Preparation of Cyclohexene

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PREPARING CYCLOHEXENE FROM CYCLOHEXANOL

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 used. 2)Measure out 4cm3 of concentrated phosphoric acid in a small, glass measuring cylinder. 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.

SEPARATION
Switch on the heater again and allow the mixture to boil gently so that all the cyclohexene vapour is condensed in the condenser. Collect the distillate that comes across between 70 and 90OC. Switch off the heater when you have finished collecting the distillate.

PURIFICATION
1)Pour the distillate into a separating (tap) funnel and shake it with an equal volume of saturated sodium chloride solution (this has a higher density than ordinary water and allows the two...
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