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

Question

Cinnamic acid is formed when \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CHO}\) 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

(b) sodium acetate

Step 1: Reaction Type Identification

To solve the problem, first recognize the type of reaction taking place. Cinnamic acid formation is typically accomplished through a Perkin reaction. This involves the condensation of aromatic aldehydes with acid anhydrides.

Step 2: Key Reagents in the Perkin Reaction

In a typical Perkin reaction, cinnamic acid is formed by the condensation of benzaldehyde (\(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{CHO}\)) and acetic anhydride (\((\mathrm{CH}_{3}\mathrm{CO})_{2}\mathrm{O}\)). This reaction specifically requires a base, typically in the form of a salt like sodium acetate, to proceed.

Step 3: Analyzing Given Options

Examine the provided options to identify which one fulfills the Perkin reaction requirements:- (a) Sodium metal: Not typically used in this reaction; acts as a strong reducing agent.- (b) Sodium acetate: Commonly used as a base in the Perkin reaction.- (c) Anhydrous \(\mathrm{ZnCl}_{2}\): Not related to the Perkin mechanism.- (d) Conc. \(\mathrm{H}_{2}\mathrm{SO}_{4}\): Acts as a strong acid; not suitable for the base-catalyzed Perkin reaction.

Step 4: Conclusion

Based on the reaction mechanism and typical reagents, option (b), sodium acetate, is the correct catalyst for the formation of cinnamic acid through the Perkin reaction.

Key Concepts

Cinnamic Acid Formation

The formation of cinnamic acid is a fascinating example of organic chemistry in action. This compound is primarily produced via a Perkin reaction, which is a notable method involving organic synthesis. The Perkin reaction is specifically used to create alpha, beta-unsaturated aromatic acids, such as cinnamic acid.
In this process, benzaldehyde, which is an aromatic aldehyde, acts as a key starting material. Combining benzaldehyde with acetic anhydride results in a condensation reaction, ultimately producing cinnamic acid. The reaction typically involves the removal of water (a dehydration step), which allows the new bond formation crucial to build the cinnamic structure.
This process highlights how manipulating simple organic compounds can lead to the formation of more complex molecules, showing both the beauty and utility of chemical transformations in creating compounds with potential applications in various industries.

Benzaldehyde Condensation

Condensation reactions are a fundamental type of chemical process that allow for the formation of larger molecules from smaller ones by removing a small molecule (often water).
In the context of cinnamic acid formation, benzaldehyde acts as the aromatic aldehyde and plays a pivotal role in its transformation. When benzaldehyde undergoes condensation with acetic anhydride, it facilitates the formation of a new carbon-carbon bond, a crucial step in transitioning from simple to complex structures like cinnamic acid.
This reaction not only shows the versatility of benzaldehyde as a reactive compound but also the importance of aldehyde groups in creating more sophisticated molecules via condensation. Through this process, we see how strategic chemical design paves the way for the creation of valuable organic substances.

Sodium Acetate Base Catalyst

A catalyst is essential in many chemical reactions to increase the rate without being consumed. In the Perkin reaction used to form cinnamic acid, sodium acetate acts as the base catalyst, making it central to the success of the chemical transformation.
Sodium acetate works by providing an acetate ion, which facilitates the removal of a proton from the acetic anhydride, thus initiating the reaction. It can be distinguished from other potential bases like sodium metal, which is too reactive, or strong acids like concentrated sulfuric acid, which are not suitable for this base-catalyzed reaction.
The choice of the right base catalyst is crucial because it ensures that the reaction proceeds efficiently and safely. Sodium acetate stands out as the preferred catalyst, promoting the desired chemical changes smoothly and guiding the reaction to yield cinnamic acid.