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

Maria Liria Turco Liveri, Renato Lombardo, Krisztina Pelle, Zoltán Noszticzius, Maria Wittmann, Klára Lovrics

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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 areperformed to find the oscillatory region in 1 M sulfuric acid at 20 °C. The removal rate of the end productbromine by an inert gas stream is a critical parameter here: oscillations can be observed only in a windowof that parameter. The “rate constant” for the physical removal of bromine is measured as a function of thegas flow rate and reactor volume; furthermore, the rate constants of three component reactions important inthis system are also determined. These are oxygen atom transfer reactions to the oxalic acid substrate fromBr(I) (hypobromous acid), from Br(III) (bromous acid), and from Br(V) (acidic bromate) compounds. Inthese second-order reactions, the partial order of each oxybromine species is 1. The measured rate constantsare 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 theHOBr-oxalic acid reaction, however, an additional parallel reaction route was found that has importance athigher HOBr concentrations. In the mechanism of that new route, the active species is Br2O, and the reactionorder is not 1 but 2 with respect to HOBr. The rate constant of this parallel reaction is kI(2) ) (1.2 ( 0.2) 105 M-2 s-1. The k values measured here are compared with those reported earlier. A comparison ofexperimental results with computer simulations shows that free radicals play a negligible role or no role inthe mechanism of the oxygen atom transfer reactions studied here.
Original languageEnglish
Pages (from-to)5377-5385
Number of pages9
JournalJOURNAL OF PHYSICAL CHEMISTRY. A, MOLECULES, SPECTROSCOPY, KINETICS, ENVIRONMENT, & GENERAL THEORY
Volume108
Publication statusPublished - 2004

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry

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