effect of different counterions of the manganese salt as catalyst on the kinetics of...

Effect of DifferentCounterions of theManganese Salt as Catalyston the Kinetics ofResorcinol-Based Belousov–Zhabotinsky ReactionNADEEM B. GANAIE, GHULAM M. PEERZADA, ISHFAQ A. SHAH

Post Graduate Department of Chemistry, University of Kashmir, Srinagar 190 006, India

Received 31 January 2012; revised 27 October 2012; accepted 8 November 2012

DOI 10.1002/kin.20769Published online in Wiley Online Library (wileyonlinelibrary.com).

ABSTRACT: Kinetic studies on the Belousov–Zhabotinsky (BZ) system with various metal ionsas catalysts have been carried out for a long time, but the effect of counteranions associatedwith the metal ion solution used as the catalyst in the BZ reaction has not been explored.Thus, we have chosen some metal salts as catalysts having the metal ion (Mnn+) but withvarious anions to study the role of different anionic moieties of catalyst on the oscillatorybehavior of the resorcinol-based BZ reaction system. It is found that organic-type anionicmoieties marginalize the role of organic substrates in the reaction system. On the other hand,the inorganic counterions of the catalyst show salting out effects, thereby increasing the ionicstrength, which affects the mobility (diffusion) of the ions in our system performed under batchconditions. C© 2012 Wiley Periodicals, Inc. Int J Chem Kinet 1–12, 2012

INTRODUCTION

The Belousov–Zhabotinsky (BZ) reaction [1–5] isan extensively well-studied oscillating chemical re-action. It includes different chemical systems, all of

Correspondence to: Nadeem B. Ganaie; e-mail: [email protected]. Ghulam M. Peerzada; e-mail: [email protected].

Contract grant sponsor: CSIR, New Delhi, India.Contract grant sponsor: UGC, New Delhi, India.

C© 2012 Wiley Periodicals, Inc.

which contain the bromate ion and an organic sub-strate in strongly acidic solution and have two majorclasses such as catalyzed and uncatalyzed. The cat-alyzed system contains the metal ion as the catalystand an aliphatic organic substrate, which is oxidizedand brominated by the bromate ion as the metal ioncycles between two oxidation states, such as Ce(IV)and Ce(III). The uncatalyzed system contains more re-active aromatic compound (mainly phenol and anilinederivatives) without any metal ion. However, the sourceof the redox potential oscillations is not very clear inuncatalyzed systems.

2 GANAIE, PEERZADA, AND SHAH

The catalyzed BZ reactions comprising Mn2+ [6],Ce3+ [7], Fe(phen)3

2+ [8], or Ru (bipy)32+ [9,10] as

catalysts have been studied extensively. Ferroin, origi-nally used by Belousov as a redox indicator to enhancethe color changes in the cerium-catalyzed system, wasused by Zhabotinsky as the catalyst. By contrast, theoscillating chemical reaction catalyzed by the macro-cyclic complex of Cu(II) and Ni(II) involving lacticacid, malonic acid, and pyruvic acid has been rarelyreported in the literature [11–17]. Generally, the bro-mide ion acts as a control intermediate switching thesystem between an oxidized and a reduced state, corre-sponding to low and high bromide ion concentrations,respectively. The basic mechanism of the oscillations isnow well established by Field, Koros, and Noyes [18](FKN mechanism), in which Br– ions play the role ofa control intermediate [19]. Some of the key reactionsof the detailed and systematic FKN mechanism, whichare necessary for oscillations to occur, are depicted asunder

2H+ + BrO−3 + Br− ↔ HBrO2 + HOBr (1)

HBrO2 + HBrO2 ↔ HOBr + BrO−3 + H+ (2)

HOBr + Br− + H+ ↔ Br2 + H2O (3)

Br− + HBrO2 + H+ ↔ 2HOBr (4)

HBrO2 + BrO−3 + H+ ↔ Br2O4 + H2O (5)

Br2O4 ↔ 2BrO2 (6)

Mn+ + BrO2 + H+ ↔ M(n+1)+ + HBrO2 (7)

The FKN mechanism is the outcome of an extensivestudy performed on the thermodynamics and kineticsof the basic quasi-elementary reaction steps involved inthe BZ reaction. However, the role of counterion moi-ety associated with the metal salt as the catalyst is notreported extensively in the literature, although Lee andJwo [20] studied the behavior of [Mn2+]/[Mn3+] us-ing a combination of Ce4+ and Mn(CH3COO)2. Also,the complex behavior of Fe2+ and Ru2+ with differentligands such as pyridine, bipyridine, and phenanthro-line and batho(SO3)2 with Fe2+ was monitored to un-derstand the effect of complexation on the oscillatorycharacteristics [21].

The motive of the present investigation is to studythe effect of different counterions of organic as wellas of inorganic nature associated with manganese ionsolution as the catalyst on the oscillatory characteris-tics of the resorcinol-based BZ system in 1.3 mol L−1

sulfuric acid as aqueous acid medium.

EXPERIMENTAL

Materials

The reagents used were resorcinol (Himedia Laborato-ries, Mumbai, India; AR), potassium bromate (Merck,Mumbai, India; LR), manganese(II)sulfate monohy-drate (Aldrich, St. Louis, MO, USA; AR), sulfu-ric acid (Merck; LR), manganese(II)acetate (Aldrich;AR), manganese(II)carbonate (Qualigens/Fischer Sci-entific, Mumbai, India; LR), manganese(III) ac-etate dihydrate (Aldrich; AR), manganese(II) bro-mide (Aldrich; AR), manganese(II) sulfide (Aldrich;AR), manganese(II) chloride tetrahydrate (ThomasBaker, Mumbai, India; AR), manganese(II) for-mate (Aldrich; AR), manganese(II) nitrate tetrahy-drate (Aldrich; AR), manganese(II) phthalocya-nine (Aldrich; AR), manganese(III) acetylacetonate(Aldrich; AR), manganese(III) fluoride (Aldrich; AR).All the reagents used were analytical-grade chem-icals with a high degree of purity. The solutionsof the desired chemicals were prepared in 1.3 molL−1 sulfuric acid using deionized double-distilledwater.

Procedure

The reaction system comprising resorcinol, inorganicbromate, and a manganese-based salt as the catalystin 1.3 mol L−1 sulfuric acid solution was kept in thereaction cell into which a platinum electrode was im-mersed as an indicator electrode. The calomel (SCE)reference electrode was kept in another reaction cellcontaining 2.5 × 10−4 mol L−1 solution of potassiumchloride. The two reaction cells (half cells) were con-nected through a salt bridge and then hooked to anOrion 4 star, pH/ISE ion analyzer (Cole Parmer, Mum-bai, India) to observe change in potential (mV) in thereaction system with time (s) at regular intervals of10 s. The two cells were used to avoid the interactionof chloride ion from the SCE with the reaction mix-ture, as the former is a strong competitor for bromideion. The desired thermostatic conditions of the reactionsystem under investigation were maintained using anAdvantec TBS451PA water bath (Cole Parmer) witha precision of ±0.1◦C. All the experiments were per-formed several times under identical conditions to havethe reproducible results.

RESULTS AND DISCUSSION

Ten reaction systems were prepared for comparativestudy of the role of different anionic moieties of themetal salts based on the manganese ion as the cata-lyst. Resorcinol and inorganic bromate were kept at

International Journal of Chemical Kinetics DOI 10.1002/kin.20769

EFFECT OF COUNTERIONS ON BELOUSOV–ZHABOTINSKY REACTION 3

constant concentrations in all the reaction systems. Assuch 10 different manganese salts were chosen, hav-ing different anions (organic/inorganic), and each saltwas used in one reaction system. The reaction systemswere studied at 30 ± 0.1◦C, and 1.3 mol L−1 sulfu-ric acid was used as the medium throughout. In thefirst instance, an attempt was made to choose the metalion for which good trials of the reaction systems weremade with Mn2+, Ce3+, Ce4+, and Fe(phen)3

2+ ionsas catalysts in the form of most stable salts, and it wasobserved that prominent oscillations are apparent withMn2+ ion as compared to the other metal ions [22,23].Thus, Mn2+ ion was chosen as the catalyst and 10 man-ganese salts varying in the nature of anionic moietieswere used later to study the effect of the anionic moi-eties associated with the manganese ion as the catalyston the oscillatory characteristics of the reaction sys-tems. It is worth mentioning that the concentration ofthe manganese ion was kept constant in all the differentmanganese salts used while selecting the concentrationrange of different manganese salts in 10 reaction sys-tems. It is quite pertinent to mention here that stirringwas not suitable for our reaction system because of theoccurrence of precipitation during the progress of thereaction. Thus, the study was performed in an unstirredbatch reactor under closed conditions. It is well knownthat manganese(II) sulfide is easily oxidized in the air,manganese(III) fluoride and manganese(III) acetate areinstantaneously hydrolyzed, formate is oxidized, ph-thalocyanine is recrystalized, and acetylacetonate isalso hydrolyzed after some time once its solution isprepared. The salient features of a chemical oscillatorare described in terms of various parameters such asinduction period (tin), time period (tp), amplitude (A),frequency(v), and number of oscillations (n). Theseparameters are estimated from the oscillatory profiledrawn by plotting potential (mV) versus time (s). Thetime period and amplitude is taken as the average of thetime (s) and potential jump (mV) for six consecutiveoscillations in the profile, respectively. The number ofoscillations (n) is taken as equal to the total number ofperiodic cycles in the oscillatory profile for a particularperiod of time. Similarly, the frequency is calculatedas the reciprocal of time period, whereas the inductionperiod (tin) is taken as the time taken up to the appear-ance of first oscillation after the mixing of bromate(oxidant) to the reaction mixture containing organicsubstrate and catalyst. The results obtained with var-ious anionic moieties of the catalyst are depicted anddiscussed.

Sulfide Ion

Figure 1a gives the potential (mV) versus time (s)plot for the system containing [MnSO4·H2O] = 4 ×

10−3 mol L−1, [BrO3−] = 0.1 mol L−1, [Resorcinol]

= 0.0225 mol L−1 at 30 ± 0.1◦C, wherein some unex-pected results in terms of dual frequency and amplitudefor the oscillations are observed. It is found that aftera definite induction period peculiar to aromatic sub-strates, there is a high-frequency region up to 830 swith time period of about 70 s and amplitude of 90 mVfollowed by a low-frequency region with a decrease inthe amplitude up to 50 mV. Considering this as the ref-erence system and changing the concentration of sul-fide ions, keeping the initial concentrations of the otherreagents constant as presented in Table I, the oscillatoryparameters show an unusual behavior. With an increasein [S2−], the induction period increases with the excep-tion at 0.66 × 10−3 mol L−1. However, there is first adecrease and then an increase in the high-frequencyregion as well as the number of oscillations up to1.00 × 10−3 mol L−1, after which chaotic behavioris observed. It is also observed that there is a gradualdecrease in the number of oscillations as compared tothe reference system, whereas the amplitude first showsan increase for both high- and low-frequency regions atlower [S2−] and then a gradual decrease with increas-ing [S2−]. The effect of sulfide ion as a counterion hasbeen confirmed by inserting 500 μL of CuSO4 solu-tion just after the induction period is over (Fig. 1d),which resulted in the removal of [S2−] as CuS (↓), andhence there is an increase in oscillatory parameters asis found in the reference system. The results obtainedabove are justified on the basis of the fact that man-ganese(II) sulfide dissolved in aqueous sulfuric acidevolves H2S gas and the S2− is a strong competitor forHOBr in acid media as per the FKN mechanism.

S2− + HBrO3 + 2H+ ↔ S(↓) + HBrO2 + H2O (8)

S2− + Cu2+ → CuS(↓) (9)

In addition to the above reaction (8), the S2− will alsoinfluence the kinetics of the reaction steps 1, 3, and 5,of the FKN mechanism as shown above.

Effect of Fluoride

Table II shows the effect of [F−] on the oscillatoryparameters for the resorcinol-based system. The os-cillations start after an induction period (Fig. 2). Itwas observed that with an increase in [F−], there is afirst increase up to 0.04 × 10−3 mol L−1 and then a de-crease and then again an increase after 0.08 × 10−3 molL−1 of [F–] for both the induction period as well ashigh-frequency regions, whereas the time period andthe amplitude show the reverse trend. This ambiguous



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Figure 1 Potential (mV) versus time (s) plots showing the effect of [sulfide] containing [Mn2+] = 4 × 10−3 mol L−1,[BrO3

−] = 0.1 mol L−1, [resorcinol] = 0.0225 mol L−1 at 30 ± 0.1◦C: (a) 0 mol L−1, (b) 0.03 mol L−1, (c) 0.16 mol L−1,(d) 0.16 mol L−1.

Table I Effect of [S2−] on the Oscillatory Parameters of the Systems Containing the [Mn2+] = 4 × 10−3 mol L−1;[BrO3

−] = 0.1 mol L−1, [Resorcinol] = 0.0225 mol L−1 at 30 ± 0.1◦C

Metal Salt [S2−] (× 10−3 Induction High-Frequency Time Period, Amplitude,Composition mol L−1) Period, tin (s) Region (s) tp (s) Number, n A (mV)

MnSO4 2 mL 0 140 830 70, 230 >20 90, 50Mn(II)sulfide 2 mL 1.33 580 Chaotic 90 >15 38MnS 1.5 mL + MnSO4

0.5 mL1.00 350 Chaotic after 900 s 90 >14 70

MnS 1.0 mL + MnSO41.0 mL

0.66 210 800 110, 220 >16 70, 90


0.33 295 600 100, 225 >13 100


0.16 200 740 70, 170 >16 118, 78


0.10 140 800 70, 230 >17 110, 97

behavior can be attributed to the direct role of F– inthe FKN mechanism as well as the increase in the ini-tial [Mn3+]/[Mn2+] ratio due to the added Mn3+ ion.This behavior is also justified since F–ion is more re-active than Cl–and Br–. It is also observed that with

an increase in [F–], the oscillatory parameters moveclose to the reference resorcinol system; this is the rea-son for choosing the lower concentrations of the F− ascounterion. The number of oscillations shows a de-creasing trend with a decrease in [F−].



Table II Effect of [F−] on the Oscillatory Parameters of the Systems Containing the [Mn] = 4 × 10−3 mol L−1;[BrO3


Metal Salt [F−] (× 10−3 Induction High-Frequency Time Period Amplitude,Composition mol L−1) Period, tin (s) Region (s) tp (s) Number, n A (mV)

Mn(III) fluoride 2 mL 1.33 165 800 76.6, 210 >20 52.6, 70Mn(III) fluoride 0.03 mL +

MnSO4 1.97 mL0.02 140 640 96.6, 247.5 >16 61.5, 76.3

Mn(III) fluoride 0.06 mL +MnSO4 1.94 mL

0.04 200 700 60, 245 >16 59, 88.3


0.06 120 450 67.5, 243.3 >19 77.6, 76


0.08 150 600 67.5, 260 >19 63.3, 99.3

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−] =0.1 mol L−1, [resorcinol] = 0.0225 mol L−1 at 30 ± 0.1◦C.

Effect of Nitrate

From Table III, it is found that by increasing [NO3−] in

the reaction system while keeping the concentrationsof other reagents constant, there is a decrease in theinduction period, whereas the time period and ampli-tude of oscillations increase. The number as well asthe frequency in the high region for oscillations re-mains constant for the nitrate containing systems withan overall decrease in the number of oscillations thanthe reference system. This behavior can be attributed tothe combined effect of nitrate and sulfate ions as coun-terion moieties. However, it is observed that the timeperiod of oscillations following the high-frequency re-gion remains constant while changing initial [NO3

−].

Effect of Phthalocyanine

Figure 3 depicts the behavior of oscillations for the sys-tem containing varying [Phthalocyanine] keeping con-

centrations of other reagents constant. Phthalocyanineis an organic substance and shows poor solubility in oursystem under normal conditions and hence the salt wasdissolved by heating the solution. As seen with otherinorganic counterions studied above, the oscillationsstart after an induction period, with no appearance ofdual-frequency regions and amplitudes. The inductionperiod decreases with a decrease in [Phthalocyanine]from 1.33 × 10−3 to 0.16 × 10−3 mol L−1. The saltsolutions used were freshly prepared. However, theinduction period decreases and the number and am-plitude of oscillations show an increase when the saltsolutions were allowed to stand undisturbed for sometime leading to the formation of supernatant liquid,which was eventually used. The increase in oscilla-tory parameters with the supernatant liquid can be dueto the activation of the organic counterion in aqueousacid medium for bromination, by which the limitingbromosubstrate concentration is attained quickly.

Effect of Formate

Table IV shows the effect of [HCOO−] ion on the oscil-latory behavior of our reaction system. It was observedthat with an increase in [HCOO−], the induction perioddecreases, whereas the high-frequency region and timeperiod show first a decrease and then an increase. Thereis also an increase in the number of oscillations with anincrease in [HCOO−], which may be attributed to therole of formate ion as a cosubstrate in the reaction andthus competing with the bromination reaction, therebycausing the limiting concentration to attain rapidly.

Effect of Acetate

Mn3+ salts are unstable in aqueous acid media andget reduced to Mn2+ ion in the solution after sometime. Thus, the salt solutions were freshly prepared forinvestigation. Both Mn2+ and Mn3+ salts of acetate ion



Table III Effect of [NO3−] on the Oscillatory Parameters of the Systems Containing the [Mn2+] = 4 × 10−3 mol L−1;

[BrO3−] = 0.1 mol L−1, [Resorcinol] = 0.0225 mol L−1 at 30 ± 0.1◦C

Metal Salt [NO3−] (× 10−3 Induction High-Frequency Time Period, Amplitude,

Composition mol L−1) Period, tin (s) Region (s) tp (s) Number, n A (mV)

Mn(II) nitrate 2 mL 1.33 180 850 105, 290 >16 80, 92.6Mn(II) nitrate 1 mL +

MnSO4 1 mL0.66 240 850 82.5, 290 >16 63.6, 83

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−] = 0.1 mol L−1, [resorcinol] =0.0225 mol L−1 at 30 ± 0.1◦C: (a) 1.33 mol L−1 (super-natant), (b) 1.33 mol L−1, and (c) 0.16 mol L−1.

were used to compare the oscillatory behaviors withdifferent oxidation states of manganese, keeping the

acetate ion constant. As reported in Table V, oscilla-tions start after an induction period for both the oxida-tion states of manganese. However, using some initial[Mn3+], which causes a decrease in [Mn2+]/[Mn3+],increases the induction period, the number as wellas the high-frequency region for oscillations, whereasthere is a decrease in the amplitude of oscillations. Theexperiment was also performed using the supernatantfluid obtained from the manganese(III) solution keptovernight. This reveals that the oscillatory parametersmove nearer to the Mn2+ system, confirming the insta-bility followed by the reduction to Mn2+ solutions inaqueous acid media.

Effect of Acetylacetonate

Table VI pertains to the effect of [acetylacetonate] ascounterion for the Mn3+ ion. Again, owing to the in-stability of Mn3+ ion in aqueous acid media, freshlyprepared solutions were used. The oscillations startafter an induction period for the systems containing[acetylacetonate] lower than 2.66 × 10−3 mol L−1.

Table IV Effect of [HCOO−] on the Oscillatory Parameters of the Systems Containing the [Mn2+] = 4 × 10−3 molL−1; [BrO3


Metal Salt [HCOO−] (× 10−3 Induction High-Frequency Time Period, Amplitude,Composition mol L−1) Period, tin (s) Region (s) tp (s) Number, n A (mV)

Mn(II) formate 2 mL 1.33 110 1050 77.5, 295 >19 61, 47Mn(II) formate 1 mL +

MnSO4 1 mL0.66 140 740 65, 215 >17 69, 76.3

Mn(II) formate 0.5 mL +MnSO4 1.5 mL

0.33 150 820 80, 235 >17 54.3, 85.6

Table V Effect of [CH3COO−] on the Oscillatory Parameters of the Systems Containing the [Mn] = 4 × 10−3 mol L−1;[BrO3


Metal Salt [CH3COO–](× 10−3 Induction High-Frequency Time Period, Amplitude,Composition mol L−1) Period, tin (s) Region (s) tp (s) Number, n A (mV)

Mn(III) acetate 2 mL (4 days) 1.33 120 500 65, 197.50 >16 83, 88Mn(III) acetate 2 mL (fresh) 1.33 120 600 60, 226 >16 52, 88Mn(II) acetate 2 mL 1.33 150 900 60, 227.50 >20 67.6, 80Mn(III) acetate 2 mL

(supernatant)1.33 170 640 62, 127.50 >19 74, 70



Table VI Effect of [Acetylacetonate] on the Oscillatory Parameters of the Systems Containing the [Mn] = 4 ×10−3 mol L−1; [BrO3


Metal Salt [Acetylacetonate] Induction Time Period, Amplitude,Composition (× 10−3 mol L−1) Period, tin (s) tp (s) Number, n A (mV)

Mn(III) acac 0.004 M, 2 mL 1.33 1000 30 <10 8.75Mn(III) acac 0.008M, 2 mL 2.66 905 ** 1 **Mn(III) acac 0.004 M, 1 mL +

MnSO4 0.004 M, 1 mL0.66 350 100, 270 >19 35

Mn(III) acac 0.004 M, 0.5 mL +MnSO4 0.004 M, 1.5 mL

0.33 180 90,228 >16 50, 80

**, No oscillations seen.

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Figure 4 Potential (mV) versus time (s) plots showing the effect of [acetylacetonate] as counterion using Mn(acac)3 containing[Mn] = 4 × 10−3 mol L−1, [BrO3

−] = 0.1 mol L−1, [resorcinol] = 0.0225 mol L−1 at 30 ± 0.1◦C: (a) 0.33 mol L−1, (b)1.33 mol L−1, (c) 2.66 mol L−1, and (d) 0.66 mol L−1.

The prominent increase in the induction period as com-pared to the reference system is because of delaying thelimiting bromosubstrate concentration, caused by thebromine scavenging effect of acetylacetonate. The in-crease in [acetylacetonate] is responsible for increasedbromine scavenging activity of acetylacetone, markedwith minimal oscillations observed at 1.33 and 2.66× 10−3 mol L−1 (Figs. 4b and 4c) with lesser am-plitude and number of oscillations. However, the de-creasing concentration of acetylacetonate results in the

appearance of dual-frequency regions and amplitude ofoscillations. It is mentioned that some minimal oscil-lations have been observed for the systems containinghigher concentrations of acetylacetonate in the absenceof main substrate, i.e., resorcinol. This is a preludeto the aforesaid statement [22] that organic speciesused as counterions can avoid the use of organic sub-strates in the catalyzed BZ system. However, this is incontradiction to the bromine-scavenging role of acety-lacetonate [24].



Table VII Effect of [CO32−] and Temperature on the Oscillatory Parameters of the Systems Containing the [Mn2+] =

4 × 10−3 mol L−1; [BrO3−] = 0.1 mol L−1; [Resorcinol] = 0.0225 mol L−1

Metal Salt [CO32−] (× 10−3– Induction High-Frequency Time Period, Amplitude,

Composition mol L−1) Period, tin (s) Region (s) tp (s) Number, n A (mV)

MnCO3 30◦C, 2 mL 1.33 150 900 85, 215 >17 84, 100MnCO3 1.5 mL + MnSO4 0.5 mL 1.00 220 2000 88, 430 >18 75, 100MnCO3 1 mL + MnSO4 1 mL 0.66 170 1500 87.5, 366 >16 42.5, 85MnCO3 0.5 mL + MnSO4 1.5 mL 0.33 190 700 95, 300 >15 49.25, 100MnCO3 25◦C 1.33 355 900 90, 230 >12 82MnCO3 35◦C 1.33 100 900 275 >16 77MnCO3 40◦C 1.33 60 900 47.5, 382.5 >18 73

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−] = 0.1 mol L−1, [resorcinol] = 0.0225 mol L−1: (a) 25 ± 0.1◦C, (b) 30 ± 0.1◦C, (c) 35 ± 0.1◦C, and(d) 40 ± 0.1◦C.

Effect of Carbonate

Table VII depicts the behavior of [CO32−] on the oscil-

latory parameters. The oscillations start after an induc-tion period, without showing any regular trend in in-duction and time periods. However, the high-frequencyregions and number of oscillations first increase andthen continuously decrease after 0.66 × 10−3 mol L−1,whereas the amplitude shows a gradual decrease andsubsequent increase. The dissolution of carbonate in

aqueous acid medium is associated with release ofCO2, so freshly prepared solutions were used to pre-vent escape of higher amounts of CO2 to determine theeffect of dissolved CO2 in the reaction system. As weknow that dissolved gases can be removed by eitherstirring or heating, the latter method was chosen forthe reaction containing [MnCO3]0 as 1.33 × 10−3 molL−1, keeping initial concentrations of other reagentsconstant but at different temperatures (Fig. 5). It is



Table VIII Effect of [Cl−] on the Oscillatory Parameters of the Systems Containing the [Mn2+] = 4 × 10−3 mol L−1;[BrO3


Metal Salt [Cl–](× 10−3 Induction High-Frequency Time Period, Amplitude,Composition mol L−1) Period, tin (s) Region (s) tp (s) Number, n A (mV)

MnCl2 2 mL 1.33 ** ** ** ** **MnCl2 0.5 mL+ MnSO4 1.5 mL 0.33 90 ** ** 2 60MnCl2 0.25 mL+ MnSO4 1.75 mL 0.16 1060 1600 90, 230 >11 88, 60MnCl2 0.15 mL+ MnSO4 1.85 mL 0.10 970 ** 85, 200 >16 40


observed that there is a steady increase in the rate ofthe reaction, attributed to a decrease in the inductionperiod. The time period showed very unusual resultsdue to the evolution of CO2 creating an inhomoge-neous behavior. Thus, no regular trend is observed inthe time period, amplitude, and number of oscillations.It is to be noted that the high-frequency region re-mains constant at different temperatures. The presenceof carbonate as well as acetylacetonate as counterionsdecreases the number of oscillations in these reaction

systems as compared to the reference system underinvestigation.

Effect of Chloride

It is known that the presence of chloride ions in thereaction system competes with the bromide-mediatedreaction steps as proposed in the FKN mechanism;therefore there is a decrease in oscillatory parameters.This effect was confirmed by varying [Cl−] used as the

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Figure 6 Potential (mV) versus time (s) plots showing the effect of [chloride] containing [Mn2+] = 4 × 10−3 mol L−1,[BrO3

−] = 0.1 mol L−1, [resorcinol] = 0.0225 mol L−1 at 30 ± 0.1◦C: (a) 1.33 mol L−1, (b) 0.10 mol L−1, (c) 0.33 mol L−1,and (d) 0.16 mol L−1.



Table IX Effect of [Br–] on the Oscillatory Parameters of the Systems Containing the [Mn2+] = 4 × 10−3 mol L−1;[BrO3

–] = 0.1 mol L−1, [Resorcinol] = 0.0225 mol L−1 at 30 ± 0.1◦C

Metal Salt [Br–](× 10−3 Induction High-Frequency Time Period, Amplitude,Composition mol L−1) Period, tin (s) Region (s) tp (s) Number, n A (mV)

MnBr2 2 mL 1.33 1200 ** 93 10 40MnBr2 0.15 mL + MnSO4 1.85 mL 0.10 255 690 50, 160 >21 26, 62.3MnBr2 0.30 mL + MnSO4 1.70 mL 0.20 230 550 80, 153.30 >16 38, 65MnBr2 0.50 mL + MnSO4 1.50 mL 0.33 200 ** 100 14 30MnBr2 1.0 mL + MnSO4 1.0 mL 0.66 660 1400 100, 170 >18 40, 50


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ox p

oten

tial (

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)

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Figure 7 Potential (mV) versus time (s) plots showing the effect of [bromide] containing [Mn2+] = 4 × 10−3 mol L−1,[BrO3

−] = 0.1 mol L−1, [resorcinol] = 0.0225 mol L−1 at 30 ± 0.1◦C: (a) 0.33 mol L−1, (b) 1.33 mol L−1, (c) 0.10 mol L−1,and (d) 0.20 mol L−1.

counterion for Mn2+ as shown in Table VIII. It wasfound that a decrease in [Cl−] up to 0.16 × 10−3 molL−1 has an inhibitory effect on oscillatory parameterssuch as the time period and amplitude (Fig. 6), af-ter which chaotic behavior is observed. The presenceof the prolonged induction period clearly shows theCl– inhibition and control on the bromination processof the BZ reaction. Hence, by controlling the [Cl–] wecan easily control the temporal behavior of oscillations,which in turn control the HOBr/Br− couple [25]. Chaos

in an open chemical system may be defined as an aperi-odically varying composition determined by the intrin-sic dynamics of the system rather than by noise or exter-nal influences, which depends sensitively on the initialconditions, i.e., two chaotic systems that differ even in-finitesimally in their initial conditions evolve in time soas to diverge exponentially from one another. Chaoticbehavior typically emerges from periodic oscillationas the control parameter is varied, often by a period-doubling route [26], in which alternate extrema become



slightly larger or smaller at a series of critical valuesof the parameter until a limit point, where the behaviorbecomes aperiodic, i.e., chaotic. Every chaotic trajec-tory contains an infinite number of unstable periodicpaths, and it has been suggested that one should be ableto “control chaos” by applying very small, carefullyselected perturbations to a chaotic system to stabilize achosen periodic behavior [27]. This approach has beenput into practice successfully in the BZ system [28].

Effect of Bromide

The use of KBr earlier in the BZ reaction confirmedthe role of Br– ion as the control intermediate for theoscillatory process [29]. Here, we have used Br– asthe counteranionic moiety of the Mn2+ion solution forobserving this trend, which showed interesting results.From Table IX, it is observed that with an increase ininitial [Br–], the induction and time periods increaseexcept at 1.33 × 10−3 mol L−1. However, the high-frequency region, number, and amplitude of oscilla-tions do not vary regularly. It is found that with 0.20and 0.66 × 10−3 mol L−1 [Br–], the oscillatory pa-rameters are very prominent (Fig. 7). In fact, theseconcentrations coincide with the intermediate Br– con-centration, which acts as positive feedback for thisreaction, whereas with other concentrations it will actas negative feedback causing a decrease in oscillatoryparameters.

SUMMARY

To design a new chemical oscillator, the choice of coun-terion associated with a metal ion to be used as thecatalyst is inevitable. The organic and inorganic coun-terions show diverse behaviors, i.e., decreasing and in-creasing trends, respectively. Thus, the control can beassociated with some of these species, which are some-how involved in some reaction steps as proposed in theFKN mechanism. The present work clearly shows thatorganic counterions can act as cosubstrates (formate,acetate) and even sometimes as substrates (acetylacet-onate), whereas inorganic counterions directly increasethe ionic strength of the medium, besides acting as con-trol (chloride, bromide, fluoride), and cause for noisybehavior (carbonate, sulfide) due to release of gasesand hence leading to inhomogeneity in the oscillatorysystem. The inhomogeneity can be observed as irreg-ular trends with respect to various oscillatory param-eters. The presence of varied counterions in differentsystems is the cause for variation in diffusion patterns,which requires a more detailed study. The concentricregions appear due to addition of ferroin on a thin layerof the reaction system (in Petri dishes with 100 mm di-

Figure 8 Diffusion patterns showing discrete regions forthe system containing 2 mL each of [Mn(NO3)2] = 4 ×10−3 mol L−1, [BrO3

−] = 0.1 mol L−1, [resorcinol] =0.0225 mol L−1 at room temperature after addition of onedrop of 0.025 mol L−1 of ferroin solution. [Color figurecan be viewed in the online issue, which is available atwileyonlinelibrary.com.]

Figure 9 Diffusion patterns showing diffused regions forthe system containing 2 mL each of [Mn(CH3COO)2] = 4 ×10−3 mol L−1, [BrO3

−] = 0.1 mol L−1, [resorcinol] =0.0225 mol L−1 at room temperature after addition of onedrop of 0.025 mol L−1 of ferroin solution. [Color figurecan be viewed in the online issue, which is available atwileyonlinelibrary.com.]

ameter and 3 mm solution thickness) because of theincrease in local ionic strength due to the addition ofinorganic counterions (Fig. 8), whereas an increase inthe hydrophobic nature due to the addition of organiccounterions is the cause for diffused patterns (Fig. 9).



The authors are thankful to the Head, Department of Chem-istry, University of Kashmir, Srinagar, India, for providinginfrastructure to undertake the investigation.

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