|Jmol-3D images||Image 1|
|Molar mass||150.08 g/mol|
|Solubility in water||Miscible|
|Main hazards||Corrosive, eye irritant|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Trifluoromethanesulfonic acid, also known as triflic acid, TFMS, TFSA, HOTf or TfOH, is a sulfonic acid with the chemical formula CF3SO3H. It is one of the strongest acids. Triflic acid is mainly used in research as a catalyst for esterification.
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 however be dangerously exothermic.
With an Ka = 8.0 ×1014 (pKa ~ −15) mol/kg, Triflic acid qualifies as a superacid. It owes many of its useful properties to its great thermal and chemical stability. Both the acid and its conjugate base CF3SO−
3, known as triflate, resist oxidation/reduction reactions, whereas many strong acids are oxidizing, e.g. HClO4 and HNO3. 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:
- C6H6 + H2SO4 → C6H5(SO3H) + H2O
Triflic acid fumes in moist air and forms a stable solid monohydrate, CF3SO3H·H2O, melting point 34 °C.
Health Precautions 
Trifluoromethanesulfonic acid is one of the strongest acids known. On eye contact it causes severe eye burns and may cause blindness. With contact with skin it causes severe burns with delayed tissue destruction. On inhalation it causes fatal spasms, inflammation and edema.
Trifluoromethanesulfonic acid was first synthesized in 1954 by Haszeldine and Kidd by the following reaction:
Trifluoromethanesulfonic acid is produced industrially by electrochemical fluorination (ECF) of methanesulfonic acid:
- CH3SO3H + 4 HF → CF3SO2F + H2O + 1.5 H2
- CF3SCl + 2 Cl2 + 2 H2O → CF3SO2OH + 4 HCl
In the laboratory, triflic acid is useful in protonations because the conjugate base of triflic acid is non-nucleophilic. It is also used as an acidic titrant in non-aqueous acid-base titration because it behaves as a strong acid in many solvents (acetonitrile, acetic acid, etc.) where common mineral acids (such as HCl or H2SO4) are only moderately strong.
Salt formation 
- CuCO3 + 2 CF3SO3H → Cu(O3SCF3)2 + H2O + CO2
Chloride ligands can be converted to the corresponding triflates:
- 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 triflate anhydrides, which are strong acylating agents, e.g. in Friedel-Crafts reactions.
- 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 of the sulfonic acid.
Triflic acid promotes other Friedel-Crafts-like reactions including the 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.
- Howells, R. D., McCown, J. D. (1977). "Trifluoromethanesulfonic Acid and Derivatives". Chemical Reviews 77 (1): 69–92. doi:10.1021/cr60305a005.
- Subramanian, L. R.; Martinez, A. G.; Hanack, M.; Prakash, G. K. S.; Hu, J. (2006). "Trifluoromethanesulfonic Acid". Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/047084289X.rt246.pub2. ISBN 0-471-93623-5.
- "Trifluoromethanesulfonic acid MSDS". ChemCAS.
- Haszeldine, R. N.; Kidd, J. M. (1954). "Perfluoroalkyl derivatives of sulphur. Part I. Trifluoromethanesulphonic acid". Journal of the Chemical Society 1954: 4228–4232. doi:10.1039/JR9540004228.
- Siegemund, G.; Schwertfeger, W.; Feiring, A.; Smart, B.; Behr, F.; Vogel, H.; McKusick, B. (2000). "Fluorine Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry. John Wiley & Sons. doi:10.1002/14356007.a11_349.
- 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. ISBN 978-0-470-13259-3.