elimination reactions in halogenoalkanes

• What reaction occurs when halogenoalkanes are heated with potassium hydroxide in ethanol?

  An elimination reaction occurs
• What is formed when 2-iodopropane is heated with KOH?

  Propene is formed
• What is the general reaction for heating 2-iodopropane with KOH?

  CH3CHICH3 + KOH ➔ CH2=CHCH3 + H2O + KI
• What characterizes an elimination reaction?

  A small group is removed without replacement
• What are the three steps in the mechanism of the elimination reaction?

  1. OH- removes a hydrogen ion (H+) from the halogenoalkane, forming water.
  2. The adjacent carbon forms a π bond with a spare electron.
  3. The carbon-halogen bond breaks heterolytically, eliminating the halide ion.
• What role does OH- play in elimination reactions?

  OH- acts as a base
• How do solvent conditions affect the reaction of halogenoalkanes with hydroxide?

  • Substitution is favoured in aqueous solution (OH- as nucleophile).
  • Elimination is favoured in ethanolic solution (OH- as base).
  • A mixture of water and alcohol allows both reactions to occur.
• What happens when halogenoalkanes are treated with hydroxide in aqueous conditions?

  Substitution reaction occurs
• What happens when halogenoalkanes are treated with hydroxide in ethanolic conditions?

  Elimination reaction occurs
• What are the outcomes of using a solvent mixture of water and alcohol with halogenoalkanes?

  • Both substitution and elimination reactions can occur.
  • A mixture of products is formed.