A dual-phase oscillatory behavior in Belousov Zhabotinsky system with vanillin as the substrate

Article abstract of DOI:10.1002/(SICI)1097-4601(1998)30:3<201::AID-KIN5>3.0.CO;2-W

Dual-phase oscillations are observed in Belousov-Zhabotinsky system with 4-hydroxy-3-methoxybenzaldehyde (vanillin) as the substrate and manganous sulphate or ammonium Ce(IV) sulphate as the catalyst. The nonoscillatory period of time between the two phases decreases with increase in the concentration of the catalyst and the substrate. Under uncatalyzed and ferroin catalyzed conditions the system exhibits single-phase oscillations. The first-phase oscillations are due to vanillin whereas the second-phase oscillations are brought about by 4-hydroxy-3-methoxybenzoic acid (vanillic acid) formed during the course of the first-phase reactions. The reactions are explained with relevant steps of the FKN mech- anism. 1998 lohn Wiley & Sons, Inc.

Full text of DOI:10.1002/(SICI)1097-4601(1998)30:3<201::AID-KIN5>3.0.CO;2-W

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A Dual-Phase Oscillatory
Behavior in Belousov–
Zhabotinsky System with
Vanillin as the Substrate
V. SRIDEVI, R. RAMASWAMY
Department of Chemistry, Indian Institute of Technology, Madras-600 036, India
Received 2 December 1996; accepted 21 April 1997
ABSTRACT: Dual-phase oscillations are observed in Belousov–Zhabotinsky system with 4-
hydroxy-3-methoxybenzaldehyde (vanillin) as the substrate and manganous sulphate or am-
monium Ce(IV) sulphate as the catalyst. The nonoscillatory period of time between the two
phases decreases with increase in the concentration of the catalyst and the substrate. Under
uncatalyzed and ferroin catalyzed conditions the system exhibits single-phase oscillations.
The first-phase oscillations are due to vanillin whereas the second-phase oscillations are
brought about by 4-hydroxy-3-methoxybenzoic acid (vanillic acid) formed during the course
of the first-phase reactions. The reactions are explained with relevant steps of the FKN mech-
anism. ᭧ 1998 John Wiley & Sons, Inc. Int J. Chem. Kinet 30: 201–206, 1998.
INTRODUCTION
EXPERIMENTAL
Extensive investigation has been carried out in the Be-
lousov–Zhabotinsky (B–Z) oscillatory system [1–3].
A variety of organic compounds have been employed
as substrate in these systems. The serious limitation of
substrate insolubility has been overcome by the use of
aqueous-organic mixed media [4–6].
Sequential oscillations with mixed organic sub-
strates have been reported [7]. Dual frequency oscil-
lations with ethylacetoacetate as the substrate have
been brought about by further addition of potassium
bromate [8]. In this article, a novel dual-phase oscil-
latory system with 4-hydroxy-3-methoxybenzalde-
hyde (vanillin) as a single substrate and Mn(II) or
Ce(IV) as catalyst is described. The single-phase os-
cillations are observed in the ferroin catalyzed and un-
catalyzed systems. The characteristics are examined so
as to unravel the sequential changes involved in the
overall process.
All the chemicals employed were of Analytical Grade
purity. The reaction was carried out under batch con-
ditions in a polythene beaker of 100 ml capacity. The
addition of the last constituent (Potassium bromate) to
the stirred and thermostated solution containing all
other constituents starts the oscillations. Simultaneous
recording of the potential profile with a platinum and
bromide ion selective electrode (against a saturated
calomel electrode) dipped in the solution was made on
a X-t recorder. An aqueous-organic, mixed medium
containing 20% (v/v) acetonitrile was employed be-
cause of the poor solubility of the substrate in water.
RESULTS AND DISCUSSION
The experimental results obtained in the uncatalyzed
system as well as the catalyzed system involving
Mn(II), Ce(IV), or ferroin provides valuable data re-
garding the course of the reaction. The composition of
experimental solution and the oscillatory characteris-
Correspondence to: R. Ramaswamy
᭧ 1998 John Wiley & Sons, Inc.
CCC 0538-8066/98/030201-06

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202
SRIDEVI AND RAMASWAMY
Table I Oscillatory Characteristics of the Platinum Profile: Vanillin9Mn(II) System.
[Vanillin] ϭ 0.03 M; [H2SO4] ϭ 0.6 M; [KBrO3] ϭ 0.09 M; Acetonitrile ϭ 20% (v/v); and
Temperature ϭ 30 Ϯ 0.1ЊC
Potential Range
V(vs SCE)
Number of
Oscillations
(n)
Time per
Oscillation
Tt (min)
Initial
Amplitude
(mV)
[Mn(II)]
(M)
Phase
Base
0.62
Peak
0.83
Phase-I
9
8
0.11
1.06
0.14
1.14
0.12
0.86
0.16
1.0
150
90
0.001
0.0025
0.005
Phase-II
Phase-I
Phase-II
Phase-I
Phase-II
Phase-I
Phase-II
–
0.75
0.63
0.7
0.83
0.83
0.84
0.86
0.80
0.90
0.94
0.85
7
150
130
160
160
160
150
160
7
8
0.62
0.62
0.65
0.69
0.58
6
8
0.01
0.03
5
13
0.38
tics of the Mn(II) and Ce(IV) system are presented in
Tables I and II respectively. The oscillatory potential
profiles with the platinum indicator electrode and bro-
mide ion selective electrode are presented in Figures
1 to 5.
The potential profile in the Mn(II) system is char-
acterized by high-frequency oscillations in the first-
phase followed by low-frequency second-phase oscil-
lations after a time lag of nearly 4 min at a concentra-
tion of 0.001 M of Mn(II) (Fig. 1(a)). The BrϪ poten-
Table II Oscillatory Characteristics of the Platinum Profile: Vanillin9Ce(IV) System.
[Vanillin] ϭ 0.03 M; [H2SO4] ϭ 0.6 M; [KBrO3] ϭ 0.09 M; Acetonitrile ϭ 20% (v/v); and
Temperature ϭ 30 Ϯ 0.1ЊC
Potential Range
V(vs SCE)
Number of
Oscillations
(n)
Time per
Oscillation
Tt (min)
Initial
Amplitude
(mV)
[Ce(IV)]
(M)
Phase
Base
0.62
Peak
0.8
Phase-I
8
8
8
6
9
5
9
2
0.11
1.62
0.14
2.0
160
60
0.001
0.0025
0.005
0.01
Phase-II
Phase-I
Phase-II
Phase-I
Phase-II
Phase-I
Phase-II
0.78
0.62
0.81
0.62
0.80
0.63
0.90
0.84
0.8
160
90
0.9
0.13
2.94
0.11
5.20
160
100
150
100
0.8
0.9
0.79
1.0

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DUAL PHASE OSCILLATORY BEHAVIOR
203
range, do not completely merge with the first-phase
oscillations (Fig. 2(e) and (f)). The time lag between
the two phases decreased when the substrate concen-
tration was increased from 0.01 to 0.04 M.
In the uncatalyzed bromate system the oscillations
are in a single phase only (Fig. 3). Moreover, the plat-
inum potential profile of the uncatalyzed system bears
a close resemblance to the corresponding first-phase
in the Mn(II) as well as Ce(IV) system in respect of
number frequency, amplitude, and potential range.
Such a resemblance is observed in the BrϪ potential
profile as well. With ferroin as the catalyst the system
shows single-phase oscillation (Fig. 4).
The reactivity of vanillin is such that the bromi-
nation step is a highly favored one in the overall re-
action and, hence, the first-phase of oscillation in-
volves bromination of vanillin as the predominant
reaction. Further, the longer time per oscillation in the
second-phase rules out its participation in this phase
of the profile. Therefore, the substrate in the second-
phase is a derivative of vanillin which could probably
be vanillic acid formed by the oxidation of vanillin by
Ce(IV) or Mn(III)
The reactivity of vanillic acid is less compared to
vanillin. Experiments were carried out by employing
vanillic acid as the substrate in the uncatalyzed and
catalyzed systems. Vanillic acid is characterized by ill-
defined oscillations in the uncatalyzed bromate sys-
tem. The platinum potential profiles of Mn(II) and
Ce(IV) system with vanillic acid as the substrate have
a striking resemblance to the second-phase oscillation
in the Mn(II) and Ce(IV) system, respectively (Fig.
5(a) and (b)). This lends further support to the above
conclusions regarding the reactions taking place in the
first-and second-phase.
Figure 1 Dual-phase oscillatory behavior of vanillin—
Mn(II) system. (a), (c), and (e) potential profiles recorded
Ϫ
with platinum electrode. (b), (d), and (f) corresponding Br
potential profiles. Concentration conditions: [Vanillin] ϭ
0.03 M, [H2SO4] ϭ 0.6 M; [KBrO3] ϭ 0.09 M; Acetonitrile
ϭ 20% (v/v); and Temperature ϭ 30 Ϯ 0.1ЊC [MnSO4] ϭ
0.001 M (a and b), 0.005 M (c and d), and 0.03 M (e and
f).
The decrease in the time interval between the two
phases as the metal ion and substrate concentration
increases, is because of the faster build up of the ox-
idized product. The oxidation of vanillin by Ce(IV) or
Mn(III), has been confirmed by following the variation
in the potential of Mn(III) and Ce(IV) in presence of
acidified vanillin under nonoscillatory conditions.
There is a drastic decrease in the potential of a plati-
num electrode dipped in a solution of acidified Ce(IV)
or Mn(III) on the addition of vanillin. However, such
a decrease in potential is not observed when acidified
ferrin is employed.
tial profile has the same frequency as the platinum
profile in both the phases (Fig. 1(b)). The amplitude
of BrϪ oscillations is small indicating a small change
in the concentration of BrϪ between the base and peak.
An increase in the concentration of Mn(II) to 0.005 M
leads to a decrease in the time lag between the two
phases (Fig. 1(c)) and an increase in the amplitude of
the platinum potential profile. An increase in the con-
centration of Mn(II) to 0.03 M results in the merging
of the two phases (Fig. 1(e)). A similar trend is ob-
served in the BrϪ potential profile with respect to the
frequency and amplitude of oscillations (Fig. 1(d) and
(f)).
The oscillatory behavior of this system can be ra-
tionalized in terms of the following steps involved in
the overall reaction [9].
The decrease in time lag between the first-and sec-
ond-phase of oscillations is a characteristic feature of
the Ce(IV) system also (Fig. 2). However, even at the
highest concentration of Ce(IV) employed, the sec-
ond-phase oscillations, being at a higher potential
Ϫ
BrϪ ϩ BrO3 ϩ 2Hϩ EF HOBr ϩ HBrO2 (1)
BrϪ ϩ HOBr ϩ Hϩ EF Br2 ϩ H2O
(2)

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204
SRIDEVI AND RAMASWAMY
Figure 2 Dual-phase oscillatory behavior of vanillin—Ce(IV) system. (a), (c), and (e) potential profiles recorded with plat-
Ϫ
inum electrode. (b), (d), and (f) corresponding Br potential profiles. Concentration conditions: [Vanillin] ϭ 0.03 M, [H2SO4]
ϭ 0.6 M; [KBrO3] ϭ 0.09 M; Acetonitrile ϭ 20% (v/v); and Temperature ϭ 30 Ϯ 0.1ЊC [Ce(IV)] ϭ 0.0025 M (a and b),
0.005 M (c and d), and 0.01 M (e and f).