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(EDTA) [255]. The oxidation of ethylenediamine (EN) was also studied to
understand the reaction mechanism of permanganate with APCs. The yields
and breakdown products of the reactions varied with pH and the concentra-
tion of permanganate. For example, the molar yield of CO
2
for the oxidation
of EDTA decreased with an increase in pH, and the highest doses of perman-
ganate were 5.0, 3.4, and 1.9 for pH 12, 13, and 14, respectively.
In the oxidation of EN by Mn(VII), mineralization of the molecules to CO
2
was more significant at pH 12 than at pH 14. High yields of ammonia and
oxalate at all pH values were obtained. Glyoxal was also detected in small
amounts. This is an indication that EN was deaminated by Mn(VII), and pos-
sible pathways A and B of the mechanism are expressed in Figure 6.21. The
mechanistic steps include sequential 1 − e
−
transfer steps, which resulted in the
formation of transient imines, their deprotonation, and hydrolysis. Glyoxal
formed as a transient product, possibly in a more oxidized state than oxalate
and CO
2
. The formation of oxalate rather than formate indicates the transfers
of both electrons were not occurring at the same sites of the EN molecule.
Following the transfer of the first electron, oxidation of the
N
′-nitrogen atom
by the second electron formed the transient,
N
,
N
′-diimine, which broke down
and released ammonia and glyoxal, a precursor of oxalate (pathway B in Fig.
6.21). The degradation of NTA by permanganate also formed CO
2
, ammonia,
and oxalate with an additional contribution of iminodiacetate (IDA). This
suggests
N
-dealkylation pathways in the reaction between NTA and Mn(VII).
The oxidation of EDTA by Mn(VII) provided a complicated outcome as
the dealkylayion reaction products of EDTA and ethylediaminediacetate
+
NH
2
-H
+
B
+
NH
2
NH
2
NH
2
NH
2
O
+H
2
O
-NH
3
H
2
N
-e
-e
H
H
H
H
2
N
H
2
N
H
2
N
H
2
N
A
-e
-e
H
O
NH
2
O
H
O
H
H
H
2
N
H
2
N
•+
-NH
3
+H
2
O
-H
+
-H
+
O
NH
2
H
NH
2
O
H
H
H
+H
2
O
-e
-e
H
H
H
-NH
3
H
H
2
N
H
2
N
H
2
N
H
2
N
+
O
oxidati
on
e
nolizati
on
oxidation
O
oxidatio
n
H
H
O
H
O
-
H
CO
2
O
-
O
-
H
O
-
O
O
O
-
O
O
oxidation
O
-
O
Figure 6.21.
Oxidation of EN by Mn(VII) in alkaline solutions (adapted from Chang
et al. [255] with the permission of the American Chemical Society).
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