Potassium bromate () is a bromate of

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

and takes the form of white crystals or powder. It is a strong oxidizing agent.

Preparation and structure

Potassium bromate is produced when

bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...

is passed through a hot solution of

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utili ...

. This first forms unstable potassium hypobromite, which quickly disproportionates into bromide and bromate: : 3

\ \xrightarrow\

2 + Electrolysis of

potassium bromide Potassium bromide ( K Br) is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, with over-the-counter use extending to 1975 in the US. Its action is due to the bromide ion ( sodium bromide is equa ...

solutions will also give bromate. Both processes are analogous to those used in the production of

chlorate Chlorate is the common name of the anion, whose chlorine atom is in the +5 oxidation state. The term can also refer to chemical compounds containing this anion, with Chlorate#Compounds (salts), chlorates being the salt (chemistry), salts of chlo ...

s. Potassium bromate is readily separated from the potassium bromide present in both methods owing to its much lower solubility; when a solution containing potassium bromate and bromide is cooled to 0°C, nearly all bromate will precipitate, while nearly all of the bromide will stay in solution. As established by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

, the O-Br-O angles are 104.5°, consistent with its pyramidal shape of the anion. The Br-O distances are 1.66 Å.

Uses in baking

Potassium bromate is typically used in the United States as a

flour Flour is a powder made by Mill (grinding), grinding raw grains, List of root vegetables, roots, beans, Nut (fruit), nuts, or seeds. Flours are used to make many different foods. Cereal flour, particularly wheat flour, is the main ingredie ...

improver (

E number E numbers, short for Europe numbers, are codes for substances used as food additives, including those found naturally in many foods, such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

E924). It acts to strengthen the

dough Dough is a malleable, sometimes elastic paste made from flour (which itself is made from grains or from leguminous or chestnut crops). Dough is typically made by mixing flour with a small amount of water or other liquid and sometimes includes ...

and to allow higher rising. It is an

oxidizing agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...

, and under the right conditions, is reduced 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-retard ...

in the baking process. However, if too much is added, or if the bread is under-baked long or baked at a low enough temperature, then a residual amount remains, which may be harmful if consumed. Potassium bromate may be used in the production of

malt Malt is any cereal grain that has been made to germinate by soaking in water and then stopped from germinating further by drying with hot air, a process known as "malting". Malted grain is used to make beer, whisky, malted milk, malt vinegar, ...

barley, but under safety conditions prescribed by the U.S. Food and Drug Administration (FDA), including labeling standards for the finished product. It is a powerful oxidizer ( electrode potential

E^\ominus

similar to

potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, which dissolves in water as K+ and ions to give an intensely pink to purple solution. Potassium permanganate is widely us ...

Regulation

Potassium bromate is classified as a category 2B

carcinogen A carcinogen () is any agent that promotes the development of cancer. Carcinogens can include synthetic chemicals, naturally occurring substances, physical agents such as ionizing and non-ionizing radiation, and biologic agents such as viruse ...

by the IARC. The FDA allowed the use of bromate before the Delaney clause of the Food, Drug, and Cosmetic Act – which bans potentially carcinogenic substances – went into effect in 1958. Since 1991, the FDA has urged bakers to not use it, but has not mandated a ban. Japanese baked goods manufacturers stopped using potassium bromate voluntarily in 1980; however, Yamazaki Baking resumed its use in 2005, claiming it had new production methods to reduce the amount of the chemical which remained in the final product. Potassium bromate is banned from food products in the European Union, Argentina, Brazil, Canada, Nigeria, South Korea, and Peru. It was banned in Sri Lanka in 2001, China in 2005, and India in 2016, but it is allowed in most of the United States. As of May 2023, the U.S. state of New York is considering banning the use of potassium bromate. In

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, a warning label is required when bromated flour is used. In October 2023,

enacted a law that banned the manufacture, sale, and distribution of potassium bromate (along with three other additives: brominated vegetable oil, propylparaben, and Red 3). The law takes effect in 2027. It was the first U.S. state to ban it.

References

{{E number infobox 920-929 Bromates Potassium compounds IARC Group 2B carcinogens Oxidizing agents Food additives