Le Chatelier's

Victor Leung 7C (10) Experiment Date: 5TH & 8TH October, 2007

EXP2 – Synthesis of Cyclohexene

by the Dehydration of Cyclohexanol

Aim:

The purpose of this experiment is to practise the synthesis of cyclohexene by dehydration of cyclohexanol and to understand the process of dehydration as an elimination reaction.

Principle:

The synthesis require an effective dehydrating agent to remove the OH group from the cyclohexanol and forms cyclohexyl cation as an intermediate; a hydrogen atom is further removed from the cation, forming cyclohexene as final product.

Method:

The experiment made use of a mixture of conc. sulphuric and phosphoric acid as dehydrating agent, which is characterized by the poor nucleophilic property of its anion. The reaction occurs slowly in normal conditions, but we chose to quicken it by heating. The reaction is set up under a simple distillation apparatus in order to remove the cyclohexene in the product mixture while it is formed. This prevented backwards reactions and other side reactions.

The distillates are washed with NaCl solution to remove cyclohexanol present in the product. The aqueous layer of the mixture is extracted by a separating funnel. The organic layer is further dried and purified by anhydrous calcium chloride, which could form molecule complex with cyclohexanol and water. The mixture requires further distillation to extract the dried cyclohexene.

Apparatus and chemicals:

• Cyclohexanol

• Concentrated sulphuric and phosphoric acid mixture.

• Anhydrous calcium chloride

• Saturated NaCl solution

• Ice-bath

• Boiling tubes

• Quick fit apparatus for simple distillation.

• Thermometer

Experiment Procedure and Observations

1. Some anti-bumping granules were added to a reflux flask.

2. 10 grams of cyclohexanol was placed in the reflux flask and 2.5cm3 of concentrated sulphuric and phosphoric acid mixture was added to the flask....