Hydrogen bromide
{{short description|Chemical compound}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 464362190
| ImageFile1 = Hydrogen-bromide-2D-dimensions.svg
| ImageFile1_Ref = {{chemboximage|correct|??}}
| ImageSize1 = 170
| ImageName1 = Skeletal formula of hydrogen bromide with the explicit hydrogen and a measurement added
| ImageFileR1 = Hydrogen-bromide-3D-vdW.svg
| ImageFileR1_Ref = {{chemboximage|correct|??}}
| ImageFileL1 = Hydrogen-bromide-3D-balls.png
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageNameL1 = Ball-and-stick model of hydrogen bromide
| IUPACName = Hydrogen bromide
| PIN = Bromane{{cite book|title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013|editor-last=Favre |editor-first=Henri A. |editor2-first=Warren H.|editor2-last=Powell|date=2014|publisher=The Royal Society of Chemistry|place=Cambridge|isbn=9781849733069 | page=131}}
| SystematicName =
| Section1 = {{Chembox Identifiers
| CASNo = 10035-10-6
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|changed|FDA}}
| UNII = 3IY7CNP8XJ
| PubChem = 260
| ChemSpiderID = 255
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| EINECS = 233-113-0
| UNNumber = 1048
| KEGG = C13645
| KEGG_Ref = {{keggcite|changed|kegg}}
| MeSHName = Hydrobromic+Acid
| ChEBI = 47266
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 1231461
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| RTECS = MW3850000
| Beilstein = 3587158
| SMILES = Br
| StdInChI = 1S/BrH/h1H
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = CPELXLSAUQHCOX-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
}}
| Section2 = {{Chembox Properties
| Formula = HBr
| Appearance = Colorless gas
| Odor = Acrid
| MolarMass = 80.91 g/mol
| Density = 3.307 g/L (25 °C){{RubberBible87th}}
| 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)
| ConjugateAcid = Bromonium
| ConjugateBase = Bromide
| pKa = −8.8 (±0.8);{{cite journal | doi = 10.1021/acs.jpca.6b02253| pmid = 27115918| title = Acidity of Strong Acids in Water and Dimethyl Sulfoxide| journal = The Journal of Physical Chemistry A| volume = 120| issue = 20| pages = 3663–9| year = 2016| last1 = Trummal| first1 = Aleksander| last2 = Lipping| first2 = Lauri| last3 = Kaljurand| first3 = Ivari| last4 = Koppel| first4 = Ilmar A| last5 = Leito| first5 = Ivo| bibcode = 2016JPCA..120.3663T| s2cid = 29697201}} ~−9Perrin, D. D. Dissociation constants of inorganic acids and bases in aqueous solution. Butterworths, London, 1969.
| pKb = ~23
| RefractIndex = 1.325{{citation needed|reason=As a liquid or at RT as a gas? Seems like the gas should be 1.00000000something|date=May 2017}}
}}
| Section3 = {{Chembox Structure
| MolShape = Linear
| Dipole = 820 mD
}}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = −36.45...−36.13 kJ/mol{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7}}
| Entropy = 198.696–198.704 J/(K·mol)
| HeatCapacity = 350.7 mJ/(K·g)
}}
| Section5 = {{Chembox Hazards
| MainHazards= Highly corrosive
| ExternalSDS = [http://hazard.com/msds/mf/baker/baker/files/h3768.htm hazard.com]
[http://physchem.ox.ac.uk/MSDS/HY/hydrogen_bromide.html physchem.ox.ac.uk]
| GHSPictograms = {{GHS corrosion}} {{GHS exclamation mark}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|314|335}}
| PPhrases = {{P-phrases|261|280|305+351+338|310}}
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S = COR
| PEL = TWA 3 ppm (10 mg/m3){{PGCH|0331}}
| LC50 = 2858 ppm (rat, 1 h)
814 ppm (mouse, 1 h){{IDLH|10035106|Hydrogen bromide}}
}}
| Section6 = {{Chembox Related
| OtherCompounds = Hydrogen fluoride
Hydrogen chloride
Hydrogen iodide
Hydrogen astatide
}}
}}
Hydrogen bromide is the inorganic compound with the formula {{Chem2|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 {{convert|124.3|°C|°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
=Organic chemistry=
Hydrogen bromide and hydrobromic acid are important reagents in the production of organobromine compounds.{{ Ullmann | author = Dagani, M. J.; Barda, H. J.; Benya, T. J.; Sanders, D. C. | title = Bromine Compounds | doi = 10.1002/14356007.a04_405 }}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. In an electrophilic addition reaction, HBr adds to alkenes:
: {{chem2|1=RCH=CH2 + HBr → R\sCHBr\sCH3}}
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:
: {{chem2|HBr + CH2Cl2 -> HCl + CH2BrCl}}
: {{chem2|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:
: {{chem2|1=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.Hercouet, A.; LeCorre, M. (1988) Triphenylphosphonium bromide: A convenient and quantitative source of gaseous hydrogen bromide. Synthesis, 157–158.
: {{chem2|P(C6H5)3 + HBr → [HP(C6H5)3]+Br-}}
=Inorganic chemistry=
Vanadium(III) bromide and molybdenum(IV) bromide were prepared by treatment of the higher chlorides with HBr. These reactions proceed via redox reactions:{{cite journal|doi=10.1039/DT9930000655|title=Low-Temperature Syntheses of Vanadium(III) and Molybdenum(IV) Bromides by Halide Exchange|journal= J. Chem. Soc., Dalton Trans.|issue=5|pages=655–658|year=1993|last1=Calderazzo|first1=Fausto|last2=Maichle-Mössmer|first2=Cäcilie|last3=Pampaloni|first3=Guido|last4=Strähle|first4=Joachim}}
: {{chem2|2 VCl4 + 8 HBr -> 2 VBr3 + 8 HCl + Br2}}
Industrial preparation
Laboratory synthesis
HBr can be prepared 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. [http://www.orgsyn.org/demo.aspx?prep=CV2P0338 "Hydrogen Bromide (Anhydrous)"] Organic Syntheses, Vol. 15, p. 35 (Coll. Vol. 2, p. 338).
Safety
HBr is highly corrosive and, if inhaled, can cause lung damage.{{cite web
| url = https://pubchem.ncbi.nlm.nih.gov/compound/hydrogen%20bromide
| title = Hydrobromic Acid
| date = 2024-02-03
| website = PubChem
| publisher = Springer Nature
| access-date = 2024-02-09
| quote =
}}
References
{{Hydrogen compounds}}
{{Bromides}}
{{Hydrides by group}}
{{Authority control}}