Hexamethyldisilazane

Description

Hexamethyldisilazane is a bulk organo silicon compound, being a quite useful silanizing agent. It is a reagent for the preparation of trimethylsilyl derivatives. It can also be used to dehydrate cells of biomaterials for scanning electron microscopy (SEM). Moreover, it is an adhesion promoter for photoresist in photolithography, and is also useful in the pyrolysis-gas chromatography-mass spectrometry to enhance the detectability of compounds with polar functional groups.

Chemical Properties

Hexamethyldisilazane, also known as HMDS, is an important organosilicon compound, a colorless and transparent liquid. It is readily hydrolyzed and gives off NH3 to produce hexamethyldisilyl ether. In the presence of a catalyst, it reacts with alcohols or phenols to produce trimethylalkoxysilane or trimethylaroxysilane. Reacts with anhydrous hydrogen chloride, releasing NH3 or NH4Cl, to produce trimethylchlorosilane.

Physical properties

Colorless transparent and easy flowing liquid. Boiling point 125℃, relative density 0.76 (20/4℃). Soluble in organic solvents, it will be rapidly hydrolyzed in contact with air to form trimethylsilanol and hexamethyldisilyl ether.

Uses

Hexamethyldisilazane mainly used as methyl silane alkylation (such as amikacin, penicillin, cephalosporins and kinds of penicillin derivatives), hydroxyl protectants of antibiotics. It is used as surface treatment agent of diatomite, white carbon black, titanium and blond additives of photoresist in the semiconductor industry. It is used as treatment agent of tearing strength resistance. It is used as a solvent in organic synthesis and organometallic chemistry. It is used as an adhesion promoter for photoresist in photolithography. it is used for the preparation of trimethylsilyl ethers from hydroxy compounds. It is used as an alternative to critical point drying during sample preparation in electron microscopy. It is added to analyte to get silylated diagnostic products during pyrolysis in gas chromatography- mass spectrometry.

Definition

ChEBI: Hexamethyldisilazane is an N-silyl compound obtained from ammonia by replacement of two of the hydrogens with trimethylsilyl groups. Hexamethyldisilazane is a derivatisation agent used in gas chromatography mass spectrometry applications. It has a role as a chromatographic reagent. It derives from a hydride of an ammonia.

Reactions

Hexamethyldisilazane(HMDS) is an extremely versatile and strong silylating agent. It is primarily used for the protection of sensitive functional groups during chemical synthesis.One of the advantages of Hexamethyldisilazane over chlorosilanes is that no base is needed as a hydrochloric acid acceptor. It produces ammonia which escapes easily from the reaction mixture during silylation.

General Description

Hexamethyldisilazane appears as a liquid. May be toxic by ingestion. Irritates skin and eyes. Vapors are heavier than air. May emit highly toxic nitrogen oxide fumes when heated to decomposition. Used to deactivate chromatography support materials and to promote adhesion of photoresists in the electronics industry.

Air & Water Reactions

Highly flammable. Moisture sensitive.

Reactivity Profile

Hexamethyldisilazane reacts with many carbonyl containing organic compounds to generate gaseous ammonia. May be incompatible with isocyanates, halogenated organics, peroxides, phenols (acidic), epoxides, anhydrides, and acid halides. Flammable gaseous hydrogen may be generated in combination with strong reducing agents, such as hydrides.

Hazard

Flammable, moderate fire risk.

Health Hazard

Inhalation or contact with material may irritate or burn skin and eyes. Fire may produce irritating, corrosive and/or toxic gases. Vapors may cause dizziness or suffocation. Runoff from fire control or dilution water may cause pollution.

Purification Methods

A possible impurity is Me3SiCl. Wash it well with pet ether and fractionate it through a vacuum jacketed column packed with Helipac using a reflux ratio of 10:1. [Langer et al. J Org Chem 23 50 1958, Beilstein 4 IV 4014.]

References

Deng, Xiang. "Hexamethyldisilazane." Synlett 2011.06(2011):881-882. Chiavari, G, D. Fabbri, and S. Prati. "Gas chromatographic-mass spectrometric analysis of products arising from pyrolysis of amino acids in the presence of hexamethyldisilazane." Journal of Chromatography A922.1–2(2001):235-241.
Nation, J. L. "A new method using hexamethyldisilazane for preparation of soft insect tissues for scanning electron microscopy." Stain Technology 58.6(1983):347-51.
http://www.sigmaaldrich.com/catalog/product/sial/52619? lang=en®ion=US
http://www.sigmaaldrich.com/catalog/product/aldrich/40215? lang=en®ion=US
http://www.sigmaaldrich.com/catalog/product/sial/86944? lang=en®ion=US