In a recent paper, we suggested that the acid-or base-catalyzed dehydration of a hydrated carbonyl compound provides a suitable foundation for an organic-based pH oscillator. Here we present the first experimental example of such an oscillator in a flow reactor, utilizing the base-catalyzed dehydration of methylene glycol as a source of positive feedback (OH -autocatalysis) coupled with the base-catalyzed hydrolysis of gluconolactone for negative feedback (H + production). The large amplitude oscillations (between pH 7 and 10) are reproduced in a kinetic model of the reaction. Such experiments present new possibilities in the design of pH oscillators.

The formaldehyde-sulfite reaction is an example of an "acid-to-alkali" clock. It displays an induction period, during which the pH varies only slowly in time, followed by a reaction event, during which the pH increases rapidly by several units. When the reaction is performed in a closed (batch) reactor, the clock time is found to increase with a decrease in initial concentrations of formaldehyde and sulfite and an increase in the total initial concentration of S(IV). At long times, following the clock event, there is a slow decrease in pH. In an open (flow) reactor, bistability between a low-pH steady state (pH approximately 6-8) and a high-pH steady state (pH approximately 11) is observed. Additionally, we report the existence of sustained, small-amplitude oscillations in pH in this system. An extended kinetic mechanism reproduces the batch behavior but fails to account for the complex behavior observed in the flow reactor. Possible additional reaction steps are discussed.

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The Methylene Glycol-Sulfite-Gluconolactone (MGSG) reaction is the first example of an organic-based pH oscillator. This reaction is of particular interest as it displays large amplitude oscillations in hydroxide ion accompanied by small amplitude (10(-3) V) oscillations in potential, indicating that it is not driven by redox processes. We investigate the reaction in a batch (closed) and flow (open) reactor and examine the role of the aging of the gluconolactone stock solution. The system is found to display oscillations and bistability for a wide range of flow rates and initial compositions. The experimental results are reproduced in numerical simulations in an extended model of the reaction in which the decay of the stock solution is incorporated. Finally, we analyse the features of the reaction that make it a suitable basis for the development of novel pH oscillators.

The influence of temperature on the oscillatory frequency of the hydrogen peroxide-iodate ion reaction is found to be two-sided: (i) the period length decreases with increasing temperature in most of the instances studied, (ii) or in some cases an opposite change is observed. A temperature-independent period length (temperature compensation) is also discovered experimentally in a rather wide temperature interval at a narrow concentration range of reactants both in a batch configuration and under flow conditions. A simple model was considered to simulate this behavior. Opposing effects of the composite reactions of the model on the calculated period length with changing temperature are shown to be responsible for temperature compensation or overcompensation.