The Complex Effect of Ascorbic Acid on the H ₂ O ₂ –SCN ⁻ –OH ⁻ –Cu ²⁺ –Type Chemical Oscillators—Experimental Studies and Numerical Modeling

ABSTRACT The complex effect of L‐ascorbic acid on the oscillatory course of the Orbán–Epstein system, in which the Cu 2+ ‐catalyzed oxidation of thiocyanate ions with hydrogen peroxide occurs, was investigated. Our studies involved both the original and EDTA‐perturbed system, analyzed in previous works. Potentiometric and spectrophotometric measurements were supported by numerical modeling of the proposed schemes of interaction of L‐ascorbic acid with the components of the system. In this way the kinetic mechanism of the effect of EDTA on the Orbán–Epstein system, based on the idea of excess production of radicals, enhancing the negative feedback loop in the oscillation cycle, was confirmed. The eventual involvement of other radicals, as, for example, OS(O)CN • is possible, but kinetically indistinguishable from that of species. The novel observation of the slowdown of oscillatory dynamics upon increasing concentrations of L‐ascorbic was explained in terms of removal of HO 2 Cu(OH) 2 − intermediate from reaction medium, presumably by the reduction of the central copper ion to elemental copper.