Experimental studies on complex oscillations in a Mn2+-catalyzed acidic bromate-glucose reaction

Article abstract of DOI:10.1246/bcsj.74.1817

Under batch-reactor conditions, the BrO₃^--glucose-Mn²⁺-H₂SO ₄ system exhibits several types of oscillations, depending on the concentrations of the reactants. In certain cases, dual-frequency oscillat

Full text of DOI:10.1246/bcsj.74.1817

c. Jpn.
© 2001 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 74, 1817–1821 (2001) 1817
e Chemical
ciety of Ja-
n
Experimental Studies on Complex Oscillations in a Mn2+-Catalyzed
Acidic Bromate–Glucose Reaction
e Chemical
ciety of Ja-
n
Complex Oscillations in a Glucose-BZ System
H. Li et al.
Hexing Li* and Qin Wang
01
17
21
SJA8
09-2673
009
Department of Chemistry, Shanghai Normal University, Shanghai 200234, P. R. China
(Received January 12, 2001)
Under batch-reactor conditions, the BrO3−–glucose–Mn2+–H2SO4 system exhibits several types of oscillations, de-
pending on the concentrations of the reactants. In certain cases, dual-frequency oscillations are observed owing to a se-
quential appearance of different types of oscillations. Since glucose is not subject to bromination, these oscillations may
be considered as being typically radical-controlled, and can be distinguished from bromide-controlled oscillations by
adding acetone, which also results in dual-frequency oscillations due to the presence of both radical-controlled and bro-
mide-controlled oscillations. Further experimental results demonstrate that the different types of oscillations observed in
the absence of acetone can be possibly attributed to the Mn2+-catalyzed reactions between bromate and glucose, or vari-
ous intermediates produced from the oxidative degradation of glucose. The effects of the [BrO3−]/[glucose] ratio and
[H2SO4] on the oscillatory behaviors are discussed on the basis of their effects on either the depth of oxidative degrada-
tion of glucose or the oxidizing ability of bromate.
01
01
.3
−
The classical Belousov–Zhabotinsky (BZ) reaction, the met-
al ion catalyzed oxidation of organic substrate by an acidic
bromate solution, is the most thoroughly characterized of the
known chemical oscillations.1 A detailed mechanism, known
as the FKN mechanism, has been proposed by Field and co-
workers,2 in which they claimed that the oscillations are con-
trolled by bromide, which is produced mainly by the reaction
between bromomalonic acid and Ce4+. However, the concept
of bromide control is not always true, since the oscillations
could also be observed even in the presence of excess silver
ions.3 Noszticzius et al. reported that, under certain cases, the
BZ oscillations could also be controlled by the malonyl radi-
cal,4–7 known as the “Rácz” system. They also claimed that the
bromide-controlled oscillations usually had an induction peri-
od before the oscillations began, while the radical-controlled
oscillations occurred immediately without an induction period.
However, most of the substrates known so far to give to BZ-
type oscillations are easily brominated.8 In the case where the
substrate is not subject to bromination, an effective brominat-
ing agent, e.g. acetone, is necessary to remove the product bro-
mine.9–15 Therefore, doubt arises whether the Rácz system
could still be bromide-controlled, because bromide might be
produced by the reaction of brominated organic substrates and
Ce4+ or Mn3+. Pojman and co-workers16 reported a promising
way to suppress the bromide-controlled oscillations by adding
acetylacetone, which could effectively consume HOBr and
Br2. They also reported dual-frequency oscillations owing to
the coexistence of both the radical-controlled and bromide-
controlled oscillations. In our previous paper, dual-frequency
oscillations were also reported in the BZ systems by using al-
dosugars and suitable acidity.12 However, two types of oscilla-
tions involved were both bromide-controlled and could be ex-
plained on the bases of the FKN mechanism, since acetone
was found to be essential in each type of oscillation. In this
paper, we report on the oscillations in the BrO3 –glucose
(Glu)–Mn2+–H2SO4 system, even without acetone as a coupled
substrate, which could be considered as typiclly radical-con-
trolled, since Glu is not subject to bromination. The first part
of this paper distinguishes the radical-controlled oscillations
from the bromide-controlled oscillations by using acetone, as
reported in our previous system. The second part analyzes
three types of radical-controlled oscillations in the present sys-
−
tem by considering the roles of the [BrO3 ]/[Glu] ratio and
[H2SO4]. On one hand, the present work might lead to a recon-
sideration of the FKN mechanism, since there is no active me-
thylene like that in malonic acid, which could be easily bromi-
nated. On the other hand, as we know, complex radical-con-
trolled oscillations have never been reported so far. Therefore,
it could supply valuable information to further elucidate the
mechanism of the radical-controlled oscillations.
Experimental
All of the materials were of analytical grade and were used
without further purification. All of the solutions were prepared in
twice-distilled water.
The oscillating reactions were performed in a stirred thermo-
stated glass beaker at 30 0.2 °C. The reactants were added in
the order of H2O, H2SO4, glucose, Mn2+, and BrO3−. The reaction
mixture was open to the ambient air. No special precautions were
attempted to exclude oxygen from the reaction mixture. The
change in [Br−] was followed by a bromide ion-selective electrode
(Br− ISE) against a Hg/Hg2SO4/K2SO4 electrode as a reference.
The potential was recorded as a function of time (E–t) on a XWT
x-t recorder. No absolute calibration of the bromide ion electrode
was attempted. The reaction products were analyzed by liquid
chromatograph with UV @ 210 nm detection under the following
conditions: column, Rezex ROA-organic acid; dimensions, 300 ×
7.8 mm; mobile phase, 0.0025 M (1 M = 1 mol dm−3) sulfuric ac-
id; flow rate, 0.5 mL/min; temperature, 55 °C.

1818 Bull. Chem. Soc. Jpn., 74, No. 10 (2001)
Complex Oscillations in a Glucose-BZ System
Results and Discussion
The Radical-Controlled and Bromide-Controlled Oscil-
−
lations. Typical experimental results on the BrO3 –Glu–
Mn2+–H2SO4 reaction with different acetone concentrations
are plotted in Fig. 1. In the absence of acetone or when [ace-
tone] < 0.080 M (1 M = 1 mol dm−3), only one type of oscil-
lation (Fig. 1a) was observed which could be considered to be
radical-controlled, since no brominated substance could be
formed in the present system, on one hand, and the oscillations
started immediately without any induction period on the other
hand. Another important reason was that the oscillations could
also be observed when a small amount of silver ions was added
into the solution. As is well known, no sufficient [Br−] could
be accumulated due to the formation of AgBr precipitate in the
presence of silver ions. Therefore, bromide could not be pro-
duced by the reaction between the brominated substance and
Mn3+. Unlike acetylacetone, the addition of acetone could
suppress radical-controlled oscillations, since the number of
oscillations decreased rapidly with an increase of [acetone].
The possible reason was that acetylacetone could be easily ox-
idized by HOBr, BrO2O, and even Br2.16 However, the oxida-
tion of acetone was relatively difficult. Therefore, the main
role of acetone in the oscillations was to consume Br2 via the
following bromination:
Fig. 1. Oscillatory traces in the Mn2+-catalyzed acidic bro-
mate–glucose reaction in the presence of acetone. (a) [ace-
tone]0 = 0.067 M, (b) [acetone]0 = 0.11 M, (c) [acetone]0
= 0.16 M. Other reaction conditions: [BrO3−]0 = 0.025
M, [Glu]0 = 0.020 M, [Mn2+]0 = 0.015 M, [H2SO4] =
0.18 M, V = 50 mL, T = 30 0.2 °C.
tions were totally suppressed and only the bromide-controlled
oscillations were observed, as shown in Fig. 1c. It was noted
that the color of the solution also changed periodically be-
tween pink(Mn3+) and colorless(Mn2+), showing the presence
of the oscillations in [Mn3+]/[Mn2+] ratio, which could be ob-
served by measuring the absorbance at 480 nm corresponding
to the maximum absorbance wavelength of Mn3+ on an HP
8451 A spectrophotometer.19 Those results demonstrated that
both the bromide- and radical-controlled oscillations were cat-
alyzed by Mn2+.
CH3COCH3 + Br2 → BrCH2COCH3 + Br− + H+,
BrCH2COCH3 + Br2 → Br2CHCOCH3 + Br− + H+.
Complex Radical-Controlled Oscillations. In the ab-
The resulting Br− during the consumption of Br2 could further
react with HOBr:
sence of acetone, the BrO3 –glucose–Mn2+–H2SO4 system,
−
i.e., a pure Rácz system, also exhibited several types of oscilla-
tions, depending on the reactants’ concentrations. Fig. 2
shows the effect of [Glu] on the oscillatory pattern when the
HOBr + Br− + H+ → Br2 + H2O.
−
concentrations of other reactants were fixed at [BrO3 ] =
Because the reaction between bromide and HOBr was very
fast, the accumulation of HOBr was delayed in the presence of
acetone. Thus, the radical-controlled oscillations were sup-
pressed since such oscillations were due to the oscillations in
[HOBr].5 An increase in [acetone] resulted in the production
of more bromide, which could account for the decrease in the
number of radical-controlled oscillations. At [acetone] >
0.080 M, a new type of oscillation was induced. This type of
oscillation was possibly bromide-controlled, since an induc-
tion period appeared before the oscillations began. Acetone
was essential for bromide-controlled oscillations in the present
system, since bromide was produced via the above-mentioned
bromination and, possibly, also the following reaction between
BrCH2COCH3 and Mn3+:
0.010 M, [H2SO4] = 1.0 M, [Mn2+] = 0.040 M. At very high
[Glu] (> 0.1 M), only one overshoot without an induction pe-
riod was observed, as shown in Fig. 2a. The addition of a
−
small amount of BrO3 resulted in another overshoot. This
implied that the absence of the sustained oscillations in the
−
present system was mainly due to the limitation of [BrO3 ].
During the reaction, no bubbles were observed. Besides Glu,
only gluconic acid was determined in the solution after the re-
action. When [Glu] decreased from 0.1 M to 0.0525 M, sus-
tained oscillations appeared immediately following the over-
shoot, which was denoted as type ꢀ. The oscillations in the
[Mn3+]/[Mn2+] ratio were also observed by measuring the ab-
sorbance at 480 nm. During the oscillations, many bubbles
were released from the solution due to the decarboxylation of
gluconic acid. According to a product analysis, gluconic acid,
arabinose, arabinonic acid, and formic acid were determined in
the reaction mixture after the oscillations. However, no signif-
icant amount of Glu was detected. In the [Glu] range of
0.0525–0.0475 M, a nonoscillatory period between the over-
shoot and the type-ꢀ oscillations was observed, as shown in
Fig. 2c. When the [Glu] further decreased, the overshoot dis-
appeared. From 0.0475 M to 0.035 M, only type-ꢀ oscillations
appeared, as shown in Fig. 2d. With a further decrease in
[Glu], the system exhibited a typical dual-frequency oscilla-
BrCH2COCH3 + Mn3+ → Br− + products.
Dual-frequency oscillations17,18 were observed in the [ace-
tone] range from 0.080 M to 0.147 M owing to the presence of
both the radical-controlled and the bromide-controlled oscilla-
tions, as shown in Fig. 1b. With an increase of [acetone], the
number of radical-controlled oscillations continued to decrease
while the number of the bromide-controlled oscillations in-
creased. At [acetone] > 0.15 M, the radical-controlled oscilla-

H. Li et al.
Bull. Chem. Soc. Jpn., 74, No. 10 (2001) 1819
Fig. 3. Dependence of the oscillatory patterns on [BrO3−]0.
(a) [BrO3−]0 = 0.0050 M, (b) [BrO3−]0 = 0.0090 M, (c)
−
−
[BrO3
] = 0.010 M, (d) [BrO3 ] = 0.0125 M, (e)
0
0
[BrO3−]0 = 0.015 M. Other reaction conditions: [Glu]0 =
0.050 M, [Mn2+]0 = 0.040 M, [H2SO4] = 1.0 M, V = 50
mL, T = 30 0.2 °C.
−
tendency was opposite, i.e., the increase of [BrO3 ] was corre-
sponded to the decrease of [Glu]. Typical results are summa-
rized in Fig. 3.
−
The above results demonstrated that the BrO3 –glucose–
Mn2+–H2SO4 system could exhibit several types of oscillations
−
depending on the [BrO3 ]/[Glu] ratio. All of these kinds of os-
cillations were radical-controlled because of the absence of a
brominating agent. Under certain cases, dual-frequency oscil-
lations were observed due to the coexistence of two types of
oscillations. Based on a product analysis and the fact that
much CO2 gas was released during the oscillations, the follow-
ing oxidative degradation of glucose by acidic bromate may
occur in the present system (Scheme 1).
Fig. 2. Dependence of the oscillatory patterns on [Glu]0. (a)
[Glu]0 = 0.12 M, (b) [Glu]0 = 0.060 M, (c) [Glu]0 = 0.050
M, (d) [Glu]0 = 0.040 M, (e) [Glu]0 = 0.025 M. Other re-
action conditions: [BrO3−]0 = 0.010 M, [Mn2+]0 = 0.040
M, [H2SO4] = 1.0 M, V = 50 mL, T = 30 0.2 °C.
tions comprised of two types of sustained oscillations.17,18 As
shown in Fig. 2e, after a short induction period, the system bi-
furcated into a first oscilatory regime, where low-frequency
and large-amplitude oscillations (Type-ꢀ) occurred. Both the
frequency and the amplitude remained nearly constant with the
elapse of the reaction time. Then, type-ꢀ oscillations suddenly
diminished and another type of oscillation, denoted as type-ꢁ,
occurred immediately. Type-ꢁ oscillations were characterized
by a relative high frequency and small amplitude and a nearly
symmetric wave form. The number of type-ꢀ oscillations de-
creased while the number of the type-ꢁ oscillations gradually
increased with the decrease of [Glu]. However, a nonoscillato-
ry period between these two types of oscillations never ap-
peared. During each type of oscillation, bubbles were released
from the solution, indicating the occurrence of decarboxyla-
tion. After the oscillations totally finished, arabinonic acid,
erythrose, and formic acid were found in the reaction mixture.
Therefore, it is reasonable to suggest that the influence of
−
the [BrO3 ]/[Glu] ratio on the oscillatory patterns was possibly
attributed to its effect on the depth of the oxidative degradation
of glucose corresponding to different intermediates, including
gluconic acid, arabinose, arabinonic acid, erythrose and formic
acid. These intermediates could construct different BZ-type
reactions, resulting in different types of oscillations. Obvious-
ly, the depth of the oxidative degradation increased with the in-
−
−
crease of the [BrO3 ]/[Glu] ratio. At very low [BrO3 ]/[Glu]
ratio, since Glu was greatly excess, a large portion of Glu was
left and only the gluconic acid was detected as the product af-
ter the reactions. Thus, the overshoot could be attributed to the
Mn2+-catalyzed bromate–glucose reaction. Only one over-
−
shoot was observed, since excess Glu consumed BrO3 very
−
rapidly. When [Glu] decreased or [BrO3 ] increased (i.e. the
−
[BrO3 ]/[Glu] ratio increased), type-ꢀ oscillations were ob-
−
served after the overshoot. According to a product analysis, it
could be concluded that the Mn2+-catalyzed bromate–gluconic
acid reaction was responsible for the type-ꢀ oscillations. This
Similar results were also observed by changing [BrO3 ]
when the other reactant concentrations were fixed at [Glu] =
0.050 M, [H2SO4] = 1.0 M, [Mn2+] = 0.040 M. However, the

1820 Bull. Chem. Soc. Jpn., 74, No. 10 (2001)
Complex Oscillations in a Glucose-BZ System
Scheme 1. Reaction scheme of glucose oxidation by bromate.
the title system, as shown in Fig. 4b. A further increase in the
−
[BrO3 ]/[Glu] ratio could accelerate the consumption of glu-
conic acid on one hand, and increase the accumulation of ara-
binose and arabinonic acid on the other hand. Therefore, the
number of type-ꢀ oscillations decreased while the number of
type-ꢁ oscillations gradually increased. It should be noted that
the shapes of the oscillations in Fig. 4 are not exactly the same
as those of type-ꢀ and type-ꢁ oscillations in Fig. 3. On one
hand, this can be understood by considering the different initial
conditions, since the type-ꢀ and type-ꢁ oscillations occurred
after the oxidation of glucose and gluconic acid, respectively.
Therefore, the concentrations of the reactants in type-ꢀ and
type-ꢁ must be different from those shown in Fig. 4. In fact,
the shapes of the oscillations in Fig. 4 depend strongly on the
initial concentrations of the reactants. On the other hand, some
intermediates in the reaction system in Fig. 3 may also disturb
the shapes of oscillations.
Fig. 4. Oscillatory traces in (a) the Mn2+-catalyzed acidic
bromate–gluconic acid reaction and (b) the Mn2+-cata-
lyzed acidic bromate–arabinonic acid reaction. Reaction
conditions: [gluconic acid]0 = [arabinonic acid]0 = 0.050
M, [BrO3−] = 0.010 M, [Mn2+]0 = 0.040 M, [H2SO4]0 =
1.0 M, V = 50 mL, T = 30 0.2 °C.
Figure 5 shows the dependence of the oscillatory patterns on
[H2SO4] when other reactant concentrations were fixed at
was strongly supported by the fact that similar oscillations to
type-ꢀ were also observed when gluconic acid was used instead
of glucose in the title system, as shown in Fig. 4a. Many cy-
cles of type-ꢀ oscillations were observed owing to the slow
−
[BrO3 ] = 0.010 M, [Glu] = 0.050 M, and [Mn2+] = 0.040
M, respectively. At medium [H2SO4] (1.12–0.083 M), the sys-
tem exhibited that an overshoot and type-ꢀ oscillations were
separated by a nonoscillatory period, as shown in Fig. 5b. At
higher [H2SO4] (> 1.12 M), the overshoot diminished and only
type-ꢀ oscillations with an induction period were observed, as
shown in Fig. 5a. A further increase in [H2SO4] caused a de-
crease in both the induction period and the number of type-ꢀ
oscillations. At lower [H2SO4] (< 0.083 M), the nonoscillato-
ry period between the overshoot and the type-ꢀ oscillations
suddenly disappeared, as shown in Fig. 5c. When the [H2SO4]
further decreased, the number of overshoots increased, as
shown in Fig. 5d. Finally, the overshoots and the sustained os-
cillations mixed completely at [H2SO4] < 0.65 M, as shown in
−
consumption of BrO3 , since the reaction between gluconic
acid and bromate was more difficult than that of glucose.
−
When the [BrO3 ]/[Glu] ratio increased further, glucose was
−
immediately oxidized by BrO3 , which could account for the
−
disappearance of the overshoot. At a very high [BrO3 ]/[Glu]
ratio, type-ꢁ oscillations appeared following type-ꢀ oscilla-
tions, which can be possibly attributed to the Mn2+-catalyzed
bromate–arabinonic acid reaction, since a deeper oxidative
degradation product, erythrose, was detected after the reac-
tions. This was confirmed by the fact that similar oscillations
were observed by using arabinonic acid instead of glucose in

H. Li et al.
Bull. Chem. Soc. Jpn., 74, No. 10 (2001) 1821
different intermediates of glucose during its oxidative degrada-
tion by acidic bromate: (1) the overshoots resulted from the
Mn2+-catalyzed acidic bromate–glucose reaction; (2) the type-
ꢀ oscillations resulted from the Mn2+-catalyzed acidic bro-
mate–gluconic acid reaction; (3) the type-ꢁ oscillations result-
ed from the Mn2+-catalyzed acidic bromate-arabinonic acid re-
−
action. The effect of the [BrO3 ]/[Glu] ratio on the oscillatory
patterns could be interpreted in terms of its effect on the depth
of oxidative degradation of glucose, which resulted in different
intermediates. However, the effect of [H2SO4] on the oscillato-
ry patterns could be interpreted in terms of its effect on the ox-
idizing ability of bromate, which resulted in the different rates
of the reactions between bromate and glucose and its corre-
sponding oxidative products.
This work was supported by the National Natural Science
Foundation of China (29973025) and Shanghai Natural Sci-
ence Foundation (98QMAI1402).
Fig. 5. Dependence of the oscillatory patterns on [H2SO4]0.
(a) [H2SO4]0 = 1.18 M, (b) [H2SO4]0 = 1.0 M, (c)
[H2SO4]0 = 0.792 M, (d) [H2SO4]0 = 0.72 M, (e) [H2SO4]0
= 0.54 M. Other reaction conditions: [BrO3−]0 = 0.010
M, [Glu]0 = 0.050 M, [Mn2+] = 0.040 M, V = 50 mL, T
= 30 0.2 °C.
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Conclusions
The Mn2+-catalyzed acidic bromate-glucose reaction exhib-
ited radical-controlled oscillations which could be distin-
guished from the bromide-controlled oscillations in the pres-
ence of acetone, an effective brominating agent. Even in the
absence of acetone, the above-mentioned system exhibited the
following three types of oscillations owing to the formation of
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