Mechanistic Investigations of the BZ Reaction with Oxalic Acid Substrate. I. The Oscillatory Parameter Region and Rate Constants Measured for the Reactions of HOBr, HBrO₂, and Acidic BrO₃^- with Oxalic Acid

Abstract

This paper is the first part of a study reinvestigating the mechanism of the Belousov−Zhabotinsky (BZ) reaction of oxalic acid, which is the simplest organic substrate for a BZ oscillator. New experiments are performed to find the oscillatory region in 1 M sulfuric acid at 20 °C. The removal rate of the end product bromine by an inert gas stream is a critical parameter here: oscillations can be observed only in a window of that parameter. The “rate constant” for the physical removal of bromine is measured as a function of the gas flow rate and reactor volume; furthermore, the rate constants of three component reactions important in this system are also determined. These are oxygen atom transfer reactions to the oxalic acid substrate from Br(I) (hypobromous acid), from Br(III) (bromous acid), and from Br(V) (acidic bromate) compounds. In these second-order reactions, the partial order of each oxybromine species is 1. The measured rate constants are k I = 17 ± 2 M-1 s-1, k III = 4.2 ± 0.5 M-1 s-1, and k V = (7.47 ± 0.1) × 10-4 M-1 s-1. In the case of the HOBr−oxalic acid reaction, however, an additional parallel reaction route was found that has importance at higher HOBr concentrations. In the mechanism of that new route, the active species is Br2O, and the reaction order is not 1 but 2 with respect to HOBr. The rate constant of this parallel reaction is k I (2) = (1.2 ± 0.2) × 105 M-2 s-1. The k values measured here are compared with those reported earlier. A comparison of experimental results with computer simulations shows that free radicals play a negligible role or no role in the mechanism of the oxygen atom transfer reactions studied here.

Iodine oxidation by hydrogen peroxide in acidic solutions, Bray-Liebhafsky reaction and other related reactions

“…The intermediate compound Br 2 O was also proposed in the mechanism of the Belousov-Zhabotinsky reaction. 72,73 In chlorine chemistry, the equilibrium 2 ClOH " Cl 2 O + H 2 O is well known 74 . The disproportionation reaction 2 HIO 2 -IOH + HIO 3 could be a third kind of oxygen transfer reactions.…”

Nonlinear Response of a Batch BZ Oscillator to the Addition of the Anionic Surfactant Sodium Dodecyl Sulfate

“…Among the model systems that have attracted the attention of researchers, the oscillating reaction of Belousov-Zhabotinsky (BZ) is one of the most extensively studied. [1][2][3][4][5][6][7] In fact, the first study was undertaken in order to mimic the Krebs cycle. In its "classic" version, the BZ reaction consists of the bromuration and oxidation of an organic substrate (the malonic acid) in strongly acidic medium, in the presence of a catalyst (one electron redox couple, usually the system Ce(IV)/Ce(III) or Ferroin/Ferriin).…”

Mapping Sequential Oscillations in the Bromate–Oxalic Acid–Acetone–Ce(IV) Reaction

“…Moreover, the Br – source cannot be a brominated organic compound, like bromomalonic in the Field–Körös–Noyes (FKN) 21 mechanism, because oxalic acid does not form any brominated product, and bromoacetone does not react at a significant speed with Ce(IV). 20,22 The Br – is mainly formed by bromine hydrolysis (eq 3 below).…”