Acetylsalicylic Acid

Acetylsalicylic acid,(Aspirin) is a well-known analgesic with the chemical formula C₉H₈O₄. It is also referred to as 2-acetoxybenzoic acid. Aspirin appears as a colourless to white crystalline powder. While typically odourless, it acquires a vinegar-like smell of acetic acid in moist air. It has a flashpoint of 482°F and is widely used for treating pain, inflammation, and fever.

Acetylsalicylic acid (ASA) is a potent and irreversible platelet aggregation inhibitor. However, its effectiveness diminishes after first-pass deacetylation to salicylic acid (SA). Introduced into the pharmaceutical industry over 100 years ago, Aspirin was initially developed as an analgesic but soon found numerous medicinal applications.

The German chemist Felix Hoffmann, working at Bayer Pharmaceutical Company in 1894, sought a remedy for his father’s arthritis. Building on earlier work with salicin and salicylic acid, Hoffmann buffered salicylic acid to create acetylsalicylic acid (ASA). This new compound had improved tolerability and reduced gastrointestinal side effects. By 1899, it was marketed under the name Aspirin.

Recognised as one of the safest and most effective medicines, Aspirin is listed on the World Health Organization’s List of Essential Medicines. It is one of the most commonly used medications worldwide.

1.0Preparation of Acetylsalicylic Acid

Dry an Erlenmeyer flask and add 3 grams of salicylic acid.
Add 5–8 drops of 85% phosphoric acid and 6 mL of acetic anhydride to the flask.
Stir the solution and place the flask in warm water for 15 minutes.
Gradually add 20 drops of cold water to neutralise excess acetic anhydride.
Cool the mixture in an ice bath to speed up crystallisation.
Filter the crystallised product using a Büchner funnel.
Wash the crystals with ice-cold water to reduce product loss.
Recrystallise for purification by dissolving the crystals in 10 mL of ethanol and adding 25 mL of warm alcohol.
Allow crystallisation in an ice bath.
Suction filtration is performed to collect the purified crystals.
Dry the crystals on paper and verify their melting point (135°C) to confirm acetylsalicylic acid.

2.0Physical Properties of Acetylsalicylic Acid

Physical Property	Value
Chemical Formula	C₉H₈O₄
Molar Mass	180.159 g/mol
State	Crystalline solid
Colour	White
Odor	No characteristic odour
Density	1.40 g/cm³
Boiling Point	140°C
Melting Point	136°C
Solubility	Soluble in water, ethanol, DMSO, and dimethylformamide.

3.0Chemical Properties of Acetylsalicylic Acid

Acetylsalicylic Acid exhibits reactivity under various conditions:

Hydrolysis in Air:
Hydrolyses when exposed to moist air but remains stable in dry air.
Dissociation:
Rapidly dissociates in the presence of ammonium acetate, carbonates, citrates, or alkali metal hydroxides.
Reaction with Acids:
Hydrolyses in contact with acetic acid and salicylic acid.
Alkaline Decomposition:
Under alkaline treatment, Acetylsalicylic Acid decomposes rapidly to form acetate and salicylate ions.

4.0Uses of Acetylsalicylic Acid

Blocks enzymes involved in inflammation and pain.
Reduces the risk of venous and arterial blood clots.
Treats various types of headaches.
Effective for both acute and chronic inflammation.
Helps to lower the risk of developing and dying from cancer.
Essential for managing patients after heart attacks.
First-line treatment for symptoms of acute rheumatic fever.