Elimination

• Describe the elimination mechanism for dehydration of alcohols

  Forms an alkene

  • The lone pair on the oxygen from the hydroxyl group attaches to the H+ ion from the acid catalyst
  • A positive charge is on the oxygen. Oxygen pulls the elctrons from the C-O bond strongly to break the bond, leaving an unstable carbocation intermediate
  • The carbication loses a H+. The electrons in C-H move to form a C=C bond
  • An alkene is made and the H+ has reformed - proving it is an acid catalyst
• What happens when non-primary alcohols are dehydrated?

  2 different alkenes have the possibility to form

  The double bond can be formed on either side of the carbon attached to the -OH group
• Describe the distillation step to making a cyclohexene

  Step 1

  • Add concentrated sulfuric or phosphoric acid and cyclohexanol into a round bottomed flask. Add several anti-bumping granules for smooth boiling
  • Use a heating mantle to warm to boiling point, not bunsen burner as alcohol is flammable
  • Chemicals with lower boiling points will evaporate into the condensor and then cool down and condense into a liquid
  • The product is collected in a vessel but will still have small amounts of impurities
• Describe the separation step to making a cyclohexene

  Step 2

  • Add the products into a separating funnel. Add water to dissolve soluble impurities and create an aqueous solution
  • After allowing the solution to settle, two layers will form: top - impure cyclohexene, bottom - aqueous layer containing water soluble impurities
  • Drain the aqueous layer
• Describe the purification step to making a cyclohexene

  Step 3

  • Take the impure cyclohexene and add to a round bottomed flask
  • Add anhydrous CaCl2. This is a dehydrating agent and will remove any aqueous substances remaining.
  • Invert the flask and leave for 30 minutes