Trifluoroacetic anhydride (TFAA) is 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 ...

trifluoroacetic acid Trifluoroacetic acid (TFA) is a synthetic organofluorine compound with the chemical formula CF3CO2H. It belongs to the subclass of per- and polyfluoroalkyl substances (PFASs) known as ultrashort-chain perfluoroalkyl acids (PFAAs). TFA is not ...

. It is the perfluorinated derivative of

acetic anhydride Acetic anhydride, or ethanoic anhydride, is the chemical compound with the chemical formula, formula . Commonly abbreviated , it is one the simplest organic acid anhydride, anhydrides of a carboxylic acid and is widely used in the production of c ...

Preparation

Trifluoroacetic anhydride was originally prepared by the dehydration of trifluoroacetic acid with

phosphorus pentoxide Phosphorus pentoxide is a chemical compound with molecular formula Phosphorus, P4Oxygen, O10 (with its common name derived from its empirical formula, P2O5). This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desic ...

. The dehydration might also be carried out with excess α-halogenated

acid chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...

s. For example, with

dichloroacetyl chloride Dichloroacetyl chloride is the organic compound with the formula CHCl2COCl. It is the acyl chloride of dichloroacetic acid. It is a colourless liquid and is used in acylation reactions. Preparation Unlike typical acid chlorides, which are often ...

: : 2 CF₃COOH + Cl₂CHCOCl → (CF₃CO)₂O + Cl₂CHCOOH + HCl

Uses

Trifluoroacetic anhydride has various uses in

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

. It may be used to introduce the corresponding trifluoroacetyl group, for which it is more convenient than the corresponding

acyl chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...

trifluoroacetyl chloride Trifluoroacetyl chloride (also known as TFAC) is a toxic gaseous chemical compound with the chemical formula C2 Cl F3O. TFAC is the perfluorinated version of acetyl chloride. The compound is a gas, but it is usually shipped as a liquid under hig ...

, which is a gas. It can be used to promote reactions of carboxylic acids, including Friedel-Crafts acylation and acylation of other unsaturated compounds. Other

electrophilic aromatic substitution Electrophilic aromatic substitution (SEAr) is an organic reaction in which an atom that is attached to an aromatic ring, aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitut ...

reactions can also be promoted with trifluoroacetic anhydride, including nitration, sulfonation and nitrosylation. Similar to

, trifluoroacetic anhydride can be used as a dehydrating agent and as an activator for the

Pummerer rearrangement The Pummerer rearrangement is an organic reaction whereby an alkyl sulfoxide rearranges to an α- acyloxy–thioether (monothioacetal-ester) in the presence of acetic anhydride. The stoichiometry of the reaction is: :RS(O)CHR'2 + Ac2O → ...

. It can be used in place of

oxalyl chloride Oxalyl chloride is an organic chemical compound with the formula . This colorless, sharp-smelling liquid, the diacyl chloride of oxalic acid, is a useful reagent in organic synthesis. Preparation Oxalyl chloride was first prepared in 1892 by the ...

in the

Swern oxidation In organic chemistry, the Swern oxidation also known as Moffatt-Swern, named after Daniel Swern, is a chemical reaction whereby a primary or secondary Alcohol (chemistry), alcohol () is redox, oxidized to an aldehyde () or ketone () using oxalyl ...

, allowing temperatures up to −30 °C. With

sodium iodide Sodium iodide (chemical formula NaI) is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations (Na+) and iodide anions ...

, it reduces

sulfoxide In organic chemistry, a sulfoxide, also called a sulphoxide, is an organosulfur compound containing a sulfinyl () functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides. E ...

s to

sulfides Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families of ...

. Trifluoroacetic anhydride is the recommended

desiccant A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccant ...

for trifluoroacetic acid.{{cite book, author1=Chai, Christina Li Lin, url=https://books.google.com/books?id=SYzm1tx2z3QC&pg=PA376, title=Purification of laboratory chemicals, author2=Armarego, W. L. F., publisher=Butterworth-Heinemann, year=2003, isbn=0-7506-7571-3, location=Oxford, pages=376, format=

Google Books Google Books (previously known as Google Book Search, Google Print, and by its code-name Project Ocean) is a service from Google that searches the full text of books and magazines that Google has scanned, converted to text using optical charac ...

excerpt

References

Carboxylic anhydrides Trifluoromethyl compounds