Anna Olexová

Oscillatory oxidation of Mn(II) ions by hexacyanoferrates(III) and bistability in the reductions of MnO2 by hexacyanoferrates(II) in a CSTR

Abstract A new transition metal oscillator based on the oxidation of Mn2+ ions by Fe(CN)3−6 ions in a CSTR has been found. As well as the oscillations of the absorbance of the Mn(IV) species, pH-oscillations have been observed. In the reduction of manganese dioxide by Fe(CN)4−6 ions a kinetic bistability has been described. A skeleton mechanism described recently for Mn(II)H2O2 and Mn(II)Br2 oscillators has been applied here and further developed by the idea of the catalytic activity of colloidal particles and of the assistance of the pH-value change of both main processes, i.e. of the Mn(II) oxidation by Fe(CN)3−6 ions and of the Mn(IV) reduction by Fe(CN)4−6 ions. This appears to be the first case where both sides of a reversible reaction are autocatalytic.

Oscillatory System I―, H2O2, HClO4: The Modified Form of the Bray-Liebhafsky Reaction

The kinetics of iodide ions oxidation with hydrogen peroxide in solutions of perchloric acid at temperature of 60 degrees C has been studied in detail. We have found conditions under which this reaction proceeds oscillatory. The Bray-Liebhafsky (BL) oscillatory reaction started by the oxidation of iodide ions with hydrogen peroxide is described for the first time. The described results support our assumption (Olexová, A.; Mrákavová, M.; Melichercík, M.; Treindl, L. Collect. Czech. Chem. Commun. 2006, 71, 91-106) that singlet oxygen ((1)O(2)) is an important intermediate of the BL oscillatory reaction in the sense of the Noyes-Treindl (N-T) skeleton mechanism (Treindl, L.; Noyes, R.M. J. Phys. Chem. 1993, 97, 11354-11362).

Kinetics of the oxidation of iodine by hydrogen peroxide catalyzed by MoO2−4 ions

Abstract The kinetics of the oxidation of iodine by hydrogen peroxide catalyzed by MoO2−4 ions with a ‘clock’ behaviour is described and the corresponding reaction scheme is proposed. The ‘clock’ behaviour is explained by the assumption that the oxidation of iodine cannot proceed until the iodide concentration drops to a certain treshold, since this reaction can only through the HOI species proceed. The noncatalyzed, direct oxidation of iodine by H2O2 is too slow to become one of the main two processes of the Bray-Liebhafsky oscillatory reaction.

A simple model for the electrochemical oscillations on a stationary mercury electrode in bromate solutions

A simple model for the electrochemical oscillations on a stationary mercury electrode in bromate solutions has been proposed and its mathematical simulation carried out on a qualitative level. We believe it can be added to the simplest mathematical models of chemical oscillators, since it consists of only four reaction components.AbstractПредложена простая модель электрохимических осцилляций на стационарном ртутном электроде в броматных растворах, математическая симуляция которой проведена качественно. Данная модель может быть добавлена к простейшим математическим моделям химических колебаний, т.к. она содержит всего четыре реагирующих компонента.

Chemical oscillators based on the oxidation of Mn(II) by some halogens

Chemical oscillators based on the oxidation of Mn(II) ions by bromine or chlorine in NaH2PO4−NaOH buffer solutions in a CSTR (continuous-flow stirred tank reactor) are described. The oscillations correspond to the two alternating processes. The first process is the oxidation of Mn(II) by HOBr or HOCl to Mn(IV) and the second one is of a micro-heterogeneous nature, consisting of the reduction of Mnc4+ and Mnc3+ centers on the surface of colloids (MnO2)col by halides.

The Effect of Perturbants on the Uncatalyzed Bromate Oscillator

Abstract The effect of cationic (CTAN), anionic (SDS) and nonionic surfactants (Brij-30 and Triton X-100) as well as of tert-butanol (t-BuOH) on the uncatalyzed bromate oscillator with phenol as substrate was investigated at 25 ± 0.1oC in non-stirred batch conditions. Addition of the surfactants influenced the oscillatory parameters: a slight increase in induction period of the first series of oscillations, a significant increase in induction period of the second series of oscillations as well as a gradual decrease in oscillation numbers of both series until complete disappearance at a certain surfactant concentration. The changes in the oscillatory parameters have been ascribed to the solubilization of phenol and of bromination products in the micelles, to the inhibition of bromination of aromatic substrate due to the bromine solubilization and to the catalytic effect of charged micelle surface. The changes in the oscillatory behaviour with increasing alcohol concentration have been discussed in terms of its ability to act as a radical scavenger and to affect the 3D-structure of water.

The Effect of Anionic, Cationic and Nonionic Surfactants on the Uncatalyzed Bromate Oscillator

The response of an uncatalyzed bromate oscillator with phenol as substrate to the increasing concentrations of cationic (CTAN), anionic (SDS) and nonionic surfactants (Brij-30 and Triton X-100) was monitored at (25±0.1) °C under stirred batch conditions. Addition of the surfactants influenced the oscillatory parameters: a slight increase of the induction period of the first series of oscillations, a significant increase of the induction period of the second series of oscillations and a gradual decrease of the oscillation numbers of both series until complete disappearance at a certain surfactant concentration. The changes in the oscillatory parameters have been ascribed to solubilization of phenol and of bromination products in the micelles, to inhibition of bromination of the aromatic substrate due to bromine solubilization, and to the catalytic effect of the charged micelle surface.