Hydrogen bromide is the diatomic molecule with the formula HBr. It is a colorless compound and a hydrogen halide. Hydrobromic acid is a solution of HBr in water. Both the anhydrous and aqueous solutions of HBr are common reagents in the preparation of bromide compounds.
|Preferred IUPAC name
Hydrogen bromide
|Systematic IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||80.91 g/mol|
|Density||3.6452 kg/m3 (0 °C, 1013 mbar)|
|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); ~−9|
Refractive index (nD)
Heat capacity (C)
Std enthalpy of
|Safety data sheet||hazard.com|
|GHS signal word||Danger|
|P261, P280, P305+351+338, P310|
|Lethal dose or concentration (LD, LC):|
LC50 (median concentration)
|2858 ppm (rat, 1 h)|
814 ppm (mouse, 1 h)
|US health exposure limits (NIOSH):|
|TWA 3 ppm (10 mg/m3)|
|TWA 3 ppm (10 mg/m3)|
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
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 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.
Uses of HBrEdit
Hydrogen bromide and hydrobromic acid are important reagents in the production of inorganic and organic bromine compounds. The free-radical addition of HBr to alkenes gives alkyl bromides:
- RCH=CH2 + HBr → R−CHBr−CH3
- HBr + CH2Cl2 → HCl + CH2BrCl
- HBr + CH2BrCl → HCl + CH2Br2
Allyl bromide is prepared by treating allyl alcohol with HBr:
- CH2=CHCH2OH + HBr → CH2=CHCH2Br + H2O
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
- RC≡CH + HBr → RC(Br)=CH2
HBr has been proposed for use in a utility-scale flow-type battery.
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.
- 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:
- 2 Br2 + S + 2 H2O → 4 HBr + SO2
- bromination of tetralin:
- C10H12 + 4 Br2 → C10H8Br4 + 4 HBr
- reduction of bromine with phosphorous acid:
- Br2 + H3PO3 + H2O → H3PO4 + 2 HBr
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.
HBr is highly corrosive and irritating to inhalation.
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- Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
- 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. doi:10.1021/acs.jpca.6b02253. PMID 27115918.
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- NIOSH Pocket Guide to Chemical Hazards. "#0331". National Institute for Occupational Safety and Health (NIOSH).
- "Hydrogen bromide". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- 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)
- Hercouet, A.; LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157–158.
- Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809–812.
- Carlin, William W. U.S. Patent 4,147,601, April 3, 1979.
- Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003.
- Ruhoff, J. R.; Burnett, R. E.; Reid, E. E. "Hydrogen Bromide (Anhydrous)" Organic Syntheses, Vol. 15, p. 35 (Coll. Vol. 2, p. 338).
- 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.