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Chemistry
234
Organic Chemistry Laboratory
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Experiment
8: 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).
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Use a heating
mantle with sand to heat the distillation flask.
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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.
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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.
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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.
III.
Report Requirements
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
9. Answer these
questions in your report:
1. Write the mechanism for
the dehydration of cyclohexanol with sulfuric acid.
2. Why was it necessary to
dry the crude cyclohexene before the final distillation?
3. Write the equation for
the addition of bromine to cyclohexene. Show the sterochemistry of the
product.
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