Kinetics of the Dushman reaction at low I- concentrations

We have reinvestigated the kinetics of the Dushman reaction, IO3−+5 I−+6 H+→3 I2+3 H2O, under the conditions of the oscillating Bray–Liebhafsky reaction, perchloric acid solutions and low iodide concentrations, using a CSTR (continuous flow stirred tank reactor) and an iodide ion selective electrode. We show that it is possible to get meaningful results with this electrode at iodide concentrations in the range [I−]=5×10−8 to 5×10−6 M. The experimental rate law is r=[IO3−][H+]2 {k′[I−]+k″[I−]2} with k′=(1200±150) M−3 s−1 and k″=(4.2±0.8)×108 M−4 s−1 at 25°C and 0.2 M ionic strength. It is the first time that the two terms, first and second order in [I−], are observed simultaneously.