Hypobromous acid is a weak, unstable acid with chemical formula HBrO. It is also called bromic(I) acid, bromanol or hydroxidobromine. It occurs only in solution and has chemical and physical properties that are very similar to those of hypochlorous acid.
In aqueous solution, hypobromous acid partially dissociates into the hypobromite anion OBr− and the cation H+. The salts of hypobromous acid are also called hypobromites. Like the acid, these salts are unstable and when evaporated or boiled to dryness, they undergo a disproportionation reaction, yielding the respective bromate and bromide salts.
When pure bromine is added to water, it forms hypobromous acid and hydrobromic acid (HBr):
- Br2(l) + H2O(l) → HOBr(aq) + HBr (aq)
HOBr is used as a bleach, an oxidizer, a deodorant, and a disinfectant, due to its ability to kill the cells of many pathogens. The compound is generated in warm-blooded vertebrate organisms especially by eosinophils, which produce it by the action of eosinophil peroxidase, an enzyme which preferentially uses bromide. Bromide is also used in hot tubs and spas as a germicidal agent, using the action of an oxidizing agent to generate hypobromite in a similar fashion to the peroxidase in eosinophils. It is especially effective when used in combination with its congener, hypochlorous acid.