- I will arrange the apparatus as shown above
- I will need to gently heat the flask to distil over the liquid
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I will then pour the distillate into a separating funnel and add 2cm3 of a saturated solution of Sodium Chloride.
- I will shake the mixture and allow the two mixtures to separate
- The organic layer will need to be transferred into a small flask and added to 8 - 9 pieces of Anhydrous Calcium Chloride
- I will then shake the mixture until it becomes clear (adding more Anhydrous Calcium Chloride if necessary)
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I then should distil the liquid collecting the liquid at 80oC and stop collecting at 82oC.
I will then record the volume of purified Cyclohexene.
NB. The final (second) distillation must be done carefully, using clean dry apparatus to obtain pure product. For best results rinse the apparatus with a little ethanol and a little acetone to speed up the drying process.
Air can also be gently blown through the glassware to speed up the drying. It is important to remove all water and organic solvents before the final distillation or the product will become contaminated.
Results
Cyclohexene Product
- Burns with a sooty yellow flame, leaves no residue
- Decolourises Bromine water (Orange >>>Colourless)
- Gives a brown solution mixture with Potassium Permanganate
- Decolourises Acidified Potassium Permanganate (Purple>>>>Colourless)
Caution; bromine is extremely hazardous to breath and causes severe burns if it touches the skin. A dilute bromine solution could be used in this test so the hazard potential is much less than if pure bromine were used.
If you accidentally allow the bromine solution to touch your skin, immediately rinse the contaminated area with dilute aqueous sodium Thiosulphate solution, then wash with soap and water.
The bromine solution is reddish-orange. Bromine reacts with an alkene to form a colourless dibromide. Thus, if a bromine solution is added to an alkene, the solution will decolourise until all of the alkene has reacted.
Alkanes on the other hand do not react with bromine in this way, so the very first drop of bromine solution will cause a reddish-orange colour to persist.
Potassium permanganate is purple. It reacts with alkenes to produce a colourless diol and a finely divided brown precipitate of manganese dioxide. Under acidic conditions the diol can further react to form a colourless dicarboxylic acid. Thus, when permanganate is added to an alkene, the purple colour disappears and a brownish suspension forms until all of the alkene has reacted.
Permanganate does not react with alkanes, so the first drop of permanganate added to an alkane immediately results in a purple solution.
