Ethylene Oxide

OVERVIEW

Ethylene oxide (ETH-ih-leen OK-side) is a flammable, colorless gas with the odor of ether. The gas is a cyclic compound, consisting of a ring of two carbon atoms and one oxygen atom. Each carbon atom also has two hydrogen atoms attached to it. Ethylene oxide was first prepared in 1859 by French chemist Charles Adolphe Wurtz (1817–1884). Wurtz produced the compound by reacting ethylene chlorhydrin (2-chloroethanol; ClCH₂CH₂OH) with an inorganic base (such as sodium hydroxide; NaOH), a process that remained the principle method for preparing the gas for more than a century. After World War II (1939–1945), a method was discovered for the direct oxidation of ethylene gas that is more efficient than the chlorhydrin process.

KEY FACTS

OTHER NAMES:

Epoxyethane; oxirane

FORMULA:

(CH₂)₂O

ELEMENTS:

Carbon, hydrogen, oxygen

COMPOUND TYPE:

Cyclic ether (organic)

STATE:

Gas

MOLECULAR WEIGHT:

44.05 g/mol

MELTING POINT:

−112.5°C (−170.5°F)

BOILING POINT:

10.6°C (51.1°F)

SOLUBILITY:

Soluble in water, ethyl alcohol, acetone, benzene, and ether

Ethylene oxide is a very unstable compound that catches fire or explodes readily and must be handled with the greatest care. Nonetheless, it is an important industrial chemical and ranks nineteenth by volume among chemicals produced in the United States. Its primary use is in the manufacture of other organic compounds.

HOW IT IS MADE

The chlorhydrin process for making ethylene oxide has been replaced commercially by the direct oxidation of ethylene gas. Oxidation takes place at temperatures of 200°C to 300°C (392°F to 572°F) over a silver catalyst. The formula for this reaction is 2CH₂=CH₂ + O₂ → 2CH₂CH₂O. The yield produced by direct oxidation is slightly less than that produced by the chlohydrin process, but the amount of chlorine wasted by the latter method outweighs the slight difference in efficiency of production.

COMMON USES AND POTENTIAL HAZARDS

The largest single use of ethylene oxide is in the manufacture of ethylene glycol (CH₂OHCH₂OH), which itself is used as an antifreeze and raw material for the production of plastics. About 60 percent of all the ethylene oxide produced is used for this purpose. The compound is also used to make higher glycols, such as diethylene and triethylene glycol (CH₂OHCH₂OCH₂CH₂OH and CH₂OHCH₂OCH₂CH₂OCH₂CH₂OH). The second most important application of ethylene oxide is in the synthesis of ethyoxylates and ethanolamines, substances used in the production of synthetic detergents. These substances act as surfactants in detergents-substances that reduce the surface tension between two materials and improve the lathering ability of a cleaner.

Ethylene oxide also has a number of other important industrial uses, although the quantity used for such purposes is small compared to the uses mentioned above. For example, it is used as a rocket propellant because of its tendency to decompose easily with the release of large amounts of energy. It is also used as a sterilizing medium, particularly for the sterilization of surgical instruments and consumer products, such as spices and cosmetics. The compound is also used as a demulsifier in the petroleum industry. A demulsifier is a material that aids in the separation of the components of complex mixtures, like those handled in the processing of petroleum. Ethylene oxide is also used as a fumigant, which is a gas used to kill insects and other pests.

Interesting Facts

• Ethylene oxide's instability is caused by its unusual three-atom ring structure. A ring with three atoms is a stressed arrangement that breaks apart with even moderate amounts of stress.
• A number of industrial accidents have been caused during the preparation, transportation, storage, and use of ethylene oxide. It is one of the most hazardous of the top twenty-five chemicals produced in the United States.
• In 2004, some 3.77 million metric tons (4.15 million short tons) of ethylene oxide were produced in the United States.

A number of health hazards are associated with exposure to ethylene oxide. It is a skin, eye, and respiratory system irritant, causing symptoms such as dizziness, nausea, headache, convulsions, blistering of the skin, coughing, tightness of the chest, difficulty in breathing, and blurred vision. Long-term exposure to the gas may produce more serious health consequences, such as damage to the nervous system, muscular weakness, paralysis of the peripheral nerves, impaired thinking, loss of memory, and severe skin irritation. Ethylene oxide is believed to be responsible for spontaneous abortions, genetic damage, and the development of some types of cancer, primarily cancer of the blood (leukemia).

Words to Know

CATALYST

A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure.

ETHER

An organic compound in which one oxygen atom is bonded to two carbon atoms: -C -O -C. Ethylene oxide is the simplest cyclic ether.

FOR FURTHER INFORMATION

Buckles, Carey, et al. Ethyleneoxide. 2nd ed. Celanese Ltd., The Dow Chemical Company, Shell Chemical Company, Sunoco, Inc., and Equistar Chemicals, LP. Also available online at http://www.ethyleneoxide.com/html/introduction.html (accessed January 3, 2006).

Environment Canada, Health Canada. Ethylene Oxide. Ottawa: Environment Canada, 2001.

"Ethylene Oxide." OSHA Fact Sheet. http://www.osha.gov/OshDoc/data_General_Facts/ethyleneoxide-factsheet.pdf (accessed on December 27, 2005).

"Ethylene Oxide Health and Safety Guide." IPCS International Programme on Chemical Safety. http://www.inchem.org/documents/hsg/hsg/hsg016.htm (accessed on December 27, 2005).

"ToxFAQs™ for Ethylene Oxide." Agency for Toxic Substances and Disease Registry. http://www.atsdr.cdc.gov/tfacts137.html (accessed on December 27, 2005).

See AlsoEthylene; Ethylene Glycol