Bisamine (also known as hexamethyldisilazane, or HMDS) is an organosilicon compound with the molecular formula [(CH₃)₃Si]₂NH. The molecule is a derivative of ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 with trimethylsilyl

Trimethylsilyl

A trimethylsilyl group is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si3], which is in turn bonded to the rest of a molecule...

 groups in place of two hydrogen atoms. This colorless liquid is a reagent and a precursor to bases that are popular in organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

 and organometallic chemistry

Organometallic chemistry

Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...

.

Preparation and reactions

Bis(trimethylsilyl)amine is prepared by treatment of trimethylsilyl chloride

Trimethylsilyl chloride

Trimethylsilyl chloride, also known as chlorotrimethylsilane is a silyl halide, with a variety of different uses in chemistry. It has the formula 3SiCl, and under standard conditions it is a colourless liquid, which is stable in the absence of water...

 with ammonia:

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

The product is usually handled using air-free technique

Air-free technique

Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen...

s since it hydrolyze

Hydrolysis

Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

s slowly in humid air.

Alkali metal bis(trimethylsilyl)amides result from the deprotonation

Deprotonation

Deprotonation is the removal of a proton from a molecule, forming the conjugate base.The relative ability of a molecule to give up a proton is measured by its pKa value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base...

 of bis(trimethylsilyl)amine. For example lithium bis(trimethylsilyl)amide

Lithium bis(trimethylsilyl)amide

Lithium bisamide is the organosilicon compound with the formula [3Si]2NLi. This colourless solid is a strong non-nucleophilic base used for deprotonation reactions and as a ligand...

 (LiHMDS) is prepared using n-butyllithium

N-Butyllithium

n-Butyllithium is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene...

:

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

Together with sodium bis(trimethylsilyl)amide

Sodium bis(trimethylsilyl)amide

Sodium bisamide is the chemical compound with the formula 2NNa. This species, usually called NaHMDS , is a strong base used for deprotonation reactions or base catalyzed reaction...

 (NaHMDS) and potassium bis(trimethylsilyl)amide

Potassium bis(trimethylsilyl)amide

Potassium bisamide is the chemical compound with the formula 2NK...

 (KHMDS), LiHMDS is used as a non-nucleophilic base.

Reactions

One of the uses of HMDS is as a reagent

Reagent

A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...

 in condensation reaction

Condensation reaction

A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule. When this small molecule is water, it is known as a dehydration reaction; other possible small molecules lost are hydrogen chloride,...

s of heterocyclic compound

Heterocyclic compound

A heterocyclic compound is a cyclic compound which has atoms of at least two different elements as members of its ring. The counterparts of heterocyclic compounds are homocyclic compounds, the rings of which are made of a single element....

s such as in the microwave synthesis

Microwave chemistry

Microwave chemistry is the science of applying microwave irradiation to chemical reactions. Microwaves act as high frequency electric fields and will generally heat any material containing mobile electric charges, such as polar molecules in a solvent or conducting ions in a solid...

 of a derivative

Derivative (chemistry)

In chemistry, a derivative is a compound that is derived from a similar compound by some chemical or physical process. In the past it was also used to mean a compound that can be imagined to arise from another compound, if one atom is replaced with another atom or group of atoms, but modern...

 of xanthine

Xanthine

Xanthine , is a purine base found in most human body tissues and fluids and in other organisms. A number of stimulants are derived from xanthine, including caffeine and theobromine....

:

HMDS can be used to convert alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s into trimethylsilyl

Trimethylsilyl

A trimethylsilyl group is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si3], which is in turn bonded to the rest of a molecule...

 ether

Ether

Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...

s. HMDS can be used to silylate laboratory glassware and make it hydrophobic, or automobile glass, just as Rain-X

Rain-X

Rain-X is a line of consumer automotive and surface care products produced by SOPUS Products , a subsidiary of Royal Dutch Shell. Industrial Rain-X products are produced by Ecolab and used in carwashes and other industrial applications...

 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

In photolithography

Photolithography

Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...

, HMDS is often used in as an adhesion promoter for photoresist

Photoresist

A photoresist is a light-sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface.-Tone:Photoresists are classified into two groups: positive resists and negative resists....

.
Best results are obtained by applying HMDS from the gas phase on heated substrates.

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

In pyrolysis

Pyrolysis

Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...

-gas chromatography-mass spectrometry

Mass spectrometry

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...

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