View source for Hypobromous acid

{{chembox
| IUPACName = Hypobromous acid{{#tag:ref|Hypobromous acid is a [[retained name]] in IUPAC nomenclature.<ref>{{RedBook2005|page=287}}.</ref>|group=note}}
| OtherNames = Bromic(I) acid<br/>Bromanol<br/>Hydroxidobromine
| Section1 = {{Chembox Identifiers
|   ChemSpiderID = 75379
|   InChI=1/BrHO/c1-2/h2H
|   InChIKey = CUILPNURFADTPE-UHFFFAOYAL 
|   StdInChI=1S/BrHO/c1-2/h2H
|   StdInChIKey = CUILPNURFADTPE-UHFFFAOYSA-N
|   CASNo = 13517-11-8
  }}
| Section2 = {{Chembox Properties
|   Reference = <ref name="C&W">{{Cotton&Wilkinson5th|pages=563–67}}.</ref>
|   Formula = HOBr
|   MolarMass = 96.911 g mol<sup>−1</sup>
|   pKa = 8.70
  }}
| Section3 = {{Chembox Structure
|   Reference = <ref name="v1">{{citation | last1 = Cohen | first1 = E. A. | last2 = Mcrae | first2 = G. A. | last3 = Tan | first3 = T. L. | last4 = Friedl | first4 = R. R. | last5 = Johns | first5 = J. W. C. | last6 = Noel | first6 = M. | title = The ν<sub>1</sub> Band of HOBr | journal = J. Mol. Spectrosc. | volume = 173 | issue = 1 | year = 1995 | pages = 55–61 | doi = 10.1006/jmsp.1995.1218}}.</ref>
|   MolShape = bent: ''r''(Br–O)&nbsp;= 182.80&nbsp;pm, ''θ''(Br–O–H)&nbsp;= 102.99°
  }}
| Section8 = {{Chembox Related
|   OtherFunctn = [[Hypofluorous acid]]<br/>[[Hypochlorous acid]]<br/>[[Hypoiodous acid]]
|    Function = hypohalous acids
|   OtherCpds = [[Hydrobromic acid]]<br/>[[Bromous acid]]<br/>[[Bromic acid]]<br/>[[Perbromic acid]]
  }}
}}
'''Hypobromous acid''', HOBr, is an [[oxoacid]] of [[bromine]]. It is often considered to be only stable in aqueous solution,<ref name="C&W"/><ref name="G&E">{{Greenwood&Earnshaw1st|pages=999–1007}}.</ref> but it can be prepared in sufficient quantities in the gas phase for spectroscopic studies.<ref name="v1"/>

==Preparation==
Hypobromous acid can be prepared in solution by the reaction of [[bromine]] with a well-stirred suspension of [[mercury(II) oxide]].<ref name="C&W"/>
:2 Br<sub>2</sub> + 2 HgO + H<sub>2</sub>O &rarr; 2 HOBr + HgO·HgBr<sub>2</sub>
It is also formed by the [[disproportionation]] of bromine in water, although the equilibrium concentration is only {{nowrap|1.15{{e|−3}} mol dm<sup>−3</sup>}} in a saturated bromine solution ({{nowrap|0.21 mol dm<sup>−3</sup>}}) at 25&nbsp;°C.<ref name="C&W"/>
:Br<sub>2</sub> + H<sub>2</sub>O {{eqm}} HOBr + H<sup>+</sup> + Br<sup>−</sup>
It can also be prepared in the gas phase by the reaction of water with [[dibromine monoxide]], which is the formal anhydride of hypobromous acid.
:Br<sub>2</sub>O + H<sub>2</sub>O {{eqm}} 2 HOBr

==Structure==
Hypobromous acid has a bent ''C''<sub>2v</sub> structure in the vapour phase, as expected from [[VSEPR theory]], with ''r''(Br–O)&nbsp;= 182.80&nbsp;pm, ''θ''(H–O–Br)&nbsp;= 102.99°.<ref name="v1"/> Its [[Rotational spectroscopy|rotational spectrum]] has been extensively studied.<ref>{{citation | first1 = Yoshinori | last1 = Koga | first2 = Harutoshi | last2 = Takeo | first3 = Shigeo | last3 = Kondo | first4 = Masaaki | last4 = Sugie | first5 = Chi | last5 = Matsumura | first6 = G. A. | last6 = McRae | first7 = E. A. | last7 = Cohen | title = The rotational spectra, molecular structure, dipole moment, and hyperfine constants of HOBr and DOBr | journal = J. Mol. Spectrosc. | volume = 138 | issue = 2 | year = 1989 | pages = 467–81 | doi = 10.1016/0022-2852(89)90013-1}}.</ref><ref>{{citation | first1 = G. A. | last1 = McRae | first2 = E. A. | last2 = Cohen | title = The ν<sub>2</sub> band of HOBr | journal = J. Mol. Spectrosc. | volume = 139 | issue = 2 | year = 1990 | pages = 369–76 | doi = 10.1016/0022-2852(90)90074-Z}}.</ref><ref>{{citation | first1 = J. | last1 = Orphal | first2 = Q. | last2 = Kou | first3 = F. | last3 = Kwabia Tchana | first4 = O. | last4 = Pirali | first5 = J.-M. | last5 = Flaud | title = The ν<sub>3</sub> bands of HOBr around 16&nbsp;μm measured by high-resolution Fourier-transform spectroscopy | journal = J. Mol. Spectrosc. | volume = 221 | issue = 2 | year = 2003 | pages = 239–43 | doi = 10.1016/S0022-2852(03)00222-4}}.</ref><ref>{{citation | first1 = J. | last1 = Orphal | first2 = J.-M. | last2 = Flaud | first3 = Q. | last3 = Kou | first4 = F. | last4 = Kwabia Tchana | first5 = O. | last5 = Pirali | title = The far infrared rotational spectrum of HOBr: line positions and intensities | journal = J. Mol. Struct. | volume = 742 | issue = 1–3 | year = 2005 | pages = 153–59 | doi = 10.1016/j.molstruc.2005.01.006}}.</ref><ref>{{citation | first1 = E. A. | last1 = Cohen | first2 = H. S. P. | last2 = Müller | first3 = T. L. | last3 = Tan | first4 = G. A. | last4 = McRae | title = High resolution spectroscopy of DOBr and molecular properties of hypobromous acid | journal = J. Mol. Spectrosc. | volume = 262 | issue = 1 | year = 2010 | pages = 30–36 | doi = 10.1016/j.jms.2010.04.009}}.</ref>

==Reactivity==
Hypobromous acid is unstable with respect to [[disproportionation]], and should be prepared at around 0&nbsp;°C.<ref name="C&W"/>
:3 HOBr &rarr; 3 H<sup>+</sup> + 2 Br<sup>−</sup> + BrO{{su|b=3|p=−}}
The rate of disproportionation depends on the pH, being highest for pH&nbsp;3–8.<ref name="disprop">{{citation | first1 = Richard C. | last1 = Beckwith | first2 = Dale W. | last2 = Margerum | title = Kinetics of Hypobromous Acid Disproportionation | journal = Inorg. Chem., 1997 | volume = 36 | issue =17 | pages = 3754–60 | doi = 10.1021/ic970155g}}.</ref>

Hypobromous acid will add to carbon–carbon double bonds to give [[bromohydrin]]s,<ref>{{citation | last = Mokievsky | journal = Zh. Russ. Fiz.-Khim. O-va. | volume = 30 | pages = 900 | year = 1898}}; {{citation | journal = Chem. Zentralbl. | volume = 1 | page = 591 | year = 1899}}.</ref><ref>{{citation | last1 = Ingold | first1 = Christopher Kelk | last2 = Smith | first2 = Henry Geoffrey | title = CCCLXXXII.—The modes of addition to conjugated unsaturated systems. Part III. Further remarks and observations bearing on the mechanism of addition of halogens and hydrogen halides  | journal = J. Chem. Soc. | year = 1931 | pages = 2752–65 | doi = 10.1039/JR9310002752}}.</ref> and will also brominate activated aromatic rings such as [[toluene]].<ref>{{citation | last = Stark | first = O. | title = Über ein neues Bromierungsverfahren, Bromieren mit wäßriger, unterbromiger Säure | journal = Ber. Dtsch. Chem. Ges. | volume = 43 | issue = 1 | pages = 670–74 | year = 1910 | doi = 10.1002/cber.191004301113}}.</ref>

==Notes and references==
===Notes===
{{reflist|group=note}}

===References===
{{reflist|2}}

==External links==
{{wikipedia|Hypobromous acid}}

[[Category:Bromine oxoacids]]

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