The water–iodine oxide system: a revised mechanism for hydration and dehydration

Abstract

Iodic acids are widely studied in atmospheric and biological applications but their inherent hydrophilic properties introduce complexities that affect their functionality and reactivity. We have shown that iodic acid (HIO₃) dehydrates directly into iodine pentoxide (I₂O₅) in contradiction to the generally accepted multi-step dehydration mechanism where HIO₃ dehydrates into HI₃O₈ first, then dehydrates into I₂O₅. The generally accepted mechanism is used to determine the concentration of iodic acid by TGA and is only valid for special conditions. The revised mechanism allows for the determination of concentrations of iodic acids under all conditions, and the more specific conditions where the accepted mechanism is valid are shown. The determination of concentration of iodic acid with the revised dehydration mechanism is dependent on assumptions of residual water and initial concentration of HI₃O₈. The validity of these assumptions is established by studying the absorption and hydration behavior of I₂O₅ from atmospheric water. These results will have an impact on the handling and use of iodine.