The hypobromite

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

, 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 simila ...

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 ble ...

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 In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...

(some undergoes reduction and some oxidation) from oxidation state 0 (Br₂) to oxidation state −1 (Br⁻) and oxidation state +1 (BrO⁻).

Sodium hypobromite Sodium hypobromite is the inorganic compound with the formula NaBrO. It is usually obtained as the pentahydrate, so the material that is usually called sodium hypobromite has the formula NaOBr • 5H2O. It is a yellow-orange solid tha ...

can be isolated as an orange solid. A secondary reaction, where hypobromite spontaneously disproportionates to

bromide A bromide ion is the negatively charged form (Br−) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant ...

(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 drinki ...

(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 Sodium hypobromite is the inorganic compound with the formula NaBrO. It is usually obtained as the pentahydrate, so the material that is usually called sodium hypobromite has the formula NaOBr • 5H2O. It is a yellow-orange solid tha ...

and potassium hypobromite.

In nature and industry

Bromide from the diet, naturally present in the blood, is used by

eosinophils Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells (WBCs) and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. A ...

, 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 Eosinophil peroxidase is an enzyme found within the eosinophil granulocytes, innate immune cells of humans and mammals. This oxidoreductase protein is encoded by the gene ''EPX'', expressed within these myeloid cells. EPO shares many similarities ...

, 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. The Nernst equation shows that hydrogen peroxide can oxidize chlori ...

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 The Hofmann rearrangement (Hofmann degradation) is the organic reaction of a primary amide to a primary amine with one fewer carbon atom. The reaction involves oxidation of the nitrogen followed by rearrangement of the carbonyl and nitrogen to gi ...

References

{{reflist Hypobromites

Preparation

Compounds

In nature and industry

See also

References