ethylene [key], H2C=CH2, a gaseous unsaturated hydrocarbon. It is the simplest alkene. Ethylene is colorless, has a faint odor, and has a slightly sweet taste; it melts at −169.4℃ and boils at −103.8℃. Because of the presence of the double bond in its molecule, ethylene is very reactive. It burns in air with a luminous flame and forms explosive mixtures with pure oxygen. It combines directly with the halogens, e.g., with chlorine to form 1,2-dichloroethane. With hydrogen it forms ethane. Ethylene may be prepared by the dehydration of ethanol with sulfuric acid at about 180℃. It is prepared commercially from natural gas and petroleum, e.g., by cracking and fractional distillation. Ethylene has many uses. It is important in the synthesis of many chemicals that are used to produce plastics and other petrochemical products. It is used in making polyethylene and saran, in the manufacture of ethanol, ethylene oxide, and ethylene glycol, and as an anesthetic. Ethylene was called olefiant gas by early chemists.
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