Methyltrichlorosilane

Methyltrichlorosilane
IUPAC name Trichloromethylsilane
Other names Methyltrichlorosilane
Identifiers
CAS number	75-79-6 Y
Properties
Molecular formula	CH3Cl3Si
Molar mass	149.48 g mol−1
Appearance	colorless liquid
Density	1.273 g cm−3
Melting point	-77 ºC
Boiling point	66 ºC
Solubility in water	reaction in water
Solubility	soluble in methylene chloride
Hazards
MSDS	Fischer Scientific MSDS
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Methyltrichlorosilane, also known as trichloromethylsilane, is an organosilicon compound with the formula CH₃SiCl₃. At room temperature, it is a colorless liquid with a sharp odor similar to that of hydrochloric acid. As methyltrichlorosilane is a reactive compound, it is mainly used a precursor for forming various cross-linked siloxane polymers.

Preparation

Methyltrichlorosilane results from the “direct reaction” of chloromethane with elemental silicon in the presence of a copper catalyst, usually at a temperature of at least 250 °C.^[1]

3 CH₃Cl + Si → CH₃SiCl₃ + C₂H₄ + H₂

While this reaction is currently the standard in industrial silicone production and is nearly identical to the first direct synthesis of methyltrichlorosilane, the overall process is inefficient with respect to methyltrichlorosilane.^[2] Even though dimethyldichlorosilane is usually the major product, if methyltrichlorosilane is needed, the amount of metal catalyst is reduced.^[1]

Reactions and Applications

Reagent in Organic Synthesis

A combination of methyltrichlorosilane and sodium iodide can be used to cleave a variety of carbon-oxygen bonds such as methyl ethers.

R'OR + MeSiCl₃ + NaI + H₂O → R'OH + RI + MeSiCl₂(OH) + NaCl

Esters and lactones can also be cleaved with methyltrichlorosilane and sodium iodide to give the corresponding carboxylic acids. Acetals convert to carbonyl compounds. Thus, methyltrichlorosilane can be used to remove acetal protecting groups from carbonyl compounds under mild conditions.^[3]

RR'C(OMe)₂ + MeSiCl₃ + NaI → RR'CO + 2 MeI + MeSiCl₂(OMe) + NaCl

Finally, methyltrichlorosilane and sodium iodide can be used as a means of converting alcohols to their corresponding iodides; however, this reaction does not work as well with primary alcohols.^[3]

ROH + MeSiCl₃ + NaI → RI + MeSiCl₂(OH) + NaCl

Silynes

Methyltrichlorosilane is mainly used to form polymers such as poly(methylsilyne).

n MeSiCl₃ + 3n Na →[MeSi]_n + 3n NaCl

Poly(methylsilyne) is soluble in organic solvents, and can be applied to surfaces before being pyrolyzed to give the ceramic material, silicon carbide.^[4] Poly(methylsilyne) can be formed into various shapes before being pyrolyzed.

Silicones

The most common reaction of methyltrichlorosilane is its hydrolysis:

MeSiCl₃ + 3 H₂O → MeSi(OH)₃ + 3 HCl

MeSi(OH)₃ → MeSiO_1.5 + 1.5 H₂O

The silanol is unstable and will eventually condense to give a polymer network and water. Thus, compounds like methyltrichlorosilane are precursors to various organo-siloxane polymers. This reaction is particularly important because silicon-alkyl bonds are thermally stable and resistant to oxidation.^[5] Methyltrichlorosilane can be used as a means of cross-linking polymers to give a three-dimensional network.

Because of the rigid nature of the polymers that methyltrichlorosilane can form, MeSiCl₃ has many industrial applications. For instance, methyltrichlorosilane vapor reacts with water on surfaces to give a thin layer of methylpolysiloxane, which changes the contact angle of the surface to water. This effect arises because of the oriented layer of methyl groups, making a water-repellent film.^[5] Filter paper treated with methyltrichlorosilane allows organic solvents to pass through, but not water. Another benefit of such water-repellent films is that the polymers formed are stable: one of the only ways to remove the siloxane film is by acid strong enough to dissolve silicone.^[5]

Another use for methyltrichlorosilane is in the production of methyl silicone resins. Because of the stability of the cross-linked polymers that form after condensation, the resin can be heated to 550 °C in a vacuum without decomposition, making it an ideal material for electrical insulation at high temperatures.^[5] Thus, these resins can be used to coat computer chips or other electronic parts since they both repel water and provide thermal isolation.

References

1. ^ ^{a b} Rösch, L; et al. “Silicon Compounds, Organic.” Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim, 2005. DOI: 10.1002/14356007.a24_021
2. ^ Rochow, E. The Direct Synthesis of Organosilicon Compounds. J. Am. Chem. Soc. 1945, 67, 963. DOI: 10.1021/ja01222a026
3. ^ ^{a b} Olah, G; et al. “Methyltrichlorosilane.” Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons, Inc., 2001. DOI: 10.1002/047084289X.rm265
4. ^ Bianconi, Patricia A.; Pitcher, Michael W.; Joray, Scott. “A method of preparing poly(methyl- or ethyl-silyne) and silicon carbide ceramics therefrom.” U.S. (2006), 15 pp. CODEN: USXXAM US 6989428 B1 20060124 CAN 144:129423 AN 2006:65860.
5. ^ ^{a b c d} Rochow, E. "An Introduction to the Chemistry of the Silicones." New York: John Wiley & Sons, Inc., 1946. ISBN: 1443722863