Method for preparing periodates

Abstract

In various aspects and embodiments the invention provides a method for preparing a metal periodate by anodic oxidation of a metal iodide in an electrolysis cell comprising one or more anodes and one or more cathodes, characterised in that the one or more anodes are carbon-comprising electrodes. In certain embodiments the method is characterised in that the one or more anodes comprise a diamond layer doped with one or more IUPAC group 13, 15 or 16 elements of the periodic table.

1 . A method for preparing a metal periodate by anodic oxidation of a metal iodide in an electrolysis cell comprising one or more anodes and one or more cathodes, characterised in that the one or more anodes are carbon-comprising electrodes. 
     
     
         2 . The method as claimed in  claim 1 , characterised in that the one or more anodes comprise a diamond layer doped with one or more IUPAC group 13, 15 or 16 elements of the periodic table. 
     
     
         3 . The method as claimed in  claim 2 , characterised in that the one or more anodes comprise a boron-doped diamond layer. 
     
     
         4 . The method as claimed in  claim 2 , where the doped diamond layer is connected to a support material, where the support material is selected from the group consisting of elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the eight afore-mentioned elements, graphite, glassy carbon, carbon fibre and combinations of the afore-mentioned materials. 
     
     
         5 . The method as claimed in  claim 1 , where the metal iodide is selected from the group consisting of alkali metal iodides, earth alkaline metal iodides and transition metal iodides. 
     
     
         6 . The method as claimed in  claim 5 , where the metal iodide is selected from the group consisting of alkali metal iodides, earth alkaline metal iodides, Cu(I) iodide and Zn(II) iodide; preferably from lithium iodide, sodium iodide, potassium iodide, caesium iodide, magnesium iodide, calcium iodide, Cu(I) iodide and Zn(II) iodide; in particular from sodium iodide, potassium iodide and Cu(I) iodide; and specifically from sodium iodide and potassium iodide. 
     
     
         7 . The method as claimed in  claim 1 , where the periodate is a para-periodate, meta-periodate, ortho-periodate or a mixture of two or three of these periodates, and is in particular a para-periodate, a meta-periodate or a mixture of a para-periodate and a meta-periodate. 
     
     
         8 . The method as claimed in  claim 1 , for preparing sodium para-periodate, sodium meta-periodate or a mixture of sodium para-periodate and sodium meta-periodate by anodic oxidation of sodium iodide; or for preparing potassium para-periodate, potassium meta-periodate or a mixture of potassium para-periodate and potassium meta-periodate by anodic oxidation of potassium iodide;
 and in particular for preparing sodium para-periodate, sodium meta-periodate or a mixture of sodium para-periodate and sodium meta-periodate by anodic oxidation of sodium iodide.   
     
     
         9 . The method as claimed in  claim 1 , comprising subjecting an aqueous solution comprising the metal iodide to anodic oxidation, where the aqueous solution comprises the metal iodide in a concentration of from 0.001 to 12 mol/l, preferably from 0.01 to 5 mol/l, more preferably from 0.05 to 2 mol/l, in particular from 0.1 to 1 mol/l, specifically from 0.2 to 0.6 mol/l, and very specifically from 0.3 to 0.5 mol/l; where the concentration refers to the amount of iodide. 
     
     
         10 . The method as claimed in  claim 1 , where the anodic oxidation is carried out at a pH of at least 8, preferably of at least 10, in particular of at least 12 and specifically of at least 14. 
     
     
         11 . The method as claimed in  claim 10 , where the anodic oxidation is carried out in the presence of a base, where the base is selected from the group consisting of metal hydroxides, metal oxides and metal carbonates. 
     
     
         12 . The method as claimed in  claim 11 , where the base is a metal hydroxide, where in case that the metal iodide is an alkali metal iodide, the metal of the base corresponds to the metal in the metal iodide. 
     
     
         13 . The method as claimed in  claim 11 , where the method comprises subjecting an aqueous solution comprising the metal iodide and a base to anodic oxidation, where the metal iodide and the base are used in a molar ratio of from 1:2 to 1:30, preferably 1:2 to 1:20, more preferably from 1:5 to 1:15, even more preferably from 1:8 to 1:12 and in particular in a molar ratio of approximately 1:10; where the molar ratio relates to moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base. 
     
     
         14 . The method as claimed in  claim 1 , where the anodic oxidation is carried out at a current density in the range of from 10 to 500 mA/cm 2 , preferably from 50 to 150 mA/cm 2 , in particular from 80 to 120 mA/cm 2  and specifically of ca. 100 mA/cm 2 . 
     
     
         15 . The method as claimed in  claim 1 , where the electrolysis cell in which the anodic oxidation is carried out comprises one or more anodes in one or more anode compartments and one or more cathodes in one or more cathode compartments, where the anode compartments are separated from the cathode compartments. 
     
     
         16 . The method as claimed in  claim 15 , where the one or more cathode compartments comprise an aqueous medium with a pH of at least 8, preferably of at least 10, in particular of at least 12 and specifically of at least 14. 
     
     
         17 . The method as claimed in  claim 15 , comprising
 introducing into the one or more anode compartments an aqueous solution containing the metal iodide and optionally a base;   subjecting said aqueous solution to an electrolysis to obtain anodic oxidation of the iodide; and   isolating the metal periodate formed in the anodic oxidation of the iodide from the one or more anode compartments.   
     
     
         18 . The method as claimed in  claim 17 , where the aqueous solution contains an alkali metal iodide in a concentration of from 0.01 to 5 mol/l, preferably from 0.01 to 5 mol/l, more preferably from 0.05 to 2 mol/l, in particular from 0.1 to 1 mol/l, specifically from 0.2 to 0.6 mol/l, very specifically from 0.3 to 0.5 mol/l; and further contains a base which is an alkali metal hydroxide, where the alkali metal of the base corresponds to the alkali metal in the alkali metal iodide; where the alkali metal iodide and the base are contained in a molar ratio of from 1:2 to 1:30, preferably 1:2 to 1:20, more preferably from 1:5 to 1:15, even more preferably from 1:8 to 1:12 and in particular in a molar ratio of approximately 1:10. 
     
     
         19 . The method as claimed in  claim 17 , where the alkali metal iodide is sodium iodide and the base is sodium hydroxide; or the alkali metal iodide is potassium iodide and the base is potassium hydroxide. 
     
     
         20 . The method as claimed in  claim 1 , where the anodic oxidation is carried out in the absence of promoters and additives. 
     
     
         21 . The method as claimed in  claim 1 , which is carried out as a semi-continuous or continuous process.