Guidote AM, del Rosario DR, Abuzo AL. Experiencing Organic Chemistry.

Quezon City:
Office of Research and Publications, Ateneo de Manila University; 2005.
Experiment 7:

Preparation of Chlorocyclohexane
Alkyl halides are important reagents of many fundamental organic reactions such as the
Gringard and Friedel-Crafts reactions. These are generally prepared from alcohols.

Chlorocyclohexane (Cyclohexyl chloride), a secondary alkyl halide, is prepared from

HCl
OH Cl
ZnCl2
chlorocyclohexane
cyclohexanol
(cyclohexyl chloride)

Figure 1. Preparation of Chlorocyclohexane from Cyclohexanol.

The reaction proceeds through the general mechanism for the substitution of secondary
alcohols. The hydroxyl group initially complexed to ZnCl2 is converted to a better leaving
group by protonation using hydrochloric acid. A carbocation is formed by the dissociation
of water complexed to ZnCl2. The resulting carbocation is attacked by chloride ions to form
chlorocyclohexane.
ZnCl2 ZnCl2
H H
O O H - H2O, - ZnCl2 Cl
H Cl Cl-

Figure 2. Reaction Mechanism of the Preparation of

The reaction proceeds though SN1 instead of E1 because the nucleophile, a chloride ion, is a
weak base. It does not have enough energy to abstract a proton from the carbon adjacent
to the carbocation. The nucleophile resorts to attack the carbocation itself instead and this
leads to the formation of chlorocyclohexane.

The reaction is heated through reflux to ensure that the reaction is carried out at high
temperatures without losing its reactants through evaporation. As a result, the reactants
collide more often and with greater force and the rate of the reaction increases.

Second Edition Draft For use only within the Ateneo de Manila University.
Guidote AM, del Rosario DR, Abuzo AL. Experiencing Organic Chemistry. Quezon City:
Office of Research and Publications, Ateneo de Manila University; 2005.

water
outlet

water condenser

water
inlet

round bottom
flask

Figure 3. A Reflux Setup.

The chlorocyclohexane formed is washed with water and sodium bisulfite to remove traces
of acid, unreacted cyclohexanol, and water. It is important to dry the product since the
presence of water can slowly revert it back to cyclohexanol or encourage elimination to
form cyclohexene.

OH2 OH
H2O - H+
H H

Cl
- Cl-

H H2O

HH

Figure 4. Some Possible Side Reactions of Chlorocyclohexane.

Second Edition Draft For use only within the Ateneo de Manila University.
Guidote AM, del Rosario DR, Abuzo AL. Experiencing Organic Chemistry. Quezon City:
Office of Research and Publications, Ateneo de Manila University; 2005.
Prelab Questions
1. How is the yield of the reaction maximized? Explain.
2. What is the use of the sodium bisulfite wash?
3. Why do you have to drain the aqueous layer before adding sodium bisulfite on the
organic layer? What gas is formed upon the addition of sodium bisulfite?
4. What step is undertaken to prevent chlorocyclohexane from reverting back to
cyclohexanol or forming cyclohexene? How does this prevent the reversal from
taking place?
5. What are the qualitative tests to verify the presence of chlorocyclohexane and
cyclohexanol? What constitutes a positive test result?

Equipment
 boiling chips

Chemicals
 cyclohexanol
 12 M hydrochloric acid
 zinc chloride
 20% sodium bisulfite

Procedures
Place about 5 mL cyclohexanol, 1.0 g zinc chloride and around 15 mL concentrated
hydrochloric acid into a round bottom flask. Swirl the flask to mix the contents until a
yellow color appears. Attach a water condenser vertically over the mouth of the round
bottom flask. Check the setup for leaks and heat the round bottom flask. A second layer
will form after 10 minutes. Continue heating the round bottom flask for at least 30 minutes.

TIP: HCl gas will evolve from the setup. Perform the experiment under the hood. Condensation
during reflux should appear around halfway in the water condenser. Adjust the flame
accordingly.

Let the mixture in the round bottom flask cool down until it is cool enough to be handled.
Decant the mixture into a separatory funnel and shake the funnel vigorously to mix the two
layers. Continue shaking until the mixture inside the funnel cools down to room temperature.

TIP: Do not forget to vent the gas out of the funnel.

Allow the mixture to stand and let the two layers separate. Drain the aqueous layer
containing concentrated hydrochloric acid and zinc chloride into flask and discard it into a
Waste Acid container. Rinse the round bottom flask used for reflux with around 8 mL
distilled water and use this to wash the organic layer in the separatory funnel. Drain the
aqueous layer. Wash the organic layer with around 8 mL 20% sodium bisulfite and then
with around 5 mL water. Discard the washings into the sink.

Decant the organic layer into an Erlenmeyer flask and dry it over sodium sulfate. Distill it if
necessary and store it in a scintillating vial. Perform qualitative tests.

Second Edition Draft For use only within the Ateneo de Manila University.
Guidote AM, del Rosario DR, Abuzo AL. Experiencing Organic Chemistry. Quezon City:
Office of Research and Publications, Ateneo de Manila University; 2005.
Postlab Questions
1. Would you expect a 100% yield in the experiment? Explain.
2. What is the purity of the product based on the results of the qualitative tests? What
factors may affect the purity of the product obtained in the experiment?
3. Which among the tests for alcohols would give a conclusive result to attest the
presence/absence of cyclohexanol in the product? Explain. Why can’t the other tests
be used?
4. What would you expect to find on the receiving flask if the organic layer were
distilled without drying it over sodium sulfate? Explain.
5. What changes on the experiment would you make if you want to prepare
bromocyclohexane instead? Explain.

References:
McMurry J. Organic Chemistry. 5th ed. USA: Brooks/Cole; 2000.

Most CF. Experimental Organic Chemistry. USA: Wiley & Sons; 1988.

Second Edition Draft For use only within the Ateneo de Manila University.