Hydrogen bromide

Hydrogen bromide
Ball-and-stick model of hydrogen bromide
Names
	Preferred IUPAC name Hydrogen bromide
	Systematic IUPAC name Bromane[1]
Identifiers
CAS Number	10035-10-6 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	3587158
ChEBI	CHEBI:47266 ;
ChEMBL	ChEMBL1231461 ;
ChemSpider	255 ;
ECHA InfoCard	100.030.090
EC Number	233-113-0;
KEGG	C13645 ;
MeSH	Hydrobromic+Acid
PubChem CID	260;
RTECS number	MW3850000;
UNII	3IY7CNP8XJ ;
UN number	1048
CompTox Dashboard (EPA)	DTXSID0029713 ;
	InChI InChI=1S/BrH/h1H Key: CPELXLSAUQHCOX-UHFFFAOYSA-N ;
	SMILES Br;
Properties
Chemical formula	HBr
Molar mass	80.91 g/mol
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)
Solubility in water	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
Refractive index (nD)	1.325
Structure
Molecular shape	Linear
Dipole moment	820 mD
Thermochemistry
Heat capacity (C)	350.7 mJ/(K·g)
Std molar; entropy (So298)	198.696–198.704 J/(K·mol)[5]
Std enthalpy of; formation (ΔfH⦵298)	−36.45...−36.13 kJ/mol[5]
Hazards
Safety data sheet	hazard.com; physchem.ox.ac.uk
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H314, H335
GHS precautionary statements	P261, P280, P305+351+338, P310
NFPA 704 (fire diamond)	0 3 0 COR
	Lethal dose or concentration (LD, LC):
LC50 (median concentration)	2858 ppm (rat, 1 h); 814 ppm (mouse, 1 h)[6]
	NIOSH (US health exposure limits):
PEL (Permissible)	TWA 3 ppm (10 mg/m3)[7]
REL (Recommended)	TWA 3 ppm (10 mg/m3)[7]
IDLH (Immediate danger)	30 ppm[7]
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).
	verify (what is ?)
	Infobox references

Hydrogen bromide is the heteronuclear diatomic molecular compound with the formula HBr, a hydrogen halide consisting of hydrogen and bromine. In pure form it is a colorless gas.

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.[8] The free-radical addition of HBr to alkenes gives alkyl bromides:

RCH=CH₂ + HBr → R−CHBr−CH₃

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:

CH₂=CHCH₂OH + HBr → CH₂=CHCH₂Br + H₂O

Other reactions

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.[9][10][11][12]

Potential applications

HBr has been proposed for use in a utility-scale flow-type battery.[13]

Industrial preparation

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.[10][14]

Laboratory synthesis

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 sulfuric acid:[15]

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:[15]
2 Br₂ + S + 2 H₂O → 4 HBr + SO₂
bromination of tetralin:[15]
C₁₀H₁₂ + 4 Br₂ → C₁₀H₈Br₄ + 4 HBr
reduction of bromine with phosphorous acid:[10]
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.[9]

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.[14]

Safety

HBr is highly corrosive and irritating to inhalation.

References

"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, 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.
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 978-0-618-94690-7.
"Hydrogen bromide". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
NIOSH Pocket Guide to Chemical Hazards. "#0331". 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.
https://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535ag.pdf
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.

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[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 Institute for Occupational Safety and Health

[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.

[b1-5] Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. ISBN 978-0-618-94690-7.

[6] "Hydrogen bromide". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).

[PGCH-7] NIOSH Pocket Guide to Chemical Hazards. "#0331". 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)

[hercouet-9] Hercouet, A.; LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157–158.

[greenwood-10] Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809–812.

[carlin-11] Carlin, William W. U.S. Patent 4,147,601, April 3, 1979.

[vollhart-12] Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003.

[EERE-13] ttps://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535ag.pdf

[ruhoff-14] Ruhoff, J. R.; Burnett, R. E.; Reid, E. E. "Hydrogen Bromide (Anhydrous)" Organic Syntheses, Vol. 15, p. 35 (Coll. Vol. 2, p. 338).

[brauer-15] 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.