Download Dehydrating Cyclohexanol

Dehydrating Cyclohexanol
Ziyue Zhu
2015/2/20
 Introduction
The objective of this lab was to prepare cyclohexene by dehydrating cyclohexanol.
And then identified the cyclohexene by using ammonium cerium nitrate test, bromine
test and refractive index.
The major reaction of this lab was:
(1)
This reaction is an elimination which means that during the reaction, H-X ( X can be
halogen or OH) will break the bonds with the molecule and form double bonds
(pi-bonds).
(2)
In this specific reaction, the H-X small molecules can be determined to be H-OH. The
reaction is also called dehydration reaction.
The presence of -OH group can be determined by ammonium cerium nitrate,
(NH4)2Ce(NO3)6. This compounds can react with alcohol and form red complex.
(NH4)2Ce(NO3)6 (yellow) + R-OH (colorless) → [alcohol + reagent] (Red)
(3)
The presence of a C=C (carbon-carbon double bond) can be determined by bromine.
Br2 can react with carbon-carbon double bonds and form some colorless product
which is different from the red-brown color of Br2.
(4)
The first step of the experiment was to set up the distillation apparatus. Then,
cyclohexanol, sulfuric acid and phosphoric acid was added into the flask and heated
up the mixture with a sand bath so that the reaction(1) began. After collecting all the
distillate in a container, the liquid was transferred into a centrifuge tube. The bottom
layer in the centrifuge tube was removed by the Pasteur pipet and labeled as ‘ Acid’.
Anhydrous calcium chloride was added into the centrifuge tube in order to dry the
water out of the top layer. After the top layer was totally dried, the top layer was
moved into a small vial and weighed. The second part of this lab was qualitative tests.
Firstly, put few drops of the products into a spot plate. Run the Br2 test in the first
three spots with Pasteur pipets so that the reaction (4) happened. The changing of
colors were recorded. Then, the ammonium cerium nitrate test was ran in the second
three spots and the changing of colors were recorded. The reaction (3). At last, the
refractive index of the product was measured and recorded.
 Data
Table 1: The results of Br2 and (NH4)2Ce(NO3)6 tests
Unknown
Cyclohexene
Br2
Orange
Orange
(NH4)2Ce(NO3)6
Faint Red
Not change
Table 2: The refractive index of the unknown product
RI at 22oC
RI at 20oC
Expected RI at
20oC
1.4469
1.4478
Table 3: The yield of the product
Actual yield
1.6457g
1.4460
Expected yield
2.43g
Figure 1: The IR data of the cyclohexene
Cyclohexanol
Not change
Red
Error percentage
0.1245%
Yield percentage
67.69%
 Discussion and Results
The results of the Br2 test was that the unknown product changed color which
meant that the cyclohexene was truly formed. The results of the (NH4)2Ce(NO3)6 was
that the unknown product did turned a little bit red which means there was still some
cyclohexanol remained in the product after distillation. The refractive index value of
product was 1.4478 at 20oC and the percentage of error was 0.1245%. This meant that
although cyclohexanol was still in the products, the percentage was quite small. The
reason why the (NH4)2Ce(NO3)6 still turned red was that this test was so sensitive that
even small contaminating amount of cyclohexanol could cause a slight color change.
This also explained why the result of the unknown product was faint red. The actual
yield of cyclohexene was 1.6457g and the percentage yield was 67.69%.
The most possible reason for the error of yield was the product was weighed, a little
of the product was used to run the qualitative tests. In addition, when pouring the top
layer in the centrifuge tube, some of the liquid stayed with the Anhydrous calcium
chloride in the centrifuge tube. For the error of the RI, the explanation was that the
limitation of the instrument: in this lab, the simple distillation was used. Besides,
differences between the boiling points of cyclohexene and cyclohexanol were not far
enough to let them be separated completely.
 Post-Lab Questions：
6. 1-methylcyclohexene
7. Faster. Because the carbon that -OH and -CH3 attached to was a tertiary carbon
which was the easiest to react.