Chemistry:Hexafluoroacetone
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.[1] 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.[2]
The term "hexafluoroacetone" can refer to the sesquihydrate (1.5 H2O), which is a hemihydrate of hexafluoropropane-2,2-diol (F3C)2C(OH)2, a geminal diol. Hydrated HFA behaves differently from the anhydrous material.
Synthesis
The industrial route to HFA involves treatment of hexachloroacetone with HF (a Finkelstein reaction):[3]
- (CCl3)2CO + 6 HF → (CF3)2CO + 6 HCl
Laboratory methods
Hydrated HFA can be converted to HFA by treatment with hot sulfuric acid.[4]
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.[5] 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.[6] 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.[7]
Uses
Hexafluoroacetone is used in the production of hexafluoroisopropanol:
- (CF3)2CO + H2 → (CF3)2CHOH
It is also used as a precursor to hexafluoroisobutylene,[3] 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.[8] 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.[9]
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:[4]
- RCH(OH)CO
2H + O=C(CF
3)
2 → RCH(O)CO
2C(CF
3)
2 + (HO)
2C(CF
3)
2
See also
References
- ↑ CDC - NIOSH Pocket Guide to Chemical Hazards
- ↑ Hilderbrandt, R. L.; Andreassen, A. L.; Bauer, Simon Harvey (1970). "Electron diffraction investigation of hexafluoroacetone, hexafluoropropylimine, and hexafluoroisobutene". The Journal of Physical Chemistry 74 (7): 1586–1592. doi:10.1021/j100702a030. Bibcode: 1970JPhCh..74.1586H.
- ↑ 3.0 3.1 Günter Siegemund; Werner Schwertfeger; Andrew Feiring; Bruce Smart; Fred Behr; Herward Vogel; Blaine McKusick (2002). "Fluorine Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_349. ISBN 978-3-527-30385-4.
- ↑ 4.0 4.1 Spengler, Jan; Böttcher, Christoph; Albericio, Fernando; Burger, Klaus (2006). "Hexafluoroacetone as Protecting and Activating Reagent: New Routes to Amino, Hydroxy, and Mercapto Acids and Their Application for Peptide and Glyco- and Depsipeptide Modification". Chemical Reviews 106 (11): 4728–4746. doi:10.1021/cr0509962. PMID 17091933.
- ↑ Millauer, Hans; Schwertfeger, Werner; Siegemund, Günter (March 1985). "Hexafluoropropene Oxide — A Key Compound in Organofluorine Chemistry". Angewandte Chemie International Edition in English 24 (3): 161–179. doi:10.1002/anie.198501611.
- ↑ Anello, Louis G.; Van der Puy, Michael (January 1982). "A convenient synthesis of hexafluoroacetone". The Journal of Organic Chemistry 47 (2): 377–378. doi:10.1021/jo00341a046.
- ↑ Van Der Puy, M.; Anello, L. G. (1985). "Hexafluoroacetone". Organic Syntheses 53: 154. doi:10.15227/orgsyn.063.015.
- ↑ Lemal, David M. (2004). "Perspective on Fluorocarbon Chemistry". The Journal of Organic Chemistry 69 (1): 1–11. doi:10.1021/jo0302556. PMID 14703372.
- ↑ W. J. Middleton; H. D. Carlson (1970). "Hexafluoroacetone imine". Org. Syntheses 50: 81–3. doi:10.15227/orgsyn.050.0081..
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