Question

\(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COOEt} \frac{\text { (i) } \mathrm{NaOEt}}{\text { (ii) } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}} \mathrm{A} \frac{\text { (i) dil. HCl }}{\text { (ii) Heat }}\) Products; Products are not in excess (a) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}+\mathrm{CO}_{2}+\mathrm{EtOH}\) (b) \(2 \mathrm{~mol}\) of \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}+\mathrm{CO}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}+2 \mathrm{EtOH}\) (d) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}+\mathrm{EtOH}+\mathrm{CO}_{2}\)

Short answer

The correct product is (d): \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3} + \mathrm{EtOH} + \mathrm{CO}_{2} \).

Step-by-step solution

Understand the Reactants and Reaction Conditions

Analyze the given reactants: \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COOEt} \) with \( \mathrm{NaOEt} \) and \( \mathrm{CH}_{3} \mathrm{CH}_{2}\mathrm{Br} \). The reaction involves an enolate formation followed by alkylation using an alkyl halide. The reaction is then followed by acid hydrolysis and decarboxylation under heat.

Formation of Enolate

The first step involves the generation of an enolate ion from the diketone ester \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COOEt} \) using \( \mathrm{NaOEt} \). The alpha hydrogen is acidic and gets deprotonated, forming the enolate ion.

Alkylation Step

The enolate ion, now nucleophilic, attacks the ethyl bromide (\( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br} \)), resulting in the formation of compound \( \mathrm{A} \, (\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{COOEt}) \), where the ester has been alkylated at the alpha position.

Acid Hydrolysis and Decarboxylation

Compound \( \mathrm{A} \) is then treated with dilute \( \mathrm{HCl} \). This hydrolyzes the ester to a carboxylic acid. Upon heating, decarboxylation occurs, resulting in the formation of \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3} \), with \( \mathrm{CO}_{2} \) and \( \mathrm{EtOH} \) as by-products.

Identifying the Resulting Products

The expected products are \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3} \), \( \mathrm{EtOH} \), and \( \mathrm{CO}_{2} \). Compare with the given options to find a match.

Key concepts

Enolate Formation

In organic chemistry, enolate formation is a key step in various reactions, notably in the transformation of diketone esters such as \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COOEt} \). This process begins when a base like \( \mathrm{NaOEt} \) deprotonates the acidic alpha hydrogen atom of the ester. The alpha hydrogen is the hydrogen atom bonded to the carbon atom next to the carbonyl group of the ester.

This deprotonation process results in the formation of an enolate ion, a resonance-stabilized ion that can exhibit nucleophilic properties. The enolate ion has a high electron density on the carbon atom adjacent to the oxygen, making it a prime candidate for nucleophilic attacks in subsequent chemical reactions.

Enolate chemistry is fundamental for forming new carbon-carbon bonds, which is why understanding the concept is crucial for further organic synthesis reactions.

Alkylation Reaction

After forming the enolate, we move to the alkylation step. In this reaction, the enolate ion acts as a nucleophile. It attacks the electrophilic alkyl halide, in this case, ethyl bromide \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br} \).

This nucleophilic attack leads to the substitution of the bromide ion in the ethyl bromide, resulting in the formation of a new carbon-carbon bond. The product formed at this stage is the compound \( \mathrm{A} \), with the structure \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{COOEt} \). The alkyl group from the ethyl bromide is now attached to the carbon that was initially part of the enolate ion.

Alkylation reactions are a critical method in organic synthesis for building complex molecules by lengthening carbon chains.

Ester Hydrolysis

Ester hydrolysis is an essential reaction where an ester is converted into a carboxylic acid through the action of an acid or a base, often involving water. In our case, the compound \( \mathrm{A} \) is treated with dilute hydrochloric acid \( \mathrm{HCl} \).

The \( \mathrm{HCl} \) acid helps to catalyze the hydrolysis, leading the ester bond to break and form the corresponding carboxylic acid. This reaction liberates alcohol, such as ethanol \( \mathrm{EtOH} \) in this context.

Ester hydrolysis is a pivotal step in synthetic pathways where the introduction of a carboxylic acid functionality is needed, offering possibilities for further transformations.

Decarboxylation

Decarboxylation is a significant chemical reaction in which a carboxyl group is removed from a molecule, releasing carbon dioxide \( \mathrm{CO}_{2} \). In our reaction, this process happens after ester hydrolysis.

Upon heating compound \( \mathrm{A} \), the carboxylic acid group is decarboxylated to form \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3} \). This decarboxylation step is crucial as it helps in simplifying the molecule structure by reducing it, an essential method in organic synthesis particularly for removing unnecessary functional groups.

Understanding decarboxylation is important for chemists aiming to develop reaction pathways that require the removal of carbon dioxide from carboxylic acids.

Alpha Hydrogen

The alpha hydrogen is a vital component in understanding reactions like enolate formation. These hydrogens are located on the carbon adjacent to the carbonyl group in a molecule.

Because of their position, alpha hydrogens are more acidic compared to other hydrogen atoms in the molecule. This acidity makes them more likely to be deprotonated by a strong base, such as \( \mathrm{NaOEt} \), resulting in enolate formation.

The concept of alpha hydrogens is significant in organic chemistry as it governs the reactivity and transformation of compounds in various reactions, particularly those involving the formation of enolates and subsequent alkylation.