Bis(trimethylsilyl)amine (also known as hexamethyldisilazane and HMDS) is an

organosilicon compound Organosilicon compounds are organometallic compounds containing carbon–silicon chemical bond, bonds. Organosilicon chemistry is the corresponding science of their preparation and properties. Most organosilicon compounds are similar to the ordin ...

with the

molecular formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

CH₃)₃Sisub>2NH. The molecule is a derivative of

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

with

trimethylsilyl A trimethylsilyl group (abbreviated TMS) is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom minus;Si(CH3)3 which is in turn bonded to the rest of a molecule. This structural group is ch ...

groups in place of two hydrogen atoms. An electron diffraction study shows that silicon-nitrogen bond length (173.5 pm) and Si-N-Si bond angle (125.5°) to be similar to disilazane (in which methyl groups are replaced by hydrogen atoms) suggesting that steric factors are not a factor in regulating angles in this case. This colorless liquid is a reagent and a precursor to bases that are popular in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

and

organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

. Additionally, HMDS is also increasingly used as molecular precursor in chemical vapor deposition techniques to deposit silicon carbonitride thin films or coatings.

Synthesis and derivatives

Bis(trimethylsilyl)amine is synthesized by treatment of

trimethylsilyl chloride Trimethylsilyl chloride, also known as chlorotrimethylsilane is an organosilicon compound ( silyl halide), with the formula (CH3)3SiCl, often abbreviated Me3SiCl or TMSCl. It is a colourless volatile liquid that is stable in the absence of water. ...

with

: :2 (CH₃)₃SiCl + 3 NH₃ → CH₃)₃Sisub>2NH + 2 NH₄Cl

Ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...

together with

triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...

can be used instead. This method is also useful for ¹⁵N isotopic enrichment of HMDS. Alkali metal bis(trimethylsilyl)amides result from the

deprotonation Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.ed ...

of bis(trimethylsilyl)amine. For example,

lithium bis(trimethylsilyl)amide Lithium bis(trimethylsilyl)amide is a lithiated organosilicon compound with the formula . It is commonly abbreviated as LiHMDS or Li(HMDS) (lithium hexamethyldisilazide - a reference to its conjugate acid HMDS) and is primarily used as a strong ...

(LiHMDS) is prepared using

n-butyllithium ''n''-Butyllithium C4H9Li (abbreviated ''n''-BuLi) is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene (SBS). Also, it is broadly emp ...

: : CH₃)₃Sisub>2NH + BuLi → CH₃)₃Sisub>2NLi + BuH LiHMDS and other similar derivatives:

sodium bis(trimethylsilyl)amide Sodium bis(trimethylsilyl)amide is the organosilicon compound with the formula . This species, usually called NaHMDS (sodium hexamethyldisilazide), is a strong base used for deprotonation reactions or base-catalyzed reactions. Its advantages are ...

(NaHMDS) and

potassium bis(trimethylsilyl)amide Potassium bis(trimethylsilyl)amide (commonly abbreviated as KHMDS, Potassium(K) HexaMethylDiSilazide) or potassium hexamethyldisilazane is the chemical compound with the formula ((CH3)3Si)2NK. It is a strong, non-nucleophilic base with an approxim ...

(KHMDS) are used as a non-nucleophilic bases in synthetic organic chemistry.

Use as reagent

Hexamethyldisilazane is employed as a reagent in many organic reactions: 1) HMDS is used as a

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...

s of

heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

s such as in the microwave synthesis of a

derivative In mathematics, the derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. F ...

xanthine Xanthine ( or ; archaically xanthic acid; systematic name 3,7-dihydropurine-2,6-dione) is a purine base (genetics), base found in most human body tissues and fluids, as well as in other organisms. Several stimulants are derived from xanthine, incl ...

: :

2) The HMDS mediated trimethylsilylation of alcohols, thiols, amines and amino acids as protective groups or for intermediary organosilicon compounds is found to be very efficient and replaced TMSCl reagent. Silylation of

glutamic acid Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can synt ...

with excess hexamethyldisilazane and catalytic TMSCl in either refluxing

xylene In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are sub ...

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...

followed by dilution with alcohol (methanol or ethanol) yields the derived lactam

pyroglutamic acid Pyroglutamic acid (also known as PCA, 5-oxoproline, pidolic acid) is a ubiquitous but little studied natural amino acid derivative in which the free amino group of glutamic acid or glutamine cyclizes to form a lactam. The names of pyroglutamic ac ...

in good yield. HMDS USES

HMDS in the presence of catalytic iodine facilitates the silylation of alcohols in excellent yields. 3) HMDS can be used to silylate laboratory glassware and make it hydrophobic, or automobile glass, just as

Rain-X Rain-X is a synthetic hydrophobic surface-applied product that causes water to bead up and run off surfaces, most commonly used on glass automobile surfaces. The brand has since been extended to a range of automotive and surface care products, inc ...

does. 4) In

gas chromatography Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, ...

, 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

photolithography In integrated circuit manufacturing, photolithography or optical lithography is a general term used for techniques that use light to produce minutely patterned thin films of suitable materials over a substrate, such as a silicon wafer, to protect ...

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

electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...

, HMDS can be used as an alternative to critical point drying during sample preparation. In

pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...

-gas chromatography-

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...

, HMDS is added to the analyte to create silylated diagnostic products during pyrolysis, in order to enhance detectability of compounds with polar functional groups. In

plasma-enhanced chemical vapor deposition Plasma-enhanced chemical vapor deposition (PECVD) is a chemical vapor deposition process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creati ...

(PECVD), HMDS is used as a molecular precursor as a replacement to highly flammable and corrosive gasses like SiH₄, CH₄, NH₃ as it can be easily handled. HMDS is used in conjunction with a

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

of various gases such as argon, helium and nitrogen to deposit SiCN thin films/coatings with excellent mechanical, optical and electronic properties.

References

{{Reflist Amines Trimethylsilyl compounds Reagents for organic chemistry

Synthesis and derivatives

Use as reagent

Other uses

See also

References