Field-Koros-Noyes mechanism

Qualitative description of mechanism of the Belousov-Zhabotinskii reaction (the Fields-Koros-Noyes mechanism)... 

The Fields-Koros-Noyes mechanism, explaining the occurrence of... 

A characteristic feature of the Fields-Koros-Noyes mechanism is the postulate of two possible reaction pathways (step 1 and step 2), controlled by the Br- concentration. 

On the basis of the preceding discussion the five most important reactions in the Fields-Koros-Noyes mechanism can be indicated. These are the following reactions ... 

The model that we take into account has been firstly proposed by H. J. Krug and coworkers in 1990 [30], to properly account for the photochemically-induced production of inhibitor bromide in the Belousov-Zhabotinsky reaction (BZ) catalyzed with the ruthenium complex Ru(bpy)3 [31, 32]. The Oregonator model was proposed in 1974 [16] on the basis Tyson-Fife reduction of the more complicated Field-Koros-Noyes mechanism [15] for the BZ reaction, the following modified model has been derived ... 

Before the appearance of the Field-Koros-Noyes mechanism, Zhabotinskii... 

Show that the differential equation (4.9) (the induced kinetic differential equation of the Field-Koros-Noyes mechanism model of the Belousov-Zhabotinskii reaction) does have periodic solutions at certain values of the parameters. 

Field, R. J. Forsterling, H. D. 1986. On the Oxybromine Chemistry Rate Constants with Cerium Ions in the Field-Koros-Noyes Mechanism of the Belousov Zhabotinskii Reaction, J. Phys. Chem. 90, 5400-5407. 

See Tyson, J. J., Scaling and reducing the Field-Koros-Noyes mechanism of the Belousov-Zhabotinsky reaction, J. Phys. Chem., 86, 1982, 3006-3012.)... 

Reaction Mechanism. Noyes, Field, Koros (1972), Field, Koros, Noyes (1972) Noyes et al. (1972) gave a mechanism for the Belousov reaction. They proposed that in an acid solution of bromate, Br03, and malonic acid, CH2(COOH)2 containing sufficient amount of bromide ion, Br, four reactions form Process A. These reactions are (Rl, R3, and R7). 

The basic features of the oscillatory mechanism of the BZ reaction are given by the Field-Koros-Noyes (FKN) model [14]. This involves three processes —A, B and C. Process A involves step (8) and step (9) from section A3.14.2.1, leading to removal of inhibitor bromide ion. Process B involves step (3) and step H) from Section A3.14.1.1 and gives the autocatalytic oxidation of the catalyst. This growth is limited partly by the disproportionation reaction... 

The Ce(IV)/Ce(III) (Br /BrOj ) system is one of several redox systems in which oscillating oxidation-reduction cycles can be observed. This particular system, with organic substrates like malonic acid (among others), is known as the Belousov-Zhabotinsky oscillator. This system has been studied for more than 15 years and has been the subject of several reviews and a number of symposia. The Ce--Br oscillating reaction system has been described in terms of a seven-step rate process (all reversible reactions), the Field-Koros-Noyes (FKN) mechanism (Field et al. 1972). 

Oscillatory reactions are a typical class of phenomena, which display unusual features. After the discovery of Belousov-Zhabotinskii (B-Z) reaction, there has been a tremendous flurry of activity [1] and a large number of such reactions have been discovered during recent years. Biochemical reactions [2-10] such as glycolytic oscillations and peroxidase catalysed oxidation of nicotinamide adenosine deoxyhydrogenase (NADH) have also generated considerable interest. The interest in such reactions is stiU sustained in view of their importance in understanding cardiac and neuronal oscillations. In the case of many oscillatory chemical reactions [1], detailed reaction mechanisms have been postulated and verified with the help of numerical computation. This has also been particularly so for B-Z reaction where Field-Koros-Noyes (FKN) mechanism [11] has been invoked. 

In order to understand the BZ system Field, Koros and Noyes developed the so-called FKN mechanism. From this, Field and Noyes later derived the Oregonator model, an especially convenient kinetic model to match individual experimental observations and predict experimental conditions under which oscillations might arise. 

RO, Fig. 3d) (2) higher-frequency, smaller amplitude, quasi-harmonic oscillations (QHO, Fig. 3a) and (3) double-frequency oscillations containing variable numbers of each of the two previous types. By far the most familiar feature of the BZ reaction, the relaxation oscillations of type 1 were explained by Field, Koros, and Noyes in their pioneering study of the detailed BZ reaction mechanism.15 Much less well known experimentally are the quasiharmonic oscillations of type 2,4,6 although they are more easily analyzed mathematically. The double frequency mode, first reported by Vavilin et al., 4 has been studied also by the present author and co-workers,6 who explained the phenomenon qualitatively on the basis of the Field-Noyes models of the BZ reaction. 

Theory of Wave-Field Interaction in BZ Medium. A model of the mechanisms behind the BZ reaction has been set forth by Field, Koros and Noyes (33) (FKN) and more recently this mechanism has been modified to incorporate more processes (3 ). 

We may now present the overall mechanism proposed by Fields, Koros and Noyes, consisting of eleven reaction (Rl)-(Rll) ... 

Field, Koros and Noyes [5] proposed the FKN mechanism (reflecting the initials of their last names) to analyze the BZ reaction. The mechanism involves 18 chemical reactions implicating 21 different compounds. It can be rationalized as a set of three successive processes [6] ... 

The best known oscillating reaction is without a doubt the Belousov-Zhabotinsky (BZ) reaction, the oxidation of an organic substrate, typically malonic acid, CH2(C00H)2, by bromate, Br03, in an acidic medium in the presence of a metalion catalyst. It was discovered by Belousov in the early 1950s [32], and modified by Zhabotinsky [497]. The mechanism of the BZ reaction was elucidated by Field, Koros, and Noyes in 1972 [326, 130, 325] and reduced to five essential steps by Field and Noyes [131]. This model is called the Oregonator and in the version presented by Tyson and Fife [442] it is given by... 

Shortly thereafter appeared a flurry of papers on temporal oscillations and spatial patterns in this reaction system. Vavilin and Zhabotinskii (1969) [and later Kasperek and Bruice (1971)] studied the kinetics of the oxidation of Ce by BrO and the oxidation of organic species by Ce. Busse (1969) reported his observation of colored bands of chemical activity propagating up and down in a long tube of unstirred solution. Zaikin and Zhabotinskii (1970) observed circular chemical waves in thin layers of solution. By using an ion-specific electrode to follow the Br concentration, and by a thorough summary of the thermodynamics and kinetics of oxybromine species in acid solution. Field, Koros and Noyes (1972) were able to suggest an elaborate mechanism for temporal oscillations. A little later Bornmann, Busse and Hess (1973) published a series of illuminating articles on the overall reaction. 

Taking a simplistic view in the early stages. Field, Koros and Noyes postulated the following mechanism (usually known os Oregonator) [27] based on the following sequence of reactions ... 

In 1972, Field, Koros and Noyes (FKN) [21] suggested a mechanism for the B-Zh reaction involving kinetic data for individual steps and thermodynamic characteristics. The high magnitude of the Gibbs free energy for the B-Zh reaction promotes its proceeding, which results in the formation of bromomalonic acid, CO2 and other products. 

Field, Koros, and Noyes (FKN) [45] developed the mechanism of BZ reaction in 1972. Basically FKN model containing a total of 11 reaction chains involving 15 different intermediates and molecules [42]. The mentioned reaction chains were additionally formulated into three major processes [46]. The first processes starts with the depletion of bromide ions by a reaction of bromate ions. During this... 

The details of the mechanism that was developed in Eugene are discussed in later chapters. The important fact is that Field, Koros, and Noyes were able to eixplain the qualitative behavior of the BZ reaction using the same principles of chemical kinetics and thermodynamics that govern ordinary chemical reactions. They published their mechanism, now known as the FKN mechanism, in a classic paper in 1972 (Field et ah, 1972 Noyes et al., 1972). A quantitative numerical simulation of the oscillatory behavior based on the FKN mechanism was published a few years later (Edelson et al., 1975). 

Field, Koros, and Noyes (Field el al., 1972) proposed a mechanism in which radicals play important roles (Br()2 , MA ) Add a drop of acrylonitrile to an oscillating reaction and explain the relevance of the white precipitate (Varadi and Beck, 1973). 

The detailed chemistry of the BZ reaction was first elucidated (in 1972) by FIELD, KOROS, and NOYES [60]. From the detailed mechanism, which involved more than 20 reactions and as many chemical constituents, FIELD and NOYES [61] then derived a reduced model (the "Oregonator") with only 3 variables. A modified Oregonator (with 7 variables) was then proposed and studied by SHOWALTER et al. [26], who were not successful in their attempt to simulate the observations by SCHMITZ et al. [4] of nonperiodic behavior. SHOWALTER et al. [26] concluded that the difference between experiment and simulation suggests that the chaotic behavior observed experimentally may result from fluctuations too small to measure in any other way. Similar conclusions have been reached in several other studies [27,28,62,63]. However, abstract models have been developed that display chaos and some of the transition sequences observed in experiments (e.g., see [64-66]). 

Belousov s reaction, the metal ion (generally Ce " ) catalyzed bromination of an organic substrate, most often malonic acid, by bromate, was developed experimentally by Zhabotlnskii (I 5 ] ). It was, however, the publication (Field, Koros and Noyes, [6 ] ) of a detailed mechanism for the system and of a simplified three-variable model (the Oregonator, Field and Noyes, [ 7 ] ) of that mechanism that spurred interest in the BZ system as a prototype o,f periodic chemical behavior. 

Mechanisms have been developed which yield predictions in reasonable agreement with experiment for bromate (Field, Koros and Noyes, [6 ] Geiseler and Bar-Eli, [26] Orban and Epstein, [27]) and iodate (Sharma and Noyes, [28] Noyes and Furrow, [29] ... 

IIIC) 1972 Noyes, R. M., Field, R. J., Koros, E. Oscillations in Chemical Systems, I. Detailed Mechanism in a System Showing Temporal Oscillations, J. Amer. Chem. Soc., vol. 94, 1394-1395... 

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