Question

Show how the acetoacetic ester synthesis can be used to prepare these compounds. (a) (b) (c)

Short answer

Question: Explain the role of the enolate ion in acetoacetic ester synthesis and describe the overall transformation of an ester into a new ketone. Answer: In acetoacetic ester synthesis, enolate ion plays a crucial role as a nucleophile, which is formed by deprotonating the ester using a strong base. The enolate ion is resonance-stabilized, allowing the negative charge to move between the carbonyl groups of the ester molecule. It then attacks an alkyl halide in an S_N2 reaction to form a new carbon-carbon bond. Finally, the ester group is hydrolyzed and decarboxylated to yield the desired ketone, thus transforming an ester into a new ketone.

Step-by-step solution

Understanding Acetoacetic Ester Synthesis

Acetoacetic ester synthesis is a process used to convert an ester into a new ketone. This reaction involves the formation of an enolate ion, which acts as a nucleophile and attacks an alkyl halide (usually an alkyl bromide) in an S_N2 reaction. The steps for this synthesis involve deprotonation of the ester, formation of the enolate ion, nucleophilic attack on alkyl halide, and finally, decarboxylation to form the desired ketone.

Deprotonation of the Ester

The first step in acetoacetic ester synthesis involves thed treatment of the ester compound with a strong base, such as sodium ethoxide (\(\ce{NaOEt}\)). This base abstracts the most acidic proton adjacent to the carbonyl group, forming a resonance-stabilized enolate ion.

Formation of the Enolate Ion

The enolate ion, formed in the previous step, is stabilized by resonance where the lone pair on the oxygen atom and the negative charge on the carbon atom can move between the two carbonyl groups of the ester molecule.

Nucleophilic Attack on Alkyl Halide

The negatively charged carbon atom of the enolate ion can now act as a nucleophile and attack an alkyl halide in an S_N2 reaction, replacing the halide group. This results in the formation of a new carbon-carbon bond, linking the ester and alkyl groups.

Hydrolysis and Decarboxylation

The final step of the acetoacetic ester synthesis involves hydrolyzing the ester group under acidic conditions, followed by a heat-induced decarboxylation. During hydrolysis, the ester is converted to a carboxylic acid. Subsequently, heating the carboxylic acid results in the loss of a carbon dioxide (\(\ce{CO2}\)) molecule, leaving behind the desired ketone. By combining these steps, we can successfully prepare various ketone compounds using acetoacetic ester synthesis. Each specific compound synthesis will require an appropriate ester starting material and alkyl halide for the desired end product.