Acetylsalicylic Acid (Aspirin)

Acetylsalicylic Acid (Aspirin)

• Aspirin, or Acetylsalicylic Acid (ASA), is a globally used medication.
• It is a common nonprescription drug for treating pain, inflammation, and fever.
• Aspirin is effective as a general pain reliever.
• Aspirin treats a wide range of painful conditions like headaches, body aches, muscle aches, and arthritis.
• Lowering aspirin doses can reduce the risk of death from heart attack or stroke.

Chemical Properties

• In solutions of hydroxides of alkali metals, aspirin decomposes rapidly.
• Aspirin is stable in dry air.
• In contact with moisture, aspirin gradually hydrolyzes into acetic acid and salicylic acids.

Physical Properties

• Acetylsalicylic Acid is a colorless to white crystalline solid.
• It smells like vinegar due to the hydrolysis into salicylic and acetic acids.
• Aspirin has a bitter taste and a melting point of 135 °C.
• Acetylsalicylic Acid decomposes at high temperatures.
• It is soluble in water, ethyl ether, ethanol, and chloroform.

Acid Hydrolysis of Esters

• Hydrolysis is a chemical reaction.
• It involves the interaction of a compound with water.
• The interaction results in the compound's decomposition.
• During acid hydrolysis, an ester reacts with water.
• This reaction produces a carboxylic acid and an alcohol.
• An acid catalyst is required for acid hydrolysis.

Base Hydrolysis

• Base hydrolysis is the reaction of an ester with a strong base.
• It produces the salt of the carboxylic acid and an alcohol.

History

• In 1897, Dr. Felix Hoffmann, a German chemist, created a pure stable acetylsalicylic acid from salicylic acid and acetic anhydride.
• Felix Hoffmann of Bayer developed and patented a process for synthesizing aspirin in Germany.
• First clinical trials began.

Synthesis of Aspirin

• To prepare aspirin, salicylic acid is reacted with an excess of acetic anhydride.
• A small amount of a strong acid is used as a catalyst to speed up the reaction.
• Sulfuric acid is used as the catalyst.
• Salicylic acid comes from Salix, the willow family of plants, and was originally derived from willow bark extracts.
• Hippocrates and Native Americans used willow bark teas as headache remedies and tonics.
• Aspirin is administered in modern times because it is less irritating to the stomach than salicylic acid.

Procedure for Aspirin Synthesis

• Add 3ml of acetic anhydride to a conical flask containing 1.5g of Salicylic Acid using a burette.
• Add 3-5 drops of concentrated sulfuric acid to the solution.
• Enclose the conical flask and heat it in a water bath at 80 °C for approximately 5 minutes.
• Add 3ml of distilled water to the hot solution.
• Add 25ml of distilled water to the solution.
• Cool the mixture at room temperature until white crystals form.
• Separate the aspirin crystals from the solution through filtration.
• Dry the crystals and calculate the percentage yield of the prepared aspirin.

Identification Test

• Aspirin is analyzed for any presence of contaminating salicylic acid.
• A small amount of aspirin is tested with iron(III) chloride (FeCl3).
• FeCl3 reacts with phenols (alcohol groups attached to aromatic rings).
• This reaction produces colored complexes.
• Salicylic acid contains a phenol functional group, unlike aspirin.
• Increased salicylic acid contamination results in a darker color when FeCl3 is added.

Purification

• Transfer synthesized aspirin to a 10 mL beaker and add 5 mL of ethanol using a plastic pipette.
• Warm the solution to 60 ºC.
• Cover the solution and allow it to cool undisturbed to room temperature.
• Set the beaker in an ice bath and scratch the inside of the flask with a glass rod to induce recrystallization.
• Collect the purified aspirin by vacuum filtration and let the crystals dry for a few minutes before weighing them.
• Determine the mass of dry purified aspirin.

Calculation for Yield

• The reaction is: Salicylic Acid + Acetic anhydride = Aspirin + Acetic acid
• 1 mole of Salicylic Acid = 1 mole of ASA
• Weight/m.wt Salicylic Acid = weight/m.wt ASA
• Weight of Salicylic Acid (gm) /138 = Weight of aspirin /180
• Percentage yield = (actual yield /theoretical yield) x 100.
• Ninety percent yield means the reaction was 90% efficient and 10% of the materials were wasted.