Chemistry Reference
In-Depth Information
9.2.5.7 Epoxidation Reactions
These addition reactions of unsaturated polymers, like liquid polybutadiene, developed into
preparations of useful commercial materials [
88
-
94
]. Patent literature describes procedures that use
hydrogen peroxide in the presence of organic acids or their heavy metal salts. Reaction conditions
place a limitation on the molecular weights of the polymers, because it is easier to handle lower
viscosity solutions. A modification of the procedures is to use peracetic acid in place of hydrogen
peroxide [
95
-
97
]. The most efficient methods rely upon formations of organic peracids in situ with
cationic exchange resins acting as catalysts [
98
]. This can be illustrated as follows:
O
H
HOOH
+
CH
3
COOH
OOH
H
2
O
+
O
O
+
+
CH
3
COOH
OOH
The reaction is accompanied by formations of by-products:
R
O
O
O
+
R-COOH
+
H
2
O
OH
Polybutadienes that are high in 1,4-structures tend to epoxidize more readily and yield less viscous
products [
100
,
101
]. The epoxidation reaction can also be carried out on poly(1,4-cyclopentadiene) [
99
]:
O
O
OOH
Perbenzoic acid is an effective reagent in chloroform and in methylene chloride solutions at
0-20
C. The conversions are high, yielding brittle materials soluble in many solvents. The products
can be cast into transparent films [
99
].
Monoperphthalic and
-nitroperbenzoic acids are also efficient epoxidizing agents. They can,
however, cause cross-linking, as is the case in epoxidation of polycyclopentadiene [
99
]. The products
react like typical epoxy compounds [
99
]:
p
HO
O
O
HO
Cl
HO
HCl
