Question

Phenol is treated with $H_{2}SO_{4}$ to give a product 'X' which on treatment with conc. $HNO_{3}$ gives compound 'Y'. The compounds 'X' and 'Y' are respectively:

• A. Phenol-2-sulphonic acid and 2-nitrophenol
• B. Phenol-2-sulphonic acid and 4-nitrophenol
• C. Phenol-2-sulphonic acid, mixture of 2-nitrophenol and 4-nitrophenol
• D. Phenol-2,4-disulphonic acid, mixture of 2-nitrophenol and 4-nitrophenol
• E. Phenol-2,4-disulphonic acid and picric acid

Hint:

Picric acid is 2,4,6-trinitrophenol.

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
This is a multi-step organic synthesis problem involving electrophilic aromatic substitution on phenol. We need to identify the products of sulfonation followed by nitration under strongly acidic conditions.
Step 2: Detailed Explanation:
Step 1: Formation of X (Sulfonation of Phenol) - Phenol reacts with concentrated sulfuric acid (Con. H\(_2\)SO\(_4\)). The -OH group is a strongly activating, ortho-para directing group. - The sulfonation of phenol is temperature-dependent. At low temperatures (around room temp), the ortho-product (Phenol-2-sulphonic acid) is kinetically favored. At higher temperatures (around 100°C), the para-product (Phenol-4-sulphonic acid) is thermodynamically favored. - However, under forcing conditions with concentrated acid, disubstitution can occur. Treating phenol with Con. H\(_2\)SO\(_4\) will lead to sulfonation at both the ortho and para positions. - Therefore, product 'X' is Phenol-2,4-disulphonic acid. Step 2: Formation of Y (Nitration of X) - Product 'X', Phenol-2,4-disulphonic acid, is then treated with concentrated nitric acid (Con. HNO\(_3\)). This is a nitration reaction. - The mixture of Con. HNO\(_3\) and Con. H\(_2\)SO\(_4\) (already present from the first step) is a powerful nitrating agent. - The -OH group is a very strong activating group. The -SO\(_3\)H groups are deactivating. However, the powerful -OH group directs substitution to the remaining available ortho and para positions. - The starting material X has -SO\(_3\)H groups at position 2 and 4. The remaining ortho position is position 6. - Nitration will occur at all the activated and available ortho/para positions: position 2, 4, and 6. - Interestingly, nitration under these strong conditions can also displace the existing sulphonic acid groups. This is a known reaction called ipso-substitution. The nitronium ion (NO\(_2^+\)) can attack the carbons bearing the -SO\(_3\)H groups, replacing them. - Therefore, nitration of Phenol-2,4-disulphonic acid with concentrated HNO\(_3\) will lead to the substitution of NO\(_2\) groups at all three activated positions (2, 4, and 6), replacing the -SO\(_3\)H groups and adding to the vacant position. - The final product 'Y' is 2,4,6-trinitrophenol, which is commonly known as picric acid. Step 3: Final Answer:
Based on this analysis, X is Phenol-2,4-disulphonic acid and Y is picric acid.