Chloride Ion Inhibition, Stirring, and Temperature Effects in an

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Chloride Ion Inhibition, Stirring and Temperature Effects in Ethylacetoacetate-Briggs-Rauscher Oscillator in Phosphoric and Hydrochloric Acids in a Batch Reactor Arun Kumar Dutt J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.9b01590 • Publication Date (Web): 21 Mar 2019 Downloaded from http://pubs.acs.org on March 27, 2019

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The Journal of Physical Chemistry

Chloride Ion Inhibition, Stirring and Temperature Effects in Ethylacetoacetate-Briggs-Rauscher Oscillator in Phosphoric and Hydrochloric Acids in a Batch Reactor

Arun K. Dutt*$



Faculty of Applied Science, University of the West of England (Frenchay Campus), Bristol BS16 1QY, UK

Abstract: Briggs-Rauscher (BR) oscillating reaction has been investigated in hydrochloric acid media and in presence of added chloride ions in phosphoric acid media in a batch reactor using ethylacetoacetate (EAAH2) as the organic substrate. The changes in key oscillation parameters, namely induction period, oscillation period and amplitude, etc. have been explained in terms of the steps of the skeleton mechanism proposed by Furrow and Noyes (FN) and by de Kepper and Epstein (DE). Inspite of several shortcomings as outlined in section 2 in the text, the same mechanistic steps are good enough to explain qualitatively most of the changes in oscillation parameters under different stirring rates and temperatures in phosphoric acid and hydrochloric acid media ; particularly, stirring effects explained nicely by the theory of imperfect mixing. Potential data indicate that 0.018M HCl medium has the ability to exhibit near-zero / zero- amplitudes before cessation of oscillations. Inhibition reactions from low Clconcentration in 0.018M HCl media appear to be responsible for this interesting dynamical transformation, since toward the end of oscillations, the difference between [I-] and [I-]crit (see equation(J) in the text) becomes very very small because of depleted component chemicals due to chemical reactions.

$

Address for Correspondence: 16 Ghanarajpur Jalapara, Dhaniakhali, Hooghly, WB 712302, India

*Email: [email protected] ; Phone : +91-3213-255752

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1.Introduction: Perhaps the most dramatic oscillating reaction known so far, has been the Briggs-Rauscher (BR) reaction1. In this reaction, appropriate amounts of acidic iodate, hydrogen peroxide, manganous sulfate, malonic acid, and starch indicator are mixed in aqueous solution and the well-stirred solution exhibits cyclic color changes from colorless to yellow to blue and again back to colorless with a strong odor of iodine, which is generated in the reaction. BR reaction has been previously studied in aqueous perchloric acid1, sulphuric acid1, nitric acid2 and phosphoric acid3 media using different organic substrates namely methyl malonic acid4, phenylmalonic acid4, acetone5, acetyl acetone1, ethylacetoacetate6, crotonic acid7, acrylic acid7, anisole7, and pnitrophenol7. It has been reported in the past that BR reaction exhibits oscillations in hydrochloric acid media8 and in presence of added chloride ions in phosphoric acid media, if the chloride ion concentration is not too high - however, no instrumental measurements were obtained in that investigation. Complex oscillations and bi-stability/hysteresis have been reported9-13 in the past in BR reaction in continuous flow stirred tank reactor (CSTR). In this communication we have made a detailed investigation of the effects of added chloride ions on BR reaction in a batch reactor using ethyl-acetoacetate (EAAH2) as the organic substrate; BR reaction investigated also in hydrochloric acid media. Stirring and temperature effects on BR reaction in phosphoric acid and hydrochloric acid media have been reported using EAAH2 as the organic substrate and the results explained in terms of the very much similar mechanisms proposed by Furrow and Noyes (FN)14-16 and de Kepper and Epstein (DE)17 - the steps (B9') and (B9") in the DE model (see Table 1) had been considered as two separate steps in the FN model. 2. BR reaction mechanism : The net chemical change (C) in BR reaction is composed of two component stoichiometric processes, A (reduction of iodate to iodine oxidation state +1) and B (iodination of organic substrate)14-16. IO3- + 2HIO2 +H+ HOI + RH





HOI +2O2 +2H2O

(A)

RI + H2O

IO3- + 2H2O2 + RH + H+



(B) RI + 2O2 + 3H2O

(C)

where RH is an organic substrate, which reacts with iodine (I) by substitution reaction B. The stoichiometry of process A can be obtained in two different paths. The non-radical path is given by (B1) + (B2) + 2(B10) and the radical path by 2(B4) + 4(B6) + 4(B7) + 2(B8) + (B5) (see Table 1). The nonradical path involves steps in which oxidation number changes by more than one equivalent, whereas the radical path includes steps with single-equivalent changes only. The rate determining step for HIO2 formation during non-radical path being the lower order manganous catalyzed reversible step (B6) because of depleted concentration of IO2  (reverse reaction being negligible because of low Mn(III) concentration) and that for the radical path being the higher order manganous catalyzed reversible step (B4). Process B is generated by the sequence (B3) + (B9') + (B9"). The small concentration of IO2  can be obtained from the pseudo-steady state approximation, d[IO2  ]/dt solution of the quadratic equation 2k -4 [IO2  ]2 + k6 [Mn+2].[ IO2  ] – 2k4[H+].[IO3-].[HIO2] = 0


(D)

 0,

from the

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Assuming that q fraction of IO2  formed by the reversible step (B4) reacts by the reversible step (B6) rather than by the reversible step (B-4), we have q defined by q = k6[Mn+2] / (k6[Mn+2] + 2k-4[ IO2  ])

(E)

The net rate (v4) of the reversible step(B4) is related to the rate (v6) of the reversible step(B6) by the relation v4 = (1/2) v6 = qk4[H+].[IO3-].[HIO2]

(F)

These relations lead to a pseudo-steady state expression for [HIO2], (d[HIO2] / dt

 0),given by

k1[H+]2.[IO3-].[I-] + { qk4[H+].[IO3-] – k2[H+].[I-]}. [HIO2] - 2k5[HIO2]2 = 0

(G)

It is important to note that when in the oxidative radical phase generating HIO 2 auto-catalytically at a high rate, consumption of Iby step (B1) practically stops because of high concentration of HIO2 , whereas when in the reductive non-radical phase, consumption of iodide by step (B2) is very low because of low HIO2 concentration. We may approximate [HIO2] by appropriate choice of equations (H) or (I) when either the radical path or the non-radical path for process A is dominant. [HIO2] r ~ (qk4/2k5)[H+].[IO3-]

(H)

[HIO2]n ~ (k1/k2)[H+].[IO3-]

(I)

; during radical path, steps involving k1 and k2 may be neglected and during nonradical path, steps involving k4 and k5 neglected. We have used subscripts r and n to indicate the two paths respectively. The system may switch rapidly between these two approximations whenever the concentration of iodide (see equation G) passes through the critical value [I-]crit as given by [I]crit = (qk4/k2)[IO3-]

(J)

, since the coefficient of [HIO2] in eq (G) has to be ~ 0 to obtain at least a low real positive value of [HIO2]. Based on recent works, the last two paragraphs of this section suggest that step (B4) may not be the main source of radicals as assumed in the original FN/DE14-17 skeleton mechanisms. This may require corrections to the above steps (D) to (J) in the future since, in its present form, the mechanistic details of the proposed active route producing HOI from HIO2 (other than by iodide) has been bypassed by using an overall process (BF11) (see Table 2) rather than by elementary mechanistic steps. In FN/DE skeleton mechanisms, the transition from low [I2] and low [I-] to high [I2] and high [I-] depends on the production of iodide from steps (B10) and (B9"). Furthermore, the shift from high [I-], low [I2], and low radical concentrations to low [I-], high [I2], and high radical concentrations occurs just as v4 begins to exceed v2 ; the order of the principal reaction rates being v10 > v4 > v2 > v3 >v9 in the radical regime, whereas in the non-radical state these rates fall in the reverse order having their values decreased by several orders in magnitude. Let us enter the oscillation cycle when there is sufficient I- to favour non-radical steps including step (B1). Iodide is being consumed in step (B1) and eventually its concentration drops below the critical level of [I-]crit ( see equation (J)). At this point, the radical step (B4) is turned on with the fast autocatalytic production of iodous acid by step (B6), while the remaining iodide being consumed by step (B2). Mn(III) produced in radical step (B6), then drives step (B7) in which Mn(III) is reduced, while iodide is being regenerated by steps (B9") and (B10). The iodide concentration level soon rises above [I-]crit and the non-radical processes involving step (B1) switch on again. The cycle is thus being completed.



The numerical results in the FN model14-16,18 containing eleven steps agree well with the experiments of Roux and Vidal9,10 in various ways. For example, during a single period of oscillation [I2] reaches its maximum value when [I-] is small but rising, and [I-] rises rapidly thereafter; likewise, [I2] reaches its minimum value when [I-] is large but decreasing, and [I-] decreases dramatically afterward. However, FN model shows the following quantitative discrepancies from the experiments of Roux and Vidal9,10 : (a) The variations in [I2] during oscillations are about 40 times larger than those reported in experiments ; (b) The concentration of the intermediate HIO2 is too high, so that the duration of the non-radical process is about a third of the oscillation period compared to that about three quarters of the oscillation period in real experiments. On the other hand, the computation of DE model17,19 (represented by 10 steps in Table 1) reproduces various kinds of nonlinear dynamic behaviours in CSTR including cross-shaped phase diagram in the [I2]o-[IO3-]o concentration space, bistability-hysteresis, oscillations, and most remarkably the inverse regulation of iodine, which exhibits a net drop in iodine concentration in the reactor when the iodine input flow is increased. But DE model has important shortcomings too – in particular, the rate constant for step(B5) is five orders of magnitude too high. That puts step (B4) in an awkward situation – does it really exist or should it be replaced by another pathway? Furthermore, we note the following additional shortcomings of the proposed BR reaction mechanisms14-19. (a) Malonic acid (MAH2) reacts with I2 via an enol mechanism to produce iodomalonic acid (IMAH), which can react similarly to form di-iodomalonic acid (I2MA)20-23. The second iodination is not included in the skeleton mechanism14-19 assuming that IMAH is an inert product. (b) De Kepper12 obtained an increase in oscillation amplitude with the increase of O2 pressure in BR reaction using MAH2 as the organic substrate - DE model containing two irreversible steps (B8) and (B10) producing O2 seems to have ignored this important experimental observation. (c) Muntean et al.24 have shown that Fenton-like radical attack on IMAH is responsible for CO2 / CO evolution in BR oscillator from decarboxylation / decarbonylation of organic free radicals. (d)Furrow et al.20-23,25,26 have reported that I2MA either decarboxylates to I2AA (diiodoacetic acid) plus CO2 or is oxidized to OA (oxalic acid) + I2 +CO2. IMAH and I2MA play critical roles following oscillations in the transition to state II (high I2 and Iconcentrations) from state I (low I2 and I- concentrations27-30). Degradation pathways for both IMAH and I2MA to OA, I2, CO2 and CO must be included in a revised mechanism for BR oscillator. e) FN/DE14-17 skeleton mechanisms apparently can’t accommodate the substrates7,22,29 containing no active methylene hydrogen viz. crotonic acid, acrylic acid, anisole, and p-nitrophenol, which exhibit BR-oscillations in a batch reactor. Modifications of the skeleton mechanisms by Furrow et al. 7,22,29: The substrates containing active methylene hydrogen react with I2 via an enol- mechanism16-17 to give a substitution iodoproduct with generation of iodide ions. But, the substrates7,22,29 containing no active methylene hydrogen viz. crotonic acid, acrylic acid, anisole and p-nitrophenol, which exhibit BRoscillations in a batch reactor, react with I2 (H2O) / HOI by either addition or substitution reactions with or without indirect formation of iodide ions from I2 hydrolysis by step B-3 - crotonic acid and acrylic acid react with I2 (H2O) / HOI to produce the


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addition compounds 2,3, diiodobutanoic acid / 3, hydroxyl 2, iodobutanoic acid and 2,3, diiodopropanoic acid / 3, hydroxy 2, iodopropanoic acid respectively without any generation of iodide ions, whereas anisole and p-nitrophenol undergo substitution reactions with I2 (H2O) to form iodophenols. The substrates without any active hydrogen effectively compete for HOI to prevent I2 or I- from accumulating. Furrow et al.7,22,29 have included steps (BF11), (BF12), and (BF13) (see Table 2) involving active reduction of HIO2 to HOI (other than by iodide) in an effort to revise the skeleton mechanisms of FN/DE 14-17 for reproducing simulation of oscillations with these substrates containing no active methylene hydrogen. Step (BF11) actively produces HOI and exhibits autocatalytic production of HIO2 after combination with steps (BF12) and (BF13). Inclusion of this feature was key to simulate oscillations with these substrates containing no active methylene hydrogen. With modified steps (see Table 2), simulation of oscillations is possible without using step (B7) from the skeleton models (FN/DE14-17) ; however, the agreement is qualitative only. It has been suggested that the main route for the reduction of IO3- is probably by HO2  radicals rather than by reaction with HIO2 by step (B4) producing IO2  radicals. 3. Experimental: The experiments were carried out in a cylindrical batch reactor (diameter 2.8 cm) at a constant temperature. The reacting solutions were prepared from analytical grade reagents. The concentration of H2O2 solution was obtained by titration with a standard KMnO4 solution. Three stock solutions were prepared separately and then mixed in equal volumes (10 ml each) to 5 ml of a solution of Cl- ion (with different concentrations) initially taken in the reactor. The first one was of H2O2, the second one of starch, manganese and ethylacetoacetate, and the third one of iodate and phosphoric acid. The oscillation cycle was initiated by adding the solution containing iodate. The solution was stirred with a Teflon-coated magnetic stirrer (dimensions 14 x 3.5 mm) at a constant stirring rate of 500 rpm in the experiments where no stirring effect was investigated. The reactor was kept open, and the gas exchange between air and the reacting chemicals was possible during the course of the reaction. The monitor was a Ptelectrode with reference to a Ag-AgCl-sodium sulphate (saturated) electrode connected as input to a pH meter. The tips of the electrodes were placed 1.5 cm above the bottom of the reactor. The output potentials from the pH-meter were recorded on a x-t chart recorder. To undertake the B-R reaction in HCl medium, a solution of iodate in hydrochloric acid (in place of phosphoric acid) was used to initiate the oscillation cycle. In temperature effect experiments, the temperature of the reacting mixture was varied keeping the stirring rate at a constant value of 500 rpm, whereas in stirring effect experiments, the temperature of the reacting mixture was kept constant while the experiments were conducted at different stirring rates. 4. Results and Discussion Amplitudes and periods are easy to get in experimental measurements, but are not particularly useful for elucidating mechanism of chemical oscillators; however they are sometimes useful for testing the validity of a proposed mechanism. The effects of added Cl- ions in BR reaction in H3PO4 media are given in Table 3a (Figs.1). The results of BR reaction in HCl media at different HCl concentrations are presented in Table3b (Figs 2).



Page 6 of 35

a) Mechanism of chloride inhibition: Cooke31 reported inhibition of BR reaction by chloride ions. Chloride may compete with iodide and iodate for iodous acid (see steps B2 and B4 respectively of Table 1) through the following reaction involving two electron process if the role of added chloride ions in the BR reaction be supposed in a way similar to that 32 in the cerium ion catalyzed BZ reaction33. Cl- + HIO2+ H+  HOI

 HOCl

;

E0 = -0.24V

(K)

E0 (Cl- /HOCl) is -1.49V34 ; E0(HIO2/HOI) =1.25V, which is calculated from ∆Gf0(HIO2)35 = -95 KJM-1 and ∆Gf0(HOI)36 = 23.67 KCalM-1. Potential data suggest that reaction K is not thermodynamically favored. Also, the following two steps (L) and (M) consuming HOI and HOCl respectively with the generation of I- are not thermodynamically feasible. Cl- + HOI = HOCl + I-

;

E0 = - 0.49V34

(L)

HOCl + HOI = I- + HClO2

;

E0 = - 0.63V34

(M)

Cervellati et al.26,28,29,37 have argued that both Br- and Cl- interfere with iodine equilibria as in the following reaction, and undergo interhalogen non-radical reactions. HOI + Cl- + H+ 

'

ICl + H2O

(B3in)

This reaction is plausible from thermodynamic point of view since the calculated 38 ∆G0 is -21.9KJmol-1. ICl is an iodinating agent for ethylacetoacetate (EAAH2) via its enol form, (EtOOC)CH=C(OH)CH3 (enol) + ICl

 (EtOOC)CHICOCH3 + Cl- + H+

(B9in)

This sequence partially inhibits normal I- recycling as given below, HOI + I- + H+  I2 + H2O I2 + (EtOOC)CH=C(OH)CH3 (enol)

(B3)



-

+

(EtOOC)CHICOCH3 + I + H

(B9*)

I2 reacting with the enol form of EAAH2 is appropriate7 in equation (B9*), since EAAH2 contains an active methylenic group. The calculated ∆G0 value for step (B3) is – 70.23 KJ mol-1 – the free energy of formation (KJ mol -1) values for ∆G0 calculations are given in Table 438. b) Explanation of the effects of Cl- ions (Including Oscillation Parameters): We define induction period as the time required when the (high iodide) slow non-radical phase of the BR reaction switches to the (low iodide) fast oxidative radical phase on the limit cycle for the first time after mixing of the component chemicals. For initiation of the first oxidative (low iodide) autocatalysis (steps B4 plus B6) it is required that, immediately after mixing of the chemicals, enough HOI / HIO2 is produced by step (B1), so that I2 producing step (B3) is initiated to make I- regeneration possible by step (B9*) / or (B9"). Since HOI is being consumed by Cl- ions (see stepB3in), some more time is required to produce enough HOI by step (B1) to initiate the I2 producing step (B3) and the autocatalytic steps (B4) plus (B6) thereafter for the first time after mixing of the chemicals. As a result the first switch from (high I-) non-radical phase to (low iodide) oxidative radical phase on the limit cycle takes place after longer time from mixing of the chemicals in presence of Cl- ions. The increase of induction period in presence of Cl- ions is, thereby, explained qualitatively (see Table 3a).


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In presence of added Cl- ions, there is more reduction in non-radical I- ion regeneration rate due to the occurrence of step (B3in) consuming additional HOI and the step (B9*) / or (B9") producing less I- ions. The net iodide concentration as well as [I2] becomes very low because step (B3) reaches equilibrium in nearly one second ( see equation 12 of ref.16 also) and the fast oxidative (low iodide) radical process starts early decreasing (slow) non-radical process time as well as oscillation period – this fast oxidative radical process continues for much longer time producing more Mn(OH)+2 species since I- concentration being very low in presence of added Cl- ions– the potential increase is more resulting in the increase of oscillation amplitude. Increase of oscillation amplitude and decrease of oscillation period in presence of added Cl- ions is thus explained qualitatively (see Table 3a and figure 1). Since iodate is being consumed much more by step (B1) because of additional consumption of HOI by Cl- by step (B3in) in presence of Cl- ions, the reaction after fewer number of oscillations remains stabilized permanently at high [I-] > [I-]crit (low potential non-radical state) at depleted concentration of iodate when the consumption rate of I- by step (B1) becomes too low indicating that oscillations have ceased. This explains qualitatively why the total number and the total time of oscillations decrease in presence of added Cl- ions (see Table 3a, Fig.1). Note that we have not included in our discussion the effects of H3PO4, which may complex the manganese ions. The results of BR experiments in HCl media are given in Table 3b (Fig.2), which demonstrate that, with the increase of HCl concentration, induction period first decreases and thereafter increases – with the increase of HCl concentration, both of oscillation period and amplitude increase. These observations should conform to those obtained in Table 3a for BR experiments in H3PO4 media at different Cl- concentrations in terms of the mechanistic considerations as given in the last paragraphs. The effects of Cl- ions on the behaviour of induction period, oscillation period, and amplitude in HCl media can’t be presented qualitatively exactly in the same way as given in the first set of experiments (see Table 3a, Fig.1) in H3PO4 media at different Clconcentrations, since as we change HCl concentration, both of [H+] and [Cl-] change. Numerical simulation of an improved kinetic mechanism14-17 (not undertaken here) of BR reaction seems to be the only way to explain it when the rate constants for EAAH2 with I2 will be known. From the potential trace in Fig.2a, it is interesting to note that BR reaction (in 0.018M HCl medium) executes oscillations of initial amplitude as high as 17 mV (second oscillation), which gradually increases further and decreases thereafter to zero mV, when the oscillations end after clear 45 oscillations due to natural aging of the reacting chemicals; this batch experiment being obviously a closed system in thermodynamic sense. Potential data in Fig.2a indicate that 0.018M HCl medium has the ability to exhibit near-zero / zero-amplitude oscillations just before cessation of oscillations. We have not established the precise HCl concentration range for which zero-amplitude oscillations were obtained before cessation of oscillations – this should lie within 0.014M -0.027M for BR reaction recipe8 used here. This experimental observation is qualitatively reproducible in a repeat experiment (see also reference 8). Inhibition reactions through steps (B3 in) and (B9in) from low values of [Cl-] in 0.018M HCl medium appear to be responsible for this gradual dynamical transformation from high amplitude to zero amplitude oscillations, since towards the end of oscillations, it seems that the difference between [I-] and [I-]crit (see equation J) becomes very small ;



Page 8 of 35

such oscillations ending with zero-amplitudes in batch experiments being nearly rare in B-Z oscillators. Oscillations of the type as presented in Fig.2a was reported in the past in MAH2-BR-Oscillator28,29 as also in crotonic acid-BR-oscillator7,22,29 (containing no active methylene hydrogens) in batch reactors implying speculation that, in those cases also , the difference between [I-] and [I-]crit may become very very small towards the end of oscillations, which inspires possibilities of discovering new ideas about the development of additional/common mechanistic steps that may be applicable to the crotonic acid-BR-Oscillator as well. It is equally interesting to compare these zero-amplitude experimental oscillations in Fig.2a with those in supercritical Hopfbifurcation theory itself as given below. Figure 3(b) shows a zero-amplitude stable periodic orbits at a soft transition / bifurcation point (supercritical Hopf- bifurcation39) – the amplitude of stable periodic orbits may be increased gradually by changing the bifurcation parameter

 appropriately.

Such a soft bifurcation point is expected to be achievable both experimentally as well as in numerical simulation. Figure 3(c) represents unstable periodic orbits at a hard transition / bifurcation point (subcritical Hopf- bifurcation39) – after a subcritical bifurcation, the unstable orbits which appear remain surrounded by stable orbits of nonzero full amplitudes as the bifurcation parameter

 is changed appropriately and the system shows a bistability/hysteresis.

Until today, only subcritical39 (see Fig.3c) Hopf bifurcations have been documented in the laboratory experiments of oscillatory chemical reactions9-12,40,41 including the well-known Belousov-Zhabotinskii33 reaction, which exhibits bistability between a steady state branch and an oscillatory state branch in a CSTR ; supercritical Hopf bifurcation (see Fig.3b) documented only in the theoretical models of chemical42 and biochemical oscillations including the reversible Sel’kov model43. Ideally, a batch reactor experiment as shown in Fig.2a has no capability to distinguish between supercritical and subcritical Hopf- bifurcations, since no stable bifurcation parameter bifurcation parameter

 , as such in Fig3,

exists in this case – a CSTR-experiment controlled by a stable

 is an essential requirement for obtaining this information. Assuming natural aging as a transient

bifurcation parameter, one may, however, argue that Fig.2a may also be an example of a transient reverse supercritical Hopfbifurcation in a batch experiment. Since 0.018M HCl media have the ability to sustain near-zero / zero-amplitude oscillations (see Fig.2a), there is no reason why it can’t also be obtained in a supercritical (soft) way (see Fig.3b), if appropriate concentrations of the component chemicals are maintained in a CSTR experiment, where a separate peristaltic pump controls the concentration of the component to be used as a stable bifurcation parameter. c) Stirring Effects : The results of stirring effect experiments at constant temperatures on BR reaction in H3PO4 and HCl media using EAAH2 as the organic substrate in a batch reactor have been reported in Table 3c (Figs.4) and Table 3d (Figs.5) respectively. The major stirring effects in BR reaction result apparently from the dispersal of reacting autocatalytic nuclei under high stirring condition. Dutt et al.(fig.1b of ref.44) obtained a stirring induced bistability in minimal bromate oscillator(MBO) in a CSTR in nonpremixed mode of mixing (NPM). That interesting result demonstrates that, within the stirring range of bistability, low stirring destabilizes the (slow) nonradical flow branch in favor of stabilizing the (fast) radical thermodynamic branch, whereas high stirring destabilizes


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the same (thermodynamic) branch. That result may be interpreted nicely from the theory of imperfect mixing.45,46 Low stirring generates more segregated heterogeneities increasing the rate of Br- consumption by steps (M1) and (M3) (see Table 5) in the backdrop that Br- feeding is the only source of Br - inside the CSTR. As a result, [Br -] < [Br -]crit (see equation 8 of ref.44) can be obtained early enough destabilizing the (slow) nonradical flow branch at a low stirring rate - contribution of step (M2) being negligible during nonradical phase because of very low concentration of HBrO2. At high stirring less segregation decreases Br cosumption rate by steps (M2) and (M3), while Br - feeding rate inside the reactor remaining unchanged. As a result, net Br concentration inside the CSTR goes up destabilizing the (low Br -) thermodynamic branch - contribution of step (M1) practically stops during radical phase at high concentration of HBrO2. Because of critical slowing down delay, the thermodynamic branch has to retain itself in the same branch for longer time generating large quantity of Ce +4 ions (via step M5), which increases Ptelectrode potential before down transition to the (high Br -) flow branch at a high stirring rate. The observation of fig.1b in ref.44 is thus nicely explained by the theory of imperfect mixing.45,46 De Kepper12 obtained an increase of oscillation period and amplitude for BR-reaction at high stirring rates using MAH2 as the organic substrate in a CSTR with NPM mode of mixing, which is now explained below. Similar to the argument as presented in the last paragraph in the case of stirring induced bistability in MBO (see fig.1b of ref.44), high stirring in BR-reaction stabilizes its (low potential) flow branch increasing the (slow) nonradical process time as well as the oscillation period itself. High stirring destabilizes the (high potential) thermodynamic branch favoring down transition to nonradical flow branch after critical slowing down delay, which generates large quantity of Mn(OH)+2 ions autocatalytically by steps (B4) plus (B6) (see Table 1) to increase oscillation amplitude substantially - de Kepper12 also obtained an increase of oscillation amplitude at high stirring. The obvious analogy between the relevant mechanistic steps of BR-reaction (Table 1) and MBO oscillator (Table 5) has been useful in explaining de Kepper's experimental results on BR-reaction by the theory of imperfect mixing.45,46 High stirring in our batch reactor in H3PO4 media using EAAH2 as the organic substrate facilitates escape of O2 gas from the reaction mixture more rapidly by gas-air interchange at the liquid-air interface. The effect of O2 gas in BR reaction is probably similar to that observed on the Bray-Liebhafsky (BL) reaction47,48. It is likely that a direct inclusion of the time lag associated with the equilibration of step (N) from BL mechanism47 would improve the BR reaction O2 (aq) 

O2(g)

(N)

mechanism, since this equilibrium apparently involves a time constant of the order of min even in well-stirred solution – -1

numerical simulation has been undertaken elsewhere30 using MAH2 as the organic substrate. The escape of O2 gas has a physical effect in the form of I2 gas loss. High stirring facilitates escape of additional I2 gas too from the reaction mixture more rapidly in our batch reactor – the escape of additional I2 gas accelerates step (B3) further enhancing the consumption of I - and decelerates I -

production rate further through step (B9*) / or (B9") . This leads to early start-up and delayed end of the (fast) oxidative radical

phase due to lower net I - production from I2 loss at high stirring (see Eqn.12 in ref.16) decreasing (low potential) nonradical (slow) process time. Thus, the normal increase of (slow) nonradical process time at high stirring rate (de Kepper12) is being nearly/completely compensated by its simultaneous decrease because of escape of more I2 gas at high stirring rate. Our



observation that oscillation period (viz. 21 sec in Table 3c) doesn't change by increasing stirring rate is thus nearly explained ; induction period (viz. 15 sec in Table 3c) not being changed by increase of stirring rate seems presumably due to similar reason. The increase of oscillation period at high stirring is not noticeable probably because the temperature being not too low 40. This is a reminder of our observation in BZ reaction experiments in CSTR that stirring has little effects on oscillation period unless the temperature is very low and stirring very high - high values of oscillation period and amplitude (viz. 39s and 48mV respectively) at a low temperature (viz. 110C) presumably predict a strong stirring effect at low temperatures (see Table 3e, Figs.6). We suggest that if the stirring effect experiments in a batch reactor were conducted at different temperatures 40,41 (not undertaken here), we could expect at least a small increase of oscillation period 12 at high stirring in our experiments too in H3PO4 media, since at low temperatures both (slow) non-radical process time and (fast) oxidative radical process time increase more due to Arrhenius effect. With an increase in O2 pressure, De Kepper12 obtained an increase in oscillation amplitude in CSTR experiment using MAH2 as the organic substrate, but no effect on oscillation period was observed. Flushing our batch BR system (EAAH 2 as organic substrate in H3PO4 media) with N2 gas (see Table 6) seems to oppose de Kepper’s O2-effect resulting in a decrease of oscillation amplitude –inert N2 atmosphere apparently deactivates the oxidative autocatalytic radical processes (B4) plus (B6) to make Mn(OH)+2 production rate less. Increase of O2 pressure has effects opposite to inert N2-gas flushing due to more activation of the oxidative radical processes (B4) plus (B6), which presumably explains de Kepper’s O 2-effect itself. Flushing N2 gas apparently has no effect on oscillation period (see Table 6) in this BR system since oxidative autocatalytic steps (B4) plus (B6) are probably too fast compared to the time scale in our time period measurement device used here. In the case of stirring effect experiments of BR reaction in HCl media (see Table 3d; Figs.5), with increase of stirring rate, induction period first increases and decreases thereafter while oscillation period decreases with increase of stirring rate, which are distinctly different from those in H3PO4 media ( see Table 3c ; Figs.4 ). With increase of stirring rate, oscillation amplitude increases,which is similar to that observed in H3PO4 media. These observations must conform to those obtained for BR experiments in H3PO4 media at different stirring rates in terms of the mechanistic considerations given in the last paragraphs. Stirring effects on the behavior of induction period, oscillation period, and amplitude in HCl media can’t be presented qualitatively exactly in the same way as given in H3PO4 media at different stirring rates, since Cl- ion in HCl media is, itself, an inhibitor (see step B3in). Numerical simulation of a revised BR mechanism (see the shortcomings of FN14-16 and DE17 mechanisms as described in section 2) is probably the only way (not undertaken here) to explain this situation when the rate constants for EAAH2 with I2 will be known. Note that in batch reactor experiments, the level of mixing (macro-mixing) is quite good with high stirring. So, we have ignored micro-mixing49-52 effects in our stirring effect discussion, which seems useful for CSTR experiments53 only. d)Temperature Effects: The results of temperature effect experiments in H3PO4 and HCl media at constant stirring rate are shown in Table 3e (Figs.6) and Table 3f (Figs.7) respectively. The overall temperature effects involve the following two major processes: (a), Immediately


Page 10 of 35

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after mixing of the component chemicals, the BR reaction in H3PO4 media resides on reductive (nonradical) phase – because of Arrhenius effects at high temperatures, the consumption of I- ions by the nonradical steps (B1) and (B3) during induction period becomes rapid whereas (b), due to escape of more I2 gas to the atmosphere at elevated temperatures, the I- regeneration rate via step (B9*) / or (B9") is decreased and I- consumption by step (B3) increased. As a result, the net rate of I- production is decreased to achieve [I-] < [I-]crit (see equation J) early for switching to oxidative radical phase for the first time, which presumably shortens the induction period (see results of Table 3e in H3PO4 media). In HCl media, because of the additional step (B3in) consuming HOI, the consumption rate of I - by steps (B1) and (B3)is increased while I- ion regeneration by step (B9*) / or (B9") decreases due to lower I2 production rate by step (B3). As a result, the net rate of I - production becomes much slower such that [I -] < [I -]crit (see Equation J) is obtained very very early making induction period very very small (~ 3 secs ; see results of Table 3f in HCl media). The length of time for the reductive (non-radical) phase and that for the oxidative (radical) phase are decreased considerably at elevated temperatures to make oscillation period shorter – the shorter length of time for the oxidative (radical) phase by steps (B4) plus (B6) at elevated temperatures generates less Mn(OH)+2, which decreases the oscillation amplitudes in potential measurements as presented in Figs.(6) and (7) (see Tables 3e and 3f respectively). 5. Conclusion : The qualitative interpretation of the effects of chloride ions (sections 4a,4b), stirring (section 4c), and temperature (section 4d) on EAAH2-BR-Oscillator as presented in this manuscript has obviously enhanced the importance of FN/DN14-17 skeleton mechanism inspite of its several shortcomings as outlined in section 2. At the same time, the experimental work reported here remains incomplete unless the discussions included are reproduced in a numerical simulation of an improved mechanism (not undertaken here) after incorporating additional unknown reaction steps into the existing FN/DN14-17 skeleton mechanism with inclusion of additional unknown/known rate parameters in the kinetic differential equations. Our future endeavours will be directed to explore these possibilities. 6. Acknowledgment: I am thankful to Dr. Norman Ratcliffe for encouragement and Dr. Ben De Lacy Costello for technical supports. This research was supported in part by EPSRC, UK.

References and Notes: (1).Briggs, T.S. ; Rauscher, W.C. An Oscillating Iodine Clock, J.Chem. Edu. 1973, 50, 496. (2).Dev, B.M. Chemical Oscillations as an Undergraduate Experiment, J.Chem.Edu. 1977, 54, 236. (3). Dutt, A.K. ; Banerjee,R.S. Iodine Clock Oscillating Reaction, J.Ind.Chem.Soc.1980, 57,751-753. (4). Furrow, S.D. Comparison of Several Substrates in the Briggs-Rauscher Oscillating System, J.Phys.Chem.1995, 99,1113111140.



(5). Cooke, D.O. The Hydrogen Peroxide–Iodic Acid–Manganese(II)–Acetone Oscillating System, J.C.S. Chem. Comm.1976, 0, 27-28. (6). Dutt, A.K. ; Banerjee, R.S. Briggs-Rauscher Oscillating Reaction Using New Compounds, J. Ind. Chem. Soc.1981, 58, 546549. (7). Furrow, S.D. ; Cervellati, R. ; Amadori, G. New Substrates for the Oscillating Briggs−Rauscher Reaction, J. Phys.Chem.A, 2002,106, 5841-5850. (8). Dutt, A.K. ; Banerjee, R.S. Oscillating Iodine Clock Reaction in Presence of Chloride Ions, J. Ind. Chem. Soc.1981, 58,717719. (9). Roux, J.C. ; Vidal, C. Synergetics - Far from Equilibrium, edited by Pacault, A. ; Vidal, C. ; Springer, Berlin, 1979, p47, and the References Therein. (10). Roux, J.C. ; Vidal, C. "Sur une Méthode d'étude Experimentale des Réactions Périodiques" Nouv. J. Chim. 1979, 3, 247. (11). Pacault, A. ; De Kepper, P. ; Hanusse, P. ; Rossi, A. Etude d'une Réaction Chimique Périodique: Diagramme des Etats, C. R. Acad. Sci. Paris, SerC,1978, 282, 215. (12). De Kepper, P. Contribution á l’étude Experimentale de Systémes Dissipatifs Chimiques : Réactions Oscillantes de BriggsRauscher et de Belousov-Zhabotinskii, D.Sc.Thesis, Bordeaux, 1978. (13). Boissonade , J ; De Kepper, P. Transitions from Bistability to Limit Cycle Oscillations : Theoretical Analysis and Experimental Evidence in an Open Chemical System, J. Phys. Chem.1980, 84, 501-506. (14). Furrow, S.D. ; Noyes,R.M. The Oscillatory Briggs-Rauscher Reaction. 1. Examination of Subsystems, J.Am.Chem.Soc. 1982, 104, 38-42. (15) Furrow, S.D. ; Noyes, R.M. The Oscillatory Briggs-Rauscher Reaction. 2. Effects of Substitutions and Additions, J. Am.Chem.Soc. 1982, 104, 42-45. (16).Noyes, R.M. ; Furrow, S.D. The Oscillatory Briggs-Rauscher Reaction. 3. A Skeleton Mechanism for Oscillations, J. Am. Chem. Soc.1982, 104, 45-48. (17). De Kepper, P ; Epstein, I.R. Mechanistic Study of Oscillations and Bi-stability in the Briggs-Rauscher Reaction, J. Am. Chem. Soc. 1982, 104, 49-55. (18).FN Rate Constants from Reference 16 : k1, 1.4 x 103 M-3s-1 ; k2, 2.0 x 109 M-2s-1 ; k3, 3.1 x 1012M-2s-1 ; k-3, 2.2 s-1 ; k4, 1.516 x 104 M-2s-1 ; k-4, 1.607 x 109 M-1s-1 ; k5, 45.30 M-1s-1 ; k6, 1.0 x 104 M-1s-1; k-6, (Neglected) ; k7, 3.2 x 104 M-1s-1 ; k8, 7.5 x 105 M-1s-1 ;

k 9 , 3.9 x 10-3s-1 ; k9 , 91s-1 ; k9 , 9.1 x 105 M-1s-1 ; k10, 37 M-1s-1.

(19). DE Rate Constants and Parameters from Reference 17: k1, 1.43 x 103 M-3s-1 ; k2, 2.0 x 1010 M-2s-1 ; k3, 3.1 x 1012M-2s-1 ; k-3, 2.2 s-1 ; k4, 7.3 x 103M-2s-1 ; k-4, 1.7 x 107 M-1s-1 ; k5, 6 x 105 M-1s-1 ; k6, 1.0 x 104 M-1s-1; k-6, (neglected) ; k7, 3.2 x 104 M-1s-1 ; k8, 7.5 x 105 M-1s-1 ;

k9  (k9k9 / k9 ) , 40 M-1s-1 ; C9  (k9 / k 9 ) , 104 M-1 ; k10, 37 M-1s-1.


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(20). Edelson, D. Sensitivity Analysis of Proposed Mechanisms for the Briggs-Rauscher Oscillating Reacrion, J.Phys.Chem. 1983, 87, 1204-1208. (21). Turanyi, T. Rate Sensitivity Analysis of a Model of the Briggs-Rauscher Reaction. React. Kinet. Catal. Lett. 1991, 45, 235241. (22). Vukojevic, V.; Sorensen, P.G.; Hynne F. Predictive Value of a Model of the Briggs-Rauscher Reaction Fitted to Quenching Experiments , J.Phys.Chem.1996, 100, 17175-17185. (23). Furrow, S.D.and Aurentz, D.J. Reactions of Iodomalonic Acid, Diiodomalonic Acid, and Other Organics in the Briggs−Rauscher Oscillating System, J. Phys. Chem. A, 2010, 114, 2526-2533. (24).Muntean, N. ; Szabó, G. ; Wittmann, M.; Lawson, T. ;Fülöp, J. ; Noszticzius, Z. ; Onel, L. Reaction Routes Leading to CO2 and CO in the Briggs−Rauscher Oscillator: Analogies between the Oscillatory BR and BZ Reactions, J. Phys. Chem. A, 2009, 113, 9102-9108. (25). Cervellati, R. ; Greco, E. ; and Furrow, S.D. Experimental and Mechanistic Investigation of an Iodomalonic Acid-Based Briggs−Rauscher Oscillator and its Perturbations by Resorcinol, J. Phys. Chem. A, 2010, 114, 12888-12892. (26). Cervellati, R. ; and Furrow, S.D. Effects of Additives on the Oscillations of the Briggs-Rauscher Reaction, Russ. J.Phys.Chem.A, 2013, 87, 2121-2126. (27). Vanag, V.K. ; Alfimov, M.V. Effects of Stirring on Photoinduced Phase Transition in a Batch-Mode Briggs-Rauscher Reaction, J. Phys. Chem., 1993, 97, 1884-1890. (28). Furrow, S.D. ; Cervellati, R. and Greco, E. Study of the Transition to Higher Iodide in the Malonic acid Briggs-Rauscher Oscillator, Reac. Kinet. Cat. Lett. 2016,118, 59-71. (29). Furrow, S.D. A Modified Recipe and Variations for the Briggs–Rauscher Oscillating Reaction, J.Chem.Educ. 2012, 89, 1421-1424. (30). Schmitz, Guy ; Furrow, S.D. Bray–Liebhafsky and Non-Catalysed Briggs–Rauscher Oscillating Reactions, Russ.J.Phys.Chem. A, 2016,90,271-275. (31). Cook, D.O. On the Effect of Copper (II) and Chloride Ions on the Iodate‐Hydrogen Peroxide Reaction in the Presence and Absence of Manganese (II), Int.J.Chem.Kinet. 1980, 12, 671-681. (32). Jacobs, S.S. ; Epstein, I.R. Effects of Chloride ion on Oscillations in the Bromate-Cerium-Malonic Acid System, J.Am. Chem. Soc., 1976, 98 , 1721-1724. (33). Belousov, B.P. Periodically Acting Reaction and Its Mechanism, 1958 Collection of Abstracts on Radiation Medicine, Medgiz, Moscow,1959, p145. (34). Latimer, W.M. Oxidation States of the Elements and Their Potentials ; Prentice Hall, NY, 1950. (35). Schmitz, Guy, Inorganic Reactions of Iodine (III) in Acidic Solutions and Free Energy of Iodous Acid Formation, Int. J. Chem. Kinet. 2008, 40, 647-652.



(36). Allen, T.L. ; Keefer, R.M. The Formation of Hypoiodous Acid and Hydrated Iodine Cation by the Hydrolysis of Iodine, J. Am. Chem. Soc. 1955, 77, 2957-2960. (37). Cervellati, R. ; and Mongiorgi, B. Inhibition of Chemical Oscillations by Bromide Ion in the Briggs–Rauscher Reaction. Int. J. Chem. Kinet. 1998, 30, 641-646. (38). Bard, A.J. ; Parsons, R. ; Jordan, J. (Eds), Standard Potentials in Aqueous Solution, Marcel Dekker Inc : New York, 1985. (39) Guckenheimer, J. ; Holmes, P. Nonlinear Oscillations, Dynamical Systems, and Bifurcations of Vector Fields ;SpringerVerlag : New York, 1983. (40). Dutt, A.K. ; Muller, S.C. Effect of Stirring and Temperature on the Belousov-Zhabotinskii Reaction in a CSTR, J. Phys. Chem. 1993, 97, 10059-10063. (41). Dutt, A.K. ; Menzinger, M. Effect of Stirring and Temperature on a Belousov-Zhabotinskii Reaction in a Batch Reactor, J. Phys. Chem.1992, 96, 8447-8449. (42). Dutt, A.K. Reversible Oregonator Model Revisited: Thermodynamic Validity, AIP Advances, 2011, 1, 042147. (43). Dutt, A.K. Asymptotically Stable Limit Cycles in a Model of Glycolytic Oscillations, Chem.Phys. Letts.1993, 208,139142. (44) Dutt, Arun K.; Menzinger, Michael, Stirring and Mixing Effects on Chemical Instabilities: Bistability of the Bromate/Bromide/Cerium(3+) System, J. Phys. Chem., 1990, 94 (12), 4867–4870. (45) Epstein, Irving R. Shaken, Stirred — But Not Mixed, Nature,1990, 346,16–17. (46) Dutt, A.K.; Datta, Avijit, Imperfect Mixing and Dead-Zone Effects in Nonlinear Dynamics: Law of Mass Action Revisited, J.Phys. Chem. A, 1998, 102, 7981–7983. (47). Sharma K.R. ; Noyes, R.M. Oscillations in Chemical Systems. 13. A Detailed Molecular Mechanism for the BrayLiebhafsky Reaction of Iodate and Hydrogen Peroxide, J. Am. Chem. Soc., 1976, 98 , 4345-4361. (48). Schmitz, Guy, Effects of Oxygen on the Bray Liebhafsky Reaction, PCCP, 1999, 1, 4605-4608. (49). Nauman, E.B. ; Buffham, B.A. Mixing in Continuous Flow Systems; Wiley: New York, 1983. (50). Westerp, K.R. ; Swaaij, W.P.M. Van ; Beenackers, A.A.C. Chemical Reactor Design and Operation;Wiley : New York, 1983. (51). Villermaux, J. Mixing in Chemical Reactors, ACS Symp. Ser.1983, 226,135-186. (52). Villermaux, J. in Encyclopedia of Fluid Mechanics ; Chereminisinoff, N.P. Ed ; Gulf Publishing : Houston, 1986; chapter 27. (53) Gyorgyi,L. ; Field,R.J. Simulation of the Effect of Stirring Rate on Bistability in the Bromate-Cerium(III)-Bromide CSTR Reaction,J. Phys. Chem., 1992, 96, 1220–1224.


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Page 15 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1: BR Mechanistic Steps Proposed by De Kepper and Epstein (DE) + ........................................................................................................................................................................................



2H+ + I- + IO3-

HOI + HIO2

HOI + I- + H+  I2 + H2O 2HIO2



HOI + IO3- + H+

;

H+ + HIO2+ I-

(B3)

;

HIO2+ IO3-+ H+  2IO2  + H2O

(B4)

IO2  + Mn+2 + H2O  HIO2 +Mn (OH)+2

(B6)

(B5)

;

H2O2 +Mn (OH)+2  HO2 + Mn+2 + H2O



(B1)

2 HO2 (B7)

;

(B9')

;

(B10)

;

MAH2  enol

2HOI

(B2)

  H2O2 + O2

I2 + enol



(B8)

IMAH + I- + H+

(B9")

HOI + H2O2  I- + O2 + H+ + H2O

........................................................................................................................................................................................ +

Malonic acid : MAH2

Table 2: BR Mechanistic Steps Revised by Furrow et al.7,* ........................................................................................................................................................................................ HOI + I- + H+  I2 + H2O



2H+ + I- + IO3-

HOI + HIO2



(BF1)

;

H+ + HIO2+ I-

(BF3)

;

H+ + HOI + substrate

2HOI



(BF2) H+ + iodohydrin

or iodosubstrate +H2O 2IO2  + H2O

H+ +IO3- +HO2 

 IO2 

+ H2O +O2

HOI + H2O2  I- + O2 + H+ + H2O I2 + enol



HIO2 + 2H2O2 + Mn+2  2HO2  + HOI + Mn+2

 HIO2 + IO3+ H+

RI + I- + H+

(BF4)

(BF10)

;

+H2O

(BF11)

(BF12)

;

IO2  + H2O2

 HIO2 + HO2 

(BF13)

(BF14)

;

RH  enol

(BF15)

(BF16)

;

2 HO2 

(BF17)

 H2O2 + O2

....................................................................................................................................................................................... *Modified steps compared with FN/DE14-17 skeleton mechanism ins Table 1 : (B3)  (BF1) ; (B2)  (BF2) ; (B1)  (BF3) ; (BF4) : Newly included to represent non-methylenic substrates ; (B4)

 (BF10) ; (B7) :

A sub-step of newly included (BF11) ;

(B4) being replaced by (BF12) ; (BF13) : Newly included to produce HIO2 auto-catalytically by coupling with (BF11) and (BF12) ; (B10)

 (BF14) ; (B9')  (BF15) ; (B9")  (BF16) ; (B8)  (BF17).



Page 16 of 35

Table 3: (a) BR Reaction in Presence of Added Chloride Ions (EAAH2/ H3PO4 System)*,+ ................................................................................................................................................................................ [NaCl]o,(M)

Induction

(2nd) Oscillation

Oscillation

Number of

Total Time of

Period (sec)

Period (sec)

Amplitude (mV)

Oscillations

Oscillations (min)

................................................................................................................................................................................ 0

18

27

17

25

18.25

0.0088

21

18

19

16

10.20

0.0176

27

21

31

14

12

0.0352

........

No Oscillations (Colorless; low potential/high I- branch)

.......

.................................................................................................................................................................................. *Other concentrations in media : [H2O2]o = 0.408M ; [Starch]o=0.019% ; [Mn+2]o = 0.009M ; [EAAH2]o = 0.033M ; [IO3]o=0.05M ; [H3PO4]o = 0.062M : +Temperature, 20oC; Stirring, 500 rpm.

(b)BR Reaction in HCl Medium (EAAH2 as the Organic Substrate)*,+ ......................................................................................................................................................................................... [HCl]o, (M)

Induction

(2nd) Oscillation

Oscillation

Number of

Total Time of

Period (sec)

Period (sec)

Amplitude (mV)

Oscillations

Oscillations (min)

........................................................................................................................................................................................ 0.014

........

No Oscillations (Low potential/ High I- branch) ........

0.018

48

18

17

45

12.5

0.027

18

24

19

8

5.3

0.037

24

36

22

6

5.7

0.046

42

66

27

4

3.6

0.064

........

No Oscillations (Low potential/High I- branch)

........

....................................................................................................................................................................................... *Other concentrations in media : [H2O2]o = 1.13M ; [Starch]o=0.016% ; [Mn+2]o = 0.011M ; [EAAH2]o = 0.04M ; [IO3]o=0.0601M : +Temperature, 20.5oC; Stirring, 500 rpm.

(c) Stirring Effects in BR Reaction (EAAH2/ H3PO4 System)*,+ ........................................................................................................................................................................................ Stirring

Induction

(2nd) Oscillation

Oscillation

Total Number

Total Time of

(rpm)

Period (sec)

Period (sec)

Amplitude (mV)

of Oscillations

Oscillations (min)


Page 17 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


........................................................................................................................................................................................ 80

15

21

30

18

10.75

1400

15

21

49

17

13.2

2600

15

21

43

20

16.3

........................................................................................................................................................................................ *Other concentrations in media : [H2O2]o = 0.445M ; [Starch]o=0.016% ; [Mn+2]o = 0.011M ; [EAAH2]o = 0.04M ; [IO3]o=0.0601M ; [H3PO4]o = 0.075M : +Temperature, 21.5oC .

(d) Stirring Effects in BR Reaction (EAAH2/HCl System)*,+ ........................................................................................................................................................................................ Stirring

Induction

(2nd) Oscillation

Oscillation

Total Number

Total Time

(rpm)

Period (sec)

Period (sec)

Amplitude (mV)

of Oscillations

of Oscillations

........................................................................................................................................................................................ 80

6

42

17

7

7.5

500

24

39

25

7

5.65

2200

18

33

56

8

9.85

........................................................................................................................................................................................ *

Concentrations in media : [H2O2]o = 1.13M ; [Starch]o=0.016% ; [Mn+2]o = 0.011M ; [EAAH2]o = 0.04M ; [IO3-]o=0.0601M

; [HCl]o = 0.037M : +Temperature, 20.5oC.

(e): Temperature Effects in BR Reaction (EAAH2/ H3PO4 system)*,+ .................................................................................................................................................................................... Temperature Induction o

( C)

Period (sec)

(2nd) Oscillation

Oscillation

Total Number

Total Time

Period (sec)

Amplitude(mV)

of Oscillations

of oscillations (min)

................................................................................................................................................................................... 11

24

39

48

13

25.6

20

18

18

37

19

17

30

21

15

42

24

8.7

35

15

12

42

29

7.7

................................................................................................................................................................................... *

Concentrations in media: Same as that in Table 3c : +Stirring, 500rpm.

(f): Temperature Effects in BR Reaction (EAAH2/ HCl System)*,+



Page 18 of 35

.................................................................................................................................................................................... Temperature Induction

(2nd) Oscillation

Oscillation

(oC)

Period (sec)

Amplitude(mV) of Oscillations

Period (sec)

Total Number

Total Time of Oscillations (min)

.................................................................................................................................................................................... 05

..... (Multiple complex oscillations: important for further investigations) ......

10

03

63

40

06

6.55

20

03

39

38

07

6.05

30

03

24

36

07

4.1

.................................................................................................................................................................................... *

Concentrations in media: Same as that in Table 3d: +Stirring, 500rpm.

Table 4: Free Energies of Formation (at 250C) of Important Species with Singlet Ground States: .................................................................................................. Species

Free Energy of Formation (KJ mol-1)34

................................................................................................... HOI (aq)

-98.67

Cl- (aq)

-131.25

H+(aq)

0

ICl (aq)

-14.85

H2O (l)

-237.19

I- (aq)

-51.67

I2 (aq)

16.43

.....................................................................................................

Table 5: Mechanistic Steps of the Minimal Bromate Oscillator (MBO): ........................................................................................................................................................................................ 2H+ + Br- + BrO3-  HOBr + HBrO2

(M1)

;

H+ + HBrO2+ Br-  2HOBr

(M2)

HOBr + Br- + H+  Br2 + H2O

(M3)

;

HBrO2+ BrO3-+ H+  2BrO2  + H2O

(M4)

Ce+3 + BrO2  + H+  HBrO2 + Ce+4

(M5)

;

2HBrO2  BrO3- + HOBr + H+

(M6)

........................................................................................................................................................................................


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Table 6: BR Reaction (EAAH2/ H3PO4 System) in N2 Atmosphere *, + ............................................................................................................................. Flow Rate of N2 -1

Gas (ml min )

2nd Oscillation Period

Oscillation Amplitude

(sec)

(mV)

............................................................................................................................. 0

24

33

30

24

28

......................................................................................................................................................................................................

*

Concentrations in media : [H2O2]o = 0.445M ; [Starch]o=0.023% ; [Mn+2]o = 0.011M ; [EAAH2]o = 0.04M ; [IO3-]o=0.06M

; [H3PO4]o = 0.075M : +Temperature, 20.5oC; Stirring, 500rpm.



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Caption to the figures: Fig.1. Potential traces of BR reaction in H3PO4 media in absence and presence of added NaCl ; (a) [NaCl] 0= 0.0M, (b) [NaCl]0=0.0176M ; (c) Induction period (sec), Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction in H3PO4 media at different concentrations of added NaCl ; the component concentrations, temperature and stirring rate as shown in Table 3a. Fig.2. Potential traces of BR reaction in HCl media; (a) [HCl]0=0.018M, (b) [HCl]0= 0.046M ; (c) Induction period (sec) , Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction at different HCl concentrations ; the component concentrations, temperature and stirring rate as shown in Table 3b. Fig.3 (a), Eigenvalues (  ) of the Jacobian matrix cross the imaginary axis as the bifurcation parameter

 passes the

bifurcation point ; (b), Stable supercritical Hopf bifurcation shown in two dimensions perpendicular to the

 axis ; (c),

Although the eigenvalues cross the imaginary axis, there is no stable periodic orbit at the bifurcation point (Subcritical Hopf bifurcation) – after a subcritical bifurcation the unstable orbits which appear remain surrounded by stable orbits for other appropriate values of



and the system becomes bi-stable (reproduced with permission from ref.39).

Fig.4. Potential traces of BR reaction in H3PO4 media at two different stirring rates ; (a) S=80 rpm, (b) S=1400rpm ; (c) Induction period (sec), Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction in H3PO4 media at different stirring rates ; the component concentrations and temperature, same as shown in Table 3c. Fig.5. Potential traces of BR reaction in HCl media at two different stirring rates; (a) S=80 rpm, (b) S=2200 rpm ; c) Induction period (sec), Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction in HCl media at different stirring rates ; the component concentrations and temperature, same as shown in Table 3d. Fig.6. Potential traces of BR reaction in H3PO4 media at two different temperatures; (a) T=110C, (b) T=350C ; c) Induction period (sec), Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction in H 3PO4 media at different temperatures ; the component concentrations and stirring rate, same as shown in Table 3e. Fig.7. Potential traces of BR reaction in HCl media at two different temperatures; (a) T=10 0C, (b) T=300C ; c) Induction period (sec), Oscillation period (sec) and Oscillation amplitude (mV) in BR reaction in HCl media at different temperatures ; the component concentrations and stirring rate, same as shown in Table 3f.

Figures:


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Fig.1. Potential traces of BR reaction in H3PO4 media in absence and presence of added NaCl ; (a) [NaCl] 0= 0.0M, (b) [NaCl]0=0.0176M ; (c) Induction period (sec), Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction in H 3PO4 media at different concentrations of added NaCl ; the component concentrations, temperature and stirring rate as shown in Table 3a.



Fig.2. Potential traces of BR reaction in HCl media; (a) [HCl]0=0.018M, (b) [HCl]0= 0.046M ; (c) Induction period (sec) , Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction at different HCl concentrations ; the component concentrations, temperature and stirring rate as shown in Table 3b.


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Fig.3 (a), Eigenvalues (  ) of the Jacobian matrix cross the imaginary axis as the bifurcation parameter

 passes the

bifurcation point ; (b), Stable supercritical Hopf bifurcation shown in two dimensions perpendicular to the

 axis ; (c),

Although the eigenvalues cross the imaginary axis, there is no stable periodic orbit at the bifurcation point (Subcritical Hopf bifurcation) – after a subcritical bifurcation the unstable orbits which appear remain surrounded by stable orbits for other appropriate values of



and the system becomes bi-stable (reproduced with permission from ref.39).



Fig.4. Potential traces of BR reaction in H3PO4 media at two different stirring rates ; (a) S=80 rpm, (b) S=1400rpm ; (c) Induction period (sec), Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction in H3PO4 media at different stirring rates ; the component concentrations and temperature, same as shown in Table 3c.


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Fig.5. Potential traces of BR reaction in HCl media at two different stirring rates; (a) S=80 rpm, (b) S=2200 rpm ; c) Induction period (sec), Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction in HCl media at different stirring rates ; the component concentrations and temperature, same as shown in Table 3d.



Fig.6. Potential traces of BR reaction in H3PO4 media at two different temperatures; (a) T=110C, (b) T=350C ; c) Induction period (sec), Oscillation period (sec), and Oscillation amplitude (mV) in BR reaction in H 3PO4 media at different temperatures ; the component concentrations and stirring rate, same as shown in Table 3e.


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Fig.7. Potential traces of BR reaction in HCl media at two different temperatures; (a) T=10 0C, (b) T=300C ; c) Induction period (sec), Oscillation period (sec) and Oscillation amplitude (mV) in BR reaction in HCl media at different temperatures ; the component concentrations and stirring rate, same as shown in Table 3f.



TOC Graphic


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Chloride Ion Inhibition, Stirring, and Temperature Effects in an

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