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In-Depth Information
Scheme 2
RS O H formation
(
)
HFeO RSH OH
−
+
+
2
−
→
HFeO
3
−
+
RS O H H O
(
)
+
(6.115a)
4
4
2
3
−
−
(6.115b)
HFeO
+
RSH H O Fe OH
+
2
→
(
)
+
RS O H OH
(
)
+
3
2
2
RS O H formation
(
)
2
−
−
3
−
(6.116a)
HFeO RS O H OH
+
(
)
+
2
→
HFeO
+
RS O H H O
(
)
+
4
2
2
3
−
−
.
(6.116b)
HFeO
+
RS O H H O Fe OH
(
)
+
2
→
(
)
+
RS O H OH
(
)
+
3
2
2
2
Again, conclusions drawn from the correlations agreed with the experimen-
tally determined stoichiometries and products of the reactions, for example,
the oxidation of Cys and Met by ferrate(VI), which formed Fe(II) and Fe(III)
as the reduced products of ferrate(VI), respectively (Eqs. 6.117 and 6.118):
HFeO HSCH CH NH COO H O
Fe OH
−
+
(
+
)
−
+
4
2
3
2
→
(
)
+
HS O CH CH NH COO
(
)
(
+
)
−
+
OH
−
(6.117)
2
2
2
3
−
−
2
HFeO
+
3
RSR
′ +
3
H O
→
2
Fe OH
(
)
+
3
RS O R
(
)
′ +
2
OH
.
(6.118)
4
2
3
The oxidation of Met thus occurs through Scheme 1, while Scheme 2 is
applied to the oxidation of Cys by ferrate(VI).
Besides inorganic and sulfur-containing compounds, ferrate(VI) also effi-
ciently oxidizes emerging contaminants such as estrogens and pharmaceuticals
[309, 370-373]. The next section describes the reactivity of ferrate(VI) with
nitrogen-containing compounds including amino acids.
6.3.2.1 Amines.
The reactions of ferrate(VI) with substrates are mostly
second order, that is, first order in the total ferrate(VI) concentration
([Fe(VI)]
tot
) and first order in the total concentration of the substrate ([S]
tot
):
−
d Fe VI /dt
[
(
)]
=
k
[
Fe VI
(
)]
[ ]
S
,
(6.119)
app
tot
tot
where
k
app
represents the apparent second-order rate constants. The values
of
k
app
have been determined by several substrates including sulfur- and nitrogen-
containing compounds and emerging contaminants in the environment [18, 18,
371]. Figure 6.33 shows the structure of organic amine substrates studied by
ferrate(VI). The reactivity of substrates with ferrate(VI) at pH 7.0 is given in
Table 6.6. Determination of
k
app
ranged from 9.5 × 10
−1
/M/s to 3.3 × 10
2
/M/s for
the aliphatic amines. Dimethyldithiocarbamate (DMDC), a sulfur-containing
substrate, had the highest reactivity (Table 6.6). The aromatic amine substrates
showed relatively higher reactivity than most of the aliphatic amines
(
k
app
= 2.8 × 10
2
- 1.6 × 10
5
). The fate of carbon and nitrogen in the oxidation
of monomethylamine (MMA), dimethylamine (DMA), and trimethylamine
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