Hypofluorous acid

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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)
3D model (JSmol)
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 < 0 °C
decomposes at 0 °C
Related compounds
Other cations
lithium hypofluorite, LiOF
Related compounds
hypochlorous acid, HOCl
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

Hypofluorous acid, HOF, is the only known oxoacid of fluorine. 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:

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°).

Hypofluorous acid in acetonitrile (generated in situ by passing gaseous fluorine through "wet" acetonitrile) serves as a highly electrophilic oxygen-transfer agent.[2][3] Treating phenanthroline with this reagent yielded the previously elusive 1,10-phenanthroline dioxide,[4] more than 50 years after the first unsuccessful attempt.[5]

This molecule is not very symmetric since the atoms are all different. It only has two symmetry operations: identity (E) and a mirror plane that goes through the three atoms. The assigned point group is Cs.


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

See also[edit]

  • 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. ^ S. Rozen; M. Brand (1986). "Epoxidation of Olefins with Elemental Fluorine in Water/Acetonitrile Mixtures". Angew. Chem. Int. Ed. 25 (6): 554–5. doi:10.1002/anie.198605541. 
  3. ^ S. Dayan; Y. Bareket; S. Rozen (1999). "An efficient α-hydroxylation of carbonyls using the HOF·CH3CN complex". Tetrahedron. 55 (12): 3657. doi:10.1016/S0040-4020(98)01173-9. 
  4. ^ S. Rozen; S. Dayan (1999). "At Last, 1,10-Phenanthroline-N,N′-dioxide, A New Type of Helicene, has been Synthesized using HOF·CH3CN". Angew. Chem. Int. Ed. 38 (23): 3471–3. doi:10.1002/(SICI)1521-3773(19991203)38:23<3471::AID-ANIE3471>3.0.CO;2-O. 
  5. ^ F. Linsker; R.L. Evans (1946). "Phenanthroline Di-N-oxides". J. Am. Chem. Soc. 68 (3): 403. doi:10.1021/ja01207a019.