Tetra-n-butylammonium fluoride

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Tetra-n-butylammonium fluoride
TBAF.svg
Identifiers
CAS number 429-41-4 YesY
[87749-50-6] (trihydrate)
PubChem 2724141
ChemSpider 2006300 YesY
ChEMBL CHEMBL1078233 YesY
Jmol-3D images Image 1
Properties
Molecular 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 noted otherwise, 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 or TBAF is a quaternary ammonium salt with the chemical formula (CH3CH2CH2CH2)4N+F. It is commercially available as the trihydrate and as a solution in tetrahydrofuran.

In the laboratory the compound is usually encountered in the latter form as a source of organic-soluble fluoride ion to remove silyl ether protecting groups. It is also used as a phase transfer catalyst and as a mild base. Upon heating it may N-alkylate amides.[1]

As fluoride is such a strong hydrogen bond acceptor it is near impossible to dry hydrated samples. Heating to 77 °C under vacuum causes decomposition to the hydrogen difluoride salt,[2] and samples dried at 40 °C under high vacuum still contain 10-30 mol% of water and some 10% of difluoride.[3] 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. Recently, a preparation of anhydrous tetra-n-butylammonium fluoride from hexafluorobenzene and tetrabutylammonium cyanide has been reported. Despite the considerable basicity of "naked" fluoride ion, in the absence of water, solutions of the salt in acetonitrile and dimethyl sulfoxide are surprisingly stable towards elimination.[4]

References[edit]

  1. ^ K. Hiroya, R. Jouka, M. Kameda, A. Yasuhara, and 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. 
  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 and Stephen G. DiMagno (2005). "Anhydrous Tetrabutylammonium Fluoride". Journal of the American Chemical Society 127 (7): 2050–1. doi:10.1021/ja0440497. PMID 15713075.