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EXPERIMENT 5B

Reduction of Ketones Using a Metal Hydride Reagent: Cyclohexanol
and cis- and trans-4-tert-Butylcyclohexanol

02/25/2015
James Choi, 2204 Section 16

EXPERIMENT 5B

OBJECTIVE:

The objective of this experiment was to reduce a ketone carbonyl (cyclohexanone) to a
corresponding alcohol (cyclohexanol) by using sodium borohydride
...


EXPERIMENTAL PROCEDURE:

Experiment 5B was carried out using the procedure outlined in pages 132 - 137 in the 5 th edition
of Microscale Organic Laboratory with Multistep and Multiscale Syntheses by Mayo
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-

-

The first part of the reaction was performed on a 2x scale
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The remainder of the experiment was not performed on a 2x scale
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If the TLC indicated that the reaction
was incomplete, another portion of sodium borohydride was added to help the reaction finish
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0 mL of cold 3
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0 mL of 0
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The methylene chloride extracts were dried using the following procedure:
o The methylene chloride layers were transferred to a screw cap test tube
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o The sodium sulfate was rinsed with another portion of methylene chloride
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An NMR spectrum was not obtained
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Formula
Amount (mg)
Amount(μL)/ (mL)
mmoles
concentration
molar mass
density (g/mL)
lit
...
mp (ºC)

4-tbutylcyclohexanone
C10H18O
106

Sodium Borohydride
NaBH4
400 μL

0
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25 g/ mol

4-tbutylcyclohexanol
C10H20O
84
0
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83 g/ mol

156
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-

After the addition of the NaBH4 solution, bubbles were formed
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After the addition of the cold 3
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The final product, is a white solid with a frothy look
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CALCULATIONS:
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Theoretical Yield of alcohol products
106

TLC Data

×

×


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=

TLC Plate 1:4 Ethyl Acetate:Hexanes

Spot

Sample

1

Ketone
Standard

2
3

Co-spot

Crude
Reaction

Solvent Front
Distance (mm)

Rf value

25 mm

48 mm

Spot(s)
Distance

0
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46, 0
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46

Spot Color

EXPERIMENT 5B
-

Rf value of Ketone Standard

-

Yield of Crude Product

-

25
48

=
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% Yield of Crude Product
84
107

× 100 =


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2
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a
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b
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One spot should
be very intense, which correlates to the trans isomer of cyclohexanol
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The difference in intensities is
related to the amount of each isomer in the crude reaction mixture; a more intense
spot indicates a higher concentration and a less intense spot indicates a lower
concentration
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a
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Based on the FTIR spectrum obtained, the reaction was successful in reducing the
ketone to an alcohol
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This indicates that the product, cyclohexanol,
has been formed
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By
looking at these two regions and seeing the presence of an OH group and absence of a
ketone, the reaction has been successful
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The provided 1H NMR spectrum indicates the trans isomer of 4-tertbutylcyclohexanol
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EXPERIMENT 5B
c
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H1a – 3
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78 ppm
H6e– 2
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Between two coupled protons, the coupling constant (J) is determined by the dihedral
angle between the adjacent coupled protons
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i
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51 ppm
This proton exhibits a multiplicity of triplet of triplets
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The proton’s dihedral angle to the two adjacent
axial protons is 180° which has a J value of about 13 Hz
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ii
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78 ppm
This proton exhibits a multiplicity of xxxx
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The proton’s dihedral angle to the two adjacent axial protons is
180° which has a J value of about 13 Hz
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iii
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00 ppm
This proton exhibits a multiplicity of a quartet
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The proton’s dihedral angle to the two adjacent axial protons is
180° which has a J value of about 13 Hz
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EXPERIMENT 5B
4
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Screenshot of trans-4-tert-butylcyclohexanol

b
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Most important protons

H6e

H1a

H6a

WORKS CITED:

1
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W
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M
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C
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; John Wiley & Sons, Inc
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2
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3
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sigmaaldrich
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Chemical Data for 4-tbutylcyclohexanol, http://www
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com

EXPERIMENT 5B



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