Hypofluorous acid, chemical formula HOF, is the only known oxyacid of fluorine and the only known oxoacid in which the main atom gains electrons from oxygen to create a negative oxidation state. The oxidation state of the oxygen in hypofluorites is 0. It is also the only hypohalous acid that can be isolated as a solid. HOF is an intermediate in the oxidation of water by fluorine, which produces hydrogen fluoride, oxygen difluoride, hydrogen peroxide, ozone and oxygen. HOF is explosive at room temperature, forming HF and O2:
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||36.0057 g mol−1|
|Appearance||pale yellow liquid above −117 °C|
white solid below −117 °C
|Melting point||−117 °C (−179 °F; 156 K)|
|Boiling point||decomposes at 0 °C |
|Occupational safety and health (OHS/OSH):|
|strong oxidizer, corrosive|
|NFPA 704 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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It was isolated in the pure form by passing F2 gas over ice at −40 °C, collecting the HOF gas, and condensing it:
The compound has been characterized in the solid phase by X-ray crystallography as a bent molecule with an angle of 101°. The O–F and O–H bond lengths are 144.2 and 96.4 picometres, respectively. The solid framework consists of chains with O–H···O linkages. The structure has also been analyzed in the gas phase, a state in which the H–O–F bond angle is slightly narrower (97.2°).
Among workers in thiophene chemistry, a solution of hypofluorous acid in acetonitrile (generated in situ by passing gaseous fluorine through acetonitrile that has water in it) is commonly known as Rozen's reagent.