|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|
|NFPA 704 (fire diamond)|
|Lethal dose or concentration (LD, LC):|
LC50 (median concentration)
|2858 ppm (rat, 1 h)|
814 ppm (mouse, 1 h)
|NIOSH (US health exposure limits):|
|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 ?)(|
Hydrogen bromide is very soluble 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.
Both the anhydrous and aqueous solutions of HBr are common reagents in the preparation of bromide compounds.
Uses of HBr
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
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- Carlin, William W. U.S. Patent 4,147,601 , April 3, 1979.
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- Ruhoff, J. R.; Burnett, R. E.; Reid, E. E. "Hydrogen Bromide (Anhydrous)" Organic Syntheses, Vol. 15, p. 35 (Coll. Vol. 2, p. 338).
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