The preparation of p-nitroaniline from aniline and nitric acid is an example of electrophilic aromatic substitution, specifically nitration. The reaction involves the formation of a nitronium ion NO2+ from nitric acid, which then attacks the aniline molecule at the para position to form p-nitroaniline.To optimize the reaction conditions, it is important to consider the following factors:1. Temperature: The nitration of aniline is an exothermic reaction. It is essential to maintain a low temperature 0-5C to control the reaction rate and minimize the formation of by-products such as o-nitroaniline and dinitroaniline. An ice bath can be used to maintain the low temperature.2. Concentration of reagents: The use of concentrated nitric acid 65-70% is required for the formation of the nitronium ion. However, aniline is highly reactive, and direct nitration with concentrated nitric acid can lead to the formation of multiple nitro groups on the aniline molecule. To avoid this, aniline is first treated with acetic anhydride to form an acetanilide, which is less reactive. The acetanilide is then nitrated with a mixture of concentrated nitric acid and concentrated sulfuric acid 1:1 ratio . The sulfuric acid acts as a catalyst, promoting the formation of the nitronium ion.3. Reaction time: The reaction time depends on the temperature and the concentration of the reagents. Typically, the reaction is complete within 30 minutes to 1 hour. The progress of the reaction can be monitored using thin-layer chromatography TLC to determine when the starting material has been consumed.Under optimal conditions, the percentage yield of p-nitroaniline can be around 80-90%. However, the actual yield may vary depending on the purity of the starting materials, the efficiency of the work-up procedure, and the effectiveness of the purification method e.g., recrystallization .