Ethylene Glycol (C₂H₆O₂) — Properties, Uses & Safety

Overview

Ethylene glycol (C2H6O2), systematically named ethane-1,2-diol, is the simplest diol (a molecule with two hydroxyl groups) with a molar mass of 62.07 g/mol. It is a colorless, odorless, viscous liquid with a dangerously sweet taste that is completely miscible with water. The two hydroxyl groups on adjacent carbon atoms allow ethylene glycol to form extensive hydrogen bonds with water molecules, which dramatically lowers the freezing point of aqueous solutions — this colligative property is the basis for its primary use as automotive antifreeze and engine coolant. A typical 50/50 mixture of ethylene glycol and water freezes at approximately −37 °C and boils at approximately 107 °C, protecting engines in both winter and summer. Beyond antifreeze, ethylene glycol is a crucial industrial chemical as the monomer for polyethylene terephthalate (PET) — the polyester plastic used in beverage bottles, food containers, and synthetic fibers like polyester clothing. It is also used in deicing fluids for aircraft, as a heat transfer fluid, and in the production of resins and inks. Despite its usefulness, ethylene glycol is highly toxic to humans and animals. Its sweet taste makes accidental poisoning a serious concern, especially for pets. The body metabolizes it into glycolic acid and oxalic acid, which cause kidney failure and can be fatal. GHS hazard codes include H302 (harmful if swallowed) and H373 (may cause damage to organs through prolonged or repeated exposure). For chemistry students, ethylene glycol illustrates diol chemistry, hydrogen bonding, colligative properties (freezing point depression), condensation polymerization (formation of PET), and toxicology. It provides a real-world context for understanding how intermolecular forces determine physical properties and why colligative properties matter in everyday applications.

IUPAC Name

ethane-1,2-diol

CAS Number

107-21-1

PubChem CID

174

Molecular Formula

C₂H₆O₂

Molar Mass

62.068 g/mol

State at STP

liquid

Appearance

Colorless, odorless, sweet-tasting viscous liquid