Dehydration of Alcohols

Clayton State University
Dr. Susan F. Hornbuckle
Experiment #6 Part 2
The dehydration of 2-methylcyclohexanol can proceed in 2 directions, giving rise to 1methylcyclohexene or 3-methylcyclohexene. In this experiment, gas chromatography
(GC) will be used to determine the product composition.
Fractional distillation apparatus:
To a 25-ml round-bottom flask, add 6 ml of 2-methylcyclohexanol, 5 ml of 85%
phosphoric acid, and a boiling stone. Attach to a fractional distillation assembly
according to the figure above.
Either use no column packing or a low hold-up packing. Slowly heat the contents of the
flask to boiling and distill out the product. The distillation temperature should be kept
below 96 degrees by regulating the rate of heating. Continue the distillation until 4 to 6
ml of liquid have been collected (a test tube or distillation receiver is a convenient
collection vessel).
Clayton State University
Dr. Susan F. Hornbuckle
Separate the product from the water layer by using a pipette. Transfer the product to a
clean, dry test tube and dry it over Na2SO4 for 10 minutes.
Inject 0.5 micro liter of the dried liquid onto a non polar gas chromatograph column.
Before doing so, be sure to fill and empty the syringe several times, discarding the
sample each time, to clean out the previous contents. Draw approximately 1 micro liter of
air into the syringe after the liquid when you are ready to analyze the sample. Insert the
needle as far as possible into the injection port before injecting the sample to insure
placing the sample directly onto the column.
Mark the point of injection on the recorder chart paper and measure accurately the
distance (or time) from this point to the olefin peak(s). By comparing the results with the
retention times of 1-methylcyclohexene and 3-metyhlcyclohexene, determine the identity
of the dehydration product(s). If both are present, determine the approximate composition
by triangulation of peak areas. Explain your results. If additional peaks are present,
attempt to identify these as well.