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 equivalent ...
of
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 a ...
. 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 col ...
.
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 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, dichloroacetyl ...
:
: 2 CF
3COOH + Cl
2CHCOCl → (CF
3CO)
2O + Cl
2CHCOOH + 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
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
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 ni ...
reactions can also be promoted with trifluoroacetic anhydride, including nitration, sulfonation and nitrosylation.
Similar to
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 col ...
, 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 (mono thioacetal-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 one ...
, 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 (I ...
, 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 (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 la ...
.
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 Inc. that searches the full text of books and magazines that Google has scanned, converted to text using optical c ...
excerpt
References
Carboxylic anhydrides
Trifluoromethyl compounds