Trimethylsilanol


Trimethylsilanol is an organosilicon compound with the formula 3SiOH. The Si centre bears three methyl groups and one hydroxyl group. It is a colourless volatile liquid.

Occurrence and Production

Occurrence

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

Production

Trimethylsilanol can not be produced by simple hydrolysis of chlorotrimethylsilane, as this reaction leads to the etherification product hexamethyldisiloxane, because of the by-product hydrochloric acid.
Trimethylsilanol is accessible by weakly basic hydrolysis, since the dimerization can thus be avoided. Trimethylsilanol can also be obtained by the basic hydrolysis of hexamethyldisiloxane.

Use

Like other silanols, trimethylsilanol is being tested for use as an antimicrobial agent.
TMS is used for hydrophobic coating on silicate surfaces. It reacts with the silanol groups of the substrate, resulting in a layer of methyl groups.

Properties

Trimethylsilanol is a volatile organic liquid with a boiling point of 98 °C. 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 = A− with A = 5.44591, B = 1767.766 and C = -44.888 in a temperature range from 291 K to 358 K. Below the melting point at -4.5 °C, the compound solidifies in a monoclinic crystal lattice. Trimethylsilanol is a weak acid with a pKa value of 11. The acidity is comparable to that of orthosilicic acid, but much higher than the one of alcohols like tert-butanol.