1,4-Cyclohexanedione
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(
(
5
(
Figure 11. Redox potential change after the oscillation. (a) Measured
redox potential (the conditions are same as in Figure 9). (b,c) Simulated
curves.
(
20) Peintler, G.: ZiTa, A ComprehensiVe Program Package for Fitting
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(
21) Hindmarsh, A. C. LiVermore SolVer for Ordinary Differential
the reaction mixture contains H2Q, bromate ion, and CHD,
where the role of CHD is comparable to that of hexacyanof-
errate(II) ion in the Edblom et al. system. Similar systems have
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2
9
been reported also during the late seventies by R a´ bai et al.
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24) R15 is a HBr elimination from the BrCHD and it is rather unusual
They observed the appearance of three extrema in halide ion
concentration vs time curves when malonic acid was added to
(
-
2-
-
a variety of Landolt-type systems (e.g., IO3 + SO3 , IO3
+
that the rate of elimination increases with an increase in acid concentration.
This can be explained in terms of an enolization preequilibrium:
AsO33 , BrO3 + ascorbic acid). Later R a´ bai and Beck
-
-
30
-
2-
-
observed that in the IO3 + S2O3 + HSO3 reacting system
a few, high amplitude, damped oscillatory pH changes occurred
even under batch configuration in narrow concentration ranges
of the reactants.
A major difference between the previously reported Landolt-
type (oligo)oscillators and the CHD-bromate-acid system is
that in the latter one of the reducing agents (H2Q) is generated
during the reaction; in the former one, however, both reductants
should be present at the start of the reaction.
2
The enol form of BrCHD has a planar geometry with three sp carbon atoms
that generate a strained state, thus facilitating the splitting off of the HBr
unit.
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published.
(28) Edblom, E. C.; Orb a´ n, M.; Epstein, I. R. J. Am. Chem. Soc. 1986,
(
Our observation might open a novel way to search for batch
oscillators that exhibit a rather prolonged oscillatory phase due
-
5
to the small portions of reactants (on the order of 10 mol
-
3
dm ) consumed in a single oscillatory step. Attempts should
be made to try to find reactions, which produce such rather stable
intermediates, that can convert Landolt-type reactions to oscil-
latory ones.
(
108, 2826. Edblom, E. C.; Gy o¨ rgyi, L.; Orb a´ n, M.; Epstein, I. R. J. Am.
Chem. Soc. 1987, 109, 4876.
(
29) R a´ bai, Gy.; Bazsa, Gy.; Beck, M. J. Am. Chem. Soc. 1979, 101,
Acknowledgment. This work was supported by the Hungar-
ian Scientific Research Fund (OTKA Grants T 016680 and F
6
746.
(30) R a´ bai, Gy.; Beck, M. J. Phys. Chem. 1988, 92, 4831
0
17073) and by the MHB (Grant 44/96/I).
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(32) F o¨ rsterling, H.D.; Mur a´ nyi, S.; H. Schreiber Z. Naturforsch. 1989,
4
4a, 555.
References and Notes
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