Laser flash photolysis and pulse radiolysis of iodate and periodate in aqueous solution. Properties of iodine(VI)

Abstract

Species containing iodine in oxidation state six are formed by photolysis and radiolysis of aqueous iodate and periodate solutions in the following reactions: IO₃^–+ O^–→ IO₄^2–; IO₃^–+ OH → IO₃; I^VII+ e_aq^–→ I_e^VI and I^VII [graphic omitted] I₀^VI+ O^–(or OH). The present pulse radiolysis and laser flash photolysis study of I_e^VI and I₀^VI suggests that the predominant I_e^VI and I₀^VI species formed are IO₄^2– and IO₃ at 3 < pH < 7, H₅IO₆^– and H₂IO₅^2– at 8 < pH < 11 and H₄IO₆^2– and HIO₅^3– at pH > 12. Redox reactions of the iodine(VI) species are fast compared with interconversion among the various iodine(VI) species. The assumed four-, five- and six-coordinated iodine(VI) species have similar spectra and decay kinetics and negative values of the standard Gibbs energy of formation. The spectrum and decay kinetics of the assumed IO₃ are markedly different. Furthermore, the standard Gibbs energy of formation of IO₃ is estimated to have a large positive value. Observations of reactivity of iodine(VI) towards tert-butanol and periodate suggest that reduction of iodine(VI) to iodate generally takes place by transfer of OH.