Chemistry Reference
In-Depth Information
are found throughout this chapter. However, the main driver in much
of this research is the principle that the raw material feedstock in a
process should be renewable. That thread is common throughout the
use of plant oils in industry, with even the USA federal government in
agreement.
5
To this end, there are many good reviews available, some of
them specifically on the uses of natural oils.
6,7
That material will not be
reproduced here, where instead you, friendly reader, can move on to a
tale of the twisting of soybean oil into carbonates, acetals, and branched-
chain esters.
2.2 Epoxidation of Soybean Oil or Alkyl Esters of
Soybean Oil
In its natural state, refined, bleached, and deodorized soybean oil consists of
a glycerol structure with three fatty chains. A common reaction, used in bio-
diesel synthesis (Scheme 2.1), involves the esterification of the three chains
of the glycerol structure producing a family of alkyl esters. Many of these
chains, both in triacylglycerols and the alkyl esters, will contain one or more
double bonds that are important for two reasons. First, it is usually these
unsaturated groups which chemists can utilize in the modification of
these fatty chains. Second, due to a variety of effects, the locations adjacent
to the double bonds are highly susceptible to different reactions such as
hydrogen abstraction and oxidation.
Whether on the full triacylglycerol, or on the ester, these double bonds
will be utilized in this chapter to form epoxides, then further to form cyclic
carbonates, esters, and acetals (Figure 2.1). This is not a comprehensive
list of possible modifications; elsewhere ethers,
8,9
amines,
10,11
azides,
12
thiols,
13,14
hydroxides,
15
and many others have been described.
A
B
B
A
O
O
R
ROH
Acid
or
base
O
O
O
O
R
O
O
O
O
R
O
O
+
Glycerol
Scheme 2.1 A soybean oil structure and its esterification to alkyl esters. A series of
non-systematic names describe the fatty chains which naturally occur
in the cis-configuration. For example, the methyl esters would be called
''methyl stearate'', ''methyl oleate'', ''methyl linoleate'', and ''methyl
linolenate'' for 18-carbon fatty chains with 0, 1, 2, and 3 double bonds,
respectively. The allylic (A) and bis-allylic (B) positions, which are
especially susceptible to oxidative reactions, are shown on the linoleic
chain.
