Effect of iodide concentration upon the kinetics of disproportionation of hypoiodous acid in borate buffer

The disproportionation of hypoiodous acid into iodide and iodate has been studied over the pH range 8–13 and in the presence of between 0.004 and 0.1 mol I–1 of iodide. The recent model incorporating pre-equilibria between I2 and HOI, I2 and I2OH–, and HOI and IO– and rate-determining steps involving these simple iodine species has been found to account for the observed variation. At low pH the predominant reaction is between I2OH– and HOI molecules, not between two HOI molecules as has been commonly thought. Values of the relevant rate constants that take account of iodide variation are supplied.