Oxidation of Cumene in the Presence
of High Concentrations of Ascorbic Acid
O. V. Smirnova, I. V. Efimova, and I. A. Opeida
Litvinenko Institute of Physicoorganic Chemistry, National Academy of Sciences of Ukraine, Donetsk, Ukraine
Received March 23, 2010
Abstract—Initiated oxidation of cumene by oxygen in the presence of ascorbic acid was studied.
ORGANIC SYNTHESIS AND INDUSTRIAL
ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 3, pp. 427–430. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © O.V. Smirnova, I.V. Efimova, I.A. Opeida, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 3, pp. 435–438.
It has been shown previously that ascorbic acid
exhibits antioxidant properties in both aqueous and
organic phases and, irrespective of the nature of a
solvent, the duration of action of vitamin C is
determined by its concentration in the system [1, 2].
The concentration range of ascorbic acid in the
reaction mixture has been determined, at which its
efficiency as an inhibitor of the radical-chain oxidation
in the organic medium is the highest.
In this study, we continued analysis of the effect of
vitamin C at its increased concentrations on the
radical-chain oxidation process.
As a model system was chosen the liquid-phase
oxidation of cumene, initiated by 2,2-azo-di-(iso-
butyronitrile) (AIBN), whose mechanism and all
elementary stages are well understood .
Because ascorbic acid is poorly soluble in cumene,
we used dimethylsulfoxide (DMSO), in which vitamin
C is fully soluble in the chosen concentration range, as
a reaction medium that provided homophase
conditions of the process. In addition, the spectral
characteristics of ascorbic acid forms produced in
DMSO are known .
The kinetics of cumene oxidation in the presence of
ascorbic acid was monitored gas-volumetrically by
measuring the amount of oxygen absorbed in the
course of time by solutions containing cumene,
initiator (AIBN), and vitamin C. The experimental data
we obtained demonstrate that a break is observed in
kinetic curves of oxygen absorption by systems
containing ascorbic acid in the concentration range
M (Fig. 1), which enables
calculation of the induction period.
The induction period duration increases with the
ascorbic acid concentration, with the oxidation rate in
the initial interval of time in the initial stage (inhibition
stage) remains low (0.4×10
) and nearly
invariable. With the ascorbic acid concentration in the
system being oxidized increasing further, from 1×10
M, the oxidation rate noticeably grows in the
initial stage, whereas the increase in the induction
period being not so significant as that at lower
concentrations of vitamin C. The induction period
duration nonlinearly depends on the ascorbic acid
concentration in the range up to 2×10
M (Fig. 2).
Addition of ascorbic acid to a mixture being
oxidized in amounts exceeding 2×10
M changes the
shape of the curve describing the oxidation kinetics:
there is no break, the oxidation rate in the initial period
of time increases with the ascorbic acid concentration,
and the time dependence of the oxygen volume
absorbed by the system is linear during the entire
oxidation period under study (Fig. 3).
It is important to note that, at ascorbic acid
concentrations higher than 0.24 M, the oxidation rate
of the mixture exceeds that of cumene in the absence
of the inhibitor, i.e., the contribution from oxidation of
ascorbic acid itself is rather noticeable. An iodometric
titration of the oxidates demonstrated that a system
free of ascorbic acid, studied after 30 min of oxidation,
contains cumene hydroperoxide (main oxidation