Problem 58 - A Complete Resource Book in Chemistry for JEE Main

Question

Aniline first reacts with acetyl chloride producing compound 'A' ' 'A' reacts with nitric acid/sulphuric acid mixture and produces compound 'B', which hydrolyses to compound ' \(\mathrm{C}^{\prime}\). What is the identity of ' \(\mathrm{C}^{\prime}\) ? (a) acetanilide (b) p-nitroacetanilide (c) p-nitroaniline (d) aniline

Step-by-Step Solution

Answer

Compound 'C' is p-nitroaniline.

Step 1: Reaction of Aniline with Acetyl Chloride

Aniline latex(C_6H_5NH_2)latex reacts with acetyl chloride latex(CH_3COCl)latex to form acetanilide. This reaction leads to the replacement of the hydrogen atom in latex-NH_2latex group of aniline with an acetyl group, leading to compound 'A', which is acetanilide latex(C_6H_5NHCOCH_3)latex.

Step 2: Nitration of Acetanilide

Compound 'A', acetanilide, is then reacted with a mixture of nitric acid latex(HNO_3)latex and sulphuric acid latex(H_2SO_4)latex. This nitration process introduces a nitro group latex(NO_2)latex to the para position (4 position) of acetanilide, forming compound 'B', which is p-nitroacetanilide latex(C_6H_4(NO_2)NHCOCH_3)latex.

Step 3: Hydrolysis of p-Nitroacetanilide

The p-nitroacetanilide 'B' is then hydrolyzed, which involves breaking the acetyl group latex(CONH_2)latex bond and releasing it as acetic acid. This reaction converts p-nitroacetanilide into compound 'C', which is p-nitroaniline latex(C_6H_4(NO_2)NH_2)latex.

Key Concepts

Aniline Reactions

Aniline is a basic organic compound with the formula \(C_6H_5NH_2\). It's known for its potential to undergo a variety of reactions due to the amino group \(-NH_2\) attached to the benzene ring. This amino group is largely responsible for the reactivity of aniline because it can easily participate in substitution reactions. In the exercise, aniline first reacts with acetyl chloride.

• This reaction replaces the hydrogen in the \(-NH_2\) group with an acetyl group \(-COCH_3\), transforming aniline into acetanilide.
• The presence of the amino group in aniline also makes it possible to undergo reactions like nitration, which can introduce various functional groups to its structure.
• Understanding these reactions lays the foundation for learning more about the chemistry of aromatic amines, which are common in pharmaceuticals and dyes.

Acetanilide

Acetanilide is a derivative of aniline and has the chemical structure \(C_6H_5NHCOCH_3\). It is formed when aniline reacts with acetyl chloride. The reaction with acetyl chloride is a type of acylation, which is a process that introduces an acetyl group into the molecule.

• This conversion reduces the basicity of aniline and stabilizes it by making it less reactive toward other electrophiles.
• Acetanilide serves as a starting point for further synthetic reactions, such as nitration.
• This compound has historical significance as a pain-relieving and fever-reducing agent before being replaced by safer alternatives.

This acylation step is crucial for modifying the reactivity of aniline, especially when selectively introducing other functional groups later on.

Nitration Process

The nitration process is a critical reaction where an aromatic compound like acetanilide undergoes substitution with a nitro group \((NO_2)\). In this exercise, compound 'A', acetanilide, goes through nitration to form p-nitroacetanilide.

• A mixture of nitric acid \((HNO_3)\) and sulphuric acid \((H_2SO_4)\) is used as the nitrating agent.
• This process targets the para position (position 4) of the acetanilide, which is favored due to electronic influences from the acetyl-protected amino group.
• Nitration enhances the reactivity and utility of the compound, preparing it for further transformations.

Understanding nitration is essential for synthesizing various pharmaceuticals and organic materials, as nitro groups can be transformed into a wide array of useful functionalities.

Hydrolysis of Amides

Hydrolysis is a chemical process where a molecule is split into two parts by the addition of a water molecule. Here, p-nitroacetanilide undergoes hydrolysis to produce p-nitroaniline.

• This reaction involves the cleavage of the acetyl group \((-CONH_2)\) from p-nitroacetanilide.
• As a result, the acetyl group is released as acetic acid, while the remaining structure forms p-nitroaniline \((C_6H_4(NO_2)NH_2)\).
• The process demonstrates how amide bonds can be strategically broken down, reverting acylated anilines back to their amine forms.

This reaction is quite valuable in synthetic organic chemistry, where altering protective groups can refine or modify a compound's functionality for further applications.