4-t-Butylcyclohexanol by the Borohydride Reduction
of 4-t-Butylcyclohexanone
Place 100 mg of 4-t-butylcyclohexanone and 1000 uL of methanol in a dry 3 mL reaction vial.
Swirl to dissolve the solid. Add to the flask, in one portion, 300 uL of the sodium borohydride
reducing solution. This solution has been prepared for you by dissolving 200 mg of sodium
methoxide and 400 mg of sodium borohydride in 10 mL of methanol. This solution must be
made fresh daily from fresh free-flowing reagents.
Sodium methoxide is a strong base. Its solutions are caustic and
can quickly cause severe tissue damage. Sodium borohydride is an
irritant and it readily decomposes in acids or hot water and gives off
heat and flammable hydrogen gas.
The reaction is exothermic and the mixture should boil briefly.
Fit the flask with an air
condenser and allow the reaction to go to completion by letting the mixture sit at room
temperature for 15 minutes. Remove the condenser and destroy any excess sodium borohydride
by cautiously adding dropwise about 1 mL of concentrated hydrochloric acid. The reaction is
exothermic and boil over can easily occur if the acid is initially added too quickly.
Extract the reaction mixture with three .5 mL portions of methylene chloride. The organic phase
is removed with a Pasteur pipet and dried by passing it down a Pasteur pipet drying column
charged with 250 mg of anhydrous magnesium sulfate. Collect the liquid in a tared 5 mL vial
containing a boiling stone. Rinse the drying column with .5 mL of methylene chloride. Set the
vial up in a hot sand bath along with an air sweep and carefully evaporate the methylene
chloride.
When the solvent has evaporated, remove the sand bath but continue the air sweep for several
additional minutes. Do not overheat the white solid product as it is somewhat volatile.
Purify 75% of your crude product by carrying out a vacuum sublimation.
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Calculate the % yield and obtain the melting point of your crude and sublimed product. Obtain
the IR spectrum of your sublimed product. Using the NMR of a typical student preparation that
follows this lab, calculate the cis/trans ratio found in the product. Turn in your sublimed sample
for marking in a properly labeled Durham tube.
Report Questions:
1.
Provide a mechanism for the reaction that you performed in this lab.
2.
In the NMR of 4-tert-butylcyclohexanol, the proton attached to the carbon atom directly
attached to the hydroxyl group (H*) in the trans isomer gives a triplet of triplets.
Conversely, the same proton in the cis isomer is split into a pentet. Explain.
H
H
H*
OH
H
*
OH
trans
3.
cis
Another useful reducing agent besides NaBH4 is LiAlH4.
Discuss the differences
between the two reducing reagents and any advantages one may have over the other.
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Checkout
Name _____________ Section ____ Room ______ Locker Number ____
During your scheduled lab period carry out, in the order listed, the following:
1.
Clean out your storage areas and line the drawer bottoms with fresh paper.
2.
Remove the labels from and clean your glassware.
3.
Equip your storage areas according to the equipment lists at the front of the manual. Leave
extra equipment on the carts. Obtain needed equipment from the carts. If the required
equipment is not on the carts, your instructor will issue you the equipment from the
storeroom. Before requesting equipment from the storeroom: check out all your areas,
make a master list of your needs and check the carts one more time to ascertain whether
any of the equipment you need has surfaced. You will be penalized if you are missing
equipment from your personal drawer.
4.
Have your instructor check your storage areas. Dirty, extra or missing equipment at this
stage will result in less than full marks being assigned for checkout. If your instructor
informs you that your areas do not check out, go back and check your work and correct
the deficiencies you encounter. Again have your instructor check your storage areas. After
the first instructor check, marks will be deducted at the rate of 1 mark per instructor check.
When your lockers check out, your instructor will initial this sheet and assign a grade.
5.
Obtain from your instructor and carry out a general cleanup task.
6.
Turn in your keys and obtain your refund. A full refund is $15. Your refund will be
decreased by $5 for missing keys and by $10 for missing safety glasses.
7.
Turn in this sheet.
INSTRUCTOR'S INITIAL _________ GRADE ASSIGNED ______/5
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