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

1.

2.a)

b)

c)

d)

e)

3.

4.

5.