Question

Give the structure and name of the product in the following reaction.

Sulphonation of chlorobenzene.

Answer 1

When chlorobenzene is treated with concentrated sulphuric acid (H₂SO₄) or fuming sulphuric acid (oleum, H₂S₂O₇), it undergoes electrophilic substitution at the aromatic ring. The sulphonation occurs at the para position relative to the chlorine atom due to its electron-withdrawing yet ortho/para-directing nature.

1. Reaction equation:
   \[\ce{C6H5Cl + H2SO4 ->[conc. H2SO4, Δ][]o-ClC6H4SO3H + p-ClC6H4SO3H}\]
   (Chlorobenzene) + (sulphonating agent) → ortho- and para-chlorobenzenesulphonic acids
2. Structure of the Product: p-Chlorobenzenesulphonic acid
   
   • The chlorine is attached to one carbon of the benzene ring.
   • The –SO₃H (sulphonic acid group) is attached to the para-position relative to Cl.
     
3. Name of the Product: para-Chlorobenzenesulphonic acid (or 4-Chlorobenzenesulphonic acid)