Question

Claisen condensation between diethyl phthalate and ethyl acetate followed by saponification, acidification, and decarboxylation forms a diketone, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{2}\). Propose structural formulas for compounds \(A, B\), and the diketone.

Short answer

Compound A: C6H4(COOCH2CH3)(COOCH2CH2COCH3) Compound B: C6H4(COOH)(COOCH2CH2COCH3) Final diketone: CH3COCOCH3

Step-by-step solution

Claisen condensation between diethyl phthalate and ethyl acetate

For this reaction, the diethyl phthalate acts as an ester, while the ethyl acetate acts as the enolizable reactant. In Claisen condensation, the enolizable ester reacts with the other ester and forms a β-keto ester. The products for this step will be compound A and ethyl alcohol. Ethyl acetate structure: CH3COOCH2CH3 Diethyl phthalate structure: C6H4(COOC2H5)2 The Claisen condensation reaction proceeds as follow: (1) Formation of the enolate ion from the ethyl acetate by abstracting the alpha-hydrogen. CH3COOCH2CH3 → CH3COOCH2CH2¯ (enolate ion) + H^+ (2) The enolate ion attacks the carbonyl carbon on the diethyl phthalate: CH3COOCH2CH3 + C6H4(COOC2H5)2 → Compound A + C2H5OH Compound A: C6H4(COOCH2CH3)(COOCH2CH2COCH3)

Saponification

In this step, compound A will undergo saponification, which is the base-catalyzed hydrolysis of the ester functional groups. This will result in compound B and ethanol. Compound A + 2OH¯ → Compound B + 2CH3CH2OH Compound B: C6H4(COOH)(COOCH2CH2COCH3)

Acidification

In this step, compound B will react with an acid HX and remove the acid hydrogen forming a diketo ester and water as a byproduct. Compound B + HX →Compound C + H2O Compound C: C6H4(COX)(COOCH2CH2COCH3)

Decarboxylation

In the final step, compound C will go through a decarboxylation reaction: the loss of CO2 and formation of the diketone. Compound C → \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{2}\) + CO2 Final diketone: CH3COCOCH3 In conclusion, the proposed structural formulas for the compounds are: Compound A: C6H4(COOCH2CH3)(COOCH2CH2COCH3) Compound B: C6H4(COOH)(COOCH2CH2COCH3) Diketone: CH3COCOCH3

Key concepts

Saponification

Saponification is a chemical reaction that involves the conversion of esters into alcohol and an acid or salt, typically using a strong base such as sodium hydroxide (NaOH). It plays a crucial role in various organic transformations. For example, in the Claisen condensation exercise, compound A undergoes saponification. Here, the ester groups present in compound A are hydrolyzed, resulting in the formation of compound B along with the release of ethanol.

The general mechanism involves these steps:

• The base attacks the carbonyl carbon of the ester, forming a tetrahedral intermediate.
• This intermediate collapses, leading to the displacement of the alcohol and the formation of a carboxylate anion.
• The carboxylate ion is then protonated, forming the corresponding carboxylic acid.

Overall, saponification transforms nonpolar esters into more polar carboxylic acids or their salts, aiding in further chemical processes.

Acylation

Acylation refers to the introduction of an acyl group into a compound, typically through reactions involving acyl chlorides or anhydrides. This process is significant in the synthesis of various organic molecules. Although not directly involved in the solution of this exercise, it complements other reactions like Claisen condensation by modifying functional groups and generating new compounds.

In general acylation reactions:

• An acyl group (\(RCO-\)) is transferred to a nucleophile.
• The nucleophile could be an alcohol, an amine, or another active group.
• This usually requires a catalyst or driving force such as heat.

Acylation is a powerful tool in organic synthesis, allowing chemists to create complex molecules by adding carbonyl groups to various substrates.

Decarboxylation

Decarboxylation is a reaction that involves the removal of a carboxyl group as carbon dioxide (\(CO_2\)). It's a common step in the degradation of organic acids and in various synthetic pathways. In the context of the original exercise, after acidification of compound B to form compound C, decarboxylation takes place, leading to the final diketone product.

During decarboxylation:

• The carboxylic group is usually destabilized by heat or a catalyst.
• This process results in the loss of CO2, often replacing the carboxylic group with a hydrogen atom or another group.
• It significantly alters the molecule by reducing its length by one carbon atom.

This reaction helps simplify molecules, making them more suitable for further synthetic evolution.

Organic Synthesis

Organic synthesis is the overarching process of constructing complex organic molecules from simpler ones. It combines various chemical reactions such as saponification, acylation, and decarboxylation, often following a sequential series of steps. The purpose is to transform starting materials into desired products, like transforming diethyl phthalate and ethyl acetate into a diketone as showcased in the exercise.

Principles of organic synthesis include:

• Step-by-step transformation using defined reaction pathways.
• Optimization of reaction conditions to maximize yield and minimize byproducts.
• Strategic planning to harness available functional groups effectively.

In essence, organic synthesis is like solving a puzzle, piecing together reactions to create specific molecules with desired properties.

Beta-keto Ester

A beta-keto ester is an organic compound that contains a ketone (\(C=O\)) group located beta to an ester (\(-COOR\)) group in the carbon chain. These compounds are typically formed through Claisen condensation, where an enolate ion from an ester reacts with another ester molecule.

Characteristics of beta-keto esters include:

• They are versatile intermediates in organic synthesis.
• They possess acidic hydrogens at the alpha-carbon, making them reactive.
• This makes them suitable for further reactions like alkylation or decarboxylation.

In the context of the exercise, the beta-keto ester produced during Claisen condensation of diethyl phthalate and ethyl acetate undergoes subsequent transformations to eventually yield a useful diketone.