Ethylene Oxide (C₂H₄O) — Properties, Uses & Safety

Overview

Ethylene oxide (C2H4O), also known by its IUPAC name oxirane, is the simplest epoxide — a three-membered cyclic ether with a molar mass of 44.05 g/mol. At standard conditions, it is a colorless, flammable gas with a faintly sweet odor. The three-membered ring in ethylene oxide is highly strained because the C-O-C bond angle is forced to approximately 60 degrees, far from the ideal tetrahedral angle of 109.5 degrees. This ring strain makes ethylene oxide exceptionally reactive, as the ring readily opens to relieve strain when attacked by nucleophiles — a property that underlies most of its industrial applications. Ethylene oxide carries severe GHS hazard codes: H220 (extremely flammable gas), H340 (may cause genetic defects — a known mutagen), H350 (may cause cancer — a confirmed human carcinogen), H331 (toxic if inhaled), H301 (toxic if swallowed), and H311 (toxic in contact with skin). It is one of the most hazardous industrial chemicals in common use and requires stringent safety controls. Despite these dangers, ethylene oxide is produced on a massive scale — over 30 million metric tons annually — because it is an incredibly versatile chemical intermediate. Its primary use is in manufacturing ethylene glycol (the main component of automotive antifreeze and a precursor to polyester fibers and PET plastic bottles) through hydration: C2H4O + H2O -> HOCH2CH2OH. Ethylene oxide is also used to sterilize heat-sensitive medical equipment and surgical instruments, as a fumigant for spices and dried foods, and as a precursor to surfactants, detergents, and other industrial chemicals. For chemistry students, ethylene oxide is an excellent introduction to ring strain and its effect on chemical reactivity, nucleophilic ring-opening reactions, the epoxide functional group in organic chemistry, and the balance between industrial utility and occupational health risks. It also connects to discussions about carcinogenicity, chemical regulation, and the importance of safety in chemical manufacturing.

IUPAC Name

oxirane

CAS Number

75-21-8

PubChem CID

6354

Molecular Formula

C₂H₄O

Molar Mass

44.053 g/mol

State at STP

gas

Appearance

Colorless flammable gas