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Structural formula of bis(trimethylsilyl)amine
Spacefill model of bis(trimethylsilyl)amine
Preferred IUPAC name
Other names
3D model (JSmol)
Abbreviations HMDS
ECHA InfoCard 100.012.425
EC Number 213-668-5
MeSH Hexamethylsilazane
RTECS number JM9230000
UN number 2924, 3286
Molar mass 161.395 g·mol−1
Appearance Colorless liquid
Density 0.77 g cm−3
Melting point −78 °C (−108 °F; 195 K)
Boiling point 126 °C (259 °F; 399 K)
Slow hydrolysis
Safety data sheet External MSDS
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no codeNFPA 704 four-colored diamond
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Bis(trimethylsilyl)amine (also known as hexamethyldisilazane and HMDS) is an organosilicon compound with the molecular formula [(CH3)3Si]2NH. The molecule is a derivative of ammonia with trimethylsilyl groups in place of two hydrogen atoms. This colorless liquid is a reagent and a precursor to bases that are popular in organic synthesis and organometallic chemistry.

Preparation and reactions[edit]

Bis(trimethylsilyl)amine is prepared by treatment of trimethylsilyl chloride with ammonia:[2]

2 (CH3)3SiCl + 3 NH3 → [(CH3)3Si]2NH + 2 NH4Cl

The product is usually handled using air-free techniques since it hydrolyzes slowly in humid air.

Alkali metal bis(trimethylsilyl)amides result from the deprotonation of bis(trimethylsilyl)amine. For example, lithium bis(trimethylsilyl)amide (LiHMDS) is prepared using n-butyllithium:

[(CH3)3Si]2NH + BuLi → [(CH3)3Si]2NLi + C4H10

Similarly to sodium bis(trimethylsilyl)amide (NaHMDS) and potassium bis(trimethylsilyl)amide (KHMDS), LiHMDS is used as a non-nucleophilic base.


One of the uses of HMDS is as a reagent in condensation reactions of heterocyclic compounds such as in the microwave synthesis of a derivative of xanthine:[3]

HMDS application

HMDS can be used to convert alcohols into trimethylsilyl ethers. HMDS can be used to silylate laboratory glassware and make it hydrophobic, or automobile glass, just as Rain-X does.

In gas chromatography, HMDS can be used to silylate OH groups of organic compounds to increase volatility, this way enabling GC-analysis of chemicals that are otherwise non-volatile.

Other uses[edit]

In photolithography, HMDS is often used as an adhesion promoter for photoresist. Best results are obtained by applying HMDS from the gas phase on heated substrates.[4]

In electron microscopy, HMDS can be used as an alternative to critical point drying during sample preparation.[5]

In pyrolysis-gas chromatography-mass spectrometry, HMDS is added to the analyte to create silylated diagnostic products during pyrolysis, in order to enhance detectability of compounds with polar functional groups.[6]

See also[edit]


  1. ^ Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 135. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
  2. ^ Robert C. Osthoff; Simon W. Kantor (1957). "Organosilazane Compounds". Inorg. Synth. Inorganic Syntheses. 5: 55–64. doi:10.1002/9780470132364.ch16. ISBN 978-0-470-13236-4.
  3. ^ Burbiel JC, Hockemeyer J, Müller CE (2006). "Microwave-assisted ring closure reactions: Synthesis of 8-substituted xanthine derivatives and related pyrimido- and diazepinopurinediones". Beilstein J Org Chem. 2: 20. doi:10.1186/1860-5397-2-20. PMC 1698928. PMID 17067400.
  4. ^ Cornell NanoScale Science & Technology Facility. "CNF - Photolithography Resist Processes and Capabilities". Retrieved 2008-01-29.
  5. ^ Bray DF, Bagu J, Koegler P (1993). "Comparison of hexamethyldisilazane (HMDS), Peldri II, and critical-point drying methods for scanning electron microscopy of biological specimens". Microsc. Res. Tech. 26 (6): 489–95. doi:10.1002/jemt.1070260603. PMID 8305726.
  6. ^ Giuseppe Chiavari; Daniele Fabbri & Silvia Prati (2001). "Gas chromatographic–mass spectrometric analysis of products arising from pyrolysis of amino acids in the presence of hexamethyldisilazane". Journal of Chromatography A. 922 (1–2): 235–241. doi:10.1016/S0021-9673(01)00936-0. PMID 11486868.