Phenol is heated with concentrated sulphuric acid at `110^(@)C`. The major product formed is

Options

A. `4-`hydroxybenzensulphonic acid
B. `3-`hydroxybezenesulphonic acid
C. `2-`hydroxybenzenesulphonic acid
D. a mixture of all these in equal amounts

Answer

A

Explanation

The product of sulphonation of phenol depends upon the tempreture of reaction: chiefly ortho at `15-20^(@)C`, chiefly para at `100^(@)C`. Once formed `o-`phenol sulphonic acid is converted into the para isomar by sulphuric acid at `100^(@)C`. This happens because the `o-`isomer is the kinetically controlled (i.e. formed faster) and the `p-`isomer is the thermodynamically controlled (more stable) product.