The preparation of 4-bromoacetanilide from acetanilide and bromine involves an electrophilic aromatic substitution reaction. The specific procedure and mechanism are as follows:Procedure:1. Dissolve a known amount of acetanilide in a suitable solvent, such as glacial acetic acid.2. Cool the solution in an ice bath to minimize side reactions.3. Slowly add a stoichiometric amount of bromine to the solution. Bromine can be dissolved in glacial acetic acid to form a solution.4. Add a catalytic amount of a Lewis acid catalyst, such as iron III bromide FeBr3 or aluminum chloride AlCl3 , to the reaction mixture. This catalyst will enhance the electrophilicity of the bromine.5. Stir the reaction mixture for a specific time, usually 30 minutes to 1 hour, to ensure the completion of the reaction.6. Pour the reaction mixture into cold water to precipitate the 4-bromoacetanilide product.7. Filter the precipitate and wash it with cold water to remove any remaining impurities.8. Recrystallize the product from a suitable solvent, such as ethanol or methanol, to obtain pure 4-bromoacetanilide.Mechanism:1. The Lewis acid catalyst e.g., FeBr3 reacts with bromine Br2 to form a highly electrophilic bromine ion Br+ .2. The electrophilic bromine ion attacks the aromatic ring of acetanilide, specifically at the para-position due to the activating effect of the amide group , forming a sigma complex.3. The sigma complex loses a proton to regenerate the aromatic ring and form the final product, 4-bromoacetanilide.Optimizing the yield:1. Use an excess of bromine to ensure complete reaction of the acetanilide.2. Maintain low temperatures during the reaction to minimize side reactions and the formation of ortho- and meta-substituted products.3. Use a suitable solvent that dissolves both the reactants and the catalyst, but does not react with them.4. Ensure proper stirring and sufficient reaction time for the reaction to reach completion.5. Optimize the recrystallization process to obtain a pure product with minimal loss.By following these steps and optimizing the reaction conditions, you can maximize the yield of 4-bromoacetanilide from acetanilide and bromine.