The optimal reaction condition for the preparation of p-nitroaniline from aniline and nitric acid involves the nitration of aniline. The nitration reaction is an electrophilic aromatic substitution reaction, where a nitro group -NO2 is introduced to the benzene ring of aniline.To obtain a high yield of p-nitroaniline, the following reaction conditions should be considered:1. Protecting the amino group: The amino group -NH2 in aniline is highly activating and ortho/para-directing, which can lead to over-nitration and formation of undesired products. To prevent this, the amino group should be protected by converting it into an acetanilide group -NHCOCH3 using acetic anhydride. This will make the ring less reactive and more selective towards the para position.2. Choice of nitrating agent: A mixture of concentrated nitric acid HNO3 and concentrated sulfuric acid H2SO4 is commonly used as the nitrating agent. The sulfuric acid acts as a catalyst, generating the nitronium ion NO2+ , which is the electrophile in the reaction.3. Temperature control: The nitration reaction is exothermic, and high temperatures can lead to over-nitration and formation of undesired products. The reaction should be carried out at low temperatures, preferably between 0-5C. The reaction mixture should be cooled in an ice bath, and the nitrating agent should be added slowly to maintain the low temperature.4. Reaction time: The reaction should be allowed to proceed until the desired product is formed. The progress of the reaction can be monitored using thin-layer chromatography TLC or other analytical techniques. Typically, the reaction takes a few hours to complete.5. Workup and purification: After the reaction is complete, the mixture should be poured into cold water to precipitate the crude product. The solid product can be collected by filtration and washed with water to remove any remaining acids. The crude product can then be purified by recrystallization from a suitable solvent, such as ethanol or water.6. Deprotection of the amino group: To obtain the final p-nitroaniline product, the protecting acetanilide group must be removed. This can be achieved by hydrolyzing the amide bond using an aqueous solution of hydrochloric acid HCl or sulfuric acid H2SO4 under reflux. The p-nitroaniline can then be isolated by filtration and recrystallization.By following these optimal reaction conditions and steps, the yield of p-nitroaniline can be significantly improved.