Chemical Properties
Colorless to amber solution
Uses
Potassium Hexamethyldisilazide is widely used as a Sterically Hindered Base for Enolate Generation in Selective Formation of Linear Conjugated Dienolates and Alkyl (Z)-3-Alkenoates.
Uses
Potassium Bis(trimethylsilyl)amide (1M in THF) is used in the preparation of 5-azacytidine, an antineoplastic drug. Also applied in the preparation of β3-AR agonists used in anti-stress formulations. It is also used as a reagent in the preparation of lanthanide complexes employed in selective cyclization reactions.
Uses
Potassium bis(trimethylsilyl)amide is a strong base used in the alkylation carbonyl compounds.1
Preparation
Potassium Hexamethyldisilazide is prepared and isolated by the procedure
of Wannagat and Niederpruem. A more convenient in situ
generation from potassium hydride and hexamethyldisilane is
described by Brown.
General Description
This product, 1.0 M in 2-methyltetrahydrofuran aligns with "Safer Solvents and Auxiliaries", "Use of Renewable Feedstocks" and "Inherently Safer Chemistry for Accident Prevention".
Synthesis
Potassium bis(trimethylsilyl)amide is an important non-nucleophilic base widely used in organic synthesis. The main method for its preparation is are interaction of hexamethyldisilazane with potassium amide) potassium hydride, potassium metal, mad styrene, isoprene, or naphthalene as electron acceptors.
An oven-dried 100 ml round-bottom flask was charged with KH (3.22 g, 20.1 mmol, 25 wt. 96 in oil) and flushed with argon. The hydride was then washed with hexane (4x5 ml). To the flask was fitted, a reflux condenser was made, and then THF (20 ml) and bis(trimethylsi1yl)amine (3.81 ml, 18.1 mmol) were added. The resultant slurry was sonicated until the hydrogen gas evolution had ceased, and almost all the potassium hydride had been consumed (3.25 h). The slurry was allowed to settle, and the supernatant was then cannulated into a Schlenk flask. Titration4 for the amide base concentration showed it to be 0.80 M, while the concentration of the total base was 0.86 M[1-2].
References
[1] I. V. Magedov. “Convenient method for the preparation of a solution of potassium bis(trimethylsilyl)amide.” Russian Chemical Bulletin 44 11 (1995): 2197–2198.
[2] J. Ahman, P. Somfai. “An Efficient Preparation of Potassium Bis (Trimethylsilyl) Amide (KHMDS).” Synthetic Communications 25 1 (1995): 2301–2303.
