Malonic ester synthesis

The malonic ester synthesis is a reaction in the organic chemistry for the preparation of alkylated malonic acid esters. It is used to obtain, after saponification and subsequent decarboxylation, substituted acetic acids. You can also doubly alkylated and shall receive double substitution with the same residual symmetrical disubstituted acetic acids, but you can introduce different substituents in two steps and then receives asymmetrical acetic acid derivatives.

Mechanism

In the first step of the malonate i.e. deprotonated by a base such as an alkoxide in the α - position to the methyl group. Subsequently, a haloalkane from the deprotonated α - carbon, nucleophilic attack. This gives an α -alkylated malonic ester. The ester groups are hydrolyzed under acid catalysis. Exposed to the heat decarboxylated (CO2 is eliminated ) below the previously formed dicarboxylic acid.

Operation

By flanking the α - carbon by two ester groups are bonded hydrogen atoms therein especially acidic ( pKa = 13). Consequently, deprotonation is favored at this position. The ester groups can be hydrolyzed under acid catalysis ( ester hydrolysis ). Due to the resulting carboxylic acid in β - position a decarboxylation is greatly facilitated by heating, and is promoted by the acidic reaction conditions still further. The nucleophilic substitution of the halogen alkane follows an SN2 mechanism. Accordingly, branched alkyl groups of the alkyl halide unfavorable because of the steric hindrance of the reaction. With respect to the nucleophilic properties of a base, a base should be used for the same ester at a substitution of one of the carbonyl carbons. For example, diethyl malonate, ethanolate.