Silanol
Encyclopedia
Silanol, also known as silyl alcohol, is a chemical
with formula
Si
H
3O
H. It is the simplest silicon alcohol
, and is a heavy, volatile
, color
less, flammable liquid. At room temperature it is a polar liquid
Silanol burns in air forming silicon dioxide and water
:
Silanols are compound
s containing silicon
atoms to which hydroxy
substituent
s bond directly. They are similar to alcohol
s just as silane
s are similar to alkane
s.
When the hydroxy group is principal, silanols are named by adding the suffix –ol to their mother name.
If the hydroxy group is not the principal one, silanols are named by using the prefix hydroxy- according to the substitutive nomenclature.
These rules are almost the same as those for alcohol
s, with the exception that silane
is used as the mother hydride.
. The first example was triethylsilanol. At that time, they were called silicols, a word that he coined.
of halosilanes, alkoxysilanes, or aminosilanes; by oxidation of hydrosilanes; or by hydrolysis
of arylsilanes in the presence of a strong acid
.
very easily, yielding disiloxanes in the presence of acid
, base
, or even heat
.
Because of this property of self-condensation, the synthesis and isolation of silanols are difficult.
Silanols have hydroxy
substituents, and so they have hydrogen bonding to each other in solution and even in crystals.
Silanols can also be crosslinked using borax
, or boric acid
, to form 3-dimensional silicon gels.
Silanols exist not only as chemical compound
s but also on the surface of silica.
From the viewpoint of organometallic chemistry
, silica can be considered as an enormous ligand
, and it is used as support for catalysts of many reactions.
In chromatography
, derivitization of accessible silanol groups in a bonded stationary phase with trimethylsilyl
groups is referred to as endcapping
.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
Si
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
3O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
H. It is the simplest silicon alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
, and is a heavy, volatile
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
, color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
less, flammable liquid. At room temperature it is a polar liquid
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
Silanol burns in air forming silicon dioxide and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
:
- 2 SiH3OH + 3 O2 → 2 SiO2 + 4 H2O
Silanols are compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s containing silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
atoms to which hydroxy
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
substituent
Substituent
In organic chemistry and biochemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon...
s bond directly. They are similar to alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s just as silane
Silane
Silane is a toxic, extremely flammable chemical compound with chemical formula SiH4. In 1857, the German chemists and Friedrich Woehler discovered silane among the products formed by the action of hydrochloric acid on aluminum silicide, which they had previously prepared...
s are similar to alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...
s.
When the hydroxy group is principal, silanols are named by adding the suffix –ol to their mother name.
If the hydroxy group is not the principal one, silanols are named by using the prefix hydroxy- according to the substitutive nomenclature.
These rules are almost the same as those for alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s, with the exception that silane
Silane
Silane is a toxic, extremely flammable chemical compound with chemical formula SiH4. In 1857, the German chemists and Friedrich Woehler discovered silane among the products formed by the action of hydrochloric acid on aluminum silicide, which they had previously prepared...
is used as the mother hydride.
History
Silanols were first synthesized in 1871 by Albert LadenburgAlbert Ladenburg
Albert Ladenburg was a German chemist.-Biography:Ladenburg was a member of a well known Jewish family in Mannheim. He was educated at a Realgymnasium at Mannheim and then, after the age of 15, at the technical school of Karlsruhe, where he studied mathematics and modern languages...
. The first example was triethylsilanol. At that time, they were called silicols, a word that he coined.
Synthesis
Silanols are generally synthesized by hydrolysisHydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of halosilanes, alkoxysilanes, or aminosilanes; by oxidation of hydrosilanes; or by hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of arylsilanes in the presence of a strong acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
.
Properties
Silanols are generally dehydratedDehydration reaction
In chemistry and the biological sciences, a dehydration reaction is usually defined as a chemical reaction that involves the loss of water from the reacting molecule. Dehydration reactions are a subset of elimination reactions...
very easily, yielding disiloxanes in the presence of acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
, base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
, or even heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
.
Because of this property of self-condensation, the synthesis and isolation of silanols are difficult.
Silanols have hydroxy
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
substituents, and so they have hydrogen bonding to each other in solution and even in crystals.
Silanols can also be crosslinked using borax
Borax
Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.Borax has a wide variety of uses...
, or boric acid
Boric acid
Boric acid, also called hydrogen borate or boracic acid or orthoboric acid or acidum boricum, is a weak acid of boron often used as an antiseptic, insecticide, flame retardant, as a neutron absorber, and as a precursor of other chemical compounds. It exists in the form of colorless crystals or a...
, to form 3-dimensional silicon gels.
Silanols exist not only as chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s but also on the surface of silica.
From the viewpoint of organometallic chemistry
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
, silica can be considered as an enormous ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
, and it is used as support for catalysts of many reactions.
In chromatography
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
, derivitization of accessible silanol groups in a bonded stationary phase with trimethylsilyl
Trimethylsilyl
A trimethylsilyl group is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si3], which is in turn bonded to the rest of a molecule...
groups is referred to as endcapping
Endcapping
Endcapping refers in chromatography to the replacement of accessible silanol groups in a bonded stationary phase by trimethylsilyl groups.Endcapping technology prevents the tailing of a polar compound's peak and shows very high durability even with an alkaline mobile phase because of the strong...
.