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Lithium bis(trimethylsilyl)amide

Product NameLithium bis(trimethylsilyl)amide
CAS4039-32-1
MFC6H18LiNSi2
MW167.33
EINECS223-725-6
MOL File4039-32-1.mol

Chemical Properties

Melting point	73°C
Boiling point	55-56 °C
Density	0.860 g/mL at 25 °C (lit.)
refractive index	n20/D 1.425(lit.)
Flash point	48 °F
storage temp.	Store below +30°C.
solubility	hydrolysis
form	Powder
color	White
Specific Gravity	0.716
Water Solubility	hydrolysis
Sensitive	Air & Moisture Sensitive
Hydrolytic Sensitivity	8: reacts rapidly with moisture, water, protic solvents
BRN	3567910
Exposure limits	ACGIH: TWA 50 ppm; STEL 100 ppm (Skin) OSHA: TWA 200 ppm(590 mg/m3) NIOSH: IDLH 2000 ppm; TWA 200 ppm(590 mg/m3); STEL 250 ppm(735 mg/m3)
InChIKey	YNESATAKKCNGOF-UHFFFAOYSA-N
CAS DataBase Reference	4039-32-1(CAS DataBase Reference)
EPA Substance Registry System	Silanamine, 1,1,1-trimethyl-N-(trimethylsilyl)-, lithium salt (4039-32-1)

Safety Information

Hazard Codes	F,C,N
Risk Statements	11-34-48/20-63-65-67-51/53-35-20-62-14-40-37-19
Safety Statements	9-16-26-29-33-36/37/39-45-61-62-57-43
RIDADR	UN 2925 4.1/PG 2
WGK Germany	3
F	10-23
TSCA	Yes
HazardClass	4.3
PackingGroup	II
HS Code	29319090

MSDS

Provider	Language
Lithium hexamethyldisilazide	English
SigmaAldrich	English
ACROS	English
ALFA	English

Usage And Synthesis

Chemical Properties

light yellow to yellow crystalline powder

Physical properties

distillable low-melting solid; mp 70–72 °C, bp 115 °C/1mmHg. LHMDS is a cyclic trimer in the solid state,3 whereas in benzene solution it exists in a monomer–dimer equilibrium. LHMDS exists as a tetramer-dimer mixture in hydrocarbons and as a dimer-monomer mixture in THF and ether. Treatment of LHMDS with trialkylamines increases the monomer concentration, whereas the use of diamines affords exclusively the corresponding chelated monomer. LHMDS is less soluble, less basic, more stable, and much less sensitive to air compared to lithium diisopropylamide. pKa 29.5 (THF, 27 °C).

Uses

Lithium Hexamethyldisilazide is widely used as strong nonnucleophilic base

Uses

Lithium bis(trimethylsilyl)amide is a base used in preparation of dienes and enolates. It is used to catalyze the addition of phosphine P-H bonds to carbodiimides leading to phosphaguanidines. Lithium bis(trimethylsilyl)amide is also used in a novel three-step synthesis of disubstituted 1,2,5-thiadiazoles.

Uses

Lithium bis(trimethylsilyl)amide is used as nonnucleophilic base to generate kinetic ketone and ester enolates. It is considerably more selective than LDA and undesired reductions (e.g., of nonenolizable ketones observed in the case of LDA) can be avoided by using LHMDS.

Preparation

It is conveniently prepared by the reaction of hexamethyldisilazane with n-butyllithium in hexane. For most uses the hexane is then evaporated and replaced with THF.

General Description

This product, 0.5 M in 2-methyltetrahydrofuran aligns with Safer Solvents and Auxiliaries, Use of Renewable Feedstocks and Inherently Safer Chemistry for Accident Prevention.

Flammability and Explosibility

Highly flammable