Endre Koros

Effect of temperature in cerium-ion-catalyzed bromate-driven oscillators

Abstract The influence of substrate composition and initial reagent concentrations on activation energies in closed Ce-ion catalyzed Belousov-Zhabotinsky (BZ) reactions is reported. While changes in the initial concentration of organic substrate, bromate ion or sulfuric acid showed different changes in activation energies for the various organic substrate BZ systems, for all systems it was found that lowering the Ce-ion concentration leads to a significant decrease in the overall activation energy of the oscillator. When comparing the performance of a malonic acid oscillator run in a batch or in a continuous stirred flow reactor (CSTR), it was found that under CSTR conditions Q 10 values may become as low as 1.3, while for the batch system the corresponding Q 10 values are about 2.3.

Temperature-triggered chemical oscillators. A peculiar temperature effect in perturbed uncatalyzed bromate-driven reactions

Some uncatalyzed bromate oscillators with p-substituted phenol derivatives as the organic substrates when perturbed with chloride ions show a remarkable behavior, namely, a sudden transition, at a well-defined threshold temperature, from the non-oscillatory to the oscillatory state, and back. The high sensitivity of the reacting systems towards chloride ion perturbation and the conditions for the occurrence of the phenomenon are described.

Perturbation of Bromate Oscillators

Bromate oscillators have been investigated from many aspects. One of the aims has been to reveal the chemical prerequisites of the oscillatory behaviour. Some quantitative results have been already published [1]. The bromate oscillators can be perturbed, e.g. by the addition of inhibitory property halides [2,3], by the supply of O2 [3–6]; by keeping low the bromide concentration (addition of Ag+) [7]; or by γ-irradiation of the reacting system [8]. From the effect the perturbation exerts on a bromate oscillator, important information can be gained on the chemical mechanism of the oscillatory reaction.

Calorimetric studies on the bromate—Malic acid-catalyst oscillating system

Calorimetic studies have been performed on the malic acid, acidic bromate and catalyst (Ce3+ or Mn2+) oscillating BZ systems, and the heat of the reaction, referred to one mole bromate, has been calculated. Its value is 329.5±12.7 kJ/mol. In light of the heat of reaction values the malic acid and malonic acid containing BZ systems are compared.AbstractКалориметрические исследования проводились в осциллирующей системе БЖ, состоящей из яблочной кислоты, кислого бромата и катализатора (Ce3+ или Mn2+), откуда была рассчитана теплота реакции, отнесенная к одному молю бромата, которая равна 329,5±12,7 кдж/моль. На основе теплот реакции сравнивались БЖ системы, содержащие яблочную и малоновую кислоты.

Chemical Oscillations During the Oxidative Bromination of Some Aromatic Compounds with Bromate

Among the few oscillatory chemical reactions proceeding in solution the BELOUSOV-ZHABOTINSKY [BZ[ reaction has been studied more thoroughly. The BZ reaction is essentially the catalytic oxidation and bromination of a variety of aliphatic compounds — mostly dicar-boxylic acids and diketones — with acid bromate. Detailed investigations revealed that the occurrence of chemical oscillation is due to the existence of two kinetic states in the system, and the transition from one state to the other is controlled by the bromide ion concentration [1]. Extensive experimental investigations disclosed that all components of the BZ system, but bromate, can be substituted. It is a widely accepted view that such types of reactions require a catalyst.