organosilicon chemistry Organosilicon chemistry is the study of organometallic compounds containing carbon–silicon bonds, to which they are called organosilicon compounds. Most organosilicon compounds are similar to the ordinary organic compounds, being colourless, fl ...

, organosilanols are a group of

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

s derived from

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

. More specifically, they are carbo

silane Silane (Silicane) is an inorganic compound with chemical formula . It is a colorless, pyrophoric gas with a sharp, repulsive, pungent smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental ...

s derived with a

hydroxy group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

() on the silicon atom. Organosilanols are the silicon analogs to

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

s. Silanols are more acidic and more basic than their alcohol counterparts and therefore show a rich structural chemistry characterized by

hydrogen bonding In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

networks which are particularly well studied for silanetriols.

Preparation

Organosilanols can be obtained by hydrolysis of organohalosilanes, such as

chlorotrimethylsilane Trimethylsilyl chloride, also known as chlorotrimethylsilane is an organosilicon compound ( silyl halide), with the formula , often abbreviated or TMSCl. It is a colourless volatile liquid that is stable in the absence of water. It is widely us ...

. They can also be prepared by the

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

of organosilanes with oxidizing agents (R =

organic residue Organic matter, organic material or natural organic matter is the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come fro ...

): :R2SiCl2 + 2 HgO -> 80^Ctoluene] R2Si(OH)2 + 2 Hg^0 or by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

in the

alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...

: :(H3C)3SiCl + H2O -> (H3C)3SiOH + HCl :R3SiH + H2O -> R3SiOH + H2 The hydrolysis of silyl ethers generally proceeds only slowly: :(H5C2)3SiOC2H5 + H2O -> (H5C2)3SiOH + HOC2H5 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 tri

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

silanes is significantly slower than that of tri

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...

silanes. 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.

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 Diphenylsilanediol, Ph2Si(OH)2, is a silanol. The tetrahedral molecule forms hydrogen-bonded columns in the solid state. It can be prepared by hydrolysis of diphenyldichlorosilane Ph2SiCl2. Diphenylsilanediol can act as an anticonvulsant, in a si ...

* organosilanols, when one hydroxy group and three organic residues are bound to a silicon atom, e. g.

trimethylsilanol Trimethylsilanol (TMS) is an organosilicon compound with the formula . The Si centre bears three methyl groups and one hydroxyl group. It is a colourless volatile liquid.Paul D. Lickiss: ''The Synthesis and Structure of Organosilanols'', Advances i ...

, triethylsilanol or triphenylsilanol.

References

Organosilicon compounds Silanols {{Commonscat, Organosilanols, Organosilanole