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Synthesis of p-Bromoaniline Why is a sodium acetate solution added in part 1? a)  The sodium ion directs the position of the acetyl group.   b) To protonate the intermediate and make it less soluble.  c)  The acetate catalyzes the formation of the amide bond.  d)  To deprotonate the intermediate and make it less soluble

Synthesis of p-Bromoaniline Why is a sodium acetate solution added in part 1? a)  The sodium ion directs the position of the acetyl group.   b) To protonate the intermediate and make it less soluble.  c)  The acetate catalyzes the formation of the amide bond.  d)  To deprotonate the intermediate and make it less soluble

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Synthesis of p-Bromoaniline

Why is a sodium acetate solution added in part 1?

a)  The sodium ion directs the position of the acetyl group. 

 b) To protonate the intermediate and make it less soluble. 

c)  The acetate catalyzes the formation of the amide bond. 

d)  To deprotonate the intermediate and make it less soluble

 

Experiment 6: Synthesis of p-Bromoaniline Introduction Since the amino group of aniline is a strong activator of the aromatic ring, direct bromination is impractical because it leads to several products (equation 1) that are difficult to separate. To make the desired product, the amino group needs to be protected as the acetamide, which also maintains the direction of the incoming electrophile into ortho and para position. It slows down the rate of reaction and introduces steric hindrance for the ortho positions (equation 2). Both factors lead to an increased selectivity for the desired para product (equation 3). The acetamide can be hydrolyzed back to the amine (equation 4). This strategy of protection and deprotection is a very important tool in organic chemistry, especially in multi-step synthesis. In this experiment, p-bromoaniline was synthesized in three steps starting from aniline. Equation 1: NH2 NH2 Br Brz plus mono-and disubstitution products Equation 2: NH3 NH Equation 3: NH Brz Equation 4: NH NH2 Acid hydrolysis Br Br
Transcribed Image Text:Experiment 6: Synthesis of p-Bromoaniline Introduction Since the amino group of aniline is a strong activator of the aromatic ring, direct bromination is impractical because it leads to several products (equation 1) that are difficult to separate. To make the desired product, the amino group needs to be protected as the acetamide, which also maintains the direction of the incoming electrophile into ortho and para position. It slows down the rate of reaction and introduces steric hindrance for the ortho positions (equation 2). Both factors lead to an increased selectivity for the desired para product (equation 3). The acetamide can be hydrolyzed back to the amine (equation 4). This strategy of protection and deprotection is a very important tool in organic chemistry, especially in multi-step synthesis. In this experiment, p-bromoaniline was synthesized in three steps starting from aniline. Equation 1: NH2 NH2 Br Brz plus mono-and disubstitution products Equation 2: NH3 NH Equation 3: NH Brz Equation 4: NH NH2 Acid hydrolysis Br Br
Bromine is very corrosive. Wear gloves. p-Bromoaniline is harmful if inhaled or absorbed through the skin. Aniline is highly toxic. It is a possible mutagen, sensitizer, and readily absorbed through the skin. Concentrated hydrochloric acid, concentrated sulfuric acid, and 10 M sodium hydroxide solution are very corrosive. Procedure Part 1: Dilute 2.0 mL of concentrated HCl in 50 mL of water in a 125 ml flask. Then add 2.05 g (2.0 mL) of aniline. Stir the mixture until the aniline completely dissolves (HCl and aniline react forming anilinium chloride). Add 2.77 g (2.56 mL) of acetic anhydride, stir until it is dissolved. Then, immediately pour a solution of 3.3 g of sodium acetate in 10 mL of water into the flask. After complete addition, stir vigorously for 5 minutes, then cool in an ice bath to cause crystallization. When no more crystals seem to form (~10 minutes), isolate the acetanilide by vacuum filtration using a small Büchner funnel, wash the crystals with small volumes of ice-cold water, and air dry for 5 minutes. Recrystallize the obtained acetanilide from a minimum of hot water. Use 10 mL of water to start and increase the amount of water depending on the amount of acetanilide. If the initial crystals were not white, add 0.5 g of decolorizing charcoal to the product in water and then heat to gently boiling. Remove the charcoal by hot gravity filtration using two pieces of fluted filter paper. To avoid contaminating the filtrate with charcoal, do not overflow the filter funnel. After recrystallization, wash the crystals again with small volumes of cold water. Dry the product, obtain the mass, an infrared spectrum, and the melting point. Pure acetanilide is usually obtained as white flakes. The typical yield for this reaction is 80 %. Part 2:
Transcribed Image Text:Bromine is very corrosive. Wear gloves. p-Bromoaniline is harmful if inhaled or absorbed through the skin. Aniline is highly toxic. It is a possible mutagen, sensitizer, and readily absorbed through the skin. Concentrated hydrochloric acid, concentrated sulfuric acid, and 10 M sodium hydroxide solution are very corrosive. Procedure Part 1: Dilute 2.0 mL of concentrated HCl in 50 mL of water in a 125 ml flask. Then add 2.05 g (2.0 mL) of aniline. Stir the mixture until the aniline completely dissolves (HCl and aniline react forming anilinium chloride). Add 2.77 g (2.56 mL) of acetic anhydride, stir until it is dissolved. Then, immediately pour a solution of 3.3 g of sodium acetate in 10 mL of water into the flask. After complete addition, stir vigorously for 5 minutes, then cool in an ice bath to cause crystallization. When no more crystals seem to form (~10 minutes), isolate the acetanilide by vacuum filtration using a small Büchner funnel, wash the crystals with small volumes of ice-cold water, and air dry for 5 minutes. Recrystallize the obtained acetanilide from a minimum of hot water. Use 10 mL of water to start and increase the amount of water depending on the amount of acetanilide. If the initial crystals were not white, add 0.5 g of decolorizing charcoal to the product in water and then heat to gently boiling. Remove the charcoal by hot gravity filtration using two pieces of fluted filter paper. To avoid contaminating the filtrate with charcoal, do not overflow the filter funnel. After recrystallization, wash the crystals again with small volumes of cold water. Dry the product, obtain the mass, an infrared spectrum, and the melting point. Pure acetanilide is usually obtained as white flakes. The typical yield for this reaction is 80 %. Part 2:
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