Hypobromite

The hypobromite ion, also called alkaline bromine water, is BrO−. Bromine is in the +1 oxidation state. Hypobromite is the bromine compound analogous to hypochlorites found in common bleaches, and in immune cells. In many ways, hyprobromite 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
Bromine is added to an aqueous hydroxide (such as sodium or potassium hydroxide). At 20 °C the reaction is rapid.


 * Br2(l) + 2OH−(aq) → Br−(aq) + BrO−(aq) + H2O(l)

In this reaction the bromine disproportionates (undergoes both reduction and oxidation) from oxidation state 0 (Br2) to oxidation state -1 (Br−) and oxidation state +1 (BrO−).

A secondary reaction, where hypobromite spontaneously disproportionates to bromide (bromine oxidation state -1) and bromate (bromine oxidation state +5) takes place rapidly at 20 °C and slowly at 0 °C.


 * 3BrO−(aq) → 2Br−(aq) + BrO3−(aq)

Hence, in reaction 2, the formation and proportions of the -1, +1 and +5 bromine oxidation state products can be controlled by temperature.

These reactions of bromine are analogous to those of chlorine forming hypochlorite and chlorate. The corresponding chlorine reaction 1 (to form ClO−) is fast at 20 °C and reaction 2 (to form ClO3−) is slow at 20 °C and fast at 70 °C.

Compounds
A hypobromite is a compound that contains this anion. Hypobromites are not common.

In nature and industry
Bromide from the diet, naturally present in the blood, is used by eosinophils, white blood cells of the granulocyte class, specialised 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.