Aspirin and Other Analgesics

A. Preparation of Aspirin Aspirin (acetylsalicylic acid) can be prepared from acetic acid and the hydroxyl group on salicylic acid. However, this is a slow reaction. The ester forms rapidly when acetic anhydride is used to provide the acetyl group. The aspirin you will prepare in this experiment is impure and must not be taken internally! C OH O OH Salicylic acid (138 g/mole) C CH3 O C CH3 O O Acetic anhydride O C OH O C O CH3 Aspirin (acetylsalicylic acid) (180 g/mole) C H3C O OH Acetic acid + + H Using the following equation, the maximum amount (yield) of aspirin that is possible from 2.00 g of salicylic acid can be calculated. 1 mole salicylic acid 1 mole aspirin 180 g 2.00 g salicylic acid 2.61 g aspirin (possible) 138 g 1 mole salicylic acid 1 mole aspirin × × ×= Suppose the total amount of aspirin you obtain has a mass of 2.25 g. A percentage yield can be calculated as follows: g aspirin obtained % Yield= 100 86.2% yield of aspirin product g aspirin calculated × = B. Testing Aspirin Products The purity of the crude sample and the recrystallized aspirin product can be tested with ferric chloride, FeCl3. The Fe3+ ion reacts with the phenol group on salicylic acid and gives a purple color. This test can also be used to determine the purity of commercially prepared aspirin. Sometimes old aspirin breaks down to give salicylic acid and acetic acid. Then the aspirin in the bottle smells like vinegar and should be discarded. C. Analysis of Analgesics Aspirin is one of several analgesics that are used to relieve pain. Other analgesics include acetaminophen, ibuprofen, and naproxen. Many aspirin products include caffeine. These products including aspirin are used to reduce fever, which means they are also antipyretics. However, aspirin also has anti-inflammatory properties and many reduce the risk of a heart attack. 

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