Acetaminophen (Paracetamol) (C₈H₉NO₂) — Properties, Uses & Safety

Overview

Acetaminophen (C8H9NO2), also known as paracetamol outside North America, is the world's most widely used over-the-counter pain reliever and fever reducer. Sold under brand names including Tylenol and Panadol, it has a molar mass of 151.16 g/mol and appears as a white crystalline powder. Unlike aspirin and ibuprofen, acetaminophen is not classified as an NSAID because it has minimal anti-inflammatory activity. Instead, it primarily works in the central nervous system, where it is believed to inhibit COX enzymes in the brain and spinal cord, reducing pain perception and the fever response. Acetaminophen was first synthesized in 1878 and has been in widespread clinical use since the 1950s. It is found in hundreds of combination medications for cold, flu, and pain relief. The compound contains an amide functional group (the acetamido group) attached to a para-substituted phenol ring, making it an excellent example of aromatic chemistry and functional group identification. Acetaminophen is moderately soluble in water and freely soluble in ethanol. In the body, it is primarily metabolized in the liver through conjugation reactions (glucuronidation and sulfation). A small fraction is converted by cytochrome P450 enzymes to a toxic metabolite called NAPQI, which is normally neutralized by glutathione. This is why acetaminophen overdose is extremely dangerous — it can cause fatal liver failure when glutathione stores are depleted. Acetaminophen overdose is the leading cause of acute liver failure in the United States, making dosage awareness critical. The maximum recommended daily dose for adults is 4,000 mg, and it should not be combined with alcohol. GHS hazard classifications include acute toxicity warnings. For chemistry students, acetaminophen offers rich learning opportunities in organic functional group identification (phenol, amide, aromatic ring), drug metabolism and biochemistry, spectroscopic analysis (IR and NMR spectra are commonly studied), and pharmaceutical synthesis. Many chemistry courses include the synthesis of acetaminophen from p-aminophenol as a laboratory exercise, teaching students about amide bond formation, purification by recrystallization, and melting point analysis to assess purity.

IUPAC Name

N-(4-hydroxyphenyl)acetamide

CAS Number

103-90-2

PubChem CID

1983

Molecular Formula

C₈H₉NO₂

Molar Mass

151.16 g/mol

State at STP

solid

Appearance

White crystalline powder

Physical Properties

Melting Point

169 °C

Density

1.293 g/cm³

Solubility in Water

14 g/L at 25 °C

Composition