HOBr

Hypobromous acid, with the chemical formula HOBr, is a weak acid belonging to the hypohalous acid family. It can be generated when bromine dissolves in water or when bromide is oxidized in aqueous solutions. In water it exists in equilibrium with its conjugate base, hypobromite: HOBr ⇌ H+ + OBr−. At pH around 8.7 (its approximate pKa at 25 °C), HOBr and OBr− are present in comparable amounts; below this pH, HOBr is more prevalent, while above it, hypobromite dominates.

Production and behavior in solution are governed by redox and pH conditions. The classic route Br2 + H2O → HOBr + H+ + Br− describes HOBr formation when bromine interacts with water. HOBr is relatively unstable and can decompose or react further, especially under light exposure or in the presence of reducing agents. In alkaline solutions, disproportionation or conversion to other bromine species such as bromide (Br−) may occur.

Applications and reactivity

HOBr is a potent oxidizing and disinfecting agent. It is used in water treatment and sanitation as an alternative or complement to hypochlorous acid, particularly in bromide-rich waters where brominated byproducts may form. Its oxidizing power enables reactions with organic matter, leading to the formation of brominated disinfection byproducts in some contexts. HOBr can react with ammonia and amines to form N-brominated species.

Safety and handling

Hypobromous acid is a corrosive, reactive species that can irritate skin, eyes, and the respiratory tract. It should be handled with appropriate barriers and ventilation, avoiding contact with incompatible materials. Decomposition products may include bromine and other reactive halogen species.