Peter Ševčík

The methylene blue‐D‐glucose‐O2 system. Oxidation of D‐glucose by methylene blue in the presence and the absence of oxygen

Quasi-oscillations in [O2] were observed during the methylene blue catalyzed oxidation of D-glucose by O2 in alkaline aqueous solutions. The kinetics of anaerobic oxidation of D-glucose (GH) by methylene blue (MB+) was investigated in a closed system. The reaction was first order with respect to the concentration of methylene blue and the observed rate constant increased with GH concentration in a saturated mode. The oxidation proceeds via complex formation between GH and MB+ and the rate constant of the decay of the complex was determined. The oxidation process was also investigated under aerobic conditions and the reaction rates and reaction orders were determined by spectrophotometric measurements of the disappearance of MB+ and by amperometric determination of O2 consumption.

Numerical simulations of the oxygen production in the oscillating Bray-Liebhafsky reaction

Abstract Numerical simulations of the oxygen production in the batch Bray–Liebhafsky (BL) oscillating reaction were performed. The dynamic behaviour of the BL reaction was modelled by a scheme suggested by Schmitz and Kolar-Anic, complemented by the physical processes of iodine and oxygen interphase transport. The calculated number and periods of oscillations of the rate of the gaseous oxygen production are in satisfactory agreement with experiment. Oscillations in iodate concentration have been found if some escape of iodine from the batch reactor was allowed.

Effect of a pressure decrease and stirring on the oscillating Bray-Liebhafsky reaction

Abstract A decrease in pressure from 101.3 to 26 kPa or less results in a dramatic change in the oscillation parameters in the batch Bray-Liebhafsky (BL) oscillatory system in an N2 or O2 atmosphere. It was confirmed that at 101.3 kPa the oscillations can be suppressed by rapid stirring. The experiments show that the rate of interphase transport of I2 is not negligible at 50°C and can be influenced by both stirring and pressure changes. It is indicated that the escape of I2 from the BL solution to the phase above it can significantly deplete the total concentration of iodine. We conclude that external pressure can be considered to be the bifurcation parameter which is associated with stability of the BL system.

The Decay of Methylene Blue in Alkaline Solution

AbstractThe decomposition of methylene blue in aqueous alkaline solution is described. The rate equation is of the form:

Are Uncatalyzed Bromate Oscillators Truly Gas-Free?

- \frac{{d\left[ {MB^ - } \right]}}{{dt}} = k\left[ {OH^ - } \right]\left[ {MB^ - } \right]

A Simple Method of Gas Evolution Measurement Suitable for Analysis of Batch Oscillating Reactions: Briggs-Rauscher System with Acetone Revisited

, where k = 9.0 × 10-4 mol- [dm3s-1 at 20°C and] = 0.5 mol dm-3.

The oscillating Belousov-Zhabotinsky reaction with saccharides in batch systems

Oxalic acid can produce oscillations in the Belousov–Zhabotinsky‐type reaction in a closed batch system without a mechanism for bromine removal. The stirring rate has a significant effect on the reaction.

Modeling of interactions between iodine interphase transport and oxygen production in the modified Briggs-Rauscher reaction with acetone.

Gas evolution is a common byproduct of chemical oscillations but is seldom treated as anything but a complication. Its precise quantification is usually underestimated, and if not obvious enough, gaseous products are easily neglected completely. Reported herein is how evolution of gas from uncatalyzed bromate oscillators with pyrocatechol, pyrogallol, and 1,4-cyclohexanedione was measured by a high-precision batch-mode gasometric method, and the data obtained with unprecedented time resolution are presented. Even though within this completely closed arrangement of measurement no oscillations in rate of gas evolution were observed, it is verified that neither of the substrates can be considered totally free of gas production. Nevertheless, the amount of gas evolved from 1,4-cyclohexanedione was confirmed to be very small, and near negligible, if only oscillatory phase is of interest. Conversely, under identical conditions, the peak rates of gas evolution from the other substrates were reached much sooner, and even though the results in all three cases suggest some extent of suppression of gas production by oscillations, as much as 1 equiv of gas in total can be produced from the phenols, especially from pyrogallol, where the degradation was measured to be approximately twice as extensive. Greater caution is, therefore, recommended whenever the gas-free nature of these oscillators is considered.