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trifluoromethanesulfonic acid

Product name trifluoromethanesulfonic acid
Synonyms triflic acid
GOST no data
CAS 1493-13-6

Trifluoromethanesulfonic acid, also known as triflic acid or TfOH, was first synthesized in 1954 by Haszeldine and Kidd. It is a sulfonic acid with the chemical formula F3CSO3H. Triflic acid is colorless, clear, hygroscopic, non-combustible liquid. It fumes on humid air. Trifluoromethanesulfonic acid is fully miscible with water. It is also soluble in polar organic solvents such as dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylsulfate, acetonitrile, dimethylsulfone, dichloromethane. Its dilution in polar solvents is accompanied with liberation of heat and may be quite vigorous. Triflic acid has a poor solubility in non-polar solvents such as hexane, carbon tetrachloride, benzene, perfluorinated liquids and so on.

Triflic acid readily absorbs water from air. It form a stable monohydrate F3CSO3H*H2O being treated with water. This adduct melts at 34°C.

Trifluoromethanesulfonic acid is one of the strongest acids and is about 1000 times stronger than sulfuric acid. It is one of a number of so-called superacids, in other words acids which Hammet acidity function Ho is more negative than for sulfuric or nitric acids. Superacidity of triflic acid is determined by extremely weak interaction between triflic anion F3CSO3- with H+ cation. This makes possible protonation of compounds which do not display basic properties, e.g. hydrocarbons. Obviously that triflic acid is fully ionized in water solutions.

Unlike other strong acids such as nitric or sulfuric, trifluoromethanesulfonic acid does not oxidaze substrate. On the other hand, in contrast to other sulfonic acids, TfOH is not a sulfonating agent. Such behaviour makes trifluoromethanesulfonic acid very effective and selective catalyst in a number of alkylation, acylation and isomerization reactions, e.g. in Friedel-Crafts reactions.

Like almost acids, triflic acid is capable to dissolve metals to release dihydrogen and to form corresponding salts triflates. Triflates can be obtained also by interaction of TfOH with metal oxides, hydroxides or by displacement of weaker acids from their salts:

Na2CO3 + 2F3CSO3H → 2F3CSO3Na + H2O + CO2

Trifluoromethanesulfonic acid reacts with acyl chlorides resulting in mixed anhydrides. This process takes place in acylation by Friedel-Crafts mechanism:

RC(O)Cl + F3CSO3H → RC(O)OSO2CF3 + HCl

RC(O)OSO2CF3 + C6H6 → PhC(O)R + F3CSO3H


Triflic acid being treated with ketene or its derivatives gives mixed anhydrides. This reaction is used for industrial preparation of triflic anhydride. Mixed anhydride comprising a trifluoromethanesulfonyl acyl residue and a carboxyl residue undergoes disproportionation to produce triflic anhydride and a higher boiling carboxylic acid anhydride.

F3CSO3H + O=C=CH2 → F3CSO2-O-C(O)CH3

2F3CSO2-O-C(O)CH3 → F3CSO2-O-SO2CF3 + H3CC(O)-O-C(O)CH3


Aliphatic hydrocarbons in the presence of TfOH undergo isomerization and dehydrogenation. Due to this property triflic acid is used in some oil processing methods to produce olefins and branched hydrocarbons.

Alcohols in the presence of trifluoromethanesulfonic acid dehydrate to give corresponding ethers and olefins. Alternative path of this reaction is esterification of triflic acid with alcohol. The ratio of products depends on alcohol nature and process conditions:

F3CSO3H + R-CH2-CH2O → F3CSO2-O-CH2CH2R + RCH2CH2-O-CH2CH2R + RCH=CH2

Triflic acid is corrosive liquid. It should be handled very carefully because of it irritate eyes, mucous membranes and skin.

Production.

Trifluoromethanesulfonic acid is produced industrially by electrochemical fluorination (EF) of methanesulfonic acid H3CSO3H or methanesulfonyl fluoride H3CSO2F:

Synthesis of triflic acid by fluorination of methanesulfofluoride


To produce anhydrous acid crude product is treated with small amount of triflic anhydride followed by distillation.

Uses.

  • In petroleum industry as an effective catalyst for isomerization of straight chain hydrocarbons into branched ones to increase the octane rating of a particular petroleum based fuel.
  • In chemical industry and in laboratory synthesis as a selective catalyst for alkylation and acylation reactions by Friedel-Crafts mechanism.
  • In synthetic organic chemistry as a catalyst for numerous cyclization, polymerization and other reactions.

Manufacturer(s) FSUE Angarsk Electrolysis Chemical Complex
Chemical structure of trifluoromethanesulfonic acid

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