Ethylene | Research & Encyclopedia Articles

Ethylene

Ethylene (C₂H ₄), also known as ethene, is a colorless, flammable gas and is an important hydrocarbon in chemical processes. Just about every home and business in the modern world contains products made with ethylene. This organic gas is the starting point for the manufacture of most plastic materials. These plastics are used to make containers for soft drinks and mouthwash, coverings for electric wires, plastic bowls and plastic food wrap. About half of the ethylene produced in the United States goes to make polyethylene, the most important derivative of ethylene. Synthetic rubber is also made with an ethylene derivative, and one of ethylene's compounds is used to make antifreeze for car radiators. Ethylene also has the ability to hasten fruit ripening makes it commercially important. U.S. production of ethylene exceeded 52 billion lb (23.6 million kg) in 1997.

Ethylene belongs to the family of hydrocarbons called olefins. It is also the simplest member of the alkene family of hydrocarbons and is highly reactive because of its double bond. Most ethylene is produced by heating ethane and propane. Oil refineries also generate some ethylene as a by-product.

In the early 1800s, scientists recognized ethylene as a gas but did not understand its composition. John Dalton, in formulating his atomic theory, analyzed methane (CH₄) and ethylene (C₂H ₄) and found that when the gases contained an equal weight of carbon, methane contained twice as much hydrogen. Later, Pierre Eugène Marcelin Berthelot synthesized an alcohol, ethanol, from ethylene and also produced ethylene from coal-gas. Through such experiments, Berthelot discredited the vital force theory by demonstrating that organic compounds, those containing carbon, could be produced from substances not present in living organisms and that the physical laws that apply to inorganic chemistry also apply to organic chemistry. The phenomenon of polymerization, a process in which two or more molecules of a substance combine to form larger molecules, was also discovered with ethylene. Butylene (C₄H₈), for example, is a polymer of ethylene, meaning that the chemical formula for butylene is a multiple of the formula for ethylene. Like ethylene, butylene molecules have two hydrogen atoms for every carbon atom, but its molecules weigh twice as much.

During the twentieth century, scientists discovered that ethylene causes fruit to ripen more quickly by functioning as a growth regulator. In the late 1800s, although people knew that gas lighting could stimulate growth in plants, they didn't realize that the effect was due to ethylene's presence in the fumes and smoke given off by the lights. Today, ethylene gas is used to regulate plant growth in greenhouses, and a form of liquid ethylene is applied to some crops before or after harvesting.