4-methylcyclohexane - experiment 24
TRANSCRIPT
Jacob LytleChemistry 2010-PA
Experiment 244-Methylcyclohexane
December 1, 2009
Introduction
Alcohol dehydration is an acid-catalyzed reaction performed by strong, concentrated
mineral acids such as sulfuric and phosphoric acids. The acid protonates the alcoholic hydroxyl
group, permitting it to dissociate as water. This is followed by the loss of a proton from the
intermediate, which brings about an alkene.
Procedure
In a pre-weighed 50 mL round bottom flask, 7.5 mL of 4-methylcyclohexanol was
weighed. Then, 2 mL of phosphoric acid and 30 drops of sulfuric acid was added to the flask.
After assembling the distillation apparatus and starting the flow of water through the
condenser, the mixture was heated slowly. Once the distillation began, the temperature was
regulated so that the rate of distillation was near three seconds per drop. The temperature
range for the distillation was recorded. After the distillation stopped, the heating mantle was
removed. The distillate was transferred to a centrifuge tube from the receiving flask using a
pipette and 2 mL of saturated sodium chloride solution was added to the receiving flask. The
remaining liquid in the receiving flask was then added to the centrifuge tube. The layers
separated and a pipette was used to remove and discard the bottom aqueous layer. The organic
layer was transferred to a 25 mL Erlenmeyer flask. Then, anhydrous sodium sulfate was added
and the flask was stoppered. The flask was set aside for 15 minutes, and then transferred to a
clean 50 mL round bottom flask. Using the same distillation apparatus, the product was distilled
into a pre-weighed receiving flask. The temperature range for the distillation was recorded.
After distillation had stopped, the receiving flask was weighed to determine the weight of the
product collected as the distillate. A sample was prepared for the gas chromatographic analysis
by adding one drop of the product and 2 mL of methylene chloride to a vial. Then, the
remaining product was used for an unsaturation test. Bromine and potassium permanganate
were added, separately, to both the product and the starting alcohol for comparison. The color
changes resulting from the qualitative test were recorded.
Results
Compound Name Boiling Point (°C)
3-methylcyclohexene 104
1-methylcyclohexene 110-111
4-methylcyclohexene 101-102
methylenecyclohexene 102-103
Product Observed Boiling Point
(oC)
Literature Boiling Point
(oC)
Molecular Weight(g mol-1)
Mass(grams) Appearance
4-methylcyclohexene 101-102 °C 96.17
Retention Time(minutes)
Percent Composition Compound Boiling Point(oC)
2.297 0.427592.518 95.798002.784 2.992263.356 0.102704.993 0.610925.070 0.06851
Discussion
The 4-methylcyclohexene required removal from the system as it was being formed to prevent the reverse reaction. To do this, distillation was used. While distilling the solution, some water was taken off with the product due to the closeness of their boiling points. However, 4-methylcyclohexene is insoluble in water, so the two liquids were easily separated.
4-methylcyclohexene is insoluble in waterDouble bonds react with a red bromine solution to decolorize it Double bonds react with a purple KMnO4 solution to create a brown precipitate
Questions
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d)
e)
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