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Hexafluoroacetone
Chemical compound From Wikipedia, the free encyclopedia
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Hexafluoroacetone (HFA) is a chemical compound with the formula (CF3)2CO. It is structurally similar to acetone; however, its reactivity is markedly different. It is a colourless, hygroscopic, nonflammable, highly reactive gas characterized by a musty odour.[2] According to electron diffraction, HFA and acetone adopt very similar structures, the C-O distance being only longer in the fluorinated compound (124.6 vs 121.0 pm), possibly due to steric effects.[3]
The term "hexafluoroacetone" can refer to the sesquihydrate (1.5 H2O), which is a hemihydrate of hexafluoropropane-2,2-diol (F
3C)
2C(OH)
2, a geminal diol. Hydrated HFA behaves differently from the anhydrous material.
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Synthesis
The industrial route to HFA involves treatment of hexachloroacetone with HF (a Finkelstein reaction):[4]
- (CCl3)2CO + 6 HF → (CF3)2CO + 6 HCl
Laboratory methods
Hydrated HFA can be converted to HFA by treatment with hot sulfuric acid.[5]
It has also be prepared from hexafluoropropylene oxide, which will rearrange to give HFA when heated in the presence of a Lewis acid such as AlCl3.[6] The Lewis acid catalysed oxidation of hexafluoropropylene will also produce HFA, via a similar mechanism.
Although it is commercially available, HFA can be prepared on the laboratory-scale from hexafluoropropylene.[7] In the first step KF catalyzes the reaction of the alkene with elemental sulfur to give the 1,3-dithietane dimer of hexafluorothioacetone. This species is then oxidized by potassium iodate to give HFA.[8]
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Uses
Hexafluoroacetone is used in the production of hexafluoroisopropanol:
- (CF3)2CO + H2 → (CF3)2CHOH
It is also used as a precursor to hexafluoroisobutylene,[4] a monomer used in polymer chemistry, and as a building block in the synthesis of midaflur, bisphenol AF, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, and alitame.
Reactivity
With water, hexafluoroacetone converts to the hydrate. The equilibrium constant (Keq) for the formation of this geminal diol is 106 M−1. The analogous equilibrium for acetone is an unfavorable 10−3 M−1.[9] Hexafluoroacetone-hydrates are acidic. In an analogous reaction, ammonia adds to hexafluoroacetone to give the hemiaminal (CF3)2C(OH)(NH2) which can be dehydrated with phosphoryl chloride to give the imine (CF3)2CNH.[10]
Nucleophiles attack occurs at the carbonyl carbon of Hexafluoroacetone, as illustrated above. Thus, HFA readily forms lactones when treated with hydroxy- and amine-substituted carboxylic acids. In such reactions, HFA serves both as electrophile and dehydrating agent:[5]
- RCH(OH)CO2H + O=C(CF3)2 → RCH(O)CO2C(CF3)2 + (HO)2C(CF3)2
See also
References
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