Chemistry Reference
In-Depth Information
O
OH
O
O
+ MeOH
+
O
OH
O
O
OH
A) Lipase/40 °C
B) K
2
CO
3
/70 °C
C) CaO/70 °C
OH
d
n
9
r
3
n
g
|
0
GLYCEROL
CARBONATE
GLYCEROL
DMC
Scheme 6.19
DMC in the synthesis of glycerol carbonate.
O
OH
d
y
y
f
n
n
3
.
O
O
scCO
2
+
HO
O
OH
+
O
O
OH
OH
Zeolite,Amberlyst/T = 70 °C
OH
GLYCEROL
ETHYLENE
CARBONATE
GLYCEROL
CARBONATE
ETHYLENE
GLYCOL
Scheme 6.20
Glycerol carbonate synthesis in supercritical CO
2
.
as carbonating agents catalysed by solid bases such as metal oxides, carbonates,
Zn-derived Lewis acids ion-exchange resins, modified zeolites or biocatalysts
such as lipases.
The use of organic carbonates is also appealing, since the production of the
carbonate could generate valuable byproducts such as methanol, which can be
recovered and recycled back into biodiesel production. An example that illus-
trates the use of scCO
2
and organic carbonate as a reagent is the trans-
esterification of glycol carbonate with glycerol, occurring in the presence of ion
exchange resins and zeolites (Scheme 6.20). This work is of value from an
environmental perspective but the extent of the reaction and the molar excess of
reagents render it unviable from a commercial point of view.
The carbonation of glycerol with CO
2
and CO/H
2
is highly attractive from
an environmental stance. Researchers have described successful examples of
conversion to glycerol carbonate by using Sn catalyst (Scheme 6.21).
Glycerol carbonate is much more reactive than glycerol, primarily towards
nucleophilic additions, having four different nucleophilic centres (one of them
pro-chiral). This factor, despite being advantageous in other synthetic routes, is
the main drawback for its synthesis. Previous research has shown the
occurrence of substitution and elimination reactions depends on the conditions
employed and is important to bear this in mind when developing a synthesis
with these products.
196
6.6.12 Other Transformations
Oxidations are relevant because they can lead to a wide number of monomers
that can be used as substitutes for oil-derived chemicals, however, the markets
for such products, with the exception of DHA (dihydroxy acetone), are not
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