Hydrogen bromide

From Wikipedia, the free encyclopedia
Jump to: navigation, search
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-3D images 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
EU classification 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 chloride

Hydrogen fluoride
Hydrogen iodide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 N verify (what isYesY/N?)
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. Hydrogen bromide and hydrobromic acid are, therefore, not the same, but they are related. Commonly, chemists refer to hydrobromic acid as "HBr", and this usage, while understood by most chemists, is imprecise and can be confusing to the non-specialist.[citation needed]

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.