|Preferred IUPAC name
Hydrogen bromide
|Systematic IUPAC name
3D model (Jmol)
|Molar mass||80.91 g·mol−1|
|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)
|350.7 mJ K−1 g−1|
|198.696-198.704 J K−1 mol−1|
Std enthalpy of
|−36.45 – −36.13 kJ mol−1|
|Safety data sheet||hazard.com
|GHS signal word||DANGER|
|P261, P280, P305+351+338, P310|
EU classification (DSD)
|S-phrases||(S1/2), S7/9, S26, S45|
|Lethal dose or concentration (LD, LC):|
LC50 (median concentration)
|2858 ppm (rat, 1 hr)
814 ppm (mouse, 1 hr)
|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 ?)(|
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.
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
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.
- 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.
- "Hydrobromic Acid - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 10 November 2011.
- Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
- Trummal, A.; Lipping, L.; Kaljurand, I.; Koppel, I. A.; Leito, I. "Acidity of Strong Acids in Water and Dimethyl Sulfoxide" J. Phys. Chem. A. 2016, 120, 3663-3669. doi:10.1021/acs.jpca.6b02253
- Perrin, D. D. Dissociation constants of inorganic acids and bases in aqueous solution. Butterworths, London, 1969.
- Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. ISBN 0-618-94690-X.
- "NIOSH Pocket Guide to Chemical Hazards #0331". National Institute for Occupational Safety and Health (NIOSH).
- "Hydrogen bromide". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
- 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
- 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). (http://www.orgsyn.org/demo.aspx?prep=CV2P0338)
- 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.