Hypofluorous acid

Hypofluorous acid IUPAC name fluoranol Other names oxygen fluoride hydride Identifiers InChI InChI=1/FHO/c1-2/h2H InChIKey AQYSYJUIMQTRMV-UHFFFAOYAN Standard InChI InChI=1S/FHO/c1-2/h2H Standard InChIKey AQYSYJUIMQTRMV-UHFFFAOYSA-N CAS number [14034-79-8] ChemSpider 109936 Properties Chemical formula HOF Molar mass 36.006 g mol−1 Appearance see text Melting point −117 °C Boiling point < 0 °C Solubility in water reacts Structure Molecular geometry bent: H–O = 96.4(10) pm, O–F = 144.2(1) pm, H–O–F = 97.2(6)° Thermochemistry Std enthalpy of formation ΔfHo298 −98.32 kJ mol−1 Standard molar entropy So298 226.77 J K−1 mol−1 Related compounds Other compounds Hypochlorous acid Hypobromous acid Hypoiodous acid Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Rozen's reagent IUPAC name acetonitrile—fluoranol (1/1) Identifiers InChI InChI=1/C2H3N.FHO/c1-2-3;1-2/h1H3;2H InChIKey MHXSJBXDLWNIAN-UHFFFAOYAK Standard InChI InChI=1S/C2H3N.FHO/c1-2-3;1-2/h1H3;2H Standard InChIKey MHXSJBXDLWNIAN-UHFFFAOYSA-N ChemSpider 9226732 Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Hypofluorous acid, HOF, is an unstable compound arising from the reaction of gaseous fluorine with water. It was first isolated in weighable quantities in 1971. Despite the name, formed by analogy with other halogen compounds of similar formula, HOF is not significantly acidic, and hypofluorite salts are unknown.

A solution of hypofluorous acid in acetonitrile is significanly more stable that the pure compound, due to the formation of a hydrogen-bonded adduct, MeCN·HOF. This species is sometimes called Rozen's reagent, and is a strong oxidizing agent through oxygen transfer: it is particularly useful for epoxidation reactions.

Preparation

Reported preparations of hypofluorous acid in the 1930s are now considered erroneous. The first clear observation of HOF was through the infrared spectrum of a matrix isolation sample, obtained by photolysis of a mixture of fluorine and water in a nitrogen matrix at 14–20 K.

Notes and references

Further reading

• Poll, Wolfgang; Pawelke, Gottfried; Mootz, Dietrich; Appelman, Evan H. The Crystal Structure of Hypofluorous Acid: Chain Formation by OH…O Hydrogen Bonds. Angew. Chem. Int. Ed. Engl. 1988, 27 (3), 392–93. DOI: 10.1002/anie.198803921.
• Kol, Moshe; Rozen, Shlomo Functionalization of aromatic molecules using HOF·CH₃CN and CH₃OF. J. Org. Chem. 1993, 58 (6), 1593–95. DOI: 10.1021/jo00058a052.
• Rozen, Shlomo; Brand, Michael; Kol, Moshe Tertiary hydroxylation using fluorine: activation of the carbon–hydrogen bond. J. Am. Chem. Soc. 1989, 111 (21), 8325–26. DOI: 10.1021/ja00203a069.