Hexafluoroacetone (HFA) is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

(CF₃)₂CO. It is structurally similar to

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

; however, its reactivity is markedly different. It is a colourless, hygroscopic, nonflammable, highly reactive gas characterized by a musty odour. According to

electron diffraction Electron diffraction is a generic term for phenomena associated with changes in the direction of electron beams due to elastic interactions with atoms. It occurs due to elastic scattering, when there is no change in the energy of the electrons. ...

, 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. The term "hexafluoroacetone" can refer to the sesquihydrate (1.5 H₂O), which is a hemihydrate of hexafluoropropane-2,2-diol , a

geminal diol A geminal diol (or gem-diol for short) is any organic compound having two hydroxyl functional groups () bound to the same carbon atom. Geminal diols are a subclass of the diols, which in turn are a special class of alcohols. Most of the geminal ...

. Hydrated HFA behaves differently from the anhydrous material.

Synthesis

The industrial route to HFA involves treatment of hexachloroacetone with HF (a Finkelstein reaction): :(CCl₃)₂CO + 6 HF → (CF₃)₂CO + 6 HCl

Laboratory methods

Hydrated HFA can be converted to HFA by treatment with hot

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

. It has also be prepared from hexafluoropropylene oxide, which will rearrange to give HFA when heated in the presence of a

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any ...

such as AlCl3. The Lewis acid catalysed oxidation of

hexafluoropropylene Hexafluoropropylene is the fluoroalkene with the formula CF3CF=CF2. It is the perfluorocarbon counterpart to the hydrocarbon propylene. It is mainly used to produce copolymers with tetrafluoroethylene. Hexafluoropropylene is used as a chemical i ...

will also produce HFA, via a similar mechanism. Although it is commercially available, HFA can be prepared on the laboratory-scale from hexafluoropropylene. 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.

Uses

Hexafluoroacetone is used in the production of hexafluoroisopropanol: :(CF₃)₂CO + H₂ → (CF₃)₂CHOH It is also used as a precursor to hexafluoroisobutylene, 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 The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency ...

(K_eq) for the formation of this

is 10⁶ M⁻¹. The analogous equilibrium for acetone is an unfavorable 10⁻³ M⁻¹. Hexafluoroacetone-hydrates are acidic. In an analogous reaction,

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

adds to hexafluoroacetone to give the

hemiaminal In organic chemistry, a hemiaminal (also carbinolamine) is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: . R can be hydrogen or an alkyl group. Hemiaminals are intermediat ...

(CF₃)₂C(OH)(NH₂) which can be dehydrated with phosphoryl chloride to give the

imine In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...

(CF₃)₂CNH..

Nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

s attack occurs at the

carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...

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: :

References

{{Reflist Trifluoromethyl compounds Ketones Perfluorinated compounds Trifluoromethyl ketones

Synthesis

Laboratory methods

Uses

Reactivity

See also

References