Tetramethylammonium fluoride
Tetramethylammonium fluoride, commonly abbreviated TMAF, is the quaternary ammonium salt with the formula 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. Because the fluoride anion is extremely basic, the salt slowly reacts with acetonitrile, inducing dimerization to CH3C=CHCN, which co-crystallizes.
Related salts
- Tetramethylphosphonium fluoride 4PF forms stable acetonitrile solutions. It is prepared from the ylide and potassium bifluoride:
- Anhydrous Tetrabutylammonium fluoride has been prepared by the reaction of hexafluorobenzene and tetrabutylammonium cyanide.