Carbolic acid (phenol) is obtained from

1)    

2)                       
3)    

4)     
 

Solution

Option 1: Aniline (C₆H₅NH₂)

Reagents: NaNO₂, HCl, H₂O

The process involves:

1. Aniline reacts with NaNO₂ and HCl to form a diazonium salt (benzene diazonium chloride, C₆H₅N₂⁺Cl^-).
2. The diazonium salt undergoes hydrolysis in the presence of water, yielding phenol (C₆H₅OH).

Correct Pathway: This is a standard method for synthesizing phenol from aniline through diazotization followed by hydrolysis.

Option 2: Tertiary butyl benzene (C₆H₅C(CH₃)₃)

Reagents: O₂, H₂O, H⁺

The process involves:

1. Oxidation of the tertiary butyl group leads to the formation of benzoic acid (C₆H₅COOH).
2. Further reaction with water and acid does not yield phenol.

Incorrect Pathway: This does not lead to the formation of phenol.

Option 3: Phenol (C₆H₅OH) with conc. HNO₃

Reagents: Concentrated HNO₃

Phenol reacts with concentrated HNO₃ to produce nitrophenols (like picric acid). This reaction is nitration and does not synthesize phenol.

Incorrect Pathway: This modifies phenol but does not form it.

Option 4: Phenol (C₆H₅OH) with Na₂Cr₂O₇ and H₂SO₄

Reagents: Na₂Cr₂O₇ and H₂SO₄

This reaction involves the oxidation of phenol, leading to the formation of quinones or other oxidized products. This does not form phenol.

Incorrect Pathway: Phenol is oxidized, not synthesized.

Correct Answer: Option 1

Phenol (carbolic acid) is obtained from aniline (C₆H₅NH₂) through diazotization followed by hydrolysis.