Organosilanols

In organosilicon chemistry, organosilanols are a group of chemical compounds derived from silicon. More specifically, they are carbosilanes derived with a hydroxy group (−OH) on the silicon atom.[1] Organosilanols are the silicon analogs to alcohols. Silanols are more acidic and more basic than their alcohol counterparts and therefore show a rich structural chemistry characterized by hydrogen bonding networks which are particularly well studied for silanetriols.[2][3]

Structure of trimethylsilanol.

Preparation

Organosilanols can be obtained by hydrolysis of organohalosilanes, such as chlorotrimethylsilane. They can also be prepared by the oxidation of organosilanes with oxidizing agents (R = organic residue):

or by hydrolysis in the alkaline:[4]


The hydrolysis of silyl ethers generally proceeds only slowly:[4]

Hydrolysis of organosilanes is a first-order reaction. The hydrolysis rate of the Si-H bond depends on the type and number of organic residues. Thus, the hydrolysis rate of trialkylsilanes is significantly slower than that of triarylsilanes. This can be explained by a stronger increase in electron density on the silicon atom by the alkyl groups. Correspondingly, the reaction rate of the tri-n-alkylsilanes decreases in the series of ethyl, propyl, butyl groups. Trialkylsilanes with n-alkyl residues react by a factor of 10 faster than the analogous silanes with branched alkyl residues.[5]

Classification

Depending on the substitution pattern of the silicon atom, a further distinction can be made. Organosilanols are classified as:

  • organosilanetriols, when three hydroxy groups and an organic residue are bound to a silicon atom, e. g. methylsilanetriol, phenylsilanetriol
  • organosilandiols, when two hydroxy groups and two organic residues are bound to a silicon atom, e. g. dimethylsilanediol, diphenylsilanediol
  • organosilanols, when one hydroxy group and three organic residues are bound to a silicon atom, e. g. trimethylsilanol, triethylsilanol or triphenylsilanol.


References
  1. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "silanols". doi:10.1351/goldbook.S05664
  2. Paul D. Lickiss (1995), "The synthesis and structure of organosilanols", Advances in Inorganic Chemistry, vol. 42, pp. 147–262, doi:10.1016/S0898-8838(08)60053-7
  3. Rudolf Pietschnig, Stefan Spirk (2016), "The Chemistry of Organo Silanetriols", Coordination Chemistry Reviews, vol. 323, pp. 87–106, doi:10.1016/j.ccr.2016.03.010
  4. Barry Arkles. "Silanes" (pdf). Gelest. p. 50. Retrieved 2016-12-10.
  5. G. Schott, C. Harzdorf (October 1960), "Silane. I Alkalische Solvolyse von Triorganosilanen", Zeitschrift für anorganische und allgemeine Chemie (in German), vol. 306, no. 3–4, pp. 180–190, doi:10.1002/zaac.19603060306
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