ethylene

ethylene or ethene , H ₂ C=CH ₂ , 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°C and boils at -103.8°C. 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°C. 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. It is used in making polyethylene and saran, in the manufacture of ethanol and ethylene oxide, and as an anesthetic. Ethylene was called olefiant gas by early chemists.

ethylene (ethene) A colourless gaseous hydrocarbon, C₂H₄, that occurs naturally in plants and acts as a growth substance in a variety of physiological roles. It is produced in response to stresses, such as water shortage, and acts as an effector for auxins: auxins stimulate tissues to produce ethylene, which diffuses rapidly to trigger responses in surrounding cells. The best known effect is the stimulation of fruit ripening: fruits such as bananas, apples, and avocados naturally produce ethylene during the later stages of ripening, and ethylene gas is used to promote the ripening of fruits, such as bananas, that are picked and shipped ‘green’. Ethylene generally suppresses flowering, except in members of the pineapple family (Bromeliaceae) – hence flowering of pineapples may be synchronized by releasing ethylene into the growing crop. Studies have shown varied and often contradictory effects of ethylene on vegetative growth. For example, in rice it acts with gibberellins to promote stem elongation, while in peas ethylene inhibits root and shoot elongation. Seed germination, bud opening, and root initiation may also be promoted by ethylene.