Hydrogen bromide

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
Skeletal formula of hydrogen bromide with the explicit hydrogen and a measurement added
Ball-and-stick model of hydrogen bromide
Hydrogen-bromide-3D-vdW.svg
Names
Preferred IUPAC name
Hydrogen bromide[citation needed]
Systematic IUPAC name
Bromane[1]
Identifiers
3D model (JSmol)
3587158
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.030.090 Edit this at Wikidata
EC Number
  • 233-113-0
KEGG
MeSH Hydrobromic+Acid
RTECS number
  • MW3850000
UNII
UN number 1048
  • InChI=1S/BrH/h1H checkY
    Key: CPELXLSAUQHCOX-UHFFFAOYSA-N checkY
  • Br
Properties
HBr
Molar mass 80.91 g/mol
Appearance Colorless gas
Odor Acrid
Density 3.307 g/mL (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]
Structure
Linear
820 mD
Thermochemistry
350.7 mJ/(K·g)
198.696–198.704 J/(K·mol)[5]
−36.45...−36.13 kJ/mol[5]
Hazards
Safety data sheet hazard.com

physchem.ox.ac.uk

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

ReactionsEdit

Organic chemistryEdit

Hydrogen bromide and hydrobromic acid are important reagents in the production of organobromine compounds.[8][9][10] In a free-radical reaction, HBr adds to alkenes:

RCH=CH2 + HBr → R−CHBr−CH3

The resulting alkyl bromides are useful alkylating agents, e.g., as precursors to fatty amine derivatives. Relaated free radical additions to allyl chloride and styrene give 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

These metathesis reactions illustrate the consumption of the stronger acid (HBr) and release of the weaker acid (HCl).

Allyl bromide is prepared by treating allyl alcohol with HBr:

CH2=CHCH2OH + HBr → CH2=CHCH2Br + H2O

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 adds epoxides and lactones, resulting in ring-opening.

With triphenylphosphine, HBr gives triphenylphosphonium bromide, a solid "source" of HBr.[11]

P(C6H5)3 + HBr → [HP(C6H5)3]+Br

Inorganic chemistryEdit

Vanadium(III) bromide and molybdenum(IV) bromide were prepared by treatment of the higher chlorides with HBr. These reactions proceed via redox reactions:[12]

2 VCl4 + 8 HBr → 2 VBr3 + 8 HCl + Br2

Industrial preparationEdit

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.[9][13]

Laboratory synthesisEdit

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:[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.[11]

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]

SafetyEdit

HBr is highly corrosive and irritating to inhalation.

ReferencesEdit

  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 c Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809–812.
  10. ^ Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003.
  11. ^ a b Hercouet, A.; LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157–158.
  12. ^ Calderazzo, Fausto; Maichle-Mössmer, Cäcilie; Pampaloni, Guido; Strähle, Joachim (1993). "Low-Temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange". J. Chem. Soc., Dalton Trans. (5): 655–658. doi:10.1039/DT9930000655.
  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.