Kinetics of Iodous Acid Disproportionation

ABSTRACT: The iodous acid disproportionation is autocatalytic, and it is not easy to measuretherateconstantofthestep2IO 2 H→IO 3− +IOH+H + separately.Hg(II)wasusedpreviouslyto suppress the autocatalytic pathway, but this method presents difficulties discussed in thiswork. A more effective method is the use of crotonic acid, an effective IOH scavenger. Itsuppresses side reactions, and a purely second-order rate law is obtained. The rate constantdecreases from 5 to 0.2 M −1 s −1 when the sulfuric acid concentration increases from 0.08to 0.60 M. The observed decrease could be explained if IO 2− reacts faster than IO 2 H. ThismayhaveconsequencesforthemechanismoftheoscillatingBray–Liebhafskyreaction. C 2013Wiley Periodicals, Inc. Int J Chem Kinet 45: 525–530, 2013 INTRODUCTION The iodous acid disproportionation in sulfuric acid so-lutions is autocatalytic [1,2]. This was explained by themechanism (R1)–(R4):2IO 2 H → IO 3− +IOH +H + (R1)IOH +IO 2 H → IO 3− +I − +2H + (R2)IO 2 H +I − +H + 2IOH (R3)IOH +I