Tetramethylammonium fluoride

Tetramethyl­ammonium fluoride, commonly abbreviated TMAF, is the quaternary ammonium salt with the formula (CH₃)₄NF. This hygroscopic white solid is a source of “naked fluoride": fluoride ions not complexed with a metal atom. Most other soluble salts of fluoride are in fact bifluorides, HF₂^–. Historically, there have been two main approaches to prepare tetramethyl­ammonium fluoride: hydrofluoric acid neutralization of tetramethyl­ammonium hydroxide, and salt metathesis between different ammonium salts and inorganic fluoride sources, such as KF or CsF.^[1] Because the fluoride anion is extremely basic, the salt slowly reacts with acetonitrile, inducing dimerization to CH₃C(NH₂)=CHCN, which co-crystallizes.^[2]

Tetramethylammonium fluoride

Names
Preferred IUPAC name N,N,N-Trimethylmethanaminium fluoride
Identifiers
CAS Number	373-68-2
3D model (JSmol)	Interactive image
ChemSpider	61120
ECHA InfoCard	100.006.154
EC Number	206-769-0
PubChem CID	67803
CompTox Dashboard (EPA)	DTXSID40883374
InChI InChI=1S/C4H12N.FH/c1-5(2,3)4;/h1-4H3;1H/q+1;/p-1 Key: GTDKXDWWMOMSFL-UHFFFAOYSA-M
SMILES C[N+](C)(C)C.[F-]
Properties
Chemical formula	C4H12FN
Molar mass	93.145 g·mol−1
Appearance	white solid
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H312, H315, H319, H332, H335
Precautionary statements	P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P322, P330, P332+P313, P337+P313, P362, P363, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Related salts

• Tetramethyl­phosphonium fluoride (CH₃)₄PF forms stable acetonitrile solutions. It is prepared from the ylide and potassium bifluoride:

(CH₃)₃P=CH₂ + KHF₂ → (CH₃)₄PF + KF

Gaseous tetramethylphosphonium fluoride exists as the phosphorane but autoionizes in acetonitrile solution.^[3] A more elaborate phosphazenium salt ([(CH₃)₂N)₃P]₂N⁺F⁻) is also known.^[4]

• Anhydrous Tetrabutylammonium fluoride has been prepared by the reaction of hexafluorobenzene and tetrabutylammonium cyanide.^[5]