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Chemical compound From Wikipedia, the free encyclopedia
Tetra-n-butylammonium fluoride, commonly abbreviated to TBAF and n-Bu4NF, is a quaternary ammonium salt with the chemical formula (CH3CH2CH2CH2)4N+F−. It is commercially available as the white solid trihydrate and as a solution in tetrahydrofuran. TBAF is used as a source of fluoride ion in organic solvents.[1]
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| Names | |
|---|---|
| Preferred IUPAC name
N,N,N-Tributylbutan-1-aminium fluoride | |
| Other names
Tetrabutylammonium fluoride; TBAF; n-Bu4NF | |
| Identifiers | |
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3D model (JSmol) |
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| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.006.417 |
PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| (C4H9)4NF | |
| Molar mass | 261.46 g/mol |
| Melting point | 58 to 60 °C (136 to 140 °F; 331 to 333 K) (trihydrate) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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TBAF can be prepared by passing hydrofluoric acid through an ion-exchange resin, followed by tetrabutylammonium bromide. Upon evaporation of the water, TBAF can be collected as an oil in quantitative yield.[1]
Preparing anhydrous samples is of interest as the basicity of fluoride increases by more than 20 pK units on passing from aqueous to aprotic solvent.[citation needed] However, heating samples of the hydrated material to 77 °C under vacuum causes decomposition to the hydrogen difluoride salt.[2] Similarly, samples dried at 40 °C under high vacuum still contain 10-30 mol% of water and some 10% of difluoride.[3] Instead, anhydrous TBAF has been prepared by the reaction of hexafluorobenzene and tetrabutylammonium cyanide. Solutions of the salt in acetonitrile and dimethyl sulfoxide are stable.[4]
Because the fluoride ion is such a strong hydrogen bond acceptor, its salts tend to be hydrated and of limited solubility in organic solvents. As a fluoride ion source, TBAF solves this problem, although the nature of the fluoride is uncertain because TBAF samples are almost always hydrated, resulting in the formation of bifluoride (HF2−) hydroxide (OH−) as well as fluoride. Many applications tolerate heterogeneous or ill-defined fluoride sources.
As a fluoride source in organic solvents, TBAF is used to remove silyl ether protecting groups. It is also used as a phase transfer catalyst and as a mild base. As a deprotecting agent, TBAF in DMSO will convert O-silylated enolates into carbonyls. With C-Si bonds, TBAF gives carbanions that can be trapped with electrophiles or undergo protonolysis.[1][5]
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