Tetra-n-butylammonium fluoride

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Tetra-n-butylammonium fluoride
TBAF.svg
Names
IUPAC name
Tetra-n-butylammonium fluoride
Other names
Tetrabutylammonium fluoride; TBAF; n-Bu4NF
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.006.417
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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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.[1]

Preparation and properties[edit]

Because fluoride is such a strong hydrogen bond acceptor, its salts tend to be hydrated and of limited solubility in organic solvents. 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.

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] Many attempts have been made to produce anhydrous TBAF. 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]

Anhydrous tetra-n-butylammonium fluoride has been prepared by the reaction of hexafluorobenzene and tetrabutylammonium cyanide. Solutions of the salt in acetonitrile and dimethyl sulfoxide are stable.[4]

Reactions[edit]

As a source of fluoride ion 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 group, 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]

References[edit]

  1. ^ a b Hui-Yin Li, Haoran Sun, Stephen G. DiMagno "Tetrabutylammonium Fluoride" e-EROS Encyclopedia of Reagents for Organic Synthesis 2007 John Wiley doi:10.1002/9780470842898.rt015.pub2
  2. ^ Ramesh K. Sharma; James L. Fry (1983). "Instability of anhydrous tetra-n-alkylammonium fluorides". Journal of Organic Chemistry. 48 (12): 2112–4. doi:10.1021/jo00160a041. 
  3. ^ D. Phillip Cox; Jacek Terpinski; Witold Lawrynowicz (1984). "'Anhydrous' tetrabutylammonium fluoride: a mild but highly efficient source of nucleophilic fluoride ion". Journal of Organic Chemistry. 49 (17): 3216–9. doi:10.1021/jo00191a035. 
  4. ^ Haoran Sun & Stephen G. DiMagno (2005). "Anhydrous Tetrabutylammonium Fluoride". Journal of the American Chemical Society. 127 (7): 2050–1. PMID 15713075. doi:10.1021/ja0440497. 
  5. ^ Nina Gommermann and Paul Knochel "N,N-Dibenzyl-N-[1-cyclohexyl-3-(trimethylsilyl)-2-propynyl]-amine from Cyclohexanecarbaldehyde, Trimethylsilylacetylene and Dibenzylamine" Org. Synth. 2007, 84, 1. doi:10.15227/orgsyn.084.0001

Further reading[edit]

  • K. Hiroya; R. Jouka; M. Kameda; A. Yasuhara & T. Sakamoto (2001). "Cyclization reactions of 2-alkynylbenzyl alcohol and 2-alkynylbenzylamine derivatives promoted by tetrabutylammonium fluoride". Tetrahedron. 57 (48): 9697–710. doi:10.1016/S0040-4020(01)00991-7. .