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Reactivity of Ethylene

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Over 20 million tonnes of ethylene are produced annually in the United States alone. About half of this goes to make polyethene (the plastic used in supermarket plastic bags, kitchen film, and many toys), while the rest is used to produce a variety of chemicals. Why is ethylene so useful?

The two bonds of a carbon carbon double bond are not created equal. The second bond (pi-bond) is weaker than the first (sigma-bond). Because of this, only a little energy needs to be put into the system in order to convert a double bond to two single bonds, if there is a molecule to which it can form a new single bond. The newly formed single bond can be to oxygen, a halogen, or another carbon compound.

There are a lot of different reactions that ethylene can undergo, all related to the high reactivity of the double bond. They include:

  • oxidation (addition of oxygen across the double bond)
  • halogenation (addition of one of the halogens (fluorine, chlorine etc) across the double bond)
  • alkylation (the addition of a carbon (alkyl) chain to the double bond)
  • hydration (the addition of water across the double bond)
  • polymerisation (the joining up of lots of molecules to form a long chain-like molecule)