VIBRATIONAL REACTIONS, complex chemical reactions characterized by fluctuations (mostly periodic) in the concentrations of some intermediate compounds and, accordingly, the rates of transformation of these compounds. Vibrational reactions are observed in the gas or liquid phase, and also (especially often) at the interface between these phases and the solid phase. The reason for the occurrence of concentration fluctuations is the presence of feedback between the individual stages of a complex reaction. Oscillatory reactions are classified as processes with positive (catalytic action of intermediate or final reaction products) or negative (inhibitory action of intermediate or final products) feedback.

For the first time, an oscillatory reaction, manifested in the form of periodic flashes of light during the oxidation of phosphorus vapor, was observed at the end of the 17th century by R. Boyle. In 1921, the American chemist W. Bray was the first to describe a liquid-phase oscillatory decomposition reaction of hydrogen peroxide catalyzed by iodates. In 1951, the Russian chemist B. P. Belousov observed fluctuations in the concentrations of the oxidized and reduced forms of the catalyst - cerium in the reaction of the interaction of citric acid with bromates. Fluctuations could be observed visually by changing the color of the solution from colorless to yellow (due to the transition Ce 3+ → Ce 4+); oscillation period 10-100 s. In 1961, the Russian biophysicist A. M. Zhabotinsky observed concentration fluctuations when malonic or malic acid was used as a reducing agent in the Belousov reaction. The reaction proceeding in the self-oscillating regime of the catalytic oxidation of various reducing agents with bromates is called the Belousov-Zhabotinsky reaction (the so-called catalyzed bromate oscillator). A fairly large number of other chemical reactions are known in which oscillatory changes in the concentrations of reagents are observed: non-catalyzed bromate oscillators, chlorite, iodate, peroxide and other oscillators. Modern stage Fundamental studies of the oscillatory reaction began with the work of I. R. Prigogine and his colleagues, in which it was shown that in an open system near a stationary state, sufficiently remote from the position of chemical equilibrium, oscillatory chemical processes are possible.

The kinetics of an oscillatory reaction is a rapidly developing branch of knowledge that has arisen at the intersection of chemistry, biology, medicine, physics, and mathematics. It is used in biochemistry, biophysics, the study of biorhythms, in the study of population dynamics, migration of organisms, in ecology, sociology (population change, economic development). Distinctive feature vibrational response is a high sensitivity to external influences, which opens up prospects for the creation of fundamentally new methods for the analysis of microquantities of various substances.

Lit .: Zhabotinsky A. M. Concentration self-oscillations. M., 1974; Garel D., Garel O. Vibrational chemical reactions. M., 1986; Oscillations and traveling waves in chemical systems/ Edited by R. Field, M. Burger. M., 1988; Babloyants A. Molecules, dynamics and life. M., 1990.

VIBRATIONAL REACTIONS- a class of redox periodic reactions. The reaction mechanism is similar to that of a retaining latch device. For the first time such reactions were discovered in 1951 by the Moscow chemist B.P. Belousov.

Oscillatory reactions proceed with the participation of a catalyst (for the first time this was discovered in the course of a reaction in the presence of cerium ions) and usually consist of two stages.

Necessary conditions for the occurrence of such reactions:

a) the speed of the first stage should significantly exceed the speed of the second stage;

b) at the second stage, a compound should appear that inhibits the course of the first stage (it is called an inhibitor).

A similar reaction can be observed when mixing aqueous solutions of a cerium (III) salt (for example, cerium sulfate), potassium bromate KBrO 3 and bromomalonic acid HO (O) C - CH (Br) - C (O) OH. The reaction mass is acidified with sulfuric acid.

At the first stage, the trivalent cerium ion (which arose during the dissociation of the cerium salt) is reduced by the bromate anion (it is supplied by potassium bromate). In this case, the Ce(III) ion is oxidized to Ce(IV), which is externally noticeable by the change in the color of the reaction solution - Ce(III) ions in an aqueous solution are colorless, and Ce(IV) are yellow.

10Ce 3+ + 2BrO 3 – + 12H + = 10Ce 4+ + Br 2 + 6H 2 O (I)

At the next stage, the resulting Ce (IV) ion reacts with bromomalonic acid, oxidizing it:

4Ce 4+ + HO(O)C – CH(Br) – C(O)OH + 2H 2 O =

4Ce 3+ + HC(O)OH + 2CO 2 + 5H + + Br - (II)

In this case, cerium again becomes the Ce (III) ion and can again participate in reaction I. In this case, it plays the role of a typical catalyst, participates in the reaction, but is not consumed, nevertheless, the reaction will not proceed without it. Potassium bromate and bromomalonic acid are consumed during the reaction, cerium only transfers electrons from one reagent to another (the starting reagents are marked in black, and the reaction products are in red):

The peculiarity of this reaction is that at stage II, the bromine anion Br – . It inhibits, that is, inhibits stage I, but does not affect stage II. As a result, the products of stage II, primarily Ce 3+ ions, accumulate in the reaction system. At a certain moment, when a lot of these ions accumulate, bromine ions can no longer inhibit stage I, and it passes at a high speed. Ce(IV) ions reappear in the system and then participate in the slow stage II. Thus, bromine ions play the role of a trigger that prevents the first stage from starting up to a certain point. Outwardly, it looks like this (Ce(III) ions in an aqueous solution are colorless, and Ce(IV) are yellow): the reaction mass instantly turns yellow, and then slowly becomes colorless (Fig. 4, beaker No. 1). The color changes approximately every minute and a half, the time interval remains unchanged for several hours. If you gradually add consumable reagents, then such a “chemical clock” will work for a very long time. As the temperature rises, the time cycle of the oscillatory response shortens.

There are other examples of oscillatory reactions. In the system described above, cerium ions can be replaced by iron ions. For this, a complex of Fe (II) sulfate with three molecules of phenanthroline is used, which is colored red in an aqueous solution (this complex is widely used for the quantitative determination of iron):

A similar Fe(III) complex, which appears as a result of oxidation, is colored blue; in the course of the reaction, the blue color instantly becomes red, which gradually turns into blue again (Fig. 4, beaker No. 2).

If we replace bromomalonic acid with citric [HOC(O)CH 2 ] 2 C(OH)C(O)OH, then in the presence of catalytic amounts of manganese salts, a system appears in which the color pulsates every two minutes (Fig. 4, glass No. 3) . Oxal-acetic acid HOC(O)CH 2 C(O)C(O)OH with cerium salts counts six-second intervals (glass No. 4). The time intervals in the animated figure are shown conditionally, the longest color change interval is in glass No. 3, the smallest is in glass No. 4

Soon after the discovery of such reactions, it was found that such processes are quite common. As a result, a general theory of oscillatory processes was developed, which include some gas-phase reactions (for example, the oxidation of hydrocarbons), heterophase oxidation of carbon monoxide, hydrogen, ammonia, ethylene on metal catalysts, and a number of polymerization processes. Oscillatory reactions determine the course of some of the most important biological processes: the generation of nerve impulses and the mechanism of muscle contraction.

Mikhail Levitsky

The essence of oscillatory reactions. Mechanism and kinetics of vibrational reactions.

Content

1. INTRODUCTION…………………………………………………………...……..…3
2. Basic concepts……………………………………………………………4
3. History…………………………..………………………………………………5
4. Significance and scope…………………….……….…………8
5. Mechanisms of reactions………………………………………………………………………………………………10
6. Kinetics of oscillatory reactions……………………………………….…14
7. The order of the experiment………………………..…………….15
8. Experimental data…………………………………….……….18
9. Conclusion………………………………………………………………..23
10. Bibliography…………..………………………………..…………24

INTRODUCTION
Vibrational reactions are one of the most interesting and attractive branches of inorganic chemistry. Attracting close attention not only to chemists, but also to physicists, mathematicians, biophysicists and many others, they are a topical issue. modern science. Therefore, in my work, I want to get acquainted with the history of oscillatory reactions, their practical application and the two most famous homogeneous oscillatory reactions, as well as to understand their mechanisms and, having set up an experiment, to get acquainted with oscillatory reactions in practice.

Basic concepts of oscillatory reactions

• Vibrational reactions- a class of redox reactions characterized by periodic fluctuations of intermediate substances and, as a result, fluctuations in color, temperature, flow rate, etc.

There are several types of oscillatory reactions:

1. catalytic
2. homogeneous
3. Reactions catalyzed by enzymes
4. Reactions catalyzed by metal ions
5. Heterogeneous (reactions on solid catalysts)
6. Non-catalytic, although it is more correct to call them autocatalytic (oxidation of aromatic compounds with bromate)

• The induction period is the time of primary formation and accumulation of the reaction catalyst.
• Oscillation period - the smallest period of time for which one complete oscillation occurs (that is, the system returns to the same state in which it was at the initial moment, chosen arbitrarily)

Story
The history of oscillatory reactions often begins with the German chemist and partly natural philosopher Friedlieb Ferdinand Runge. In 1850 and 1855, he successively published two books in which he described the colorful periodic structures that appear on filter paper when solutions of various substances are poured onto it one after the other. Actually one of them - "Substance in the quest to form" was an "album with pasted sheets of filter paper, on which the corresponding reactions were carried out. For example, filter paper was impregnated with a solution of copper sulphate, dried and re-impregnated with a solution of aluminum phosphate, drops of ferrous-cyanide potassium were applied to it in the middle, after which the formation of periodic layers was observed. After Runge, Raphael Liesegang enters the history of oscillatory reactions. In 1896, he published his experiments with rhythmic structures (Liesegang rings) obtained by depositing silver bichromate in gelatin. Liesegang poured a heated gelatin solution containing potassium bichromate onto a glass plate. When the solution solidified, he applied a drop of silver nitrate solution to the center of the plate. Silver bichromate precipitated not as a solid spot, but as concentric circles. Liesegang, who was familiar with Runge's books, initially inclined towards a natural-philosophical and organismic explanation of the periodic process he had obtained. At the same time, he also reacted positively to the physical explanation of his "rings", given in 1898 by Wilhelm Ostwald, which was based on the concept of a metastable state. This explanation has gone down in history as the supersaturation theory.
So far, we have not been talking about actual oscillatory chemical reactions, but rather about periodic physical and chemical processes, where the chemical transformation was accompanied by a phase transition. David Albertovich Frank-Kamenetsky came closer to the actual chemical oscillations, who began to publish his experiments on chemical oscillations since 1939. He described periodic phenomena during the oxidation of hydrocarbons: if, for example, mixtures of higher hydrocarbons are passed through a turbulent reactor, then periodic flashes (pulsations) are observed ) cold flame.
In 1949, a large article by I.E. Salnikova, summing up his work, begun by joint research with D.A. Frank-Kamenetsky. In this article, the concept of thermokinetic oscillations was formed. During these oscillations, the temperature changes, and their necessary condition is a balance between the release of heat and its dissipation in environment. And yet, the most weighty argument in favor of chemical vibrations was the article by Boris Pavlovich Belousov, which he unsuccessfully tried to publish twice - in 1951 and 1955. Although thermokinetic oscillations occur in homogeneous systems (unlike, say, Liesegang or oscillating chromium systems), they are provided by the physical (or physico-chemical) process of thermocatalysis. Discovery of B.P. Belousov almost completed almost 150 years of searching for oscillatory regimes in chemical processes. It was already a purely chemical oscillatory reaction. In the 1950s, however, there were other events related to the Belousov reaction. After all, although the article by B.P. Belousov was rejected, information about his reaction was distributed at the level of scientific folklore.
One of the recipients of this information was Simon Elevich Shnol, who was already involved in periodic processes in biochemistry. He was interested in the nature of chemical periodicity. Having received the manuscript of his article from Belousov in 1958, Shnol began to experiment with his reaction. And in 1961, he instructed his graduate student Anatoly Markovich Zhabotinsky to continue the work of B.P. Belousov, and he, conducting research first under the guidance of Shnoll, and then independently of him, made a decisive contribution to elucidating the kinetics of the Belousov reaction and to its mathematical modeling. As a result, this reaction became known as the Belousov-Zhabotinsky reaction.

Reaction mechanisms
To date, several dozens of homogeneous and heterogeneous chemical reactions have been studied. The study of kinetic models of such complex reactions made it possible to formulate a number of general conditions necessary for the occurrence of stable oscillations of the reaction rate and concentrations of intermediate substances:

1. Stable fluctuations occur in most cases in open systems in which it is possible to keep the concentrations of the participating reactants constant.
2. An oscillatory reaction should include autocatalytic and reversible stages, as well as stages that are inhibited by the reaction products.
3. The reaction mechanism must include steps with an order higher than the first.

These conditions are necessary, but not sufficient conditions for the occurrence of self-oscillations in the system. It should be noted that the ratio between the rate constants of individual stages and the values ​​of the initial concentrations of the reagents also plays a significant role.

3HOOC(OH)C(CH 2 COOH) 2 + BrO 3 - Ce(3+/4+), H+→ Br - + 3CO 2 + 3H 2 O
The Belousov-Zhabotinsky reaction is the first of the discovered and studied oscillatory reactions. In this connection, it can perhaps be called one of the most studied reactions of this group. On the this moment in one way or another, the presence of eighty intermediate stages (and side reactions) occurring in the system was confirmed.
One of the very first and simple circuits reactions was a scheme that consists of two stages:

1. Oxidation of trivalent cerium with bromate

Ce 3+ BrO3(-), H+→ Ce 4+

1. And reduction of tetravalent cerium with citric acid

Ce 3+ OK→ Ce 4+
However, it does not provide an understanding of how and as a result of which oscillations occur in the system, which leads us to consider the reaction mechanism proposed, in 1972, by Noyes and others:

1. BrO 3 - + Br - + 2H + ↔ HBrO 2 + HBrO
2. HBrO 2 + Br - + H + ↔ 2HBrO
3. HBrO + Br - + H + ↔ Br 2 + H 2 O
4. Br 2 + HOOC(OH)C(CH 2 COOH) 2 → Br - + H + + HOOC(OH)C(CHBrCOOH)CH 2 COOH
5. BrO 3 - + HBrO 2 + H + ↔ 2BrO 2. + H2O
6. BrO2. + Ce 3+ + H + → HBrO 2 + Ce 4+
7. 2HBrO 2 ↔ BrO 3 - + HBrO + H +
8. HBrO + HOOC(OH)C(CH 2 COOH) 2 → H 2 O + HOOC(OH)C(CHBrCOOH)CH 2 COOH
9. 18Ce 4+ + HOOC(OH)C(CH 2 COOH) 2 + 5H 2 O → 18Ce 3+ + 6CO 2 + 18H +

10) 16Ce 4+ + HOOC(OH)C(CHBrCOOH)CH 2 COOH → 16Ce 3+ + 6CO 2 + 18H + + Br -

So, let us consider the Ce 3+ / Ce 4+ oscillations in this system. Suppose we have a small, gradually increasing amount of Ce 4+ in solution, which means that the concentration of Br - is also small and grows due to reaction (10). Therefore, as soon as a certain critical concentration of Ce 4+ is reached, the concentration of Br - will increase sharply, which will lead to the binding of HBrO 2 stage (2), necessary for the catalytic oxidation of Ce 3+ , stage (5), (6). It follows from this that the accumulation of Ce 4+ in the solution will stop and its concentration will decrease according to reactions (9), (10). A high concentration of Br - will cause an increase in the rate of their consumption according to reactions (1) - (3). In this case, after reducing the concentration of Br - below a certain value, it will practically stop the reactions (2) and (3), leading to the accumulation of HBrO 2 . From which follows an increase in the concentration of Ce 4+ and a repetition of the cycle we have passed.

Briggs-Rauscher reaction:
IO 3 - + 2H 2 O 2 + H + + RH Mn(2+/3+)→ RI + 2O 2 + 3H 2 O
Where RH is malonic acid and RI is the iodine derivative of malonic acid.
This reaction was discovered in 1973. The essence of the reaction is the oxidation of malonic acid with iodate ions in the presence of hydrogen peroxide and a catalyst (Mn 2+/3+ ions). When starch is added as an indicator, fluctuations in the color of the solution are observed from colorless to yellow, and then to blue, caused by fluctuations in iodine concentrations. A complete study of the mechanism of the Briggs-Rauscher reaction is a complex and still unsolved, perhaps, first of all, kinetic problem. According to modern concepts, the mechanism of this reaction includes up to thirty stages. At the same time, in order to understand the causes of fluctuations, it is enough to consider a simplified reaction mechanism, consisting of the eleven stages below:

1. IO 3 - + H 2 O 2 + H + → HIO 2 + O 2 + H 2 O
2. IO 3 - + HIO 2 + H + ↔ 2IO 2 . + H2O
3. HIO 2 + H 2 O 2 → HIO + O 2 + H 2 O
4. IO2. + Mn 2+ + H 2 O ↔ HIO 2 + MnOH 2+
5. 2HIO + H 2 O 2 → 2I - + 4O 2 + 4H +
6. MnOH 2+ + I - + H + ↔ I. + Mn2+ + H2O
7. HIO + I - + H + ↔ I 2 + H2O
8. 2HIO 2 → IO 3 - + HIO + H +
9. RH↔enol
10. HIO + enol → RI + H2O
11. I 2 + enol → RI + I - + H +

Consider the fluctuations in this reaction using the example of the I 2 /I - pair, since it is the presence or absence of iodine that is easiest to fix in solution due to the blue starch complexes formed.
So, if the concentration of I is low (or these ions are absent in the solution, which corresponds to the initial moment of time), then in accordance with stage (5), and with further fluctuations and stage (11), as well as the reverse reaction of stage (7), they begin to accumulate in the solution, which leads to a decrease (if available) in the concentration of I 2 . From the decrease in the concentration of I 2 follows the fall in the rate of accumulation of I - . At the same time, a large concentration of ions I - causes a high rate of its consumption in the direct reaction of stage (7) and the increased concentration of I - decreases again, leading us to the beginning of this reasoning and repeating the described cycle.

Kinetics of vibrational reactions

The problems of studying kinetics are, at the moment, the most complex, and still unresolved issues of oscillatory reactions. In view of the large number of interdependent and parallel processes occurring in this class of reactions, compiling systems of differential equations that give at least approximate values ​​of the rate constants of intermediate stages becomes an extremely nontrivial task. And although now there are several simplified models that allow us to consider the main features of the complex behavior of oscillatory reactions, this topic seems to be rather little studied and therefore extremely interesting for subsequent generations of researchers. At the same time, despite this, in this work this section of the study of oscillatory reactions will not receive further development due to the lack of time and funds necessary for its study.

The order of the experiment
Belousov-Zhabotinsky reaction.

Reagents: Citric acid, potassium bromate, cerium(III) sulfate, sulfuric acid.
Utensils: Measuring cylinder 50 ml, heat-resistant glasses 300 ml and 100 ml, glass rod, spatula.
Equipment: Analytical balances, tiles.
To carry out the Belousov-Zhabotinsky reaction, it is necessary to prepare the following solutions and samples:

1. Prepare a solution of citric acid and heat it to 50 o C.
2. Add weighed portions of potassium bromate and cerium (III) sulfate, stir with a glass rod.
3. Remove grout from tiles.
4. Add sulfuric acid.

Briggs-Rauscher reaction.
Necessary reagents, utensils and equipment:
Reagents: Potassium iodate, sulfuric acid, malonic acid, manganese (II) sulfate, starch, hydrogen peroxide.
Utensils: measuring cylinder 50 ml, 2 cups 500 ml, 3 cups 100 ml, glass rod, spatula.
Equipment: Analytical balance, magnetic stirrer, magnet.
To carry out the Briggs-Rauscher reaction, it is necessary to prepare the following solutions:
Solution #1:

Solution #2:

Solution #3

The order of the experiment:

1. Prepare all necessary solutions.
2. Pour 50 ml of solution No. 1 into a 500 ml beaker containing a magnet and place it on a magnetic stirrer. Turn it on.
3. Measure separately 25 ml of solution No. 2 and 40 ml of solution No. 3 into two other glasses.
4. Add, simultaneously, solutions No. 2 and No. 3 to solution No. 1.
5. Record the induction period and periods of oscillation.

Experiment
Belousov-Zhabotinsky reaction:
To carry out the reaction, a solution of citric acid (20 g per 80 ml of water) was prepared. For complete dissolution of citric acid, the solution had to be heated on an electric stove. Next, weighed portions of potassium bromate (8 g) and cerium sulfate III (1.5 g) were prepared and sequentially poured into a solution of citric acid. After stirring with a glass rod, sulfuric acid was added carefully, continuing stirring, after which fluctuations in the white-yellow color were recorded.

№	Period, s	Colour	№	Period, s	Colour
1	23	white	12	12	yellow
2	11	yellow	13	66	white
3	41	white	14	8	yellow
4	12	yellow	15	43	white
5	71	white	16	6	yellow
6	11	yellow	17	56	white
7	43	white	18	5	yellow
8	13	yellow	19	43	white
9	19	white	20	5	yellow
10	10	yellow	21	56	white
11	40	white	22	4	yellow

It is also worth noting the increase in the amount of gas released when the solution darkens.
Conclusion: Based on the recorded data, one can judge a stable decrease in the time spent in a solution of tetravalent cerium (which indirectly indicates a decrease in the pH of the medium, since the more acidic the medium, the stronger the oxidizing agent is cerium and the less stable it is).
An amazing regularity was also found, since during the course of the reaction not only the concentrations of intermediate substances fluctuate, but also the time of the oscillation periods (damped harmonic oscillation):

Briggs-Rauscher reaction:
Three solutions were prepared for the reaction: potassium iodate sulfate solution (c (KIO 3) \u003d 0.067 mol / l; c (H 2 SO 4) \u003d 0.053 mol / l) - 50 ml, starch solution of malonic acid with the addition of a catalytic amount of manganese sulfate two (c (MnSO 4) \u003d 0.0067 mol / l; c (CH 2 (COOH) 2) \u003d 0.05 mol / l; starch 0.1%) - 25 ml and a seven-molar solution of hydrogen peroxide - 40 ml. Solution No. 1 was poured into a beaker, in which the magnet was located, for 250 ml. The beaker was placed on a magnetic stirrer, which was subsequently turned on, and intensive stirring was turned on so that the color change occurred abruptly. Then, without stopping stirring, the contents of the beakers with solutions No. 2 and No. 3 were added, simultaneously and quickly. The stopwatch measured the appearance of the first yellow color - the induction period and the beginning of the appearance of blue stains - the oscillation period.

The induction period is 2 seconds.

№	1	2	3	4	5	6	7	8	9	10	11	12
Period, s	13	12	14	12	13	14	13	14	14	15	15	16
№	13	14	15	16	17	18	19	20	21	22	23	24
Period, s	16	16	17	17	17	18	17	18	17	18	18	17

Conclusion: As the reaction proceeds, a gradual increase in the period of oscillations is observed, which is especially clearly visible on the graph:

Conclusion
In this paper, oscillatory reactions and their properties were considered, in particular:

1. The field of application of oscillatory reactions in the modern world has been studied
2. The history of oscillatory reactions has been studied
3. The mechanisms of two oscillatory reactions are analyzed: Briggs-Rauscher

and Belousov-Zhabotinsky

1. The Belousov-Zhabotinsky reaction mechanism was adapted for

considering citric acid as a reducing agent

1. A control synthesis was carried out for visual acquaintance with oscillatory reactions.

List of used literature

1. D. Garel, O. Garel "Vibrational chemical reactions" translated from English by L.P. Tikhonova. Publishing house "Mir" 1986. Page 13-25, 92-112.
2. A.M. Zhabotinsky "Concentration self-oscillations". Publishing house "Nauka" 1974. Page 87-89
3. OK. Pervukhin, Vibrational reactions. Toolkit". Publishing house of St. Petersburg State University 1999. Page 3-11.
4. S. P. MUShTAKOVA “Vibrational reactions in chemistry” Saratov State University named after V.I. N.G. Chernyshevsky
5. "Investigation of the conditions for the occurrence of an oscillatory regime in the process of oxidative carbonylation of phenylacetylene". Page 2-4.
6. I.D. Ikramov, S.A. Mustafin. "AN ALGORITHM FOR SEARCHING THE RATE CONSTANTS OF THE VIBRATIONAL RESPONSE BY THE EXAMPLE OF THE BELousOV-ZHABOTSKY REACTION". Bashkir chemical journal 2015
7. Pechenkin A.A. "The ideological significance of oscillatory chemical reactions"
8. Field R. J., Koros E., Noyes R. M., Oscillations in Chemical Systems II. Thorough Analisis of Temperal Oscillations in the Bromat-Cerium-Malonic Acid System., J. Amer. Chem. Soc., 94, 8649-8664 (1972).
9. Noyes R. M., Field R. J., Koros E., J. Amer. Chem. Soc., 94, 1394-1395 (1972).

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The discovery of vibrational
chemical reactions

2001 marked the 50th anniversary of the discovery by B.P. Belousov of a self-oscillatory chemical reaction, which made it possible to observe periodic changes in the concentration of reagents and the propagation of autowaves in a homogeneous chemical system.

“You are looking at a glass of red-purple liquid, and it suddenly turns bright blue. And then red-purple again. And blue again. And you involuntarily begin to breathe in time with the vibrations. And when the liquid is poured in a thin layer, waves of color change propagate in it. Complex patterns are formed, circles, spirals, whirlwinds, or everything takes on a completely chaotic appearance” – this is how Professor S.E.
In 1958, a seminar was held at the Institute of Chemical Physics of the USSR Academy of Sciences. The speaker, a young biophysicist Shnoll, talking about biorhythms, developed his hypothesis that chemical reactions control biological clocks. To confirm this, real examples of chemical vibrations were needed, and the speaker asked the audience if anyone could indicate them. No one gave such examples; moreover, some considerations were expressed about the fundamental impossibility of concentration fluctuations in chemical reactions. The issue was resolved in an unexpected way. After the closing of the seminar, when almost all the participants had left, a young graduate student approached the speaker and said that his uncle had studied chemical vibrations five or six years ago.

Such difficult story

It turned out that Shnol had been looking for this man for a long time. As early as 1951, Boris Pavlovich Belousov, an uncle, or rather great-uncle of graduate student Boris Smirnov, discovered fluctuations in the concentrations of oxidized and reduced forms of cerium in the reaction of citric acid with potassium bromate, catalyzed by cerium ions. The solution regularly changed its color from colorless to yellow due to the presence of cerium(IV), then again to colorless due to cerium(III), etc. Belousov conducted a fairly detailed study of this reaction and, in particular, found that the oscillation period decreases significantly with an increase in the acidity of the medium and temperature.
The reaction also turned out to be convenient for laboratory studies. The oscillations could be easily observed visually, and their period was in the range of 10–100 s.
Really, modern history studies of oscillatory chemical reactions in the liquid phase began in 1951 with the discovery of Belousov, although for the author himself, everything did not go so smoothly. His paper describing the oscillatory reaction was twice rejected by the editors of academic chemical journals. Only in 1958 was its abridged version published in the little-known Collection of Abstracts on Radiation Medicine.
It now seems that the main reason for the rejection of this phenomenon by chemists was the widespread belief that far from the equilibrium position, concentration fluctuations are forbidden by the second law of thermodynamics.
While chemists, joined by biochemists, unanimously rejected chemical vibrations, the latter continued to attract the attention of mathematicians and physicists interested in biology. In 1952, the English scientist A.M. Turing published an article “Chemical foundations of morphogenesis”, in which he reported that the combination of chemical vibrations with the diffusion of molecules can lead to the appearance of stable spatial structures, the regions of high and low concentrations of which alternate. Turing set himself a purely theoretical problem: can stable configurations of intermediate products be formed in a reactor under the conditions of a chemical reaction? And he gave a positive answer, creating a certain mathematical model of the process. At that time, due importance was not attached to this work, especially since neither Turing himself nor his colleagues could know about Belousov's work and his futile attempts to publish it.
In 1955, the Belgian physicist and physical chemist, the author of the theory of thermodynamics of irreversible processes, I.R. Prigogine showed that in an open system, near a stationary state, sufficiently remote from chemical equilibrium, chemical oscillations are possible. It was he who drew the attention of the Western scientific community to the work of Soviet scientists. As a result, some oscillatory heterogeneous chemical reactions discovered back in late XIX c. have been widely accepted. It was they who began to be considered as analogues of a number of periodic processes, for example, "biological clocks".
It became clear to researchers that the second law of thermodynamics is not violated in living systems and does not interfere with their complex behavior and evolution. But for the existence of life or any of its physical or chemical models, it is necessary that the system be away from thermodynamic equilibrium for a sufficiently long time. And homogeneous chemical systems could become a convenient model for studying such processes.
It was at this time that Professor Shnoll received a "recipe" for an oscillatory reaction from Belousov and offered him cooperation, which he categorically refused, although he did not object to the continuation of these works.
In 1961, Academician I.E. Tamm, a prominent theoretical physicist, decided to "inspect" the state of affairs at the newly created Department of Biophysics of the Faculty of Physics of Moscow State University. Shnol showed him Belousov's reaction. Here is how Shnol himself tells about it: “Igor Evgenievich saw and stopped for a long time, enjoyed. Then he said: “Well, you know what, brothers, having such a reaction, you don’t have to worry: there will be enough riddles and work for many years.” The words of Igor Evgenievich had an effect on many. Tolya Zhabotinsky from our first issue, a hereditary, as he said to himself, a physicist, decided to take up the reaction.
Shnol supported the young scientist and suggested that post-graduate student A.M. Zhabotinsky begin research into the mechanism of the Belousov reaction, which he enthusiastically engaged in. “A remarkable feature of the work of Zhabotinsky and the group of collaborators that formed around him,” Shnol recalls, “was the combination of a chemical experiment, physical recording methods, and the construction of mathematical models. In these models - systems of differential equations - kinetic constants were substituted from experimental data. After that, it was possible to compare the experimental recordings of vibrations with the curves that were obtained by computer simulation.”
Later, these works were continued in the Laboratory of Physical Biochemistry of the Institute of Biological Physics of the USSR Academy of Sciences. Doctor of Physical and Mathematical Sciences V.A. Vavilin recalls: “Zhabotinsky and I, a graduate student of the Department of Biophysics of the Faculty of Physics of Moscow State University, had the task of detecting oscillations in the Bray system using continuous spectrophotometric registration of iodine concentration. The comparison of the mechanisms of the Belousov and Bray reactions was also of interest. The fact is that oscillations in a liquid-phase chemical system were discovered in 1921 by W. Bray. During the decomposition of hydrogen peroxide by potassium iodate, he discovered a periodic release of oxygen from the system, fixing several periods of strongly damped oscillations. Some researchers, referring to the intense gas evolution, expressed doubts about the homogeneous nature of this reaction, so the existence of an oscillatory reaction in a homogeneous medium was not proved by Bray's experiments.
A kind of "competition" immediately arose between the two periodic reactions of Bray and Belousov. Nevertheless, the easy reproduction of the results and the beautiful visual effects observed in the Belousov reaction contributed to the emergence of a large number of its adherents, and it became widely known (later it was called the Belousov–Zhabotinsky reaction, or BZ reaction, and the periodic Bray reaction, the Bray– Libavsky). According to Vavilin, the discovery and study of self-oscillations and autowaves in the course of the Belousov reaction by S.E. Shnoll, A.M. Zhabotinsky, V.I. Krinsky, A.N. Zaikin, G.R. fundamental domestic science in the postwar period. By the way, Zhabotinsky owns one of the first books in this area.
The rapid and successful study of the Belousov–Zhabotinsky reaction acted as a trigger in science: it was immediately remembered that processes of this kind had been known before. However, the value of the Belousov reaction, according to Professor B.V. with the help of this interesting transformation by A.M. Zhabotinsky, A.N. Zaikin, E.E. Selkov and others. If we turn to the past, the first descriptions of fluctuations in concentration systems date back to the 19th century.

Concentration studies
hesitation before opening
reactions Belousov

It turned out that one of the first publications on chemical vibrations dates back to 1828. In it, T. Fechner outlined the results of a study of the oscillations of an electrochemical reaction. In 1833, W. Herschel published a similar study of fluctuations in a catalytic heterogeneous reaction. The most interesting is the work of M. Rosenskiöld, dating back to 1834. Its author quite by chance noticed that a small flask containing a little phosphorus emits quite intense light in the dark. There was nothing surprising in the very fact of the glow of phosphorus, but the fact that this glow was regularly repeated every seventh second was interesting. Rosenskiöld's publication gives a detailed study of bulb flickering. Forty years later, these experiments with the "flickering flask" were continued by the Frenchman M. Joubert (1874). He managed to observe the periodic formation of "luminous clouds" in a test tube. Twenty years later, the German scientist A. Zentnershwer also studied the effect of air pressure on periodic flashes of phosphorus. In his experiments, the flash period began at 20 s and decreased with decreasing pressure. At the same time, in England, chemists T. Thorpe and A. Tatton observed periodic flashes of the oxidation reaction of phosphorus trioxide in a sealed glass vessel.
A particularly bright page in the history of chemical vibrations is associated with the so-called Liesegang rings. In 1896, the German chemist R. Liesegang, experimenting with photochemicals, discovered that if you drop lapis on a glass plate coated with gelatin containing chromium peak, then the reaction product, precipitating, is located on the plate in concentric circles. Liesegang became fascinated with this phenomenon and studied it for almost half a century. It also found practical applications. In applied art, Liesegang's rings were used to decorate various products with imitation of jasper, malachite, agate, etc. Liesegang himself proposed the technology for making artificial pearls. Nevertheless, the discovery of Liesegang, which had a great resonance in scientific chemical circles, was not the first. And before him, chemical waves were studied, and in 1855 a book by F. Runge was published, in which numerous examples of such experiments were collected.
The list of such examples could be continued. Following these, oscillatory reactions were discovered at the interface between two phases. Of these, the most well-known are the reactions at the metal-solution interface, which received specific names - "iron nerve" and "mercury heart". The first of them - the reaction of dissolving iron (wire) in nitric acid - got its name because of the external resemblance to the dynamics of an excited nerve, noticed by VF Ostwald. The second, or rather one of its variants, is the decomposition reaction of H 2 O 2 on the surface of metallic mercury. In the reaction, periodic formation and dissolution of an oxide film on the mercury surface occurs. Fluctuations in the surface tension of mercury cause rhythmic pulsations of the drop, reminiscent of the beating of the heart. But all these reactions did not attract much attention of chemists, since the ideas about the course of a chemical reaction were still rather vague.
Only in the second half of the XIX century. thermodynamics and chemical kinetics arose, which laid the foundation for a specific interest in oscillatory reactions and methods for their analysis. And at the same time, it was the development of equilibrium thermodynamics that at first served as a brake on the study of such processes. The point, apparently, was in the "inertia of previous knowledge." According to Professor Shnol, “an educated person could not imagine macroscopic order in the random thermal motion of a huge number of molecules: all the molecules are in one state, then in another! As if to recognize the existence of a perpetual motion machine. This cannot be. And indeed it cannot be. It cannot be near the equilibrium state, but only it was considered by the thermodynamics of those years. However, there are no restrictions on complex, including oscillatory, modes for non-equilibrium chemical systems, when the reactions have not yet been completed, and the concentrations of the reagents have not reached the equilibrium level. But this circumstance escaped the attention of chemists ... It took an extraordinary intellectual effort to break out of the "iron fetters of complete knowledge" and investigate the behavior of systems far from equilibrium.
Nevertheless, already in 1910, the Italian A. Lotka, based on the analysis of a system of differential equations, predicted the possibility of oscillations in chemical systems. However, the first mathematical models corresponded only to damped oscillations. Only 10 years later, Lotka proposed a system with two subsequent autocatalytic reactions, and in this model the oscillations could already be undamped.
However, the positions of physicists and chemists diverged here. One of the most striking achievements of physics and mathematics of the XX century. – creation of the theory of oscillations. Great, universally recognized merits here belong to Soviet physicists. In 1928, post-graduate student A. A. Andronov, a future academician, made a presentation at the congress of physicists "Poincaré limit cycles and the theory of self-oscillations."
In the early 1930s at the Institute of Chemical Physics of the USSR Academy of Sciences, fluctuations in luminescence in "cold flames" similar to the vibrational luminescence of phosphorus vapor were discovered, which interested the famous physicist D.A. Frank-Kamenetsky, who explained these fluctuations on the basis of Lotka's kinetic model. And in 1947, at the same institute, a thesis was presented for defense on the topic “On the theory of periodic occurrence of homogeneous chemical reactions,” written by I.E. Salnikov under the scientific guidance of Frank-Kamenetsky. This dissertation contained extensive information about more than a century of history of the study of chemical vibrations and the first results of their theoretical study using the methods of the theory of nonlinear vibrations developed by the school of Academician Andronov. But then her defense did not take place. According to Voltaire, “the works of Frank-Kamenetsky and Salnikov on chemical self-oscillations, presented in a dissertation, in a book and in a number of articles, were certainly innovative for the then chemical science. But few people understood this innovation. “Vibrational ideology” (Andronov's term) was alien to the non-oscillatory routine of chemical science and practice, and this can explain the fact that the work of Frank-Kamenetsky and Salnikov in the 1940s. were received with hostility, and when the second discovery of chemical vibrations took place, no one remembered them. It remains a mystery whether Belousov had any idea about these works. In any case, his two papers do not cite the work of his predecessors.

Belousov's reaction
and elucidation of its mechanism

Let us return to the consideration of the essence of a homogeneous oscillatory reaction. Belousov used citric acid, and cerium derivatives as an oxidizing agent–reductant pair. A.P. Safronov, a student and collaborator of Belousov, advised adding an iron complex with phenantronyl to the solution. In this situation, the color changed spectacularly: from lilac-red to bright blue. Zhabotinsky, who undertook a detailed study of the reaction mechanism, finally showed that the self-oscillating reaction can also occur when citric acid is replaced by any other dicarboxylic acid with an active methylene group, and the catalytic redox pair Ce(IV)/Ce(III) is replaced by the Mn(III)/Mn(II) pair or, as already used by Belousov, by the ferroin/ferriin pair. The flask looked most elegant, aesthetically spectacular if malonic acid was used, and iron ions Fe2+ instead of cerium ions. Then the solution in the flask can change color for hours with strict periodicity in the entire visible range from ruby ​​red to sky blue. The overall formula of the reaction looks quite simple, but the reaction proceeds in more than 20 stages and, accordingly, with the formation of the same amount of intermediate products. Let us consider this reaction in more detail.
In order to implement it, two solutions are prepared - A and B.
A – solution of ferroin, iron(II) complex with about-phenanthroline (phen) - 2+:

Fe2+ ​​+ 3phen = 2+.

The solution can be prepared in advance.
B - bromomalonic acid solution (prepared immediately before the demonstration):

The resulting bromomalonic acid is unstable, but it can be stored at a low temperature for some time.
For a direct demonstration of the experiment, a Petri dish is placed on a glass plate covering the light window, into which a saturated solution of potassium bromate, a solution of bromomalonic acid and a solution of ferroin are successively added using pipettes. Within a few minutes, blue areas appear on a red background in the cup. This is due to the formation of another ferriin 3+ complex during the redox reaction of the ferroin 2+ complex with bromate ions:

This process proceeds with auto-acceleration. Then the resulting complex 3+ oxidizes bromomalonic acid with the formation of bromide ions:

4 3+ + BrCH(COOH) 2 + 7H 2 O =
4 2+ + 2CO 2 + 5H 3 O+ + Br – + HCOOH.

The liberated bromide ions are inhibitors of the oxidation of the iron(II) complex by bromate ions. Only when the concentration of 2+ becomes high enough, the inhibitory effect of bromide ions is overcome, and the reactions of producing bromomalonic acid and oxidizing the complex begin to proceed again. The process is repeated again, and this is reflected in the color of the solution. Concentric circular red-blue “waves” of coloring diverge in all directions from the blue areas in the cup.
If the contents of the cup are mixed with a glass rod, the solution will become monochromatic for a short time, and then the periodic process will be repeated. Eventually the reaction stops due to the release of carbon dioxide.
In addition to all the listed reagents, several crystals of cerium(III) nitrate hexahydrate can be added to the Petri dish, then the range of colors will expand: yellow color will appear due to cerium(IV) derivatives and green due to the superposition of blue and yellow colors.
The mathematical description of these processes turned out to be rather complicated. It led to unexpected results. It turned out that one of the simplest chemical schemes describing oscillations in a system of two successive autocatalytic reactions is mathematically identical to the equations that the Italian scientist V. Volterra in the early 1930s. used to describe ecological processes. This is currently famous model Lotka-Volterra, which describes periodic changes in the number of "prey" and "predator" in ecological systems. S.P. Mushtakova, professor of Saratov state university them. N.G. Chernyshevsky, considers an oscillatory reaction as the interaction of two systems, one of which draws the energy, substance or other components it needs for development from the other. This problem is called the predator-prey problem.
For clarity, let's imagine that wolves and hares live in some limited environment. In this ecological system, grass grows, which feed on hares, which in turn are food for wolves. As you know, if you have any set of living beings, then under favorable conditions, their population will increase indefinitely. In fact, external factors, such as a lack of energy or food, limit this growth process. Let us imagine that up to a certain moment the interaction of two subsystems, i.e., populations of wolves and hares, was balanced: hares (taking into account their natural replenishment) were just enough to feed a certain number of wolves. Then, at the moment taken as zero of the time count, due to some fluctuation, the number of hares increased. This increased the amount of food for the wolves and, therefore, their number. There was a fluctuation in the number of wolves. Moreover, the number of wolves and hares will change over time periodically around a certain average (equilibrium) value. Well-fed wolves begin to multiply intensively, giving new offspring, which, on abundant food, quickly matures and gives new offspring. There is a situation when the "hare" is no longer able to feed all the wolves - the number of hares begins to fall, and the wolves (for the time being) continue to grow. Finally, the ecosystem is overpopulated with wolves, and hares have a place almost in the Red Book. But, having become an ecological rarity, hares become difficult prey for wolves. The ecosystem is entering the next phase: the number of hares has already fallen to a minimum level at which they are almost elusive for wolves. The livestock of the latter, having passed through a maximum, begins to decline, and this reduction continues until such a level is reached that the hares are able to feed at their minimum number. Now that the number of wolves has reached a minimum, there is no one to hunt for hares. Hares begin to breed, and the meager livestock of wolves can no longer keep track of them. The number of hares in a short time will reach a level at which they will be able to feed on grass. Once again there is an abundance of hares.
What conclusions can be drawn from a comparison of this example and the oscillatory response?
We note the main points, without which the described oscillatory process would be impossible.
First of all , the cooperative behavior of molecules in solution is impossible without feedback. The meaning of the latter can be understood by the example of the interaction between hares and wolves: an increase in the number of predator individuals leads to a decrease in the prey population, and vice versa. The presence of such feedback ensures the sustainable existence of the ecosystem. If we describe oscillatory chemical reactions in terms of "predator-prey", then the role of "predators" is played by intermediate products that slow down or completely block individual stages of the process - inhibitors. The role of "victims" is performed by catalysts that speed up the course of the reaction. Although, as is known, the catalyst molecules themselves (Fe) are not consumed in the reaction, the ratio of ion concentrations /, as studies have shown, undergoes a complex evolution. This simplified scheme allows a general idea of ​​the molecular feedback mechanism in solution.
Secondly , the oscillatory process is impossible without an energy source, the role of which in the Lotka–Volterra model was played by grass eaten by hares. It is obvious that there can be no question of any fluctuations, let alone the stability of the “predator-prey” cycle, if the entire territory is concreted in the reserve - the wolves will eat the hares and then die out themselves. In the Belousov–Zhabotinsky reaction, organic malonic acid serves as an energy source. Indeed, when it is completely oxidized, the oscillations in the reaction die out, and then the reaction itself stops.
By 1963, the main qualitative stage in the study of the Belousov reaction was completed. The scientist knew about this, but he did not want to get involved in the work. In 1966, in March, the 1st All-Union Symposium on Oscillatory Processes in Chemistry and Biochemistry was convened. The reports of Zhabotinsky and his co-authors M.D. Korzukhin, V.A. Vavilin occupied the central place. Belousov refused to participate in the symposium.
Much later, in 1974, Professor of Chemistry and Biology at the University of Arizona (USA) A.T. rings, spirals, wave fronts, etc.). Since then, interest in such systems has been constantly growing, indicating the promise of research in this direction.
Thus, applied research is gaining more and more weight, for example, in the field of modeling alternative means of information processing (in particular, the analysis of complex mosaics with gradation of object brightness). Another new direction of applied research is the study of the features of polymerization in the BZ system or similar ones.
The complex spatio-temporal organization exhibited by the BZ-system in the absence of mixing eventually found analogies in nature, in biological systems (for example, the study of cardiac muscle fibrillation from the point of view of considering the myocardium as a self-organizing biological system).
To date, the Belousov–Zhabotinsky reaction has taken its rightful place in world science. It actually stimulated the emergence of its new field - synergetics (self-organization), and experimental work initiated the development of the modern theory of dynamical systems. Although at present much of such reactions is already understood, however, the causes that cause oscillatory chemical processes remain unclear to the end. A dynamic description of oscillatory chemical reactions can be of great help in this, in particular, indirectly to establish the missing reaction rate constants.
The fundamental changes in natural science that gave rise to the so-called self-organization theory are largely due to the initial impetus given to it by Russian scientists at the turn of the 1950s–1960s, when Belousov discovered the redox chemical reaction. At the same time, striking analogies were discovered, it turned out that many natural phenomena, ranging from the formation of galaxies to tornadoes, cyclones and the play of light on reflective surfaces, in fact, are processes of self-organization. They can have a very different nature: chemical, mechanical, optical, electrical, etc.
At present, the kinetics of oscillatory reactions is a rapidly developing branch of knowledge that has arisen at the intersection of chemistry, biology, medicine, physics, and mathematics.

LITERATURE

Wolter B.V. Legend and true story about chemical vibrations. Knowledge is power, 1988, no. 4, p. 33–37; Zhabotinsky A.M. concentration fluctuations. M.: Nauka, 1974, 179 p.;
Shnol S.E. Heroes, villains, conformists of Russian science. M.: Kron-Press, 2001, 875 p.;
Mushtakova S.P. Vibrational reactions in chemistry. Soros Educational Journal, 1997, No. 7, p. 31–37;
Vavilin V.A. Self-oscillations in liquid-phase chemical systems. Priroda, 2000, No. 5, p. 19–25.

BELOUSOV Boris Pavlovich(19.II.1893–12.VI.1970) - Soviet chemist. Born in Moscow in the family of a bank employee, the sixth child in the family. Together with his brothers, he was early involved in revolutionary activities and was arrested at the age of 12. His mother was offered a choice: either Siberian exile or emigration. The family ended up in Switzerland in a Bolshevik colony. The future scientist had a chance to play chess with V.I. Lenin. Boris was surprised at his passion, how he denigrates his opponent in every possible way, trying to demoralize him. This was the end of Belousov's revolutionary political activity. He never joined the party. In Zurich, his passion for chemistry began, but there was no opportunity to get an education, since he had to pay tuition. At the beginning of the First World War, Boris returned to Russia, wishing to voluntarily join the army, but for health reasons he was not accepted.
Belousov goes to work in the chemical laboratory of the Goujon metallurgical plant (now the Hammer and Sickle plant). This laboratory was ideologically headed by V.N.
Becoming a military chemist, since 1923, Belousov, on the recommendation of Academician P.P. Lazarev, has been teaching chemistry to Red Army commanders at the Higher Military Chemical School of the Red Army (Workers 'and Peasants' Red Army, 1918–1946), giving a course of lectures on general and special chemistry in school for the improvement of the command staff of the Red Army. In 1933, Belousov was a senior lecturer at the Military Red Banner Academy of Chemical Defense named after S.K. Timoshenko.
The specificity of Belousov's scientific activity was such that none of his scientific works has ever been published anywhere. Academician A.N. Terenin called Belousov an outstanding chemist. In his review, written in connection with the possibility of awarding Belousov a doctoral degree without defending a dissertation, it is noted that “B.P. Belousov started a completely new direction in gas analysis, which consists in changing the color of film gels during the sorption of active gases by them. The task was to create specific and universal indicators for harmful gaseous compounds with their detection in extremely low concentrations. This task was brilliantly accomplished ... a number of optical instruments were developed that allow automatic or semi-automatic qualitative analysis of air for harmful gases ... In this group of works, B.P. Belousov proved himself to be a scientist who poses the problem in a new way and solves it in a completely original way. In addition to these studies, B.P. Belousov owns a number of equally original and interesting scientific works, which leave no doubt that he certainly deserves to be awarded the degree of Doctor of Chemical Sciences without defending a dissertation.” The difficult character of Boris Pavlovich manifested itself here too, he "did not want any diplomas."
Nevertheless, the military chemist Belousov was awarded the rank of brigade commander, equivalent to the rank of major general. True, in 1935 he went on a long leave, and in 1938 he resigned. This, perhaps, explains the fact that Belousov himself did not suffer during the period of mass repressions of 1937-1938. However, the loss of many colleagues and friends left an indelible imprint on his character. The exact name of the secret medical institute where Belousov worked in subsequent years is unknown. But, according to colleagues, he had remarkable discoveries in the field of creating drugs that reduce the effect of radiation, he was appreciated: without having a higher education, the scientist was in charge of the laboratory and, on the written instructions of I.V. Stalin, received the salary of a doctor of science.
After analyzing the cyclic reactions discovered in the postwar years by biochemists, Belousov decided to make a chemical analogy of biological cycles. Investigating the oxidation of citric acid with bromate in the presence of a catalyst, he discovered concentration fluctuations of the reagents - this is how the oscillatory reaction was discovered. In 1951 and 1955, Belousov made attempts to publish his discovery in the journals Kinetics and Catalysis and Journal of General Chemistry. The responses to his articles were categorically negative and, as it turned out later, just as categorically erroneous. It is known that this affected the scientist so much that he simply threw away the laboratory recipe for the reaction and forgot about it.
A few years later, when biochemists became interested in the reaction discovered by Belousov, he had to look for the initial components and their proportions by sequential enumeration. We can say that the discovery was made by Belousov twice - the first time by accident, the second time as a result of a systematic search. But he no longer wanted to actively participate in the work of the scientific team. All that colleagues managed was to persuade Belousov to try to publish his article again. As a result, the only lifetime publication of the scientist appeared in the "Collection of Abstracts on Radiation Medicine" for 1958.
But even when recognition came and the international scientific community named the oscillatory reaction after Belousov-Zhabotinsky, attempts to involve the retired brigade commander in its further study were unsuccessful. Those who knew him in last years, claimed that Belousov's creative activity remained very high. He left the institute shortly before his death - on June 12, 1970. Ten years remained before Belousov was awarded the Lenin Prize.

Vibrational chemical reactions

In this term paper, I will consider a special case of a problematic experiment, oscillatory chemical reactions. Vibrational reactions are a whole class of oxidation reactions organic matter with the participation of a catalyst with redox properties. This process proceeds cyclically, that is, it consists of multiple repetitions.

Vibrational chemical reactions were discovered and scientifically substantiated in 1951 by the Soviet scientist Boris Petrovich Belousov. B.P. Belousov studied the oxidation of citric acid during its reaction with sodium bromate in a solution of sulfuric acid. To enhance the reaction, he added cerium salt to the solution. Cerium is a metal with a variable valence (3+ or 4+), so it can be a catalyst for redox transformations. The reaction is accompanied by the release of CO 2 bubbles, and therefore it seems that the entire reaction mixture "boils". And against the background of this boiling, B.P. Belousov noticed an amazing thing: the color of the solution periodically changed - it became either yellow or colorless. Belousov added a complex of phenanthroline with ferrous iron (ferroin) to the solution, and the color of the solution began to periodically change from purple-red to blue and back.

Thus was discovered the reaction that became famous. Now it is known all over the world, it is called the Belousov-Zhabotinsky reaction. A. M. Zhabotinsky did a lot to understand this amazing phenomenon. Since then, a large number of similar reactions have been discovered.

The history of the discovery of oscillatory reactions.

IP Belousov made the discovery of an oscillatory chemical reaction in an attempt to create a simple chemical model of some stages of the system of key biochemical transformations of carboxylic acids in a cell. However, the first report of its discovery was not published. The reviewer of a chemical journal doubted the fundamental possibility of the reaction described in the article. Most chemists in those years believed that there were no purely chemical oscillations, although the existence of oscillatory reactions was predicted in 1910 by A. Lotkoy on the basis of the mathematical theory of periodic processes.

The second attempt to publish the results of the study was made by the scientist in 1957, and again he was refused, despite the work of the Belgian physicist and physicochemist I. R. Prigozhin that appeared at that time. In these works, the possibility and probability of oscillatory chemical reactions was shown.

Only in 1959 was it published short abstract about the discovery by B. P. Belousov of a periodically acting oscillatory chemical reaction in a little-known publication "Collection of Abstracts on Radiation Medicine".

And the thing is that when B.P. Belousov made his discovery, periodic changes in the concentration of reagents seemed to be a violation of the laws of thermodynamics. Indeed, how can a reaction go either in the forward or in the opposite direction? It is impossible to imagine that the entire huge number of molecules in the vessel was either in one or another state (either all “blue”, then all “red” ...).

The direction of the reaction is determined by the chemical (thermodynamic) potential - the reactions are carried out in the direction of more probable states, in the direction of reducing the free energy of the system. When a reaction in a given direction is completed, this means that its potential has been exhausted, thermodynamic equilibrium is reached, and without the expenditure of energy, spontaneously, the process cannot go in the opposite direction. And then ... the reaction goes in one direction or the other.

However, there was no violation of laws in this reaction. There were fluctuations - periodic changes - in the concentrations of intermediates, and not the initial reactants or final products. CO 2 does not turn into citric acid in this reaction, this is actually impossible. The reviewers didn't take into account that while the system is far from equilibrium, many wonderful things can happen in it. The detailed trajectories of a system from its initial state to its final state can be very complex. Only in recent decades has the thermodynamics of systems far from equilibrium begun to deal with these problems. This new science became the basis of a new science - synergetics (the theory of self-organization).

Belousov's reaction, as noted above, was studied in detail by A. M. Zhabotinsky and his colleagues. They replaced citric acid with malonic acid. Oxidation of malonic acid is not accompanied by the formation of CO 2 bubbles, so the change in the color of the solution can be recorded without interference by photoelectric devices. Later it turned out that ferroin without cerium serves as a catalyst for this reaction. B. P. Belousov already in the first experiments noticed another remarkable property of his reaction: when stirring is stopped, the color change in the solution propagates in waves. This propagation of chemical vibrations in space became especially evident when, in 1970, A. M. Zhabotinsky and A. N. Zaikin poured a thin layer of the reaction mixture into a Petri dish. Bizarre figures are formed in the cup - concentric circles, spirals, "vortices" propagating at a speed of about 1 mm / min. Chemical waves have a number of unusual properties. So, when they collide, they are extinguished and cannot pass through each other.