Potassium bromate

Potassium bromate is produced when bromine is passed through a hot solution of potassium hydroxide. Initially formed is potassium hypobromite, which quickly disproportionates into bromide and bromate:^[4]

3 BrO⁻ ⇌ 2 Br⁻ + BrO−3

Electrolysis of potassium bromide solutions will also give bromate.^[1] Both processes are analogous to those used in the production of chlorates. Because it can be obtained in high purity, potassium bromate is used as an analytical reagent ("primary standard").^[1]

Potassium bromate can separated from the potassium bromide owing to its lower solubility. When a solution containing potassium bromate and bromide is cooled to 0 °C, nearly all bromate salt will precipitate, while nearly all of the bromide salt will stay in solution.^[4]

As established by X-ray crystallography, the O-Br-O angles are 104.5°, consistent with its pyramidal shape of the anion. The Br-O distances are 1.66 Å.^[2]

Potassium bromate has some uses as a reagent in organic synthesis. In the presence of acid, it serves as a source of Br⁺ and can thus be used to brominate otherwise recalcitrant aromatic substrates, such as nitrobenzene. When treated with acid in the presence of bromide salts, potassium bromate serves as a source of bromine:^[5]

3 RCH=CHR' + KBrO₃ + 5 Br⁻ + 6 H⁺ → 3 RCH(Br)−C(Br)HR' + 3 H₂O

Aryl iodides can be oxidized with potassium bromate to the corresponding iodinane oxides.^[6]

Potassium bromate is typically used in the United States as a flour improver (E number E924). It acts to strengthen the dough and to allow higher rising. It is an oxidizing agent, and under the right conditions, is reduced to bromide in the baking process.^[7][8] However, if too much is added, or if the bread is underbaked or baked at a low enough temperature, then a residual amount remains, which may be harmful if consumed.^[8]

Potassium bromate may be used in the production of malt barley, but under safety conditions prescribed by the U.S. Food and Drug Administration (FDA), including labeling standards for the finished product.^[9] It is a powerful oxidizer (electrode potential ${\displaystyle E^{\ominus }}$ = 1.5 volts, similar to potassium permanganate).^{[citation needed]}