Chemistry 233
Organic Chemistry Laboratory

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Experiment 6: Dehydration of Cyclohexanol

I. Summary

In this experiment, you will synthesize cyclohexene via acid-catalyzed dehydration of cyclohexanol. This reaction will be carried out by heating the components and collecting impure product. A second distillation will be necessary to purify cyclohexene. Purity will be determined by the boiling point of the collected product. The product will be tested for unsaturation using the Baeyer test.

II. Procedure

Bring a clean, dry 25 x 150 mm test tube to the storeroom manager, and trade it for a sample of cyclohexanol. Obtain a weight or volume for the sample (around 14.2g or 15 mL). Be sure to use the mass of your sample for all of your calculations. Into a 50 mL round bottom flask, add the cyclohexanol, 9 M sulfuric acid (7.5 mL), and a few boiling chips. Mix the contents of the flask with gentle swirling.

Equip the flask for fractional distillation (see experiment 3).

Suspend the flask in a thermowell to heat it for the distillation.

Do NOT put sand around the flask because this can result in overheating and damage the thermowell..

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Use an Erlenmeyer flask as the collection vessel, and cool it in an ice bath during the distillation. Heat the reaction mixture, and collect all distillates while maintaining a head temperature in the range of 80-85 °C. Discontinue heating once about 5 mL remains in the distillation flask.

If water separates as a distinct layer, remove it with a pipet.

Add several spatula-tips full of potassium carbonate to the crude product in the Erlenmeyer flask. Swirl the mixture occasionally over a 10-15 minute period, and add more potassium carbonate IF the liquid remains cloudy.


Thorough drying is very important (why?).Transfer the product to an 25 mL round bottomed flask by decanting or using a pipet.

Add a few boiling stones to the flask, and purify the product by simple distillation. Use a tared vial as a receiver, and cool the receiver in an ice bath.


Collect distillate with a head temperature between 80-85 °C. Obtain a weight of your purified product. Note: If product is cloudy, add several spatula-tips full of potassium carbonate to the vial, and transfer the dried product to another tared vial by pipet before weighing.

Baeyer Test for Unsaturation:
To test your product for unsaturation, follow the procedure on pages 769-770 of your lab text for the Baeyer test. Perform both the test and the blank.

 

IR Spectra of cyclohexanol and cyclohexene

III. Formal Report Requirements

In additon to the requirements listed in the formal lab report handout, your report should contain the following information:
1. Reference to procedure with changes noted.

2. Equation of the reaction showing structures and products. Below each reactant, list molecular weight, amount used in grams (or mL) and moles. Below each product list the molecular weight and theoretical yield in grams and moles.

3. Mechanism of the reaction showing structures of intermediates and arrows to demonstrate electron movement.

4. Experimental yield and percent yield (show calculations)

5. Weight of product.

6. Boiling point range of product.

7. For the Baeyer test, include both the equation for the reaction and your results for cyclohexene and the blank.

8. Interpretation of data and conclusions

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