Hypofluorous acid


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:

Hypofluorous acid
Hypofluorous acid
Gas-phase structure
Hypofluorous acid
IUPAC name
Hypofluorous acid
Other names
Hydrogen hypofluorite
Hydrogen fluorate(-I)
Fluoric(-I) acid
Hydrogen monofluoroxygenate(0)
hydroxyl fluoride
  • 14034-79-8 checkY
3D model (JSmol)
  • Interactive image
  • 109936 ☒N
  • 123334
  • DTXSID10896951 Edit this at Wikidata
  • InChI=1S/FHO/c1-2/h2H ☒N
  • InChI=1/FHO/c1-2/h2H
  • OF
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 [citation needed] 
Occupational safety and health (OHS/OSH):
Main hazards
strong oxidizer, corrosive
NFPA 704 (fire diamond)
Related compounds
Other cations
lithium hypofluorite
Related compounds
hypochlorous acid
hydrogen cyanide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
2 HOF → 2 HF + O2[1]

It was isolated in the pure form by passing F2 gas over ice at −40 °C, collecting the HOF gas, and condensing it:

F2 + H2O → HOF + HF

The compound has been characterized in the solid phase by X-ray crystallography[1] 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.[2]


Hypofluorites are formally derivatives of OF, which is the conjugate base of hypofluorous acid. One example is trifluoromethyl hypofluorite (CF3OF).

See alsoEdit

  • Hypochlorous acid, a related compound that is more technologically important but has not been obtained in pure form.


  1. ^ a b W. Poll; G. Pawelke; D. Mootz; E. H. Appelman (1988). "The Crystal Structure of Hypofluorous Acid : Chain Formation by O-H · · · O Hydrogen Bonds". Angew. Chem. Int. Ed. Engl. 27 (3): 392–3. doi:10.1002/anie.198803921.
  2. ^ For Rozen's original popularizations, see:
    • Rozen, Shlomo (2001). "Hypofluorous Acid". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rh074. ISBN 0471936235.
    • Rozen, Shlomo (2014). "HOF·CH3CN: Probably the Best Oxygen Transfer Agent Organic Chemistry Has To Offer". Acc. Chem. Res. 47 (8): 2378–2389. doi:10.1021/ar500107b. PMID 24871453.
    For subsequent use, see, e.g.
    • Singh, Raman; Kaur, Rajneesh; Gupta, Tarang; Kulbir, Kulbir; Singh, Kuldeep (2019). "Applications of Rozen's Reagent in Oxygen-Transfer and C-H Activation Reactions". Synthesis. 51 (2): 371–383. doi:10.1055/s-0037-1609638. S2CID 104572566.
    • Dell, Emma J.; Campos, Luis M. (2012). "The preparation of thiophene-S,S-dioxides and their role in organic electronics". J. Mater. Chem. 22 (26): 12945–12952. doi:10.1039/C2JM31220D.