Photolysis of periodate and periodic acid in aqueous solution

Abstract

The photochemistry of periodate and periodic acid in aqueous solution was studied (i) by quantum yield measurements at low light intensity (ii) by flash photolysis, and (iii) by photolysis of glassy samples at 77 K. The photochemical studies were supplemented with pulse radiolysis studies of aqueous periodate solutions and with kinetic studies using stopped-flow technique. In strongly alkaline solution the photodecomposition of periodate proceeds via formation of O^– and I^VI. At pH < 12 an additional primary process is the formation of I^V and H₂O₂. In neutral solution O³P is formed in a small yield. The energetics of the reaction of O¹D with H₂O with formation of H₂O₂ is discussed. It is suggested that oxygen atoms are formed only from IO⁴_– and not from other I^VII species. Mechanisms for the secondary processes involving I^VIII and I^VI are given. I^VIII and its relatively stable complex with I^VII both form I^V I^VII and O₂. Depending on pH and concentration, I^VI either disproportionates to I^V and I^VII, reacts with I^VII with formation of I^V and I^VIII or dissociates into O^–(OH) and I^V.