Trifluoromethanesulfonic acid

Trifluoromethanesulfonic acid
IUPAC name Trifluoromethanesulfonic acid
Other names Triflic acid
CAS number 1493-13-6
Molecular formula CF3SO3H
Molar mass 150.08 g/mol
Appearance Colorless liquid
Density 1.696 g/mL
Melting point

-40 °C

Boiling point

162 °C

Solubility in water Miscible
Main hazards Corrosive, eye irritant
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 organic chemistry.[1][2]


Triflic acid is a exothermic.

With an fluorosulfuric acid, and chlorosulfonic acid. Below is a prototypical sulfonation, which HOTf does not undergo:

C6H6 + H2SO4 → C6H5(SO3H) + H2O

Triflic 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:[3]

Other ways to synthesize trifluoromethanesulfonic acid including electrochemical fluorination (ECF).[citation needed]

The industrial synthesis involves hydrolysis of CF3SO2F, followed by acidification. Triflic acid is purified by triflic anhydride.[2]


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 hydroxides. Illustrative is the synthesis of Cu(OTf)2.[citation needed]

CuCO3 + 2 CF3SO3H → Cu(O3SCF3)2 + H2O + CO2

Far 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 → [Co(NH3)5O3SCF3](O3SCF3)2 + 3 HCl

This conversion 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.[citation needed]

CH3C(O)Cl + CF3SO3H → CH3C(O)OSO2CF3 + HCl
CH3C(O)OSO2CF3 + C6H6 → CH3C(O)C6H5 + CF3SO3H

Triflic acid catalyzes the reaction of aromatic compounds with sulfonyl chlorides, probably also via the intermediacy of a mixed anhydride.[citation needed]

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.[citation needed] It can be used as a catalyst for the condensation of alcohols and carboxylic acids.


  1. ^ Howells, R. D., McCown, J. D. (1977). "Trifluoromethanesulfonic Acid and Derivatives". Chemical Reviews 77: 69 - 92. doi:10.1021/cr60305a005.
  2. ^ a b "Trifluoromethanesulfonic Acid". Encyclopedia of Reagents for Organic Synthesis. (2006). John Wiley & Sons, Ltd. DOI:10.1002/047084289X.rt246.pub2. 
  3. ^ R. N. Haszeldine and J. M. Kidd (1954). "Perfluoroalkyl derivatives of sulphur. Part I. Trifluoromethanesulphonic acid". J. Chem. Soc.: 4228 - 4232. doi:10.1039/JR9540004228.

Further reading

  • Dixon, N. E.; Lawrance, G. A.; Lay, P. A.; Sargeson, A. M.; Taube, H. (1990). "Trifluoromethanesulfonates and trifluoromethanesulfonato-O complexes". Inorganic Syntheses 28: 70 - 76. doi:10.1002/9780470132593.ch16.
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