Reactions of Alkenes

React via additional reaction

• The carbon-carbon double bond will open up and add additional atoms on
• New atoms are added to each carbon

Reactions with hydrogen:

• Open up the double bond and form the equivalent saturated alkane
• Needs a catalyst

Reaction with steam/water:

• Water is added across the double bond and an alcohol is formed
  • For example ethene and water makes ethanol
  • After reactions, mixture is passed from the reactor into a condenser
  • Ethanol and water have a higher boiling point then ethene so both condense whilst any unreacted ethene gas is recycled back into the reactor
  • Alcohol can then be purified through fractional distillation

Reactions with halogens

• Halogens include bromine, chlorine and iodine
• Molecules formed are saturated, with the C=C carbons each becoming bonded to a halogen atom
• Form di(halogen-ine)(alkane)

Test for alkene:

• The addition of bromine to a double bond can be used to test for alkenes
  • When orange bromine water is added to a saturated compound, like an alkene, no reaction will happen and it remains bright orange
  • If it’s added to an alkene the bromine will add across the double bond making a colourless dibromo-compound, so the bromine water is decolourised