1) A- In this reaction, the position of equilibrium can be shifted to the right

Question

1) A- In this reaction, the position of equilibrium can be shifted to the right by continuously removing cyclohexene or water as they are formed. If we use a fractional distillation column for instance, can we actually ensure that the cyclohexene (BP 83ºC) product is not contaminated with the starting material cyclohexanol (BP 161ºC)?

B-The distillate does not, however boil at 83ºC because cyclohexene and water forms a minimum-boiling azeotrope whose boiling point is 70ºC. So, what exactly will the distillate mixture be composed of?

C-The distillate is transferred to a separatory funnel and aqueous NaOH solution is added to the funnel. (called “washing”). Why wash the product mixture with base?

D-The aqueous layer is carefully removed, hopefully leaving the product in the funnel. The product is then transferred to a sample vial and treated with an anyhydrous reagent such as calcium chloride, CaCl2. Why?

Explanation / Answer

1.Since the product cyclohexene has a lower boiling point(83°C ) than the starting material cyclohexanol( 161°C ) ,it is possible to separate the product by fractional distillation without any contamination only if we can maintain steady boiling temperature around 83 °C.Elevation in temperature will increase the risk of contamination by cyclohexanol.

2.As cyclohexene and water forms a minimum boiling azeotrope at 70 °C,the distillate will contain water and cyclohexene mixture.(Note:90% cyclohexene-10% water mixture boils at 71°C).

3.The distillate containing cyclohexene and water is treated with base NaOH to neutralise any traces of H2SO4 if present.

4.CaCl2 is an excellent drying agent.It forms molecular complexes with water.As cyclohexene and water forms azeotrope,the product needs to be dried to free it from water.Even after removal of aqueous layer,there may be traces of water in the product so CaCl2 is used to ensure that the product is completely free from water.

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