Question

Other conceivable products of the Claisen condensation of ethyl acetate are and Explain how these products might be formed and why they are not formed in significant amounts.

Short answer

The other conceivable products of the Claisen condensation of ethyl acetate are ethyl 3-oxobutanoate, formed from an intramolecular reaction, and diethyl oxalate, formed from a different intermolecular reaction. These products are not formed in significant amounts because the intramolecular reaction has a lower probability of occurring and the formation of diethyl oxalate requires unfavorable conditions. Instead, the preferred intermolecular Claisen condensation pathway is more likely and kinetically favored to occur.

Step-by-step solution

Recap the Claisen condensation

End The Claisen condensation is a nucleophilic acyl substitution reaction involving two esters or an ester and a carbonyl compound in the presence of a base. In this case, we are considering the reaction of ethyl acetate. The reaction involves the deprotonation of the α-hydrogen of an ester by a strong base, followed by the nucleophilic attack of the enolate ion on the ester carbonyl group, and finally the protonation of the alkoxide ion, forming a β-keto ester product.

Other conceivable products

Other conceivable products of the Claisen condensation of ethyl acetate could be: 1. Ethyl 3-oxobutanoate (a result of intramolecular reaction) 2. Diethyl oxalate (a result of intermolecular reaction) These products might be formed if the enolate ion, generated after deprotonation, reacts in different ways than intended in the Claisen condensation reaction. Ethyl 3-oxobutanoate could be formed if the enolate ion attacks the carbonyl group of the same ethyl acetate molecule (intramolecular reaction) instead of another ester molecule. Diethyl oxalate could be formed if two ethyl acetate molecules react with each other in an intermolecular reaction.

Reasons for not forming in significant amounts

Although these other conceivable products are theoretically possible, they are not formed in significant amounts due to the following reasons: 1. Ethyl 3-oxobutanoate: The intramolecular reaction has a lower probability of occurring compared to the desired intermolecular Claisen condensation, because the enolate ion must rotate to approach the carbonyl group of the same molecule, which would happen with difficulty in comparison to an intermolecular reaction where the enolate ion is free to attack the carbonyl group of another ester molecule. 2. Diethyl oxalate: The formation of diethyl oxalate requires two ethyl acetate molecules to both be deprotonated and their enolate ions to act as nucleophiles and electrophiles simultaneously, which is less likely because there is typically only enough base present to deprotonate a single molecule. Moreover, the Claisen condensation product is kinetically favored as it takes less energy for the carbonyl group of one ester to be attacked by the enolate ion of another ester as opposed to ester groups reacting with each other. In conclusion, these additional conceivable products of the Claisen condensation of ethyl acetate might be formed through intramolecular and different intermolecular reactions, but they are not formed in significant amounts because the preferred intermolecular Claisen condensation pathway is more likely and kinetically favored to occur.

Key concepts

Nucleophilic Acyl Substitution

The Claisen condensation is a classic example of a nucleophilic acyl substitution. In this type of reaction, an acyl group—which is essentially a carbonyl (C=O) bonded to an alkyl group—is replaced by a different nucleophile. Here, the nucleophile involved is an enolate ion, which acts on the carbonyl carbon of the ester. Through this reaction pathway, the ester undergoes transformation, facilitated by a base, leading to the creation of a β-keto ester.

The process begins with the deprotonation of the ester to form the enolate ion. This ion then attacks the carbonyl carbon, one of the most stressed and reactive sites on the ester molecule, resetting the structure with a substitution. This substitution is pivotal to forming the desired products, as seen in the case of the Claisen condensation reaction. The resulting structure will typically have new ester functionalities or modifications—apparent in the formation of distinct types of esters during the reaction.

• The carbonyl carbon is the main electrophilic center.
• Nucleophilic attack follows the formation of enolate ions.
• The product is usually a more stable compound, like a β-keto ester.

Enolate Ion

The enolate ion is a crucial intermediate in Claisen condensation. It is formed when a strong base abstracts a proton from the α-carbon of an ester, such as ethyl acetate. This removal of a hydrogen atom results in the formation of a negatively charged ion, known for its stability due to resonance.

Enolate ions serve as powerful nucleophiles, allowing them to partake in nucleophilic acyl substitution reactions. They target the electrophilic carbonyl carbon, adding their electrons and initiating molecular transformations.

• Formed by deprotonating the α-carbon of the ester.
• Plays a key role in attacking carbonyl carbon.
• Essential for creating the desired β-keto ester product.

The propagation of the enolate ion reactivity is what drives the Claisen condensation to successfully convert basic reactants into more intricate chemical structures efficiently.

β-Keto Ester

A β-keto ester is the primary product of Claisen condensation, serving as an indicator of a successful reaction. This compound features a keto group (C=O) located at the β-position relative to the ester group.

The formation of β-keto esters arises once the enolate ion successfully attacks the carbonyl carbon, followed by several further reactions and rearrangements. This unique location of the keto group is pivotal as it introduces remarkable properties, making β-keto esters highly versatile in further syntheses.

• Characterized by a keto group adjacent to the ester.
• Acts as a synthetically valuable intermediate.
• Results from successful nucleophilic acyl substitution.

Their synthesis undoubtedly showcases the proficiency of Claisen condensation in producing complex structures from simpler starting materials, essentially broadening paths in organic synthesis.

Ethyl Acetate

In Claisen condensation, ethyl acetate serves as a fundamental reactant. It is a simple ester that consists of an ethyl group linked to an acetate.

As the reaction proceeds, ethyl acetate plays a vital role due to its structure, which is highly reactive and facilitates enolate ion formation upon deprotonation. The role of ethyl acetate extends further as it acts both as an electrophile to undergo nucleophilic acyl substitution by the formed enolate ion, leading to the formation of more complex molecules like the β-keto ester.

• Key reactant in Claisen condensation.
• Leads to formation of enolate ions.
• Participates in forming β-keto esters through nucleophilic attack.

The fundamental reactions of ethyl acetate underpin the synthesis process, illustrating its versatility in forming various structural frameworks through specified reaction pathways.