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Industrial Importance of Alkenes

Ethylene as Industrial Feedstock

Ethylene is an important monomeric feedstock in the chemical industry. It is used among other things for the production of polyethylene and other industrial intermediates. Ethylene is obtained by pyrolysis of naphtha or other hydrocarbons such as ethane or propane. At temperatures between 750°C and 900°C, the pyrolysis of naphtha yields 20 to 30 percent ethylene.

Ethylene is used not only as a monomeric raw material for polymerization but also as a starting material for the synthesis of important industrial chemicals, e.g. vinyl acetate which is obtained from the reaction of ethylene and acetic acid on exposure to air in the presence of a palladium(II) catalyst and copper(II) chloride .

Fig.1
Synthesis of vinyl acetate (ethenyl acetate)

If water is used instead of acetic acid, the reaction yields vinyl alcohol which almost completely tautomerizes to acetaldehyde. The catalytic production of acetaldehyde from ethylene and water is called the Wacker process.

Fig.2
Synthesis of acetaldehyde (ethanal): Wacker process

Vinyl chloride, prepared by chlorination and subsequent dehydrochlorination of ethylene, is the monomeric starting material for the synthesis of the frequently used polyvinyl chloride (PVC). Instead of using expensive chlorine, the chlorination is carried out with hydrogen chloride and copper(II) chloride in the presence of oxygen to yield the desired intermediate 1,2-dichloroethane, which subsequently is converted into vinyl chloride by thermal elimination of hydrogen chloride.

Fig.3
Synthesis of vinyl chloride (chloroethylene)

Ethylene oxide (1,2-epoxyethane, oxirane) is synthesized by the oxidation of ethylene with oxygen in the presence of a silver catalyst. Hydrolysis of ethylene oxide yields ethylene glycol.

Fig.4
Synthesis of ethylene glycol (1,2-ethanediol)

Exercise

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