thumb|180 px|Structure of [[trimethylsilanol]]

A silanol is a functional group in silicon chemistry with the connectivity Si–O–H. It is related to the hydroxy functional group (C–O–H) found in all alcohols. Silanols are often invoked as intermediates in organosilicon chemistry and silicate mineralogy. If a silanol contains one or more organic residues, it is an organosilanol.

Preparation

From alkoxysilanes

The first isolated example of a silanol was , reported in 1871 by Albert Ladenburg. He prepared the “silicol” by hydrolysis of (Et = ethyl group|).

Silanols are generally synthesized by hydrolysis of halosilanes, alkoxysilanes, or aminosilanes. Chlorosilanes are the most common reactants:

:R<sub>3</sub>Si&ndash;Cl + H<sub>2</sub>O → R<sub>3</sub>Si&ndash;OH + HCl

The hydrolysis of fluorosilanes requires more forcing reagents, i.e. alkali. The alkoxysilanes (silyl ethers) of the type are slow to hydrolyze. Compared to the silyl ethers, silyl acetates are faster to hydrolyze, with the advantage that the released acetic acid is less aggressive. For this reason silyl acetates are sometimes recommended for applications. In the solid state, silanols engage in hydrogen-bonding.

Most silanols have only one OH group, e.g. trimethylsilanol. Also known are some silanediols, e.g., diphenylsilanediol. For sterically bulky substituents, even silanetriols have been prepared. In chromatography, derivatization of accessible silanol groups in a bonded stationary phase with trimethylsilyl groups is referred to as endcapping. Organosilanols occur as intermediates in industrial processes such as the manufacturing of silicones. Moreover, organosilanols occur as metabolites in the biodegradation of small ring silicones in mammals.

thumb|Trisilanol intermediate in the formation of a cubic [[silsesquioxane]]

Biorelevance

Some silanediols and silanetriols inhibit hydrolytic enzymes such as thermolysin and acetylcholinesterase.

Parent silanols

Literally, silanol refers to a single compound with the formula (Chemical Abstracts number 14475-38-8). The family (n = 1, 2, 3, 4) are highly unstable and are mainly of interest to theoretical chemists. The perhydroxylated silanol, sometimes called orthosilicic acid, is often discussed in vague terms, but has not been well characterized.

References

  • EL Salmawy, M.S., Nakahiro, Y., and Wakamatsu, T. (1993). The role of silanol group in flotation separation of quartz from feldspar using non-ionic surfactants, 18th IMPC, pp.&nbsp;845–849, The Australian Institute of Mining and Metallurgical Engineering, Sydney, Australia.