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

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Aspirin SynthesisAspirin Synthesis

General Chemistry 101/102General Chemistry 101/102Laboratory ManualLaboratory Manual

University of North Carolina WilmingtonUniversity of North Carolina Wilmington

CHM 101/102CHM 101/102


Aspirin SynthesisAspirin Synthesis• PurposePurpose

To introduce organic chemistry by synthesizing Aspirin. To introduce organic chemistry by synthesizing Aspirin. To review the concept of limiting reagent and stochiometric To review the concept of limiting reagent and stochiometric

factor.factor. To learn how to calculate the theoretical yield and percent yield To learn how to calculate the theoretical yield and percent yield

of the aspirin synthesized.of the aspirin synthesized.

• Safety ConsiderationsSafety Considerations Exercise care not to burn yourself on hot ringstands, rings, and beakers.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 Avoid inhaling any vapors from Acetic anhydride (in fume hood) as it is a

strong corrosive agent and a lachrymator.strong corrosive agent and a lachrymator. Phosphoric acid (in fume hood) should also be handled with care as it is Phosphoric acid (in fume hood) should also be handled with care as it is

a fairly strong acid and will cause burns.a fairly strong acid and will cause burns. Do NOT ingest your synthesized Aspirin, no matter how much you may Do NOT ingest your synthesized Aspirin, no matter how much you may

have a headache!!have a headache!!

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Aspirin SynthesisAspirin Synthesis• IntroductionIntroduction

• In this experiment you will be synthesizing an organic compound, acetylsalicylic In this experiment you will be synthesizing an organic compound, acetylsalicylic acid (known as Aspirin) using an organic reaction. This reaction is called acid (known as Aspirin) using an organic reaction. This reaction is called esterification, and it will add an ester group, a –COCHesterification, and it will add an ester group, a –COCH33 group to the benzene ring of group to the benzene ring of

a salicylic acid compound.a salicylic acid compound.

• Many painkillers contain the benzene ring as their central structure, as shown in Many painkillers contain the benzene ring as their central structure, as shown in the diagram above right.the diagram above right.

• Salicylic acid, the main component of Aspirin and one of the reactants in this 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 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 was originally derived from natural materials, such as the bark of the willow tree and the meadowsweet flower.and the meadowsweet flower.

• Although effective, salicylic acid caused many undesirable side effects due to its Although effective, salicylic acid caused many undesirable side effects due to its high acidity. In 1893 a German chemist synthesized acetylsalicylic acid by adding high acidity. In 1893 a German chemist synthesized acetylsalicylic acid by adding the acetyl group (-COCHthe acetyl group (-COCH33) to mask these irritations caused by ingestion of salicylic ) to mask these irritations caused by ingestion of salicylic

acid alone. acid alone.

C

C

C

C

C

C

H

H

H

H

H

H

CHM 101/102CHM 101/102


Aspirin SynthesisAspirin Synthesis• ProcedureProcedure

Add about 2 g of salicylic Add about 2 g of salicylic acid to a pre-weighed 50 acid to a pre-weighed 50 mL Erlenmeyer flask.mL Erlenmeyer flask.

Add 5.0 mL of acetic Add 5.0 mL of acetic anhydride to the flask.anhydride to the flask.

Add 5 drops of phosphoric Add 5 drops of phosphoric acid to the mixture and stir acid to the mixture and stir with a clean glass stirring with a clean glass stirring rod.rod.

Caution: acetic anhydride Caution: acetic anhydride and phosphoric acid can and phosphoric acid can produce burns. They are produce burns. They are located in the fume hood. located in the fume hood.

CHM 101/102CHM 101/102



• Clamp the flask to a ring Clamp the flask to a ring stand and immerse it in a 400 stand and immerse it in a 400 mL beaker containing tap mL beaker containing tap water. water.

• Heat the bath to 75Heat the bath to 75ooC and C and maintain this temperature for maintain this temperature for 5 minutes while stirring the 5 minutes while stirring the mixture to dissolve the mixture to dissolve the contents.contents.

CHM 101/102CHM 101/102



• After heating, cautiously add After heating, cautiously add 2 mL DI water to the flask 2 mL DI water to the flask and stir.and stir.

• Remove the mixture from Remove the mixture from the water bath and let cool the water bath and let cool to room temperature (25to room temperature (25ooC).C).

• Remember DO NOT touch Remember DO NOT touch the hot ring clamp until has the hot ring clamp until has had sufficient time to cool.had sufficient time to cool.

CHM 101/102CHM 101/102



• Once the flask is cooled to room Once the flask is cooled to room temperature, add 20 mL of DI water temperature, add 20 mL of DI water and stir.and stir.

• Place the flask in an ice bath to Place the flask in an ice bath to speed the crystallization process.speed the crystallization process.

• Allow the flask to remain in the ice Allow the flask to remain in the ice bath for 5 minutes.bath for 5 minutes.

• If crystals have not formed after 5 If crystals have not formed after 5 minutes, vigorously scratch the minutes, vigorously scratch the inside of the flask with a glass inside of the flask with a glass stirring rod.stirring rod.

CHM 101/102CHM 101/102



• Collect the Aspirin crystals by Collect the Aspirin crystals by vacuum filtration using a vacuum filtration using a Buchner funnel. Buchner funnel.

• Secure the funnel by clamping it Secure the funnel by clamping it to a ring stand to prevent spilling to a ring stand to prevent spilling your residue. your residue.

• Remember moisten the filter Remember moisten the filter paper once it is inside the funnel paper once it is inside the funnel by using a small amount of DI by using a small amount of DI water in a squeeze bottle. This water in a squeeze bottle. This will secure the filter paper so will secure the filter paper so that it is “flush” to the bottom that it is “flush” to the bottom surface of the funnel.surface of the funnel.

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• Wash the aspirin crystals Wash the aspirin crystals with a 5 mL portion of ice-with a 5 mL portion of ice-cold DI water. cold DI water.

• Turn on the suction to Turn on the suction to remove the wash water and remove the wash water and repeat the washing with repeat the washing with another 5 mL portion of ice-another 5 mL portion of ice-cold DI water.cold DI water.

• Allow air to be drawn over the Allow air to be drawn over the crystals by suction for 3 crystals by suction for 3 minutes until the crystals are minutes until the crystals are dry. dry.

CHM 101/102CHM 101/102


Aspirin SynthesisAspirin Synthesis• When the crystals are dry and fluffy, When the crystals are dry and fluffy,

determine the mass of your aspirin. determine the mass of your aspirin. Record this weight as your Record this weight as your actual yield of actual yield of aspirinaspirin..

• Calculate the amount of aspirin you could Calculate the amount of aspirin you could produce, called the produce, called the theoretical yield of theoretical yield of aspirinaspirin. This value is based on the . This value is based on the stochiometric amountsstochiometric amounts of reactants in the of reactants in the balanced equation and the balanced equation and the limiting limiting reagent.reagent.

• Calculate the Calculate the percent yield of aspirinpercent yield of aspirin you you produced by dividing the produced by dividing the actual yieldactual yield by by the the theoretical yield of aspirin theoretical yield of aspirin and and multiply by 100%.multiply by 100%.

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