Hypofluorous acid

For many years it was thought that fluorine did not form any 0x0-acids or oxo-acid anions. Recent work, however, indicates the existence of fluoric(I) acid (hypofluorous acid), HFO, formed by the reaction of fluorine with water at 273 K. The acid forms colourless crystals, m.p. 156 K, is very unstable and has, as expected, very strong oxidising properties. 

A more efficient agent than peroxy compounds for the epoxidation of fluoro-olefins with nonfluonnated double bond is the hypofluorous acid-acetomtrile complex [22] Perfluoroalkylethenes react with this agent at room temperature within 2-3 h with moderate yields (equation 13), whereas olefins with strongly electron-deficient double bond or electron-poor, sterically hindered olefins, for example l,2-bis(perfluorobutyl)ethene and perfluoro-(l-alkylethyl)ethenes, are practically inert [22] Epoxidation of a mixture of 3 perfluoroalkyl-1-propenes at 0 C IS finished after 10 mm in 80% yield [22] The trifluorovinyl group in partially fluorinated dienes is not affected by this agent [22] (equation 13)... 

A terminal 1,13 diene with interstitial deka(difluoromethylene) chain is converted to the corresponding diepoxide by repeated reacUon with a very large excess of hypofluorous acid-acetonitrile complex [22](equation 14)... 

Hypofluorous acid is the most recent of the halogen oxoacids to be prepared. Traces were obtained in 1968 by photolysis of a mixture of F2 and H2O in a matrix of solid N2 at 14-20 K but weighable amounts of the compound were first obtained by M. H. Studier and E. H. Appelman in 1971 by the fluorination of ice ... 

Hypofluorous acid, HOF, is extremely unstable at room temperature. The fallowing data apply to the decomposition of HOF to HF and 03 gases at a certain temperature. 

Perhaps the best demonstration of the unwillingness of covalently bonded fluorine to participate in hydrogen bonding is hypofluorous acid, HOF. This... 

Hypofluorous acid decomposes very rapidly above -100 °C but, by passing fluorine through aqueous acetonitrile, a complex of HOF with acetonitrile is formed which is stable for several hours at room temperature. The chemistry of this interesting reagent has been reviewed recently [6,19,199]. 

The reaction of fluorine with water, producing hypofluorous acid (HOF) and subsequently oxygen difluoride (OF2), has been the subject of intensive study over the last fifty years.1 Additionally, hypofluorous acid in acetonitrile has been characterized.5 The reagents are potentially explosive and present a toxicity hazard similar to fluorine therefore, work should be carried out in an efficient hood and proper safety equipment is required. It was established in the earliest investigations that the reaction of hypofluorous acid with alkenes in nonpolar solvents gives fluoro hydrins, e.g. 1, in high yield.6 However, it is now clear that epoxides are initially formed in acetonitrile7 and 1,2-epoxycyclohexane (2) is formed in reactions with cyclohexene in various solvents.5... 

Stilbene is also converted into the epoxide and the preparation of the lsO-isomcr 3 in high isotopic purity can also be performed, while 1,1-diphenylethene is transformed to 1.1-di-phenylethane-l,2-diol (4),8 and (T)-stilbene to a mixture of benzophenone9 and //wo-2-fluoro-1.2-diphenylethanol. Fluoro-substituted alkenes can also be converted with a hypofluorous acid/acetonitrile mixture into epoxides 5 in high yield.10... 

The course of the reaction of hypofluorous acid with acetylenes in carbon tetrachloride at — 50 C depends on the structure of the acetylene phenylacetylene (6, R = Ph) gives 2-fluoro-1-phenylethanone and phenylacetyl fluoride, while 3,3-dimethylbut-l-ync (6, R = -Bu) gives 2-fluoro-3,3-dimethylbutanal in 60% yield.6... 

When hypofluorous acid reacts with aromatic substrates 7 the isomeric distribution of phenols formed suggests the nature of the transformation is electrophilic, rather than radical 4-methoxy(2-2H)phenol (8) isolated from (4-2H)anisole shows a marked NIH effect (77% incorporation of deuterium).11 A similar reaction with naphthalene gives a mixture of up to three products in low yield (1-naphthol 2.9%, 2-naphthol 0.75% and 1.4-naphthoquinone 7.4%).9... 

Various substituted anilines are converted into nitroarenes 9.12 while octaethylporphyrin N-oxide is obtained in the reaction of hypofluorous acid with octaethylporphyrin.13... 

Antipyrine (10) is converted into the 3- and 4-fluoro-substituted products, while the 18F-labeled products of antipyrine and 5-(18F)fluorouracil (11) are prepared by in situ generation of hypofluorous acid starting from l8F2.14 Bcnzothiophene is readily converted into the 1,1-dioxide 12 in 74% yield.9... 

Tertiary carbon atoms have been successfully hydroxylated with the mixture of hypofluorous acid/acetonitrile, e.g. formation of 13. and this method has also been used for the introduction of, 80.15... 

The hypofluorous acid/acetonitrile complex has also been used for the oxidation of secondary alcohols and for the Baeyer Villiger oxidation of ketones.24-25... 

Limited data are available on hypofluorous acid, which is a very reactive, explosive reagent.145 Exceptionally among hypohalous acids, it is polarized in the sense H08+-F8. It converts alkenes into fluoroalkanols with regioselectivites opposite to other hypohalous acids [Eq. (6.24)] the large amount of HF present may affect the actual mechanism of addition ... 

The reactivity of a terminal 1,13-diene with an interstitial deca(difluoromethylene) chain 1 is lower towards expoxidation with hypofluorous acid/acetonitrile complex21 due to the electron-withdrawing effect of the perfluoroalkyl chain attached directly to the C = C bond. The diepoxide 2 is obtained by repeated reaction with a very large excess of the oxidizing agent.21... 

Disulfides are generally oxidized with cleavage of the S —S bond. Hypofluorous acid in acetonitrile solution oxidizes sulfur atoms in bis(trifluoromethyl) disulfide to the highest oxidation state and, in addition, inserts an oxygen bridge between the sulfur atoms (Table 19).304 A sulfonyl chloride 18 is similarly obtained by the reaction of a substituted diphenyl disulfide with hypochlorous acid generated from chlorine and aqueous acetic acid.305... 

Trifluoromethaneseleninyl chloride (3) can be prepared by the reaction of trifluoromethane-sclcnenyl chloride with ozone whereas nitrogen dioxide transforms the initially formed acid choride to the anhydride (CF3Se0)20.316 Trifluoromethaneselenenic acid chloride and bromide are oxidized with hypofluorous acid in acetonitrile to the corresponding seleninyl halides 3 and 4, respectively.204 When an excess of hypofluorous acid is employed, the selenenyl halides and trifluoromethaneseleninic acid (5) are oxidized to the anhydride 6.304... 

Hypofluorous acid is so unstable that it survives only below the freezing point of water. 

Trifluoro-iV- [(trifluormethyl)sulfonyl]methanesulfonimidic acid, anhydride with hypofluorous acid, see lV-(Trifluoromethanesulfonyl)trifluoromethane-sulfonimidyl hypofluorite, 0640c... 

At room temperature hypofluorous acid HOF is a gas. Its colorless solid (mp = 156 K) melts to a pale yellow liquid. In the crystal structure, O-F = 144.2 pm, angle H-O-F =101°, and the HOF molecules are linked by O-H- O hydrogen bonds (bond length 289.5 pm and bond angle O-H- O 163°) to form a planar zigzag chain, as shown below ... 

In some cases, this has been shown to be a consequence of the very high chemical reactivity of the molecules. Thus hypofluorous acid, HOF, has never been isolated. It was not until 1967 that its short-lived presence was detected spectroscopically. It is now believed that the molecule is stable, but that the products obtained when it reacts with itself are so much more stable that it decomposes almost as fast as it is formed ... 

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