2-bromo-1-chloro-4-nitrobenzene is synthesized from benzene in the following sequence.
Chlorination of benzene:
This is the halogenation reaction of benzene. In this step, benzene is reacted with chlorine gas in the presence of a Lewis acid (i.e. FeCl3). This leads to the formation of chlorobenzene as shown in the red step below.
Nitration of chlorobenzene:
The chlorine atom of benzene has an ortho-paradirecting effect. Nitration of chlorobenzene thus yields para-nitrochlorobenzene as shown in the blue step below.
Bromination of 1-chloro-4-nitrobenzene:
Bromination is carried out in this step by reacting bromine in the presence of a Lewis acid. The chlorine, which is ortho-paratropic in nature, and the nitro group, which is metatropic in nature, orient the incoming Br+. (electrophilic) to the desired location. Therefore, 2-bromo-1-chloro-4-nitrobenzene is synthesized in good yield.
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