Chemistry Reference
In-Depth Information
The alcohols and open-chain ethers have comparable basicities toward the coordinated acid ROH:
BF
3
. Ethylene oxide, on the other hand, is much less basic than the open-chain ethers [
6
]. In the
initiation step, therefore, the monomer reacts with the coordinated acid [
1
]:
BF
3
BF
3
O
+
O
O
O
R
H
R
H
BF
3
O
R
OH
During propagation three different reactions can occur [
2
]:
BF
3
BF
3
O
O
OH
R
1.
R
H
O
OH
BF
3
BF
3
H
O
O
O
2.
R
H
O
H
O
H
R
H
+
+
BF
3
O
O
O
3.
O
R
H
+
O
BF
3
O
RO
HO
OH
O
O
RO
O
O
OH
+
O
R
H
O
RO
BF
3
O
O
This reaction is also accompanied by formation of dioxane.
It
is actually a step of
depolymerization:
OH
ROBF
3
OH
ROBF
3
O
O
O
O
O
+
O
O
O
O
The ring-opening reaction, a nucleophilic substitution, usually takes place with an inversion of
configuration at the carbon atom that undergoes the nucleophilic attack [
8
,
9
,
11
]. This can be
illustrated as follows:
H
H
(S)
(S)
(S)
+
H
H
(R)
O
O
O
(S)
O
H
(S)
(S)
H
