Problem 117 - A Complete Resource Book in Chemistry for JEE Main

Question

Cinnamic acid is formed when \(\mathrm{C}_{6} \mathrm{H}_{5}\) CHO condensation with \(\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}\) in presence of (a) sodium metal (b) sodium acetate (c) anhydrous \(\mathrm{ZnCl}_{2}\) (d) conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

Step-by-Step Solution

Answer

Option (b) sodium acetate is the correct catalyst for the formation of cinnamic acid.

Step 1: Identify Reaction Type

The given reaction involves the condensation of benzaldehyde (\(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CHO}\)) with acetic anhydride (\(\left( \mathrm{CH}_3 \mathrm{CO} \right)_2 \mathrm{O}\)). This is a condensation reaction which leads to the formation of cinnamic acid, a product typical of a Perkin reaction.

Step 2: Determine Suitable Catalyst

In the Perkin reaction, the condensation between an aromatic aldehyde and an acid anhydride typically uses sodium acetate as the catalyst. This acts to promote the formation of the α,β-unsaturated carboxylic acid from the reactants.

Step 3: Choose the Correct Option

Given the options, the correct catalyst for the formation of cinnamic acid through this reaction is sodium acetate. Hence, option (b) sodium acetate is the correct answer.

Key Concepts

Cinnamic Acid Synthesis

The synthesis of cinnamic acid is a classic example of the Perkin reaction, a well-regarded method in organic chemistry. This involves the reaction between an aromatic aldehyde, such as benzaldehyde, and an acid anhydride like acetic anhydride. Together, they undergo a condensation reaction that results in the formation of cinnamic acid, an important organic compound.

Cinnamic acid itself is a useful compound, often found in perfumes, flavoring agents, and as a building block in the synthesis of various pharmaceuticals. The Perkin reaction and the resulting synthesis of cinnamic acid are particularly valued for being straightforward, efficient, and providing good yields.

Understanding the process of cinnamic acid synthesis helps underline important principles in organic reactions, especially the importance of choosing appropriate reactants and conditions to achieve the desired chemical transformation.

Condensation Reaction

A condensation reaction is a type of chemical reaction where two molecules combine to form a larger molecule, releasing a smaller molecule in the process, often water. In the context of the cinnamic acid synthesis, a condensation reaction occurs between benzaldehyde and acetic anhydride.

One of the defining aspects of condensation reactions is the loss of a molecule, which in many organic reactions is either water or alcohol. The Perkin reaction specifically involves this type of reaction, where the aromatic aldehyde and the acid anhydride condense, and a small molecule (usually acetic acid) is lost, forming the product cinnamic acid.

These reactions are pivotal in organic chemistry as they form the basis of many synthesis processes, resulting in complex molecules from simpler starting materials. They reflect broader principles of chemical transformations, illustrating how molecular structures can be manipulated to generate new compounds.

Sodium Acetate Catalyst

In the Perkin reaction for synthesize cinnamic acid, sodium acetate plays a crucial role as a catalyst. Catalysts are substances that increase the rate of a reaction without being consumed in the process themselves.

The presence of sodium acetate is essential as it aids the condensation between the aromatic aldehyde and the acid anhydride. It promotes the rearrangement of intermediates and facilitates the formation of the α,β-unsaturated carboxylic acid product effectively. Without an appropriate catalyst, reactions may proceed very slowly, or might not occur at all under normal conditions.

Using sodium acetate not only speeds up the reaction but also helps in achieving a higher yield of the desired product, cinnamic acid, by stabilizing the reaction intermediates and ensuring that the reaction pathway leads efficiently to the desired outcome.