Question

Claisen condensation is a reaction between (a) \(\mathrm{HCOOH}+\mathrm{HCOOH}\) (b) \(\mathrm{HCOOH}+\mathrm{HCHO}\) (c) \(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}\) (d)

Short answer

(a) \(\mathrm{HCOOH}+\mathrm{HCOOH}\) (b) \(\mathrm{HCOOH}+\mathrm{HCHO}\) (c) \(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}\) (d) \(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{CH}_{3} \mathrm{COOH}\) Answer: (c) \(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}\)

Step-by-step solution

Identify ester reactants and the resulting products

Analyze each given reaction to see if the reactants are esters and the products are either β-keto esters or β-diketones. (a) \(\mathrm{HCOOH}+\mathrm{HCOOH}\): Both reactants are formic acid, not esters. This reaction is not Claisen condensation. (b) \(\mathrm{HCOOH}+\mathrm{HCHO}\): One reactant is formic acid and the other is formaldehyde. Neither are esters, so this reaction is not Claisen condensation. (c) \(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}\): Both reactants are esters (ethyl acetate). This reaction could potentially be Claisen condensation. (d) \(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{CH}_{3} \mathrm{COOH}\): One reactant is an ester (ethyl acetate) and the other is a carboxylic acid (acetic acid). This reaction is not Claisen condensation.

Choose the correct option

Only option (c) involves the reaction of two esters, which matches the description of Claisen condensation. Therefore, the correct answer is: (c) \(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}+\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5}\)

Key concepts

Ester Reactants

In the context of the Claisen condensation, understanding the role of ester reactants is crucial. Esters are organic compounds characterized by the presence of an ester functional group, which is typically represented as -COOR, where 'R' is an organic substituent.

Esters are derived from carboxylic acids and alcohols, and in the Claisen condensation, they serve as the starting materials. The reaction involves two ester molecules, where one acts as an electrophile (an electron acceptor) and the other as a nucleophile (an electron donor).

Identification of Esters

When examining a potential Claisen condensation reaction, we look for reactants that are indeed esters. In the given exercise, options (a) and (b) were quickly disregarded because they did not contain ester reactants. Option (c), featuring ethyl acetate \(\mathrm{CH}_3\mathrm{COOC}_2\mathrm{H}_5\), provided a pair of ester molecules, qualifying it to potentially undergo Claisen condensation.

Understanding the structural components of esters and their reactivity is essential for predicting the outcome of organic reactions involving these compounds.

β-keto Esters

β-keto esters are the hallmark product of the Claisen condensation reaction. They possess both an ester functional group and a ketone functional group within the same molecule. The naming derives from the position of the keto group, which is adjacent to the ester group – 'β' indicating the second position from the ester.

Properties and Formation of β-keto Esters

A β-keto ester has the general structure \(R-CO-CH_2-COOR^1\), where 'R' and 'R^1' can be the same or different alkyl or aryl groups. The formation of a β-keto ester involves the nucleophilic addition of an enolate ion, formed from one ester molecule, to another ester's carbonyl carbon, followed by a series of steps including the elimination of an alcohol.

The significance of forming β-keto esters lies in their versatility in organic synthesis. They can be used to synthesize a variety of other compounds through further reactions, such as decarboxylation or reductions.

β-diketones

β-diketones are another potential product of Claisen condensation, particularly when diketone esters undergo subsequent decomposition. They contain two keto groups (carbonyl groups) within the same molecule, situated two carbons apart (the α- and β-positions).

The general structure of a β-diketone is \(R-CO-CH_2-CO-R\). These compounds are important intermediates in organic synthesis because they can be used to generate various other compounds, including cyclic structures like rings through intramolecular reactions.

Formation of β-diketones

The β-diketone can be formed through Claisen-type reactions followed by the loss of an ester group. This kind of transformation showcases the complexity and diversity of reactions that esters can undergo, leading to valuable compounds for further chemical transformations.

Organic Chemical Reactions

Understanding organic chemical reactions like Claisen condensation is fundamental in organic chemistry. These reactions involve the breaking and forming of chemical bonds within organic molecules to produce new compounds.

Mechanisms and Conditions

Each organic reaction has its own unique mechanism and requirements for conditions like temperature, solvent, and catalysts. In the case of Claisen condensation, a strong base is typically required to form the enolate ion from the ester reactant, initiating the reaction.

Reactions like Claisen condensation are not only important for the formation of complex molecules but are also instrumental in understanding the behaviors of organic compounds in biological systems. Knowledge of these reactions allows chemists to design and synthesize compounds with desired properties, making it a cornerstone of pharmaceutical development and material science.