Question

Show how the malonic ester synthesis can be used to prepare the following substituted acetic acids. (a) (b) (c)

Short answer

The malonic ester synthesis can be used to prepare substituted acetic acids. To demonstrate this, please provide the specific substituted acetic acids you wish to prepare so that a customized step-by-step synthesis can be provided.

Step-by-step solution

Esterification

To perform esterification, add diethyl malonate to an alkaline solution (like sodium ethoxide). Diethyl malonate reacts with the alkoxide to form a monoalkylated ester in a reversible nucleophilic substitution reaction. The reaction will be: \(C_2H_5O^− + H_2C(COOEt)_2 ⟶ C_2H_5OCOCH(COOEt)_2\)

Alkylation

In this step, the monoalkylated ester reacts with an alkyl halide to form a disubstituted product. First, treat the monoalkylated ester with an excess of strong base (sodium ethoxide) to abstract the acidic alpha-proton, generating a resonance-stabilized enolate anion: \(C_2H_5OCOCH(COOEt)_2 →−H^+ C_2H_5OCOCH(COOEt)_2^−\) Now, add a suitable alkyl halide (R-X), which will react with the enolate anion through a nucleophilic substitution (SN2) reaction forming the desired diethyl disubstituted malonate ester: \(C_2H_5OCOCH(COOEt)_2^− + R-X ⟶ C_2H_5OCOCR(COOEt)_2 + X^−\)

Decarboxylation

Heat the disubstituted malonate ester under acidic conditions (aqueous HCl) to hydrolyze the ester groups and promote decarboxylation. The decarboxylation reaction will remove one of the carboxylate groups, leaving the desired substituted acetic acid: \(C_2H_5OCOCR(COOEt)_2 + 3H_2O ⟶ HOOCR-COOH + 2CH_3CH_2OH\) For the given exercise, please list the original substituted acetic acids or desired end products to apply these steps and provide a custom step-by-step synthesis.