Thermolysis of disubstituted lithium and sodium orthoperiodates

Na₂H₃IO₆ decomposes with water and oxygen evolution in the range of 180–250°C under the atmospheric pressure or in a dynamic vacuum. The solid residue is an equimolar mixture of NaIO₃ and Na₃IO₅. Na₃IO₅ likely occurs in the form of the dimer Na₆I₂O₁₀. An intermediate thermolysis stage is the elimination of a water molecule from the salt molecule with simultaneous disproportionation of the salt to trisubstituted orthoperiodate and metaperiodate: Na₂H₃IO₆ = 0.5Na₃H₂IO₆ + 0.5NaIO₄ + H₂O. Li₂H₃IO₆ thermolysis under the atmospheric pressure proceeds in the same way; however in vacuum, the thermolysis yields LiIO₃ and Li₅IO₆ in the ratio of 3: 1 (mol/mol). The reason for the different thermolysis routes lies in the different stability of the intermediates M₃H₂IO₆ and MIO₄.