In this study we explored nonlinear spatial–temporal behavior in the oxidation of sulfite by hydrogen peroxide,in which thiosulfate was added to implement a negative feedback,which consequently led to a transition from propagating fronts to target patterns.Our investigation in the homogeneous system showed that increasing the concentration of hydrogen peroxide or decreasing the concentration of sulfite accelerated both the positive and negative feedbacks and therefore could facilitate the transition from front waves to target patterns.On the other hand,increasing the initial concentration of hydrogen ions or decreasing the concentration of thiosulfate mainly accelerated the autocatalytic production of hydrogen ions.The experimental observations were qualitatively reproduced with a model developed recently by Rabai and Hanazaki.In reaction–diffusion media,spontaneous formation of propagating pH fronts was obtained within a narrow range of sulfite and thiosulfate concentrations.The velocity of these traveling fronts was found to decrease with respect to increasing concentrations of thiosulfate and sulfite or decreasing concentrations of hydrogen ion and hydrogen peroxide.