The concentration effect of nonionic surfactants (Triton X‐100, Brij 30, Brij 58, Tween 20, and Tween 80) and tert‐butanol was investigated on the Briggs–Rauscher oscillatory reaction in a stirred batch reactor at 25 ± 0.1°C in both the absence and presence of nonionic surfactant and tert‐butanol as well. The addition of Triton X‐100, Brij 58, and Tween 20 influenced the oscillatory parameters in a similar fashion: a decrease of the induction period until its disappearance, an increase of the oscillation period, an increase of the oscillation amplitude, an increase of the duration of the oscillation, and a gradual increase of the oscillation numbers. The addition of Brij 30 has no significant effect on the oscillation parameters of the Briggs‐Rauscher oscillatory reaction. The effect of tert‐butanol on the Briggs–Rauscher oscillatory reaction is very similar to the effect of Brij 58; however, we were unable to observe the disappearance of the induction period on the studied concentration range. The addition of Tween 80 to the reaction mixture has a similar effect as the addition of Triton X‐100, Brij 58, or Tween 20, except for the induction period, which in the case of Tween 80, it becomes larger. The observed effects are explained in terms of micellar catalysis or inhibition, that is, in a different extent of individual reactants of solubilization.
The
bromate–aniline oscillatory reaction was discovered
4 decades ago, but neither the detailed mechanism nor the key products
or intermediates of the reaction were described. We report herein
a detailed study of this reaction, which yielded new insights. We
found that oscillatory oxidation of aniline by acidic bromate proceeds,
to a significant extent, via a novel reaction pathway with the periodic
release of carbon dioxide. Several products were isolated, and their
structures, not described so far, were justified on the basis of MS
and NMR. One of the main products of the reaction associated with
the CO2 release route can be assigned to 2,2-dibromo-5-(phenylimino)cyclopent-3-en-1-one.
A number of known compounds produced in the studied reaction, including
unexpected brominated 1-phenylpyrroles and 1-phenylmaleimides, were
identified by comparison with standards. A mechanism is suggested
to explain the appearance of the detected compounds, based on coupling
of the anilino radical with the produced 1,4-benzoquinone. We assume
that the radical adduct reacts with bromine to form a cyclopropanone
intermediate that undergoes a Favorskii-type rearrangement. Further
oxidation and bromination steps including decarboxylation lead to
the found brominated phenyliminocyclopentenones. The detected derivatives
of 1-phenylpyrrole could be produced by a one-electron oxidation of
a proposed intermediate 2-phenylamino-5-bromocyclopenta-1,3-dien-1-ol
followed by β-scission with the abstraction of carbon monoxide.
Such a mechanism is known from the combustion chemistry of cyclopentadiene.
The proposed mechanism of this reaction provides a framework for understanding
the observed oscillatory kinetics.
The concentration effect of ionic surfactants (sodium dodecyl sulphate, N‐hexadecyl‐N,N,N‐trimethylammonium hydrogensulphate, 3‐(N,N‐dimethyl‐N‐myristylammonio)propanesulfonate) and tetrabutylammonium hydrogensulphate was investigated on the Briggs‐Rauscher (BR) oscillatory reaction in a stirred batch reactor at 25 ± 0.1 °C in both the absence and presence of an ionic surfactant. In the presence of the anionic surfactant, the induction period (IP) and the oscillation period (OP) increase markedly, and the amplitude of oscillations decreases with increasing concentration of sodium dodecyl sulphate. These effects have been observed when the concentration of surfactant is much higher than its critical micelle concentration. Another effect on IP and OP has been observed in the presence of cationic and zwitterionic surfactants. A decrease in IP leads to its extinction at a certain concentration and at the same time, chemical oscillations divide into two series of chemical oscillations. TBAH does not have a major influence on IP and OP of the BR oscillatory reaction. The observed effects are explained in terms of micellar catalysis or inhibition in different extents of individual reactants solubilisation respectively.
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