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

trifluoroacetic acid Trifluoroacetic acid (TFA) is an organofluorine compound with the chemical formula CF3CO2H. It is a structural analogue of acetic acid with all three of the acetyl group's hydrogen atoms replaced by fluorine atoms and is a colorless liquid with ...

. It is the perfluorinated derivative of

acetic anhydride Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a colo ...

Preparation

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

phosphorus pentoxide Phosphorus pentoxide is a chemical compound with molecular formula P4 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 desiccant and dehydra ...

. 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 ...

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, dichloroacetyl ...

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

Uses

Trifluoroacetic anhydride has various uses in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. 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, which is a gas. It can be used to promote reactions of carboxylic acids, including

nucleophilic acyl substitution Nucleophilic acyl substitution describe a class of substitution reactions involving nucleophiles and acyl compounds. In this type of reaction, a nucleophile – such as an alcohol, amine, or enolate – displaces the leaving group of an acyl deriv ...

, Friedel-Crafts acylation, and acylation of other unsaturated compounds. Other

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

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 (COCl)2. 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 ...

in the

Swern oxidation The Swern oxidation, named after Daniel Swern, is a chemical reaction whereby a primary or secondary alcohol is oxidized to an aldehyde or ketone using oxalyl chloride, dimethyl sulfoxide (DMSO) and an organic base, such as triethylamine. It is ...

, 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 anion ...

, 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. ...

s to

sulfides Sulfide (British English also sulphide) 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 chemical compounds lar ...

. 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. Desiccants ...

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 Inc. that searches the full text of books and magazines that Google has scanned, converted to text using optical ...

excerpt

References

Carboxylic anhydrides Trifluoromethyl compounds