CHM!2201!
Organic!Chemistry Lab I
Fall!2009!
Department!of!Chemistry!
Villanova University
Dehydration of 2-Methylcyclohexanol
Bell, Clark & Taber, pgs. 205 – 209
Carry out this reaction in your hood
U
1. Add to a 25 mL round-bottom flask:
a. 6 mL of 2-methylcyclohexanol (Avoid contact with skin; do not breath
vapors)
b. 5 mL of 85% phosphoric acid (CAUTION!!: corrosive liquid)
c. TWO or THREE boiling stones
2. Attach the flask to a simple distillation apparatus as illustrated on the next page.
Use a centrifuge tube as the collection receiver.
3. Heat the flask slowly to boiling and distill the formed alkenes while keeping the
distillation head temperature below ~96°C by regulating the rate of heating.
4. Collect a total of 4 to 6 mL of distillate in a centrifuge tube receiver. (A small
narrow tube is best for your distillation receiver since it will be easier to separate
and isolate the product). The distillate that you collect in your receiver may
consist of two layers:
a. Upper layer: the majority of the distillate is contained in this layer and it
consists of the desired mixture of cyclohexenes. (Remember from last
week’s experiment that hydrocarbons are less dense than water!!)
b. Lower layer: if this layer is present, it should be present in a smaller
amount and consists of water which codistilled with the cyclohexene
products.
5. Using a disposable pipet, carefully separate the desired upper layer of the
distillate from the lower water layer and transfer it to a clean dry pre-weighed test
tube (HINT: Place the test tube in a beaker to hold it for weighing). Try not to
contaminate the cyclohexenes with water from the lower layer if it is present.
6. After the cyclohexenes have been transferred to the pre-weighed test tube,
reweigh the test tube (use the beaker method) and its contents to obtain the weight
of the product so that you can calculate your approximate % yield.
7. After weighing the test tube and its contents, dry the product by adding some
solid anhydrous sodium sulfate to the liquid product in the test tube; initially, add
enough sodium sulfate to amount to about ¼ of the total volume of liquid. Stir the
contents with a spatula to mix the drying agent with the liquid. If you observe
only large chunks of drying agent, add another small portion of sodium sulfate,
stir it and observe if the added sodium sulfate is loose and finely divided and not
chunky after stirring the mixture; if it is finely divided, you have added enough
drying agent. Allow the mixture to sit for ~5 – 10 minutes with intermittent
stirring to ensure that the sodium sulfate contacts all of the liquid to maximize
thorough drying of the liquid.
U
U
U
Page 1 of 2
U
CHM!2201!
Organic!Chemistry Lab I
Fall!2008!
Department!of!Chemistry!
Villanova University
8. Using a clean disposable pipette, transfer 10 drops of the clear dried product
(avoid allowing particles of sodium sulfate drying agent to get into the pipette) to
a small vial with a screw cap and use this small sample for subsequent GC and IR
analysis.
9. Analyze the composition of the product by GC analysis. The TAs will inject the
sample for you. Identify the two main components of the reaction product by
comparison of retention times (previously determined for each instrument) with
authentic samples of 1-methycyclohexene (bp 110°C) and 3-methylcyclohexene
(bp 104°C).
a. Which cyclohexene isomer was formed in greatest amount? What is the
approximate % composition of the two isomers?
b. Why was the predominant isomer formed in the greatest amount?
c. Based on the boiling points of the two major cyclohexene products, which
would you predict to have the shortest GC retention time? Why? Does
your prediction correlate with your experimental observations?
d. Did you observe any additional peaks other than the two expected main
products?
e. Another product that could be formed in small amounts from this
dehydration reaction is methylenecyclohexane (bp 102 - 103°C).
Did you observe a small gc peak that might correspond to
methylenecyclohexane based on its boiling point?
f. Theoretically, how could methylenecyclohexane be formed in this
reaction? Show a mechanism for its formation.
10. Take an infrared (IR) spectrum of your dried dehydration product (request a TA
to help take the IR); compare the IRs of starting material (2-methylcyclohexanol,
provided to you as a handout) and your product mixture and explain key
functional group absorption band changes which indicate that the alcohol
dehydration occurred to provide the desired alkene products.
11. Compare the IR of your product with the IRs of pure 1-methylcyclohexene and 3methylcyclohexene (both spectra provided to you as handouts).
a. Can you observe absorption bands in the IR of your product mixture that
are unique to either of the pure cyclohexene isomers?
b. If you did not have a GC analysis to determine the relative amounts of the
cyclohexene isomers formed, could you, by closely examining the IRs of
your product and the two individual pure cyclohexene isomers, predict
which isomer is present in the greatest amount? How could you do this?
U
U
Simple Distillation Apparatus
U
Page 2 of 2
TMBare (10/12/2009)