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Experiment 14. Preparation of Acetylsalicylic Acid. Objectives. Obtain experience in Organic Synthesis To isolate and purify your synthesized product Gain experience in organic chemistry techniques. Aspirin. The pharmaceutical ingredient in Aspirin tablets is acetylsalicylic acid

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Experiment 14

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Experiment 14

Preparation of Acetylsalicylic Acid

  • Obtain experience in Organic Synthesis
  • To isolate and purify your synthesized product
  • Gain experience in organic chemistry techniques
  • The pharmaceutical ingredient in Aspirin tablets is acetylsalicylic acid
  • Synthesized from salicylic acid
  • Known since around 500 BC
  • Bitter powder extracted from willow bark that could ease pain
  • In the 1700s chemists elucidated that the chemical responsible was salicin
  • When consumed, salicin is metabolised to salicylic acid
  • Salicylic acid is the active ingredient
  • In 1829 Leroux showed that the active ingredient was salicylic acid
  • Used for years to treat pain, swelling and fevers
  • However not ideal as caused irritation to user’s stomach
  • High doses caused bleeding
  • Hoffmann reasoned the irritation was due to the phenol group
  • Converted salicylic acid to acetylsalicylic acid
  • Derivative reduced fever, pains and swelling, was less irritating
  • Worked even better than salicylic acid
how does aspirin work
How does Aspirin work?
  • Dr. J.Vane – won 1982 Nobel Prize for Medicine for his discovery
  • Pain signals are relayed to the brain from nerve endings by chemicals called prostaglandins
  • Aspirin inhibits the synthesis of these neurotransmitters by an enzyme called cyclooxygenase-2
how does aspirin work9
How does Aspirin work?
  • Cyclooxygenase-2 is responsible for pain transmission
  • Cyclooxygenase-1 is responsible for maintenance of the gastric lining
  • Aspirin affects both enzymes
  • Lead to development of other pain killing drugs
actions of aspirin
Actions of Aspirin
  • Analgesic - kills pain
  • Antipyretic – lowers temperature
  • Prevents blood clots by inhibiting platelet aggregation
  • Lowers blood pressure
  • Anti-inflammatory – treatment of arthritis/swelling
acetylation reaction
Acetylation Reaction

One of many ways by which this acetylation can be achieved

  • Mix 1.0g of salicylic acid and 2ml of acetic anhydride in a 50ml flask and add 5 drops of conc. H2SO4
  • Heat on the steam bath for 10 mins*
  • Allow to cool – crystallization
  • Cool in ice to ensure complete crystallization of the acetylated product - add 15ml water*
  • Isolate the crystals on the Hirsch funnel
  • Wash with cold water (5-10ml)
  • Transfer crystals to a beaker
  • Add 15ml of 5% aq NaHCO3*
  • Filter the solution of the sodium salt of aspirin through a fluted filter paper
  • Pour solution on to 5ml of 3M HCl
  • Acetylsalicylic acid precipitates
  • Filter the crystals on the Hirsch funnel
  • Recrystalize from ethanol/water soln.
  • Isolate crystals, allow to dry, get melting point and % yield