The hypobromite ion, also called alkaline

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...

water, is BrO⁻. Bromine is in the +1

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

. The Br–O bond length is 1.82 Å. Hypobromite is the bromine compound analogous to

hypochlorite In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ...

s found in common bleaches, and in immune cells. In many ways, hypobromite functions in the same manner as hypochlorite, and is also used as a germicide and antiparasitic in both industrial applications, and in the immune system.

Preparation

Hypobromite salts form upon treating bromine with aqueous alkali, such as sodium or potassium hydroxide. At 20 °C the reaction is rapid. : Br₂ + 2 OH⁻(aq) → Br⁻ + BrO⁻ + H₂O In this reaction the bromine disproportionates (some undergoes reduction and some oxidation) from oxidation state 0 (Br₂) to oxidation state −1 (Br⁻) and oxidation state +1 (BrO⁻). Sodium hypobromite can be isolated as an orange solid. A secondary reaction, where hypobromite spontaneously disproportionates to bromide (bromine oxidation state −1) and

bromate The bromate anion, BrO, is a bromine-based oxoanion. A bromate is a chemical compound that contains this ion. Examples of bromates include sodium bromate, (), and potassium bromate, (). Bromates are formed many different ways in municipal drin ...

(bromine oxidation state +5) takes place rapidly at 20 °C and slowly at 0 °C. : 3 BrO⁻ → 2 Br⁻ + Hence, in reaction 2, the formation and proportions of the −1, +1 and +5 bromine oxidation state products can be controlled by temperature. Hypobromite is not thermodynamically stable at any pH (see Pourbaix diagram for bromine at http://www.eosremediation.com/download/Chemistry/Chemical%20Properties/Eh_pH_Diagrams.pdf ), but it is kinetically locked toward a further disproportion into bromate and bromide above the pKa of HBrO. These reactions of bromine are analogous to those of chlorine forming

and

chlorate The chlorate anion has the formula ClO3-. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by ...

. The corresponding chlorine reaction 1 (to form ClO⁻) is fast at 20 °C and reaction 2 (to form ) is slow at 20 °C and fast at 70 °C.

Compounds

A hypobromite is a compound that contains this anion. Examples include sodium hypobromite and potassium hypobromite.

In nature and industry

Bromide from the diet, naturally present in the blood, is used by eosinophils, white blood cells of the granulocyte class, specialized for dealing with multi-cellular parasites. These cells react the bromide with peroxide to generate hypobromite by the action of eosinophil peroxidase, a haloperoxidase enzyme which preferentially uses bromide over chloride for this purpose. Simple bromide salts (such as sodium bromide) are also sometimes used in hot tubs and spas as mild germicidal agents, using the action of an added oxidizing agent (such as hydrogen peroxide) to generate ''in situ'' hypobromite, in a similar fashion to the action of peroxidase on bromide in eosinophils. Hypobromite has been proposed to be a reactive intermediate in the Hofmann rearrangement.

References

{{reflist Hypobromites

Preparation

Compounds

In nature and industry

See also

References