The preparation of 2-chloro-4-nitroaniline from aniline and chlorine gas via the intermediate formation of 2,4-dichloronitrobenzene can be achieved through the following step-wise mechanism:Step 1: Nitration of AnilineAniline C6H5NH2 is first nitrated to form 4-nitroaniline C6H4 NO2 NH2 . This is done by treating aniline with a mixture of concentrated nitric acid HNO3 and concentrated sulfuric acid H2SO4 . The nitronium ion NO2+ generated from the reaction between HNO3 and H2SO4 acts as an electrophile, attacking the aniline molecule at the para position.Step 2: Acetylation of 4-Nitroaniline4-Nitroaniline is then acetylated to form N-acetyl-4-nitroaniline C6H4 NO2 NHCOCH3 . This is done by treating 4-nitroaniline with acetic anhydride CH3CO 2O. The acetyl group CH3CO acts as a protecting group for the amino group, preventing it from reacting in the next step.Step 3: Chlorination of N-acetyl-4-nitroanilineN-acetyl-4-nitroaniline is then chlorinated to form 2,4-dichloro-N-acetyl-nitrobenzene C6H3 NO2 Cl2NHCOCH3 . This is done by treating N-acetyl-4-nitroaniline with chlorine gas Cl2 in the presence of a catalyst, such as ferric chloride FeCl3 . The chlorine molecules act as electrophiles, attacking the N-acetyl-4-nitroaniline molecule at the ortho and para positions.Step 4: Hydrolysis of 2,4-dichloro-N-acetyl-nitrobenzene2,4-dichloro-N-acetyl-nitrobenzene is then hydrolyzed to form 2,4-dichloronitrobenzene C6H3 NO2 Cl2 and acetic acid CH3COOH . This is done by treating 2,4-dichloro-N-acetyl-nitrobenzene with water H2O and a base, such as sodium hydroxide NaOH .Step 5: Reduction of 2,4-dichloronitrobenzene2,4-dichloronitrobenzene is then reduced to form 2-chloro-4-nitroaniline C6H4 NO2 ClNH2 . This is done by treating 2,4-dichloronitrobenzene with a reducing agent, such as iron Fe and hydrochloric acid HCl , or sodium sulfide Na2S and ammonium chloride NH4Cl . The nitro group NO2 is reduced to an amino group NH2 , while one of the chlorine atoms remains attached to the benzene ring.The final product is 2-chloro-4-nitroaniline C6H4 NO2 ClNH2 .