KINETICS OF TECHNETIUM REACTIONS: XV. Tc(IV) OXIDATION
167
.
The mechanism of the thermal decomposition of
S2O8 ions [reaction (7)], suggested in [9], is re-
presented above.
TcOOH+ + HSO5
TcO +2 + SO + H O,
(29)
4
2
2
TcO +2 + S O2 + 2H O
TcO4 + 2H SO , (30)
2 4
2
8
2
As for the mechanism of the reaction between
2
with stage (29) being the rate-determining stage, and
Tc(IV) and S O8 ions along the noncatalytic path-
.
2
the other stages being fast. The SO radical ions are
4
way, we can suggest that, in accordance with the
experimental orders with respect to the reactants (first
reduced in stages (23) (26).
+
order) and H ions (zero order), the limiting stage of
It should be noted that slow stages (22) and (29)
involve reactions between ions of opposite charges,
which agrees with the negative electrolytic effect
observed.
this reaction pathway involves the charge transfer
between the reactants existing in their main ionic
forms TcO2+ and S O , i.e.,
2
2
8
.
4
TcO2+ + S O
2
TcO3+ + SO + SO .
2
(22)
REFERENCES
2
8
4
1
2
. Koltunov, V.S., Marchenko, V.I., Nikiforov, V.S.,
et al., At. Energ., 1986, vol. 60, no. 1, pp. 35 42.
. Gomonova, T.V. and Koltunov, V.S., Radiokhimiya,
Equation (22) is represented assuming that Tc(IV) in
solutions of noncomplexing acids exists as TcO2+
cation [12]. Peroxydisulfuric acid H S O is a strong
2
2 8
1
995, vol. 37, no. 5, pp. 415 417.
dibasic acid, and in solutions it exists in the form of
2
the S O8 ions. For Tc(V) in HClO solutions,
3. Koltunov, V.S., Taylor, R.J., Gomonova, T.V., and
Dennis, I.S., Radiochim. Acta, 1997, vol. 76, no. 1,
pp. 71 76.
2
4
3+
+
the species TcO , TcO , and TcO are postulated
13, 14].
3
2
[
4
. Koltunov, V.S. and Gomonova, T.V., in Int. Conf.
Technetium and Rhenium in Chemistry and Nuclear
Medicine (September 1989, Padova, Italy), New
York: Raven, 1990, pp. 35 37.
Similarly to [9, 10], fast stages of reduction of
.
4
radical ions SO formed in slow stage (22) can be
represented as follows:
.
5. Koltunov, V.S. and Gomonova, T.V., Radiokhimiya,
988, vol. 30, no. 6, pp. 756 760.
6. Jezowska-Trzebiatowska, B., Vaida, S., and Balu-
ka, M., Zh. Struct. Khim., 1967, vol. 8, no. 3, pp. 519
523.
SO + H O
HSO4 + OH,
(23)
(24)
(25)
4
2
1
TcO2+ + OH
H+ + OH
TcO3+ + S O2 + 3H O
TcO3+ + OH ,
H O,
2
7
8
9
. Shukla, S.K., Chromatographia, 1971, vol. 4, no. 8,
pp. 337 340.
. Koltunov, V.S. and Gomonova, T.V., Radiokhimiya,
1984, vol. 26, no. 3, pp. 322 327.
+
TcO + 2H SO + 2H . (26)
2
8
2
4
2
4
Taking into account that, for the autocatalytic path-
way, the reaction order with respect to H ions is
equal to 1, we can assume that in the limiting stage
of this reaction pathway Tc(IV) reacts in the form of
hydrolyzed ions TcOOH , whose concentration is
inversely proportional to the concentration of H ions.
The second reactant, Caro acid, reacts in the slow
stage of the reaction in the form of the HSO anion,
since Caro acid dissociates as a monobasic acid [15].
+
. Kolthoff, I.M. and Miller, I.K., J. Am. Chem. Soc.,
1
951, vol. 73, no. 1, pp. 3055 3059.
1
1
0. Ermakov, V.A., Rykov, A.G., Timofeev, G.A., et al.,
Radiokhimiya, 1971, vol. 13, no. 6, pp. 826 830.
1. Kryuchkov, S.V., Pikaev, A.K., Kuzina, A.F., and
Spitsyn, V.I., Dokl. Akad. Nauk SSSR, 1979, vol. 247,
no. 5, pp. 1187 1190.
+
+
5
1
2. Gorski, D. and Koch, H., J. Inorg. Nucl. Chem., 1969,
Thus, the mechanism of the reaction between
vol. 31, no. 1, pp. 3565 3571.
13. Jortscher, M., Koch, H., and Kupsch, H., Isotopen-
praxis, 1975, vol. 11, no. 11, pp. 369 412.
2
Tc(IV) and S O ions along the autocatalytic path-
2
8
way can be represented as follows:
1
4. Davison, A. and Jones, A.G., Int. J. Appl. Radiat.
Isot., 1982, vol. 33, pp. 875 881.
5. Remy, H., Lehrbuch der anorganischen Chemie, Leip-
zig: Geest und Portig, 1961. Translated under the title
Kurs neorganicheskoi khimii, Moscow: Mir, 1972,
vol. 1, pp. 685 686.
S2O 28 + H+
SO + HSO4,
.
(4)
(27)
(28)
4
1
.
HSO5 + H+,
SO + H O
4
2
TcO2+ + H O
TcOOH+ + H+,
2
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