Bromomalonic Acid Research Articles

Effects of Selenium Species on the Belousov-Zhabotinsky Reaction.

The effects of selenium species on the Belousov-Zhabotinsky (B-Z) reaction were investigated by adding them to the system before and during oscillation. When selenium species were added into the system before oscillation, sodium selenite prolonged the induction period, whose effect was strong as sodium selenite could consume malonic acid to prohibit the accumulation of bromomalonic acid. For selenomethionine and selenocystine, their effects were derived from their reaction with •CH2COOH and •Br2- producing a radical cation of selenoamino acids, which prohibited the accumulation of bromomalonic acid. Here, the selenium atoms in selenoamino acids, as reactive centers, took part in the redox reaction. As a result, the induction period was prolonged. However, as a diselenide, selenocystine can reduce bromate in acidic medium, which led to shortening of the induction period. Therefore, the effect of selenocystine on the induction period was the result of two opposite effects. Nanoselenium shortened the induction period in a certain concentration range because bromate was directly reduced by nanoselenium and the accumulation of bromomalonic acid was promoted. Furthermore, the dose perturbation effect was investigated by the injection of nanoselenium during oscillation. It was found that the amplitude was increased or decreased in a dose-dependent fashion when nanoselenium was injected at peak or trough of the time-dependent redox potential curve.

Batch pH Oscillations in the Belousov-Zhabotinsky Reaction.

No single-phase system has been previously reported to give significant pH oscillations in a closed (batch) reactor. We report here sustained pH oscillations in batch for the Belousov-Zhabotinsky reaction using much lower [H+]0 and much higher [BrO3-]0 than in traditional studies of this reaction. In fact, pH oscillations were obtained in the presence of only BrO3-, malonic acid (MA), and Mn2+. The amplitude, frequency, and duration of oscillations tend to depend primarily on the ratio of [BrO3-]0 to [MA]0. A critical part of the proposed mechanism involves the reversible formation of a manganese(III) complex with bromomalonic acid, followed by two-electron oxidation to tartraric acid and Mn2+. Estimates of the corresponding rate constant values for these reactions have been obtained by simulation. It is suggested that the presence of a supercatalytic reaction in H+ may be a sufficient, if not necessary, requirement for the occurrence of pH oscillations in a batch system.

Measurements and Simulations of the Acidity Dependence of the Kinetics of the Iron-Catalyzed Belousov-Zhabotinsky Reaction: Proton-Catalysis in the Electron Transfer Reaction Involving the [Fe(phen)3]3+ Species.

The acidity dependence of the iron-catalyzed bromate-malonic acid Belousov-Zhabotinsky reaction was studied in the range 0.36 M < [H2SO4]0 < 1.20 M, and the temporal evolutions of the oscillation patterns were analyzed. The experimental results show that the period times PT i decrease exponentially with increasing acidity and that the period times parallel the decrease of the reduction times RT with increasing acidity. Simulations using the reactions of the commonly accepted core reaction mechanism failed to match the measurements even in a qualitative fashion. However, we found that compelling agreement between the experiments and the simulations can be achieved over the entire range with the inclusion of second-order proton-catalysis of the oxidation of bromomalonic acid (BrMA) by the [Fe(phen)3]3+ species in the reaction identified in this paper as reaction 9 (R9), and this [H+] dependence is informative about the species involved in the outer sphere electron transfer reaction. The trication [Fe(phen)3]3+ species is stabilized by ion pairing and solvation, and one may anticipate the presence of [Fe(phen)3(HSO4) n(H2O) m](3- n)+ species ( n = 0-3). Our results suggest that the removal of aggregating HSO4- ions by protonation creates a better oxidant and facilitates the approach of the reductant BrMA, and the second-order [H+] dependence further suggests that BrMA is primarily oxidized by a doubly charged [Fe(phen)3(HSO4)1(L) k]2+ species. Considering the complexity of the BZ system and the uncertainties in the many reaction rate constants, we were somewhat surprised to find this high level of agreement by (just) the replacement of R9 by R9'. In fact, the near-quantitative agreement presents a powerful corroboration of the core reaction mechanism of the BrMA-rich BZ reaction, and the replacement of R9 by R9' extends the validity of this core reaction mechanism to acidities above and below the typical acidity of BZ reactions ([H+] ≈ 1 M).

Chaos in the Belousov–Zhabotinsky reaction

The dynamics of reacting chemical systems is governed by typically polynomial differential equations that may contain nonlinear terms and/or embedded feedback loops. Thus the dynamics of such systems may exhibit features associated with nonlinear dynamical systems, including (among others): temporal oscillations, excitability, multistability, reaction-diffusion-driven formation of spatial patterns, and deterministic chaos. These behaviors are exhibited in the concentrations of intermediate chemical species. Bifurcations occur between particular dynamic behaviors as system parameters are varied. The governing differential equations of reacting chemical systems have as variables the concentrations of all chemical species involved, as well as controllable parameters, including temperature, the initial concentrations of all chemical species, and fixed reaction-rate constants. A discussion is presented of the kinetics of chemical reactions as well as some thermodynamic considerations important to the appearance of temporal oscillations and other nonlinear dynamic behaviors, e.g., deterministic chaos. The behavior, chemical details, and mechanism of the oscillatory Belousov–Zhabotinsky Reaction (BZR) are described. Furthermore, experimental and mathematical evidence is presented that the BZR does indeed exhibit deterministic chaos when run in a flow reactor. The origin of this chaos seems to be in toroidal dynamics in which flow-driven oscillations in the control species bromomalonic acid couple with the BZR limit cycle.

Synthesis and Characterization of [60]Fullerene-Glycidyl Azide Polymer and Its Thermal Decomposition

A new functionalized [60]fullerene-glycidyl azide polymer (C60-GAP) was synthesized for the first time using a modified Bingel reaction of [60]fullerene (C60) and bromomalonic acid glycidyl azide polymer ester (BM-GAP). The product was characterized by Fourier transform infrared (FTIR), ultraviolet-visible (UV-Vis), and nuclear magnetic resonance spectroscopy (NMR) analyses. Results confirmed the successful preparation of C60-GAP. Moreover, the thermal decomposition of C60-GAP was analyzed by differential scanning calorimetry (DSC), thermogravimetric analysis coupled with infrared spectroscopy (TGA-IR), and in situ FTIR. C60-GAP decomposition showed a three-step thermal process. The first step was due to the reaction of the azide group and fullerene at approximately 150 °C. The second step was ascribed to the remainder decomposition of the GAP main chain and N-heterocyclic at approximately 240 °C. The final step was attributed to the burning decomposition of amorphous carbon and carbon cage at around 600 °C.

Synthesis and Characterization of [60]Fullerene-Poly(glycidyl nitrate) and Its Thermal Decomposition

A new energetic fullerene derivative [60]fullerene-poly(glycidyl nitrate) (C60-PGN) was synthesized through a modified Bingel reaction of C60 and bromomalonic acid PGN ester in the presence of amino acid and dimethyl sulfoxide. The obtained product was characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and ultraviolet–visible spectroscopy. Results confirmed that C60-PGN was synthesized successfully. The thermal decomposition analysis of C60-PGN was investigated by differential scanning calorimetry and thermogravimetric analysis with infrared spectroscopy, which revealed that C60-PGN exhibits good resistance to thermal decomposition up to 200 °C. The kinetic parameters of the thermal decomposition of C60-PGN were also obtained from the differential thermal analysis data by Kissinger and Ozawa–Doyle methods, with Ea = 170.85 and 168.29 kJ·mol–1, respectively. C60-PGN exhibits stability higher than that of any other known polynitrofullerenes.

Chemical activity induces dynamical force with global structure in a reaction-diffusion-convection system

We found a rotating global structure induced by the dynamical force of local chemical activity in a thin solution layer of excitable Belousov-Zhabotinsky reaction coupled with diffusion. The surface flow and deformation associated with chemical spiral waves (wavelength about 1 mm) represents a global unidirectional structure and a global tilt in the entire Petri dish (100 mm in diameter), respectively. For these observations, we scanned the condition of hierarchal pattern selection. From this result, the bromomalonic acid has an important role to induce the rotating global structure. An interaction between a reaction-diffusion process and a surface-tension-driven effect leads to such hierarchal pattern with different scales.

The Source of the Carbon Monoxide in the Classical Belousov−Zhabotinsky Reaction

CO and CO2 evolution was measured in a cerium and in a ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction. These gases were stripped from the reaction mixture by a N2 carrier gas, mixed with H2, converted to methane on a Ni catalyst, and then measured by a flame ionization detector (FID). CO could be detected separately by absorbing CO2 on a soda lime column. In separate experiments it was proven that CO is produced in a reaction of BrO2* radicals with bromomalonic acid (BrMA). To this end BrO2(.-) radicals were generated in two different ways: (i) in the reaction HBrO2 + HBrO3 <--> 2 BrO2(.-) + H2O and (ii) by reducing HBrO3 to BrO2(.-) by Fe(2+). It was found that (.-)OH radicals--produced by Fenton's reagent--can also generate CO from BrMA. We propose that CO can be formed when an inorganic radical (like BrO2(.-) or (.-)OH) reacts with the enol form of BrMA producing an acyl radical which decarbonylates in the next step. Malonic acid (MA)-BrMA mixtures were prepared by a new method modifying Zaikin and Zhabotinsky's original recipe to minimize the production of dibromomalonic acid (Br2MA).

Contribution to the Chemistry of the Belousov−Zhabotinsky Reaction. Products of the Ferriin−Bromomalonic Acid and the Ferriin−Malonic Acid Reactions

In the present mechanistic schemes of the ferroin-catalyzed oscillatory Belousov-Zhabotinsky (BZ) reaction the oxidation of the organic substrates (bromomalonic or malonic acid) by ferriin (the oxidized form of the catalyst) plays an important role. As the organic products of these reactions were not yet identified experimentally, they were studied here by an HPLC technique. It was found that the main organic oxidation product of bromomalonic acid is bromo-ethene-tricarboxylic acid (BrEETRA), the same compound that is formed when bromomalonic acid is oxidized by Ce4+ (another catalyst of the BZ reaction). Formation of BrEETRA is explained here by a new mechanism that is more realistic than the one suggested earlier. To find any oxidation product of malonic acid in the ferriin-malonic acid reaction was not successful, however. Neither ethane-tetracarboxylic acid (ETA) nor malonyl malonate (MAMA), the usual products of the Ce4+- malonic acid reaction, nor any other organic acid, not even CO2, was found as a product of the reaction. We propose that malonic acid is not oxidized in the ferriin-malonic acid reaction, and it plays only the role of a complex forming catalyst in a process where Fe3+ oxidizes mostly its phenantroline ligand.

Reaction of organozinc reagents prepared from bromomalonic acid esters and zinc with 3-aryl-2-cyanopropenoic acid primary amides

Organozinc compounds prepared from bromomalonic acid esters and zinc react with 3-aryl-2-cyanopropenoic acid primary amides giving a single diastereomer of the corresponding 1-R′-4-aryl-2,6-dioxo-5-cyanopiperidine-3-carboxylic acid esters, or 3-R′-6-aryl-2,4-dioxo-5-cyano-3-azabicyclo[3.1.0]hexene-1-carboxylic acid esters.

Uncatalyzed Reactions in the Classical Belousov−Zhabotinsky System. 2. The Malonic Acid−Bromate Reaction in Acidic Media

The title reaction was studied with various techniques in 1 M sulfuric acid, a usual medium for the oscillatory Belousov-Zhabotinsky (BZ) reaction. It was found to be a more complex process than the bromomalonic acid (BrMA)-BrO3- reaction studied previously in the first part of this work. Malonic acid (MA) can react with acidic bromate by two parallel mechanisms. The main aim of the present research was to determine the mechanisms, the rate laws, and the rate constants for these parallel channels. In one reaction channel the first molecular products are glyoxalic acid (GOA) and CO2 while in the other channel mesoxalic acid (MOA) is the first molecular intermediate, that is, no CO2 is formed in this step. To prove these two independent routes specific colorimetric techniques were developed to determine GOA and MOA selectively. The rate of the GOA channel was determined by following the rate of the carbon dioxide evolution characteristic for this reaction route. In this step, regarding it as an overall process, one MA is oxidized to GOA and CO2 and one BrO3- is reduced to HOBr, which forms BrMA with another MA. The initial rate of the GOA channel is a bilinear function of the initial MA and BrO3- concentrations with a second-order rate constant k(GOA)= 2.4 x 10(-7) M(-1) s(-1). The rate of the other channel was calculated from the rate of the BrO3- consumption measured in separate experiments, assuming that the measured depletion is a sum of two separate terms reflecting the consumptions due to the two independent channels. In the MOA channel one MA is oxidized to MOA and one BrO3- is consumed while another MA is brominated as in the GOA channel. It was found that the initial rate of the MOA channel is also a bilinear function of the MA and BrO3- concentrations with a second-order rate constant k(MOA)= 2.46 x 10(-6) M(-1) s(-1). Separate chemical mechanisms are suggested for both channels. In all of the various bromate-substrate reactions of these mechanisms oxygen atom transfer from the bromate to the substrate occurs generating bromous acid intermediate. This can be of high importance in BZ systems as bromous acid is the autocatalytic intermediate there. GOA and MOA also can be oxidized by acidic bromate but a study of these reactions will be published later.

Uncatalyzed Reactions in the Classical Belousov−Zhabotinsky System. I. Reactions of Bromomalonic Acid with Acidic Bromate and with HOBr

The uncatalyzed reactions of bromomalonic acid (BrMA) with acidic bromate and with hypobromous acid were studied in 1 M sulfuric acid, a usual medium for the oscillatory Belousov-Zhabotinsky (BZ) reaction, by following the rate of the carbon dioxide evolution associated with these reactions. In addition, the decarboxylation rate of dibromomalonic acid (Br2MA) was also measured to determine the first-order rate constant of its decomposition (4.65 x 10(-5) s(-1) in 1 M H2SO4). The dependence of that rate constant on the hydrogen ion concentration suggests a carbocation formation. A slow oligomerization of BrMA observed in sulfuric acid solutions is also rationalized as a carbocationic process. The initial rate of the BrMA-BrO3- reaction is a bilinear function of the BrMA and BrO3- concentrations with a second-order rate constant of 3.8 x 10(-4) M(-1) s(-1). When a great excess of BrO3- is applied, then BrMA is oxidized mostly to CO2. A reaction scheme compatible with the experimental finding is also given. On the other hand, when less BrO3- and more organic substrate - BrMA or malonic acid (MA)--is applied, then addition reactions of various carbocations with the enol form of the organic substrates should be taken into account in later stages of the reaction. It was discovered that HOBr, which brominates BrMA to Br2MA when BrMA is in excess, can also oxidize BrMA when HOBr is in excess. As Br2MA does not react with HOBr, it is assumed that the acyl hypobromite, formed in the first step of the HOBr and BrMA reaction, can react with an additional HOBr to give oxidation products. It was found that the initial rate of the reaction can be described by the following experimental rate law: k(BHOB)[BrMA]0[HOBr]0(2), where k(BHOB) = 5 M(-2) s(-1). A reaction scheme for the oxidation of BrMA by HOBr is given for conditions where HOBr is in excess. Model calculations illustrate qualitatively that the suggested reaction schemes are able to mimic the experiments. (More quantitative simulations are prevented by kinetic data missing for the various carbocation intermediates.) Finally, the effects of these newly observed reactions on oscillatory BZ systems are discussed briefly.

Density Changes Accompanying Wave Propagation in the Cerium-Catalyzed Belousov−Zhabotinsky Reaction

Refractive index measurement using an interferometric imaging system and observation of chemical wave shapes were carried out during chemical wave propagation of a cerium-catalyzed Belousov-Zhabotinsky (BZ) reaction. Densities increased as chemical waves propagated in samples without NaBr, and decreased in samples with NaBr. Concentration changes of malonic acid, bromomalonic acid, and BrO3- were estimated from Raman spectral measurements in a stirred batch BZ reaction, and these also exhibited differences between samples with and without NaBr. It is proposed that a reaction subset yielding low molecular weight carboxylic acids is predominant in samples with NaBr, whereas a pathway leading to dibromoacetic acid or tribromoacetic acid production is the major process in samples without NaBr.

HPLC analysis of complete BZ systems. Evolution of the chemical composition in cerium and ferroin catalysed batch oscillators: experiments and model calculations.

In the last few years many new reaction routes and intermediates have been discovered in the mechanism of the Belousov-Zhabotinsky (BZ) reaction with the aid of high performance liquid chromatography (HPLC). These previous HPLC studies, however, were limited to the Ce(4+)-organic substrate (malonic or bromomalonic acid) systems only. Very recently some measurements were made on a cerium catalysed full BZ system but only in its induction period. The present work follows the evolution of the main chemical components in a cerium and in a ferroin catalysed full BZ system from the start until the end of the oscillatory regime in a batch reactor. While recording the potential oscillations of a bromide selective electrode we measured from time to time the concentration of the following components: malonic and bromomalonic acids and bromate as main components; malonyl malonate, ethanetetracarboxylic and bromoethenetricarboxylic acids which are recombination products of organic free radicals; oxidized intermediates: tartronic, oxalic (OA) and mesoxalic (MOA) acids, and brominated products: dibromoacetic and tribromoacetic acids. Recombination products are generated in the intervals when the autocatalytic reaction is "switched off". In the course of the autocatalytic periods, however, the organic radicals react with the inorganic bromine dioxide radical mainly which leads to the formation of MOA and OA. Due to a very fast Ce(4+)-MOA reaction, MOA can be detected in the ferroin catalysed BZ system only. Our model calculations deal exclusively with the cerium catalysed system. The suggested new Marburg-Budapest-Missoula (MBM) model includes both negative feedback loops (bromous acid-bromide ion Oregonator type and bromine dioxide-organic free radicals Radicalator type feedback) and the recently discovered radical-radical recombination reactions. Comparison of the experimental data with the model calculations shows a good qualitative agreement but some open problems still remain. To overcome these problems oxygen atom transfer and other redox reactions are proposed.

The Light-Perturbed Ru-Catalyzed Belousov−Zhabotinsky Reaction: Evidence for Photochemically Produced Bromous Acid and Bromide Ions by Phase Response Analysis

Phase response analysis of light-perturbed closed and aging Ru-catalyzed Belousov−Zhabotinsky (BZ) reactions with malonic, methyl-, ethyl-, butyl-, and phenylmalonic acids as organic substrates suggests two major responses of the light-perturbed Ru-catalyzed BZ system. One is the photoproduction of bromous acid (HBrO2) in the beginning of the reaction when little bromoorganic species are present, while another response is the photoproduction of bromide ions in the presence of bromomalonic acid or bromomalonic acid derivatives. From this analysis the light-induced production of bromide ions directly from bromate can be excluded. The experimentally observed phase response curves agree well with calculations performed with the Oregonator model. An oxidative quenching mechanism for the photoproduction of bromide is suggested. Interestingly, during illumination of theRu(II)/MA subsystem, i.e., in the absence of BrMA and bromate, the oxidative quenching does also occur.

Bromomalonic-acid-induced transition from trigger wave to big wave in the Belousov-Zhabotinsky reaction

The Marangoni effects on chemical waves in the ferroin-catalyzed Belousov-Zhabotinsky reaction were studied. The main purpose of the present study was to understand the mechanism of the big wave, an accelerative chemical wave involving surface-tension-driven fluid motions. Spatiotemporal variations of surface tension caused by a chemical wave were measured using the Wilhelmy method. The transition from conventional trigger waves to big waves, due to a concentration change of bromomalonic acid, was observed. The strong surface activity of the bromomalonic acid which was responsible for the transition was also observed. It led to an acceleration of the big waves through the Marangoni effect.

Oscillations in the Bromomalonic Acid/Bromate System Catalyzed by [Ru(phen)3]2+

We investigated the oscillatory behavior of a BZ system with bromomalonic acid and bromate as substrates and with [Ru(phen)3] SO4 as a catalyst. The observed oscillations can be well modeled with a theory based on two different feedback loops originally developed for a corresponding BZ system with [Ru(bipy)3] SO4 as a catalyst. Furthermore, we have reexamined the decomposition of acidic bromate. We conclude that the products of this reaction are HOBr and O2 rather than HOBr and perbromate; the rate constant for the decomposition reaction turns out to be 1000 times smaller for 1 M sulfuric acid solution than expected from earlier experiments performed with 3 M sulfuric acid solutions.

Chemical mechanism of the radical feedback loop in the classical BZ reaction. Malonyl bromite and oxalic acid as flow-through intermediates

High-pressure liquid chromatography (HPLC) and measurements of the CO2 produced were performed in the induction period of the classical Belousov–Zhabotinsky (BZ) reaction (malonic acid–bromate–cerium catalyst in sulfuric acid medium). It was found that oxalic acid is a flow-through intermediate of the reaction. This was confirmed with an independent qualitative test with thiobarbituric acid. The concentration of oxalic acid grows in the induction period together with that of bromomalonic acid and dibromomalonic acid intermediates. It is known that there are two negative feedback loops in the BZ reaction: one is ia bromide and the other ia organic free radicals. Oxalic acid and also CO2 are products of this second loop where organic radicals react with BrO2 radicals. The induction period was chosen for the present experimental studies because the above radical–radical reactions are most intense during that time. Based on the experimental results mechanistic proposals are made for the radical feedback loop. A method to accumulate multivalent organic acids present in very low concentrations in the BZ reaction was also developed. Applying this and a thermal decomposition method ethenetetracarboxylic acid (EETA) was identified as an oxidation product of ethanetetracarboxylic acid (ETA).

An Oregonator-Class Model for Photoinduced Behavior in the Ru(bpy)32+-Catalyzed Belousov−Zhabotinsky Reaction

A modified Oregonator model exhibiting photoinduced behavior in the Ru(bpy)32+-catalyzed Belousov−Zhabotinsky (BZ) reaction is presented. We incorporate the concentration of bromomalonic acid as a new variable into the Oregonator model and also take into account two separate photochemical processes: the production of bromide from bromomalonic acid and bromous acid from bromate. The resulting four-variable model can reproduce a variety of photoinduced behavior reported experimentally in both batch and flow systems. The model also exhibits photoinduced chaos in the photosensitive BZ system under certain flow-rate and illumination conditions.

Kinetic study of the Ce(III)-, Mn(II)- or Fe(phen)32+-catalyzed Belousov-Zhabotinsky reaction with ethyl hydrogen malonate

In a stirred batch reaction, Fe(phen)32+ ion behaves differently from Ce(III) or Mn(II) ion in catalyzing the bromate-driven oscillating reaction with ethyl hydrogen malonate [CH2COOHCOOEt, ethyl hydrogen malonate (EHM)]. The effects of N2 atmosphere, concentrations of bromate ion, EHM, metal ion catalyst, sulfuric acid, and additive (bromide ion or bromomalonic acid) on the pattern of oscillations were investigated. The kinetic study of the reaction of EHM with Ce(IV), Mn(III), or Fe(phen)33+ ion indicates that under aerobic or anaerobic conditions the order of reactivity toward reacting with EHM is Mn(III) > Ce(IV) ≫ Fe(phen)33+, which follows the same trend as that of the malonic acid system. The presence of the ester group in EHM lowers the reactivity of the two methylene hydrogen atoms toward bromination or oxidation by Ce(IV), Mn(III), or Fe(phen)33+ ion. No good oscillations were observed for the BrO3−-CH2(COOEt)2 reaction catalyzed by Ce(III), Mn(II), or Fe(phen)32+ ion. A discussion of the effects of oxygen on the reactions of malonic acid and its derivatives (RCHCOOHCOOR′) with Ce(IV), Mn(III), or Fe(phen)33+ ion is also presented. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 52–61, 2000