Question

Cinnamaldehyde, the aromatic constituent of cinnamon oil. can be synthesized by a mixed aldol condensation between two different carbonyl compounds. Show the starting materials you would use, and write the reaction.

Short answer

Use benzaldehyde and acetaldehyde with a base for the aldol condensation reaction to synthesize cinnamaldehyde.

Step-by-step solution

Identify the Structure of Cinnamaldehyde

Cinnamaldehyde has the chemical structure \( C_9H_8O \), consisting of a phenyl group attached to a propenal chain (a benzene ring bonded to a two-carbon chain with a terminal aldehyde group).

Determine the Carbonyl Components

To synthesize cinnamaldehyde via a mixed aldol condensation, identify two suitable carbonyl compounds that together can produce the required structure. Here, benzaldehyde (\( C_6H_5CHO \)) will provide the phenyl group, and acetaldehyde (\( CH_3CHO \)) will supply the necessary two-carbon structure.

Write the Aldol Condensation Reaction

During the aldol condensation, acetaldehyde acts as the nucleophile. The reaction progresses through the deprotonation of acetaldehyde to form an enolate ion, which then attacks the carbonyl carbon of benzaldehyde, resulting in a \( \beta \)-hydroxy aldehyde intermediate. Write this mechanism:1. Enolate formation: \[ CH_3CHO + ext{Base} \rightarrow CH_2=CHO^- + ext{BaseH}^+ \]2. Nucleophilic addition: \[ CH_2=CHO^- + C_6H_5CHO \rightarrow C_6H_5CH(OH)CH_2CHO \]3. Dehydration to produce cinnamaldehyde: \[ C_6H_5CH(OH)CH_2CHO \rightarrow C_6H_5CH=CHCHO + H_2O \]

Present the Overall Reaction

The overall reaction can be summarized as: Benzaldehyde + Acetaldehyde + Base \( \rightarrow \) Cinnamaldehyde + Water. This describes the conversion of the two starting materials into cinnamaldehyde via the aldol condensation.

Key concepts

Cinnamaldehyde Synthesis

Cinnamaldehyde is the key aromatic compound found in cinnamon oil, giving it its distinctive smell and flavor. This compound can be synthesized through a chemical process known as a mixed aldol condensation.
To create cinnamaldehyde, two different carbonyl compounds must be combined. The process primarily involves benzaldehyde, which contributes the phenyl group, and acetaldehyde, which provides the two-carbon structure needed to complete the molecule.
The reaction is a multi-step process that involves the formation of an intermediate that is then dehydrated to yield the final product. This intermediate, a \( \beta \)-hydroxy aldehyde, is formed through the addition of acetaldehyde to benzaldehyde. Ultimately, through careful reaction conditions and the presence of a base, cinnamaldehyde is produced efficiently.

• The transformation of these starting materials into cinnamaldehyde is a classic example of how natural products can be synthesized in a lab setting.
• This reaction not only produces an important flavoring agent but also demonstrates the utility of aldol condensations in organic chemistry.

Carbonyl Compounds

Carbonyl compounds contain a carbon-oxygen double bond and are essential in forming many organic molecules.
In the synthesis of cinnamaldehyde, benzaldehyde and acetaldehyde are the two carbonyl compounds needed. Each plays a critical role in the process.
Benzaldehyde (\(C_6H_5CHO\)), provides the phenyl ring, a notable component of the cinnamaldehyde's structure. This aromatic carbonyl compound undergoes a reaction with the enolate ion derived from acetaldehyde.

• Acetaldehyde (\(CH_3CHO\)) contains a simpler carbonyl structure, which makes it a suitable partner for forming the enolate ion in aldol condensations.
• These compounds are reactive due to the polar nature of the carbon-oxygen bond, making them excellent candidates for nucleophilic reactions, including those involved in aldol condensations.

Organic Chemistry Reaction Mechanism

In organic chemistry, understanding reaction mechanisms is key to predicting and controlling the outcomes of chemical reactions.
The aldol condensation used in cinnamaldehyde synthesis is a wonderful illustration of this.
This mechanism includes an enolate ion formation, nucleophilic addition, and a dehydration step:

• Enolate Formation: The base deprotonates acetaldehyde to form an enolate ion, a species with an extra electron pair, making it highly nucleophilic.
• Nucleophilic Addition: The enolate ion attacks the carbonyl carbon of benzaldehyde, resulting in the formation of a \( \beta \)-hydroxy aldehyde intermediate.
• Dehydration: The intermediate undergoes dehydration, losing a water molecule to form the double bond in cinnamaldehyde.

This controlled sequence ensures a successful synthesis of cinnamaldehyde. The mechanism highlights how the choice of reagents and reaction conditions, such as the presence of a base, greatly influence the course and outcome of the reaction.