The dehydration of Cyclohexanol to form Cyclohexene.

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The dehydration of Cyclohexanol to form Cyclohexene.

In order to dehydrate Cyclohexanol it is required that a dehydration agent, in this case phosphoric acid, be added and for the mixture to be distilled with the Cyclohexene being taken off between 343K and 363K. This reaction gives the formula:

 

In order to keep the experiment at a manageable size 0.1 mole of Cyclohexanol was used along with 4cm3 of concentrated Phosphoric acid.

  1. mole of Cyclohexanol  x  100.2 = 10.2

           100.2

           0.962 = 10.4 cm3

However because the measuring cylinder only measured to the nearest 1cm3 ,10cm3 had to be used instead. This volume was placed into a 50cm3 pear shaped and the 4cm3 of phosphoric acid was added slowly while shaking the flask. The flask was then attached to the rest of the apparatus as shown below;

Because the boiling point of Cyclohexene is 356K and for water it is373K it was decide best to reflux the mixture between the 343K and 368K or 70oC and 90oC as read off the thermometer. Because of this all products collected in the vented receiver below 340K were discarded. In order that water was not present inside the vented receiver or any other component of the apparatus before the experiment began, all components were cleaned with acitone. Once the experiment had been set up the mixture was heated with a Bunsen burner to a temperature of around 363K where it was kept in order to increase the speed at which the Cyclohexene was collected in the vented receiver. The temperature was measured with a thermometer with the mercury tip placed at the entrance to the condenser in order to be most accurate for the temperature of the gas being collected in the vented receiver. When a large proportion of the mixture had been distilled the experiment was discontinued and the product was moved into a separating funnel to begin the process of purification of the Cyclohexene.

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The first stage of the purification was completed with a separating funnel such as the one in the diagram on the right. To the mixture, an equal amount of sodium chloride solution was added, in order to increase the density of the water and ease the separation of the water and Cyclohexene. The funnel was then shaken, with a stopper in the opening and the two layers allowed to separate. Because Cyclohexene has a density of

0.81g cm-3 and the water's density has been increased by the sodium chloride solution the two layers separated easily and most of the ...

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