Action of conc. sulphuric acid at different temperatures on phenol:
Pheno reacts with conc. sulphuric acid to form a mixture of o-, and p-phenol sulphonic acid.
At low temperature about 288 to 293 K, o-phenol sulphonic acid is the main product formed.
At high temperature about 373 K, p-phenol sulphonic acid is the main product formed.