PAG 5.2- Preparation of cyclohexene from cyclohexanol

Question 1

Method (preparation+reflux)

Answer 1

• Pour desired volume of cyclohexanol into 50cm^3 round-bottomed flask.
• Using plastic graduated dropping pipette, carefully add around 4cm^3 of concentrated phosphoric acid to the flask.
• Add a few anti-bumping granules, then assemble reflux apparatus.
• Heat the flask gently at about 70°C for 15-20 minutes, ensuring all condensation happens in lower half of condenser.
• Stop heating and allow apparatus to cool before assembling for distillation.
• Slowly heat flask, collecting any liquid which boils below 100°C.

Question 2

Method (purification)

Answer 2

• Pour distillate into separating funnel and add an equal amount of sodium chloride solution.
• Shake funnel, allowing layers to separate.
• Run off bottom aqueous layer into beaker, collect top organic layer into small conical flask.
• Add few lumps of anhydrous calcium chloride, to remove any traces of water.
• Place stopper on flask, shake contents, and allow to stand until solid settles.
• Weigh a sample tube and then decant liquid into the container.
• Reweigh the tube and calculate the mass of cyclohexene produced, also determine percentage yield.
• Can also conduct bromine water to test for alkene.
• Can redistill product to obtain purer sample.