New Experimental and Computational Results on the Radical-Controlled Oscillating Belousov−Zhabotinsky Reaction

Abstract

New experimental results on the oscillatory dynamics of the radical-controlled Belousov-Zhabotinsky reaction (the Ra ´cz system) in a batch reactor are reported. The system exhibits oscillations with no induction period, a typical feature of the radical-controlled mechanism. However, in the presence of acetylacetone (CH 2 -(COCH 3 ) 2 ), an induction period is observed before oscillations start, which increases with increasing acetylacetone concentration. There is a critical concentration of acetylacetone at which no oscillations occur. Quenching of radical-controlled oscillations is also observed at low and high malonic acid concentrations as well as at low and high sulfuric acid concentrations. An induction period is observed before the onset of radical-controlled oscillations at sulfuric acid concentrations g5.5 M. The duration of radical-controlled oscillations reaches a maximum at an intermediate sulfuric acid concentration. Numerical simulations based on the Radicalator model predict limits of malonic acid and sulfuric acid concentration within which oscillations are observed. The Radicalator model with additional reactions involving (i) CH 2 (COCH 3 ) 2 + Ce 4+ f • CH-(COCH 3 ) 2 , (ii) • CH(COCH 3 ) 2 + BrO 2 • f products, and (iii) • CH(COCH 3 ) 2 + • CH(COCH 3 ) 2 f products also predicts lengthening of induction period with the increase of acetylacetone concentration and suppression of oscillations at high acetylacetone concentration. Inclusion of the reaction between acetylacetone and HOBr had no effect.

Effect of mixed methyl ketones on the catalyzed resorcinol based oscillatory reaction at different temperatures

“…It is reported in literature [31] that acetyl acetone is scavenger for HOBr and Br 2 and the small amplitude oscillations shown here are purely radical controlled at higher concentrations of ketone, which is also true in our system.…”

Mixed Mode, Sequential and Relaxation Oscillations in the Belousov-Zhabotinsky System

“…Explanation of sequential oscillations [7] by two BZ reaction processes, i. e., between radicals and by means of Br − control, seems not to be useful in our case. This is because some sequential oscillations from [7] could not be observed without removing gaseous oxygen, present (in small amounts) in solutions of the substrates (prior to the reaction).…”

“…This is because some sequential oscillations from [7] could not be observed without removing gaseous oxygen, present (in small amounts) in solutions of the substrates (prior to the reaction). In our case all experimental results shown above were obtained without removing oxygen from substrates' solutions before the experiment.…”

“…More discussion regarding the chemistry of some sequential oscillations in the system MA, NaBrO 3 , H 2 SO 4 , CeNH 4 (NO 3 ) 4 is given in [7]. At several initial concentrations of the substances [7], some oscillations were observed at the very beginning of the reaction followed by no oscillations and again some oscillations. The first group of oscillations was radical-controlled and the second group was bromide-controlled.…”

Models for Oscillating Polymerization: Activation by Product in a System with Flow

“…the system that is similar to a proposed chemical multivibrator [40,41], which is an alternative to the Oregonator model (45,46) of the Belousov oscillating reaction.…”