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Experiment 2
Preparation of Cyclohexene
Introduction Cyclohexanol is an aliphatic hydroxyl compound. It undergoes dehydration to form cyclohexene and water. In this experiment, concentrated phosphoric acid is used as the dehydrating agent. The rough product is purified to determine its yield. The purified product is then tested with bromine water and acidified potassium permanganate to identify the presence of the functional group of alkene.
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Chemicals Cyclohexanol, concentrated phosphoric acid (ortho) , anhydrous calcium chloride, bromine water, 0.10 M potassium permanganate, 0.50 M sulphuric acid. Apparatus Electronic balance, quick-fit apparatus, thermometer (-10oC to 110oC), rubber tubing, 50cm3 separating funnel, filter paper and filter funnel, 10 cm3 measuring cylinder, anti-bumping granules, grease Caution Bromine water is harmful. Cyclohexanol and cyclohexene are flammable and harmful. Concentrated phosphoric acid is corrosive. Anhydrous calcium chloride is irritating. Wear safety glass during the experiment. Procedures Part 1: Preparation of Cyclohexene (one triple periods) Weigh and record the mass of a clean and dry 50 cm3 pear-shaped flask accurately. 2. Put about 30 cm3 of cyclohexanol in the pear-shaped flask. Weigh and record its mass accurately again. Then fit it in a beaker. 3. Measure about 8 cm3 of concentrated phosphoric acid using a measuring cylinder. Pour it to the flask in small portions. Shake the flask to mix the contents. 1.
4. 5. 6.
Add several pieces of anti-bumping granules to the flask. Construct a reflux set up to carry out reflux for 15 minutes. Cool the flask and the mixture by immersing in a beaker of tap water for 5 minutes. 7. Construct a distillation set up to carry out distillation. Collect the distillate boiling at 70-90oC. Part 2: Purification of cyclohexene (One triple periods) 1. 2. 3.
Pour the distillate into a clean 50 cm3 separating funnel. Add about 5 cm3 of saturated sodium chloride solution. Shake the mixture vigorously for two minutes. Open the valve occasionally to release pressure. Allow the separating funnel to stand for about 3 minutes until two clear and
immiscible layers appear. 4. Run off the lower layer. 5. Run the original upper layer into a dry 100 cm3 conical flask. 6. Add anhydrous calcium chloride to the flask using a spatula until the liquid is clear. 7. Filter to remove the calcium chloride solid. Use a clean and dry 50 cm3 round bottom flask fitted in a beaker to collect the filtrate. 8. Add several pieces of anti-bumping granules to the flask. 9. Weigh and record the mass of a clean and dry 100 cm3 conical flask. 10. Construct a set up to distill the filtrate in step 7. Collect the distillate boiling 81-85oC using the weighed conical flask in step 9. 11. Record the exact boiling point, physical appearance, and smell of the distillate in a table. 12. Weigh and record the mass of the flask containing the distillate. Test of cyclohexene 1. Pour about 2 cm3 of bromine water into a clean test tube. 2. 3. 4. 5. 6.
Add the distillate in part B to the tube drop by drop and shake the tube until there is no further change. Pour about 1 cm3 of 0.10 M potassium permanganate into a clean test tube. Pour about 1 cm3 of 0.50 M sulphuric acid. Add the distillate in part B to the tube drop by drop and shake the tube until there is no further change. Record the observation in a table.