Predict the products, A and B in the following reaction sequence:

The correct answer is Option (2) → 

 

Step 1: Reaction with concentrated $H_{2}SO_{4}$

Phenol undergoes sulphonation when treated with concentrated sulfuric acid.

The $-OH$ group on phenol is a strong activating ortho/para directing group, so sulphonation occurs at ortho and para positions.

Under strong sulphonation conditions (conc. $H_{2}SO_{4}$), two sulfonic acid groups are introduced to give:

Phenol-2,4-disulphonic acid

Thus,

$A =$ Phenol-2,4-disulphonic acid

Step 2: Reaction with concentrated $HNO_3$

When this compound is treated with concentrated nitric acid:

• The $-SO_3H$ groups are replaced by $-NO_2$ groups.
• Nitration occurs strongly because the $-OH$ group activates the ring.

This ultimately forms 2,4,6-trinitrophenol, commonly known as picric acid.

Thus,

B = 2,4,6-trinitrophenol

Option 1

Although A resembles the disulphonation product, the nitration product given is 2,4-dinitrophenol, whereas the reaction actually produces 2,4,6-trinitrophenol.

Option 2

$A =$ Phenol-2,4-disulphonic acid $B =$ 2,4,6-trinitrophenol (picric acid)

This correctly represents the reaction sequence.

Option 3

This assumes only monosulphonation occurs, which is not correct under strong sulphonation conditions.

Option 4

This product retains the $-SO_3H$ group after nitration, which does not occur in this reaction.

Incorrect.