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[[Image:Alkoxide.png|thumb|right|The structure of a typical alkoxide group.]] An '''alkoxide''' is the [[conjugate base]] of an [[alcohol]] and therefore consists of an organic group bonded to a negatively charged [[oxygen]] atom.  They can be written as RO<sup>&ndash;</sup>, where R is the organic substituent.  Alkoxides are strong [[Base (chemistry)|bases]] and, when R is not bulky, good [[nucleophile]]s and good ligands.  .  Alkoxides, although generally not stable in [[protic solvent]]s such as water, occur widely as intermediates in various reactions, including the [[Williamson ether synthesis]].  [[Transition metal]] alkoxides are widely used for coatings and as [[catalyst]]s.<ref>Bradley, D. C.; Mehrotra, R.; Rothwell, I.; Singh, A. “Alkoxo and Aryloxo Derivatives of Metals” Academic Press, San Diego, 2001. ISBN 0121241408.</ref>

[[Enolate]]s are unsaturated alkoxide derived by deprotonation of a C-H bond adjacent to a [[ketone]] or [[aldehyde]].  The nucleophilic center for simple alkoxides is located on the oxygen, whereas the nucleophilic site on enolates is delocalized onto both carbon and oxygen sites.

Phenoxides represent a special class of anions that are closely related to alkoxides, except the organic substitutent is a derivative of [[benzene]].  Phenol is significantly more acidic than a typical alcohol, thus phenoxides are correspondingly less basic and less nucleophilic.  They are however often easier to handle and afford derivatives that are more crystalline than the alkoxides.

==Preparation==
===From reducing metals===
Alkoxides can be produced by several routes starting from an [[alcohol]].  Highly reducing metals react directly with alcohols to give the corresponding metal alkoxide.  The alcohol serves as an [[acid]], and [[hydrogen]] is produced as a by-product.  A classic case is sodium methoxide produced by the addition of sodium metal to methanol:
:CH<sub>3</sub>OH  + Na   &rarr;  CH3ONa + 1⁄2H<sub>2</sub>
Other [[alkali metal]]s can be used in place of sodium, and most alcohols can be used in place of methanol.

===From electrophilic chlorides===
The tetrachloride of titanium reacts with alcohols to give the corresponding tetraalkoxides, concomitant with the evolution of [[hydrogen chloride]]:
:[[Titanium tetrachloride|TiCl<sub>4</sub>]]  +  4 [[isopropanol|(CH<sub>3</sub>)<sub>2</sub>CHOH]]  &rarr;  [[Titanium isopropoxide|Ti(OCH(CH<sub>3</sub>)<sub>2</sub>}<sub>4</sub>]]  +  4  HCl
The reaction can be accelerated by the addition of a base, such as a [[tertiary amine]].  Many other metal and main group halides can be used instead of titanium, for example SiCl<sub>4</sub>, ZrCl<sub>4</sub>, and PCl<sub>3</sub>. 

===By metathesis reactions===
Many alkoxides are prepared by salt-forming reactions from a metal chloride and sodium alkoxide:
:NaOR  +  MCl<sub>n</sub>  &rarr;  M(OR)<sub>n</sub>  +  n NaCl
Such reactions are favored by the [[lattice energy]] of the NaCl, and purification of the product alkoxide is simplified by the fact that NaCl is insoluble in common organic solvents.

===By electrochemical processes===
Many alkoxides can be prepared by anodic dissolution of the corresponding metals in water-free alcohols in the presence of electroconductive additive. The metals may be Sc, Ga, Y, La, Ln, Si, Ti, Ge, Zr, Hf, Nb, Ta, Mo, W, Fe, Co, Ni, Re, etc. The conductive additive may be lithium chloride, quaternary ammonium halogenide, or other. Some examples of metal alkoxides obtained by this technique: Ti(OC<sub>3</sub>H<sub>7</sub>-''iso'')<sub>4</sub>, Nb<sub>2</sub>(OCH<sub>3</sub>)<sub>10</sub>, Ta<sub>2</sub>(OCH<sub>3</sub>)<sub>10</sub>, [MoO(OCH<sub>3</sub>)<sub>4</sub>]<sub>2</sub>, Re<sub>2</sub>O<sub>3</sub>(OCH<sub>3</sub>)<sub>6</sub>, Re<sub>4</sub>O<sub>6</sub>(OCH<sub>3</sub>)<sub>12</sub>, and Re<sub>4</sub>O<sub>6</sub>(OC<sub>3</sub>H<sub>7</sub>-''iso'')<sub>10</sub>.

==Properties==
===Hydrolysis and transesterification===
Metal alkoxides [[hydrolysis|hydrolyse]] with water according to the following equation:
:2 L<sub>n</sub>MOR  +  H<sub>2</sub>O  &rarr;  [L<sub>n</sub>M]<sub>2</sub>O  +  2 ROH
where R is an organic substituent and L is an unspecified [[ligand]] (often an alkoxide)
A well-studied case is the irreversible hydrolysis of titanium ethoxide:
:1/n [Ti(OCH<sub>2</sub>CH<sub>3</sub>)<sub>4</sub>]<sub>n</sub>  +  2 H<sub>2</sub>O  &rarr;  TiO<sub>2</sub>  +  4 HOCH<sub>2</sub>CH<sub>3</sub>
By controlling the [[stoichiometry]] of [[steric hindrance|steric]] properties of the alkoxide, such reactions can be arrested leading to metal-oxy-alkoxide [[cluster compound|clusters]].  Other alcohols can be employed in place of water.  In this way one alkoxide can be converted to another, a process sometimes called [[transesterification]]. Sodium methoxide, for example, is commonly used for this purpose, a reaction that is relevant to the production of "[[bio-diesel]]."  The position of the [[chemical equilibrium|equilibrium]] can be controlled by the [[acidity]] of the alcohol; for example [[phenols]] typically react with alkoxides to release alcohols, giving the corresponding phenoxide.  More simply, the trans-esterification can be controlled by selectively [[evaporation|evaporating]] the more volatile component.  In this way, ethoxides can be converted to butoxides, since ethanol (b.p. 78 °C) is more volatile than butanol (b.p. 118 °C).

===Formation of oxo-ligands===
Many metal alkoxide compounds also feature oxo-ligands in their coordination sphere. Oxo-ligands typically arise via the hydrolysis, often accidentally, and via ether elimination:
:2 L<sub>n</sub>MOR  &rarr;  [L<sub>n</sub>M]<sub>2</sub>O  +  R<sub>2</sub>O

Additionally, low valent metal alkoxides are susceptible to oxidation by air.

===Formation of polynuclear and heterometallic derivatives===
Characteristically, transition metal alkoxides and oxides are polynuclear, that is they contain more than one metal.  Oxides and alkoxides are sterically undemanding and highly basic ligands that tend to bridge metals. 

Upon the isomorphic substitution of metal atoms close in properties crystalline complexes of variable composition are formed. The metal ratio in such compounds can vary over a broad range. For instance, the substitution of [[molybdenum]] and [[tungsten]] for [[rhenium]] in the complexes Re<sub>4</sub>O<sub>6-y</sub>(OCH<sub>3</sub>)<sub>12+y</sub> allowed one to obtain complexes Re<sub>4-x</sub>Mo<sub>x</sub>O<sub>6-y</sub>(OCH<sub>3</sub>)<sub>12+y</sub> in the range of x=[0 to 2.82] and Re<sub>4-x</sub>W<sub>x</sub>O<sub>6-y</sub>(OCH<sub>3</sub>)<sub>12+y</sub> in the range of x=[0 to 2].

===Thermal stability===
Many metal alkoxides [[thermal decomposition|thermally decompose]] in the range ~100-300 °C. Depending on process conditions, this thermolysis can afford [[nanometer|nanosized]] powders of oxide or metallic phases. This approach is a basis of processes of fabrication of functional materials intended for aircraft, space, electronic fields, and chemical industry: individual oxides, their solid solutions, complex oxides, powders of metals and alloys active towards sintering.  Decomposition of mixtures of mono- and heterometallic alkoxide derivatives has also been examined. This method represents a prospective approach possessing an advantage of capability of obtaining functional materials with increased phase and chemical homogeneity and controllable grain size (including the preparation of nanosized materials) at relatively low temperature (less than 500-900°C) as compared with the conventional techniques.

==Illustrative alkoxides==
[[Image:ReOOMe.jpg|thumb||The structure of tetranuclear rhenium oxomethoxide (hydrogen atoms omitted for the sake of simplicity)]]
*[[titanium isopropoxide]], used as a catalyst in [[organic synthesis]] and a precursor to TiO<sub>2</sub>.
*[[aluminium isopropoxide]], used as a reagent in organic synthesis.
*[[tetraethylorthosilicate]], used as a precursor to SiO<sub>2</sub>.
*Potassium tert-butoxide, used as a base for organic [[elimination reaction]]s.
*Rhenium oxomethoxide Re<sub>4</sub>O<sub>6</sub>(OCH<sub>3</sub>)<sub>12</sub>, a tetranuclear rhenium derivative.

==References==
<references/>
* P.A. Shcheglov, D.V. Drobot.  ''Rhenium Alkoxides (Review)''. Russian Chemical Bulletin. 2005. V. 54, No. 10. P. 2247-2258. [http://dx.doi.org/10.1007/s11172-006-0106-5 DOI: 10.1007/s11172-006-0106-5]

* N.Ya. Turova.  ''Metal oxoalkoxides. Synthesis, properties and structures (Review)''. Russian Chemical Reviews. 2004. V. 73, No. 11. P. 1041-1064. [http://dx.doi.org/10.1070/RC2004v073n11ABEH000855 DOI: 10.1070/RC2004v073n11ABEH000855]

[[Category:Functional groups]]
[[Category:Bases]]

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[[et:Alkoholaadid]]
[[ja:アルコキシド]]
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