In chemistry, the perbromate ion is the anion having the chemical formula BrO−
4. It is an oxyanion of bromine, the conjugate base of perbromic acid, in which bromine has the oxidation state +7. Unlike its chlorine and iodine analogs (perchlorate and periodate), it is difficult to synthesize. It has tetrahedral molecular geometry.
The term perbromate also refers to a compound that contains the BrO−
4 anion or the –OBrO
3 functional group.
The perbromate ion is a strong oxidizing agent. The reduction potential for the BrO−
4/Br− couple is +0.68 V at pH 14. This is comparable to selenite's reduction potential.
Attempted syntheses of perbromates were unsuccessful until 1968, when it was finally obtained by the beta decay of selenium-83 in a selenate salt:83
Subsequently, it was successfully synthesized again by the electrolysis of LiBrO
3, although only in low yield. Later, it was obtained by the oxidation of bromate with xenon difluoride. Once perbromates are obtained, perbromic acid can be produced by protonating BrO−
One effective method of producing perbromate is by the oxidation of bromate with fluorine under alkaline conditions:BrO−
+ 2 OH−
+ 2 F−
This synthesis is much easier to perform on a large scale than the electrolysis route or oxidation by xenon difluoride.
In 2011 a new, more effective synthesis was discovered: perbromate ions were formed through the reaction of hypobromite and bromate ions in an alkaline sodium hypobromite solution.
Diperiodatonickelate anions in alkaline solution can oxidise bromate to perbromate. This is a relatively lower cost and fluorine free synthesis.