Chemistry Reference
In-Depth Information
3.2.2 Bimolecular Initiating Systems
Decompositions of peroxides into initiating radicals are also possible through bimolecular reactions
involving electron transfer mechanisms. Such reactions are often called
redox
initiations and can be
illustrated as follows:
R-O-O-R
0
electron acceptor
!
A
electron donor
þ
A
þ
RO
þ
OR
0
where, A is the reducing agent and ROOR
0
is the peroxide.
The above can be illustrated on a decomposition of a persulfate (an inorganic peroxide) by the
ferrous ion:
O
O
O
O
+
+
O
S
O
O
S
O
Fe
+
O
S
O
O
S
O
Fe
O
O
O
O
electron acceptor
electron donor
initiating ion-radical
Side reactions are possible in the presence of sufficient quantities of reducing ions:
O
+
+
SO
4
Fe
O
S
O
Fe
O
A redox reaction can also take place between the peroxide and an electron acceptor:
+
+
+
R-O-O
Ce
R-O-O-H
Ce
H
Side reactions with an excess of the ceric ion can occur as well:
+
R-O-O
+
+
Ce
R
O
2
Ce
Another example is a redox reaction of
-butyl hydroperoxide with a cobaltous ion [
17
]:
The cobaltic ion that forms can act as an electron acceptor:
t
O
H
O
+
Co
Co
+
O
+
OH
The cobaltic ion that forms can act as an electron acceptor:
O
O
H
+
+
Co
+
Co
H
O
O
