Experiment 20
SODIUM BOROHYDRIDE REDUCTION
OF A KETONE
OH
O
1. NaBH4
2. H3O+
Objectives:




To synthesize a tertiary alcohol from a
ketone using a sodium borohydride
reduction.
To purify the product using fractional
distillation.
To analyze the purity of the product using
GC.
To characterize the reactants and
products using NMR and IR spectroscopy.
Before coming to lab…

Review these techniques:

Fractional distillation

Vacuum filtration

GC Analysis
REDUCTION USING NaBH4


NaBH4 (sodium borohydride) is a versatile
and useful reducing agent in organic
chemistry.
A reducing agent causes a reaction (a
reduction) in which the product has more
bonds from carbon to hydrogen (or fewer
bond to oxygen)
OH
O
4 R C
4 R C
R' + 1 NaBH4
then H2O
H
R'
MECHANISM
CH3O
H3C
C
C
CH3
CH3
H
(from
NaBH4)
NaBH4 transfers a
hydride ion to the
carbonyl carbon.
NaBH4
H
CH3O
H3C
C
C
CH3H
CH3
CH3OH
O
H
H
(from
6M HCl)
The oxygen anion
eventually removes a
proton from water.
H 3C
C
C
CH3H
CH3
TODAY’S REACTION
O
OH
4 (CH3)3CCCH3 + NaBH4
4 (CH3)3CCCH3
then H2O
H
Pinacolone


Pinacolone is reduced using sodium borohydride.
Note that
ketone.
1
mole of NaBH4 will reduce
4
moles of
EXPERIMENTAL PROCEDURE
(Synthesis)







Add 3,3-dimethyl-2-butanone and
methanol to 100 mL beaker.
Place in ice water bath.
Add NaBH4 while stirring with glass
rod.
Continue to react at 0oC for 5min,
then 10 min more at RT.
Add 6M HCl dropwise.
Suction filter to remove separate
solid from liquid filtrate.
Transfer to 50 mL round bottom
flask.
100
mL
50
mL
EXPERIMENTAL PROCEDURE
(Purification and GC Analysis)





Set up fractional distillation
apparatus.
Apply heat and collect
distillate below 70oC in a small
flask.
Switch to 25 mL round bottom
flask and collect distillate
between 70-85oC.
Cool flask, reweigh.
Prepare GC sample.
to
voltage
regulator
water out
water in
heating
mantle
iron ring
Table 20.1
Theoretical yield (g)
 Calculated based on limiting
reactant
Actual yield (g)
Percent yield
Distillation Range (oC)
Product Appearance
(Actual yield/Theoretical yield)
X 100
 Give Ti-Tf of distillate
collected in 25 mL round bottom
flask
 Give physical state and color of
product
Table 20.2
Atom Economy (%)
Calculate based 3,3-dimethyl-2butanone and sodium borohydride ONLY!

Experimental
Atom Economy (%)
“Eproduct”
Cost per synthesis ($)
Cost per gram ($/g)
o Review Experiment 13 for calculations!
WASTE MANAGEMENT
o
Place the solid boric acid waste from the filtration
into the container labeled “SOLID WASTE”
located in the waste hood.
o
Place all liquid waste into the container labeled
“LIQUID WASTE”.
SAFETY CONCERNS



3,3-dimethyl-2-butanone, 3,3dimethyl-2-butanol, methanol and
sodium borohydride are all FLAMMABLE
materials.
Methanol and sodium borohydride are
TOXIC in large concentrations.
Hydrochloric acid is CORROSIVE.