CID 6354

C₂H₄O

Ethylene oxide

Ball-and-stick Stick Space-filling

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7 atoms, 7 single bonds.

IUPAC name: oxirane
Molar mass: 44.0530(58) g/mol
Atoms: 7
SMILES: C1CO1
InChIKey: IAYPIBMASNFSPL-UHFFFAOYSA-N
PubChem CID: 6354

Made of

Structural formula of ethylene oxide. Each unlabelled corner is a carbon atom, and the four hydrogens on carbon are not drawn. It shows which atoms are joined to which, not the shape. The model above shows the shape.

Ethylene oxide is named oxirane under the rules of IUPAC, the International Union of Pure and Applied Chemistry. It is built on a ring just three atoms around: two of carbon and one of oxygen. The National Toxicology Program (NTP) describes it as the simplest epoxy compound, one in which an oxygen atom bridges two bonded carbons. ChEBI (Chemical Entities of Biological Interest) classes the ring as saturated, meaning it holds no double bond. Its formula, C₂H₄O at 44.05 g/mol, matches acetaldehyde atom for atom, but in ethylene oxide those atoms close into a ring.

At room temperature it is a colourless gas that boils at 10.6 °C. HSDB, the Hazardous Substances Data Bank, likens its smell to bruised apples. ATSDR, the federal Agency for Toxic Substances and Disease Registry, notes a somewhat sweet odour at very high levels. It mixes with water in any proportion. The liquid is less dense than water, and the vapour is heavier than air.

Structure and bonding

Ethylene oxide’s seven atoms hang on seven single bonds, and three of those bonds close a narrow triangle: one carbon–carbon bond and two carbon–oxygen bonds. Each carbon fills out its four bonds with two hydrogen atoms. PubChem’s computed model puts the ring angles at 63.2° at the oxygen and 58.4° at each carbon. That is roughly half the 109.5° Chem1 gives between the bonds of methane’s tetrahedral carbon. In the same computed model, each H–C–H angle opens to 115.2°.

Turned edge-on, the triangle collapses to a single line, with one hydrogen of each pair above it and one below. The Stick view keeps only the bonds, and the ring’s sharp corners stand out. In the Space-filling view the red oxygen and the two grey carbons swell into one compact, rounded body fringed by four white hydrogens. The Labels button prints one O, two C and four H.

The drawing matches the real bonding: no double bond, no charge and no alternative form. Every hydrogen sits on carbon, none on the oxygen. In water the compound reacts slowly, turning into ethylene glycol.

Where it turns up

The US Environmental Protection Agency (EPA) lists heart valves, pacemakers, ventilators, syringes and catheters among the equipment sterilised with it. Some 20 billion medical devices a year are treated this way, half the US total. As a fumigant it treats whole and ground spices, books, musical instruments, beehives, and artefacts, archives and library objects.

Small amounts form when tobacco burns, and it has been identified in car and diesel exhaust. ATSDR reports very small amounts in nature and low levels in the air of many parts of the United States. The human body makes some too, during the breakdown of ethylene, and bacteria in the intestines produce it.

US releases dropped from roughly 5 million pounds a year in 1988 to about 280,000 by 2018, almost all of them to air, NTP reports. People living near plants that make or use ethylene oxide can be exposed to what escapes while it is stored and handled there.

Why it matters

Over 97 per cent of US output is an intermediate for other chemicals, and about 60 per cent becomes ethylene glycol. Other chemicals made from it include non-ionic surfactants, surface-active ingredients of detergents and dishwashing liquids, along with glycol ethers, ethanolamines for soaps and textile chemicals, and polyethylene glycol. HSDB records that all production worldwide now uses direct oxidation of ethylene with air or oxygen over a silver catalyst. First made in the United States in 1921, it came from the chlorohydrin process until 1937, a route that could not compete on cost.

It is an alkylating agent: it bonds to electron-rich groups in large biological molecules, forming combined products called adducts. Its chief adduct in DNA is N⁷-(2-hydroxyethyl)guanine. NTP traces both its power as a sterilant and its cancer risk to this damage to DNA. It kills bacteria, fungi and spores, and most other microorganisms, viruses included. Hospitals use it on plastic devices that cannot go through steam, and HSDB reports no current substitute for some heat- and radiation-sensitive materials.

Properties

Properties of ethylene oxide Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 6354.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₂H₄O
Molar mass	44.0530(58) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	2
Hydrogen atoms	4
Oxygen atoms	1
Bonds	7
PubChem molecular weight	44.05 g/mol	g/mol	PubChem

Safety

Ethylene oxide is an extremely flammable, toxic gas, and NTP lists it as a known human carcinogen. Under its EU classification, signal word Danger, it is toxic if swallowed or inhaled, burns skin and eyes severely and may cause genetic defects or damage fertility. NIOSH, the US government’s workplace-health research institute, treats it as a potential occupational carcinogen, and its card lists workplace exposure limits. The PubChem Laboratory Chemical Safety Summary gathers the full classification.

Questions

Is ethylene oxide an ether?

Yes, a cyclic one. In the 3D model its single oxygen is bonded to two carbon atoms, the –O– link that Chem1 treats as what makes a compound an ether. Those two carbons are bonded to each other as well, which closes a triangle, and CAMEO Chemicals files the compound with the epoxides. Each carbon carries two hydrogens, and all seven bonds are single.

Does ethylene oxide cause cancer?

The US National Toxicology Program listed it in 1985 as reasonably anticipated to cause cancer, then as a known human carcinogen from 2000. The US Environmental Protection Agency judges it carcinogenic by inhalation, linked to lymphoid cancers and, in women, breast cancer. Some worker studies found no rise in cancer, the US federal Agency for Toxic Substances and Disease Registry reports.

What happens to ethylene oxide in the body?

Two detoxifying routes break it down, and one of them, reaction with water, yields ethylene glycol. Once exposure stops, it is gone within hours or days. Some of it bonds to haemoglobin, and those haemoglobin adducts have been measured to monitor exposed workers. In a 2015–2016 US national health survey reported by the National Toxicology Program, cigarette smokers carried the highest levels. Ethylene and ethylene oxide formed inside the body add a background of such adducts.

Does ethylene oxide stay on food after fumigation?

Very little of it. Freshly fumigated goods can hold high levels, but the gas breaks down or drifts away within a few days. It passes off into the air, which leaves at most small traces on food. Because it is so reactive, it also combines with vitamins, amino acids and other components of food, and with many medicines, the Hazardous Substances Data Bank notes.

Made of the same elements

CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₂H₆O₂ Ethylene glycol 10 atoms, 9 single bonds.

All 51 compounds made of carbon, hydrogen and oxygen

CH₂O Formaldehyde 4 atoms, 3 bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
C₃H₈O Isopropyl alcohol 12 atoms, 11 single bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 bonds.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single bonds.
C₁₀H₂₀O Menthol 31 atoms, 31 single bonds.
C₁₄H₁₄O₃ Naproxen 31 atoms, 32 bonds.
C₁₅H₁₆O₂ Bisphenol A 33 atoms, 34 bonds.
C₁₃H₁₈O₂ Ibuprofen 33 atoms, 33 bonds.
C₂₀H₁₄O₄ Phenolphthalein 38 atoms, 41 bonds.
C₁₈H₂₄O₂ Estradiol 44 atoms, 47 bonds.
C₁₂H₂₂O₁₁ Lactose 45 atoms, 46 single bonds.
C₁₂H₂₂O₁₁ Sucrose 45 atoms, 46 single bonds.
C₁₉H₂₈O₂ Testosterone 49 atoms, 52 bonds.
C₁₆H₃₂O₂ Palmitic acid 50 atoms, 49 bonds.
C₂₁H₃₀O₂ Progesterone 53 atoms, 56 bonds.
C₁₈H₃₄O₂ Oleic acid 54 atoms, 53 bonds.
C₂₁H₃₀O₅ Cortisol 56 atoms, 59 bonds.
C₂₇H₄₄O Cholecalciferol 72 atoms, 74 bonds.
C₂₇H₄₆O Cholesterol 74 atoms, 77 bonds.