1
776
SHILOV, GOGOLEV
It was supposed that Fe(VIII) could be generated by
the disproportionation of Fe(VI) or by its oxidation by
Therefore Е[Fe(VIII)/Fe(VI)] ≥ 1 V. The potentials of
the couples Os(VIII)/Os(VII) and Ru(VIII)/Ru(VII)
are 0.2 and 0.85 V [1]. The extrapolation to the
Fe(VIII)/Fe(VII) couple also gives a value higher than
1 V. The potential of the couple Am(VII)/Am(VI) in
1 M NaOH is 1.05 V [9], but ozone oxidizes Am(VI)
at t < 0°С [9]. The absence of the Fe(VI) oxidation,
3–
Fe(CN)6 ions. A gas stream should carry along FeO4,
which should be absorbed by HCl solution with the
conversion Fe(VIII) → Fe(III). Iron(III) chloride
complexes have an absorption band in the nearest UV
region of the spectrum and are intensively colored. The
barbotage within 2 h has not led to discoloration of the
HCl solution. Then we added water in the alkaline Fe
2
–
though it goes without restructuring (FeO → FeO ),
4
4
points to the fact that the potential Fe(VIII)/Fe(VI) ≥
(
VI) solution and continued the oxygen barbotage.
1.05 V.
Such operation was repeated several times, KОН
concentration being varied from 11 up to 5 M. A
bubbler with the alkaline Fe(VI) solution was placed in
water at 60–90°С. No discoloration of the HCl solution
was observed.
The assertion of the authors [8] about Fe(VI) dis-
proportionation is erroneous. Though they determined
the oxidative equivalent of the compound distilled with
СCl , they have not tested this compound for the
4
presence of iron.
The possibility of detecting a volatile compound
has been checked up in the experiment with ruthenium.
We loaded 25 mg of metallic ruthenium in the form of
a fine powder in a bubbler with 4 M NaOH solution
and passed through an ozone-oxygen mixture. Within
EXPERIMENTAL
Concentrated solutions of KOH and NaOH (special-
purity grade) and Fe(NO ) , K Fe(CN) , K Fe(CN) ·
3
3
3
6
4
6
1
h an HCl solution in a bubbler connected sequen-
3Н О, H O, KNO , KF, K CO , К С О , КСН СОО,
2 2 2 2 3 2 2 4 3
tially turned yellow and then became brown. A black
thin coat was formed in connective tubes. Ruthenium
and NaFe(EDTA)·H O (Chemically-pure or analytical
2
grade) were used in the work. The study was carried
out using Shimadzu UV 3100 spectrophotometer
(Japan). Spectra of solutions were recorded in quartz
cells (l 1 cm).
was oxidized up to RuO , which was transferred by a
4
gas stream, partially reduced, and precipitated on the
walls in the form of RuO . Remaining RuO was
2
4
reduced by chloride ions, and ruthenium chloride
complexes colored the solution.
Concentrations of the initial alkali solutions were
determined by acidometry, and concentrations of the
other reagents, in weighted samples taken analytically.
The experiment with the assumed FeO distillation
4
was fulfilled with the use of ozone. It is necessary to
note that Fe(VI) is not formed if Fe(III) is mixed with
K Fe(CN) not in advance, but in an ozone current.
Experiments on assumed obtaining Fe(VIII). a.
In a tube with a ground-glass stopper 0.050 ml of
3
6
0
2
.1 M Fe(NO ) , 0.100 ml of 0.5 M K Fe(CN) , and
.85 ml of 11.8 M KOH solutions, and 3 ml of CCl4
Therefore we used a solution with ready Fe(VI) and an
excess of K Fe(CN) in the experiment with the ozone
3 3
3 6
3
6
2
–
were placed. The mixture was shaken for 5 min. After
separating phases into layers the upper aqueous layer
was red-violet and the lower was colorless. The tube
was stored in darkness for 3 days. The higher layer
remained brightly colored and the lower, colorless.
The phases were mixed again. After separating phases
a sample of 1 ml was taken from the lower layer and
barbotage. It was supposed that FeO4 would be
oxidized either by ozone or by ozonide ions. However
within a 7 h ozonation a color of HCl solution in the
bubbler has not changed.
Let us consider how much the hopes to obtain
Fe(VIII) under the experimental conditions were
justified. Potentials of the couples with the maximal
oxidation state for an element in solution with 1 M
mixed with an aqueous solution of NH OH·HCl + o-
2
phenanthroline. It was expected that hydroxylamine
would reduce iron in the higher oxidation states up to
Fe(II), which gives a bright coloring with o-
phenanthroline.
–
OH concentration in the series Ti(IV)/Ti(III), V(V)/V(IV),
Cr(VI)/Cr(V), and Mn(VII)/Mn(VI) are –1.2, –0.8, 0.1,
and 0.56 V [1], i.e. they almost monotonically in-
crease. For the couple Fe(VIII)/Fe(VII) the potential
should be no less than 1 V. The potentials of the
previous couples are close to the potentials of couples
with the maximal oxidation states. For example, for the
couple Mn(VI)/Mn(V) the potential is 0.27 V [1].
b. 3 ml of an 11 M KOH solution containing 3.4
mmol of Fe(III) and 17 mmol of K Fe(CN) were
3
6
placed in a bubbler (no. 1) and oxygen was passed
through. A bubbler no. 2 was sequentially connected to
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 9 2009