Bray-Liebhafsky reaction

The Bray-Liebhafsky reaction is an oscillating chemical reaction . It was described as the first such reaction for a homogeneous system.

history

In 1916, William C. Bray (1879–1946) and his colleague AL Caulkins began to investigate the role of hydrogen peroxide in the oxidation of iodine and the reduction of iodate, respectively . Bray noticed that the evolution of oxygen in accordance with the reaction

${\displaystyle \mathrm {2\ H_{2}O_{2}\longrightarrow 2\ H_{2}O+O_{2}} }$

not continuously, but oscillating. In 1921 Bray published his work, which for the first time described an oscillating reaction in a homogeneous medium. However, the publication received little attention at the time and even met with rejection from the specialist audience. It was claimed that the periodic behavior was based on impurities that would create heterophasic interfaces, which at that time were considered a prerequisite for the occurrence of such oscillations. After Ilya Prigogine created the theoretical basis for oscillating reactions in the 1960s , Bray's former colleague Herman A. Liebhafsky continued to investigate the reaction. This reaction is therefore called the Bray-Liebhafsky reaction.

Only Kumud R. Sharma and Richard M. Noyes were able to explain the reaction mechanism in 1976.

Reaction mechanism

The complex reaction involves several steps, both radical and non-radical. A fundamental property of the system is that H ₂ O _{2 has} the necessary redox potential to convert both I ₂ to IO ₃ ^- according to

${\displaystyle \mathrm {5\;H_{2}O_{2}+I_{2}\longrightarrow 2\;IO_{3}^{-}+2\;H^{+}+4\;H_{2}O} }$

to oxidize , as well as IO ₃ ^- to I ₂ according to

${\displaystyle \mathrm {5\;H_{2}O_{2}+2\;IO_{3}^{-}+2\;H^{+}\longrightarrow I_{2}+5\;O_{2}+6\;H_{2}O} }$

to reduce . The system oscillates back and forth between these two mentioned reactions, causing simultaneous jumps in the concentration of iodide and oxygen production (dO ₂ / dt), as well as causing thermal oscillations. An increase in temperature causes an increase in the period.

The following reaction can be given as the net stoichiometry of the reaction

${\displaystyle \mathrm {2\;H_{2}O_{2}\longrightarrow 2\;H_{2}O+O_{2}} ,}$

with a catalyst and IO ₃ ^- must be present.

literature

• K. Höner, R. Cervellati: Free radicals, antioxidants and the oscillating Briggs-Rauscher reaction . Lit, Münster 2004, ISBN 3825882896 .

Individual evidence

1. ^ William C. Bray: A Periodic Reaction in Homogeneous Solution and its Relation to Catalysis. In: Journal of the American Chemical Society. 43, No. 6, 1921, pp. 1262-1267, doi : 10.1021 / ja01439a007 .
2. ↑ Kumud R. Sharma, Richard M. Noyes: Oscillations in chemical systems. 13. A detailed molecular mechanism for the Bray-Liebhafsky reaction of iodate and hydrogen peroxide. In: Journal of the American Chemical Society. 98, No. 15, 1976, pp. 4345-4361, doi : 10.1021 / ja00431a001 .