CHAPTER FIVE Structure and Preparation of Alkenes: Elimination Reactions CH-CH CH3 CH=CH2 IUPAC ethene IUPAC name: propene Ethylene is an acceptable synonym for ethene in the IUPAC system. Propylene, isobuty lene, and other common names ending in -ylene are not acceptable IUPAC names thylene was known to chemists in the eigh- Ethylene is the cornerstone of the world's mam- teenth century and isolated in pure form in moth petrochemical industry and is produced in vast 1795. An early name for ethylene was gaz olefi. quantities. In a typical year the amount of ethylene ant(French for oil-forming gas"), a term suggested produced in the United States(5X"lb)exceeds to describe the fact that an oily liquid product is the combined weight of all of its people. In one formed when two gases--ethylene and chlorine -re- process, ethane from natural gas is heated to bring act with each other bout its dissociation into ethylene and hydrogen CHaCH CH2=CH2 H2 Chlorine 1. 2-Dichloroethane Ethane (bp:83° Ethylene Hydrogen This reaction is known as dehydrogenation and is si- The term gaz olefiant was the forerunner of the gen- multaneously both a source of ethylene and one of eral term olefin, formerly used as the name of the the methods by which hydrogen is prepared on an in- class of compounds we now call alkenes dustrial scale. Most of the hydrogen so generated is Ethylene occurs naturally in small amounts as a subsequently used to reduce nitrogen to ammonia plant hormone. Hormones are substances that act as for the preparation of fertilizer. messengers and play regulatory roles in biological processes. Ethylene is involved in the ripening of Similarly, dehydrogenation of propane gives many fruits, in which it is formed in a complex series propene of steps from a compound containing a cyclopropane CH3CH2 CH3-CH3 CH=CH2+ H rIng -CH2-CH2+ other products Propene is the second most important petrochemical and is produced on a scale about half that of ethylene cyclopropane- Almost any hydrocarbon can serve as a starting material for production of ethylene and propene. Cracking of petroleum(Section 2. 13)gives ethylene Even minute amounts of ethylene can stimulate and propene by processes involving cleavage of ripening, and the rate of ripening increases with the carbon-carbon bonds of higher molecular weight concentration of ethylene This property is used to hydrocarbons advantage, for example, in the marketing of ba- The major uses of ethylene and propene are as green by being stored with adequate ventilation to ene and polypropylene plastics, fibers, and films. mit the amount of ethylene present, and then in- These and other applications will be described in duced to ripen at their destination by passing ethyl- Chapter 6. ene over the fruit.* "For a review, see"Ethylene--An Unusual Plant Hormone"in the April 1992 issue of the Journal of Chemical Education (pp. 315-318). Back Forward Main MenuToc Study Guide ToC Student o MHHE Website168 CHAPTER FIVE Structure and Preparation of Alkenes: Elimination Reactions Ethylene is an acceptable synonym for ethene in the IUPAC system. Propylene, isobuty￾lene, and other common names ending in -ylene are not acceptable IUPAC names. CH2œCH2 IUPAC name: ethene Common name: ethylene CH3CHœCH2 IUPAC name: propene Common name: propylene ETHYLENE Ethylene was known to chemists in the eigh￾teenth century and isolated in pure form in 1795. An early name for ethylene was gaz oléfi- ant (French for “oil-forming gas”), a term suggested to describe the fact that an oily liquid product is formed when two gases—ethylene and chlorine—re￾act with each other. The term gaz oléfiant was the forerunner of the gen￾eral term olefin, formerly used as the name of the class of compounds we now call alkenes. Ethylene occurs naturally in small amounts as a plant hormone. Hormones are substances that act as messengers and play regulatory roles in biological processes. Ethylene is involved in the ripening of many fruits, in which it is formed in a complex series of steps from a compound containing a cyclopropane ring: Even minute amounts of ethylene can stimulate ripening, and the rate of ripening increases with the concentration of ethylene. This property is used to advantage, for example, in the marketing of ba￾nanas. Bananas are picked green in the tropics, kept green by being stored with adequate ventilation to limit the amount of ethylene present, and then in￾duced to ripen at their destination by passing ethyl￾ene over the fruit.* several NH3 steps CO2 1-Amino￾cyclopropane￾carboxylic acid CH2 CH2 Ethylene other products CH2œCH2 Ethylene (bp: 104°C) Cl2 Chlorine (bp: 34°C) ClCH2CH2Cl 1,2-Dichloroethane (bp: 83°C) Ethylene is the cornerstone of the world’s mam￾moth petrochemical industry and is produced in vast quantities. In a typical year the amount of ethylene produced in the United States (5 1010lb) exceeds the combined weight of all of its people. In one process, ethane from natural gas is heated to bring about its dissociation into ethylene and hydrogen: This reaction is known as dehydrogenation and is si￾multaneously both a source of ethylene and one of the methods by which hydrogen is prepared on an in￾dustrial scale. Most of the hydrogen so generated is subsequently used to reduce nitrogen to ammonia for the preparation of fertilizer. Similarly, dehydrogenation of propane gives propene: Propene is the second most important petrochemical and is produced on a scale about half that of ethylene. Almost any hydrocarbon can serve as a starting material for production of ethylene and propene. Cracking of petroleum (Section 2.13) gives ethylene and propene by processes involving cleavage of carbon–carbon bonds of higher molecular weight hydrocarbons. The major uses of ethylene and propene are as starting materials for the preparation of polyethyl￾ene and polypropylene plastics, fibers, and films. These and other applications will be described in Chapter 6. CH3CH2CH3 Propane H2 Hydrogen CH3CHœCH2 Propene 750°C CH3CH3 Ethane H2 Hydrogen CH2œCH2 Ethylene 750°C *For a review, see “Ethylene—An Unusual Plant Hormone” in the April 1992 issue of the Journal of Chemical Education (pp. 315–318). Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website