Aspirin (C₉H₈O₄) — Properties, Uses & Safety

Overview

Aspirin, chemically known as acetylsalicylic acid (C9H8O4), is one of the most widely used medications in human history. With a molar mass of 180.16 g/mol, aspirin is a white crystalline solid that belongs to the class of drugs called nonsteroidal anti-inflammatory drugs (NSAIDs). It works by irreversibly inhibiting cyclooxygenase (COX) enzymes, which are responsible for producing prostaglandins — chemicals that promote inflammation, pain, and fever. The story of aspirin begins with willow bark, which has been used as a pain remedy for thousands of years. The active compound in willow bark, salicin, is metabolized to salicylic acid in the body. In 1897, Felix Hoffmann at Bayer synthesized acetylsalicylic acid by acetylating salicylic acid with acetic anhydride, creating a compound that was effective but gentler on the stomach. This synthesis — an esterification reaction — is now a classic experiment in organic chemistry labs worldwide. Aspirin is used to relieve mild to moderate pain (headaches, toothaches, muscle aches), reduce fever, treat inflammation in conditions like arthritis, and at low doses, prevent blood clots by inhibiting platelet aggregation, which reduces the risk of heart attacks and strokes. It is on the World Health Organization's List of Essential Medicines. The compound is slightly soluble in water but more soluble in ethanol and ether, illustrating the concept of like dissolves like. In the body, aspirin is hydrolyzed back to salicylic acid and acetic acid, demonstrating ester hydrolysis. Safety considerations include stomach irritation and bleeding risk, especially with prolonged use. It should not be given to children with viral infections due to the risk of Reye's syndrome. GHS classifications include health hazard warnings. For chemistry students, aspirin is a perfect compound for learning about esterification and hydrolysis reactions, functional groups (ester, carboxylic acid, aromatic ring), organic synthesis techniques (reflux, recrystallization, melting point determination), and the connection between molecular structure and biological activity. The aspirin synthesis lab is one of the most popular experiments in high school and college chemistry courses, giving students hands-on experience with real-world pharmaceutical chemistry.

IUPAC Name

2-acetoxybenzoic acid

CAS Number

50-78-2

PubChem CID

2244

Molecular Formula

C₉H₈O₄

Molar Mass

180.16 g/mol

State at STP

solid

Appearance

White crystalline powder

Physical Properties

Melting Point

135 °C

Density

1.4 g/cm³

Composition