Reinvestigation of periodate chemistry challenges conventional view

Periodate—an ion composed of iodine, oxygen, and hydrogen—was studied in water-based solutions extensively from the 1950s to the 1980s. Ever since those studies, chemists have accepted that periodate exists in solution as orthoperiodate (H₅IO₆) and metaperiodate (IO₄^–) species in equilibrium with each other, along with a dimer (H₂I₂O₁₀^4–). Periodate is a strong oxidizing agent that today finds use in many synthetic strategies, including C–H functionalization and iodination.

Recently, a team led by Attila K. Horváth of the University of Pécs decided to study periodate equilibria again after finding that periodate reactions run in their lab didn’t align with the literature. Horváth and colleagues’ conclusion: Orthoperiodate actually exists in aqueous solution with its three successively deprotonated siblings—H₄IO₆^–, H₃IO₆^2–, and H₂IO₆^3– (Inorg. Chem. 2017, DOI: 10.1021/acs.inorgchem.7b01911). They did not find any evidence for metaperiodate or the dimer.

The team studied periodate equilibria through gravimetric analysis, potentiometry, ultraviolet absorption spectroscopy, and Raman spectroscopy—recreating literature experiments and adding new ones, investigating the effects of different electrolytes, controlling for pH, and staying within periodate’s solubility range. In the end, the researchers’ results align with those reported by Carl E. Crouthamel and coworkers in the 1950s (J. Am. Chem. Soc. 1951, DOI: 10.1021/ja01145a030).

Clarifying periodate’s composition in aqueous solution may contribute to a better understanding of the role its various species play in chemical processes, Horváth and colleagues say.