The hypobromite ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

, also called alkaline bromine water, is BrO. Bromine is in the +1 oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

. Hypobromite is the bromine compound analogous to hypochlorite
The hypochlorite ion, also known as chlorate anion is ClO−. A hypochlorite compound is a chemical compound containing this group, with chlorine in oxidation state +1.Hypochlorites are the salts of hypochlorous acid...

s 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.


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
A bromide is a chemical compound containing bromide ion, that is bromine atom with effective charge of −1. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.-Natural occurrence:...

 (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 drinking water...

 (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
The hypochlorite ion, also known as chlorate anion is ClO−. A hypochlorite compound is a chemical compound containing this group, with chlorine in oxidation state +1.Hypochlorites are the salts of hypochlorous acid...

 and chlorate
The chlorate anion has the formula ClO. 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 a roman numeral in parentheses, e.g...

. 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.


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
Eosinophil peroxidase
Eosinophil peroxidase is a haloperoxidase enzyme that in humans is encoded by the EPX gene. The enzyme is a heterodimeric 71-77 kD peroxidase consisting of a heavier glycosylated chain and a lighter nonglycosylated chain...

, a haloperoxidase
Haloperoxidases are peroxidases that are able to mediate the oxidation of halides by hydrogen peroxide. Both halides and hydrogen peroxide are widely available in the environment....

 enzyme which preferentially uses bromide over chloride for this purpose.

Simple bromide salts (such as sodium bromide) are also sometimes used in hot tub
Hot tub
A hot tub is a large tub or small pool full of heated water and used for soaking, relaxation, massage, or hydrotherapy. In most cases, they have jets for massage purposes. Hot tubs are usually located outdoors, and are often sheltered for protection from the elements, as well as for privacy....

s 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.
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