EXP 5

• Aspirin


  An effective analgesic (pain reliever), antipyretic (fever reducer) and anti-inflammatory agent and is one of the most widely used non-prescription drugs

  
• Aspirin had its origin when it was found that an extract from the bark of willow trees was useful in reducing pain and fever

  18th century

  
• Salicylic acid


  The active ingredient in willow bark
• Although salicylic acid was effective at reducing pain and fever, it also had some unpleasant side effects
• Salicylic acid is irritating to the lining of the mouth, esophagus, and stomach, and can cause hemorrhaging of the stomach lining
• The Bayer Company in Germany patented a drug they called aspirin, which was a modification of salicylic acid


  1899

  
• Aspirin


  A modification of salicylic acid where the phenol group was replaced with an ester group, making it less irritating
• Aspirin is still irritating to the stomach and can cause hemorrhaging of the stomach walls
• Aspirin tablet


  Contains a small amount of aspirin (usually 300-400 mg) in a starch "binder" and sometimes contains other ingredients like caffeine and buffers

  
• Aspirin synthesis


  1. Salicylic acid reacts with acetic acid in the presence of an acid catalyst to form aspirin

  2. Acetic anhydride can be used instead of acetic acid for a faster reaction with higher yield

  
• In this experiment, the salicylic acid is the limiting reactant and the acetic anhydride is in excess

  
• Purification of aspirin


  1. Excess unreacted acetic anhydride is destroyed by the addition of water

  2. Aspirin precipitates out and is collected by vacuum filtration

  3. Aspirin is tested for purity using FeCl3 (aq)

  4. Aspirin is further purified by recrystallization

  
• A percent yield of 80%-90% is usually considered good to excellent
• In the experiment, an 88.23% yield of aspirin was obtained which indicates a high yield and good purity of aspirin

  
• Yields close to 100% are called quantitative, above 90% are excellent, above 80% are very good, above 70% are good, above 50% are fair, and below 40% are poor
• Acetic acid is unlikely to be a contaminant in the solid aspirin because it is soluble in water and will be removed during the purification process

  
• The low melting point of 122-128°C for the aspirin product indicates the presence of impurities

  
• Hydrolysis


  The chemical breakdown of a compound through a reaction with water, which can cause aspirin to develop a vinegar-like odor and give a purple color with FeCl3

  
• Aspirin is a more potent inhibitor of prostaglandin synthesis and platelet aggregation than other salicylic acid derivatives, due to the acetyl group
• Aspirin undergoes phase 1 hydrolysis to salicylic acid, and in phase 2 it is conjugated with either glycine or glucuronic acid forming ionized metabolites that can be excreted in the urine

  
• Salicylates in high doses can induce methemoglobinemia through increased vascular release of nitric oxide and carboxyhemoglobinemia via lipid peroxidation
• Methemoglobinemia


  A condition where hemoglobin is oxidized from the normal ferrous (Fe2+) state to the abnormal ferric (Fe3+) state, making it incapable of carrying oxygen and altering the oxygen-hemoglobin dissociation curve