Perbromate
# Perbromate

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 (ClO−4) and iodine (IO−4) analogs, 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.

## Synthesis

Attempted syntheses of perbromates were unsuccessful until 1968, when it was finally obtained by the beta decay of selenium-83 in a selenate salt:

    $^{83}$ $SeO^{2−}$ $_4$ → $^{83}$ $BrO^−$ $_4$ + $β^−$

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 $BrO^−$ $_4.$

One effective method of producing perbromate is by the oxidation of bromate with fluorine under alkaline conditions:

    $BrO^−$ $_3$ + F $_2$ + 2 $OH^−$ → $BrO^−$ $_4$ + 2 $F^−$ + H $_2O$

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.

