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

Authors:
  • UKUlrik K. Kläning
    Ulrik K. Kläning
  • KSKnud Sehested
    Knud Sehested
  • TWThomas Wolff
    Thomas Wolff
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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; IVII+ eaq –→ Ie VI and IVII [graphic omitted] I0 VI+ O–(or OH). The present pulse radiolysis and laser flash photolysis study of Ie VI and I0 VI suggests that the predominant Ie 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.