The preparation of 2-chloro-4-nitroaniline from aniline and chlorine gas involves a two-step process: nitration followed by chlorination. Here's the mechanism for each step and some suggestions to maximize the yield and minimize side products:1. Nitration of aniline:Aniline C6H5NH2 is first nitrated to form 4-nitroaniline. This is done by treating aniline with a mixture of concentrated nitric acid HNO3 and concentrated sulfuric acid H2SO4 . The mechanism involves the formation of a nitronium ion NO2+ from nitric acid, which acts as the electrophile. The aniline molecule acts as a nucleophile, attacking the nitronium ion at the para position due to the activating effect of the amino group to form 4-nitroaniline.To maximize the yield of 4-nitroaniline and minimize the formation of ortho- and meta-nitroaniline, the reaction should be carried out at low temperatures 0-5C and with a slight excess of aniline. Additionally, aniline should be acetylated with acetic anhydride before nitration to protect the amino group and prevent the formation of meta-nitroaniline. After nitration, the acetyl group can be removed by hydrolysis to obtain 4-nitroaniline.2. Chlorination of 4-nitroaniline:The second step involves the chlorination of 4-nitroaniline to form 2-chloro-4-nitroaniline. This can be achieved by treating 4-nitroaniline with chlorine gas Cl2 in the presence of a catalyst, such as ferric chloride FeCl3 or aluminum chloride AlCl3 . The mechanism involves the electrophilic aromatic substitution of a chlorine atom at the ortho position of the 4-nitroaniline molecule.To maximize the yield of 2-chloro-4-nitroaniline and minimize side products, the reaction should be carried out at low temperatures 0-5C and with a slight excess of chlorine gas. The use of a catalyst, such as ferric chloride or aluminum chloride, will also help to improve the selectivity of the reaction.In summary, to maximize the yield of 2-chloro-4-nitroaniline and minimize side products, the nitration and chlorination reactions should be carried out at low temperatures, with a slight excess of aniline and chlorine gas, respectively. Additionally, protecting the amino group during nitration and using a catalyst during chlorination will help to improve the selectivity of the reactions.