Commercial benzene obtained from coal-tar distillation contains 3-5% thiophene as impurity. Suggest a simple method to purify it.

Commercial benzene obtained from coal-tar distillation contains 3-5% t

1.	Commercial benzene obtained from coal-tar distillation contains 3-5% thiophene as impurity. Suggest a simple method to purify it.
Answer» Solution :It is usually not easy to SEPARATE thiophene from benzene by fractional DISTILLATION because their boiling points are very close : benzene = 353 K, thiophene = 357 K. However, thiophene can be removed from commercial benzene by extraction with conc. `H_(2)SO_(4)`. The purification is based upon the fact that thiophene undergoes sulphonation much more easily than benzene. Thus, when commercial benzene is shaken with conc. `H_(2)SO_(4)` in a separating FUNNEL, thiophene undergoessulphonation to form thiophene-2-sulphonic ACID which dissolves in conc. `H_(2)SO_(4)` while benzene does not