Alcoholates

Alcoholates from top to bottom: General formula of a sodium alcoholate and a lithium alcoholate. Formula of sodium methoxide and lithium methoxide. The alcoholate anion is marked in blue . R is an aliphatically bonded radical.

Alcoholates , also known as alkoxides , are salts of metal cations and alcoholate anions . The general formula is (RO) _n M (M = metal ion; n corresponds to the valence of this metal ion). Alcoholate ions arise through deprotonation from alcohols . No alcoholates can be produced in an aqueous medium because the hydroxide ion is too weakly basic to deprotonate the hydroxyl group of the alcohols. That is why stronger bases such as sodium amide or elemental sodium are used. Alcoholates are used, among other things, for ether synthesis and as condensation, deprotonating and alkylating agents.

presentation

Alcoholates can be synthesized by reacting elemental alkali metals with alcohols .

For example, sodium ethoxide (sodium ethoxide, C ₂ H ₅ ONa) is formed as a white to yellowish, hygroscopic powder through the action of sodium on ethanol , whereby hydrogen gas escapes:

${\displaystyle \mathrm {2\ C_{2}H_{5}OH+2\ Na\longrightarrow 2\ C_{2}H_{5}ONa+H_{2}\uparrow } }$

Ethanol reacts with sodium to form sodium ethanolate and hydrogen.

properties

In their pure form, alcoholates are strongly basic solids, but they attract water vapor from the air and gradually dissolve, creating the corresponding alcohol and metal hydroxide , e.g. B. after:

${\displaystyle \mathrm {C_{2}H_{5}ONa+H_{2}O\longrightarrow C_{2}H_{5}OH+NaOH} }$

Sodium ethanolate and water produce ethanol and sodium hydroxide .

Usage and reactions

Alcoholates are used industrially in asymmetric ether synthesis ( Williamson ether synthesis with haloalkanes ) (1) or as strong bases. Esters can be prepared with carboxylic acid halides (2); secondary amines are obtained with primary amines (3). Upon contact with water , alcoholates react in an acid-base reaction to form the corresponding alcohol and hydroxide ions (4).

${\displaystyle \mathrm {1)\ R^{1}{-}O^{-}+X-R^{2}\longrightarrow R^{1}{-}O{-}R^{2}+X^{-}} }$

${\displaystyle \mathrm {2)\ R^{1}{-}O^{-}+X{-}(CO){-}R^{2}\longrightarrow R^{1}{-}O{-}(CO){-}R^{2}+X^{-}} }$

${\displaystyle \mathrm {3)\ R^{1}{-}O^{-}+H_{2}N{-}R^{2}\longrightarrow R^{1}{-}NH{-}R^{2}+OH^{-}} }$

${\displaystyle \mathrm {4)\ R{-}O^{-}+H_{2}O\longrightarrow R{-}OH+OH^{-}} }$

Alcoholates are mainly used by the agricultural and pharmaceutical industries . Alcoholates are also used in the production of biodiesel and cosmetics .

Furthermore, alcoholates are increasingly used in sol-gel processes for the production of thin films , nanoparticles and highly porous materials. In this way, functional (e.g. self-disinfecting layers activated by UV light), optical (e.g. anti-reflective layers , porous silicon dioxide ) and electronically active (semiconducting) layers (e.g. indium tin oxide , zinc oxide and titanium dioxide ) can be created become.

See also

• Methanolates
• Ethanolates
• Propanolates

Web links

• Manufacturer information from Evonik
• Manufacturer information of BASF
• Entry on alcoholates. In: Römpp Online . Georg Thieme Verlag, accessed on August 13, 2015.