Ethylene oxide

November 18, 2019
I’m in the midst of an air pollution controversy.
What molecule am I?
Image of Ethylene oxide 3D Image of Ethylene oxide

Ethylene oxide is the smallest of the oxirane family of molecules. It is a sweet-smelling, colorless gas that has many uses; but its high reactivity presents many hazards.

Back in 1859, A. Wurtz treated ethylene chlorohydrin with potassium hydroxide to make ethylene oxide and potassium chloride. In 1914, BASF built the first ethylene oxide plant, which used the chlorohydrin method, but with calcium hydroxide instead of KOH. This process was eventually superseded by the direct oxidation of ethylene, which is used exclusively today.

The uses of ethylene oxide are numerous. By far, its primary use is as a raw material for the industrial manufacture of ethylene glycol and its oligomers, glycol ethers, and ethanolamines. Minor, but important, direct applications include a fumigant for foods and textiles; an agricultural fungicide and insecticide; and a sterilant for medical equipment.

As shown in the hazard information table, many of ethylene oxide’s uses also make it extremely dangerous. Its carcinogenicity is of special concern. The US Environmental Protection Agency is under a court order to decide by March 13, 2020, whether to tighten the 2006 standards set for air pollution by ethylene oxide and other organic chemicals.

There is broad disagreement between environmental and industrial advocates as to the safe concentration of ethylene oxide in air. Proposals range from 0.1 ppt to 4 ppb—a factor of 40,000. Both sides are beginning to pressure EPA to see things their way.

Ethylene oxide hazard information

GHS classification**: flammable gases, category 1
H220—Extremely flammable gas Chemical Safety Warning
GHS classification: gases under pressure, liquefied gas
H280—Contains gas under pressure; may explode if heated Chemical Safety Warning
GHS classification: skin corrosion/irritation, category 2
H315—Causes skin irritation Chemical Safety Warning
GHS classification: eye damage/eye irritation, category 2A
H319—Causes serious eye irritation Chemical Safety Warning
GHS classification: acute toxicity, inhalation, category 3
H331—Toxic if inhaled Chemical Safety Warning
GHS classification: specific target organ toxicity, single exposure, respiratory tract irritation, category 3
H335—May cause respiratory irritation Chemical Safety Warning
GHS classification: germ cell mutagenicity, category 1B
H340—May cause genetic defects Chemical Safety Warning
GHS classification: carcinogenicity, category 1B
H350—May cause cancer Chemical Safety Warning
GHS classification: hazardous to the aquatic environment, acute hazard, category 3
H402—Harmful to aquatic life Chemical Safety Warning
GHS classification: hazardous to the aquatic environment, long-term hazard, category 3
H412—Harmful to aquatic life with long-lasting effects Chemical Safety Warning

*Data from Sigma–Aldrich; other vendors’ data vary.
**Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

Ethylene oxide fast facts

CAS Reg. No. 75-21-8
Empirical formula C2H4O
Molar mass 44.05 g/mol
Appearance Colorless gas
Boiling point 10.4–11.0 ºC
Water solubility Miscible

MOTW update: 
May 04, 2020

Ethylene oxide is used extensively in chemical manufacturing, agriculture, and fumigation, but it is extremely hazardous. In March 2020, the US Environmental Protection Agency’s Office of the Inspector General found that the agency had not done enough to inform people who are living near ethylene oxide–emitting chemical plants that they are likely to have an increased risk of cancer. The OIG even recommended that EPA use unverified data to warn neighbors of the hazard.

MOTW update:
November 18, 2019

Former Molecules of the Week 1,4-dioxane, hexabromocyclododecane, 1-bromopropane, N-methyl-2-pyrrolidone, and dichloromethane, among several other chemicals, are at the center of a controversy about how the EPA’s scientific advisory committees are evaluating risks of air pollution. The problems are the lack of expertise in some of the committees and a shortage of adquate data to evaluate the chemicals. Industrial and environmental stakeholders are critical of the latest risk assessments.

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