|Sodium bis(trimethylsilyl)amide 150px|
|Systematic name||Sodium bis(trimethylsilyl)amide|
|Other names||sodium hexamethyldisilazane,|
|Molar mass||183.37 g/mol|
|Density and phase||0.9 g/cm3, solid|
|Solubility in water||reacts with water|
|Other solvents||THF, benzene|
|Melting point||171-175 °C (approx 446 K)|
|Boiling point||170 °C/2 mmHg|
(pKa) of conj. acid:
26 (in THF), 30 in DMSO)
|Molecular shape||Bent at nitrogen|
|Dipole moment||? D|
|Main hazards||Highly flammable, corrosive|
|Flash point||? °C|
|R/S statement||R: 11,15,34|
S: 16, 24/25
|Supplementary data page|
|n, εr, etc.|
Solid, liquid, gas
|Spectral data||UV, IR, NMR, MS|
|Related compounds||Lithium diisopropylamide (LDA)|
|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.
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.
- Lithium bis(trimethylsilyl)amide - ((CH3)3Si)2NLi
- Potassium bis(trimethylsilyl)amide - ((CH3)3Si)2NK
- 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.