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{{chembox {{chembox
⚫ | verifiedrevid = 443429816
| Watchedfields = changed
⚫ | verifiedrevid = 399696621
| ImageFile = Bromige saeure.png | ImageFile = Bromige saeure.png
| ImageSize = | ImageSize =
| ImageFile2 = Bromous_acid_molecule_ball.png
| ImageSize2 = 160
| ImageFile1 = Bromous acid molecule spacefill.png
| ImageSize1 = 160
| ImageAlt1 = Space-filling model of the bromous acid molecule
| ImageAlt2 = Ball and stick model of the bromous acid molecule
| IUPACName = hydroxy-λ<sup>3</sup>-bromanone<br />hydroxidooxidobromine<br />bromous acid | IUPACName = hydroxy-λ<sup>3</sup>-bromanone<br />hydroxidooxidobromine<br />bromous acid
⚫ |Section1={{Chembox Identifiers
| OtherNames =
| CASNo =37691-27-3
⚫ | Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 145144 | ChemSpiderID = 145144
Line 15: Line 20:
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = DKSMCEUSSQTGBK-UHFFFAOYSA-N | StdInChIKey = DKSMCEUSSQTGBK-UHFFFAOYSA-N
| CASNo =
| PubChem = 165616 | PubChem = 165616
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 29247 | ChEBI = 29247
| SMILES = O=BrO | SMILES = O
}} }}
| Section2 = {{Chembox Properties |Section2={{Chembox Properties
| Formula = HBrO<sub>2</sub> | Formula = HBrO<sub>2</sub>
| MolarMass = 112.911 g/mol | MolarMass = 112.911 g/mol
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| MeltingPt = | MeltingPt =
| BoilingPt = | BoilingPt =
| Solubility = }} | Solubility =
| ConjugateBase = Bromite}}
| Section3 = {{Chembox Hazards |Section3={{Chembox Hazards
| MainHazards = | MainHazards =
| FlashPt = | FlashPt =
| Autoignition = }} | AutoignitionPt = }}
| Section4 = {{Chembox Other |Section4={{Chembox Related
| OtherAnions = ]; ]; ]; ]}} | OtherAnions = ]; ]; ]; ]}}
}} }}
'''Bromous acid''' with the formula HBrO<sub>2</sub> has bromine in the +3 ]. The salts of bromous acid are called bromites. The acid is not stable and only occurs as an intermediate, for example in the oxidation of ]s.<ref name = "Wiberg&Holleman">Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier ISBN 0-12-352651-5</ref> '''Bromous acid''' is the ] with the formula of HBrO<sub>2</sub>. It is an unstable compound, although salts of its conjugate base – bromites – have been isolated. In acidic solution, bromites decompose to bromine.<ref name="Wiberg&Holleman">{{cite book |chapter=Oxygen Acids of Bromine |pages=449–451 |chapter-url={{GBurl|Mtth5g59dEIC|p=449}} |editor1-first=Nils |editor1-last=Wiberg |editor2-first=A. F. |editor2-last=Holleman |editor3-first=Egon |editor3-last=Wiberg |title=Inorganic Chemistry |date=2001 |publisher=Academic Press |isbn=978-0-12-352651-9 }}</ref>


== Chemistry == == Discovery ==
In 1905, Richards A. H. proved the existence of bromous acid through a series of experiments involving ] (AgNO<sub>3</sub>) and bromine.<ref name=":3">{{cite journal |last1=Richards |first1=A. H. |title=The existence of bromous acid ({{chem|H|Br|O|2}}) |journal=Journal of the Society of Chemical Industry |volume=25 |issue=1 Suppl |date=15 January 1906 |pages=4–5 |hdl=2027/mdp.39015030318508?urlappend=%3Bseq=144%3Bownerid=13510798902008078-170 |hdl-access=free }}</ref> The reaction of excess cold aqueous to form ] (HBrO), ] (AgBr) and ] (HNO<sub>3</sub>):
Bromous acid can be produced by classical chemical or electrochemicals method via ] oxidation.{{Fact|date=January 2009}}
:Br<sub>2</sub> + AgNO<sub>3</sub> + H<sub>2</sub>O → HBrO + AgBr + HNO<sub>3</sub>
Richards discovered that the effect of adding excess liquid bromine in a concentrated ] (AgNO<sub>3</sub>) resulted in a different reaction mechanism. From numbers of equivalent portions of acid bromine formed from the previous reaction, the ratio between oxygen and bromine was calculated, with the exact value of O:Br (0.149975:0.3745), suggesting the acid compound contains two oxygen atom to one bromine atom. Thus, the chemical structure of the acid compound was deducted as HBrO<sub>2</sub>.<ref name=":3" />


According to Richards, ] (HBrO) arises by the reaction of bromine and silver nitrate solution:<ref name=":3" />
⚫ :HBrO + HClO &rarr; HBrO<sub>2</sub> + HCl
:Br<sub>2</sub> + AgNO<sub>3</sub> + H<sub>2</sub>O → HBrO + AgBr + HNO<sub>3</sub>
:2&nbsp;AgNO<sub>3</sub> + HBrO + Br<sub>2</sub> + H<sub>2</sub>O → HBrO<sub>2</sub> + 2&nbsp;AgBr + 2 HNO<sub>3</sub>


== Isomerism ==
Also disproportioning of hypobromous acid will give bromous acid and ].{{Fact|date=January 2009}}
The molecule HBrO<sub>2</sub> has a bent structure with ∠(H−O−Br) angles of 106.1°. HOBrO also adopts a non-planar conformation with one isomer structure (2a) adopting a dihedral angle ∠(H−O−Br−O) of 74.2°. Moreover, the planar structures of two other isomers (2b-''cis'' and 2c-''trans'') are transition state for fast enantiomerization.<ref>{{cite journal |last1=Glaser |first1=Rainer |last2=Jost |first2=Mary |title=Disproportionation of Bromous Acid HOBrO by Direct O-Transfer and via Anhydrides O(BrO)<sub>2</sub> and BrO-BrO<sub>2</sub>. An Ab Initio Study of the Mechanism of a Key Step of the Belousov–Zhabotinsky Oscillating Reaction |journal=The Journal of Physical Chemistry A |date=16 August 2012 |volume=116 |issue=32 |pages=8352–8365 |doi=10.1021/jp301329g |pmid=22871057 |bibcode=2012JPCA..116.8352G }}</ref>
<!-- Deleted image removed: ] -->


Another study identified three isomers: HOOBr, HOBrO, and HBr(O)O.<ref>{{cite journal |last1=de Souza |first1=Gabriel L. C. |last2=Brown |first2=Alex |title=The ground and excited states of HBrO<sub>2</sub> and HBrO<sub>3</sub> (HOOOBr and HOOBrO) isomers |journal=Theoretical Chemistry Accounts |date=July 2016 |volume=135 |issue=7 |doi=10.1007/s00214-016-1931-8 }}</ref>
⚫ :2 HBrO &rarr; HBrO<sub>2</sub> + HBr
<!-- Deleted image removed: ] -->


== Synthesis ==
Lastly, a synproportion reaction of bromic acid and hydrobromic acid gives bromous acid.{{Fact|date=January 2009}}
A oxidation reaction between ] (HBrO) and ] (HClO) can be used to produce bromous acid (HBrO<sub>2</sub>) and ] (HCl).{{cn|date=September 2023}}
⚫ :HBrO + HClO → HBrO<sub>2</sub> + HCl


A redox reaction of ] (HBrO) can form bromous acid (HBrO<sub>2</sub>) as its product:{{cn|date=September 2023}}
⚫ :2 HBrO<sub>3</sub> + HBr &rarr; 3 HBrO<sub>2</sub>
:HBrO + H<sub>2</sub>O − 2e<sup>−</sup> → HBrO<sub>2</sub> + 2H<sup>+</sup>


The ] of two equivalents ] (HBrO) results in the formation of both bromous acid (HBrO<sub>2</sub>) and ] (HBr):{{cn|date=September 2023}}
==Compounds==
⚫ : 2&nbsp;HBrO → HBrO<sub>2</sub> + HBr


A rearrangement reaction, which results from the syn-proportion of ] (HBrO<sub>3</sub>) and ] (HBr) gives bromous acid (HBrO<sub>2</sub>):{{cn|date=September 2023}}
Several bromites are stable and have been isolated. For example NaBrO<sub>2</sub>· 3H<sub>2</sub>O and Ba(BrO<sub>2</sub>)<sub>2</sub>·H<sub>2</sub>O.<ref name = "Wiberg&Holleman"/>
⚫ :2&nbsp;HBrO<sub>3</sub> + HBr → 3&nbsp;HBrO<sub>2</sub>


==Use== ==Salts==
]
The salts ] and ] have been crystallized. Upon treatment of these aqueous solutions with salts of Pb<sup>2+</sup>, Hg<sup>2+</sup>, and Ag<sup>+</sup>, the corresponding heavy metal bromites precipitate as solids.<ref name = "Wiberg&Holleman"/>


== Belousov–Zhabotinsky reaction ==
⚫ Bromites can be used for the reduction of ]s to ]s.<ref name = "Wiberg&Holleman"/>
Bromous acid is a product of the ] resulting from the combination of potassium bromate, cerium(IV) sulfate, propanedioic acid and citric acid in dilute sulfuric acid. Bromous acid is an intermediate stage of the reaction between bromate ion ({{chem|BrO|3|−}} ) and bromine (Br<sup>−</sup>):<ref name=":0">{{cite journal |last1=Vassalini |first1=Irene |last2=Alessandri |first2=Ivano |title=Spatial and Temporal Control of Information Storage in Cellulose by Chemically Activated Oscillations |journal=ACS Applied Materials & Interfaces |date=30 December 2015 |volume=7 |issue=51 |pages=28708–28713 |doi=10.1021/acsami.5b11857 |pmid=26654462 |url=https://figshare.com/articles/journal_contribution/2093821 }}</ref><ref name=":1">{{cite journal |last1=Field |first1=Richard J. |last2=Koros |first2=Endre |last3=Noyes |first3=Richard M. |title=Oscillations in chemical systems. II. Thorough analysis of temporal oscillation in the bromate-cerium-malonic acid system |journal=Journal of the American Chemical Society |date=December 1972 |volume=94 |issue=25 |pages=8649–8664 |doi=10.1021/ja00780a001 |bibcode=1972JAChS..94.8649F }}</ref>
* {{chem|BrO|3|−}} + 2&nbsp;Br<sup>−</sup> → HBrO<sub>2</sub> + HBrO


Other relevant reactions in such oscillating reactions are:
⚫ :2MnO{{su|b=4|p=−}} + BrO{{su|b=2|p=−}} + OH<sup>−</sup> → 2MnO{{su|b=4|p=2−}} + BrO{{su|b=3|p=−}} + H<sub>2</sub>O
* HBrO<sub>2</sub> + {{chem|BrO|3|−}} + H<sup>+</sup> → 2&nbsp;{{chem|BrO|2|•}} + H<sub>2</sub>O
* 2&nbsp;HBrO<sub>2</sub> → {{chem|BrO|3|−}} + HOBr + H<sup>+</sup>

⚫ Bromites reduce ]s to ]s (VI):<ref name="Wiberg&Holleman" />
⚫ * 2&nbsp;{{chem|MnO|4|−}} + {{chem|BrO|2|−}} + OH<sup>−</sup> → 2&nbsp;{{chem|MnO|4|2−}} + {{chem|BrO|3|−}} + H<sub>2</sub>O

== p''K''<sub>a</sub> measurement ==
The acid dissociation constant of bromous acid, ''K''<sub>a</sub> = <big>{{sfrac||}}</big>, was determined using different methods.

The value of the p''K''<sub>a</sub> for bromous acid was estimated in research studying the decomposition of bromites. The research measured the rate of bromite decomposition as a function of hydrogen and bromite ion concentrations. The experimental data of the log of the initial velocity were plotted against pH. Using this method, the estimated p''K''<sub>a</sub> value for bromous acid was 6.25.<ref>{{cite journal |last1=Massagli |first1=A. |last2=Indelli |first2=A. |last3=Pergola |first3=F. |title=Kinetic investigation of the decomposition of bromite |journal=Inorganica Chimica Acta |date=1970 |volume=4 |pages=593–596 |doi=10.1016/S0020-1693(00)93357-7 }}</ref>

Using another method, the pK<sub>a</sub> for bromous acid was measured based on the initial velocity of the reaction between sodium bromites and potassium iodine in a pH range of 2.9–8.0, at 25&nbsp;°C and ionic strength of 0.06&nbsp;M. The first order dependence of the initial velocity of this ] on in a pH range of 4.5–8.0. The value of acid dissociation constant measured by this method is ''K''<sub>a</sub> = {{val|3.7|0.9|e=-4|u=M}} and p''K''<sub>a</sub> = {{val|3.43|0.05}}.<ref>{{cite journal |last1=Faria |first1=R. B. |last2=Epstein |first2=Irving R. |last3=Kustin |first3=Kenneth |title=Kinetics of Disproportionation and pKa of Bromous Acid |journal=The Journal of Physical Chemistry |date=January 1994 |volume=98 |issue=4 |pages=1363–1367 |doi=10.1021/j100055a051 }}</ref>

== Reactivity ==
In comparison to other oxygen-centered oxidants (hypohalites, anions of peroxides) and in line with its low basicity, bromite is a rather weak nucleophile.<ref>{{cite journal |last1=Mayer |first1=Robert J. |last2=Ofial |first2=Armin R. |title=Nucleophilic Reactivities of Bleach Reagents |journal=Organic Letters |date=18 May 2018 |volume=20 |issue=10 |pages=2816–2820 |doi=10.1021/acs.orglett.8b00645 |pmid=29741385 }}</ref> Rate constants of bromite towards carbocations and acceptor-substituted olefins are by 1–3 orders of magnitude lower than the ones measured with hypobromite.


==References== ==References==
{{reflist}} {{reflist}}

==Further reading==
* {{cite book |doi=10.1002/0471238961.0218151321110512.a01 |chapter=Bromine, Inorganic Compounds |title=Kirk-Othmer Encyclopedia of Chemical Technology |date=2002 |last1=Ukeles |first1=S.D. |last2=Freiberg |first2=M. |isbn=978-0-471-48494-3 }}


{{Hydrogen compounds}} {{Hydrogen compounds}}


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Latest revision as of 14:01, 13 December 2024

Bromous acid
Space-filling model of the bromous acid molecule
Ball and stick model of the bromous acid molecule
Names
IUPAC names hydroxy-λ-bromanone
hydroxidooxidobromine
bromous acid
Identifiers
CAS Number
3D model (JSmol)
ChEBI
ChemSpider
PubChem CID
CompTox Dashboard (EPA)
InChI
  • InChI=1S/BrHO2/c2-1-3/h(H,2,3)Key: DKSMCEUSSQTGBK-UHFFFAOYSA-N
  • InChI=1/BrHO2/c2-1-3/h(H,2,3)Key: DKSMCEUSSQTGBK-UHFFFAOYAC
SMILES
  • O
Properties
Chemical formula HBrO2
Molar mass 112.911 g/mol
Conjugate base Bromite
Related compounds
Other anions Hydrobromic acid; hypobromous acid; bromic acid; perbromic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). checkY verify (what is  ?) Infobox references
Chemical compound

Bromous acid is the inorganic compound with the formula of HBrO2. It is an unstable compound, although salts of its conjugate base – bromites – have been isolated. In acidic solution, bromites decompose to bromine.

Discovery

In 1905, Richards A. H. proved the existence of bromous acid through a series of experiments involving silver nitrate (AgNO3) and bromine. The reaction of excess cold aqueous to form hypobromous acid (HBrO), silver bromide (AgBr) and nitric acid (HNO3):

Br2 + AgNO3 + H2O → HBrO + AgBr + HNO3

Richards discovered that the effect of adding excess liquid bromine in a concentrated silver nitrate (AgNO3) resulted in a different reaction mechanism. From numbers of equivalent portions of acid bromine formed from the previous reaction, the ratio between oxygen and bromine was calculated, with the exact value of O:Br (0.149975:0.3745), suggesting the acid compound contains two oxygen atom to one bromine atom. Thus, the chemical structure of the acid compound was deducted as HBrO2.

According to Richards, hypobromous acid (HBrO) arises by the reaction of bromine and silver nitrate solution:

Br2 + AgNO3 + H2O → HBrO + AgBr + HNO3
2 AgNO3 + HBrO + Br2 + H2O → HBrO2 + 2 AgBr + 2 HNO3

Isomerism

The molecule HBrO2 has a bent structure with ∠(H−O−Br) angles of 106.1°. HOBrO also adopts a non-planar conformation with one isomer structure (2a) adopting a dihedral angle ∠(H−O−Br−O) of 74.2°. Moreover, the planar structures of two other isomers (2b-cis and 2c-trans) are transition state for fast enantiomerization.

Another study identified three isomers: HOOBr, HOBrO, and HBr(O)O.

Synthesis

A oxidation reaction between hypobromous acid (HBrO) and hypochlorous acid (HClO) can be used to produce bromous acid (HBrO2) and hydrochloric acid (HCl).

HBrO + HClO → HBrO2 + HCl

A redox reaction of hypobromous acid (HBrO) can form bromous acid (HBrO2) as its product:

HBrO + H2O − 2e → HBrO2 + 2H

The disproportionation reaction of two equivalents hypobromous acid (HBrO) results in the formation of both bromous acid (HBrO2) and hydrobromic acid (HBr):

2 HBrO → HBrO2 + HBr

A rearrangement reaction, which results from the syn-proportion of bromic acid (HBrO3) and hydrobromic acid (HBr) gives bromous acid (HBrO2):

2 HBrO3 + HBr → 3 HBrO2

Salts

The bromite ion in sodium bromite.

The salts NaBrO2·3H2O and Ba(BrO2)2·H2O have been crystallized. Upon treatment of these aqueous solutions with salts of Pb, Hg, and Ag, the corresponding heavy metal bromites precipitate as solids.

Belousov–Zhabotinsky reaction

Bromous acid is a product of the Belousov–Zhabotinsky reaction resulting from the combination of potassium bromate, cerium(IV) sulfate, propanedioic acid and citric acid in dilute sulfuric acid. Bromous acid is an intermediate stage of the reaction between bromate ion (BrO
3 ) and bromine (Br):

  • BrO
    3 + 2 Br → HBrO2 + HBrO

Other relevant reactions in such oscillating reactions are:

  • HBrO2 + BrO
    3 + H → 2 BrO
    2 + H2O
  • 2 HBrO2 → BrO
    3 + HOBr + H

Bromites reduce permanganates to manganates (VI):

  • 2 MnO
    4 + BrO
    2 + OH → 2 MnO
    4 + BrO
    3 + H2O

pKa measurement

The acid dissociation constant of bromous acid, Ka = ⁠/⁠, was determined using different methods.

The value of the pKa for bromous acid was estimated in research studying the decomposition of bromites. The research measured the rate of bromite decomposition as a function of hydrogen and bromite ion concentrations. The experimental data of the log of the initial velocity were plotted against pH. Using this method, the estimated pKa value for bromous acid was 6.25.

Using another method, the pKa for bromous acid was measured based on the initial velocity of the reaction between sodium bromites and potassium iodine in a pH range of 2.9–8.0, at 25 °C and ionic strength of 0.06 M. The first order dependence of the initial velocity of this disproportionation reaction on in a pH range of 4.5–8.0. The value of acid dissociation constant measured by this method is Ka = (3.7±0.9)×10 M and pKa = 3.43±0.05.

Reactivity

In comparison to other oxygen-centered oxidants (hypohalites, anions of peroxides) and in line with its low basicity, bromite is a rather weak nucleophile. Rate constants of bromite towards carbocations and acceptor-substituted olefins are by 1–3 orders of magnitude lower than the ones measured with hypobromite.

References

  1. ^ Wiberg, Nils; Holleman, A. F.; Wiberg, Egon, eds. (2001). "Oxygen Acids of Bromine". Inorganic Chemistry. Academic Press. pp. 449–451. ISBN 978-0-12-352651-9.
  2. ^ Richards, A. H. (15 January 1906). "The existence of bromous acid (HBrO
    2)". Journal of the Society of Chemical Industry. 25 (1 Suppl): 4–5. hdl:2027/mdp.39015030318508.
  3. Glaser, Rainer; Jost, Mary (16 August 2012). "Disproportionation of Bromous Acid HOBrO by Direct O-Transfer and via Anhydrides O(BrO)2 and BrO-BrO2. An Ab Initio Study of the Mechanism of a Key Step of the Belousov–Zhabotinsky Oscillating Reaction". The Journal of Physical Chemistry A. 116 (32): 8352–8365. Bibcode:2012JPCA..116.8352G. doi:10.1021/jp301329g. PMID 22871057.
  4. de Souza, Gabriel L. C.; Brown, Alex (July 2016). "The ground and excited states of HBrO2 and HBrO3 (HOOOBr and HOOBrO) isomers". Theoretical Chemistry Accounts. 135 (7). doi:10.1007/s00214-016-1931-8.
  5. Vassalini, Irene; Alessandri, Ivano (30 December 2015). "Spatial and Temporal Control of Information Storage in Cellulose by Chemically Activated Oscillations". ACS Applied Materials & Interfaces. 7 (51): 28708–28713. doi:10.1021/acsami.5b11857. PMID 26654462.
  6. Field, Richard J.; Koros, Endre; Noyes, Richard M. (December 1972). "Oscillations in chemical systems. II. Thorough analysis of temporal oscillation in the bromate-cerium-malonic acid system". Journal of the American Chemical Society. 94 (25): 8649–8664. Bibcode:1972JAChS..94.8649F. doi:10.1021/ja00780a001.
  7. Massagli, A.; Indelli, A.; Pergola, F. (1970). "Kinetic investigation of the decomposition of bromite". Inorganica Chimica Acta. 4: 593–596. doi:10.1016/S0020-1693(00)93357-7.
  8. Faria, R. B.; Epstein, Irving R.; Kustin, Kenneth (January 1994). "Kinetics of Disproportionation and pKa of Bromous Acid". The Journal of Physical Chemistry. 98 (4): 1363–1367. doi:10.1021/j100055a051.
  9. Mayer, Robert J.; Ofial, Armin R. (18 May 2018). "Nucleophilic Reactivities of Bleach Reagents". Organic Letters. 20 (10): 2816–2820. doi:10.1021/acs.orglett.8b00645. PMID 29741385.

Further reading

Hydrogen compounds
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