22. Dehydration of Cyclohexanol
Dehydration of an alcohol to form an alkene is one of the fundamental
reactions of organic chemistry. In this week’s example, we will transform
cyclohexanol into cyclohexene. The reaction itself and the procedure are
fairly simple, but you should realize that several processes take place in the
bottom part of the microscale distillation apparatus called a Hickman still.
Phosphoric acid catalyzes the dehydration of cyclohexanol, while
granules of Drierite® adsorb both the water that forms and that already
present in 85% H3PO4. At the same time granules of Drierite serve the
purpose of a pseudo-fractional distillation column that allows purification of
the product. The product that condenses and runs down into the collection
ring of the Hickman still should be dry and ready for yield determination.
Almost everything in the procedure is purposefully done in a particular
way, so it is a good idea to follow it to achieve a good yield of the product. A
reasonable yield of the alkene product is 40-70 %. Learn about different
parts of a Hickman still before using and handle it with care.
PRE-EXPERIMENT ASSIGNMENT
Study this chapter of the manual, the lecture notes on the Chemistry
Department web site, and pages 287-290 in Williamson. You will also find it
helpful to study the sections on the dehydration of alcohols reaction in your
lecture textbook. Do the first parts of your notebook writeup.
A student who has prepared for the Dehydration of Cyclohexanol
experiment should be able to:
1. Identify the process occurring (dehydration is an elimination reaction).
Identify the role of the Drierite in the process.
2. Give the equation and the mechanism for the dehydration of cyclohexanol
and other alcohols, including those that rearrange (this is review material
from the CHEM 2210 lecture).
3. Give a drawing of, and identify the components from a drawing of, the
Hickman still apparatus used for distillation. Explain the function of each
part of the apparatus and compare them to the parts of a regular distillation
setup that you used for fractional distillation.
4. Calculate the theoretical yield and the percent yield for this and similar
experiments given the necessary data, and perform any of the intermediate
calculations required by this process.
5. Draw the structure given the name, or give the name from the structure,
of the compounds used in the day’s experiment, and give the role of each
(reactant, solvent, catalyst, etc.).
6. Interpret IR spectra of cyclohexanol and cyclohexene. List and assign
