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

Krisztina Pelle, M. Wittmann, Klára Lovrics, Z. Noszticzius, Maria L Turco Liveri, Renato Lombardo

Research output: Contribution to journalArticle

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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 die 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 kI = 17 ± 2 M-1 s-1, kIII = 4.2 ± 0.5 M-1 s-1, and kv = (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.

Original languageEnglish
Pages (from-to)5377-5385
Number of pages9
JournalJournal of Physical Chemistry A
Volume108
Issue number25
DOIs
Publication statusPublished - Jun 24 2004

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Oxalic Acid
oxalic acid
Rate constants
Bromine
Substrates
Bromates
Oxygen
Noble Gases
Atoms
bromine
Free Radicals
Flow of gases
oxygen atoms
Flow rate
routes
Acids
bromates
hypobromous acid
Computer simulation
acids

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

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. / Pelle, Krisztina; Wittmann, M.; Lovrics, Klára; Noszticzius, Z.; Liveri, Maria L Turco; Lombardo, Renato.

In: Journal of Physical Chemistry A, Vol. 108, No. 25, 24.06.2004, p. 5377-5385.

Research output: Contribution to journalArticle

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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 die 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 kI = 17 ± 2 M-1 s-1, kIII = 4.2 ± 0.5 M-1 s-1, and kv = (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.",
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AU - Liveri, Maria L Turco

AU - Lombardo, Renato

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