Triflic acid, the short name for trifluoromethanesulfonic acid, TFMS, TFSA, HOTf or TfOH, is a sulfonic acid with the chemical formula CF₃SO₃H. It is one of the strongest known

acids In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...

. Triflic acid is mainly used in research as a

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

for

esterification In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glyceride ...

. It is a hygroscopic, 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 of trifluoromethyl

sulfenyl chloride In organosulfur chemistry, a sulfenyl chloride is a functional group with the connectivity , where R is alkyl or aryl. Sulfenyl chlorides are reactive compounds that behave as sources of . They are used in the formation of and bonds. According ...

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

distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...

from triflic anhydride.

Historical

Trifluoromethanesulfonic acid was first synthesized in 1954 by

Robert Haszeldine Robert Neville Haszeldine FRS, FRSC (3 May 1925 – 13 October 2016) was a British chemist. Life He was educated at Stockport Grammar School and the University of Birmingham. Moving to the University of Cambridge he rose to Assistant Dire ...

and Kidd by the following reaction: : 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,

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 componen ...

, etc.) where common mineral acids (such as HCl or H₂SO₄) are only moderately strong. With a ''K''_a = 5×10¹⁴, p''K''_a −14.7±2.0, 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 A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...

CF₃SO, known as triflate, resist oxidation/reduction reactions, whereas many strong acids are oxidizing, e.g. perchloric or

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...

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

chlorosulfonic acid Chlorosulfuric acid (IUPAC name: sulfurochloridic acid) is the inorganic compound with the formula HSO3Cl. It is also known as chlorosulfonic acid, being the sulfonic acid of chlorine. It is a distillable, colorless liquid which is hygroscopic and ...

. Below is a prototypical sulfonation, which triflic acid 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.

Salt and complex formation

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

carbonate A carbonate is a salt of carbonic acid (H2CO3), 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 carbonat ...

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 ...

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)5Cl O, or o, is the fifteenth letter and the fourth vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''o'' (pronounced ), ...

l2 ->

o(NH3)5O3SCF3 O, or o, is the fifteenth letter and the fourth vowel letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''o'' (pronounced ), ...

O3SCF3)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 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 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 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 R(CO)O(CO)R'. Organic acid anhydrides often form when one equiva ...

, 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, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...

. 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 energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way t ...

References

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