ISSN 0036-0244, Russian Journal of Physical Chemistry, 2006, Vol. 80, No. 3, pp. 353–356. © Pleiades Publishing, Inc., 2006.
Original Russian Text © V.P. Kheidorov, Yu.A. Ershov, O.A. Zyabkina, 2006, published in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 3, pp. 432–435.
CHEMICAL KINETICS
AND CATALYSIS
The Kinetics of Pentoxyl Oxidation by Hypochlorite Ions
V. P. Kheidorov1, Yu. A. Ershov2, and O. A. Zyabkina1
1 Vitebsk State Medical University, Vitebsk, Belarus
2 Sechenov Medical Academy, Moscow, Russia
E-mail: heidorov@mail.ru
Received April 19, 2005
Abstract—The kinetics of pentoxyl (I) oxidation in aqueous media under the action of hypochlorite ions was
studied at pH 8.8 and 273–298 K. The order of the reaction with respect to both participants was found to be
one. The temperature dependence of the reaction rate obeyed the Arrhenius law. The reaction activation param-
eters were found to be E‡ = 11.08 kJ/mol, ∆H≠ = 8.73 kJ/mol, ∆S≠ = –200.70 J/(mol K), and ∆G≠ = 66.88 kJ/mol.
Reaction stoichiometry was studied, the chemical characteristics of the process considered, and a mechanism
of the oxidative transformation of I under the action of OCl– suggested.
DOI: 10.1134/S0036024406030083
INTRODUCTION
EXPERIMENTAL
Solutions were prepared from doubly distilled
water. Sodium hypochlorite containing hypochlorite
ions OCl– was synthesized by bubbling chlorine
through an aqueous solution of sodium hydroxide. The
solutions were stored in dark-glass vessels, and the
activity of OCl– was periodically checked by iodome-
try. Under the conditions specified, it remained con-
stant for a long time. Solutions of I were prepared by
dissolving samples in water. The reagents used were
either of ch.d.a. (pure for analysis) grade or subjected
to the required purification.
Experiments were conducted while maintaining
reagent solutions at a constant temperature with an
accuracy of 0.1 K. The kinetics was monitored photo-
metrically by the accumulation of the product of the
transformation of I. The concentration of the initial
solution of I was 0.001 M. Reaction medium pH was
set at 8.8 using a hydrogen-phosphate buffer. The reac-
tion was performed with OCl– taken in excess. Excess
phenol solution was then added to instantaneously stop
the process. The colored product formed was subjected
to photometry at λ = 630 nm. Reaction stoichiometry
was determined from the composition of the reaction
medium containing various initial concentrations of I
and OCl– 24 h after initiating the reaction at ≈20°C.
This work continues studies of the chemical trans-
formations of biologically active substances under the
action of oxidative reagents containing the high-reac-
tivity hypochlorite group [1–8]. Pyrimidine base deriv-
atives, including pentoxyl (6-methyl-5-oxymethylu-
racil) (I), are pharmacologically important substances.
They find wide use in medicine. The problems of chem-
ical and biochemical transformations of these com-
pounds [9, 10] and their interactions with various
reagents are still a subject of discussion in the literature
[11, 12].
The kinetics of oxidative transformations of I is of
interest for science and practical applications in rela-
tion to metabolism problems and the development of
methods for controlling the content of I. The oxidation
of its structural analogues in various objects, including
biological materials, is also of interest.
The oxidation of methyluracil with ammonium per-
sulfate in alkaline media according to the Elbs reaction
[13–16], sodium hypochlorite [8], and potassium
permanganate in acetic acid with the formation of
5-hydroxy-6-methyluracil [17] are well-known reac-
tions. The kinetics and mechanism of the oxidative
transformations of pyrimidine base derivatives have
scarcely been studied.
RESULTS AND DISCUSSION
Data processing was performed using the results of
kinetic measurements. The oxidation of I under the
action of OCl– occurred at a high rate under our exper-
imental conditions and was complete in ≈2 min (0°ë).
The concentration of I rapidly decreased, and reaction
product concentrations increased. The kinetic curves of
substrate consumption and product accumulation can
be divided into two regions with different rate laws
In this work, we studied the kinetics and mechanism
of the interaction of I with hypochlorite ions. The
results obtained in this work will be used as a basis and
model for further studies of kinetic patterns of reactions
involving structural analogues of I and for optimizing
the corresponding analytic reactions and methods.
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