Catalytic Transfer Hydrogenation of Cooking Oil, and
Fatty Acid Content of the Hydrogenated Cooking Oil
Reference: A. M. Schoffstall, B. A. Gaddis, and M. L. Druelinger, Microscale and Miniscale
Organic Laboratory Experiments, 2nd Edition, McGraw-Hill: New York, 2004, Experiment 6.1C,
page 241.
Introduction:
Oils are triesters derived from plants, and are usually liquids. They contain cis C=C’s. They are
not uniform in structure. They are biosynthesized formed from long-chain carboxylic acids
(“fatty acids”) and a triol, glycerol. An example structure is shown below.
HC
H2C
H2C
O C
O
(CH2)7
O C
O
(CH2)7
O C
O
(CH2)7
C
C
C
C (CH2)7CH3
C (CH2)7CH3
C (CH2)7CH3
H H
H H
HH
E x a m p l e o f a C o o k i n g O i l M o l e c u l e
Some of the C=C’s in oils are reduced to form semisolid products, which can be used in
margarines, for example. These reductions are usually carried out using hydrogen gas, and a
catalyst such as platinum or palladium. Since hydrogen gas is highly flammable, and the
glassware to do the reductions is highly specialized, hydrogenations are usually not done in
organic labs. There is another process, called catalytic transfer hydrogenation (CTH), which
avoids the use of hydrogen gas. Since addition of hydrogen to an alkene is reversible, CTH uses
an organic compound as the source of hydrogen. In our experiment, we will use cyclohexene as
the hydrogen source. Cyclohexene is a good source of hydrogen, since it can produce the stable
aromatic compound, benzene, as a byproduct when two equivalents of hydrogen are lost from it.
You can learn more about the stability of benzene in chapter 16 of your lecture text. The
palladium removes hydrogens from the cyclohexene, and transfers them to the olive oil. Since
the palladium is just transferring hydrogens from cyclohexene to the cooking oil, we only need a
small amount of it, so it is functioning as a catalyst. We are using an excess of cyclohexene to
drive the reaction toward products, since the reaction could be an equilibrium reaction. See the
reaction scheme below.
