INTRODUCTION
Alkenes can be prepared in the lab by dehydrating the corresponding alcohol. Concentrated sulphuric and phosphoric acids both act as dehydrating agents. Phosphoric acid is preferred because it gives a higher yield of the alkene. Concentrated H2SO4 reacts with alkenes.
SAFETY
Eye protection must be worn. Concentrated phosphoric acid is corrosive. Mop up spillages immediately with plenty of water.
Cyclohexene and cyclohexanol are highly flammable. Keep away from naked flames. Anhydrous calcium chloride is an irritant.
PREPARATION
1) Weigh out between 9 and 10 grams of cyclohexanol directly into a 250cm3 round-bottomed, quickfit flask. Record accurately the mass of alcohol …show more content…
Add this SLOWLY to the cyclohexanol in the flask and mix thoroughly by swirling cautiously.
3) Add an anti-bumping granule to the flask and set it up in the electric heating mantle with a reflux condenser fixed vertically to the top.
4) Heat the mixture until it boils. Adjust the heat control so that the mixture refluxes gently for about 10 to 15 minutes.
5) Allow to cool, then rearrange the apparatus to allow for distillation of the crude product. Do this by inserting a still head fitted with a thermometer between the top of the flask and the condenser. Attach a 100cm3 round-bottomed flask to the end of the condenser to collect the distillate. …show more content…
Note the appearance of the flame.
2) Shake 1cm3 (1 teat pipette full) of bromine water with 3 or 4 drops of cyclohexene in a test tube. Observe what happens.
3) Add 2 or 3 drops of potassium manganate (VII) solution to 2cm3 of bench sulphuric acid in a clean test tube. Add 3 or 4 drops of cyclohexene and shake. Observe what happens.
4) Place 3 or 4 drops of cyclohexene in a clean test tube. Carefully add 2 or 3 drops of concentrated sulphuric acid and observe what happens.
When you have completed your tests, put any remaining cyclohexene into the “Solvents Residues” bottle in the fume cupboard. Rinse used glassware and place it on the wet tray. Clear away all apparatus and leave your bench clean and tidy.
QUESTIONS
1) 1 mole of cyclohexanol (C6H11OH) forms 1 mole of cyclohexene (C6H10).
a) Use your starting mass of cyclohexanol and the appropriate relative atomic masses to calculate the mass of cyclohexene you would expect to get if all the alcohol reacted (this is called the theoretical yield).
b) Calculate your actual yield of cyclohexene as a % of the theoretical