Hydrogen bromide
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| Names | |||
|---|---|---|---|
| IUPAC name
Hydrogen bromide
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| Preferred IUPAC name
Bromane[1] | |||
| Identifiers | |||
3D model (JSmol)
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| 3587158 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.030.090 | ||
| EC Number |
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| KEGG | |||
| MeSH | Hydrobromic+Acid | ||
PubChem CID
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| RTECS number |
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| UNII | |||
| UN number | 1048 | ||
CompTox Dashboard (EPA)
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| Properties | |||
| HBr | |||
| Molar mass | 80.91 g/mol | ||
| Appearance | Colorless gas | ||
| Odor | Acrid | ||
| Density | 3.307 g/L (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 | ||
Refractive index (nD)
|
1.325[citation needed] | ||
| Structure | |||
| Linear | |||
| 820 mD | |||
| Thermochemistry | |||
Heat capacity (C)
|
350.7 mJ/(K·g) | ||
Std molar
entropy (S⦵298) |
198.696–198.704 J/(K·mol)[5] | ||
Std enthalpy of
formation (ΔfH⦵298) |
−36.45...−36.13 kJ/mol[5] | ||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards
|
Highly corrosive | ||
| GHS labelling: | |||
 
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| Danger | |||
| H314, H335 | |||
| P261, P280, P305+P351+P338, P310 | |||
| NFPA 704 (fire diamond) | |||
| Lethal dose or concentration (LD, LC): | |||
LC50 (median concentration)
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2858 ppm (rat, 1 h) 814 ppm (mouse, 1 h)[7] | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible)
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TWA 3 ppm (10 mg/m3)[6] | ||
REL (Recommended)
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TWA 3 ppm (10 mg/m3)[6] | ||
IDLH (Immediate danger)
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30 ppm[6] | ||
| Safety data sheet (SDS) | hazard.com | ||
| 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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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 (255.7 °F). Boiling less concentrated solutions releases H2O until the constant-boiling mixture composition is reached.
Hydrogen bromide, and its aqueous solution, hydrobromic acid, are commonly used reagents in the preparation of bromide compounds.
Reactions
[edit]Organic chemistry
[edit]Hydrogen bromide and hydrobromic acid are important reagents in the production of organobromine compounds.[8][9][10] In an electrophilic addition 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. Related 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 chemistry
[edit]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 preparation
[edit]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 synthesis
[edit]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]
Safety
[edit]HBr is highly corrosive and, if inhaled, can cause lung damage.[15]
References
[edit]- ^ Favre, Henri A.; Powell, Warren H., eds. (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. Cambridge: The Royal Society of Chemistry. p. 131. ISBN 9781849733069.
- ^ Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, Florida: CRC Press. ISBN 0-8493-0487-3.
- ^ 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. S2CID 29697201.
- ^ Perrin, D. D. Dissociation constants of inorganic acids and bases in aqueous solution. Butterworths, London, 1969.
- ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. ISBN 978-0-618-94690-7.
- ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0331". National Institute for Occupational Safety and Health (NIOSH).
- ^ "Hydrogen bromide". Immediately Dangerous to Life or Health Concentrations (IDLH). 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. ISBN 978-3527306732.
{{cite encyclopedia}}: CS1 maint: multiple names: authors list (link) - ^ a b c Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809–812.
- ^ Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003.
- ^ a b Hercouet, A.; LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157–158.
- ^ 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.
- ^ 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).
- ^ 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.
- ^ "Hydrobromic Acid". PubChem. Springer Nature. 2024-02-03. Retrieved 2024-02-09.