Mechanistic studies on the bromate-1,4-cyclohexanedione-ferroin oscillatory system

Article abstract of DOI:10.1039/b109388f

A chemical mechanism including 22 reactions and 15 species is suggested for describing the dynamical behavior of the ferroin controlled BrO₃^--1,4-cyclohexanedione (CHD) batch oscillator. The model represents an extended version of the mechanism developed to explain the oscillations in the ferroin-free BrO₃^--CHD system. The kinetics and rate constants for some additional reactions such as ones between ferriin and CHD, BrCHD (2-bromo-1,4-cyclohexanedione) and H₂Q (1,4-hydroquinone) and between ferroin and bromate were determined and incorporated in the mechanism of the BrO₃^--CHD reaction. The model proposed here simulates satisfactorily the behavior of the BrO₃^--CHD-ferroin oscillator at increasing concentration of ferroin and at the condition of [ferroin] = 0 mol dm^-3.

Full text of DOI:10.1039/b109388f

View Article Online / Journal Homepage / Table of Contents for this issue
Mechanistic studies on the bromate–1,4-cyclohexanedione–ferroin
oscillatory system
´ ´ ´
¨
Istvan Szalai, Krisztina Kurin-Csorgei and Miklos Orban*
Department of Inorganic and Analytical Chemistry, L. Eo¨tvo¨s University, P.O. Box 32,
H-1518 Budapest 112, Hungary
Received 15th October 2001, Accepted 15th January 2002
First published as an Advance Article on the web 13th March 2002
A chemical mechanism including 22 reactions and 15 species is suggested for describing the dynamical behavior
of the ferroin controlled BrO3ꢀ–1,4-cyclohexanedione (CHD) batch oscillator. The model represents an
extended version of the mechanism developed to explain the oscillations in the ferroin-free BrO3ꢀ–CHD system.
The kinetics and rate constants for some additional reactions such as ones between ferriin and CHD, BrCHD
(2-bromo-1,4-cyclohexanedione) and H2Q (1,4-hydroquinone) and between ferroin and bromate were
determined and incorporated in the mechanism of the BrO3ꢀ–CHD reaction. The model proposed here
simulates satisfactorily the behavior of the BrO3ꢀ–CHD–ferroin oscillator at increasing concentration of ferroin
and at the condition of [ferroin] ¼ 0 mol dmꢀ3
.
Stock solution of ferriin was prepared from the stock solu-
tion of ferroin by oxidation with solid PbO2 followed by filtra-
tion. Because of its instability, the ferriin solution was stored in
the dark and used within 1 h.
1
Introduction
The bromate–1,4-cyclohexanedione(CHD)–indicator oscilla-
tory batch systems, where the indicator can be ferroin,
Ru(II)–bipyridine complex, erioglaucine, diphenylamine and
its derivatives, or some azo-dyestuffs, like p-ethoxychrysoidine
and chrysoidine, were shown to be well suited for generating
two-dimensional patterns.1,2 Due to their bubble-free, long-
lived and light sensitive character these systems are, in some
sense, superior to the classical bromate–malonic acid–catalyst
reaction (known as the BZ reaction) in studying reaction–diffu-
sion structures. Especially the bromate–CHD–ferroin system
has become the subject of many recent studies. Winfree et al.
The bromo derivative of CHD, abbreviated as BrCHD, was
prepared by mixing CHD with stoichiometric amount of bro-
mine. The reaction is regarded to be complete when the color
of bromine disappears. It takes a relatively long time, and
therefore the decomposition of BrCHD according to eqns.
(R9) and (R10) should be considered when the initial concen-
tration of BrCHD used in the ferriin–BrCHD reaction is calcu-
lated. For example, when 5 ꢂ 10ꢀ3 mol dmꢀ3 CHD and
5 ꢂ 10ꢀ3 mol dmꢀ3 bromine were mixed, 90 min was needed
for the consumption of bromine, and in a good approximation
3 ꢂ 10ꢀ3 mol dmꢀ3 BrCHD was calculated and used as initial
concentration in the experiments shown in Fig. 2.
The spectra for the kinetic measurements were taken on a
Milton Roy 3000 diode array spectrophotometer equipped
with quartz cells (path length 1 cm, volume 2 ml). The uncata-
lyzed oscillatory reaction occurring between bromate and 1,4-
cyclohexanedione was monitored by using a smooth Pt elec-
trode (Radelkis) and a Hg/Hg2SO4/K2SO4(sat.) reference
electrode (Radiometer). The analog signals were digitized by
a 12-bit AD converter (Labtech PCL-711 S) and processed
by a PC. The temperature was kept at 20.0(ꢃ0.1) ꢄC, and the
solutions in the cell were mixed by a magnetic stirrer.
The simulations were done with the program LSODE.8 The
parameter estimations were carried out by the MULTIMRQ
program, which uses the Marquardt method. Fitted para-
meters are given at 95% significance level.
preferred to use this reaction instead of BZ to visualize orga-
´
3
nizing centers in an excitable chemical medium. Komlosi et
al. studied the interaction of chemical waves and convection
in the bubble-free BrO3ꢀ–CHD–ferroin reaction.4 Various
bifurcation points and bistability were shown to exist during
the long lifetime of the bromate–CHD–ferroin batch reaction
and different propagation speeds for the reduction and oxida-
tion waves were measured in 1D capillary tube by Chen.5 One
of the most striking results obtained in the 1D and 2D bro-
mate–CHD–ferroin excitable systems were reported by Stein-
bock et al.6,7 who observed an anomalous dispersion relation
resulting in new dynamical phenomena, like stacking and mer-
ging of waves, which are not known for the BZ reaction with
malonic acid.
The major drawback in the application of the bromate–
CHD–ferroin system as model reaction for studying nonlinear
chemical behaviour is its poorly known chemistry. Here we
propose a chemical mechanism which hopefully helps to
describe and to model the temporal and spatial phenomena
observed in the title reaction.
3
Results
3.1 The bromate–CHD oscillator
2
Experimental
The reaction between acidic bromate and CHD was reported
to exhibit long-lasting (200–300 cycles) batch oscillations
which could be recorded in a galvanic cell arrangement using
Pt vs. reference electrodes. Adding ferroin redox indicator to
the reaction mixture, the oscillations can be visualized, i.e.
the color changes periodically between blue and red.1,9
H2SO4 (Chemolab 96%), 1,4-cyclohexanedione (Aldrich 98%),
KBr (Reanal p.a.), NaBrO3 (Fluka p.a.), 0.025 mol dmꢀ3 fer-
roin (prepared from a calculated amount of FeSO4ꢁ7H2O
(Reanal p.a.) and 1,10-phenanthroline (Aldrich 99%)) and
bidistilled water were used to prepare the working solutions.
DOI: 10.1039/b109388f
Phys. Chem. Chem. Phys., 2002, 4, 1271–1275
This journal is # The Owner Societies 2002
1271

View Article Online
A chemical mechanism for explaining the origin of the batch
oscillations in the ferroin-free system was proposed by
10,11
}
Szalai and Koro¨s.
In the mechanism the CHD is oxidized
by bromate ions to 1,4-benzoquinone (Q) through a stable
intermediate 1,4-hydroquinone (H2Q), which is produced con-
tinuously from 2-bromo-1,4-cyclohexanedione (BrCHD) via 2-
cyclohexene-1,4-dione (CHED) but oxidized in an autocataly-
ꢅ
tic fashion by BrO2 . A protonation equilibrium leading to
the enol form of CHD (CHDE) precedes the bromination.
Schematically the oxidation of CHD can be described as
follows:
Hþ
Hþ
Br2
ƒƒƒƒ!
CHD
CHDE
BrCHD
ƒƒƒƒ!
ꢅ
Hþ
BrO2
CHED
H Q
2
Q
ƒƒƒƒ!
ƒƒƒƒ!
Fig. 1 Oxidation of CHD by ferriin. Experimental conditioꢀn3s:
[H2SO4] ¼ 1.0 mol dmꢀ3
;
[ferriin] ¼ 7.0 ꢂ 10ꢀ4 mol dm
;
This sequence of reactions for the oxidation of CHD by bro-
mate may be applied in the presence of ferroin as well.
[CHD] ¼ 5.0 ꢂ 10ꢀ2 mol dmꢀ3 (M); [CHD] ¼ 2.5 ꢂ 10ꢀ2 mol dmꢀ3
(ꢆ); e600
¼ 1010 molꢀ1 dm3 cmꢀ1; e600
¼ 270 molꢀ1 dm3
ferriin
ferroin
cmꢀ1; T ¼ 20 ꢄC.
3.2 Effect of ferroin on the BrO3ꢀ–CHD oscillator
3.3 Oxidation of CHD and BrCHD by ferriin
Adding ferroin to the BrO3ꢀ–CHD oscillator strongly affects
its dynamical behaviour. For example:
(i) In a well stirred mixture, the amplitude increases and the
period decreases proportionally with increasing concentration
of ferroin. [At high value of ferroin concentration the system
approaches the oxidized (blue) state.]1
(ii) The added ferroin is able to reinitiate new oscillations
after the oscillations have terminated in a ferroin-free system.2
(iii) There is a pronounced dependence of the wave velocity
on the initial concentration of ferroin in the BrO3ꢀ–CHD sys-
tem, while the dynamics of the ferroin front is independent of
the catalyst concentration in the classical BZ with malonic
acid.7
The rate of the reaction between CHD or BrCHD and ferriin
was measured by following the decrease in the absorbance vs.
time at l ¼ 600 nm (characteristic of the absorption of ferriin).
The rate equation and the rate constant related to the CHD–
ferriin reaction were established from experiments carried out
at 10 combinations of the initial concentrations of CHD (0.01–
0.1 mol dmꢀ3), ferriin (10ꢀ5–10ꢀ4 mol dmꢀ3) and sulfuric acid
(1.0–2.5 mol dmꢀ3). Fig. 1 presents the experimentally
obtained absorbance vs. time curves at two initial concentra-
tions of CHD (symbols M and ꢆ) and it shows the fitted
curves (dotted lines) for determination of the rate constants.
The results are summarized in reaction (R16) (see section 3.6
and Tables 1 and 2):
In order to construct a chemically realistic model for the
BrO3ꢀ–CHD–ferroin oscillator we have to combine the
mechanism developed for the BrO3ꢀ–CHD system and the
reactions of ferriin and ferroin with initial reagents and some
intermediates. The oxidation of CHD, BrCHD and H2Q by
2FeðphenÞ33þ þ CHD ! 2FeðphenÞ32þ þ H2Q þ 2Hþ
k16
Â
3þÃ
v16
¼
FeðphenÞ3 ½CHDꢇ
k16 ¼ 0 14ðꢃ0 01Þsꢀ1
½Hþꢇ
ꢀ
ferriin and the reduction of BrO3 by ferroin were studied in
detail.
ðR16Þ
Table 1 Model for the bromate–CHD–ferroin oscillatory system. Symbols for the organic species: CHD ¼ 1,4-cyclohexanedione; CHDE ¼ enol
form of CHD; BrCHD ¼ 2-bromo-1,4-cyclohexanedione; CHED ¼ 2-cyclohexene-1,4-dione; H2Q ¼ 1,4-hydroquinone; Q ¼ 1,4-benzoquinone
Reactions
(R1)
(R2)
Brꢀ + HOBr + H+ Ð Br2 + H2O
Brꢀ + HBrO2 + H+ Ð 2HOBr
(R3)
Brꢀ + BrO3ꢀ + 2H+ Ð 2HOBr + HBrO2
HBrO2 + H+ Ð H2BrO2
+
(R4a)
(R4b)
(R5a)
(R5b)
(R6a)
(R6b)
(R7)
HBrO2 + H2BrO2 ! BrO3ꢀ + HOBr + H+
+
HBrO2 + BrO3ꢀ + H+ Ð Br2O4 + H2O
ꢅ
Br2O4 Ð 2BrO2
H2Q + 2BrO2ꢅ ! 2HBrO2 + Q
ꢅ
Fe(phen)32+ + BrO2 + H+ ! Fe(phen)33+ + HBrO2
CHD + H+ Ð CHDE + H+
(R8)
(R9)
CHDE + Br2 ! BrCHD + Brꢀ + H+
BrCHD + H+ ! CHED + Brꢀ + 2H+
CHED + H+ ! H2Q + H+
(R10)
(R11)
(R12)
(R13)
(R14)
(R15)
(R16)
(R17)
(R18)
(R19)
CHD + BrO3ꢀ + H+ ! H2Q + HBrO2 + H2O
CHD + HBrO2 ! H2Q + HOBr + H2O
H2Q + BrO3ꢀ + H+ ! Q + HBrO2 + H2O
H2Q + HOBr ! Q + Brꢀ + H+ + H2O
H2Q + Br2 ! Q + 2Brꢀ + 2H+
2Fe(phen)33+ + CHD ! 2Fe(phen)32+ + H2Q + 2H+
2Fe(phen)33+ + BrCHD ! Q + Brꢀ + 3H+ + 2Fe(phen)3
2Fe(phen)33+ + H2Q ! 2Fe(phen)32+ + Q + 2H+
2+
2Fe(phen)32+ + BrO3ꢀ + 3H+ ! 2Fe(phen)33+ + HBrO2 + H2O
1272
Phys. Chem. Chem. Phys., 2002, 4, 1271–1275

View Article Online
Table 2 Rate constants for the model of the bromate–CHD–ferroin oscillatory system. The values refer to a temperature of 20 ꢄC. [H2O] ¼ 55 mol
dmꢀ3 is included in the rate constant. We used hydrogen ion concentrations reported by Robertson and Dunford.19 This is a mass action kinetic
model with the exception of v6a ¼ k6a ꢂ [H2Q] ꢂ [BrO2ꢅ], v16 ¼ (k16/[H+]) ꢂ [Fe(phen)33+] ꢂ [CHD], v17 ¼ k17 ꢂ [Fe(phen)33+] ꢂ [BrCHD],
v18 ¼ k18 ꢂ [Fe(phen)33+] ꢂ [H2Q], v19 ¼ k19 ꢂ [Fe(phen)32+] ꢂ [BrO3ꢀ] ꢂ [H+]2.Values marked by an asterisk are slightly modified compared to
ref. 10.
kforward
kreverse
Ref.
(R1)
(R2)
8 ꢂ 109 molꢀ2 dm6 sꢀ1
2.5 ꢂ 106 molꢀ2 dm6 sꢀ1
1.2 molꢀ3 dm9 sꢀ1
80 sꢀ1
16
16
2 ꢂ 10ꢀ5 molꢀ1 dm3 sꢀ1
3.2 molꢀ2 dm6 sꢀ1
1 ꢂ 108 sꢀ1
(R3)
18
17
(R4a)
(R4b)
(R5a)
(R5b)
(R6a)
(R6b)
(R7)
2 ꢂ 106 molꢀ1 dm3 sꢀ1
1.7 ꢂ 105 molꢀ1 dm3 sꢀ1
48 molꢀ2 dm6 sꢀ1
17
18
3.2 ꢂ 103 sꢀ1
7.5 ꢂ 104 sꢀ1
1.4 ꢂ 109 molꢀ1 dm3 sꢀ1
18
10*
2 ꢂ 106 molꢀ1 dm3 sꢀ1
1 ꢂ 107 molꢀ1 dm3 sꢀ1
2.1 ꢂ 10ꢀ4 molꢀ1 dm3 sꢀ1
2.8 ꢂ 109 molꢀ1 dm3 sꢀ1
5 ꢂ 10ꢀ5 molꢀ1 dm3 sꢀ1
1.9 ꢂ 10ꢀ4 molꢀ1 dm3 sꢀ1
2 ꢂ 10ꢀ5 molꢀ2 dm6 sꢀ1
5 molꢀ2 dm6 sꢀ1
15
10
5.2 ꢂ 102 molꢀ1 dm3 sꢀ1
(R8)
(R9)
10
10
(R10)
(R11)
(R12)
(R13)
(R14)
(R15)
(R16)
(R17)
(R18)
(R19)
10
10*
this work
10
10
2 ꢂ 10ꢀ2 molꢀ2 dm6 sꢀ1
6 ꢂ 105 molꢀ1 dm3 sꢀ1
1 ꢂ 104 molꢀ1 dm3 sꢀ1
0.14 sꢀ1
0.051 molꢀ1 dm3 sꢀ1
6 ꢂ 103 molꢀ1 dm3 sꢀ1
2 ꢂ 10ꢀ2 molꢀ3 dm9 sꢀ1
10*
this work
this work
this work
this work
Mn3+ and Fe3+ studied by Wells and Kuritsyn12 and Baxen-
Fig. 2 shows the absorbance vs. time curve taken for the
reaction between BrCHD and ferriin (symbol M) and the
result of simulation (dotted line) for determining the rate of
process (R17):
dale et al..13 Thus:
2FeðphenÞ33þ þ H2Q ! 2FeðphenÞ32þ þ Q þ 2Hþ
Â
3þÃ
v18 ¼ k18 FeðphenÞ3 ½H2Qꢇ
2FeðphenÞ33þ þ BrCHD ! Q þ Brꢀ þ 3Hþ þ 2FeðphenÞ3
2þ
k18 ¼ 6 ꢂ 103 molꢀ1 dm3 sꢀ1
ðR18Þ
Â
3þÃ
v17 ¼ k17 FeðphenÞ3 ½BrCHDꢇ
The rate constant for reaction (R18) was treated as an adjus-
table parameter in the simulations, but its final value falls
within the range found for similar reactions discussed in refs.
11 and 12.
k17 ¼ 0 051ðꢃ0 001Þ molꢀ1 dm3 sꢀ1
ðR17Þ
3.4 Oxidation of H2Q by ferriin
3.5 Reduction of bromate by ferroin
The oxidation of H2Q, one of the key intermediates in the
BrO3ꢀ–CHD oscillator, by ferriin is too fast to be able to mea-
sure its rate with our experimental setup. The reaction is sup-
posed to take place according to the stoichiometry of reaction
(R18). This assumption is based on analogous reactions occur-
Keki et al.14 pointed out that the reactions between the ferroin
´
ꢅ
and oxybromine species (BrO3ꢀ, BrO2 , HBrO2) play an
important role in the dynamics of the ferroin-catalyzed BZ
reaction. In our model we considered only two reactions,
(R6b) and (R19), to be essential for simulation of the autoca-
talysis in the bromate–ferroin reaction:
ring between H2Q and one-electron oxidants, like Ce4+, Co3+
,
ꢅ
FeðphenÞ32þ þ BrO2 þ Hþ ! FeðphenÞ33þ þ HBrO2
Â
2þÃ
ꢅ
v6b ¼ k6b FeðphenÞ3 ½BrO2 ꢇ½Hþꢇ
k6b ¼ 1 ꢂ 107 molꢀ2 dm6 sꢀ1
ðR6bÞ
2FeðphenÞ32þ þ BrO3ꢀ þ 3Hþ
! 2FeðphenÞ33þ þ HBrO2 þ H2O
Â
2þÃ
2
v19 ¼ k19 FeðphenÞ3 ½BrO3ꢀꢇ½Hþꢇ
k19 ¼ 2 ꢂ 10ꢀ2 molꢀ3 dm9 sꢀ1
ðR19Þ
Fig. 3 shows the experimental and simulated autocatalytic
curves. For simulations k6b was taken from ref. 14 and k19
was derived from the simulated curve of Fig. 3.
3.6 The model for the BrO3ꢀ–CHD–ferroin oscillator
Fig. 2 Oxidation of BrCHD by ferriin. Experimental conditions:
[H2SO4] ¼ 1.0 mol dmꢀ3
;
[BrCHD] ¼ 3.0 ꢂ 10ꢀ3 mol dmꢀ3
;
;
The mechanistic model constructed for the BrO3ꢀ–CHD–fer-
roin oscillator is an extended version of the mechanism devel-
[ferriin] ¼ 9.0 ꢂ 10ꢀ4 mol dmꢀ3; e600
¼ 1010 molꢀ1 dm3 cmꢀ1
ferriin
¼ 270 molꢀ1 dm3 cmꢀ1; T ¼ 20 ꢄC.
ferroin
e600
Phys. Chem. Chem. Phys., 2002, 4, 1271–1275
1273

View Article Online
(R1)–(R3) are identical with those involved in the ferroin-free
version. The reaction between ferriin and Brꢀ is too slow to be
considered as a Brꢀ removal step in the mechanism. There are
two pathways for the autocatalytic production of HBrO2 .
ꢅ
BrO2 is reduced to HBrO2 concurrently by intermediate
H2Q (R6a) and ferroin (R6b). Regeneration of Brꢀ can occur
in several steps, but the major source of Brꢀ is BrCHD formed
in step (R8) and decomposed in (R9) and its oxidation by fer-
riin in step (R17).
The attractive feature of the mechanism is its applicability to
both BrO3ꢀ–CHD–ferroin and BrO3ꢀ–CHD oscillators. The
model includes all essential steps required to simulate the oscil-
lations observed in the ferroin-free BrO3ꢀ–CHD system but it
also works well in its more complex form when all important
reactions of ferroin and ferriin are incorporated. Using the
mechanism in Table 1 and rate constants in Table 2, the dyna-
mical behavior at [BrO3ꢀ] ¼ [CHD] ¼ 0.1 mol dmꢀ3 and
[H2SO4] ¼ 1.0 mol dmꢀ3 was calculated using a concentration
of ferroin from 0 to 8 ꢂ 10ꢀ5 mol dmꢀ3. The agreement
between the experimental and simulated behaviors is satisfac-
tory.
We can conclude that the mechanism proposed in Table 1
provides a qualitative description of the BrO3ꢀ–CHD–ferroin
oscillator. Further improvement of the model requires addi-
tional rate measurements, e.g. the dependence of some rate
constants on the acidity and temperature should be deter-
mined. In order to simulate the reported bistability, target pat-
terns, some wave phenomena, like stacking or merging, etc.,
we plan also to construct a reduced model containing no more
than three variables. For abstracting a reduced model, sensitiv-
ity analysis will be applied to identify the most important reac-
tions in the present mechanism.
Fig. 3 Autocatalytic reaction between bromate and ferroin. Experi-
mental conditions: [H2SO4] ¼ 1.0 mol dmꢀ3; [ferroin] ¼ 5ꢀ.0 ꢂ 10ꢀ5
mol dmꢀ3; [BrO3
]
¼ 5.0 ꢂ 10ꢀ2 mol dmꢀ3 (M); [BrO3
]
¼ 2.5
ꢀ
0
0
ꢂ 10ꢀ3 mol dmꢀ3 (ꢆ); T ¼ 20 ꢄC.
oped for the ferroin-free BrO3ꢀ–CHD oscillatory system.
Some sequences of reactions are common in both models, like
reactions (R1)–(R6a), which represent the known chemistry of
the oxybromine species, and steps (R7)–(R15) showing the oxi-
dation of CHD to 1,4-benzoquinone. For a better description
of the induction period, the rate constants of reactions (R6a),
(R11) and (R15) were slightly modified and a new step, the
reaction between CHD and HBrO2 , was added as reaction
(R12). The model was completed with all the important reac-
tions that take place between ferroin and bromo species or
between ferriin and CHD derivatives. The complete model
and corresponding rate constants are summarized in Tables
1 and 2.
4
Discussion
In the mechanism suggested for the BrO3ꢀ–CHD–ferroin oscil-
lator and presented in Table 1, the Brꢀ consumption processes
Acknowledgement
This work was financially supported by grants from the Hun-
garian Academy of Sciences (OTKA T 029791, OTKA F
034976) and by the Hungarian Ministry of Education (FKFP
0088/2001). We are grateful for the support of the ESF (Col-
laborative Research Programme: REACTOR: Nonlinear
Chemistry in Complex Reactors: Models and Experiments).
The program MULTIMRQ was provided by the Femtochem-
istry Group of the Department of Physical Chemistry, Eo¨tvo¨s
University.
References
´
K. Kurin-Cso¨rgei, A. M. Zhabotinsky, M. Orban and I. R.
1
2
3
4
Epstein, J. Phys. Chem., 1996, 100, 5393.
´
M. Orban, K. Kurin-Cso¨rgei, A. M. Zhabotinsky and I. R.
Epstein, J. Am. Chem. Soc., 1998, 120, 1146.
A. T. Winfree, S. Caudle, G. Chen, P. McGuire and Z. Szilagyi,
Chaos, 1996, 6, 617.
´
A. Komlosi, I. P. Nagy and G. Bazsa, J. Phys. Chem. A, 1998,
102, 9136.
5
6
G. Chen, Physica D, 2000, 120, 309.
N. Manz, S. C. Muller and O. Steinbock, J. Phys. Chem. A, 2000,
¨
104, 5895.
C. T. Hamik, N. Manz and O. Steinbock, J. Phys. Chem. A, 2001,
105, 6144.
7
8
A. C. Hindmarsh, Livermore Solver for Ordinary Differential
Equations, Technical Report No. UCID-3001, Lawrence Liver-
more Laboratory, Livermore, CA, 1972.
(a) V. J. Farage and D. Janjic, Chem. Phys. Lett., 1982, 102, 301;
(b) V. J. Farage and D. Janjic, Chem. Phys. Lett., 1982, 93, 621.
}
Fig. 4 Comparison of experimental [curves (a)–(c)] and simulated
[curves (d)–(f)] results. Experimental conditions: [CHD] ¼ 0.1 mol
dmꢀ3; [BrO3ꢀ] ¼ 0.1 mol dmꢀ3; (a) and (d) ferroin-free system; (b)
9
10 I. Szalai and E. Koro¨s, J. Phys. Chem. A, 1998, 102, 6892.
and (e) [ferroin] ¼ 1.0 ꢂ 10ꢀ5 mol dmꢀ3
8.0 ꢂ 10ꢀ5 mol dmꢀ3; T ¼ 20 ꢄC.
;
(c) and (f) [ferroin] ¼
11 I. Szalai, E. Koro¨s and L. Gyo¨rgyi, J. Phys. Chem. A, 1999, 103,
243.
}
1274
Phys. Chem. Chem. Phys., 2002, 4, 1271–1275

View Article Online
12 (a) C. F. Wells and L. V. Kuritsyn, J. Chem. Soc. A, 1969, 2575;
(b) C. F. Wells and L. V. Kuritsyn, J. Chem. Soc. A, 1969, 2930;
(c) C. F. Wells and L. V. Kuritsyn, J. Chem. Soc. A, 1970, 676.
13 J. H. Baxendale, H. R. Hardy and L. H. Sutcliffe, Trans. Faraday
Soc., 1951, 47, 963.
15 E. Mori, I. Schreiber and J. Ross, J. Phys. Chem., 1991, 95, 9395.
´
16 H. D. Fo¨rsterling, S. Muranyi and H. Schreiber, Z. Naturforsch.
A, 1989, 44, 555.
17 H. D. Fo¨rsterling and M. Varga, J. Phys. Chem., 1993, 97, 7932.
18 Y. Gao and H. D. Fo¨rsterling, J. Phys. Chem., 1995, 99, 8638.
19 E. B. Robertson and H. B. Dunford, J. Am. Chem. Soc., 1964, 86,
5080.
´
´
14 S. Keki, I. Magyar, M. T. Beck and V. Gaspar, J. Phys. Chem.,
´
1992, 96, 1725.
Phys. Chem. Chem. Phys., 2002, 4, 1271–1275
1275