Effect of initial reagent concentrations on the oscillatory behavior of the BZ reaction in a batch reactor

Article abstract of DOI:10.1002/kin.20442

A detailed investigation on resorcinol as the Belousov-Zhabotinsky (BZ) oscillator in manganese(II) ion catalyzed reaction system with inorganic bromate (oxidant) and acetone (cosubstrate) was carried out in aqueous sulfuric acid medium (1.3 M). The aforesaid reagents were mixed with various concentrations to evolve the effective concentrations at which the reaction system exhibited better oscillations. The various oscillatory parameters such as time period (t _p ), induction period (t _in), frequency (v), amplitude (A), and number of oscillations (n) were derived, and the dependence of concentration of the reacting species on these oscillatory parameters was interpreted on the basis of the Field-Koros-Noyes mechanism. 2009 Wiley Periodicals, Inc.

Full text of DOI:10.1002/kin.20442

Effect of Initial Reagent
Concentrations on the
Oscillatory Behavior of the
BZ Reaction in a Batch
Reactor
NADEEM B. GANAIE, G. M. PEERZADA
Post Graduate Department of Chemistry, University of Kashmir, Srinagar 190 006, Jammu & Kashmir, India
Received 5 January 2009; revised 9 June 2009; accepted 10 June 2009
DOI 10.1002/kin.20442
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A detailed investigation on resorcinol as the Belousov–Zhabotinsky (BZ) oscillator
in manganese(II) ion catalyzed reaction system with inorganic bromate (oxidant) and acetone
(cosubstrate) was carried out in aqueous sulfuric acid medium (1.3 M). The aforesaid reagents
were mixed with various concentrations to evolve the effective concentrations at which the
reaction system exhibited better oscillations. The various oscillatory parameters such as time
period (t p ), induction period (tin), frequency (v), amplitude (A), and number of oscillations (n)
were derived, and the dependence of concentration of the reacting species on these oscillatory
parameters was interpreted on the basis of the Field–Koros–Noyes mechanism. ꢀC 2009 Wiley
Periodicals, Inc. Int J Chem Kinet 41: 650–657, 2009
INTRODUCTION
under acidic conditions. Metal ions, such as cerium,
iron, and manganese, are widely used as catalysts
[7–13]. The mechanism of such reactions is explained
in detail by Field, Koros, and Noyes (FKN) [3–5]. In
the present work, resorcinol is chosen as BZ oscillator
to study its oscillatory behavior in the reaction system,
comprising inorganic bromate as the oxidant and
manganese(II) ion as catalyst in 1.3 M sulfuric acid
medium. The compound has sufficient solubility in
aqueous acid medium and exhibits dynamic behavior
over a wide range of concentrations. Moreover, owing
to the presence of two phenolic OH groups, resorcinol
has some similarity with biomolecules and, therefore,
the present study can serve as a prototype example
in understanding the behaviors possible in biology
such as signal transmission and membrane transport
in living organisms. The oscillations were also studied
The Belousov–Zhabotinsky (BZ) reaction [1,2]
has been a research subject of nonlinear dynamics
including chemical, physical, and biological interest.
The BZ reaction shows temporal and spatio-temporal
structures such as redox oscillation of the catalyst and
travelling waves [1–6]. The overall process of the BZ
reaction is the oxidation of an organic substrate such
as citric acid or malonic acid by an oxidizing agent
(bromate) in the presence of metal ions as catalyst
Correspondence to: Nadeem B. Ganaie; e-mail: nadeemganaie@
rediffmail.com.
Contract grant sponsor: Council of Scientific and Industrial Re-
search, New Delhi, India.
c 2009 Wiley Periodicals, Inc.
ꢀ

EFFECT OF INITIAL REAGENT CONCENTRATIONS ON THE BZ REACTION
651
in the presence of acetone as a mixed substrate
system.
of a 2 mL 0.1 M solution of potassium bromate to a
solution containing 2 mL 0.0225 M resorcinol and 2
mL 0.004 M manganese(II) sulfate monohydrate.
EXPERIMENTAL
Materials
RESULTS AND DISCUSSION
Table I shows the variation in oscillatory parameters at
different concentrations of resorcinol, keeping the con-
centrations of other reagents constant. From the data, it
is apparent that with the increase in the concentration
of resorcinol, the induction period decreases. The in-
duction period is observed due to the accumulation of
crucial concentration of the organic brominated species
prior to the commencement of oscillations [3,6]. With
the increase in the substrate concentration, the rate
of formation of bromo-organic derivative increases
and hence there is shortening of the induction period
All reagents used were either analytical grade chemi-
cals or else of high purity. The reagents used were re-
sorcinol 99% (Himedia Laboratories, Mumbai, India;
AR), potassium bromate 99% (Merck, Mumbai, India),
acetone 99% (Ranbaxy Fine Chemicals, New Delhi,
India), manganese(II) sulfate monohydrate (s.d. fine,
Biosar, India). All desired solutions of these reagents
were prepared in 1.3 M sulfuric acid 98% (Merck; LR).
Procedure
(Fig. 1). The dependence of the induction period on
The ion analyzer (ELICO LI-126) having pH as well
as mV option was calibrated in the oxidation reduction
potential (ORP) mode with the standard solutions,
using a platinum electrode as the indicator and calomel
[resorcinol] fits well with the mechanistic explanations
based on the FKN model. The time period of oscilla-
tions of the BZ reaction varies depending on the initial
substrate concentrations [9,14]. The time period is an
indicator for the overall BZ reaction. So, before seeing
insight of the oscillation waveforms, the dependence
of initial substrate concentrations on the time period
was observed (Fig. 2). It is mentioned that the concen-
tration of substrate at a certain measuring time may be
approximated to its initial concentration, and in this
study the average value of the time between the second
and sixth oscillations was taken as the time period.
From the results shown in Figs. 1 and 3, it is clear
that there are prominent variations in the time period of
the BZ reaction with the increase in [resorcinol]0. In all
cases, the time period becomes shorter with increasing
initial substrate concentration. The dependence of the
initial substrate concentration on the oscillation pe-
riod is justified on the basis of the FKN mechanism
[3–5]. According to this mechanism, the overall BZ
(SCE) as the reference electrodes. The equipment was
hooked to two half cells, one containing any one of
the reaction systems under investigation into which
the platinum electrode was dipped as an indicator
electrode. Another half cell was filled with a 2.5
−
4
×
10 M solution of potassium chloride, and the
calomel electrode was dipped into it as a reference
electrode. The two half cells were connected through a
salt bridge containing saturated solution of potassium
nitrate (Merck) and kept immersed in a high precision
water bath (Jindal SM Scientific Instruments, New
◦
Delhi, India) setup at a temperature of 30 ± 0.1 C. All
the solutions used in the reaction system were first kept
under thermostatic conditions at the desired tempera-
ture for about 10 min to acquire uniform temperature
in the system. The reaction started by the addition
Table I Variation in [Resorcinol] Having Other Species Such as [Mn2+] = 0.004 M, [BrO3¯] = 0.1 M, [H2SO4] = 1.3 M;
◦
Temperature = 30 ± 0.1 C
Number of
[
Resorcinol] (M) Induction Period tin (s) Time Period tp (s) Frequency v (s 1) Amplitude (mV) Oscillations (n)
−
0.0100
0.0150
0.0175
0.0200
0.0225
0.0250
0.0300
0.0400
0.0600
190
170
160
140
130
110
80
280.0
150.0
100.0
85.0
67.5
60.0
0.0035
0.0066
0.0100
0.0117
0.0148
0.0166
0.0200
<30
80
75
70
65
<5
>10
>20
>30
>40
>30
>20
60
34
50.0
60
20.0
0.0500
<20
>5
∗
∗
∗∗
∗∗
∗∗
∗∗
∗∗
No oscillations are seen.
International Journal of Chemical Kinetics DOI 10.1002/kin

6
52
GANAIE AND PEERZADA
1100
1100
1
000
1000
900
800
700
9
00
00
00
8
7
0
500
1000
1500
2000
0
500
1000
Time / s
(b)
1500
2000
Time / s
(
a)
1100
1100
1000
1000
9
00
00
00
900
800
700
8
7
0
500
1000
1500
2000
500
1000
Time / s
(d)
1500
2000
Time / s
(
c)
Figure 1 Potential (mV) verses time (s) plots showing variation of oscillatory characteristics for the system containing
−
2+
−3
[
(
BrO3 ] = 0.1 M, [Mn ] = 4 ×10 M, and [H2SO4] = 1.3 M. [Resorcinol]: (a) 0.0100 M, (b) 0.0200 M, (c) 0.0225 M, and
◦
d) 0.0300 M. Temperature = 30 ± 0.1 C.
reaction may be divided into the following three main
processes: consumption of bromide ion (process A),
autocatalytic reaction of the bromous acid with oxida-
tion of the catalyst (process B), and organic reaction
with the reduction of the catalyst (process C).
Following the FKN mechanism, we divided the wave-
forms for one of the reaction systems involving
−
0.0225 M [resorcinol], 0.1 M [BrO3 ], 0.004 M
2+
[Mn ] in 1.3 M H2SO4 into processes A, B, and C,
signifying each process as follows:
•
•
•
Process A represents the region where potential
increases very slowly,
Process B is the region where potential increases
rapidly, and
−
−
+
BrO + 2Br + 3H → 3HOBr
(A)
3
−
+
BrO + HBrO2 + 2Mred + 2H → 2HBrO2
3
Process C is the region where potential decreases.
+
2Mox + H2O
Mox + Substrate + Bromoderivative → f Br
2Mred + other products
(B)
−
2
The dependence of the oscillation frequency and
amplitude on [resorcinol]0 is plotted in Fig. 3. With
+
(C)
International Journal of Chemical Kinetics DOI 10.1002/kin

EFFECT OF INITIAL REAGENT CONCENTRATIONS ON THE BZ REACTION
653
11 00
Oscillation
period
B
B
C
C
A
A
1000
9
00
1
000
1500
Time / s
2000
Figure 2 Typical oscillating profiles of the system containing [Mn2+] = 4 × 10−3 M, [BrO3 ] = 0.1 M, [resorcinol] = 0.0225
−
◦
M at 30 ± 0.1 C.
increasing [resorcinol]0, it was found that the fre-
quency first increases rapidly up to 0.0175 M, then in-
creases slowly up to 0.025 M, and afterward increases
rapidly, until the concentration limit approaches,
i.e. 0.04 M, after which no oscillation is observed.
However, a good number of oscillations with better
amplitude were observed at [resorcinol] = 0.0225 M.
Table II gives the variation of oscillatory parameters
due to the inhibition effects of the HBrO2 (autocatal-
ysis process) where bromide competes with HBrO2
for bromate, and the autocatalysis process would not
−
start until the [Br ] drops to a certain critical value.
We assume that the increase in the bromate concen-
tration causes the faster accumulation of the bromod-
erivative of the substrate, and hence a shorter induction
period is observed first and after certain concentration
−
−
−
with varying [BrO3 ]0. With the increase in [BrO3 ]0,
the induction period decreases first up to 0.1 M and then
increases as seen in Fig. 4. This unusual trend can be
value demands longer time for the reduction of [Br ]
to the threshold value [6]. In fact, the tendency for
−
the longer induction period with increasing [BrO3 ]0
2+
becomes stronger when [Mn ]0 becomes limiting.
3
2
2
1
1
00
50
00
50
00
tin (s)
tin (s)
tp (s)
600
tp (s)
Amplitude (mV)
No. of Osc. (n)
5
4
3
2
1
00
00
00
00
00
0
Amplitude (mV)
No. of Osc. (n)
5
0
0
0
0.01
0.02
0.03
0.04
0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
[Resorcinol] / M
[BrO3 ] / M
Figure 3 Effect of the initial substrate concentration on
the induction period (tin, s), time period (tp, s), ampli-
tude (mV), and number of oscillations (n) while keep-
ing concentrations of other reagents constant. [Color fig-
ure can be viewed in the online issue, which is available at
www.interscience.wiley.com.]
Figure 4 Effect of the initial bromate concentration on
the induction period (tin, s), time period (tp, s), ampli-
tude (mV) and number of oscillations (n) while keep-
ing concentrations of other reagents constant. [Color fig-
ure can be viewed in the online issue, which is available at
www.interscience.wiley.com.]
International Journal of Chemical Kinetics DOI 10.1002/kin

6
54
GANAIE AND PEERZADA
Table II Variation in [BrO3¯]0 Having Other Species Such as [Mn2+] = 0.004 M, [Resorcinol] = 0.0225 M,
◦
[
H2SO4] = 1.3 M; Temperature = 30 ± 0.1 C
Number of
Amplitude (mV) Oscillations (n)
−
−1
)
[
BrO3 ] (M) Induction Period tin (s) Time Period tp (s) Frequency v (s
0.025
0.050
0.100
0.150
0.200
0.250
0.300
480
200
130
140
180
210
290.0
110.0
67.5
75.0
77.0
0.0034
0.0091
0.0148
0.0133
0.0129
>10
40
65
70
40
5
>15
>40
>20
>5
410.0
0.0024
>15
<5
∗
∗
∗∗
∗∗
∗∗
∗∗
∗∗
No oscillations are seen.
Accordingly, an increase in the bromate concentra-
tion would lead to first a decrease and then an increase
in the induction time. At high [resorcinol]/[BrO3 ],
tin (s)
3
2
00
50
tp (s)
−
Amplitude (mV)
No. of Osc. (n)
the effect of another inhibitor, i.e., organic radical
•
C6H4(OH)O , generated by the catalyst becomes in-
200
creasingly important, as noted by Field et al. [3]. The
other oscillating parameters such as the time period,
frequency, amplitude, and number of oscillations also
1
1
50
00
−
vary with the increase in the concentration of [BrO3 ].
−
50
The time period decreases up to 0.15 M [BrO3 ] and
then increases until the limiting concentration value
of 0.025 M [BrO3 ]. The reason for this is similar
0
0
−
.002
0.003
0.004
0.005
0.006
0.007
to the induction period, where accumulation of bromo-
derivative and reduction of [Br ] to the threshold value
2+
[Mn ] / M
−
Figure 5 Effect of the initial Mn2 ion concentration
on the induction period (t,in, s), time period (tp, s), am-
plitude (mV), and number of oscillations (n) while keep-
ing concentrations of other reagents constant. [Color fig-
ure can be viewed in the online issue, which is available at
www.interscience.wiley.com.]
+
affects the processes A, B, and C and hence unusual
variations of time period and frequency are observed.
The trend for amplitude and the number of oscillations
first show an increase and then decrease following the
FKN mechanism (Fig. 4), although we cannot explain
the particular reaction in detail due to the complexity
of the BZ reaction.
Table III shows the oscillatory parameters for the
bined effect of the processes B and C, wherein the
[Mn ]/[Mn ] depends on the autocatalysis process,
2+
2+
3+
varying [Mn ]0. With the increase in the concentra-
2+
tion of Mn ion, the time period decreases follow-
ing the FKN mechanism, whereas the induction period
and frequency of oscillations first decrease and then
increase (Fig. 5). This can be because of the com-
giving rise to the formation of HBrO . The amplitude
2
and number of oscillations first increase and then de-
2+
crease with the increase in [Mn ] following the FKN
mechanism.
Table III Variation in [Mn2 ]0 Having Other Species Such as [Resorcinol] = 0.0225 M, [BrO3 ] = 0.1 M,
+
−
◦
[
H2SO4] = 1.3 M; Temperature = 30 ± 0.1 C
Number of
Amplitude (mV) Oscillations (n)
Mn2 ] (M) Induction Period tin (s) Time Period tp (s) Frequency v (s
+
−1
)
[
∗
∗
∗∗
∗∗
∗∗
∗∗
0.001
0.003
0.004
0.005
0.006
0.008
160
130
110
240
150.0
67.5
60.0
0.0066
0.0148
0.0166
35
65
25
>20
>40
>9
50.0
0.0100
<10
>5
∗
∗
∗∗
∗∗
∗∗
∗∗
∗∗
No oscillations are seen.
International Journal of Chemical Kinetics DOI 10.1002/kin

EFFECT OF INITIAL REAGENT CONCENTRATIONS ON THE BZ REACTION
655
Table IV Variation in [H2SO4]0 Having Other Species Such as [Mn2+] = 0.004 M, [Resorcinol] = 0.0225 M,
−
◦
[
BrO3 ] = 0.1 M; Temperature = 30 ± 0.1 C
Number of
Oscillations (n)
[
H2SO4] (M)
Induction Period tin (s)
Time Period tp (s)
Frequency v (s 1)
−
Amplitude (mV)
∗
∗
∗
∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
∗∗
0.5
0.8
1.0
1.3
1.8
a
b
330
130
300.0
0.0033
25 , 18
>10
67.5
0.0148
65
>40
∗
∗
∗∗
∗∗
∗∗
∗∗
∗
a
b
∗
No oscillations are seen.
Large peak.
Small peak.
1
100
substantially smaller amplitudes as compared to L,
and n = 0, 1, 2, . . . . In this system n = 1, so we can
have only one small amplitude oscillation between
two larger amplitude oscillations. Such behavior of
periodic mixed-mode oscillations can be explained
by considering the models [15,16] that qualitatively
describe regularities observed in transients as well as
asymptotic mixed-mode oscillations in the BZ reac-
tion. The variables can be treated as the autocatalytic
1000
9
00
00
00
−
reagent, i.e., HBrO2, Br , which is involved in nega-
8
7
2+
tive feedback, [Mn ], and concentration of acid, i.e.,
1
1
.0 M
.3 M
+
[H ] [17].
Table V shows the variation of oscillatory parame-
0
400
800
1200
1600
2000
ters with changing [acetone] as cosubstrate. With the
0
Time / s
increase in the concentration of acetone (% v/v), there
Figure 6 Comparative potential (mV) verses time (s) plots
is first increase in the induction period [18] and then
it decreases, showing a parabolic behavior, whereas
the time period shows a gradual decrease (Fig. 7).
However, the induction time is larger as compared to
the values observed with changing concentrations of
other reagents (as mentioned earlier). As suggested
by the FKN mechanism, the bromoderivative acts as
positive feedback for the bromination of resorcinol.
As the mechanism suggests that the induction period
corresponds to the saturation of the system with
bromoderivative (autocatalyst), which is apparent in
this experiment visually. The larger induction period
is because of the bromination of acetone to give rise
to bromoacetone in addition to the bromosubstrate
derivative. The acetone hence competes with resorcinol
showing mixed-mode oscillations for 1.0 M H2SO4 and
−
1
.3 M H2SO4, [resorcinol] = 0.0225 M, [BrO3 ] = 0.1 M,
2+
−3
◦
◦
[
Mn ] = 4 × 10
M, and temperature = 30 ± 0.1 C.
[
Color figure can be viewed in the online issue, which is
available at www.interscience.wiley.com.]
Table IV gives the variation of oscillatory parame-
ters with varying [H2SO4]0, keeping concentrations of
other reagents constant. Good results were obtained in
1.3 M H2SO4, while as in 1.0 M H2SO4 mixed-mode
oscillations with small and large peak amplitudes were
observed (Fig. 6). The oscillations observed exhibit
patterns of the type LSn, where L denotes oscillations
with large amplitudes and S means oscillations with
Table V Variation in [Acetone]0 in % (v/v) Having Other Species Such as [Resorcinol] = 0.0225 M, [Mn2+] = 0.004 M,
◦
[
BrO3¯] = 0.1 M, [H2SO4] = 1.3 M; Temperature = 30 ± 0.1 C
[
%
Acetone]
(v/v)
Induction
Period tin (s)
Time
Period tp (s)
Frequency
Number of
Oscillations (n)
Amplitude
(mV)
−
1
v (s
)
5
190
220
305
250
66.25
50.00
47.50
45.00
0.0151
0.0200
0.0211
0.0222
>60
>70
>60
>50
54
70
28
18
1
1
2
0
5
0
International Journal of Chemical Kinetics DOI 10.1002/kin

6
56
GANAIE AND PEERZADA
of the reagents at which better oscillations were ex-
hibited by the reaction system. Furthermore, it is in-
ferred that the increase in the bromate concentration
enhances the reaction rate and lesser chances of neg-
ative feedback owing to the critical bromide ion con-
centration are seen. As such, either a few or no oscilla-
tions were observed. This holds good for the metal ion
concentration as well. Moreover, mixed-mode oscilla-
tions are observed for the reaction system when studied
in lower concentration of sulfuric acid medium. It is
also observed that the single substrate system (with-
out acetone) shows prominent oscillatory behavior as
compared to the mixed substrate system with acetone,
which is in cognizance with the fact that acetone also
behaves as a bromide ion scavenger in such reactions
tin (s)
3
3
2
2
1
1
50
00
50
00
50
00
tp (s)
Amplitude (mV)
No. of Osc. (n)
5
0
0
0
5
10
15
20
25
[
Acetone] / (v/v)
Figure 7 Effect of initial [acetone] as cosubstrate on
the induction period (tin, s), time period (tp, s), ampli-
tude (mV), and number of oscillations (n) while keep-
ing concentrations of other reagents constant. [Color fig-
ure can be viewed in the online issue, which is available at
www.interscience.wiley.com.]
[20].
The authors are thankful to the Head, Department of Chem-
istry, University of Kashmir, Srinagar, India, for providing
infrastructure to undertake this investigation.
in the bromination reaction and thus leads to the longer
time for accumulation of the bromoderivative.
O
OH
O
Enolization
Br2
Br
HBr
H C
CH3
H2C
CH3
CH3
3
Enol form
Bromoderivative
Keto form
The enol form acts as a nucleophilic site for bromo at-
tack and forms bromoacetone as a product intermediate
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volvement of acetone in processes B and C and thus
competing with resorcinol in these reactions.
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International Journal of Chemical Kinetics DOI 10.1002/kin

EFFECT OF INITIAL REAGENT CONCENTRATIONS ON THE BZ REACTION
657
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International Journal of Chemical Kinetics DOI 10.1002/kin