Chemistry Reference
In-Depth Information
HMnO NH CH COO
−
+
−
→
H MnO
2
−
+
NH CH CO
=
+
k
(6.77)
4
2
2
2
4
2
2
77
H MnO
2
−
+ →
H
+
MnO H O OH
+
+
−
k
(6.78)
2
4
2
2
78
NH CH H O NH HCHO
=
+
→
+
7
k
(6.79)
2
2
3
MnO NH CH COO
+
−
MnO -NH CH COO
−
K
(6.80)
2
2
2
2
2
2
80
MnO -NH CH COO H PO
−
+
−
MnO -H PO NH CH COO
−
+
−
K
(6.81)
2
2
2
2
4
2
2
4
2
2
81
MnO -NH CH COO MnO
−
+
−
→
MnO HMnO NH CH COO
+
−
+
•
−
k
.
(6.82)
2
2
2
4
2
4
2
82
In the noncatalytic reaction, a one-electron (1 − e
−
) transfer step was the
rate-determining step (Eq. 6.75), which leads to the formation of Mn(VI) and
the glycine radical. A radical formation was observed in the reaction mixture
of permanganate-L-serine [234, 247]. The products of the reaction (Eqs. 6.77
and 6.78) were in agreement with the experimental stoichiometric reaction
(Eq. 6.68).
In the autocatalytic pathway, adsorption of Gly onto MnO
2
colloidal par-
ticles occurred (Eq. 6.80). Competition of the
H PO
2
−
ion for the same site
displaced Gly from the MnO
2
colloidal surface (Eq. 6.81). It is a possibility
that the remaining glycine molecules reacted with Mn(VII) from the solution
surrounding the colloidal particles (Eq. 6.82). The Mn(VI) compound and a
glycine radical, formed in reaction (6.82), could then participate in the reac-
tions suggested for the noncatalytic pathways (Eqs. 6.74-6.79). The mechanism
shows the
H PO
2
4
−
species was used to stabilize the MnO
2
colloidal particles
rather than the
HPO
2−
species of the phosphate ion because the
H PO
4
−
species has a higher tendency to adsorb onto the colloidal MnO
2
surface than
that of the
HPO
−
species. The stabilization processes suggest that the forma-
tion of the hydrogen bond between the hydrogen atom of the
H PO
2
2
4
−
species
and the oxygen atom of MnO
2
occurred. Furthermore, the MnO
2
particle size
also participated in the stabilization process. The size of the colloidal MnO
2
surface increased with an increase in the molar ratio of either [MnO
2
]/[phos-
phate] or [MnO
2
/[ammonium ion]. using Equations (6.74)-(6.82) and assum-
ing Equation (6.82) was the rate-determining step, the values of
k
1
and
k
2
for
the autocatalytic reaction were expressed as
4
+
−
+
(6.83)
k K k
=
[
NH CH COO /
]
(
K
+
[
H
])
1
74
75
3
2
T
74
+
−
+
−
k
=
K K k
[
NH CH COO /
]
{
K K
[
NH CH COO
]
2
74
80
82
3
2
T
74
80
3
2
T
(6.84)
+
(
K
+
[
H
+
]
)(
1
+
K K
H PO
[
−
]},
74
80
81
2
4
+ − + − −
= +
represents the
total concentration of Gly (in large excess with respect to permanganate).
Overall, the differential method (Eq. 6.73) has some advantages over the
where
[
NH CH CO
]
[
NH CH CO
]
[
NH CH CO
]
3
2
2
T
3
2
2
2
2
2
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