Chemistry Reference
In-Depth Information
O
R
HO
O
O
O
R'
R
O
O
O
O
Figure 2.1 The alkene, epoxide, cyclic carbonate, (left side), mid-chain ester, and
acetal (right side) structures discussed in this chapter. The acetal struc-
ture is also sometimes referred to as a ''ketal''.
The epoxidation of soybean oil involves the synthesis of a three-membered
ring which contains an oxygen group, called an ''oxirane''. There are several
methods for the synthesis of this material, which has been used as a
plasticizer in large volumes.
16,17
It also has properties which make it good
for use in lubricants
18-21
and as a starting material in fuel additives,
8,22
polymers,
23-25
hydrogels,
26,27
coatings,
28
resins,
29
and surfactants.
30
The
epoxide structure itself has long been known, although the best chemical
representation of the moiety was a past controversy.
31
Its primary reactivity
involves ring opening, which can be accomplished readily under acidic
conditions.
2.2.1 Overview of Methods
The epoxidation of soybean oil directly with oxygen over a metal catalyst
such as silver, as is done when converting ethene to ethylene oxide, would be
ideal. Unfortunately, the active allylic hydrogens in soybean oil are a prob-
lem for this process, and, along with the added steric hindrance at double
bonds, render this type of process ineffective. What has been done for the
last half century is to use hydrogen peroxide as the oxygen source, along with
some type of catalyst.
The use of carboxylic acids, such as formic or acetic acids,
32,33
has been
shown to be effective (Scheme 2.2). In this reaction, a peracid is formed
which then reacts with the substrate and regenerates the carboxylic acid. If
hydrogen peroxide is used, the reaction is bi-phasic, which makes is dicult
to study. However, it has proven effective, and a slight modification of this
procedure was the method of choice used for the generation of epoxides
studied here, as well as to get the intermediate materials for follow-up
syntheses.
34
