Question:

Phenol, when it first reacts with concentrated sulphuric acid and then with concentrated nitric acid, gives

• 2,4,6-trinitrobenzene
• o-nitrophenol
• p-nitrophenol
• nitrobenzene

Source: AIEEE 2008

Solution:

Sulphonation blocks the para position and reduces the reactivity of the phenolic group against HNO_3 and hence NO_2 is attached to the ortho position. Also, because we have a very strong acidic medium, desulphonation takes place as well.