Question

In the following series of reactions identify the major products A & B respectively

• A. Product A: p-Bromobenzenesulfonic acid, Product B: 2,4-Dibromobenzenesulfonic acid

Answer 1

Answer: (A)

Product A: p-Bromobenzenesulfonic acid, Product B: 2,4-Dibromobenzenesulfonic acid

Answer 2

1. First Reaction: Bromobenzene treated with SO₃/H₂SO₄ undergoes sulfonation. Bromine is an ortho/para director, so the sulfonic acid group (–SO₃H) attaches predominantly at the para-position. Product A: p-Bromobenzenesulfonic acid

2. Second Reaction: The p-bromobenzenesulfonic acid is then treated with Br₂/Fe. Here, the substituents on the ring are –Br and –SO₃H. Bromine directs ortho/para but since –SO₃H is a strong deactivator and directs meta, the available position activated by the bromine is at the ortho position (which is meta to –SO₃H). This results in bromination at the 2-position (or 6‑position, which is equivalent by symmetry). Product B: 2,4-Dibromobenzenesulfonic acid