2 + HBr → R−CHBr−CH3

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 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.[9][10][11][12]

Industrial preparation[edit]

Hydrogen bromide (along with hydrobromic acid) is produced by combining hydrogen and bromine at temperatures between 200 and 400 °C. The reaction is typically catalyzed by platinum or asbestos.[10][13]

Laboratory synthesis[edit]

HBr can be prepared by distillation of a solution of sodium bromide or potassium bromide with phosphoric acid or sulfuric acid:[14]

KBr + H2SO4 → KHSO4 + HBr

Concentrated sulfuric acid is less effective because it oxidizes HBr to bromine:

2 HBr + H2SO4 → Br2 + SO2 + 2 H2O

The acid may be prepared by:

  • reaction of bromine with water and sulfur:[14]
    2 Br2 + S + 2 H2O → 4 HBr + SO2
  • bromination of tetralin:[14]
    C10H12 + 4 Br2 → C10H8Br4 + 4 HBr
  • reduction of bromine with phosphorous acid:[10]
    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.[9]

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 or copper gauze 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. ^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0487-3.
  3. ^ Trummal, Aleksander; Lipping, Lauri; Kaljurand, Ivari; Koppel, Ilmar A; Leito, Ivo (2016). "Acidity of Strong Acids in Water and Dimethyl Sulfoxide". The Journal of Physical Chemistry A. 120 (20): 3663–9. Bibcode:2016JPCA..120.3663T. doi:10.1021/acs.jpca.6b02253. PMID 27115918.
  4. ^ Perrin, D. D. Dissociation constants of inorganic acids and bases in aqueous solution. Butterworths, London, 1969.
  5. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. ISBN 978-0-618-94690-7.
  6. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0331". National Institute for Occupational Safety and Health (NIOSH).
  7. ^ "Hydrogen bromide". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  8. ^ Dagani, M. J.; Barda, H. J.; Benya, T. J.; Sanders, D. C. "Bromine Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a04_405.CS1 maint: multiple names: authors list (link)
  9. ^ a b Hercouet, A.; LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157–158.
  10. ^ a b c Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809–812.
  11. ^ Carlin, William W. U.S. Patent 4,147,601, April 3, 1979.
  12. ^ Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003.
  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).
  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.