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Hydrogen bromide

|Section2={{Chembox Properties | Formula = HBr | Appearance = Colorless gas | Odor = Acrid | MolarMass = 80.91 g/mol | Density = 3.6452 kg/m3 (0 °C, 1013 mbar) | MeltingPtC = −86.9 | BoilingPtC = −66.8 | Solubility = 221 g/100 mL (0 °C) 204 g/100 mL (15 °C) 193 g/100 mL (20 °C) 130 g/100 mL (100 °C) | SolubleOther = Soluble in alcohol, organic solvents | VaporPressure = 2.308 MPa (at 21 °C) | pKa = -8.8 (±0.8);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. ~−9Perrin, D. D. Dissociation constants of inorganic acids and bases in aqueous solution. Butterworths, London, 1969. | pKb = ~23 | RefractIndex = 1.325 }} |Section3={{Chembox Structure | MolShape = Linear | Dipole = 820 mD }} |Section4={{Chembox Thermochemistry | DeltaHf = −36.45 – −36.13 kJ mol−1 | Entropy = 198.696-198.704 J K−1 mol−1 | HeatCapacity = 350.7 mJ K−1 g−1 }} |Section5={{Chembox Hazards | ExternalSDS = hazard.com physchem.ox.ac.uk | GHSPictograms = | GHSSignalWord = DANGER | HPhrases = | PPhrases = | NFPA-H = 3 | NFPA-F = 0 | NFPA-R = 0 | NFPA-S = COR | PEL = TWA 3 ppm (10 mg/m3) | IDLH = 30 ppm | REL = TWA 3 ppm (10 mg/m3) | LC50 = 2858 ppm (rat, 1 hr)814 ppm (mouse, 1 hr) }} |Section6={{Chembox Related | OtherCompounds = Hydrogen fluoride Hydrogen chloride Hydrogen iodide Hydrogen astatide }} }} Hydrogen bromide is the diatomic molecule with the formula . 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 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.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. , April 3, 1979Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function; 4th Ed.; W. H. Freeman and Company: New York, NY; 2003.

Potential applications

HBr has been proposed for use in a utility-scale flow-type battery.http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/30535ag.pdf

Industrial preparation

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.

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: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. 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
Anhydrous hydrogen bromide can also be produced on a small scale by thermolysis of triphenylphosphonium bromide in refluxing xylene. 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.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)

Safety

HBr is highly corrosive and irritating to inhalation.

References

"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Hydrogen_bromide, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Hydrogen_bromide&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany