Hexafluoro-2-butyne

Hexafluoro-2-butyne (HFB) is a fluorocarbon with the chemical structure CF3C≡CCF3. HFB is a particularly electrophilic acetylene derivative, and hence a potent dienophile for Diels–Alder reactions.[1][2]

## Synthesis and reactions

HFB is prepared by the action of sulfur tetrafluoride on acetylenedicarboxylic acid or by the reaction of potassium fluoride (KF) with hexachlorobutadiene.

In the presence of the strong Lewis acid aluminium chlorofluoride, hexafluorobutadiene isomerizes to HFB:[3]

2=CFCF=CF
2 → CF
3C≡CCF

HFB reacts with sulfur to give 3,4-bis(trifluoromethyl)-1,2-dithiete.

Cycloaddition of HFB and dithionitronium (NS2+) gives the 1,2,5-dithiazolium cation. This derivative can be reduced to the 7 electron neutral radical. This particular 1,3,5-dithiazole is also rare example of a radical that can be obtained as solid, liquid, and gaseous states. As a gas, it is blue.[4]

As an electrophilic alkyne, HFB forms a variety of alkyne complexes by reaction with low-valent metal complexes.[5]

## References

1. ↑ Essers, Michael; Haufe, Günter (2006). "Hexafluoro-2-butyne". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00669. ISBN 0471936235.
2. ↑ E S Turbanova, A A Petrov (1991). "Perfluoroalkyl(aryl)acetylenes". Russian Chemical Reviews 60 (5): 501–523. doi:10.1070/RC1991v060n05ABEH001092. Bibcode: 1991RuCRv..60..501T.
3. ↑ Petrov, V.A.; Krespan, C.G.; Smart, B.E. (1996). "Electrophilic reactions of fluorocarbons under the action of aluminum chlorofluoride, a potent Lewis acid". Journal of Fluorine Chemistry 77 (2): 139–142. doi:10.1016/0022-1139(96)03391-x. Bibcode: 1996JFluC..77..139P.
4. ↑ Brownridge, Scott; Du, Hongbin; Fairhurst, Shirley A.; Haddon, Robert C.; Oberhammer, Heinz; Parsons, Simon; Passmore, Jack; Schriver, Melbourne J. et al. (2000). "The Isolation, Characterisation, Gas Phase Electron Diffraction and Crystal Structure of the Thermally Stable Radical CF3CSNSCCF3". Journal of the Chemical Society, Dalton Transactions (19): 3365–3382. doi:10.1039/B001489N.
5. ↑ Morales-Becerril, Illán; Flores-Álamo, Marcos; Tlahuext-Aca, Adrián; Arévalo, Alma; García, Juventino J. (2014). "Synthesis of Low-Valent Nickel Complexes in Aqueous Media, Mechanistic Insights, and Selected Applications". Organometallics 33 (23): 6796–6802. doi:10.1021/om500767p.

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