Diethyl malonate

Diethyl malonate, also known as DEM, is the diethyl ester of malonic acid. It occurs naturally in grapes and strawberries as a colourless liquid with an apple-like odour, and is used in perfumes. It is also used to synthesize other compounds such as barbiturates, artificial flavourings, vitamin B1, and vitamin B6.

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Chemistry

Malonic acid is a rather simple dicarboxylic acid, with two carboxyl groups close together in its molecule. In forming diethyl malonate from malonic acid, the hydroxyl group (-OH) on both of the carboxyl groups is replaced by an ethoxy group (-OEt; -OCH₂CH₃). The methylene group (-CH₂-) in the middle of the malonic part of the diethyl malonate molecule is neighboured by two carbonyl groups (-C(=O)-).

Acidity

The hydrogen atoms on the carbon adjacent to the a carbonyl group in a molecule is slightly more acidic than hydrogen atoms on a carbon adjacent to alkyl groups. (This is known as the α position with respect to the carbonyl.) The hydrogen atoms on a carbon adjacent to two carbonyl groups are even more acidic because on the – the carbonyl groups helps stabilize the carbanion resulting from the removal of a proton from the methylene group between them.

This carbanion can be made from treating diethyl malonate with a base such as sodium ethoxide in ethanol. If aqueous sodium hydroxide were used, base hydrolysis of the ester can happen giving sodium malonate and ethanol. When sodium ethoxide is used, instead, any nucleophilic attack at the carboxylate by the ethoxide will not give any side product. Thus sodium ethoxide is preferred.

This carbanion is neutralized by the sodium cation from the sodium ethoxide. This resulting salt is useful in malonic ester syntheses.

Other examples of 1,3-diketo compounds with labile hydrogens include acetylacetone, acetoacetate esters. Synthetically, malonic esters are often used in Claisen ester condensations because unwanted self-condensation reactions are avoided. Another malonate reaction is the Malonic ester synthesis:

forming a monosubstituted acetic acid.

See also

• Barbituric acid