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preparation Multistep of 4-bromo-2-chloro-6-iodoaniline Locker A-15 March 5, 2007 Monday 12:30-5:00 Step 1: Preparation of acetanilide Introduction: This is the first step in our synthesis of 4-bromo-2-chloro-6-iodoaniline. The first product to be synthesized is acetanilide from aniline. This is done by putting aniline into a hydrochloric acid solution. This would put the amine in equilibrium and then add acetic anhydride and sodium acetate to allow for the acetanilide functional group to substitute the amine group. Main Reaction: Data: Actual: Theoretical: Acetanilide Melting Point 101 -104 114 Amount Collected 17.85 g 15.75g Summary of Procedure: We started out by mixing aniline and .4N of hydrochloric acid. We stirred the mixture and warmed it up. In another flask we prepared a solution of 6.0g of sodium acetate trihydrate in 20ml of water. In a third container, we put 4.4 ml of acetic anhydride. We then added the acetic anhydride to the anilinium hydrochloride then added the solution of sodium acetate immediately after. We then cooled the reaction and vacuum filtrated the acetanilide that was created. Observations: o The acetanilide came as a powder in a very moist state o There was a lot of acetanilide that was produced from the synthesis Results and Calculations: Percent Yield Acetanilide Amount Collected 100% Summary of results: By mixing anilinium hydrochloride with acetic anhydride and sodium acetate, we were able to successfully form acetanilide. Our percent yield for the acetanilide was actually more than 100% but it was only this high because it was still wet and the weight of the water had an effect on the mass. Since we don't know the actual weight of the acetanilide, we must scale up for the next two steps to accommodate for the acetanilide. Post-Lab Questions: 20) The sodium acetate must be added quickly because the protonated ammonium species is a non-nucleophile because the lone pair of electrons on the nitrogen is not available. When acetic anhydride and amine hydrochloride are mixed, no acetylation occurs. The sodium acetate allows free amines to be liberated and allows acetic anhydride to react forming the acetylated product. 22) Aniline is soluble in aqueous hydrochloric acid because it has an NH2 group attached to the benzene ring that is a little bit more polar than the NHCOCH3 group on the acetanilide. This makes aniline soluble in hydrochloric acid and acetanilide insoluble. 25) IR of aniline: The NH parts of amines are in regions 3300-3000cm-1. This looks weaker than OH. These are sharp and distinguishable bands. The NH bending vibration of primary amines is seen in region 1650-1580 cm-1. Another region of amines is 910665 cm-1. The IR of acetanilide has a sharp peak around 3300. Step 2: Preparation of 4-bromoacetanilide Introduction: Step 2 of the 5 step synthesis requires the bromination of the previously synthesized acetanilide. This is a simple step and requires only bromine to brominate it. We expect to get the bromo functional group to substitute at the para position to the acetanilide group because the acetanilide group is a para or ortho director, but the ortho position is too hindered for bromo substitution to occur there, therefore the para product will be the major product in this reaction. Main Reaction: Data: 4-Bromoacetanilide Actual: Melting Point 158 -161 Amount Collected 15.94 g Summary of Procedure: Theoretical: 168 25.26g We first set up two containers, one of bromine in 6ml of glacial acetic acid and one with acetanilide in glacial acetic acid. We then add the bromine to the acetanilide and then stirred for 10 minutes. Then we added 100ml of ice-cold water and then added sodium bisulfite to discharge the color of the mixture. Next, we cooled the solution and then did a vacuum filtration. Observations: o As the sodium bisulfite was added, the color of the mixture went from a yellow solution to a milkier, whiter solution. Results and Calculations: Percent Yield 4-Bromoacetanilide Amount Collected 63.1% Summary of results: The preparation of 4-bromoacetanilide required the mixture of bromine with the acetanilide that we had prepared from the lab before. This resulted in adding a bromine function group to our acetanilide compound. The bromine was likely to add para to the acetanilide group because it is ortho or para directing and ortho to usually too hindered to have occurred. Our percent yield was only 63.1% this time. This could have been due to human error in lab process. Post-Lab Questions: 8) The steric hindrance of the acetanilide group is the reason why bromo substitution occurs at the para position for major products. This can be seen in the higher melting points of the product which para products tend to have over ortho products because of it's rigid structure. 14) NMR: There is an 8.3 double which is the H next to the nitrogen. The 7.58 singlets are the aromatic H's meta to Cl. The 7.53 singlet are the aromatic Hs that are ortho to the Cl. The H next to the Cl is indicated by the 7.4 quadruplet. Step 3: Preparation of 4-bromo-2-chloroacetanilide Introduction: The third step of the multistep synthesis requires the addition of the chlorine functional group. Since the bromo group is now occupying the para position of the ring, the chloro group will be forced to the position ortho to the acetanilide since acetanilide is a better director than the bromo group. Chlorine gas is needed to chlorinate the product and this is done by the reaction of sodium chlorate and hydrochloric acid. Main Reaction: Data: Actual: 4-bromo-2chloroacetanilide Melting Point 130 -133 Amount Collected 15.82 g Theoretical: 151 -152 18.47g Summary of Procedure: We mixed the 4-bromoacetanilide formed from the previous step with hydrochloric acid and glacial acetic acid. We then heated the mixture until it became homogenized. Afterwards, we cooled the solution in an ice-water bath. In another container we made a solution of sodium chlorate and water. We then added this sodium chlorate solution to the previous solution. This could take up to an hour because of the exothermic reaction and mass release of heat. Finally, we vacuum filtrated the solution to collect 4-bromo-2chloro-acetanilide. Observations: o The addition of the sodium hydroxide solution made a very quick reaction and it took awhile to add all of it because we didn't want the reaction to get too hot or it would decompose Results and Calculations: Percent Yield 4-bromo-2-chloroacetanilide Amount Collected 85.7% Summary of results: By adding sodium chlorate and hydrochloric acid together, we were able form to a chloride substance that would eventually add a functional group to the 4bromoacetanilide. This function group would be a chlorine ion and add onto the group ortho to the acetanilide. This is because the acetanilide is a stronger director than the bromine group on the ring. Our percent yield for this 85.7% which is impressively high. Some of the loss can once again be attributed to human error. Post-Lab Questions: 18) 4-bromoacetanilide is more reactive than 4-bromo-2-chloroacetanilide toward electrophilic substitution because the addition of the chlorine group deactivates the ring eve more. The ring reactivity decreases as every halogen group is added. 21) NMR: There is an 8.3 doublet which is the H next to the nitrogen. The 7.58 singlets are the H's meta to the Cl. The 7.53 singlet is are the aromatic H's ortho to the Cl group. The 7.4 quadruplet is the H next to the Cl. Step 4: Preparation of 4-bromo-2-chloroaniline Introduction: This fourth step of the multistep synthesis is necessary because it allows the fifth step to occur. The acetanilide group must be changed into an aniline group again since the ring is too deactivated with the halogen groups on it. To change it back into an aniline group, we must mix it with hydrochloric acid and sodium hydroxide solution as is done in this step. Main Reaction: Data: Actual: Theoretical: 4-bromo-2chloroaniline Melting Point 54 -56 72 Amount Collected 9.60 g 13.14g Summary of Procedure: Using all the 4-bromo-2-chloroacetanilide and mixing it with ethanol and hydrochloric acid, we set up the solution for a reflux. After heating the mixture for reflux for about half an hour, we added hot water to dissolve any solid and then we poured the hot solution onto 250g of ice in a beaker. While stirring the mixture, we added 14N sodium hydroxide solution. We then added more ice if all the initial ice melted. Next, we checked the pH of the mixture to make sure it was basic and then we collected the solid by vacuum filtration. To purify the product, we recrystallized it by putting it in methanol and collecting the product by vacuum filtration again. We washed this product with cold water just to purify it a little more. Observations: o Use the 14N NaOH. This is very dangerous, if you fingers or hands begin to feel slippery you should wash with lost of water until the slippery feeling goes away. o The pH of the solution was basic as we tested with pH and the color came out blue indicating it was a basic solution. o Crystals were retrieved as the end result Results and Calculations: 4-bromo-2-chloroaniline Amount Collected Percent Yield 73.1% Summary of results: After mixing the 4-bromo-2-chloroacetanilide with ethanol and hydrochloric acid, we were to successfully form 4-bromo-2-chloroaniline. The purpose of this step of the synthesis is to make the compound more reactive to iodination in the final step. Our percent yield this time was only 73.1%. This is a decent amount but not as good as the last step. Our total percent yield thus far is 39.53%. This aniline functional group is better for iodination because it is a stronger activator than the acetanilide when compared to the bromo and chloro groups. The melting points of the actual and theoretical products are pretty close to each other. This means that this is likely 4-bromo-2-chloroaniline. Post-Lab Questions: 22) The white precipitate that is formed is a salt. The HCl addition followed by NaOH makes this salt. 27) NMR: There is a 7.3 doublet which is the H ortho the Cl. The 7.15 quadruplet is the aromatic H para to the Cl. The 6.62 doublet is the aromatic H meta to the Cl and the 2 4.0 singlets are the two Hs from the NH2. Step 5: Preparation of 4-bromo-2-chloro-6-iodoaniline Introduction: This final step is the iodination of the 4-bromo-2-chloroaniline. This is done by reacting iodine monochloride with the 4-bromo-2-chloroaniline. Iodination is possible because the aniline group is back on the ring and helps activate the ring to further substitution. Previously, the two halogen groups (bromo and chloro) deactivated the ring too much to allow for effective substitution, but changing the acetanilide group back into an aniline group allows for this. Main Reaction: Data: 4-bromo-2-chloro6-iodoaniline Melting Point Amount Collected Actual: 78 -81 3.23 g Theoretical: 120 -122 4.0g Summary of Procedure: To set up, we put 2.5g of the recrystallized 4-bromo-2-chloroaniline in 40ml of glacial acetic acid along with 10ml of water. In an Erlenmeyer flask, we put 2.5g of iodine monochloride in 10mL of glacial acetic acid. As the aniline is solution is stirred, we slowly added the iodine solution to the mixture. We then heated the solution to 90 and then cooled it back down to 50 . We added sodium bisulfite to discolor the solution, which meant that it removed any excess iodine. Water was then added so that the total volume of the water added and sodium bisulfite added came out to 15mL. Next, we cooled the solution in an ice-water bath and then performed a vacuum filtration. To purify the product we put it in 80mL of glacial acetic acid and then slow added 20ml of water to the product as it was heating. We then let the mixture cool and then performed another vacuum filtration. This final product was our 4-bromo-2-chloro-6-iodoaniline. Observations: o The addition of the iodine make the product very brown colored o The addition of sodium bisulfite fixed this by discoloring the solution and turn it back into a peachy, white color Results and Calculations: Percent Yield 4-bromo-2-chloro-6-iodoaniline Amount Collected 80.1% Summary of results: Our final product, 4-bromo-2-chloro-6-iodoaniline came out in a 80.1% yield. The total percentage from step one of the synthesis is 31.2%. Starting out with aniline, we were able to make acetanilide and brominates that to make 4-bromoacetanilide and then chlorinate that to make 4-bromo-2-chloroacetanilide and then convert is back into its aniline group to make 4-bromo-2-chloroaniline and then finally iodinate that to make our final product, 4-bromo-2-chloro-6-iodoaniline. My melting point and the literature melting point differ quite a bit in this one. This may be because of human error throughout the lab that could have contributed to this. Post-Lab Questions: 29b) The bromination with BrCl would result in a Br compound at the 6 poistion and it would be 4,6-dibromo-2-chloroaniline. 36) NMR: There is a 7.65 doublet which is the aromatic H ortho to the I. The 7.38 doublet is the aromatic H ortho to Cl, and there are 2 4.6 singlets which are the H's from the NH2. ... View Full Document

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