Triflic acid, the short name for trifluoromethanesulfonic acid, TFMS, TFSA, HOTf or TfOH, is a

sulfonic acid In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...

with the chemical formula CF₃SO₃H. It is one of the strongest known

acids An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

. Triflic acid is mainly used in research as a

catalyst Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

for

esterification In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

. It is a

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...

, colorless, slightly viscous liquid and is soluble in polar solvents.

Synthesis

Trifluoromethanesulfonic acid is produced industrially by electrochemical fluorination (ECF) of methanesulfonic acid CH3SO3H + 4 HF ->CF3SO2F + H2O + 3 H2 The resulting CF₃SO₂F is hydrolyzed, and the resulting triflate salt is reprotonated. Alternatively, trifluoromethanesulfonic acid arises by

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

of trifluoromethylsulfenyl chloride: CF3SCl + 2 Cl2 + 3 H2O -> CF3SO3H + 5 HCl Triflic acid is purified by

distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

from triflic anhydride.

Historical

Trifluoromethanesulfonic acid was first synthesized in 1954 by Robert Haszeldine and Kidd by the following reaction: : Synthesis_Trifluoromethanesulfonic_acid_1

Synthesis_Trifluoromethanesulfonic_acid_1

Reactions

As an acid

In the laboratory, triflic acid is useful in protonations because the conjugate base of triflic acid is nonnucleophilic. It is also used as an acidic titrant in nonaqueous acid-base titration because it behaves as a strong acid in many solvents (

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not class ...

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...

, etc.) where common mineral acids (such as HCl or H₂SO₄) are only moderately strong. With a ''K''_a = , p''K''_a = , triflic acid qualifies as a

superacid In chemistry, a superacid (according to the original definition) is an acid with an acidity greater than that of 100% pure sulfuric acid (), which has a Hammett acidity function (''H''0) of −12. According to the modern definition, a superacid i ...

. It owes many of its useful properties to its great thermal and chemical stability. Both the acid and its

conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid gives a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as it loses a hydrogen ion in the reve ...

CF₃SO, known as

triflate In organic chemistry, triflate (Preferred IUPAC name, systematic name: trifluoromethanesulfonate), is a functional group with the Chemical formula, formula and Chemical structure, structure . The triflate group is often represented by , as opp ...

, resist oxidation/reduction reactions, whereas many strong acids are oxidizing, such as perchloric or

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

. Further recommending its use, triflic acid does not sulfonate substrates, which can be a problem with

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, ...

, fluorosulfuric acid, and chlorosulfonic acid. Below is a prototypical sulfonation, which triflic acid does ''not'' undergo: : C6H6 + H2SO4 -> ceC6H5(SO3H) + H2O Triflic acid fumes in moist air and forms a stable solid monohydrate, CF₃SO₃H·H₂O, melting point 34 °C.

Salt and complex formation

The triflate ligand is labile, reflecting its low basicity. Trifluoromethanesulfonic acid reacts exothermically with metal

carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...

s, and oxides. Illustrative is the synthesis of Cu(OTf)₂. :Cu2CO3(OH)2 + 4 CF3SO3H -> 2 Cu(O3SCF3)2 + 3 H2O + CO2 Chloride ligands can be converted to the corresponding triflates: :3 CF3SO3H + o(NH3)5Cll2 -> o(NH3)5O3SCF3O3SCF3)2 + 3 HCl This conversion is conducted in neat HOTf at 100 °C, followed by precipitation of the salt upon the addition of ether.

Organic chemistry

Triflic acid reacts with acyl halides to give mixed triflate anhydrides, which are strong acylating agents, e.g. in

Friedel–Crafts reaction The Friedel–Crafts reactions are a set of organic reaction, reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an Aromatic hydrocarbon, aromatic ring. Friedel–Crafts reactions are of two main types: alky ...

s. :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 through 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 An octane rating, or octane number, is a standard measure of a liquid fuel, fuel's ability to withstand Compression ratio, compression in an internal combustion engine without causing engine knocking. The higher the octane number, the more compres ...

of a particular petroleum-based fuel. Triflic acid reacts exothermically with alcohols to produce ethers and olefins. TfOH-condensation-2D

Dehydration gives the

acid anhydride An acid anhydride is a type of chemical compound derived by the removal of water molecules from an acid. In organic chemistry, organic acid anhydrides contain the functional group . Organic acid anhydrides often form when one equivalent of wa ...

, trifluoromethanesulfonic anhydride, (CF₃SO₂)₂O.

Safety

Triflic acid is one of the strongest acids. Contact with skin causes severe burns with delayed tissue destruction. On inhalation it causes fatal spasms, inflammation and

edema Edema (American English), also spelled oedema (British English), and also known as fluid retention, swelling, dropsy and hydropsy, is the build-up of fluid in the body's tissue (biology), tissue. Most commonly, the legs or arms are affected. S ...

. Like sulfuric acid, triflic acid must be slowly added to polar solvents to prevent

thermal runaway Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing Thermal energy, energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the cond ...

References

{{hydrogen compounds Inorganic carbon compounds Reagents for organic chemistry Superacids Perfluorosulfonic acids