The most efficient method to prepare 2-chloro-4-nitroaniline from aniline and chlorine gas involves a two-step process:Step 1: Nitration of anilineFirst, you need to protect the amino group of aniline by acetylating it with acetic anhydride. This will form N-acetylaniline. The purpose of this step is to prevent the amino group from reacting with the nitration reagents in the next step.Next, nitrate the N-acetylaniline using a mixture of concentrated nitric acid HNO3 and concentrated sulfuric acid H2SO4 . This will form 4-nitro-N-acetylaniline.Step 2: ChlorinationIn this step, you will chlorinate the 4-nitro-N-acetylaniline. To do this, dissolve the 4-nitro-N-acetylaniline in an appropriate solvent, such as carbon tetrachloride CCl4 or chloroform CHCl3 . Then, bubble chlorine gas Cl2 through the solution under controlled conditions e.g., low temperature, controlled rate of Cl2 addition . This will form 2-chloro-4-nitro-N-acetylaniline.Finally, hydrolyze the 2-chloro-4-nitro-N-acetylaniline using aqueous hydrochloric acid HCl to remove the acetyl protecting group. This will yield the desired product, 2-chloro-4-nitroaniline.To ensure optimal yield and purity, it is crucial to monitor reaction conditions e.g., temperature, concentration, and reaction time and use appropriate purification techniques, such as recrystallization or column chromatography, after each step.