Kinetic study of the Ce(III)-, Mn(II)- or Fe(phen)32+-catalyzed Belousov-Zhabotinsky reaction with 2-ketoglutaric acid

Article abstract of DOI:10.1002/1097-4601(200102)33:2<101::AID-KIN1001>3.0.CO;2-9

The Belousov-Zhabotinsky (BZ) reaction of bromate ion with 2-ketoglutaric acid (KGA) in aqueous sulfuric acid catalyzed by Ce(III), Mn(II), or Fe(phen)₃²⁺ ion exhibits sustained barely damped oscillations under aerobic conditions. In general, the reaction oscillates without an induction period. Fe(phen)₃²⁺ ion behaves differently from Ce(III) and Mn(II) ions in catalyzing this oscillating system. The gem-diol form of KGA exhibits different behavior from that of the keto form of KGA in the BZ reaction. The kinetics and mechanism of the reaction of KGA with Ce(IV), Mn(III), or Fe(phen)₃³⁺ ion was investigated. The order of relative reactivities of metal ions toward reaction with KGA is Mn(III)>Ce(IV)?Fe(phen)₃³⁺. Experimental results are rationalized.

Full text of DOI:10.1002/1097-4601(200102)33:2<101::AID-KIN1001>3.0.CO;2-9

Kinetic Study of the Ce(III)-,
2؉
Mn(II)- or Fe(phen)3 -
Catalyzed Belousov-
Zhabotinsky Reaction with
2-Ketoglutaric Acid
REAY-FUN TSAI, JING-JER JWO*
Department of Chemistry, National Cheng Kung University, Tainan, Taiwan 701, Republic of China
Received 22 February 2000; accepted 10 August 2000
ABSTRACT: The Belousov-Zhabotinsky (BZ) reaction of bromate ion with 2-ketoglutaric acid
2ϩ
(KGA) in aqueous sulfuric acid catalyzed by Ce(III), Mn(II), or Fe(phen)3 ion exhibits sus-
tained barely damped oscillations under aerobic conditions. In general, the reaction oscillates
2ϩ
without an induction period. Fe(phen)3 ion behaves differently from Ce(III) and Mn(II) ions
in catalyzing this oscillating system. The gem-diol form of KGA exhibits different behavior from
that of the keto form of KGA in the BZ reaction. The kinetics and mechanism of the reaction
of KGA with Ce(IV), Mn(III), or Fe(phen)3 ϩ ion was investigated. The order of relative reactiv-
3
3
ities of metal ions toward reaction with KGA is Mn(III) Ͼ Ce(IV) ϾϾ Fe(phen)3 ϩ. Experimental
results are rationalized. ᭧ 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 101–107, 2001
INTRODUCTION
action catalyzed by 2-ketoglutarate dehydrogenase
complex to form succinyl-CoA and CO2 . In 1950, Be-
lousov [1] studied the model catalysis in the Krebs
cycle using cerium ion instead of the protein-bound
metal ions and discovered the cerium-ion-catalyzed
bromate ion–citric acid or malonic acid oscillation re-
action. Similar oscillations were observed by Zhabo-
tinsky [2] when the malonic acid was replaced by an-
other organic substrate with an active methylene
hydrogen atom or when the Ce(IV)/Ce(III) couple was
replaced by the Mn(III)/Mn(II) couple or by the
It is well known that the catabolic pathways converge
in stage III toward the Krebs citric acid cycle (tricar-
boxylic acid cycle) where most energy-yielding nutri-
ents are ultimately oxidized to carbon dioxide. 2-Ke-
toglutaric acid is an important metabolite in the Krebs
cycle and is a substrate (or product) of several enzy-
matic reactions. In the Krebs cycle, isocitrate is de-
hydrogenated to 2-ketoglutarate and CO2 by NAD- or
NADP-linked isocitrate dehydrogenase, which re-
quires Mg(II) or Mn(II) ion. In the next step, 2-keto-
glutarate undergoes oxidative decarboxylation re-
ϩ/2ϩ
Fe(phen)33
couple. The Belousov-Zhabotinsky
(BZ) reaction has attracted much attention and has
been studied most thoroughly. The first detailed mech-
anism of the Ce(III)-catalyzed BZ reaction with ma-
lonic acid was elucidated by Field, Ko¨ro¨s, and Noyes
(FKN) [3]. Gyo¨rgyi, Tura´nyi, and Field (GTF) pre-
sented a detailed mechanism of the complete organic
and inorganic chemistry of the BZ reaction with ma-
Correspondence to: J-J Jwo (jjjwo@mail.ncku.edu.tw)
Contract grant sponsor: National Science Council of the Repub-
lic of China
Contract grant number: NSC85-2113-M-006-011, NSC8-2113-
M-006-011, and NSC87-2113-M-006-011
᭧ 2001 John Wiley & Sons, Inc.

102
TSAI AND JWO
lonic acid, which is strongly supported by the mod-
eling computations [4]. In previous articles, we studied
the BZ reactions with saccharides, mixed organic acid/
ketone substrate, and malonic acid and its derivatives
(methyl-, ethyl-, butyl-, phenyl-, and dibromomalonic
d is about half of the time needed to reach the maxi-
mum absorbance.
NMR Spectra. The 1H NMR spectra of KGA,
NaKGA, and Na2KGA obtained using a Bruker AC-
200 FT-NMR is shown in Figure 1. The spectrum of
KGA in acetone-d6 shows a slightly distorted A2B2
multiplet for the ␤-CH2-group (3.11–3.18 ppm) and
the ␥-CH2-group (2.58–2.68 ppm) of the nonhydrated
keto-KGA (Fig. 1A). The spectrum of KGA in D2O
and D2O containing 1 M D2SO4 shows both the con-
siderably distorted A2B2 multiplet of the nonhydrated
keto-KGA and the cyclic-KGA (lactol) (a broad peak
at 2.97 ppm for ␤-CH2-group and a multiplet at 2.62–
2.69 ppm for ␥-CH2-group) and the undistorted A2B2
multiplet of the hydrated gem-diol-KGA (2.05–2.12
ppm for ␤-CH2-group and 2.37–2.45 ppm for ␥-CH2-
group) (Fig. 1, B–D). These results are consistent with
those reported by Redfield et al. [14]. The multiplet
for the ␤-CH2-group (2.93–2.99 ppm) in the spectrum
of NaKGA in D2O shows significant distortion and
lack of detail in contrast to that for the ␥-CH2-group
(2.62–2.69 ppm) (Fig. 1E). Similar to the spectrum of
KGA in acetone-d6 (Fig. 1A), the spectrum of
Na2KGA in D2O shows a slightly distorted A2B2 mul-
tiplet of the nonhydrated keto-KGA (2.89–3.10 ppm
for the ␤-CH2-group and 2.38–2.50 ppm for the ␥-
CH2-group) (Fig. 1F).
acids) catalyzed by Ce(III), Mn(II), or Fe(phen)3 ϩ ion
2
[5–10]. In this article, we demonstrate that the Ce(III)-,
Mn(II)-, or Fe(phen)3 ϩ-catalyzed bromate ion-2-
2
ketoglutaric acid reaction in aqueous sulfuric acid ex-
hibits oscillations in bromide ion concentration. The
kinetics and mechanism of the reactions of 2-ketoglu-
3ϩ
taric acid with Ce(IV), Mn(III), and Fe(phen)3 ion
are investigated. The experimental results are ration-
alized.
EXPERIMENTAL
Materials
2- or ␣-Ketoglutaric acid (KGA, Lancaster), 2-keto-
glutaric acid monosodium salt (NaKGA, Sigma), 2-
ketoglutaric acid disodium salt (Na2KGA, Sigma), am-
monium ceric nitrate (Hanawa), cerium(III) nitrate
hexahydrate (Riedel de Hae¨n), manganese(II) acetate
tetrahydrate (Merck), ammonium ferrous sulfate
(Merck), and 1, 10-phenanthroline (Ishizu) were used
in this work. Other reagents used were of the highest
grade chemicals commercially available. Solutions of
ferroin (Fe(phen)3 ϩ) and ferriin (Fe(phen)3 ϩ) ions
were freshly prepared as described elsewhere
[7,11,12]. Deionized water from reverse osmosis (Mil-
lipore Milli-RO 20) was used.
2
3
Procedures
Kinetic Experiment. The potentiometric traces of the
BZ reaction were recorded by following the reaction
with a bromide ion selective electrode (Orion 94-35)
against a double junction reference electrode (Orion
90-02) [13]. The kinetics of the oxidation reactions of
2-ketoglutaric acid (KGA) by Ce(IV), Mn(III), and
Fe(phen)3 ϩ ions were studied spectrophotometrically
3
by following [Ce(IV)], [Mn(III)], and [Fe(phen)3 ϩ] at
3
1
1
360 nm (␧ ϭ 3.18 ϫ 103 MϪ cmϪ ), 310 nm (␧ ϭ
1.31 ϫ 103 MϪ cmϪ ), and 500 nm (ϭ 1.10 ϫ 104
1
1
MϪ cmϪ ), respectively, with either a stopped-flow
spectrophotometer (Photol RA-401) or a conventional
spectrophotometer (Hitachi U-2000). The pseudo-
first-order rate constant (kobs) was calculated from
the linear least-squares (LLS) fit of the plot of
ln(At Ϫ Aϱ) vs. time for the Ce(IV)- and Mn(III)-KGA
1
1
Figure 1 1H NMR spectra. (A) KGA in acetone-d6;
(B) KGA in D2O; (C) KGA in 1 M D2SO4/D2O (Ͻ30 min);
(D) KGA in 1 M D2SO4/D2O (3h); (E) NaKGA in D2O;
(F) Na2KGA in D2O.
reactions or from the plot of ln(Atϩ Ϫ At) vs. time for
d
the Fe(phen)3 ϩ-KGA reaction, where the time interval
3

KINETIC STUDY OF THE BELOUSOV-ZHABOTINSKY REACTION WITH 2-KETOGLUTARIC ACID
103
RESULTS AND DISCUSSION
indicates that these reactions follow a second-order ki-
netics (Figs. 4 and 5). The values of the second-order
rate constant (kЈ ϭ kobs/[KGA]0) obtained at various
temperatures are shown in Table I. For the Mn(III)-
The BZ Reaction with 2-Ketoglutaric Acid
Under stirred aerobic conditions, the reaction of bro-
mate ion with 2-ketoglutaric acid (KGA) in aqueous
sulfuric acid catalyzed by Ce(III), Mn(II), or
KGA reaction, the plot of kobs 1 vs. [KGA]0 1 is linear
(Fig. 6). As shown below (Eq.(1)), kobs can be ex-
pressed as kobs ϭ k[KGA]t /(1 ϩ Km[KGA]t). The val-
ues of k and Km obtained from the LLS fits of the plot
Ϫ
Ϫ
2ϩ
Fe(phen)3 ion exhibits sustained barely damped os-
cillations in bromide ion concentration. Typical oscil-
latory responses of the bromide ion selective electrode
are shown in Figure 2 (A–C). In general, the reaction
oscillates without an induction period. The frequency
of oscillations follows the sequence of Mn(II)
Ϫ
1
Ϫ1
of kobs vs. [KGA]0 at various temperatures are
given in Table I. The apparent activation energies cal-
culated from the LLS fits of the Arrhenius plots are
also given in Table I. The order of relative reactivities
of metal ions toward reaction with KGA is
2
ϩ
system Ͼ Ce(III) system Ͼ Fe(phen)3 system. Fig-
ures 2D–F show the oscillatory patterns under anaer-
obic conditions (deaerated with N2). For the Mn(II)-
or Ce(III)-catalyzed system, the oscillating reaction is
catalyzed by the presence of oxygen molecules, and
the oscillatory behavior depends on the degree of
deaeration of the solution with nitrogen gas (Figs. 2E
and 2F). In contrast, under anaerobic conditions the
3
Mn(III) Ͼ Ce(IV) ϾϾ Fe(phen)3 ϩ. The mechanism
proposed to explain these kinetic results is shown in
ϩ
1)
Scheme I. If initially [KGA]0 ϾϾ [M(n ϩ]0 , the rate
law (Eq. (1)) can be derived by applying the steady-
state approximation to three metal-ion complexes.
k1
k-KGA ϩ H2O E
R
F d-KGA
K1
K2
(M1)
(M2)
kϪ
1
Fe(phen)3 ϩ-catalyzed system exhibits a higher fre-
2
quency of oscillations (Fig. 2D). The concentration of
sulfuric acid, which is 0.6–1.2 M for the Ce-(III)- and
Mn(II)-catalyzed systems and 0.3–0.6 M for the
c-KGA ϩ H2O EF k-KGA
k3
ϩ
1)
ϩ
ϩ
ϩ
ϩ
1)ϩ
M(n
M(n
M(n
ϩ k-KGA E
R
F [M(n
k-KGA] (M3)
d-KGA] (M4)
Fe(phen)3 ϩ-catalyzed system, also plays an important
2
kϪ
3
role in generating the oscillations. As shown in Figures
2G and 2H, the Ce(III)-catalyzed system using
NaKGA or Na2KGA initially instead of KGA exhibits
an oscillating pattern quite similar to that of the KGA
system except that it exhibits an induction period and
a smaller amplitude of oscillations during the initial
stage of reaction.
k4
ϩ d-KGA ER
F [M(n
kϪ
4
ϩ
1)
ϩ
1)ϩ
k5
ϩ
1)
ϩ
1)ϩ
ϩ c-KGA E
R
F [M(n
c-KGA] (M5)
kϪ
5
k3Ј
ϩ
ϩ
ϩ
1)
ϩ
ϩ
ϩ
ϩ
[M(n
[M(n
[M(n
k-KGA] 99
: Mn ϩ R1 ϩ CO2 ϩ H
(M6)
(M7)
k4Ј
Kinetics and Mechanism
d-KGA] 99
: Mn ϩ R2 ϩ CO2 ϩ H
1)
ϩ
ϩ
The stopped-flow technique was applied to study the
kinetics of the Mn(III)-KGA reaction. The kinetics of
k5Ј
1)
ϩ
ϩ
ϩ
c-KGA] 99
: Mn ϩ R3 ϩ CO2 ϩ H
(M8)
(M9)
the Ce(IV)-KGA and Fe(phen)3 ϩ-KGA reactions
3
ϩ
1)ϩ
ϩ
ϩ
M(n
ϩ R1 ϩ H2O !: Mn ϩ SA ϩ H
were studied by using a conventional spectrophoto-
metric method. Typical plots of ln(At Ϫ Aϱ) or
ϩ
1)
ϩ
ϩ
ϩ
M(n
ϩ R2 !: Mn ϩ SA ϩ H
(M10)
(M11)
ln(Atϩ Ϫ At) vs. time are shown in Figure 3. For the
d
M(n
ϩ R3 ϩ H2O !: Mn ϩ SA ϩ H
ϩ
1)
ϩ
ϩ
ϩ
Ce(IV)-KGA reaction, the value of the observed
pseudo-first-order rate constant (kobs) measured under
aerobic conditions is not significantly different from
that measured under deaerated conditions. Under sim-
ilar reaction conditions, no significant effect on the
value of kobs is observed if using NaKGA or Na2KGA
initially instead of KGA. The kinetics of the
ϩ
1)
ϩ
3ϩ
M(n
:Ce(IV), Mn(III), or Fe(phen)3 ;
k-KGA ϭ keto-KGA; d-KGA ϭ gem-diol-KGA;
c-KGA ϭ cyclic-KGA;
R1 ϭ ·COCH2CH2CO2H;
R2 ϭ ·C(OH)2CH2CH2CO2H;
Fe(phen)3 ϩ-KGA reaction was studied under deaer-
3
;
R3 ϭ
OH
ated conditions since it was observed that oxygen mol-
ecules exhibited an inhibitory effect on the reaction
rate. For both the Ce(IV)-KGA and Mn(III)-KGA re-
actions, the plot of kobs vs. [KGA]0 is linear, which
O
O
SA ϭ HO2CCH2CH2CO2H
Scheme I

104
TSAI AND JWO
Ϫ
Figure 2 Potentiometric traces oflog[Br ] vs. time for the oscillating reaction of bromate ion and 2-ketoglutaric acid catalyzed
2
ϩ
Ϫ
Ϫ
by Ce(III), Mn(II), or Fe(phen)3 ion at 25ЊC. (A): [Ce(III)]0 ϭ 1.00 ϫ 10 3 M, [BrO3 ]0 ϭ 0.020 M, [KGA]0 ϭ 0.170 M,
Ϫ
3
Ϫ
[H2SO4]0 ϭ 0.800 M; (B): [Mn(II)]0 ϭ 1.00 ϫ 10 M, [BrO3 ]0 ϭ 0.020 M, [KGA]0 ϭ 0.170 M, [H2SO4]0 ϭ 1.00 M; (C):
[Fe(phen)3 ]0 ϭ 1.00 ϫ 10 3 M, [BrO3 ]0 ϭ 0.020 M, [KGA]0 ϭ 0.075 M, [H2SO4]0 ϭ 0.400 M; (D): (C) deaerated with N2
gas; (E): (B) deaerated with N2 gas; (F): (A) deaerated with N2 gas; (G): [Ce(III)]0 ϭ 1.00 ϫ 10 M, [BrO3 ]0 ϭ 0.015 M,
[NaKGA]0 ϭ 0.180 M, [H2SO4]0 ϭ 1.00 M; (H): [Ce(III)]0 ϭ 1.00 ϫ 10 3 M, [BrO3 ]0 ϭ 0.015 M, [Na2KGA]0 ϭ 0.180 M,
2
ϩ
Ϫ
Ϫ
Ϫ
3
Ϫ
Ϫ
Ϫ
[H2SO4]0 ϭ 1.00 M.
ϩ
1)
ϩ1)
Ϫd[M(n ϩ]/dt ϭ k[KGA]t [M(n ϩ]t/
Km3 ϭ k3/(kϪ ϩ kЈ3)
3
ϩ1)ϩ
(1 ϩ Km [KGA]t) ϭ kobs [M(n
]
t
(1)
Km4 ϭ k4/(kϪ ϩ kЈ4)
4
Km5 ϭ k5/(kϪ ϩ kЈ5)
5
ϩ
1)
In Eq. (1), [M(n ϩ]t is the total concentration of
K1 ϭ [diol-KGA]/[keto-KGA]
K2 ϭ [keto-KGA]/[cyclic-KGA]
kobs ϭ k[KGA]t/(1 ϩ Km [KGA]t)
ϩ1)ϩ
M(n
species, [KGA]t is the total concentration of
KGA species,
k ϭ (kЈ3 Km3 K2 ϩ k4Ј Km4 K1 K2 ϩ kЈ5 Km5)/
This rate equation (Eq. (1)) is similar to the Michae-
lis–Menten-like kinetics as suggested by Kasperek
and Bruice [15]. The kinetics of the Mn(III)-KGA re-
action is consistent with Eq. (1). However, under the
(1 ϩ K2 ϩ K1 K2)
Km ϭ (Km3 K2 ϩ Km4 K1 K2 ϩ Km5)/
(1 ϩ K2 ϩ K1 K2)

KINETIC STUDY OF THE BELOUSOV-ZHABOTINSKY REACTION WITH 2-KETOGLUTARIC ACID
105
Figure 4 Plots of kobs vs. [KGA]0 for the Ce(IV)-KGA re-
Figure 3 Plots of In(At Ϫ Aϱ) (A, B) or In(Atϩ Ϫ At)
d
Ϫ
action at various temperatures. [Ce(IV)]0 ϭ 3.00 ϫ 10 4 M,
(C) vs. time for the Ce(IV)-KGA (A), Mn(III)-KGA (B),
[H2SO4] ϭ 1.00 M, 360 nm. (A): 15ЊC, (B): 18ЊC, (C): 20ЊC,
(D): 23ЊC, (E), 25ЊC.
3ϩ
and Fe(phen)3 -KGA (C) reactions in 1 M H2SO4. (A):
Ϫ
Ϫ
[Ce(IV)]0 ϭ 3.00 ϫ 10 4 M, [KGA]0 ϭ 3.00 ϫ 10 3 M, 20ЊC,
360 nm; (B): [Mn(III)]0 ϭ 5.00 ϫ 10 4 M, [KGA]0 ϭ 0.0100
M, 25ЊC, 310 nm; (C): [Fe(phen)3 ]0 ϭ 1.50 ϫ 10 M,
[KGA]0 ϭ 0.0240 M, 25ЊC, 500 nm, deaerated with N2 gas.
Ϫ
3
ϩ
Ϫ4
present reaction conditions, this reaction is quite in-
sensitive to the change in [KGA] due to the relatively
large value of Km (Table I). On the other hand, if the
value of Km is small, then at sufficiently low [KGA]
(Km [KGA]t ϽϽ 1), kobs reduces to kobs ϭ k [KGA]t
and a second-order kinetics is obtained, as observed
3
in the Ce(IV)-KGA and Fe(phen)3 ϩ-KGA reactions.
Discussion
It is well known that ␣-keto acids (XCH2COCO2H)
are of major importance in intermediary metabolism.
If the X group in XCH2COCO2H is a simple aliphatic
group or is linked through one or more methylene
groups (e.g., as in KGA), the enol form is quantita-
tively unimportant in neutral or acidic solutions [16].
Most ␣-keto acids in aqueous solution exist in
equilibrium with the hydrate (gem-diol) form (as in
step (M1)). The position of equilibrium favors the
nonhydrated keto form at neutral pH, whereas at
low pH values (below the pKa value of the ␣-car-
boxylic acid group) the hydrate form predominates.
3
ϩ
Figure 5 Plots of kobs vs. [KGA]0 for the Fe(phen)3 -KGA
3
ϩ
reaction at various temperatures. [Fe(phen)3 ]0 ϭ 1.50 ϫ
10 4 M, [H2SO4] ϭ 1.00 M, 500 nm, deaerated with N2 gas.
(A): 15ЊC, (B): 17ЊC, (C): 20ЊC, (D): 23ЊC, (E): 25ЊC.
Ϫ

106
TSAI AND JWO
Table I Rate Constants and Apparent Activation Energies of the Reactions of 2-Ketoglutaric Acid with Ce(IV),
Mn(III), and Fe(phen)33ϩ Ions
ϩ
Fe(phen)33 –KGA
Ce(IV)–KGA Reaction
Reaction
Ϫ
Ϫ1
Ϫ
Ϫ1
T/ЊC
kЈ/M 1 s
T/ЊC
kЈ/M 1 s
15
18
20
23
25
2.76
3.85
4.46
5.37
6.59
15
17
20
23
25
1.20
1.42
1.66
1.97
2.16
Ϫ1
Ea/kJ mol
59.3 Ϯ 3.7
41.2 Ϯ 1.9
Mn(III)–KGA Reaction
Ϫ
Ϫ1
Ϫ1
T/ЊC
k/M 1 s
Km/M
15
20
23
25
28
89.6
110
174
164
163
340
222
265
184
115
Ϫ1
Ea/kJ mol
38.0 Ϯ 10.9
A third equilibrium form (cyclic-KGA or lactol) was
observed for KGA in contrast to 2-ketoadipic acid
(HO2CCH2CH2CH2COCO2H). As reported by Fisher
et al. [17], the cyclic-KGA L keto-KGA interconver-
sion (step (M2)) is extremely rapid, which leads to the
broad peak for ␤-CH2-group shown in Figure 1B–D.
The cyclic-KGA L gem-diol-KGA interconversion is
very slow in the NMR time scale. The rate constants
of solvent-catalyzed hydration (k1) and dehydration
1
1
(kϪ ) of KGA at 25ЊC are 0.34 sϪ and 0.19 sϪ ,
1
respectively [18]. Furthermore, the equilibria of
steps (M1) and (M2) can be maintained under
the present reaction conditions, since [KGA]0 ϾϾ
[M(n ϩ]0 . The enol form of KGA is negligible and
the keto-KGA L enol-KGA interconversion is very
slow. No deuteration of the ␤-carbon atom was ob-
served in 1 M DCI after one day at 25ЊC, and enoli-
zation of keto-KGA appeared to be base-catalyzed but
not acid-catalyzed [14]. However, the results in Fig-
ures 1C and 1D indicate that the rate of isotope ex-
change (or bromination) reaction of the gem-diol-
KGA is faster than that of the keto- or cyclic-KGA.
The appearance of the induction in the Ce(III)-cata-
lyzed BZ reaction with NaKGA or Na2KGA (Figs. 2G
and 2H) supports this argument, since initially the
amount of the hydrate form in NaKGA or Na2KGA
solution is less than that in KGA solution. As reported
by Fisher et al. [17], the keto form of 2-ketoglutarate
is the substrate for the enzyme, bovine liver glutamate
dehydrogenase, and the gem-diol form is not, which
becomes a substrate only after nonenzymatic conver-
sion to the keto form. In this work, we demonstrate
that gem-diol-KGA exhibits different behavior from
keto-KGA in the BZ reaction. The presence of gem-
diol-KGA shortens the induction period and increases
ϩ
1)
Ϫ
Ϫ
Figure 6 Plots of kobs 1 vs. [KGA]0 1 for the Mn(III)-KGA
Ϫ
4
reaction at various temperatures. Mn(III)]0 ϭ 5.00 ϫ 10
M, [H2SO4] ϭ 1.00 M, 310 nm. (A): 15ЊC, (B): 20ЊC, (C):
23ЊC, (D): 25ЊC, (E): 28ЊC.

KINETIC STUDY OF THE BELOUSOV-ZHABOTINSKY REACTION WITH 2-KETOGLUTARIC ACID
107
We thank the National Science Council of the Republic of
China for the financial support of this work (NSC85-2113-
M-006-011, NSC86—2113-M-006-011, and NSC87-2113-
M-006-011).
the amplitude of oscillations during the initial stage of
the Ce(III)-catalyzed BZ reaction with KGA. How-
ever, we are not in a position to differentiate the reac-
tivities between keto-KGA and gem-diol-KGA toward
3ϩ
reaction with Ce(IV), Mn(III), and Fe(phen)3 ions
by using the present kinetic results. Similar to the BZ
BIBLIOGRAPHY
reaction with malonic acids [7,9,10], Fe(phen)3 ϩ ion
2
behaves differently from Ce(III) or Mn(II) ion as a
catalyst for the BZ reaction with KGA. This result also
can be rationalized by invoking the different reactivity
1. Belousov, B. P. SbRef Radiat Med Moscow 1959, 145.
2. Zhabotinsky, A. M. Dokl Akad Nauk SSSR 1964, 157,
392.
3. Field, R. J.; Ko¨ro¨s, E. Noyes, R. M. J Am Chem Soc
1972, 94, 8649.
3ϩ/2ϩ
of the Fe(phen)3
couple from the Ce(IV)/Ce(III)
or Mn(III)/Mn(II) couple toward reaction with KGA
Ϫ
and with bromine species (BrO3 , HBrO2 , DBrO2 ,
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SUMMARY
In a stirred batch experiment, the reaction of bromate
ion with 2-ketoglutaric acid (KGA) in aqueous sulfuric
2ϩ
acid catalyzed by Ce(III), Mn(II), or Fe(phen)3 ion
exhibits sustained barely damped oscillations under
aerobic conditions. In general, the reaction oscillates
without an induction period. The presence of oxygen
molecules catalyzed the oscillations in the Ce(III)-
or Mn(II)-catalyzed BZ system. In contrast, the
Fe(phen)3 ϩ-catalyzed system exhibits a higher fre-
2
quency of oscillations under anaerobic conditions than
under aerobic conditions. Fe(phen)3 ϩ ion behaves dif-
ferently from Ce(III) and Mn(II) ions in catalyzing this
oscillating system. The order of relative reactivities of
the metal ions toward reaction with KGA is
2
19. Ke´ki, S.; Magyar, I.; Beck, M. T.; Ga´spa´r, V. J Phys
Chem 1992, 96, 1725.
3
ϩ
Mn(III) Ͼ Ce(IV) ϾϾ Fe(phen)3
.