Problem 52 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following reaction: \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}_{2} \stackrel{\mathrm{Sn} / \mathrm{HCl}}{\longrightarrow} \mathrm{X} \stackrel{\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COCl}}{\longrightarrow} \mathrm{Y}+\mathrm{HCl}\) The product \(\mathrm{Y}\) is (a) azobenzene (b) acetanilide (c) benzanilide (d) hydrazobenzene

Step-by-Step Solution

Answer

The product Y is benzanilide (c).

Step 1: Analyze the Reaction Pathway

The reaction involves the reduction of nitrobenzene (C_{6}H_{5}NO_{2}) in the presence of Sn/HCl. This typically leads to the conversion of the nitro group (NO_2) to an amine group (NH_2), forming aniline (C_{6}H_{5}NH_2). Therefore, X is aniline.

Step 2: Characterize the Second Reaction

The aniline (X) formed in the first step is then treated with benzoyl chloride (C_{6}H_{5}COCl). This reaction is a typical example of acylation where the amine group in aniline reacts with benzoyl chloride to form an amide linkage, producing benzanilide (C_{6}H_{5}NHCOC_{6}H_{5}) as Y.

Step 3: Conclusion based on Product Identification

Based on the analysis, the second step of the reaction forms benzanilide as the product (Y). Therefore, the final product Y is identified as benzanilide.

Key Concepts

Reduction Reactions

Reduction reactions are pivotal in organic chemistry, as they allow the transformation of one functional group into another through the addition of electrons or hydrogen. For instance, when nitrobenzene \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NO}_{2}\) undergoes a reduction reaction with tin (Sn) and hydrochloric acid (HCl), it transforms the nitro group \(\mathrm{NO}_{2}\) into an amine group \(\mathrm{NH}_{2}\). This is because the reduction process adds hydrogen atoms to replace the oxygen atoms in the nitro group.
This chemical transformation is essential for modifying the functional properties of a molecule, preparing it for further reactions. In this specific reaction, the product of this reduction is aniline \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NH}_{2}\), a compound that is much more reactive for subsequent chemical reactions, such as acylation.
Overall, reduction reactions like this play a critical role in synthetic organic chemistry by enabling the conversion of more oxidized functional groups into less oxidized forms.

Acylation

Acylation is a significant chemical reaction in organic synthesis, where an acyl group is introduced into a compound. This is typically accomplished through the reaction of an acyl chloride with a suitable nucleophile like an amine. In our example, the aniline formed in the reduction step serves as the nucleophile.
When aniline \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NH}_{2}\) is treated with benzoyl chloride \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{COCl}\), it undergoes acylation. This involves the displacement of the chlorine atom in benzoyl chloride by the nitrogen atom in aniline, forming a new chemical bond.

• The reaction essentially replaces the hydrogen atom on the amine group with a benzoyl group.
• This produces an amide linkage, which is a fundamental feature in creating complex organic molecules.

The product formed in this specific acylation reaction is benzanilide \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NHCOC}_{6}\mathrm{H}_{5}\), which highlights the reactivity and utility of acylation in forming new carbon-nitrogen bonds in organic chemistry.

Amide Formation

Amide formation is a crucial reaction in organic and peptide chemistry, allowing the connection of functional groups to form more complex structures. In this reaction process, an amine reacts with an acyl chloride, resulting in the formation of an amide bond. The reaction mechanism involves nucleophilic acyl substitution.
The nitrogen atom in the amine acts as a nucleophile and attacks the carbon of the carbonyl group in the acyl chloride. This leads to the release of a chloride ion and formation of the amide linkage. In our example, when aniline \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NH}_{2}\) reacts with benzoyl chloride \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{COCl}\), benzanilide \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{NHCOC}_{6}\mathrm{H}_{5}\) is formed as a product.
This process highlights how amide bonds are formed, which are key structural components in peptides and proteins. These bonds are also stable under physiological conditions, rendering them integral in biosynthetic pathways as well as in pharmaceutical applications.