Chlorosilane
Encyclopedia
Chlorosilanes are a group of reactive, chlorine
-containing chemical compound
s, related to silane
and used in many chemical processes. Each such chemical has at least one silicon
-chlorine bond.
at elevated temperatures in the presence of a copper
catalyst. The idealized equation is
Trichlorosilane
(HSiCl3) is the main product; dichlorosilane
(H2SiCl2) and silicon tetrachloride
(SiCl4) are obtained as byproducts. The process was independently discovered by Eugene G. Rochow
and Richard Müller
in 1940.
to produce hydrogen chloride
. The remaining hydroxyl group bonds to the silicon, initially forming a silol group (analogous to alcohol
). In general, this will eventually bond to a solid oxide
surface or react with another chlorosilane or silol molecule. In the latter cases, the oxygen atom forms a link between two silicon atoms, analogous to the ether
linkage in organic chemicals, and identical to the bonding in silicon dioxide
.
(SiCl4) and trichlorosilane
(HSiCl3) are intermediates in the production of ultrapure silicon in the semiconductor industry. Chlorosilanes obtained from crude silicon are purified by fractional distillation
techniques and then reduced with hydrogen to give silicon of purity.
Organic
chlorosilanes are frequently used as coating
s for silicon
and glass
surfaces, and in the production of silicone
(polysiloxane) polymers. While phenyl chlorosilanes and many others can be used, methylsiloxanes are produced in the greatest quantities.
Methyl chlorosilanes have one to three methyl group
s. In the case of dichlorodimethylsilane, 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 polyethers, these flexible linkages produce a rubbery polymer, polydimethylsiloxane
(PDMS). Trichloromethylsilane can be used to induce branching and cross-link
ing in PDMS molecules, while chlorotrimethylsilane serves to end backbone chains, limiting molecular weight.
Other acid-forming species, especially acetate
, 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.
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
-containing chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s, related to silane
Silane
Silane is a toxic, extremely flammable chemical compound with chemical formula SiH4. In 1857, the German chemists and Friedrich Woehler discovered silane among the products formed by the action of hydrochloric acid on aluminum silicide, which they had previously prepared...
and used in many chemical processes. Each such chemical has at least one silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
-chlorine bond.
Synthesis
They are prepared by the Müller-Rochow process, which involves treating silicon with hydrogen chlorideHydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
at elevated temperatures in the presence of a copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
catalyst. The idealized equation is
- 2 Si + 6 HCl → 2 HSiCl3 + 2 H2,
Trichlorosilane
Trichlorosilane
Trichlorosilane is a chemical compound containing silicon, hydrogen, and chlorine. At high temperatures, it decomposes to produce silicon, and therefore purified trichlorosilane is the principal source of ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce...
(HSiCl3) is the main product; dichlorosilane
Dichlorosilane
Dichlorosilane , or DCS as it is commonly known, is usually mixed with ammonia in LPCVD chambers to grow silicon nitride in semiconductor processing.A higher concentration of DCS:NH3 Dichlorosilane (H2SiCl2), or DCS as it is commonly known, is usually mixed with ammonia (NH3) in LPCVD chambers to...
(H2SiCl2) and silicon tetrachloride
Silicon tetrachloride
Silicon tetrachloride 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:...
(SiCl4) are obtained as byproducts. The process was independently discovered by Eugene G. Rochow
Eugene G. Rochow
Eugene George Rochow 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....
and Richard Müller
Richard Müller (chemist)
Richard Gustav Müller was a German chemist. Independent of Eugene G. Rochow he discovered the Direct process of organosilicon compounds in 1941. The synthesis which is also known as Müller-Rochow process is the copper catalysed reaction of chloromethane with silicon. Müller was awarded the...
in 1940.
Chemistry
All chlorosilanes react with waterWater
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
to produce hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
. The remaining hydroxyl group bonds to the silicon, initially forming a silol group (analogous to 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....
). In general, this will eventually bond to a solid oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
surface or react with another chlorosilane or silol molecule. In the latter cases, the oxygen atom forms a link between two silicon atoms, analogous to the 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"...
linkage in organic chemicals, and identical to the bonding in silicon dioxide
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
.
Use
Silicon tetrachlorideSilicon tetrachloride
Silicon tetrachloride 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:...
(SiCl4) and trichlorosilane
Trichlorosilane
Trichlorosilane is a chemical compound containing silicon, hydrogen, and chlorine. At high temperatures, it decomposes to produce silicon, and therefore purified trichlorosilane is the principal source of ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce...
(HSiCl3) are intermediates in the production of ultrapure silicon in the semiconductor industry. Chlorosilanes obtained from crude silicon are purified by fractional distillation
Fractional distillation
Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...
techniques and then reduced with hydrogen to give silicon of purity.
Organic
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
chlorosilanes are frequently used as coating
Coating
Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...
s for silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
and glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
surfaces, and in the production of silicone
Silicone
Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....
(polysiloxane) polymers. While phenyl chlorosilanes and many others can be used, methylsiloxanes are produced in the greatest quantities.
Methyl chlorosilanes have one to three methyl group
Methyl group
Methyl group is a functional group derived from methane, containing one carbon atom bonded to three hydrogen atoms —CH3. The group is often abbreviated Me. Such hydrocarbon groups occur in many organic compounds. The methyl group can be found in three forms: anion, cation and radical. The anion...
s. In the case of dichlorodimethylsilane, 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 polyethers, these flexible linkages produce a rubbery polymer, polydimethylsiloxane
Polydimethylsiloxane
Polydimethylsiloxane 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, and is particularly known for its unusual rheological properties. PDMS is optically clear, and, in general, is...
(PDMS). Trichloromethylsilane can be used to induce branching and cross-link
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
ing in PDMS molecules, while chlorotrimethylsilane serves to end backbone chains, limiting molecular weight.
Other acid-forming species, especially acetate
Acetate
An acetate is a derivative of acetic acid. This term includes salts and esters, as well as the anion found in solution. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In...
, 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.