Hypohalous acid

Article By:

Hurst, James K. Department of Biochemistry and Biophysics, Washington State University, Pullman, Washington.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.334300

An oxyacid of a halogen [fluorine (F), chlorine (Cl), bromine (Br), iodine (I), or astatine (At)] possessing the general chemical formula HOX, where X is the halogen atom. The chemical behavior of hypofluorous acid (HOF) is dramatically different from the heavier hypohalous acids which, as a group, exhibit similar properties. These differences are attributed primarily to the high electronegativity and small size of the fluorine atom, which cause HOF to be an extremely strong oxidant with an anomalously weak O-F bond. Thus, the molecule is highly reactive and relatively unstable. (Gaseous HOF decomposes to HF and O₂ at room temperature with a half-life of about 1 h, and the liquid has a tendency to explode.) Because the most electronegative element in HOF is fluorine, whereas the other halogen atoms are less electronegative than oxygen, the O-X bond polarities are reversed in HOF and the heavier congeners. HOF therefore acts primarily as an oxygenating and hydroxylating agent, whereas the other hypohalous acids are electrophilic halogenating agents. For example, HOF hydroxylates aromatic compounds to form phenols and reacts instantaneously with water to give hydrogen peroxide [reaction (1)],

(1)

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