Bromous acid

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Bromous acid
IUPAC name
Bromous acid
Other names
Molar mass 112.911 g/mol
Appearance Unstable yellowish solution
Odor Bromine-like, suffocating
Melting point Decomposes
Boiling point Decomposes
Solubility Reacts with bases
Acidity (pKa) 3.43-6.25 (est.)
-72 kJ/mol[1]
Safety data sheet None
Flash point Non-flammable
Related compounds
Related compounds
Hydrobromic acid
Hypobromous acid
Bromic acid
Perbromic acid
Chlorous acid
Iodic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

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.



Bromous acid is unstable and will rapidly decompose in aq. solution to hypobromite and bromate.[3]

Addition of hydrogen peroxide to bromous acid will produce hypobromous acid, oxygen and water:[4]

HBrO2 + H2O2 → HBrO + H2O + O2

Bromites reduce permanganates to manganates:

2 MnO
+ BrO
+ OH → 2 MnO2−
+ BrO
+ H2O


Due to its instability, the compound is poorly characterized, thus any properties of the compound are derived from its dilute solution.


Bromous acid is unstable and thus it is not commercially available.


Addition of acid to bromite salts will produce bromous acid, which is unstable and will rapidly decompose.

Addition of elemental bromine to a solution of silver nitrate will yield hypobromous acid which is further oxidized to bromous acid:[5]

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

Oxidizing hypobromous acid with hypochlorous acid will alos produce bromous acid as well as hydrochloric acid:

HBrO + HClO → HBrO2 + HCl

A redox reaction of hypobromous acid can form bromous acid as its product:

HBrO + H2O − 2e → HBrO2 + 2H+

The |disproportionation reaction of two equivalents hypobromous acid results in the formation of both bromous acid and hydrobromic acid:

2 HBrO → HBrO2 + HBr

A rearrangement reaction, which results from the syn-proportion of bromic acid and hydrobromic acid gives pure bromous acid:

2 HBrO3 + HBr → 3 HBrO2




Bromous acid is unstable and corrosive.


Cannot be stored due to its instability.


Thiosulfates, sulfites, metabisulfites can be used to neutralize the compound to bromide.


  1. Kshirsagar, Girish; Field, Richard J.; Journal of Physical Chemistry; vol. 92; nb. 25; (1988); p. 7074 - 7079
  2. Field, Richard J.; Foersterling, Horst-Dieter; Journal of Physical Chemistry; vol. 90; nb. 21; (1986); p. 5400 - 5407
  3. Ariese, Freek; Ungvarai-Nagy, Zsuzsanna; Journal of Physical Chemistry; vol. 90; nb. 1; (1986); p. 1 - 4
  4. Bray, W. C.; Davis, P. R.; Journal of the American Chemical Society; vol. 52; (1930); p. 1427
  5. Richards, A. H.; Journal of the Society of Chemical Industry, London; vol. 25; (1906); p. 4

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