answer:The preparation of 4-bromoacetanilide from acetanilide and bromine involves electrophilic aromatic substitution (EAS) reaction. Here is the step-by-step mechanism: 1. Activation of the aromatic ring: The lone pair of electrons on the nitrogen atom in the acetanilide molecule forms a resonance structure with the aromatic ring, activating the ring towards electrophilic substitution. The electron-donating nature of the nitrogen atom makes the ortho and para positions more electron-rich and susceptible to attack by electrophiles. 2. Generation of the electrophile: Bromine (Br2) reacts with a Lewis acid catalyst, such as aluminum bromide (AlBr3) or iron(III) bromide (FeBr3), to form a highly electrophilic bromonium ion (Br+). 3. Electrophilic attack: The electrophilic bromonium ion attacks the electron-rich ortho or para position of the activated aromatic ring, forming a sigma complex (also known as an arenium ion). 4. Deprotonation: A base, typically the bromide ion (Br-) generated in step 2, abstracts a proton from the sigma complex, restoring the aromaticity of the ring and yielding the final product, 4-bromoacetanilide. The reaction mechanism affects the yield of the product in several ways: 1. Regioselectivity: Since both ortho and para positions are activated, a mixture of ortho and para products (2-bromoacetanilide and 4-bromoacetanilide) is formed. However, due to steric hindrance, the para product (4-bromoacetanilide) is the major product, while the ortho product (2-bromoacetanilide) is the minor product. 2. Reaction conditions: The use of a Lewis acid catalyst, such as AlBr3 or FeBr3, is crucial for generating the electrophilic bromonium ion and promoting the reaction. The reaction temperature and concentration of reactants also affect the yield of the product. 3. Side reactions: Overbromination can occur, leading to the formation of di- or tri-bromoacetanilide products, which can decrease the yield of the desired 4-bromoacetanilide product. This can be minimized by using a stoichiometric amount of bromine and a controlled reaction temperature. In summary, the reaction mechanism of the preparation of 4-bromoacetanilide from acetanilide and bromine involves electrophilic aromatic substitution. The yield of the product is affected by regioselectivity, reaction conditions, and side reactions.

answer:The most efficient method for the preparation of 4-bromoacetanilide from acetanilide and bromine is the electrophilic aromatic substitution reaction, specifically bromination. In this reaction, the bromine atom acts as an electrophile and reacts with the aromatic ring of acetanilide, resulting in the formation of 4-bromoacetanilide. To achieve the highest yield and purity in the reaction, the following optimization conditions should be considered: 1. Use of a catalyst: A Lewis acid catalyst, such as aluminum bromide (AlBr3) or iron(III) bromide (FeBr3), can be used to enhance the reactivity of bromine and facilitate the electrophilic aromatic substitution reaction. 2. Reaction temperature: The reaction should be carried out at a low temperature, preferably between 0°C and 5°C, to minimize side reactions and improve the selectivity of the desired product. 3. Reaction time: The reaction should be monitored to determine the optimal reaction time for the highest yield and purity. Generally, a longer reaction time may lead to higher yields, but it can also increase the chances of side reactions and impurities. 4. Molar ratio: The molar ratio of acetanilide to bromine should be optimized to ensure that there is enough bromine to react with all the acetanilide, but not so much that it leads to the formation of undesired by-products. 5. Solvent: A suitable solvent, such as glacial acetic acid or dichloromethane, should be used to dissolve both the reactants and the catalyst. The solvent should be inert and non-reactive under the reaction conditions. 6. Purification: After the reaction is complete, the product mixture should be purified using appropriate techniques, such as recrystallization, column chromatography, or filtration, to remove any unreacted starting materials, catalysts, and by-products. By optimizing these conditions, it is possible to achieve the highest yield and purity of 4-bromoacetanilide from the reaction of acetanilide and bromine.

answer:To solve this problem, we will need to use stoichiometry, which involves using the balanced chemical equation to determine the mass of bromine required to prepare 25 grams of 4-bromoacetanilide. First, let's write the balanced chemical equation for the reaction: Acetanilide (C8H9NO) + Br2 → 4-bromoacetanilide (C8H8BrNO) + HBr Now, we need to determine the molar mass of acetanilide, 4-bromoacetanilide, and bromine: Acetanilide: (12.01 * 8) + (1.01 * 9) + (14.01 * 1) + (16.00 * 1) = 135.17 g/mol 4-bromoacetanilide: (12.01 * 8) + (1.01 * 8) + (79.90 * 1) + (14.01 * 1) + (16.00 * 1) = 214.07 g/mol Bromine (Br2): 2 * 79.90 = 159.80 g/mol Now, we can use stoichiometry to determine the mass of bromine required to prepare 25 grams of 4-bromoacetanilide: 1. Convert the mass of 4-bromoacetanilide to moles: 25 g / 214.07 g/mol = 0.1167 mol 2. Use the stoichiometry from the balanced equation: 1 mol Acetanilide : 1 mol Br2 : 1 mol 4-bromoacetanilide 3. Calculate the moles of bromine required: 0.1167 mol 4-bromoacetanilide * (1 mol Br2 / 1 mol 4-bromoacetanilide) = 0.1167 mol Br2 4. Convert the moles of bromine to mass: 0.1167 mol Br2 * 159.80 g/mol = 18.65 g Therefore, 18.65 grams of bromine (Br2) are required to prepare 25 grams of 4-bromoacetanilide from acetanilide.

answer:To determine the maximum yield of 4-bromoacetanilide, we first need to find the limiting reagent in the reaction. The reaction is as follows: Acetanilide + Br2 → 4-bromoacetanilide + HBr First, we need to calculate the moles of each reactant: 1. Acetanilide: The molecular weight of acetanilide (C8H9NO) is 135.17 g/mol. 5 g of acetanilide / 135.17 g/mol = 0.0370 mol of acetanilide 2. Bromine: Since there is a 25% excess of bromine, we need to calculate the moles of bromine required for the reaction and then add the excess. The molecular weight of bromine (Br2) is 159.81 g/mol. 0.0370 mol of acetanilide * 1 mol of Br2 / 1 mol of acetanilide = 0.0370 mol of Br2 (required for the reaction) 25% excess of bromine: 0.0370 mol * 1.25 = 0.0462 mol of Br2 (total) Since acetanilide is present in a lesser amount, it is the limiting reagent. Now, we can calculate the theoretical yield of 4-bromoacetanilide: The molecular weight of 4-bromoacetanilide (C8H8BrNO) is 214.06 g/mol. 0.0370 mol of acetanilide * 1 mol of 4-bromoacetanilide / 1 mol of acetanilide = 0.0370 mol of 4-bromoacetanilide 0.0370 mol of 4-bromoacetanilide * 214.06 g/mol = 7.92 g The theoretical yield of 4-bromoacetanilide is 7.92 g. The maximum yield of 4-bromoacetanilide that can be obtained from 5 grams of acetanilide and a 25% excess of bromine is 7.92 g.