Photolysis of Periodate and Periodic Acid in Aqueous Solution

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 IVI. At pH <12 an additional primary process is the formation of IV and H2O2. In neutral solution O3 P is formed in a small yield. The energetics of the reaction of O1 D with H2O with formation of H2O2 is discussed. It is suggested that oxygen atoms are formed only from IO4– and not from other IVII species. Mechanisms for the secondary processes involving IVIII and IVI are given. IVIII and its relatively stable complex with IVII both form IV IVII and O2. Depending on pH and concentration, IVI either disproportionates to IV and IVII, reacts with IVII with formation of IV and IVIII or dissociates into O–(OH) and IV.