Synthesis of Aspirin Lab Report

8 August 2016

The goal of this experiment was to synthesize aspirin. In this experiment aspirin, also known as acetylsalicylic acid, was synthesized from salicylic acid and acetic anhydride. In the reaction the hydroxyl group on the benzene ring in salicylic acid reacted with acetic anhydride to form an ester functional group. This method of forming acetylsalicylic acid is an esterification reaction. Since this esterification reaction is not spontaneous, sulfuric acid was used as a catalyst to initiate the reaction.

After the reaction was complete some unreacted acetic anhydride and salicylic acid was still be present in the solution as well as some sulfuric acid, aspirin, and acetic acid. Crystallization, which uses the principle of solubility, was then used to remove most of the impurities and caused the acetylsalicylic acid to precipitate out of the solution. Next, the crude product was then purified by adding water which further lowered the solubility of acetylsalicylic acid and dissolved some impurities from the crystal of aspirin.

Synthesis of Aspirin Lab Report Essay Example

The aspirin was then isolated from the solution using a vacuum filtration apparatus. The percent yield of crude aspirin product was 91. 89%. To purify the crude aspirin product a recrystallization procedure was performed. The percent yield of the purified aspirin product was 5. 77%. Next a phenol test was performed on the crude aspirin product, the purified aspirin product, and salicylic acid as a control. The phenol test was to test the purity of the aspirin product that was created during the experiment.

The crude aspirin product and the purified aspirin product had no color changes and remained orange when mixed with the iron (III) chloride solution, which means that there were no phenol groups in both the crude aspirin product and the purified aspirin product. The lack of reaction with the iron (III) chloride revealed that both the crude aspirin product and the purified aspirin product were pure aspirin. The salicylic acid turned into a dark purple color when mixed with the iron (III) chloride solution, which was expected since salicylic acid has phenol groups. Next a melting point test was performed on the purified aspirin product.

The purified product started to melt at 86 degrees Celsius and finished completely melting at 102 degrees Celsius. The melting point of the purified product was lower than the expected 135 degree Celsius melting point of aspirin, which revealed to us that the purified aspirin product still contained some impurities. Introduction: As early as 3000 BC ancient cultures such as Greek, Roman, Egyptian, and Chinese found that extracts from plants such as willow bark, meadowsweet, and myrtle possessed the ability to alleviate fever, pain, and inflammation. These plants contain a compound called salicylate, which creates these curative attributes.

Several of years later the folk remedy of plants containing salicylate transformed into the cure-all medication known as aspirin. Today aspirin, also known as acetylsalicylic acid, is an over the counter medication that is extremely popular and is used for relieving pain, reducing fever, reducing swelling, and slowing blood clotting. The history of aspirin began in 1763 when Edward Stone wrote a paper to the Royal Society of London that claimed that willow bark could cure ague, which is now known as malaria. Later it was found that the treatment did not actually cure malaria, but instead just reduced the fever of those with the disease.

Nearly a century later, a Scottish physician found that Edward Stone’s extract could also be used to relieve the symptoms of acute rheumatism. Organic chemists began working with willow bark and many other plants to try and extract and isolate the active ingredients from them, in doing so it was found that the active ingredient was salicylic acid. Salicylic acid was then industrialized for medicinal use, but soon after industrialization it was found that salicylic acid was extremely limited as a treatment because of the acidic properties that cause severe irritation in the digestive tract.

In 1893, Felix Hofmann synthesized acetylsalicylic acid, which has all of the same medicinal benefits as salicylic acid but it did not have the side effect of irritating the digestive tract. Hofmann worked for Bayer, which then named acetylsalicylic acid compound aspirin. Aspirin became commercially available in 1899 and today it is estimated that over a trillion aspirin tablets have been consumed by those in need of its curative effects. In this experiment aspirin was synthesized from salicylic acid and acetic anhydride.

Salicylic acid was esterfied using acetic acid and sulfuric acid acting as a catalyst to produce acetylsalicylic acid and acetic acid. The phenol group that will attack the carbonyl carbon of the acetic anhydride is the –OH group that is directly attached to the benzene since it is more basic than the –OH group attached to the carbonyl group. This method of forming acetylsalicylic acid is an esterification reaction. Since this esterification reaction is not spontaneous, sulfuric acid was used as a catalyst to initiate the reaction.

Sulfuric acid serves as the acid catalyst since its conjugate base is a strong deprotonating group that is necessary in order for this reaction to be reversible. The need for the strong conjugate base is the reason why other strong acids such as HCl is not used since its conjugate base Cl- is very weak compared to HSO3-. After the reaction was complete some unreacted acetic anhydride and salicylic acid was still be present in the solution as well as some sulfuric acid, aspirin, and acetic acid.

Crystallization, which uses the principle of solubility, was then used to remove most of the impurities and caused the acetylsalicylic acid to precipitate out of the solution. This precipitation happens because the solvent can no longer hold all of the solute molecules, and the molecules begin to leave the solution and form solid crystals. During this cooling, each solute molecule in turn approaches a growing crystal and rests on the crystal surface. If the geometry of the molecule fits that of the crystal, it will be more likely to remain on the crystal than it is to go back into the solution.

Therefore, each growing crystal consists of only one type of molecule, the solute. The acetylsalicylic acid’s solubility decreased and caused it to gradually precipitate out of the solution while the other compounds were left in solution because they were either a liquid at room temperature or have higher solubilities and would not completely crystallize out of the solution. After the solution had come to room temperature, it was carefully submerged in an ice bath to complete the crystallization process.

To purify the crude product, water was added to solution to further lower the solubility of acetylsalicylic acid and to dissolve some of the impurities from the crystal. The chilled solution was then filtered through vacuum filtration to isolate the pure crystals. Vacuum filtration was the technique used for separating the solid aspirin product from the solvent or liquid reaction mixture. The mixture of solid and liquid was poured through a filter paper in a Buchner funnel. The solid aspirin product was trapped by the filter and the liquid was drawn through the funnel into the flask below it by a vacuum.

The aspirin product that was collected still contained some impurities. The general reaction equation and the reaction mechanism are as follows: To purify the crude aspirin product a recrystallization procedure needed to be performed to remove impurities and to further purify it. Recrystallization utilizes the different solubilities of the desired product and impurities included in the reaction mixture. So, when the solvent cools, only the impurities will remain dissolved and the “pure” product will crystallize out of the solution.

The information we gather will allow us to determine the percent yield of the crude aspirin product and of the purified aspirin product. The percent yield is a way of measuring how successful a reaction has been. Percent yield problems allow us to calculate what percent of the expected product we are able to account for by the end of our experiment. Actual amount of product Percent yield = —————————————- x 100 Expected amount of product Next, a phenol test must be performed to determine the purity of the aspirin product.

The impurities that could be in the purified aspirin product could be salicylic acid and other compounds that contain a hydroxyl group on a benzene ring and are known as phenols. Phenols form a highly colored complex with iron (III) chloride that can range from a pale to dark purple depending on the concentration of the phenol group present in the solution. Pure aspirin does not contain any phenol groups and should be unreactive when mixed with the iron (III) chloride solution and should remain orange in color. Another way the purity of the sample is tested is through a melting point test on the purified aspirin product.

A pure compound has a specific range in which it melts and it is normally a fairly small range. If the melting point of the purified aspirin sample is lower than the expected or if it has a very broad range compared to the actual range, then the sample still contains some impurities. Experimental: In a 125 mL Erlenmeyer flask add 5 mL of acetic anhydride, 1. 999g of salicylic acid, and 5 drops of sulfuric acid. Swirl the mixture in the Erlenmeyer flask for approximately one minute so that all of its contents have completely dissolved.

Heat the mixture using a water bath for 10 minutes. The water bath temperature should not exceed 50 degrees Celsius. While heating the mixture, measure out 70 mL of DI water and then put it in a 100 mL beaker. Also, set up an ice bath for the mixture in the Erlenmeyer flask as well as a second ice bath for the 100 mL beaker while waiting for the mixture in the Erlenmeyer flask to heat. After the mixture has heated for 10 minutes, remove it from the water bath and allow it to cool to room temperature. Crystallization should begin once the solution reaches room temperature.

If crystallization does not occur use a glass stirring rod and with strong force scratch the bottom of the Erlenmeyer flask. Cool the Erlenmeyer flask containing the mixture in the ice bath set up previously for 20 minutes. At the same time place the 100 mL beaker containing 70 mL DI water in the second ice bath set up previously for 20 minutes. While waiting for those items to cool, set up the vacuum filtration apparatus. After 20 minutes of cooling, take 50 mL of the 70 mL now cooled DI water from the 100 mL beaker and add it to the 125 mL Erlenmeyer flask that contains the mixture.

Leave the 125 mL Erlenmeyer flask that contains the mixture in its ice bath and allow it to cool for an extra 5 minutes. Also leave the remaining 20 mL of DI water in the 100 mL beaker in its ice bath. After cooling for an additional 5 minutes, pour the contents in the 125mL Erlenmeyer flask into a Buchner funnel attached to the vacuum filtration apparatus. Make sure to get as much of the product into the Buchner funnel as possible. Use the remaining 20 mL of DI water in the 100 mL beaker to rinse out the 125 mL Erlenmeyer flask and wash the product in the Buchner funnel.

Allow the sample to vacuum dry for 5 minutes. While waiting for the sample to vacuum dry weigh a weigh boat. After the sample has dried for 5 minutes, turn off the vacuum filtration apparatus and retrieve the crude product from the Buchner funnel and place it in the previously weighed weigh boat. Weigh the weigh boat with sample inside and record the mass of the crude product formed. Calculate the percent yield of the product formed. Next, place a few crystals of the crude product in a test tube labeled A and put to the side for later use. Reweigh your sample and record the new mass

sample. Now place the crude product from the weigh boat in a 25 mL Erlenmeyer flask and add 3 mL of ethyl acetate. Heat the 25 mL Erlenmeyer flask in a water bath (not to exceed 50 degrees Celsius) until all of the product has dissolved. After 5 minutes if the product has not completely dissolved, add 5mL more of ethyl acetate. Place the 25 mL Erlenmeyer flask containing the product and ethyl acetate directly on the hot plate at 50 degrees Celsius. Raise the temperature of the hot plate to 125 degrees Celsius so that the solution boils. Keep a close eye on the Erlenmeyer flask.

Heat the mixture for 5 minutes. After heating the mixture for 5 minutes, gravity filter what is in the 25 mL Erlenmeyer flask through filter paper. Put what goes through the filter paper back in the 25 mL Erlenmeyer flask and add petroleum ether drop by drop until crystals begin to form. If crystals do not form, place the 25 mL Erlenmeyer flask on a hot plate at 125 degrees Celsius with a boiling stone in the mixture. Wait for the mixture to boil and then let it boil for 5 minutes. After boiling for 5 minutes remove the 25 mL Erlenmeyer flask and remove the boiling stone.

Allow the mixture to cool to room temperature. Scratch the bottom of the Erlenmeyer flask with a glass stirring rod with strong force. Place the Erlenmeyer flask in an ice bath for 30 minutes. Pour the contents in the 25 mL Erlenmeyer flask into a Buchner funnel attached to a vacuum filtration apparatus. Allow the product to vacuum dry for 5 minutes. While waiting for the sample to vacuum dry weigh a weigh boat. After the sample has dried for 5 minutes, turn off the vacuum filtration apparatus and retrieve the purified product from the Buchner funnel and place it in the previously weighed weigh boat.

Weigh the weigh boat with sample inside and record the mass of the purified product formed. Calculate the percent yield of the product formed. Next, place a few crystals of the purified product in a test tube labeled B. Next perform the phenol test. You must have three test tubes, one labeled A with the crude aspirin product in it, one labeled B with the purified aspirin product in it, and one labeled C with salicylic acid in it. The third test tube labeled C is a control. Add 10 drops of iron (III) chloride to each test tube. Record the color observations. After recording the color

of each test tube dispose of the waste into the appropriate waste container. Next, obtain a capillary tube. Fill the capillary tube with dry purified product. Invert the capillary tube and stick the open end of the capillary tube in the densest part of the crystal sample. Turn the capillary tube back to the upright position. The crystal product will be stuck at the top of the capillary tube. Tap the crystal product down to the bottom of the capillary tube. Load the capillary tube into the melting point apparatus and begin heating. Record the temperature range that the sample melts within.

Once the melting point has been determined turn off the apparatus so it may cool and dispose of your capillary tube in the appropriate waste bin. Clean and dry any glassware used and return it to the appropriate location. Results: Conclusion: The mass of the crude aspirin product was 4. 791g. Due to apparent wetness of the product it is estimated that half of the mass is due to moisture. Taking this into account, the actual mass of the crude aspirin product is reduced to 2. 396g. The theoretical yield of crude aspirin product is 2. 607g. This information gave us a percent yield of 91.

89%. The mass of the purified aspirin product was 0. 301g. Due to apparent wetness of the product it is estimated that half of the mass is due to moisture. Taking this into account, the actual mass of the purified aspirin product is reduced to 0. 1505g. The percent yield of purified aspirin product was 5. 77%. This low percent yield of purified aspirin product was due to a few different factors. The first factor that caused a low percent yield was caused because we lost some crude product when we were moving our crude product from the weigh boat to the 25 mL Erlenmeyer flask.

Another factor that could have caused a low percent yield was that when no crystals formed after adding drops of petroleum ether we placed our 25 mL Erlenmeyer flask back on the hot plate at 125 degrees Celsius. We could have accidentally boiled off some of our product. The third factor that caused a low percent yield of our purified product was that when we vacuum filtered our purified product, some of our purified product fell through the filter and into the side arm flask. Maybe if we hadn’t turned the water on so high it might not have fell through the filter.

The results of the phenol test were that test tube A, which contained crude aspirin product, had no change in color and remained orange upon adding iron (III) chloride. This led us to believe that our crude aspirin product did not contain any phenol groups and was pure aspirin. Test tube B, which contained purified aspirin product also had no change in color and remained orange upon adding iron (III) chloride. This led us to believe that our purified aspirin product did not contain any phenol group and was pure aspirin. Test tube C, which contained salicylic acid, had an extreme change in color and turned dark purple.

This was an expected result because salicylic acid has phenol groups and when iron (III) chloride is added it turned dark purple due to the concentration of the phenol groups present in the solution. Test tube C was our control. The results of the melting point test were that our purified aspirin product started melting at 86 degrees Celsius and at 102 degrees Celsius the entire purified aspirin product had completely melted. The melting point of the purified product was lower than the expected 135 degree Celsius melting point of aspirin, which revealed to us that the purified aspirin product still contained some impurities.

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