ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 1, p. 150. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © V.I. Porkhun, A.I. Rakhimov, 2010, published in Zhurnal Obshchei Khimii, 2010, Vol. 80, No. 1, p. 155.
LETTERS
TO THE EDITOR
Features of Reaction of p-Benzosemiquinone Radicals
with Iron Salts
V. I. Porkhun and A. I. Rakhimov
Volgograd State Technical University, pr. Lenina 28, Volgograd, 400131 Russia
e-mail: organic@vstu.ru
Received May 15, 2009
DOI: 10.1134/S1070363210010238
We have earlier examined some intracellular
mechanisms of photoreactions of semiquinone radicals
with various reagents by means of chemical nuclear
polarization [1–3].
At high concentrations of Mohr’s salt the kinetics
–
·
of Q disappearance adheres to the first order equation.
5
–1 –1
The value K = 4.3×10 m s was calculated from the
2
linear dependence between the effective constant and
Mohr’s salt concentration. The semiquinone radicals
·
In the present work we studied the reactions of
QН are generated in the neutral medium. They
para-benzosemiquinone radicals with Fe (SO ) and
2
4 3
disproportionate by themselves and also react with the
bi- and trivalent iron:
Mohr’s salts at the flash-photolysis. These reactions
were carried out in the aqueous-alcoholic solutions
+
H+
·
2+
3+
(
the water–propanol ratio 9:1 by volume) with neutral
QН + Fe
QН
2
+ Fe ,
(3)
(4)
and acidic (рН = 4.6) media. To avoid the influence of
the changing ionic strength we used solutions
containing sodium sulfate (0.1 М). To prevent the
occurrence of additional dark reactions of oxidation
and reduction at the use of Fe (SO ) we used p-
+
2H+
·
3+
Q + Fe2+.
QH + Fe
The reactions (3) and (4) are the pseudofirst order
–4
2
4 3
reactions at the salt concentrations 10 М and above
benzoquinone as a source of the semiquinone radicals,
and with Mohr’s salt, hydroquinone. The pulse
photoexcitation of hydroquinone or p-benzoquinone
using a UFS-2 (280–350 nm) filter in the presence of
the hydrogen donor (alcohol) leads to the formation of
p-semiquinone radicals. At рН = 4.6 the semiquinone
5
–1 –1
5
–1 –1
with the constants K = 10 m s and K = 7×10 m s .
3
4
The oxidation-reduction reactions between the iron
·
salts and radicals QН proceed through complexes
formation. The latter are destroyed by the reaction with
the hydrogen ions.
–
·
anion-radical Q forms. These radicals are terminated
not only as a result of the disproportionation, but they
react with the bivalent iron to give hydroquinone and
trivalent iron:
REFERENCES
1
2
.
.
Porkhun, V.I., Sviridov, B.D., and Rygalov, L.N., Zh.
Obshch. Khim., 1991, vol. 60, p. 1607.
Porkhun, V.I., Rykov, S.V., and Nikiforov, G.A., Zh.
Obshch. Khim., 1991, vol. 61, p. 244.
Porkhun, V.I. and Rakhimov, A.I., Izv. Vuzov Khim. i
Khim. Tekhn., 2005, vol. 48, no. 6, p. 58.
·
·
QН + QН → Q + QН
2
,
(1)
2)
2+ +2H+
3.
–
·
3+
Q + Fe
QН + Fe .
2
(
1
50
Porkhun
