Trimethylsilanol

Trimethylsilanol (TMS) is an organosilicon compound with the formula (CH3)3SiOH. The Si centre bears three methyl groups and one hydroxyl group. It is a colourless volatile liquid.[3][4]

Trimethylsilanol
Structural formula of trimethylsilanol
Ball and stick model of trimethylsilanol
Names
Preferred IUPAC name
Trimethylsilanol[1]
Other names
Hydroxy(trimethyl)silane[1]
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.012.650
EC Number
  • 213-914-1
MeSH Trimethylsilanol
UNII
Properties
C3H10OSi
Molar mass 90.197 g·mol−1
Appearance Colourless liquid
Boiling point 99 °C (210 °F; 372 K)
Vapor pressure 21 mbar (20 °C) [2]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Occurrence and Production

Occurrence

TMS is a contaminant in the atmospheres of spacecraft, where it arises from the degradation of silicone-based materials.[5] Specifically, it is the volatile product from the hydrolysis of polydimethylsiloxane, which are generally terminated with trimethylsilyl groups:

(CH3)3SiO[Si(CH3)2O]nR + H2O → (CH3)3SiOH + HO[Si(CH3)2O]nR

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

Traces of trimethylsilanol, together with other volatile siloxanes, are present in biogas and landfill gas, again resulting from the degradation of silicones. As their combustion forms particles of silicates and microcrystalline quartz, which cause abrasion of combustion engine parts, they pose problems for the use of such gases in combustion engines.[6]

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.[7]

Trimethylsilanol is accessible by weakly basic hydrolysis, since the dimerization can thus be avoided.[8] Trimethylsilanol can also be obtained by the basic hydrolysis of hexamethyldisiloxane.[9]

Use

Like other silanols, trimethylsilanol is being tested for use as an antimicrobial agent.[10]

TMS is used for hydrophobic coating on silicate surfaces. It reacts with the silanol groups (R3SiOH) of the substrate, resulting in a layer of methyl groups.

Properties

Trimethylsilanol is a volatile organic liquid with a boiling point of 98 °C.[11] The heat of evaporation is 45.64 kJ·mol−1, the evaporation entropy 123 J·K−1·mol−1.[2] The vapor pressure function according to Antoine is obtained as log10(P/1 bar) = A − B/(T + C) (P in bar, T in K) with A = 5.44591, B = 1767.766 K and C = −44.888 K in a temperature range from 291 K to 358 K.[2] Below the melting point at −4.5 °C,[12] the compound solidifies in a monoclinic crystal lattice.[13] Trimethylsilanol is a weak acid with a pKa value of 11.[14] The acidity is comparable to that of orthosilicic acid, but much higher than the one of alcohols like tert-butanol (pKa 19[14]).

References
  1. Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 696. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
  2. Grubb, W.T.; Osthoff, R.C.: Physical Properties of Organosilicon Compounds. II. Trimethylsilanol and Triethylsilanol in J. Am. Chem. Soc. 75 (1953) 2230–2232; doi:10.1021/ja01105a061.
  3. Paul D. Lickiss: The Synthesis and Structure of Organosilanols, Advances in Inorganic Chemistry 1995, Volume 42, Pages 147–262, doi:10.1016/S0898-8838(08)60053-7.
  4. Vadapalli Chandrasekhar, Ramamoorthy Boomishankar, Selvarajan Nagendran: Recent Developments in the Synthesis and Structure of Organosilanols, Chem. Rev. 2004, volume 104, pp 5847–5910, doi:10.1021/cr0306135.
  5. Trimethylsilanol, Harold L. Kaplan, Martin E. Coleman, John T. James: Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Volume 1 (1994).
  6. http://epics.ecn.purdue.edu/bgi/Documents/Fall%25202009/Removal_of_Siloxanes_.pdf
  7. Didier Astruc: Organometallic Chemistry and Catalysis. Springer Science & Business Media, 2007, ISBN 978-3-540-46129-6, S. 331 (, p. 331, at Google Books).
  8. J.A. Cella, J.C. Carpenter: Procedures for the preparation of silanols in J. Organomet. Chem. 480 (1994), 23–23; doi:10.1016/0022-328X(94)87098-5
  9. M. Lovric, I. Cepanec, M. Litvic, A. Bartolincic, V. Vinkovic: Croatia Chem. Acta 80 (2007), 109–115
  10. Yun-mi Kim, Samuel Farrah, Ronald H. Baney (2006). "Silanol – A novel class of antimicrobial agent". Electronic Journal of Biotechnology. 9 (2): 176. doi:10.2225/vol9-issue2-fulltext-4.CS1 maint: multiple names: authors list (link)
  11. Stepovik, L. P.; Kazakina, S. V.; Martynova, I. M. in Russian Journal of General Chemistry – English Version 70 (2000) 1371–1377 oder Zhurnal Obshchei Khimii 70 (2000) 1459–1461.
  12. Batuew et al. in Doklady Akademii Nauk SSSR 95 (1954) 531.
  13. Template:ZNaturforsch
  14. 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.
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