Belousov–Zhabotinsky Reaction
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A Belousov–Zhabotinsky reaction, or BZ reaction, is one of a class of reactions that serve as a classical example of
non-equilibrium thermodynamics Non-equilibrium thermodynamics is a branch of thermodynamics that deals with physical systems that are not in thermodynamic equilibrium but can be described in terms of macroscopic quantities (non-equilibrium state variables) that represent an ext ...
, resulting in the establishment of a
nonlinear In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...
chemical oscillator A chemical oscillator is a complex mixture of reacting chemical compounds in which the concentration of one or more components exhibits periodic changes. They are a class of reactions that serve as an example of non-equilibrium thermodynamics wit ...
. The only common element in these oscillators is the inclusion of
bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simila ...
and an acid. The reactions are important to theoretical chemistry in that they show that chemical reactions do not have to be dominated by equilibrium thermodynamic behavior. These reactions are far from equilibrium and remain so for a significant length of time and evolve chaotically. In this sense, they provide an interesting chemical model of nonequilibrium biological phenomena; as such, mathematical models and simulations of the BZ reactions themselves are of theoretical interest, showing phenomenon as noise-induced order. An essential aspect of the BZ reaction is its so called "excitability"; under the influence of stimuli, patterns develop in what would otherwise be a perfectly quiescent medium. Some clock reactions such as Briggs–Rauscher and BZ using the
tris(bipyridine)ruthenium(II) chloride Tris(bipyridine)ruthenium(II) chloride is the chloride salt coordination complex with the formula u(bpy)3sup>2+ 2Cl−. This polypyridine complex is a red crystalline salt obtained as the hexahydrate, although all of the properties of interest ...
as catalyst can be excited into
self-organising Self-organization, also called spontaneous order in the social sciences, is a process where some form of overall order arises from local interactions between parts of an initially disordered system. The process can be spontaneous when suffici ...
activity through the influence of light.


History

The discovery of the phenomenon is credited to Boris Belousov. In 1951, while trying to find the non-organic analog to the
Krebs cycle The citric acid cycle (CAC)—also known as the Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and protein ...
, he noted that in a mix of
potassium bromate Potassium bromate (KBrO3), is a bromate of potassium and takes the form of white crystals or powder. It is a strong oxidizing agent. It is a toxic and carcinogenic compound. Preparation Potassium bromate is produced when bromine is passed throug ...
,
cerium(IV) sulfate Cerium(IV) sulfate, also called ceric sulfate, is an inorganic compound. It exists as the anhydrous salt Ce( SO4)2 as well as a few hydrated forms: Ce(SO4)2(H2O)x, with x equal to 4, 8, or 12. These salts are yellow to yellow/orange solids th ...
,
malonic acid Malonic acid (IUPAC systematic name: propanedioic acid) is a dicarboxylic acid with structure CH2(COOH)2. The ionized form of malonic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is malonic acid' ...
, and
citric acid Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...
in dilute
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
, the ratio of concentration of the cerium(IV) and cerium(III) ions oscillated, causing the colour of the solution to oscillate between a yellow solution and a colorless solution. This is due to the cerium(IV) ions being reduced by malonic acid to cerium(III) ions, which are then oxidized back to cerium(IV) ions by bromate(V) ions. Belousov made two attempts to publish his finding, but was rejected on the grounds that he could not explain his results to the satisfaction of the editors of the journals to which he submitted his results. Soviet biochemist
Simon El'evich Shnoll Simon El'evich Shnol (russian: Симон Эльевич Шноль; 21 March 1930 – 11 September 2021) was a biophysicist, and a historian of Soviet science. He was a professor at Physics Department of Moscow State University and a member of ...
encouraged Belousov to continue his efforts to publish his results. In 1959 his work was finally published in a less respectable, nonreviewed journal. After Belousov's publication, Shnoll gave the project in 1961 to a graduate student,
Anatol Zhabotinsky Anatol Markovich Zhabotinsky (Анато́лий Ма́ркович Жаботи́нский) (January 17, 1938 – September 16, 2008) was a Soviet biophysicist who created a theory of the chemical clock known as Belousov–Zhabotinsky reactio ...
, who investigated the reaction sequence in detail; however, the results of these men's work were still not widely disseminated, and were not known in the West until a conference in
Prague Prague ( ; cs, Praha ; german: Prag, ; la, Praga) is the capital and largest city in the Czech Republic, and the historical capital of Bohemia. On the Vltava river, Prague is home to about 1.3 million people. The city has a temperate ...
in 1968. A number of BZ cocktails are available in the chemical literature and on the web.
Ferroin Ferroin is the chemical compound with the formula e(''o''-phen)3O4, where ''o''-phen is an abbreviation for 1,10-phenanthroline, a bidentate ligand. The term "ferroin" is used loosely and includes salts of other anions such as chloride. Redox ...
, a
complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...
of
phenanthroline 1,10-Phenanthroline (phen) is a heterocyclic organic compound. It is a white solid that is soluble in organic solvents. The 1,10 refer to the location of the nitrogen atoms that replace CH's in the hydrocarbon called phenanthrene. Abbreviated ...
and
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
, is a common
indicator Indicator may refer to: Biology * Environmental indicator of environmental health (pressures, conditions and responses) * Ecological indicator of ecosystem health (ecological processes) * Health indicator, which is used to describe the health ...
. These reactions, if carried out in
petri dish A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured,R. C. Dubey (2014): ''A Textbook Of Biotechnology For Class- ...
es, result in the formation first of colored spots. These spots grow into a series of expanding concentric rings or perhaps expanding spirals similar to the patterns generated by a
cyclic cellular automaton A cyclic cellular automaton is a kind of cellular automaton rule developed by David Griffeath and studied by several other cellular automaton researchers. In this system, each cell remains unchanged until some neighboring cell has a modular value ...
. The colors disappear if the dishes are shaken, and then reappear. The waves continue until the reagents are consumed. The reaction can also be performed in a beaker using a
magnetic stirrer A magnetic stirrer or magnetic mixer is a laboratory device that employs a rotating magnetic field to cause a stir bar (or ''flea'') immersed in a liquid to spin very quickly, thus stirring it. The rotating field may be created either by a rota ...
.
Andrew Adamatzky Andrew Adamatzky is a British computer scientist, who is a Director of the Unconventional Computing Laboratory and Professor in Unconventional Computing at the Department of Computer Science and Creative Technology, University of the West of Engl ...
, a computer scientist in the
University of the West of England The University of the West of England (also known as UWE Bristol) is a public research university, located in and around Bristol, England. The institution was know as the Bristol Polytechnic in 1970; it received university status in 1992 and ...
, reported on liquid logic gates using the BZ reaction. The BZ reaction has also been used by Juan Pérez-Mercader and his group at
Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher le ...
to create an entirely chemical Turing machine, capable of recognizing a Chomsky type-1 language. Strikingly similar oscillatory spiral patterns appear elsewhere in nature, at very different spatial and temporal scales, for example the growth pattern of ''
Dictyostelium discoideum ''Dictyostelium discoideum'' is a species of soil-dwelling amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, ''D. discoideum'' is a eukaryote that transitions from a collection of unicellular ...
'', a soil-dwelling
amoeba An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of Cell (biology), cell or unicellular organism with the ability to alter its shape, primarily by extending and ret ...
colony. In the BZ reaction, the size of the interacting elements is molecular and the time scale of the reaction is minutes. In the case of the soil amoeba, the size of the elements is typical of single-celled organisms and the times involved are on the order of days to years. Investigators are also exploring the creation of a "wet computer", using self-creating "cells" and other techniques to mimic certain properties of
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
s.


Chemical mechanism

The mechanism for this reaction is very complex and is thought to involve around 18 different steps which have been the subject of a number of research papers. In a way similar to the
Briggs–Rauscher reaction The Briggs–Rauscher oscillating reaction is one of a small number of known oscillating chemical reactions. It is especially well suited for demonstration purposes because of its visually striking colour changes: the freshly prepared colourless s ...
, two key processes (both of which are auto-catalytic) occur; process A generates molecular bromine, giving the red colour, and process B consumes the bromine to give bromide ions. Theoretically, the reaction resembles the ideal
Turing pattern The Turing pattern is a concept introduced by English mathematician Alan Turing in a 1952 paper titled "The Chemical Basis of Morphogenesis" which describes how patterns in nature, such as stripes and spots, can arise naturally and autonomousl ...
, a system that emerges qualitatively from solving the
reaction diffusion Reaction may refer to a process or to a response to an action, event, or exposure: Physics and chemistry *Chemical reaction *Nuclear reaction *Reaction (physics), as defined by Newton's third law * Chain reaction (disambiguation). Biology and m ...
equations for a reaction that generates both a reaction inhibitor and a reaction promoter, of which the two diffuse across the medium at different rates. One of the most common variations on this reaction uses
malonic acid Malonic acid (IUPAC systematic name: propanedioic acid) is a dicarboxylic acid with structure CH2(COOH)2. The ionized form of malonic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is malonic acid' ...
(CH2(CO2H)2) as the acid and
potassium bromate Potassium bromate (KBrO3), is a bromate of potassium and takes the form of white crystals or powder. It is a strong oxidizing agent. It is a toxic and carcinogenic compound. Preparation Potassium bromate is produced when bromine is passed throug ...
(KBrO3) as the source of bromine. The overall equation is: : 3 CH2(CO2H)2 + 4 → 4 Br + 9 CO2 + 6 H2O


Variants

Many variants of the reaction exist. The only key chemical is the bromate oxidizer. The catalyst ion is most often cerium, but it can be also manganese, or complexes of iron, ruthenium, cobalt, copper, chromium, silver, nickel and osmium. Many different reductants can be used. (Zhabotinsky, 1964b; Field and Burger, 1985) Many different patterns can be observed when the reaction is run in a
microemulsion Microemulsions are clear, thermodynamically stable isotropic liquid mixtures of oil, water and surfactant, frequently in combination with a cosurfactant. The aqueous phase may contain salt(s) and/or other ingredients, and the "oil" may actually be ...
.


See also

* Autowave *
Autowave reverberator In the theory of autowave phenomena an autowave reverberator is an autowave vortex in a two-dimensional active medium. A reverberator appears a result of a rupture in the front of a plane autowave. Such a rupture may occur, for example, via coll ...
*
Briggs–Rauscher reaction The Briggs–Rauscher oscillating reaction is one of a small number of known oscillating chemical reactions. It is especially well suited for demonstration purposes because of its visually striking colour changes: the freshly prepared colourless s ...
*
Dissipation In thermodynamics, dissipation is the result of an irreversible process that takes place in homogeneous thermodynamic systems. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to a ...
*
Excitable medium An excitable medium is a nonlinear dynamical system which has the capacity to propagate a wave of some description, and which cannot support the passing of another wave until a certain amount of time has passed (known as the refractory time). A fo ...
* Noise-induced order *
Patterns in nature Patterns in nature are visible regularities of form found in the natural world. These patterns recur in different contexts and can sometimes be modelled mathematically. Natural patterns include symmetries, trees, spirals, meanders, waves, foa ...
* Reaction–diffusion *
Self-oscillation Self-oscillation is the generation and maintenance of a periodic motion by a source of power that lacks any corresponding periodicity. The oscillator itself controls the phase with which the external power acts on it. Self-oscillators are therefor ...
*
Self-organization Self-organization, also called spontaneous order in the social sciences, is a process where some form of overall order arises from local interactions between parts of an initially disordered system. The process can be spontaneous when suffi ...
* Stochastic Resonance *
Alan Turing Alan Mathison Turing (; 23 June 1912 – 7 June 1954) was an English mathematician, computer scientist, logician, cryptanalyst, philosopher, and theoretical biologist. Turing was highly influential in the development of theoretical com ...
who mathematically predicted oscillating chemical reactions in the early 1950s * Brusselator *
Oregonator The Oregonator is a theoretical model for a type of autocatalytic reaction. The Oregonator is the simplest realistic model of the chemical dynamics of the oscillatory Belousov–Zhabotinsky reaction. It was created by Richard Field and Richard M. ...


References


Further reading

* * *


External links


Interactive Science Experiment Showcasing the BZ Reaction (A-Level)

A Survey Article on the Mathematics of the BZ Reaction

The Scholarpedia article on the Belousov-Zhabotinsky reaction



The Belousov–Zhabotinsky Reaction


* ttps://www.youtube.com/watch?v=uWh8reiXq58 BZ reaction and explanationat
The Periodic Table of Videos ''Periodic Videos'' (also known as ''The Periodic Table of Videos'') is a video project and YouTube channel on chemistry. It consists of a series of videos about chemical elements and the periodic table, with additional videos on other topics i ...

The Belousov–Zhabotinski Reaction
(PDF file)

Oscillating chemical waves induced by BZ reactions can propel small objects, ''New Scientist'', 18 February 2008



A simulation of the Belousov–Zhabotinsky reaction running inside Flash Player {{DEFAULTSORT:Belousov-Zhabotinsky Reaction Name reactions Non-equilibrium thermodynamics Pattern formation Clock reactions