Trimethylsilanol

 ( Silanols ) 

Trimethylsilanol ( TMS) is an organosilicon compound with the formula . The Si centre bears three methyl groups and one hydroxyl group. It is a colourless volatile liquid.Paul D. Lickiss: The Synthesis and Structure of Organosilanols, Advances in Inorganic Chemistry 1995, Volume 42, Pages 147–262, .Vadapalli Chandrasekhar, Ramamoorthy Boomishankar, Selvarajan Nagendran: Recent Developments in the Synthesis and Structure of Organosilanols, Chem. Rev. 2004, volume 104, pp 5847–5910, .

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Occurrence TMS is a contaminant in the atmospheres of spacecraft, where it arises from the degradation of silicone-based materials. Trimethylsilanol, Harold L. Kaplan, Martin E. Coleman, John T. James: Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Volume 1 (1994). Specifically, it is the volatile product from the hydrolysis of polydimethylsiloxane, which are generally terminated with trimethylsilyl groups:

TMS and related volatile are formed by hydrolysis of silicones-based containing materials, which are found in and cosmetic products.

Traces of trimethylsilanol, together with other volatile , are present in biogas and landfill gas, again resulting from the degradation of . As their combustion forms particles of and microcrystalline quartz, which cause abrasion of combustion engine parts, they pose problems for the use of such gases in combustion engines.http://epics.ecn.purdue.edu/bgi/Documents/Fall%25202009/Removal_of_Siloxanes_.pdf

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Production Trimethylsilanol cannot be produced by simple hydrolysis of chlorotrimethylsilane as this reaction leads to the etherification product hexamethyldisiloxane, because of the by-product hydrochloric acid.Didier Astruc: Organometallic Chemistry and Catalysis. Springer Science & Business Media, 2007, , S. 331 ().$$\backslash ce\{2ClSi(CH3)3\; ->\{\}\backslash atop\backslash ce\{+H2O,\}\; \backslash ce\{2HOSi(CH3)3\; ->\{\}\backslash atop\backslash ce\{-H2O\}\; (CH3)3Si-O-Si(CH3)3\}$$

Trimethylsilanol is accessible by weakly basic hydrolysis of chlorotrimethylsilane, since the dimerization can thus be avoided.J.A. Cella, J.C. Carpenter: Procedures for the preparation of silanols in J. Organomet. Chem. 480 (1994), 23–23; Trimethylsilanol can also be obtained by the basic hydrolysis of hexamethyldisiloxane.M. Lovric, I. Cepanec, M. Litvic, A. Bartolincic, V. Vinkovic: Croatia Chem. Acta 80 (2007), 109–115

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Reactions Trimethylsilanol is a weak acid with a p K_a value of 11.T. Kagiya, Y. Sumida, T. Tachi: An Infrared Spectroscopic Study of hydrogen Bonding Interaction. Structural Studies of Proton-donating and -accepting Powers in Bull. Chem. Soc. Jpn. 43 (1970), 3716–3722. The acidity is comparable to that of orthosilicic acid, but much higher than the one of alcohols like Tert-Butanol (p K_a 19). Deprotonation with sodium hydroxide gives sodium trimethylsiloxide.

TMS reacts with the Silanol () giving silyl ethers.

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Structure

In terms of its structure, the molecule is tetrahedral. The compound forms monoclinic crystals.R. Minkwitz, S. Schneider: Die Tieftemperaturkristallstruktur von Trimethylsilanol. In: Zeitschrift für Naturforschung B. 53, 1998, S. 426–429 ( PDF, freier Volltext).

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Additional properties

The heat of evaporation is 45.64 kJ·mol⁻¹, the evaporation entropy 123 J·K⁻¹·mol⁻¹. The vapor pressure function according to Antoine is obtained as log₁₀(P/1bar) = A − B/(T + C) (P in bar, T in K) with A = 5.44591, B = 1767.766K and C = −44.888K in a temperature range from 291K to 358K. Below the melting point at −4.5 °C,Batuew et al. in Doklady Akademii Nauk SSSR 95 (1954) 531. The ¹H NMR in CDCl₃ shows a singlet at δ=0.14 ppm.

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Bioactivity

Like other silanols, trimethylsilanol exhibits antimicrobial properties.

Categories: Silanols, Trimethylsilyl Compounds

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