The Bray-Liebhafsky oscillatory reaction: Kinetic investigations in reduction and oxidation pathways based on hydrogen peroxide concentration monitoring

By direct monitoring of the hydrogen concentration during its catalytic decomposition into water and oxygen in the presence of potassium iodate and sulfuric acid, that is in the Bray-Liebhafsky system, the pseudo-rate constants of overall reduction and oxidation pathways were determined The dependence of the obtained rate constants on acidity was evaluated. It was found that the pseudo-rate constant of the overall reduction process increases with increasing acidity, whereas the pseudo-rate constant of the overall oxidation process decreases with increasing acidity. The corresponding activation energies were also calculated using values of this constant at two temperatures.Direktnim praćenjem koncentracije vodonik-peroksida u toku njegovog katalitičkog razlaganja na vodu i kiseonik u prisustvu kalijum-jodata i sumporne kiseline, odnosno u Bray-Lievhafsky sistemu, analizirane su konstante brzina celokupnog redukcionog i oksidacionog puta kao konstante brzina pseudo-prvog reda. izvedene su njihove zavisnosti od kiselosti. Nađeno je da pseudo-konstanta brzine celokupnog redukcionog procesa raste sa porastom kiselosti, dok pseudo-konstanta brzine celokupnog oksidacionog procesa opada sa porastom kiselosti. korišćenjem njihovih vrednosti na dve temperature izračunate su odgovarajuće energije aktivacija

Doprinosi Beogradske grupe izučavanju oscilatornih reakcija

Oscillatory dynamic states as one form of selforganization of nonlinear systems can be found in almost all sciences, like mechanics, physical chemistry or biomedicine. Although origin of these oscillations is different, computational challenges in modelling oscillatory phenomena remain similar in all fields. Since 1979 researchers from Belgrade's group perform systematic examinations of oscillatory reactions. As stability of steady states is the central point in modelling oscillatory reactions, in last 10 years they have adapted and improved powerful tool of the Stoichiometric Network Analysis for this goal. Moreover, bifurcations of few types were identified in several models of oscillatory reactions. Even very complex chaotic motions in phase space were characterized and quantified by several numerical techniques. Multiple time scale behaviour is found within the core of the complex dynamic behaviour of mixed-mode oscillations. Analytical applications were developed, too.Oscilatorna dinamička stanja, kao oblik samoorganizacije nelinearnih sistema, mogu se naći u gotovo svim naukama, kao što su mehanika, fizička hemija ili biomedicina. Iako je poreklo ovih oscilacija različito, teškoće u modeliranju oscilatornih fenomena su zajedničke na svim poljima. Od 1979. godine istraživači Beogradske grupe sistematski istražuju oscilatorne reakcije. Kako je stabilnost ustaljenih stanja ključni problem u modeliranju oscilatornih reakcija, u poslednjih 10 godina oni su za tu namenu usvojili i unapredili moćnu tehniku Analize stehiometrijskih mreža. Zatim je identifikovano više tipova bifurkacija u nekoliko modela oscilatornih reakcija. Čak su i veoma složena haotična kretanja u koncentracionom faznom prostoru okarakterisana i kvantifikovana različitim numeričkim tehnikama. Ustanovljeno je da izvor oscilacija mešanih modova i drugih uočenih složenih oblika dinamike predstavljaju procesi koji se odigravaju na različitim vremenskim skalama. Takođe su razvijene i analitičke primene oscilatornih reakcija

Belousov-Žabotinski oscilatorna reakcija - kinetika razlaganja malonske kiseline

The kinetics of the Belousov-Zhabotinsky (BZ) oscillatory reaction was analyzed. With this aim, the time evolution of a reaction mixture composed of malonic acid, bromate, sulfuric acid and cerium(III) was studied at 298 K. Pseudo-first order kinetics with respect to malonic acid as the species undergoing decomposition with a corresponding rate constant, k = 7.5x10-3 min-1, was found.Sa ciljem da se analizira kinetika Belousov-Žabotinski oscilatorne reakcije, proučavana je vremenska evolucija reakcione smeše koja se sastoji od malonske kiseline, sumporne kiseline i cerijuma(III) na 298 K. Nađena je kinetika pseudo-prvog reda u odnosu na malonsku kiselinu kao vrstu koja podleže razlaganju i odgovarajuća konstanta brzine, k = 7.5x10-3 min-1

The Bray-Liebhafsky oscillatory reaction: Kinetic investigations in reduction and oxidation pathways based on hydrogen peroxide concentration monitoring

By direct monitoring of the hydrogen concentration during its catalytic decomposition into water and oxygen in the presence of potassium iodate and sulfuric acid, that is in the Bray-Liebhafsky system, the pseudo-rate constants of overall reduction and oxidation pathways were determined The dependence of the obtained rate constants on acidity was evaluated. It was found that the pseudo-rate constant of the overall reduction process increases with increasing acidity, whereas the pseudo-rate constant of the overall oxidation process decreases with increasing acidity. The corresponding activation energies were also calculated using values of this constant at two temperatures.Direktnim praćenjem koncentracije vodonik-peroksida u toku njegovog katalitičkog razlaganja na vodu i kiseonik u prisustvu kalijum-jodata i sumporne kiseline, odnosno u Bray-Lievhafsky sistemu, analizirane su konstante brzina celokupnog redukcionog i oksidacionog puta kao konstante brzina pseudo-prvog reda. izvedene su njihove zavisnosti od kiselosti. Nađeno je da pseudo-konstanta brzine celokupnog redukcionog procesa raste sa porastom kiselosti, dok pseudo-konstanta brzine celokupnog oksidacionog procesa opada sa porastom kiselosti. korišćenjem njihovih vrednosti na dve temperature izračunate su odgovarajuće energije aktivacija

Stoichiometric network analysis of a reaction system with conservation constraints

Stoichiometric Network Analysis (SNA) is a powerful method that can be used to examine instabilities in modelling a broad range of reaction systems without knowing the explicit values of reaction rate constants. Due to a lack of understanding, SNA is rarely used and its full potential is not yet fulfilled. Using the oscillatory carbonylation of a polymeric substrate [poly(ethylene glycol) methyl ether acetylene] as a case study, in this work, we consider two mathematical methods for the application of SNA to the reaction models when conservation constraints between species have an important role. The first method takes conservation constraints into account and uses only independent intermediate species, while the second method applies to the full set of intermediate species, without the separation of independent and dependent variables. Both methods are used for examination of steady state stability by means of a characteristic polynomial and related Jacobian matrix. It was shown that both methods give the same results. Therefore, as the second method is simpler, we suggest it as a more straightforward method for the applications. Published by AIP Publishing

Pulse perturbation technique for determination of piroxicam in pharmaceuticals using an oscillatory reaction system

A simple and reliable novel kinetic method for the determination of piroxicam (PX) was proposed and validated. For quantitative determination of PX, the Bray-Liebhafsky (BL) oscillatory reaction was used in a stable non-equilibrium stationary state close to the bifurcation point. Under the optimized reaction conditions (T = 55.0A degrees C, [H2SO4](0) = 7.60x10(-2) mol L-1, [KIO3](0) = 5.90x10(-2) mol L-1, [H2O2](0) = 1.50x10(-1) mol L-1 and j (0) = 2.95x10(-2) min(-1)), the linear relationship between maximal potential shift Delta E (m) , and PX concentration was obtained in the concentration range 11.2-480.5 A mu g mL(-1) with a detection limit of 9.9 A mu g mL(-1). The method had a rather good sample throughput of 25 samples h(-1) with a precision RSD = 4.7% as well as recoveries RCV a parts per thousand currency sign 104.4%. Applicability of the proposed method to the direct determination of piroxicam in different pharmaceutical formulations (tablets, ampoules and gel) was demonstrated

Applicability of Bray-Liebhafsky reaction for chemical computing

The first discovered homogeneous oscillatory reaction was the Bray-Liebhafsky (BL) one, described in a paper published exactly 100 years ago. However, the applicability of oscillatory reactions in chemical computing was recently discovered. Here we intend to expose the native computing concept applied to intermittent states of the BL reaction, because we believe that this particular state may have some advantages. For this purpose, numerical simulations will be used based on the known model. Sequences of perturbations will be introduced by adding iodate (IO3 - ) and hydrogen peroxide (H2O2), separately, as well as in various combinations with one another. It will be shown that dynamic states obtained after perturbations with same species depend very much on the sequence in which these species were used in perturbations. Additionally, it will be shown that obtained dynamic states shift the system from chaotic intermittent dynamic state to different complex periodic states. Hence, the applicability of the BL reaction system in chemical computing was demonstrated

Intermittent Chaos in the CSTR Bray–Liebhafsky Oscillator-Specific Flow Rate Dependence

Dynamic states with intermittent oscillations consist of a chaotic mixture of large amplitude relaxation oscillations grouped in bursts, and between them, small-amplitude sinusoidal oscillations, or even the quiescent parts, known as gaps. In this study, intermittent dynamic states were generated in Bray–Liebhafsky (BL) oscillatory reaction in an isothermal continuously-fed, well-stirred tank reactor (CSTR) controled by changes of specific flow rate. The intermittent states were found between two regular periodic states and obtained for specific flow rate values from 0.020 to 0.082 min−1 . Phenomenological analysis based on the quantitative characteristics of intermittent oscillations, as well as, the largest Lyapunov exponents calculated from experimentally obtained time series, both indicated the same type of behavior. Namely, fully developed chaos arises when approaching to the vertical asymptote which is somewhere between two bifurcations. Hence, this study proposes described route to fully developed chaos in the Bray-Liebhafsky oscillatory reaction as an explanation for experimentally observed intermittent dynamics. This is in correlation with our previously obtained results where the most chaotic intermittent chaos was achieved between the periodic oscillatory dynamic state and stable steady state, generated in BL under CSTR conditions by varying temperature and inflow potassium iodate concentration. Moreover, it was shown that, besides the largest Lyapunov exponent, analysis of chaos in experimentally obtained intermittent states can be achieved by a simpler approach which involves using the quantitative characteristics of the BL reaction evolution, that is, the number and length of gaps and bursts obtained for the various values of specific flow rates

Gallic acid effect on the Briggs-Rauscher reaction dynamics

The effect of different concentration of gallic acid (GA) on the oscillatory behavior of the Briggs-Rauscher (BR) reaction is reported. In this work, the sample was injected before the start of oscillations. The main effect is the appearance of an induction time that increases with the concentration of GA added. Other parameters as a number of oscillations and oscillatory period are affected. These latter linearly depend on the concentration and can be used for quantitative GA analytical assay in a GA concentration range 3.00×10-5 M − 4.00×10-4 M. The perturbation is very different from that previously reported, in which samples of phenolics were added to an active BR mixture, indicating that the mechanism of perturbation largely depends on the injection point

Tourbillion in the phase space of the Bray-Liebhafsky nonlinear oscillatory reaction and related multiple-time-scale model

The mixed-mode dynamical states found experimentally in the concentration phase space of the iodate catalyzed hydrogen peroxide decomposition (The Bray-Liebhafsky oscillatory reaction) are discussed theoretically in a related multiple-time-scale model, from the viewpoint of tourbillion. With aim to explain the mixed-mode oscillations obtained by numerical simulations of the various dynamical states of a model for the Bray-Liebhafsky reaction under CSTR conditions, the folded singularity points on the critical manifold of the full system and Andronov-Hopf bifurcation of the fast subsystem are calculated. The interaction between those singularities causes occurrence of tourbillion structure