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Phuc Nguyen
Lab:Th-1pm
Partner: Leah
11/7/2012
Experiment 21: Dehydration of 4-methyl cyclohexanol
Introduction: In this experiment, we had to carry out the dehydration of 2-methylcyclohexanol
and 4-methylcyclohexanol by heating the alcohols in the presence of phosphoric acid. Both
alcohols have cis and trans isomer in the measure, and both or one of either may exhibit an
Evelyn Effect. We carry out the experiment in a distillation apparatus so that the products (water
and alkene) will continuously distill from the reaction mixture as they are formed. Collecting the
two fraction fill with the reaction mixture to measure for the mass of alkene. The major point of
this experiment is to observe Zaitzev’s rules and the Evelyn effect.
Results:
Compound
Molecular
Weight or
concentration
14.2
2methylcyclohexanol
Phosphoric acid
98.0
Sodium
84.007
Bicarbonate
Drying Agent
XXXXX
Volume collected (ml)
Observed Boiling Point Temp
Mass od Dry Product
Density
Amounts used
(gm/ml)
Moles
XX
2.31 g
20.23
XX
XXX
.7ml
1.5ml/each
7.14
17.86
XXXX
2 drops
XXXXXX
First conical Vial
1ml
77 degrees
XXXX
Second conical Vial
1ml
85 degrees
XXXX
Chemical Name
Molecular weight (g/mol) Boiling point Density(g/mL)
4-methylcyclohexanol 114.2
173
0.914
Phosphoric Acid
98.0
143.4
1.70
Discussion: The boiling point of the first conical vial is 77 degrees, and the second conical vial
is 85 degrees. The boiling point seems to be far off from the desire boiling point but we are still
able to figure out the mechanism of the experiment. At the end of the of the experiment when 2
drops of anhydrous calcium chloride got added to the mixture a precipitation formed indicating
the presents of alkene. The precipitation turns into a brownish red color. This process was an
E1, because it showed first order kinetics as the breaking of the C-H bond occurred after the
rate limiting step. The primary reactant, 4-methylcyclohexanol is a secondary alcohol, and was
therefore required highly concentrated phosphoric acid coupled with high heat to react. As
opposed to tertiary alcohols which are react more easily under E1 conditions.
Conclusion: Even though our boiling point turn out not to be correct, we still got the result that
we wanted. The precipitation to prove that there is an alkene in the mixture at the end of the
experiment by performing a dehydration of 4-mrthylcyclohexanol to produce 4methylcyclohexene and water. We did the experiment to demonstrate Zaitzev’s rule and the
Evelyn effect. One suggestion to making this experiment better is to use the standard scale.