Organosilanols
Organic compounds of the form R3–Si–OH
From Wikipedia, the free encyclopedia
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]
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):
![{\displaystyle {\mathrm {R} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {SiCl} {\vphantom {A}}_{\smash[{t}]{2}}{}+{}2\,\mathrm {HgO} {}\mathrel {\xrightarrow[{\mathrm {toluene} }]{{-80}{\vphantom {A}}^{\circ }\mathrm {C} }} {}\mathrm {R} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {Si} (\mathrm {OH} ){\vphantom {A}}_{\smash[{t}]{2}}{}+{}2\,\mathrm {Hg} {\vphantom {A}}^{0}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/e2e8b9b56ea709f9ed4762e1bbe42fd503c22585)
or by hydrolysis in the alkaline:[4]
![{\displaystyle {(\mathrm {H} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {C} ){\vphantom {A}}_{\smash[{t}]{3}}\mathrm {SiCl} {}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} {}\mathrel {\longrightarrow } {}(\mathrm {H} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {C} ){\vphantom {A}}_{\smash[{t}]{3}}\mathrm {SiOH} {}+{}\mathrm {HCl} }}](http://wikimedia.org/api/rest_v1/media/math/render/svg/10a5583be34ca6a41909395349114c2faef7f83f)
![{\displaystyle {\mathrm {R} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {SiH} {}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} {}\mathrel {\longrightarrow } {}\mathrm {R} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {SiOH} {}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{2}}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/02f9fad300130e612416b79c290a2746e01856f1)
The hydrolysis of silyl ethers generally proceeds only slowly:[4]
![{\displaystyle {(\mathrm {H} {\vphantom {A}}_{\smash[{t}]{5}}\mathrm {C} {\vphantom {A}}_{\smash[{t}]{2}}){\vphantom {A}}_{\smash[{t}]{3}}\mathrm {SiOC} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{5}}{}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} {}\mathrel {\longrightarrow } {}(\mathrm {H} {\vphantom {A}}_{\smash[{t}]{5}}\mathrm {C} {\vphantom {A}}_{\smash[{t}]{2}}){\vphantom {A}}_{\smash[{t}]{3}}\mathrm {SiOH} {}+{}\mathrm {HOC} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{5}}}}](http://wikimedia.org/api/rest_v1/media/math/render/svg/c7260b64f4944ae6a90ac3f23804533f039c86da)
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.
