Tetra-n-butylammonium fluoride

Tetra-n-butylammonium fluoride

File:TBAF.svg
Names
Preferred IUPAC name N,N,N-Tributylbutan-1-aminium fluoride
Other names Tetrabutylammonium fluoride; TBAF; n-Bu4NF
Identifiers
CAS Number	429-41-4 checkY 87749-50-6 (trihydrate) ☒N
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL1078233 checkY
ChemSpider	2006300 checkY
ECHA InfoCard
E number
PubChem CID	2724141
UNII	2618F0C37I checkY
CompTox Dashboard (EPA)	{{#property:P3117}}
InChI InChI=1S/C16H36N.FH/c1-5-9-13-17(14-10-6-2,15-11-7-3)16-12-8-4;/h5-16H2,1-4H3;1H/q+1;/p-1 checkY Key: FPGGTKZVZWFYPV-UHFFFAOYSA-M checkY InChI=1/C16H36N.FH/c1-5-9-13-17(14-10-6-2,15-11-7-3)16-12-8-4;/h5-16H2,1-4H3;1H/q+1;/p-1 Key: FPGGTKZVZWFYPV-REWHXWOFAO
SMILES [F-].CCCC[N+](CCCC)(CCCC)CCCC
Properties
Chemical formula	(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). ☒N verify (what is checkY☒N ?) Infobox references

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.

Preparation and properties

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.

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. However, heating samples of the hydrated material to 77 °C under vacuum causes decomposition to the hydrogen difluoride salt. Similarly, samples dried at 40 °C under high vacuum still contain 10-30 mol% of water and some 10% of difluoride. 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.

Reactions and uses

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.

TBAF is also used, when in an organic solvent, as an activator compound to allow super glue to stick to low surface energy polymers such as polyethylene and polypropylene.

Further reading

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