Sequential oscillations in the Belousov–Zhabotinski system with ascorbic acid–acetone/cyclohexanone as the mixed organic substrate

Abstract

Temporal oscillations in BrO^–₃–H₂SO₄–Ce⁴⁺–ascorbic acid–acetone/cyclohexanone have been studied in detail. It is observed that two types of oscillatory regimes separated by a time pause occur. Synchronous oscillations in colour and redox potentials are also observed, as are oscillations in [Br^–] of very low amplitude (ca. 15 mV). The lower and upper limits of reactant concentrations and the temperature between which oscillations occur have been determined. Addition of a sufficient amount of Ag⁺, Hg²⁺, liquid Br₂ and CCl₄ stops the oscillations which can be revived by the addition of potassium bromate solution in all cases except CCl₄. Oscillations in a CSTR (continuously stirred tank reactor) have also been observed. It is suggested that sequential oscillations occur on account of decomposition of ascorbic acid into oxalic acid. The first type of oscillation occurs on account of ascorbic acid–acetone acting as a mixed substrate while type II oscillations occur after a pause due to decomposition of ascorbic acid into oxalic acid so that oxalic acid with acetone or cyclohexanone acts as the second mixed substrate.