Hypohalous acid
Class of chemical compounds
From Wikipedia, the free encyclopedia
A hypohalous acid is an oxyacid consisting of a hydroxyl group single-bonded to any halogen. Examples include hypofluorous acid, hypochlorous acid, hypobromous acid, and hypoiodous acid. The conjugate base is a hypohalite. They can be formed by reacting the corresponding diatomic halogen molecule (F2, Cl2, Br2, I2) with water in the reaction:
- X2 + H2O ⇌ HXO + HX
This also results in the corresponding hydrogen halide, which is also acidic. A pseudohalogen would instead generate a hypopseudohalous acid.
It is uncertain that whether hypoastatous acid (AtOH), the hypohalous acid for astatine, is more similar to other hypohalous acids or to metal hydroxides.[1]
Stability
Hypohalous acids tend to be unstable. Only hypofluorous acid has been isolated as a solid, and even it is explosive at room temperature.[2] Hypochlorous acid cannot be prepared in anhydrous form.[3] Hypobromous acid, hypoiodous acid, and their conjugate bases (hypobromite and hypoiodite) are also unstable, undergoing disproportionation reactions like
and
that result in the corresponding hydrogen halides/halide ions and halic acids/halates.[4]
Uses
Hypochlorous acid and hypobromous acid are each dissolved in water to sanitize it, hypochlorous acid in swimming pools and hypobromous acid in hot tubs and spas.[5]
Acidity
Hypohalous acids tend to be weak acids, and they typically get weaker as the halogen progresses further down the periodic table. Hypochlorous acid has a pKa of 7.53.[6] The pKa values of hypobromous acid is higher (meaning that it is an even weaker acid),[7] at 8.65. The pKa of hypoiodous acid is even higher, at 10.6.