Chemical oscillatory reactions are an example of nonlinear dynamical systems in chemistry. The course of such, redox processes usually require either the presence of a metal catalyst that changes its oxidation state during oscillations, or a catalytic role is played by the intermediates formed from the reactants. Since the discovery of the first oscillatory chemical reaction that took place in a homogeneous phase, many other oscillatory processes have been discovered. One of the most extensively studied and best understood oscillating processes is the Belousov–Zhabotinsky (BZ) reaction, which in its original version involves the oxidation of organic compounds with bromate ions and catalyzed with redox metal catalyst. It is well-known that oscillations in the BZ process are mainly due to complex, multistep reduction processes of bromate ions, which allow positive and negative feedback loops to develop in kinetic mechanisms in a manner that destabilizes the steady-state. In line with this finding, removal of the metal catalyst under appropriate conditions allowed the oscillations to persist, and in this way, a wide class of uncatalyzed bromate oscillators (UBOs) was discovered. In such systems, various organic substrates can be used, e.g., phenols and anilines, as well as non-aromatic compounds, which upon oxidation form stable semiquinone radical intermediates that are capable of substituting the role of a redox catalyst. Several kinetic mechanisms have been proposed to explain the oscillatory instability in such systems. However, detailed mechanisms of UBOs, as well as the source of oscillations, have not yet been recognized.

Graphical abstract