An ionic organic compound created by the reaction of an alcohol or phenol with a metal.

Hydroxyl groups, -OH, the functional groups of alcohols, are mildly acidic. They won't react as an acid with most bases (e.g. sodium carbonate, which will react with carboxylic acids), but metals are basic enough to get them going. When an alcoholic or phenolic compound reacts with a metal, the hydrogen atom on the -OH group comes off and is replaced by the metal ion. Thus the alcohol acts as a base according to the Bronsted-Lowry theory. The original compound was covalent, but the alkoxide formed is ionic, with an oxygen anion and a metal cation.

Consider the reaction between ethanol and sodium:

    H   H
    |   |
H - C - C - O - H      +      Na
    |   |
    H   H

The hydrogen is replaced by the sodium:

    H   H
    |   |
H - C - C - O - Na     (really O- and Na+)
    |   |
    H   H
The resulting compound is known as sodium ethoxide. If the alcohol had been propanol, the product would be sodium propoxide, if phenol, then sodium phenoxide, etc.

Alkoxides are among the less common derivatives of alcohols. Their main use is in the synthesis of ethers and esters. In ester synthesis, the carboxylic acid is reacted with the alkoxide instead of the parent alcohol to make the reaction less reversible. In ether synthesis, the negative charge on the alkoxide oxygen is used to attack the carbon in a haloalkane and link the two molecules.

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