BZ reaction
OSCILLATIONS OF chemical origin have been present as long as life itself. Every living system contains scores, perhaps hundreds, of chemical oscillators.

Alfred Lotka was one of the more interesting characters in the history of science. He wrote papers on chemical oscillation during the early decades of XX century.  In 1910, Lotka  showed that a set of consecutive reactions can give rise to damped oscillations on the way to equilibrium. Vito Volterra used ideas similar to Lotka's to investigate a wide range of ecological problems, including the effects of migration and of several species simultaneously interacting. The best known model of this type is called the Lotka-Volterra model and is often used to characterize predator-prey interactions

Simula'l al Laboratori COMSOC
   

Oscillating reactions

 The complete mechanism of the BZ reaction was explained by R. M. Noyes, R. J. Fields and E. Körös. It involves 18 reactions with 21 different chemical species. A simplified mechanism was proposed by the same authors. It was named "Oregonator" in reference to the University of Oregon where they worked in this period. Here I shall try to explain it as well as I can.

 The global reaction can be separated in three steps (called A, B and C). In step A, Br2 is produced from BrO3- and Br-. We can split step B in two other steps (called B1 and B2). In step B1 a catalytic production of HBrO2 takes place and produces the oxidation of Fe2+ to Fe3+ (which gives the blue color). In step B2, HBrO2 turns into BrO3- feeding back steps A and B. Finally, in step C not only are the products from steps A and B2 (Br2 and Fe3+) are involved but also malonic acid. As a result of this step Br- appears and feedbacks to step A; the ion Fe3+ is reduced and while a certain amount of malonic acid is formed again, another portion is transformed into different complex organic products. This is the summary of the reactions that take place. When malonic acid disappears the reaction reaches the equilibrium.

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