Kinetics of Iodous Acid Disproportionation

The iodous acid disproportionation is autocatalytic, and it is not easy to measure the rate constant of the step 2IO₂H → IO₃^? + IOH + H⁺ separately. Hg(II) was used previously to suppress the autocatalytic pathway, but this method presents difficulties discussed in this work. A more effective method is the use of crotonic acid, an effective IOH scavenger. It suppresses side reactions, and a purely second‐order rate law is obtained. The rate constant decreases from 5 to 0.2 M^?1 s^?1 when the sulfuric acid concentration increases from 0.08 to 0.60 M. The observed decrease could be explained if IO₂^? reacts faster than IO₂H. This may have consequences for the mechanism of the oscillating Bray–Liebhafsky reaction.