Question

Design a synthesis of 2-bromo-1-chloro-4-nitrobenzene from benzene or any mono-substituted benzene. Part 1 out of 6 choose the best option for the immediate precursor to the target molecule.

Answer 1

2-bromo-1-chloro-4-nitrobenzene  is being synthesized in following sequence:

Step 1: Chlorination of Benzene:

                                                     This is Halogenation reaction of benzene. In this step benzene is reacted with Chlorine gas in the presence of lewis acid (i.e. FeCl₃). This results in the formation of Chlorobenzene as shown in red step below.

Step 2: Nitration of Chlorobenzene:

                                                          The chlorine atom on benzene has a ortho para directing effect. Therefore, the nitration of chlorobenzene will yield para nitro chlorobenzene as shown in blue step below.

Step 3: Bromination of 1-chloro-4-nitrobenzene:

                                                                               In this step bromination is done by reacting bromine in the presence of lewis acid. The chlorine being ortho para directing in nature and nitro group being meta directing in nature will direct the incoming Br⁺ (electrophile) to the desired location. Hence, 2-bromo-1-chloro-4-nitrobenzene is synthesized in good yield.