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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, and is one of a number of so-called "superacids". It is about 1000 times stronger than sulfuric acid. Triflic acid is widely used especially as a catalyst and a precursor in organic chemistry.
Additional recommended knowledge
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 Ka = 8.0 *1014 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:
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:
Triflic acid is useful in protonations because the conjugate base of triflic acid will not react with other reagents.
Trifluoromethanesulfonic acid exothermically reacts with metal carbonates and hydroxides. Illustrative is the synthesis of Cu(OTf)2.
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+:
This conversion is conducted in neat HOTf at 100 °C, followed by precipitation of the salt by the addition of ether.
Triflic acid reacts with acyl halides to give mixed anhydrides, which are strong acylating agents, e.g. in Friedel-Crafts reactions.
Triflic acid catalyzes the reaction of aromatic compounds with sulfonyl chlorides, probably also via the intermediacy of a mixed anhydride.
Triflic acid reacts exothermically with alcohols to produce ethers and olefins. It can be used as a catalyst for the condensation of alcohols and carboxylic acids.
Categories: Inorganic carbon compounds | Sulfonic acids | Reagents for organic chemistry
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Trifluoromethanesulfonic_acid". A list of authors is available in Wikipedia.|