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(EDDA) were not predominating. However, a relatively high concentration
of IDA occurred while EDDA was absent at pH 12-14 [255]. This suggests the
attack was on the ethylene group rather than on the acetate groups of EDTA.
The formation of IDA and other products, glycolate and oxalate, from the
oxidation of EDTA and EDDA by Mn(VII) could not be ruled out completely.
The postulated mechanism of the formation of IDA without the involvement
of EDTA is displayed in Figure 6.22. The mechanism involved two pathways,
A and B, which represent the electron transfer steps in the breakdown of
EDTA. In pathway A, the electron transfer occurred at the same nitrogen
atom while the formation of
N
,
N
′-diimine proceeded through a mechanism
given for the oxidation of EN (see Fig. 6.21). The reduction of Mn(VII)
resulted in Mn(VI), which was observed spectroscopically. The oxidized prod-
ucts were formed through oxygen transfer from the water molecules (Fig.
6.22).
O
O
•
•
O
N
H
O
O
O
N
H
-H
+
H
O
O
O
O
N
O
O
N
O
O
+•
•
O
O
A
-e
-e
O
O
O
O
•
•
O
O
N
O
O
N
+
O
O
N
H
-H
+
-e
O
O
N
H
O
O
O
O
O
O
H
O
O
N
O O
N
O O
N
O O
N
O
O
•
O
O
O
O
EDTA
B
-e
H
2
O
O
+
O
O
N
H
O
-
O
H
O
O
O
H
N
O
-
N
O O
•
O
O
-e
H
2
O
H
2
O
O
O
-
O
O
H
-2e -H
+
-O
HN
N
O
-
H
2
O
O
-O
O
IDA
Figure 6.22.
Suggested pathway of oxidation of EDTA by permanganate to result
in IDA at high pH via oxidative pathway on the ethylene group (adapted from Chang
et al. [255] with the permission of the American Chemical Society).
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