Sodium bis(trimethylsilyl)amide
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| Sodium bis(trimethylsilyl)amide | |
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| 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 |
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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]
NaHMDS is quickly destroyed by water to form sodium hydroxide, and bis(trimethylsilyl)amine.
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[edit] 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 is a better representation - the sodium atom is attached to the nitrogen atom via a polar covalent bond.
[edit] 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.
[edit] See also
- Lithium bis(trimethylsilyl)amide - ((CH3)3Si)2NLi
- Potassium bis(trimethylsilyl)amide - ((CH3)3Si)2NK
[edit] References
- ^ 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.
