In chemistry, the perbromate ion is the anion having the chemical formula . It is an oxyanion of bromine, the conjugate base of perbromic acid, in which bromine has the oxidation state +7.[1] Unlike its chlorine and iodine analogs, it is difficult to synthesize. It has tetrahedral molecular geometry.
The term perbromate also refers to a compound that contains the anion or the functional group.
The perbromate ion is a strong oxidizing agent. The reduction potential for the /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:[2]
→ + β−
Subsequently, it was successfully synthesized again by the electrolysis of, although only in low yield.[3] [4] Later, it was obtained by the oxidation of bromate with xenon difluoride.[5] [6] Once perbromates are obtained, perbromic acid can be produced by protonating .
One effective method of producing perbromate is by the oxidation of bromate with fluorine under alkaline conditions:[7]
+ + 2 → + 2 +
This synthesis is much easier to perform on a large scale than the electrolysis route or oxidation by xenon difluoride.[8]
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. The reaction (and its perchlorate analogue) occurs naturally, but very slowly, requiring several days to complete.[9]
Diperiodatonickelate anions in alkaline solution can oxidise bromate to perbromate. This is a relatively lower cost and fluorine free synthesis.[10]
Other bromine anions:
| Bromine oxidation state | −1 | +1 | +3 | +5 | +7 | |
|---|---|---|---|---|---|---|
| Name | bromide | hypobromite | bromite | bromate | perbromate | |
| Formula | Br− | BrO− | ||||
| Structure |