The preparation of p-nitroaniline from aniline and nitric acid is an example of an electrophilic aromatic substitution reaction, specifically nitration. To achieve maximum yield, the reaction conditions must be carefully controlled.The optimal temperature for the nitration of aniline to form p-nitroaniline is around 0-5C. This low temperature is necessary to minimize the formation of undesired by-products, such as dinitroaniline or ortho-nitroaniline. The reaction should be carried out in an ice bath to maintain the low temperature.Before the nitration, aniline should be converted to its acetate salt anilinium acetate by treating it with acetic acid. This step helps to protect the amino group and directs the nitration to the para position.The duration of the reaction depends on the rate at which the nitric acid is added to the reaction mixture. It is crucial to add the nitric acid slowly and carefully to avoid a rapid increase in temperature, which can lead to the formation of undesired by-products. The addition of nitric acid should take around 30-60 minutes. After the addition is complete, the reaction mixture should be stirred for an additional 30 minutes to ensure complete nitration.In summary, the optimal conditions for the preparation of p-nitroaniline from aniline and nitric acid are:1. Temperature: 0-5C maintained using an ice bath 2. Duration: 60-90 minutes 30-60 minutes for nitric acid addition, followed by 30 minutes of stirring Please note that this reaction involves hazardous chemicals, and proper safety precautions should be taken while performing the experiment.