Chlorosilanes are a group of reactive,

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

-containing

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

s, related to

silane Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...

and used in many chemical processes. Each such chemical has at least one

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

-chlorine bond.

Trichlorosilane Trichlorosilane is an inorganic compound with the formula HCl3Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to pr ...

is produced on the largest scale. The parent chlorosilane is

silicon tetrachloride Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. Preparation Silic ...

()..

Synthesis

Hydrochlorosilanes

They are prepared by the Müller-Rochow process, which involves treating silicon with

hydrogen chloride The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...

at elevated temperatures in the presence of a

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

. The idealized equation is :2 Si + 6 HCl → 2 HSiCl₃ + 2 H₂,

(HSiCl₃) is the main product;

dichlorosilane Dichlorosilane, or DCS as it is commonly known, is a chemical compound with the formula H2SiCl2. In its major use, it is mixed with ammonia (NH3) in LPCVD chambers to grow silicon nitride in semiconductor processing. A higher concentration of DCS ...

(H₂SiCl₂) and

(SiCl₄) are obtained as byproducts. The process was independently discovered by

Eugene G. Rochow Eugene George Rochow (October 4, 1909 – March 21, 2002) was an American inorganic chemist. Rochow worked on organosilicon chemistry; in the 1940s, he described the direct process, also known as the Rochow process or Müller-Rochow process. Bo ...

and Richard Müller in 1940.

Methylchlorosilanes

Methyltrichlorosilane Methyltrichlorosilane, also known as trichloromethylsilane, is a monomer and organosilicon compound with the formula CH3SiCl3. It is a colorless liquid with a sharp odor similar to that of hydrochloric acid. As methyltrichlorosilane is a reacti ...

(CH₃SiCl₃),

dimethyldichlorosilane Dimethyldichlorosilane is a tetrahedral, organosilicon compound with the formula Si(CH3)2Cl2. At room temperature it is a colorless liquid that readily reacts with water to form both linear and cyclic Si-O chains. Dimethyldichlorosilane is made ...

((CH₃)₂SiCl₂), and

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. ...

((CH₃)₃SiCl) are produced by the direct process. They are key reagents in organosilicon chemistry.

Reactions

Chlorosilanes react with

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

to produce

, giving siloxanes and eventually silicon dioxide. In the case of trimethylsilyl chloride, the hydrolyzed product is

hexamethyldisiloxane Hexamethyldisiloxane (HMDSO) is an organosilicon compound with the formula O i(CH3)3sub>2. This volatile colourless liquid is used as a solvent and as a reagent in organic synthesis. It is prepared by the hydrolysis of trimethylsilyl chloride. ...

: :2 ((CH₃)₃SiCl + H₂O → CH₃)₃Sisub>2O + 2 HCl The analogous reaction of dimethyldichlorosilane gives siloxane polymers or rings: : n (CH₃)₂SiCl₂ + n H₂O → CH₃)₂SiOsub>n + 2n HCl

Use

Silicon tetrachloride and trichlorosilane are intermediates in the production of ultrapure silicon in the semiconductor industry. Chlorosilanes obtained from crude silicon are purified by

fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation to ...

techniques and then reduced with hydrogen to give silicon of purity. Organic chlorosilanes are frequently used as

coating A coating is a covering that is applied to the surface of an object, usually referred to as the Substrate (materials science), substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquid ...

s for

and

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...

surfaces, and in the production of

silicone A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking ...

(polysiloxane) polymers. While

phenyl In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen ...

chlorosilanes and many others can be used, methylsiloxanes are produced in the greatest quantities. Methyl chlorosilanes have one to three

methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...

s. In the case of

, two chlorine atoms are available, so that a reaction with excess water produces a linear chain of ether-like linkages between silicon atoms. As in

polyether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again be c ...

s, these flexible linkages produce a rubbery polymer,

polydimethylsiloxane Polydimethylsiloxane (PDMS), also known as dimethylpolysiloxane or dimethicone, belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, as its ...

(PDMS).

can be used to induce branching and

cross-link In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...

ing in PDMS molecules, while

chlorotrimethylsilane 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. ...

serves to end backbone chains, limiting molecular weight. Other acid-forming species, especially

acetate An acetate is a salt (chemistry), salt formed by the combination of acetic acid with a base (e.g. Alkali metal, alkaline, Alkaline earth metal, earthy, Transition metal, metallic, nonmetallic or radical Radical (chemistry), base). "Acetate" als ...

, can replace chlorine in silicone synthesis with little difference in the chemistry of the finished polymer. These analogues of chlorosilanes are quite common in the sealants and adhesives marketed to consumers, and as precursors for medical-grade silicone, because of reduced toxicity.

References

{{Reflist