Trifluoromethanesulfonic acid

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Trifluoromethanesulfonic acid
General
Systematic name	Trifluoromethanesulfonic acid
Other names	Triflic Acid
Molecular formula	CF3SO3H
Acidic Power (Ho Value)	- 14.9
Molar mass	150.08 g/mole
Appearance	limpid liquid
CAS number
Properties
Density and phase	1.696 g cmâ€"3
Solubility in water	Completely miscible
Freezing Point	-40.0°C at 760 mmHg
Boiling point	162 °C at 760 mmHg
Hazards
MSDS
Main hazards	Corrosive, eye irritant
Flash point	Non-flammable
R/S statement	R: none S: none
RTECS number
Related compounds
Related acids	FSO3H H2SO4
Other s
Related salts	CF3SO3Li CF3SO3Na CF3SO3K
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Trifluoromethanesulfonic acid, also known as triflic acid or TfOH, is a sulfonic acid with the chemical formula CF₃SO₃H . It is often regarded as one of the strongest acids. It is about 1000 times stronger than sulfuric acid. Triflic acid is widely used especially as a catalyst and a precursor in organic chemistry .

Properties

Triflic acid is a hygroscopic, colorless liquid at room temperature. It is soluble in polar solvents such as DMF, DMSO, acetonitrile, and dimethyl sulfone. Addition of triflic acid to polar solvents can be dangerously exothermic.

With an K_a = 8.0 *10^-4 mole kg^-1, HOTf qualifies as a superacid. Triflic acid owes many of its useful properties to its great thermal and chemical stability. Both the acid and its conjugate base CF₃SO₃^-, known as triflate, resist oxidation/reduction reactions, whereas many strong acids are oxidizing, e.g. HClO₄ and HNO₃. The triflate anion is immune to attack by even strong nucleophiles. Because of it resistance to oxidation and reduction, triflic acid is a very useful and versatile reagent. Further recommending its use, triflic acid does not sulfonate substrates, which can be a problem with sulfuric acid, fluorosulfuric acid, and chlorosulfonic acid. Below is a prototypical sulfonation, which HOTf does not undergo: ::C₆H₅ + H₂SO₄ â†' C₆H₄(SO₃H) + H₂O

Ttriflic acid fumes in moist air and forms a stable solid monohydrate, CF₃SO₃H*H₂O, melting point 34 °C.

History and syntheses

Trifluoromethanesulfonic acid was first synthesized in 1954 by Haszeldine and Kidd by the following reaction:⁽¹⁾

Trifluoromethanesulfonate_synthesis1_transp.gif

Other ways to synthesize trifluoromethanesulfonic acid including electrochemical fluorination (aka ECF)⁽¹⁾

Trifluoromethanesulfonate_synthesis2_transp.gif

The industrial synthesis involves hydrolysis of CF₃SO₂F, followed by acidification. Triflic acid is purified by distillation with a small amount of Tf₂O.

Uses

Triflic acid is useful in protonations because the conjugate base of triflic acid will not react with other reagents.

Salt formation

Trifluoromethanesulfonic acid exothermically reacts with metal carbonates and hydroxides. Illustrative is the synthesis of Cu(OTf)2⁽¹⁾. ::CuCO₃ + 2 CF₃SO₃H â†' Cu(O₃SCF₃)₂ + H₂O + CO₂Far more interesting to the synthetic chemist is the conversion of chloro complexes to the corresponding triflates. Illustrative is the synthesis of [Co(NH₃)₅OTf]²⁺:::3 CF₃SO₃H + [Co(NH₃)₅Cl]Cl₂ â†' [Co(NH₃)₅O₃SCF₃](O₃SCF₃)₂ + 3 HClThis convesion is conducted in neat HOTf at 100 °C, followed by precipitation of the salt by the addition of ether.

Organic reactions

Triflic acid reacts with acyl halides to give mixed anhydrides, which are strong acylating agents, e.g. in Friedel-Crafts reactions.⁽¹⁾::CH₃C(O)Cl + CF₃SO₃H â†' CH₃C(O)OSO₂CF₃ + HCl::CH₃C(O)OSO₂CF₃ + C₆H₆ â†' CH₃C(O)C₆H₅ + CF₃SO₃HTriflic acid catalyzes the reaction of aromatic compounds with sulfonyl chlorides, probably also via the intermediacy of a mixed anhydride.⁽¹⁾This is a very similar reaction to what would be done if one wanted to create polymers using triflic acid in the synthesis. Other Friedel-Crafts type reactions using triflic acid include cracking of alkanes and alkylation of alkenes which are very important to the petroleum industry. These triflic acid derivative catalysts are very effective in isomerizing straight chain or slightly branched hydrocarbons that can increase the octane rating of a particular petroleum based fuel.

Triflic acid reacts exothermically with alcohols to produce ethers and olefins ⁽¹⁾. It can be used as a catalyst for the condensation of alcohols and carboxylic acids.

Triflic_acid_ester_formation.gif

References

# Howells, R. D., McCown, J. D. "Trifluoromethanesulfonic Acid and Derivatives." Chemical Reviews, 1977. Vol. 77, pp 69 - 92; DOI: 10.1021/cr60305a005# Lakshminarayanapuram, R. S. "Trifluoromethanesulfonic Acid". Encyclopedia of Reagents for Organic Synthesis. 2001 John Wiley & Sons, Ltd. DOI: 10.1002/047084289X.rt246

See also

Dixon, N. E.; Lawrance, G. A.; Lay, P. A.; Sargeson, A. M.; Taube, H. "Trifluoromethanesulfonates and trifluoromethanesulfonato-O complexes" Inorganic Syntheses (1990), vol. 28, pp. 70-6.

External links