The preparation of 2,4-dichloronitrobenzene from nitrobenzene and chlorine gas involves electrophilic aromatic substitution. The optimal reaction conditions for this reaction are as follows:1. Temperature: The reaction is typically carried out at a temperature range of 40-60C. Higher temperatures can lead to the formation of undesired by-products, while lower temperatures can result in a slower reaction rate.2. Pressure: The reaction can be performed under atmospheric pressure. However, increasing the pressure can help improve the solubility of chlorine gas in the reaction mixture, which may lead to a higher yield.3. Concentration: The reaction is usually carried out in the presence of a catalyst, such as ferric chloride FeCl3 or aluminum chloride AlCl3 , to increase the electrophilicity of the chlorine gas. The concentration of the catalyst should be around 1-2 mol% relative to nitrobenzene. The molar ratio of nitrobenzene to chlorine gas should be close to 1:2 to ensure complete conversion of nitrobenzene to 2,4-dichloronitrobenzene.These reaction conditions affect the yield of the reaction in the following ways:- Temperature: Higher temperatures can increase the reaction rate but may also lead to the formation of undesired by-products, reducing the selectivity towards 2,4-dichloronitrobenzene. Maintaining an optimal temperature range ensures a good balance between reaction rate and selectivity.- Pressure: Increasing the pressure can improve the solubility of chlorine gas in the reaction mixture, leading to a higher yield. However, extremely high pressures may not be necessary and can add to the complexity and cost of the reaction setup.- Concentration: Using an appropriate catalyst concentration and maintaining the correct molar ratio of nitrobenzene to chlorine gas ensures complete conversion of nitrobenzene to 2,4-dichloronitrobenzene, maximizing the yield. Excessive amounts of catalyst or an incorrect molar ratio can lead to the formation of undesired by-products or incomplete conversion, reducing the overall yield.