Aspirin Synthesis General Chemistry 101/102 Laboratory Manual University of North Carolina Wilmington

Aspirin Synthesis Purpose Safety Considerations To introduce organic chemistry by synthesizing Aspirin. To review the concept of limiting reagent and stochiometric factor. To learn how to calculate the theoretical yield and percent yield of the aspirin synthesized. Safety Considerations Exercise care not to burn yourself on hot ringstands, rings, and beakers. Avoid inhaling any vapors from Acetic anhydride (in fume hood) as it is a strong corrosive agent and a lachrymator. Phosphoric acid (in fume hood) should also be handled with care as it is a fairly strong acid and will cause burns. Do NOT ingest your synthesized Aspirin, no matter how much you may have a headache!!

Aspirin Synthesis Introduction In this experiment you will be synthesizing an organic compound, acetylsalicylic acid (known as Aspirin) using an organic reaction. This reaction is called esterification, and it will add an ester group, a –COCH3 group to the benzene ring of a salicylic acid compound. Many painkillers contain the benzene ring as their central structure, as shown in the diagram above right. Salicylic acid, the main component of Aspirin and one of the reactants in this reaction was first recognized for its curative powers by many native cultures. It was originally derived from natural materials, such as the bark of the willow tree and the meadowsweet flower. Although effective, salicylic acid caused many undesirable side effects due to its high acidity. In 1893 a German chemist synthesized acetylsalicylic acid by adding the acetyl group (-COCH3) to mask these irritations caused by ingestion of salicylic acid alone.

Aspirin Synthesis Procedure Add about 2 g of salicylic acid to a pre-weighed 50 mL Erlenmeyer flask. Add 5.0 mL of acetic anhydride to the flask. Add 5 drops of phosphoric acid to the mixture and stir with a clean glass stirring rod. Caution: acetic anhydride and phosphoric acid can produce burns. They are located in the fume hood.

Aspirin Synthesis Procedure Clamp the flask to a ring stand and immerse it in a 400 mL beaker containing tap water. Heat the bath to 75oC and maintain this temperature for 5 minutes while stirring the mixture to dissolve the contents.

Aspirin Synthesis Procedure After heating, cautiously add 2 mL DI water to the flask and stir. Remove the mixture from the water bath and let cool to room temperature (25oC). Remember DO NOT touch the hot ring clamp until has had sufficient time to cool.

Aspirin Synthesis Procedure Once the flask is cooled to room temperature, add 20 mL of DI water and stir. Place the flask in an ice bath to speed the crystallization process. Allow the flask to remain in the ice bath for 5 minutes. If crystals have not formed after 5 minutes, vigorously scratch the inside of the flask with a glass stirring rod.

Aspirin Synthesis Procedure Collect the Aspirin crystals by vacuum filtration using a Buchner funnel. Secure the funnel by clamping it to a ring stand to prevent spilling your residue. Remember moisten the filter paper once it is inside the funnel by using a small amount of DI water in a squeeze bottle. This will secure the filter paper so that it is “flush” to the bottom surface of the funnel.

Aspirin Synthesis Procedure Wash the aspirin crystals with a 5 mL portion of ice-cold DI water. Turn on the suction to remove the wash water and repeat the washing with another 5 mL portion of ice-cold DI water. Allow air to be drawn over the crystals by suction for 3 minutes until the crystals are dry.

Aspirin Synthesis When the crystals are dry and fluffy, determine the mass of your aspirin. Record this weight as your actual yield of aspirin. Calculate the amount of aspirin you could produce, called the theoretical yield of aspirin. This value is based on the stochiometric amounts of reactants in the balanced equation and the limiting reagent. Calculate the percent yield of aspirin you produced by dividing the actual yield by the theoretical yield of aspirin and multiply by 100%.