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Sodium bis(trimethylsilyl)amide



Sodium bis(trimethylsilyl)amide
General
Systematic name Sodium bis(trimethylsilyl)amide
Other names sodium hexamethyldisilazane,
sodium hexamethyldisilazide,
NaHMDS
Molecular formula C6H18NNaSi2
Molar mass 183.37 g/mol
Appearance off-white solid
CAS number [1070-89-9]
Properties
Density and phase 0.9 g/cm3, solid
Solubility in water reacts with water
Other solvents THF, benzene
toluene
Melting point 171-175 °C (approx 446 K)
Boiling point 170 °C/2 mmHg
Basicity
(pKa) of conj. acid:

26 (in THF), 30 in DMSO)
Structure
Molecular shape Bent at nitrogen
Crystal structure  ?
Dipole moment  ? D
Hazards
MSDS External MSDS
Main hazards Highly flammable, corrosive
NFPA 704
Flash point  ? °C
R/S statement R: 11,15,34
S: 16, 24/25
RTECS number  ?
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other anions  ?
Other cations Lithium
bis(trimethylsilyl)amide
(LiHMDS)
Potassium
bis(trimethylsilyl)amide
Related compounds Lithium diisopropylamide (LDA)
KH
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Sodium bis(trimethylsilyl)amide is the chemical compound with the formula ((CH3)3Si)2NNa. This species, usually called NaHMDS (sodium hexamethyldisilazide), is a strong base used for deprotonation reactions or base catalyzed reaction. Its advantages are that it is available as a solid and it is soluble in a wide range of nonpolar solvents by virtue of the lipophilic TMS groups.[1]

Additional recommended knowledge

NaHMDS is quickly destroyed by water to form sodium hydroxide and bis(trimethylsilyl)amine.

Structure

It is common that polar organometallic reagents are depicted as ions, when in fact such species are rarely ionic. The structure shown in the figure is a better representation - the sodium atom is attached to the nitrogen atom via a polar covalent bond.

Applications in synthesis

NaHMDS is widely used as a base for C-H acids. Typical reactions:

  • To deprotonate ketones and esters to generate enolate derivatives.
  • Generate halocarbenes such as CHBr and CHI by dehydrohalogenation of the CH2X2 (X = Br, I). These carbene reagents add to alkenes to give substituted cyclopropanes.
  • To generate Wittig reagents via deprotonation of phosphonium salts.
  • Deprotonate cyanohydrins.

NaHMDS is also used as a base for N-H acids.

NaHMDS reacts with alkyl halides to give amine derivatives:

(CH3)3Si)2NNa + RBr → (CH3)3Si)2NR + NaBr
(CH3)3Si)2NR + H2O → (CH3)3Si)2O + RNH2

This method has been extended to aminomethylation via the reagent (CH3)3Si)2NCH2OMe, which contains a displacable methoxy group.

  • To deprotonate precursors to give stable carbenes.

References

  1. ^ Watson, B. T.; Lebel, H. "Sodium bis(trimethylsilyl)amide" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sodium_bis(trimethylsilyl)amide". A list of authors is available in Wikipedia.
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