JP2023504839A - Method for preparing periodate - Google Patents

Abstract

The present invention relates to a method for preparing metal periodates by anodic oxidation of metal iodides using carbon-based anodes.

Description

The present invention relates to a method for preparing metal periodates by anodic oxidation of metal iodides using a carbon-based anode.

Periodate is a strong oxidizing agent widely used in chemical synthesis. Economic and compliant production methods for their production, especially when periodates are used at some point in the synthesis of products for use in the pharmaceutical, cosmetic or nutritional fields. is always needed.

Periodates or periodic acids can be produced electrochemically by anodic oxidation starting from elemental iodine or iodates in which the oxidation state of iodine is less than +VII.

For example, the anodic oxidation of iodine to periodic acid using a _PbO2 anode is described in US Pat.

The anodic oxidation of iodate or iodate to periodic acid or periodate is described, for example, in Non-Patent Document 1, Non-Patent Document 2, Non-Patent Document 3 or Non-Patent Document 4. Oxidation takes place at the _PbO2 anode.

However, metal-based electrodes such as lead dioxide, ruthenium dioxide, and iridium dioxide can dissolve under anodic conditions and can contribute to metallic impurities in the desired product. In particular, lead-based anodes are well known to dissolve under anodic conditions, with 0.05 g/Ah or 2.5 g/Ah, as reported by of mass loss can occur. However, the presence of such metal impurities is unacceptable for certain applications such as pharmaceuticals, cosmetics and nutritionals. Thus, for example, in order to comply with pharmaceutical guideline regulations, it is necessary to remove these impurities, which is cumbersome and uneconomical.

Another drawback of the above methods is the use of iodine or iodates as starting materials. Iodine easily sublimes at room temperature, producing toxic vapors. Moreover, it is sparingly soluble in water, a common medium for such electrolysis. Iodate, on the other hand, is safe to handle, but has a significantly higher molar cost.

Iodides as starting materials are of interest both from an economic and handling point of view.

The direct electrochemical oxidation of iodide (I ⁻ ) to periodate was investigated by Kim and Nam for lead dioxide as an anode material (6). Here, a 1 molar aqueous solution of potassium iodide was electrolyzed at 60° C. in an undivided cell with an applied current density of 150 mA/cm ² . Potassium dichromate (K ₂ Cr ₂ O ₇ , 0.5 g/L) was added to prevent cathodic reduction.

However, even here the lead dioxide electrode can dissolve under anodic conditions and introduce metallic impurities into the intended product. This is unacceptable for certain applications. Additionally, the presence of chromium is unacceptable for certain applications such as health, personal care, and nutritional supplements.

US Pat. No. 5,300,000 relates to an electrochemical process for producing high purity grade hydrogen iodide by cathodic reduction of solubilized iodine. At the same time, the anode is used to generate useful products selected from periodic acid, oxygen or protons. For this purpose, the anode compartment contains an aqueous solution containing an oxidant. Preferably the aqueous solution is acidic. The anode can be any of those used commercially. Among many others, graphite is mentioned as a suitable anode material. However, anodic processes are not used to provide metal periodates. In fact, the presence of extraneous cations such as sodium and potassium is undesirable as they can contaminate the catholyte by back-migration or passage through the cell diaphragm.

US Pat. No. 5,300,000 uses an electrode with a doped diamond layer as the anode to prepare inorganic peroxy compounds such as perhalic acids, perhalates or permanganates starting from lower oxidation state halogen or magnesium compounds. of the electrolytic manufacturing process. Specifically, only the oxidation of sodium chlorate or chlorine to sodium perchlorate is described. Oxidation of chlorine is carried out at pH 0 using an electrolyte containing NaCl. NaCl is said to be oxidized first to chlorine and then to perchlorate. The current 65% efficiency is unsatisfactory.

2001, 2003, 2004, 2003, 2004, 2003, 2003, 2003, 2003, 2003 and 2003, describe the electrochemical synthesis of lithium periodate from lithium iodate using a boron doped diamond (BDD) anode. The importance of using lithium salts is emphasized in the context of both starting materials and products.

However, as already explained, iodate is a fairly expensive starting material, and even more expensive when used as the lithium salt. Lithium salts are generally quite expensive.

US 2,830,941 US 5,520,793 WO 2004/055243 NL 1013348 C2

Y. Aiya et al. , Journal of the Electrochemical Society 1962, 109, 419 H. H. Willard et al. , Trans. Electrochem. Soc. 1932, 62, 239 A. Hickling et al. , J. Chem. Soc. 1940, 256 C. W. Nam et al. , Journal of the Korean Chemical Society 1971, 16, 324 C. W. Nam et al. , Journal of the Korean Chemical Society 1974, 18, 373 C. W. Nam and H. J. Kim, Journal of the Korean Chemical Society 1974, 18, 373-380 Janssen et al. , Electrochimica Acta 2003, 48, 3959

It was an object of the present invention to provide a method for the electrochemical production of periodate which avoids the drawbacks of prior art processes. More precisely, this method produces periodates free of undesirable metals, especially lead-free, in certain applications such as pharmaceuticals, cosmetics and nutritionals, and is inexpensive and readily available. , it is necessary to start with easy-to-handle starting materials. The method should allow high current efficiency and be suitable for scale-up. Furthermore, it should be possible to avoid the use of toxic anti-reduction agents.

[Summary of Invention]
This objective is achieved by an electrochemical method using metal iodides as starting materials and carbon-based anodes.

Thus, the present invention provides a method of preparing a metal periodate by anodic oxidation of a metal iodide in an electrolytic cell comprising one or more anodes and one or more cathodes, wherein the one or more anodes is a carbon-containing electrode.

[Detailed description of the invention]
The references made below to preferred embodiments of the invention are valid on their own and preferably in connection with each other.

[Embodiment (E.x) of the present invention]
General and Preferred Embodiment E. x are summarized in the non-exhaustive list below. Further preferred embodiments will become apparent from the paragraphs following this listing.

E. 1: A method of preparing a metal periodate by anodic oxidation of a metal iodide in an electrolytic cell comprising one or more anodes and one or more cathodes, wherein the one or more anodes are carbon-containing electrodes. A method characterized by:

E. Embodiment E.2: The one or more anodes comprises a diamond layer doped with one or more elements of Groups 13, 15 or 16 of the IUPAC Periodic Table. 1. The method according to 1.

E. Embodiment E.3: The one or more anodes comprises a boron-doped diamond layer. 2. The method described in 2.

E. 4: The doped diamond layer is connected to a support material, the support material being elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the aforementioned eight elements, graphite, vitreous carbon, carbon. Embodiment E. selected from the group consisting of fibers, and combinations of these materials. 2 or E. 3. The method described in 3.

E. 5: The method of any of the preceding embodiments, wherein the metal iodide is selected from the group consisting of alkali metal iodides, alkaline earth metal iodides and transition metal iodides.

E. Embodiment E.6: The metal iodide is selected from the group consisting of alkali metal iodides, alkaline earth metal iodides, Cu(I) iodides and Zn(II) iodides. 5. The method described in 5.

E. 7: the metal iodide is selected from the group consisting of lithium iodide, sodium iodide, potassium iodide, cesium iodide, magnesium iodide, calcium iodide, Cu(I) iodide and Zn(II) iodide; , embodiment E. 6. The method according to 6.

E. Embodiment E.8: The metal iodide is selected from the group consisting of sodium iodide, potassium iodide and Cu(I) iodide. 7. The method according to 7.

E. Embodiment E.9: The metal iodide is selected from the group consisting of sodium iodide and potassium iodide. 8. The method according to 8.

E. 10: Any of the preceding embodiments, wherein the periodate is paraperiodate, metaperiodate, orthoperiodate, or a mixture of two or three of these periodates. The method described in .

E. Embodiment E.11: The periodate is paraperiodate, metaperiodate, or a mixture of paraperiodate and metaperiodate. 10. The method according to 10.

E. 12: for preparing sodium paraperiodate, sodium metaperiodate, or a mixture of sodium paraperiodate and sodium metaperiodate by anodic oxidation of sodium iodide; or anodic oxidation of potassium iodide. A method according to any of the preceding embodiments for preparing potassium paraperiodate, potassium metaperiodate, or a mixture of potassium paraperiodate and potassium metaperiodate by.

E. 13: For preparing sodium paraperiodate, sodium metaperiodate, or a mixture of sodium paraperiodate and sodium metaperiodate by anodic oxidation of sodium iodide, Embodiment E. 12. The method according to 12.

E. 14: The method of the preceding embodiment, comprising subjecting an aqueous solution containing a metal iodide to anodic oxidation, wherein the aqueous solution contains the metal iodide at a concentration of 0.001 to 12 mol/l (concentration refers to the amount of iodide). Any method described.

E. Embodiment E.15: The aqueous solution contains a metal iodide at a concentration of 0.05 to 2 mol/l (concentration refers to the amount of iodide). 14. The method according to 14.

E. Embodiment E.16: The aqueous solution contains a metal iodide at a concentration of 0.1 to 1 mol/l (concentration refers to the amount of iodide). 15. The method according to 15.

E. Embodiment E.17: The aqueous solution contains a metal iodide at a concentration of 0.2-0.6 mol/l (concentration refers to the amount of iodide). 16. The method according to 16.

E. Embodiment E.18: The aqueous solution contains a metal iodide at a concentration of 0.3-0.5 mol/l (concentration refers to the amount of iodide). 17. The method according to 17.

E. 19: The method of any of the preceding embodiments, wherein the anodization is performed at a pH of at least 8.

E. 20: Embodiment E in which the anodization is performed at a pH of at least 10. 19. The method according to 19.

E. 21: Embodiment E, wherein the anodization is carried out at a pH of at least 12. 20. The method according to 20.

E. 22: Embodiment E, wherein the anodization is carried out at a pH of at least 14. 21. The method according to 21.

E. Embodiment E.23: The anodic oxidation is carried out in the presence of a base, the base being selected from the group consisting of metal hydroxides, metal oxides and metal carbonates. 19-E. 23. The method according to any of 22.

E. 24: When the base is a metal hydroxide and the metal iodide is an alkali metal iodide, the metal of the base matches the metal of the metal iodide, Embodiment E. 23. The method according to 23.

E. 25: An aqueous solution containing a metal iodide and a base is subjected to anodic oxidation, wherein the metal iodide and the base have a molar ratio of 1:2 to 1:30 (the molar ratio is the amount of iodide present in the metal iodide). related to the number of moles and the number of moles of hydroxide present in or obtained from the base), embodiment E. 23 or E. 25. The method according to any of 24.

E. 26: An aqueous solution containing a metal iodide and a base is subjected to anodic oxidation, wherein the metal iodide and the base have a molar ratio of 1:2 to 1:20 (the molar ratio is the amount of iodide present in the metal iodide). related to the number of moles and the number of moles of hydroxide present in or obtained from the base), embodiment E. 25. The method according to 25.

E. 27: A molar ratio of metal iodide to base of 1:5 to 1:15 (the molar ratio being the number of moles of iodide present in the metal iodide and the hydroxylation present in or resulting from the base). related to the number of moles of a substance), embodiment E. 26. The method according to 26.

E. 28: A molar ratio of metal iodide to base of 1:8 to 1:12 (the molar ratio being the number of moles of iodide present in the metal iodide and the hydroxylation present in or resulting from the base). related to the number of moles of a substance), embodiment E. 27. The method according to 27.

E. 29: molar ratio of metal iodide to base of about 1:10 (the molar ratio being the number of moles of iodide present in the metal iodide and the number of moles of hydroxide present in or resulting from the base). number), embodiment E. 28. The method according to 28.

E. 30: The method of any of the preceding embodiments, wherein the anodization is performed at a current density of 10-500 mA/cm ² .

E. 31: Embodiment E in which the anodization is performed at a current density of 50-150 mA/cm ² . 30. The method according to 30.

E. 32: Embodiment E in which the anodization is performed at a current density of 80-120 mA/cm ² . 31. The method according to 31.

E. 33: Embodiment E in which the anodization is performed at a current density of about 100 mA/cm ² . 32. The method according to 32.

E. 34: The electrolytic cell in which the anodization takes place contains one or more anodes in one or more anode compartments and one or more cathodes in one or more cathode compartments (the anode and cathode compartments are separate and in particular the electrolytic cell is a split cell in which the anode and cathode compartments are separated by a conventional dividing means (separator) such as a semipermeable membrane or diaphragm), the method according to any of the preceding embodiments. .

E. 35: Embodiment E. wherein said one or more cathode compartments comprises an aqueous medium having a pH of at least 8. 34. The method according to 34.

E. 36: Embodiment E. wherein said one or more cathode compartments comprises an aqueous medium having a pH of at least 10. 35. The method according to 35.

E. Embodiment E.37: Said one or more cathode compartments comprise an aqueous medium having a pH of at least 12. 36. The method according to 36.

E. 38: Embodiment E. wherein said one or more cathode compartments comprises an aqueous medium having a pH of at least 14. 37. The method according to 37.

E. 39: The method of any of the preceding embodiments, comprising the steps of:
- introducing into said one or more anode compartments an aqueous solution comprising a metal iodide and optionally a base;
- subjecting the aqueous solution to electrolysis to achieve anodic oxidation of iodide; and
- Separating the metal periodate formed from the anodic oxidation of iodide from said one or more anode compartments.

E. 40: The aqueous solution contains an alkali metal iodide at a concentration of 0.01 to 5 mol / l, further contains a base that is an alkali metal hydroxide, the alkali metal of the base matches the alkali metal of the alkali metal iodide, and the alkali Embodiment E. wherein the metal iodide and base are present in a molar ratio of 1:2 to 1:30. 39. The method according to 39.

E. 41: Embodiment E. wherein the aqueous solution contains an alkali metal iodide at a concentration of 0.05 to 2 mol/l. 40. The method according to 40.

E. 42: Embodiment E wherein the aqueous solution contains an alkali metal iodide at a concentration of 0.1 to 1 mol/l. 41. The method according to 41.

E. Embodiment E.43: The aqueous solution contains an alkali metal iodide at a concentration of 0.2-0.6 mol/l. 42. The method according to 42.

E. Embodiment E.44: The aqueous solution contains an alkali metal iodide at a concentration of 0.3-0.5 mol/l. 43. The method according to 43.

E. Embodiment E.45: The alkali metal iodide and the base are included in a molar ratio of 1:2 to 1:20. 39-E. 44. The method according to any of 44.

E. Embodiment E.46: The alkali metal iodide and the base are included in a molar ratio of 1:5 to 1:15. 45. The method according to 45.

E. Embodiment E.47: The alkali metal iodide and the base are included in a molar ratio of 1:8 to 1:12. 46. The method according to 46.

E. Embodiment E.48: comprises about a 1:10 molar ratio of alkali metal iodide and base. 47. The method according to 47.

E. 49: Any of embodiments 39-48, wherein 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 The method described in .

E. 50: The method of any of the preceding embodiments, wherein the anodization is performed in the absence of accelerators and additives.

E. 51: A method according to any of the preceding embodiments, conducted as a semi-continuous process.

E. 52: Embodiment E.5 performed as a continuous process. 1 to E. 50. The method according to any of 50.

E. 53: Embodiment E. performed as a batch process. 1 to E. 50. The method according to any of 50.

Periodate metal salts are metal salts of various periodic acids. In periodic acid, the corresponding anions consist of iodine and oxygen in oxidation state +VII. Periodates include inter alia: orthoperiodates (IO ₆ ⁵⁻ ; i.e. metal orthoperiodates of formula M ₅ IO ₆ ), metaperiodates (IO ₄ ⁻ ; i.e. metal metaperiodates of the formula MIO ₄ ), dimesoperiodates (I ₂ O ₉ ⁴⁻ ; i.e. metal dimesoperiodates of the formula M ₄ I ₂ O ₉ ), mesoperiodates (IO ₅ ³⁻ ; ie, the metal mesoperiodate of formula M ₃ IO ₅ ), and paraperiodate.

Paraperiodate is a salt of the formula M ₃ H ₂ IO ₆ and is also known as the corresponding double salt MIO ₄ *2MOH. M in the above formula is the metal equivalent [(M ⁿ⁺ ) _{1/n where} n is the number of charges]. For example, for alkali metal periodates, ie M is an alkali metal cation, and for alkaline earth metal periodates, ie M is (M ²⁺ ) _1/2 .

In periodates with more than one negative charge, more than one metal equivalent M can have the same or different meanings. As an example, in paraperiodate M ₃ H ₂ IO ₆ or MIO ₄ *2MOH, all three metal equivalents M can have the same meaning or can be derived from different metals (e.g. starting Situations that may occur if the counter cation of the iodide used as material is optionally present during the anodization or differs from the counter cation present in the base used during work-up of the reaction product). For more information, see:

The metal iodides are preferably selected from the group consisting of alkali metal iodides, alkaline earth metal iodides and transition metal iodides.

Alkali metal iodides suitable for use as starting materials in the process of the invention are, for example, lithium iodide, sodium iodide, potassium iodide or cesium iodide.

Alkaline earth metal iodides suitable for use as starting materials in the process of the invention are, for example, magnesium iodide or calcium iodide.

Transition metal iodides suitable for use as starting materials in the process of the present invention are those which are stable under atmospheric conditions (air, water vapor) and at least partially soluble at the desired concentration in the reaction medium. . Usually the reaction medium for anodization is aqueous.

However, low solubility in pure water does not necessarily mean that the reaction (anodic oxidation) can be carried out under acidic or preferably basic conditions, which can dramatically increase the solubility in the reaction medium, for example. It does not disqualify transition metal iodides. For example, CuI is essentially insoluble in water at a pH of about 7, but nevertheless the reaction medium is basic, in particular the reaction medium contains inorganic compounds whose cations, as bases, form water-soluble iodides. It is a preferred starting compound if it contains a basic salt (eg in the case of NaOH or KOH).

Suitable transition metal iodides are those of Sc(III), Y(III), La(III), Co(II), Ni(II), Cu(I) and Zn(II). Among these, Cu(I) iodide(I)(CuI) and Zn(II) iodide(II)(ZnI ₂ ) are preferred from the viewpoint of economy and availability.

Therefore, the process of the present invention preferably uses alkali metal iodides, alkaline earth metal iodides, or transition metal iodides that are stable under atmospheric conditions (air, water vapor) and can be dissolved in the reaction medium at the desired concentration. It is useful for the preparation of metal periodates by anodic oxidation of oxides. The transition metal iodides here are preferably selected from iodides of Sc(III), Y(III), La(III), Co(II), Ni(II), Cu(I) and Zn(II) be.

More preferably, the process of the present invention serves the preparation of metal periodates by anodic oxidation of alkali metal iodides, alkaline earth metal iodides, Cu(I) iodides or Zn(II) iodides.

More preferably, the process of the present invention serves for the preparation of metal periodates by anodic oxidation of alkali metal iodides or alkaline earth metal iodides. As mentioned above, suitable alkali metal iodides are those of lithium, sodium, potassium or cesium. Among these, preference is given to iodides of lithium, sodium or potassium. More preferred is sodium or potassium iodide. Preferred alkaline earth metal iodides are those of magnesium or calcium. Of these, preference is given to calcium iodide.

The process of the invention is particularly useful for the preparation of alkali metal periodates by anodic oxidation of alkali metal iodides. Suitable and preferred alkali metal iodides are described above. Suitable alkali metal periodates are those of lithium, sodium, potassium or cesium. Among these, preference is given to lithium periodate, sodium periodate or potassium periodate. Further preference is given to sodium periodate or periodic acid. Specifically, the method of the present invention is useful for the preparation of sodium periodate by anodic oxidation of sodium iodide or the preparation of potassium periodate by anodic oxidation of potassium iodide. Quite specifically, the method of the present invention is useful for the preparation of sodium periodate by anodic oxidation of sodium iodide.

The periodate prepared according to the invention is preferably paraperiodate, metaperiodate, orthoperiodate, or a mixture of two or three of these periodates. Thus, in a preferred embodiment, the process of the invention comprises the preparation of a metal paraperiodate, a metal metaperiodate, a metal orthoperiodate, or a mixture of two or three of these periodates. (by anodic oxidation of metal iodides, of course). Suitable and preferred metal iodides are described above.

More preferably, the process of the present invention comprises paraperiodate, metaperiodate, by anodic oxidation of an alkali metal iodide, alkaline earth metal iodide, Cu(I) iodide or Zn(II) iodide. It is useful for preparing salts, orthoperiodates, or mixtures of two or three of these periodates. Even more preferably, the process of the present invention comprises paraperiodate, metaperiodate, orthoperiodate, or a periodate thereof by anodic oxidation of an alkali metal iodide or an alkaline earth metal iodide. Useful for preparing two or three mixtures of iodates.

Particularly preferably, the process of the present invention comprises alkali metal paraperiodate, alkali metal metaperiodate, alkali metal orthoperiodate, or periodates thereof, by anodic oxidation of alkali metal iodides. is useful for preparing mixtures of two or three of In particular, the method of the present invention provides for the preparation of sodium paraperiodate, sodium metaperiodate, sodium orthoperiodate, or a mixture of two or three of these periodates by anodic oxidation of sodium iodide. Alternatively, for the preparation of potassium paraperiodate, potassium metaperiodate, potassium orthoperiodate, or mixtures of two or three of these periodates by anodic oxidation of potassium iodide. Specifically, the method of the present invention comprises the addition of sodium paraperiodate, sodium metaperiodate, sodium orthoperiodate, or two or three of these periodates by anodic oxidation of sodium iodide. Useful in preparing mixtures.

The periodate prepared according to the present invention is more preferably paraperiodate, metaperiodate, or a mixture of paraperiodate and metaperiodate. Thus, in a more preferred embodiment, the process of the invention comprises the preparation of a metal paraperiodate, a metal metaperiodate, or a mixture of a metal paraperiodate and a metal metaperiodate (of course, by anodic oxidation of metal iodides). Suitable and preferred metal iodides are described above.

More preferably, the process of the present invention provides metal paraperiodate, metaperiodate, by anodic oxidation of an alkali metal iodide, alkaline earth metal iodide, Cu(I) iodide, or Zn(II) iodide. It is useful for preparing metal iodates or mixtures of metal paraperiodates and metal metaperiodates. More preferably, the process of the present invention comprises metal paraperiodate, metaperiodate, or metal paraperiodate and metaperiodate by anodic oxidation of an alkali metal iodide or an alkaline earth metal iodide. It is useful for preparing mixtures of metal periodates.

Particularly preferably, the method of the present invention comprises alkali metal paraperiodate, alkali metal metaperiodate, or alkali metal paraperiodate and alkali metal metaperiodate by anodic oxidation of an alkali metal iodide. Useful in preparing salt mixtures. In particular, the method of the present invention involves the preparation of sodium paraperiodate, sodium metaperiodate, or a mixture of sodium paraperiodate and sodium metaperiodate, or potassium iodide, by anodic oxidation of sodium iodide. anodic oxidation of potassium paraperiodate, potassium metaperiodate, or a mixture of potassium paraperiodate and potassium metaperiodate. Specifically, the method of the present invention is useful for preparing sodium paraperiodate, sodium metaperiodate, or a mixture of sodium paraperiodate and sodium metaperiodate by anodic oxidation of sodium iodide.

Carbon-containing anodes (or, more generally, electrodes) or carbon-based anodes/electrodes, also listed below, are well known in the art, e.g., graphite electrodes, glassy carbon ) electrodes, reticulated glassy carbon electrodes, carbon fiber electrodes, carbon composite-based electrodes, carbon-silicon composite-based electrodes, graphene-based electrodes, and diamond-based electrodes.

A carbon-containing anode is not necessarily composed entirely of carbonaceous material. Graphite electrodes are often composed of graphite alone or graphite as the main material, but other carbonaceous materials are present as or as part of the outer layer of the electrode (i.e., the portion in direct contact with the electrolyte). Sometimes. Details are as follows.

Of the above anodes, preference is given to diamond-based electrodes. Such electrodes are characterized by very high overpotentials for both oxygen and hydrogen evolution, leading to wide potential windows.

Due to its large bandgap of more than 5 eV, diamond is usually an electrical insulator by nature and is therefore not suitable as an electrode material. However, diamond can be made conductive by doping it with certain elements. Another method of making diamond conductive is to anneal thin films of undoped diamond in vacuum at elevated temperatures of 1550° C. or higher. These dramatic conditions presumably result in the formation of a network of conductive carbon phases within the diamond film.

However, the former method is more practical and reliable. Accordingly, the diamond-based electrode is preferably an electrode comprising conductively doped diamond.

Suitable dopants are selected from the elements of Groups 13, 15 or 16 of the IUPAC Periodic Table.

Accordingly, in preferred embodiments, the one or more anodes used in the method of the present invention comprise diamond doped with one or more elements of Groups 13, 15 or 16 of the IUPAC Periodic Table.

A preferred Group 13 dopant is boron. Preferred group 15 dopants are nitrogen and phosphorus. A preferred Group 16 dopant is sulfur. Boron doping results in a p-type semiconductor, while nitrogen, phosphorus and sulfur doping results in n-type conductivity. It is also possible to use two or more different dopants, for example resulting in boron-nitrogen co-doping or boron-sulfur co-doping. In the case of codoping, two or more dopants have different conductivities, such as in the case of BN- or BS-codoping, the type of conductance obtained in co-doped diamond is inter alia It is possible to rely on the concentration of a single dopant and tune it to the desired type.

Among the above dopants, preference is given to boron doping. Accordingly, in a more preferred embodiment, the one or more anodes used in the method of the present invention comprise boron doped diamond.

Boron-doped diamond preferably comprises 0.02 to 1 wt.% (200 to 10,000 ppm), more preferably 0.04 to 0.2 wt.%, especially 0 Boron in an amount of 0.06-0.09% by weight.

As already mentioned above, such electrodes usually do not consist solely of doped diamond. Rather, the doped diamond adheres to the substrate. Most often, doped diamond is present as a layer on a conductive substrate. However, diamond particle electrodes in which doped diamond particles are embedded in a conductive or non-conductive substrate are suitable as well. Preference is, however, given to anodes in which the doped diamond is present as a layer on a conductive substrate.

Thus, in particular, the one or more anodes used in the method of the invention comprise a boron-doped diamond layer.

Suitable support materials for electrodes containing boron-doped diamond layers are silicon, self-passivating metals, metal carbides, graphite, vitreous carbon, carbon fibers and combinations thereof.

Suitable self-passivating metals are eg germanium, zirconium, niobium, titanium, tantalum, molybdenum and tungsten.

A suitable combination is, for example, a metal carbide layer on the corresponding metal (such an intermediate layer may be formed in situ when applying the diamond layer to the metal support), two of the above support materials One or more composite materials and combinations of carbon with one or more of the other elements listed above. Examples of composites include siliconized carbon fiber carbon composites (CFC) and partially carbonized composites.

Preferably, the support material comprises elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the eight aforementioned metals, graphite, vitreous carbon, carbon fibers, and combinations thereof (especially composites). materials).

Further preference is given to elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten and combinations of one of the seven metals mentioned above with the respective metal carbide.

Doped diamond electrodes and methods for their preparation are known in the art and are described, for example, in Janssen's article in Electrochimica Acta 2003, 48, 3959, supra, NL 1013348 C2, and references cited therein. It is Suitable preparation methods include, for example, chemical vapor deposition (CVD) such as hot filament CVD or microwave plasma CVD to prepare electrodes with doped diamond films; and electrodes with doped diamond particles. High temperature and high pressure (HTHP) methods for preparation are included. Doped diamond electrodes are commercially available.

Preferably the electrochemical oxidation of iodide is carried out in an aqueous medium. Accordingly, the method of the present invention involves subjecting an aqueous solution containing a metal iodide to anodization.

The aqueous solution preferably contains 0.001 to 12 mol/l, more preferably 0.01 to 5 mol/l, still more preferably 0.05 to 2 mol/l, particularly 0.1 to 1 mol/l, specifically 0.05 to 2 mol/l. It contains metal iodides in a concentration of 2 to 0.6 mol/l, quite particularly 0.3 to 0.5 mol/l. Here, concentration refers to the amount of iodide. "Concentration refers to the amount of iodide" means, for example, to obtain an aqueous solution containing 1 mol/l of iodide, iodide (M ⁺ ) (I ⁻ ) is used at 1 mol/l and iodide (M ²⁺ )(I ⁻ ) ₂ at exactly 0.5 mol/l and iodide (M ³⁺ )(I ⁻ ) ₃ at exactly 0.33 mol/l.

When the reaction is run in batch, the concentration of iodide naturally decreases during the conversion to periodate, so the above concentrations naturally refer to the concentration at the start of the reaction. In the case of continuous reactions, the above concentrations refer to concentrations in the aqueous medium continuously introduced to the reaction. For semi-continuous reactions, the above concentrations refer to concentrations in the aqueous medium introduced during the course of the reaction.

Anodization can be carried out in an essentially acidic, neutral or basic medium. However, under neutral or acidic conditions, the intermediately formed iodine does not immediately oxidize further, but may evaporate or precipitate and thus be eluted from further reactions. In acidic media this is exacerbated by the presence of three additional reaction pathways that produce iodine, undoubtedly increasing the problem of iodine leaching:

IO ⁻ +I ⁻ +2H ⁺ →I ₂ +H ₂ O
IO ₃ ⁻ +5I ⁻ +6H ⁺ →3I ₂ +3H ₂ O
IO ₄ ⁻ +7I ⁻ +8H ⁺ →4I ₂ +4H ₂ O

In contrast, in basic media, the iodine stage further disproportionates directly with OH- to subiodate ^and iodide (I ₂ +OH ^- →I ^- +HIO). Basic reaction conditions are therefore preferred. A further advantage of alkaline pH is the low open-circuit voltage and thus the high efficiency of electrolysis.

Preferably, the anodization is carried out at a pH of at least 8, preferably at least 10, especially at least 12, especially at least 14.

Anodization is therefore preferably carried out in the presence of a base. Suitable bases are all those which are water-soluble and form hydroxyl ions in the aqueous phase. Inorganic bases such as metal hydroxides, metal oxides, and metal carbonates are preferred.

To avoid separation problems, for these bases the counter cation preferably matches the metal cation in the iodide used. Since anodic oxidation typically employs an aqueous medium, an exception to this preference is required if the base whose cation matches the metal cation in the iodide is not (sufficiently) water soluble. For example, CuO, Cu(OH) ₂ and _CuCO3 are essentially insoluble in water.

Therefore, the use of CuI as the iodide suggests the use of a water-soluble base that is not Cu-based, such as NaOH or KOH. The same is true when using certain alkaline earth metal iodides, especially _MgI2 or _CaI2 , since the corresponding hydroxides, oxides and carbonates are poorly water soluble. Again, the use of water-soluble bases that are not Mg-based or Ca-based, such as NaOH or KOH, are indicated. By "not sufficiently water soluble" is meant that the base is not soluble at the concentration required to obtain the desired iodide to base ratio (at a particular iodide concentration) or the desired pH.

Preferably the base is a metal hydroxide. More preferably, the base is a metal hydroxide and the metal of the base matches the metal in the metal iodide used (except for the cases mentioned above where the corresponding base is not (sufficiently) water soluble). ). Considering the preferred use of alkali metal iodides, alkaline earth metal iodides, and certain transition metal iodides as starting materials, looking at the solubility of the corresponding hydroxides in the aqueous reaction medium, Preference is given to using alkali metal hydroxides. When alkali metal iodides are used as starting materials, the metal of the base preferably matches the metal in the alkali metal iodides used.

Preferably, the metal iodide and base are 1:2 to 1:30, more preferably 1:2 to 1:20, more preferably 1:5 to 1:15, particularly preferably 1:8 to 1:12. , in particular in a molar ratio of 1:10 to 1:11. The molar ratios here are calculated based on the number of moles of iodide present in the metal iodide and the number of moles of hydroxide present in or obtained from the base. For metal iodides whose metal cations form water-soluble hydroxides (such as alkali metal iodides), the molar ratio is quite specifically about 1:10. On the other hand, in the case of iodides whose metal cations form poorly water-soluble or insoluble hydroxides (such as alkaline earth metal iodides, Cu(I) iodides and Zn(II) iodides), the molar ratio is considerably Specifically, it is about 1:11.

Therefore, the method of the present invention preferably comprises subjecting an aqueous solution containing a metal iodide and a base to anodic oxidation, wherein the metal iodide and the base are 1:2 to 1:30, more preferably 1:2 to It is used in a molar ratio of 1:30, more preferably 1:5 to 1:15, particularly preferably 1:8 to 1:12, specifically 1:10 to 1:11. The molar ratio here relates to the number of moles of iodide present in the metal iodide and the number of moles of hydroxide present in or obtained from the base.

For metal iodides whose metal cations form water-soluble hydroxides (such as alkali metal iodides), the molar ratio is quite specifically about 1:10. On the other hand, in the case of iodides whose metal cations form poorly water-soluble or insoluble hydroxides (such as alkaline earth metal iodides, Cu(I) iodides and Zn(II) iodides), the molar ratio is considerably Specifically, it is about 1:11.

"Molar ratio calculated on the basis of the number of moles of iodide present in the metal iodide and the number of moles of hydroxide present in or obtained from the base" is understood as follows : x moles of iodide M ^a+ (I ⁻ ) _a and y moles of base M ^b+ (OH ⁻ ) _b , the relevant molar ratio is calculated as (x*a):(y*b). be. If x moles of iodide M ^a+ (I ⁻ ) _a and y moles of base (M ⁺ ) ₂ (CO ₃ ²⁻ ) or (M ⁺ ) ₂ (O ²⁻ ) are used, 1 mole of oxide Or 2 moles of hydroxide are produced from carbonate, so the relevant molar ratio is calculated as (x·a):(y·2). Similarly, when using x moles of iodide M ^a+ (I ⁻ ) _a and y moles of base (M ²⁺ )(CO ₃ ²⁻ ) or (M ²⁺ )(O ²⁻ ), the relevant molar ratios is calculated as (x·a):(y·2). When using x moles of iodide M ^a+ (I ⁻ ) _a and y moles of base (M ³⁺ ) ₂ (CO ₃ ²⁻ ) ₃ or (M ³⁺ ) ₂ (O ²⁻ ) ₃ , the relevant moles The ratio is calculated as (x·a):(y·6).

A molar ratio of "about" 1:10 or 1:11 means that it includes uncertainty due to weighing errors and the like, and usually includes a deviation of ±15%.

A specific 1:10 ratio is consistent with the theoretical optimum stoichiometry for the formation of paraperiodate, as can be seen from the reaction at the electrode under basic conditions:

Therefore, 8 equivalents of OH ^- are required for optimal conversion at the anode. An additional 2 equivalents of OH 2 ⁻ are required to obtain the particularly desired target periodate, paraperiodate, prepared by the process of the present invention.

When using iodides whose metal cations form poorly water-soluble or insoluble hydroxides, to compensate for hydroxyl ions precipitated and removed from the reaction by formation of poorly soluble or insoluble salts with said cations, In addition, equivalent hydroxyl groups are required per equivalent of iodide. Thus, for this type of iodide, a specific 1:11 ratio is required as the optimum stoichiometry.

Electrolysis can be galvanostatically controlled (applied current controlled; voltage may be measured but not controlled) or potentiostatically controlled (applied voltage controlled; current may be measured but not controlled). can be done, the former being preferred.

In the case of the preferred constant current control, the observed voltage is usually 0-30V, more often 1-20V, especially 1-10V.

For potentiostatic control, the applied voltage is usually in the same range, ie 1-30V, preferably 1-20V, especially 2-10V.

Anodization is preferably carried out at a current density of 10-500 mA/cm ² , more preferably 50-150 mA/cm ² , especially 80-120 mA/cm ² , especially about 100 mA/cm ² .

preferably at least 660,000 C (about 7 F), more preferably at least 772,000 C (about 8 F) per mole of iodide anion oxidized to maximize the conversion of iodide to periodate; In particular, an amount of charge of at least 868,000 C (about 9 F), specifically at least 964,000 (about 10 F) is applied (for example, preferably 660,000 to 1,000 per mole of I ^- anion oxidized). 928,000 C (about 7 to 20 F), more preferably 772,000 to 1,446,000 C (about 8 to 15 F), especially 868,000 to 1,156,000 C (about 9 to 12 F), specifically 964,000 to 1,060,000 C (approximately 10 to 11 F) charge amount).

Anodization is preferably carried out at a temperature of 5-80°C, more preferably 10-60°C, particularly preferably 20-30°C, specifically 20-25°C.

Reaction pressure is not critical. Therefore, anodization is usually carried out at atmospheric pressure. However, when conducting the reaction at temperatures above the normal boiling point of the aqueous medium, high pressures may be indicated to avoid blowouts.

An electrolytic cell in which anodization is performed includes one or more anodes in one or more anode compartments and one or more cathodes in one or more cathode compartments, the anode compartments being separated from the cathode compartments. is preferred.

Separation of the anode compartment from the cathode compartment can be achieved by using different electrolytic cells for the cathode and anode and connecting the cells with a salt bridge for charge equalization. However, preference is given to using a common electrolytic cell in which the anode compartment is separated from the cathode compartment by a conventional dividing means (separator) such as a semipermeable membrane or diaphragm or frit. Alternatively, the electrolytic cell is a split cell.

The separator separates the anolyte [the liquid medium in the anode compartment] from the catholyte [the liquid medium in the cathode compartment], but allows for charge equalization. A diaphragm is a separator comprising a porous structure of an oxide material such as silicate, for example in the form of porcelain or ceramic. However, semipermeable membranes are generally preferred due to the sensitivity of diaphragm materials to more severe conditions. It is preferred, especially if the reaction is carried out at basic pH. The semipermeable membrane is preferably resistant to such conditions, especially basic pH.

Suitable semipermeable membranes are in particular cation exchange membranes, i.e. membranes composed of a material which allows the passage of cations [and a fluid (usually water)] but not anions. More specifically, the semipermeable membrane is a proton exchange membrane (PEM). Membrane materials that withstand more severe conditions, especially basic pH, are based on fluorinated polymers.

Examples of materials suitable for this type of membrane are the Nafion™ brand from DuPont de Nemours or W.W. L. Gore & Associates, Inc. fluoropolymer copolymers based on sulfonated tetrafluoroethylene, such as the Gore-Select™ brand of the Company. However, when using iodides with divalent or higher counter cations, preference is given to using a separate semipermeable membrane separator that is permeable only to monovalent cations. In this case, priority is given to the diaphragm.

The reaction at the cathode naturally depends on the catholyte present in the cathode compartment. As already mentioned above, the one or more cathode compartments usually contain an aqueous medium as catholyte. In this case, the reaction occurring at the cathode is the reduction of water to hydrogen (under formation of the hydroxyl anion; see formula above). Preferably, one or more of the cathode compartments comprises an aqueous medium with a pH of at least 8, preferably at least 10, especially at least 12, especially at least 14.

Suitably, an inorganic base is used to obtain a basic pH of the aqueous medium in the cathode compartment. Suitable and preferred inorganic bases have already been mentioned above in connection with the medium in the anode compartment. That is, they are preferably selected from metal hydroxides, metal oxides and metal carbonates. Preference is given to hydroxides. Further preference is given to alkali metal hydroxides, in particular sodium hydroxide and potassium hydroxide.

The material of the cathode is not critical and any commonly used material is suitable, such as stainless steel, chromium-nickel steel, platinum, nickel, bronze, tin, zirconium, or carbon. In a specific embodiment, a stainless steel electrode is used as the cathode.

Preferably, the method of the invention comprises:
- introducing into one or more anode compartments an aqueous solution comprising a metal iodide and optionally a base;
- subjecting the aqueous solution to electrolysis to achieve anodic oxidation of iodide; and
- Separating the metal periodate formed from the anodic oxidation of iodide from said one or more anode compartments.

The aqueous solution introduced into one or more anode compartments is preferably from 0.001 to 12 mol/l, more preferably from 0.01 to 5 mol/l, even more preferably from 0.05 to 2 mol/l, especially from 0.1 to It contains metal iodides in a concentration of 1 mol/l, in particular 0.2 to 0.6 mol/l, quite particularly 0.3 to 0.5 mol/l. Concentration here refers to the amount of iodide; see above.

As regards the preferred metal iodides, reference is made to what has been said above. As already mentioned above, when the reaction is carried out batchwise, the concentration of iodide naturally decreases in the course of the conversion to periodate, so the concentration naturally refers to the concentration at the start of the reaction. In the case of continuous or semi-continuous reactions, the above concentrations refer to concentrations in the aqueous medium introduced continuously or partially during the course of the reaction.

The aqueous solution preferably contains a base. As regards preferred bases, reference is made to what has been said above. Preferably the counter cation in the base matches the metal cation in the iodide. An exception from this preference is when the corresponding base is not (sufficiently) water soluble. See description above.

The aqueous solution introduced into the one or more anode compartments preferably contains metal iodide and base in a ratio of 1:2 to 1:30, more preferably 1:2 to 1:20, more preferably 1:5 to 1:5. 15, particularly preferably in a molar ratio of 1:8 to 1:12, in particular 1:10 to 1:11. For metal iodides whose metal cations form water-soluble hydroxides (such as alkali metal iodides), the molar ratio is quite specifically about 1:10. On the other hand, in the case of iodides whose metal cations form poorly water-soluble or insoluble hydroxides (such as alkaline earth metal iodides, Cu(I) iodides and Zn(II) iodides), the molar ratio is considerably Specifically, it is about 1:11. The molar ratio relates to the number of moles of iodide present in the metal iodide and the number of moles of hydroxide present in or derived from the base. See description above.

More preferably, the aqueous solution is preferably 0.01 to 5 mol/l, more preferably 0.05 to 2 mol/l, especially 0.1 to 1 mol/l, especially 0.2 to 0.6 mol/l , quite specifically an alkali metal iodide in a concentration of 0.3 to 0.5, and furthermore a base which is an alkali metal hydroxide. The alkali metal of this base matches the alkali metal in the alkali metal iodide. Here, the alkali metal iodide and the base are preferably 1:2 to 1:30, more preferably 1:2 to 1:20, still more preferably 1:5 to 1:15, particularly preferably 1:8 to It is contained in a molar ratio of 1:12, especially in a molar ratio of about 1:10.

More preferably, the aqueous solution contains 0.01 to 5 mol/l of sodium iodide or potassium iodide, preferably 0.05 to 2 mol/l, especially 0.1 to 1 mol/l, specifically 0.2 to 0.2 mol/l. .6 mol/l, quite particularly 0.3 to 0.5 mol/l, and further a base which is sodium hydroxide or potassium hydroxide. The alkali metal of this base is consistent with the alkali metal in the alkali metal iodide (i.e., sodium hydroxide if the iodide is sodium iodide and potassium hydroxide if the iodide is potassium iodide). ). Here, sodium iodide or potassium iodide and sodium hydroxide or potassium hydroxide are preferably 1:2 to 1:30, more preferably 1:2 to 1:20, still more preferably 1:5 to 1: 15, particularly preferably in a molar ratio of 1:8 to 1:12, in particular in a molar ratio of about 1:10.

Specifically, the aqueous solution contains 0.01 to 5 mol/l of sodium iodide, preferably 0.05 to 2 mol/l, particularly 0.1 to 1 mol/l, specifically 0.2 to 0.6 mol/l. l, quite particularly in a concentration of 0.3 to 0.5 mol/l, and also sodium hydroxide. Here, sodium iodide and sodium hydroxide are preferably 1:2 to 1:30, more preferably 1:2 to 1:20, still more preferably 1:5 to 1:15, particularly preferably 1:8. It is contained in a molar ratio of ˜1:12, especially in a molar ratio of about 1:10.

In another more preferred embodiment, the aqueous solution contains an alkaline earth metal iodide, preferably 0.005 to 2.5 mol/l, more preferably 0.025 to 1 mol/l, especially 0.05 to 0.5 mol/l. 1 concentration and further contains a base which is an alkali metal hydroxide. Here, the alkaline earth metal iodide and the base are preferably 1.4 to 1:60, more preferably 1:4 to 1:40, still more preferably 1:10 to 1:30, particularly preferably 1:1. It is contained in a molar ratio of 16-1:24, especially in a molar ratio of about 1:22.

More preferably, the aqueous solution contains calcium iodide in a concentration of 0.005 to 2.5 mol/l, preferably 0.025 to 1 mol/l, especially 0.05 to 0.5 mol/l, and further Contains the base, which is sodium. Here, calcium iodide and sodium hydroxide are preferably 1:4 to 1:60, more preferably 1:4 to 1:40, still more preferably 1:10 to 1:30, particularly preferably 1:16. It is contained in a molar ratio of ~1:24, especially in a molar ratio of about 1:22.

In yet another more preferred embodiment, the aqueous solution contains Cu(I) iodide, preferably 0.01 to 5 mol/l, more preferably 0.05 to 2 mol/l, especially 0.1 to 1 mol/l, especially Specifically, it is contained at a concentration of 0.2 to 0.6 mol/l, more specifically 0.3 to 0.5 mol/l, and further contains a base which is an alkali metal hydroxide. Here, Cu(I) iodide and the base are preferably 1:2 to 1:30, more preferably 1:2 to 1:20, still more preferably 1:5 to 1:15, particularly preferably 1: It is contained in a molar ratio of 8-1:12, especially in a molar ratio of about 1:11.

In the process of the invention, the anodization is preferably carried out in the absence of accelerators and additives. In the context of the present invention, promoters are understood as anti-reduction agents and pro-oxidants (eg polarizable substances). Additives are understood to refer to any substance different from the starting compounds, products formed in the course of the reaction, acids, bases, electrolytic medium (usually water) and accelerators. Prior art processes often require the presence of accelerators or additives in order to obtain a satisfactory yield of periodate.

For example, the Nam et al. method described in the Journal of the Korean Chemical Society 1974, 18, 373 requires the presence of potassium dichromate as an anti-reduction agent. It is clear that chromium should be avoided in certain applications such as health, personal care, or nutritional supplements. Fluorides such as lithium fluoride and silicon fluoride are also often used and are said to increase the oxygen overpotential at the anode and improve the oxidation efficiency. In particular, in the process of the invention, the anodic oxidation is preferably carried out in the absence of any promoters, in particular in the absence of any chromium salts, and in the absence of any fluorides such as lithium fluoride or silicon fluoride. takes place in the presence

When more than one anode is used, the two or more anodes may be placed in the same anode compartment or in separate compartments. When two or more anodes are present in the same compartment, they may be placed adjacent to each other or on top of each other. If more than one anode compartment is used, they may also be placed adjacent to each other or on top of each other.

The same applies when using one or more cathodes.

Alternatively, when the electrolyzer includes more than one anode and more than one cathode, the electrolyzer includes more than one electrolytic cell (each cell including one anode compartment and one cathode compartment). be able to. The electrolytic cells may be arranged adjacent to each other or may be arranged on top of each other.

Suitable constructions and arrangements of electrolyzers, including one or more anodes and/or cathodes, are known to those skilled in the art.

The method of the invention is suitable for both laboratory scale reactions and industrial scale reactions.

The method of the invention can be carried out as a discontinuous (batch) process, a semi-continuous process or a continuous process, but is preferably carried out as a semi-continuous process or a continuous process.

In a batch (or discontinuous; temporal) mode, the iodide-containing electrolyte is subjected to electrolysis, which is stopped after a period of time and the product is separated from the anode compartment, while in a continuous process mode, the electrolysis The liquid is continuously passed through the cell, so that the iodide-containing electrolyte is continuously added and reacted, and the resulting reaction mixture is continuously withdrawn from the process. A semi-continuous process scheme includes elements of both types. The process is essentially continuous, but the iodide-containing electrolyte is added at some point and the resulting reaction mixture is withdrawn at some point.

If the reaction is carried out in batch, the anode and cathode compartments are usually designed as batch cells. For semi-continuous or continuous reactions, the anode and cathode compartments are usually designed as flow cells.

Various designs and constructions of batch cells and flow cells are known in the art and can be applied to the methods of the present invention.

A suitable design for the electrolyzer depends on whether the reaction is conducted in a batch, continuous or semi-continuous process and can be determined by those skilled in the art. The electrolyser typically comprises heat exchangers, thermometers, mixing means, and gas outlets from the cathode and anode compartments. In the case of a continuous or semi-continuous process, means are provided for continuous feeding and recovery (eg in the form of a recirculation loop with a pump).

After anodization has taken place, the periodate is isolated from the anode compartment. Periodate is then optionally isolated from the aqueous medium recovered from the anode compartment. Isolation methods and work-ups depend inter alia on the desired product and reaction conditions and are known in principle to those skilled in the art.

For example, to obtain a paraperiodate that is not highly water soluble, it can simply be precipitated from the aqueous reaction medium (after concentration if necessary) if the aqueous reaction medium is sufficiently basic. . Concentration, if desired, can be accomplished by conventional means (eg, partial evaporation of the solvent, optionally under reduced pressure, partial lyophilization, partial reverse osmosis, etc.). The precipitated product can be isolated by conventional means (eg filtration or decantation of the supernatant). If desired, the precipitate may then be subjected to further purification steps (e.g., washing with water or water-containing solvent mixtures, water or digestion using a water-containing solvent mixture, or recrystallization, etc.).

Alternatively, water can be removed from the aqueous reaction medium (eg, by evaporation of the solvent optionally under reduced pressure, freeze-drying, reverse osmosis followed by evaporation of residual water, if desired, etc.). Also, if desired, the residue can be purified as described above for the precipitate. If the reaction medium is not sufficiently basic, the paraperiodate is obtained after adding more base to the reaction medium. Subsequent work-up can be performed as described above.

If the reaction medium is sufficiently basic to form paraperiodate, it must be neutralized to obtain metaperiodate. Basically any acid can be used, provided that the corresponding anion is difficult to oxidize. Suitable acids are, for example, sulfuric acid, hydrogen sulphate, phosphoric acid, dihydrogen phosphate, hydrogen phosphate, nitric acid, silicic acid and the like.

When a hydrogen sulfate, dihydrogen phosphate, or hydrogen phosphate is used, preferably its counter cation is the same as the counter cation of the iodide used as starting product, or the base pair Same as cation. Where the base and iodide countercations are different—provided the corresponding hydrogen sulfate, dihydrogen phosphate or hydrogen phosphate is water soluble. The metaperiodate can then be isolated from the aqueous medium by conventional means as described above. However, given the good water solubility of metaperiodate, it is usually necessary to concentrate the aqueous medium before the metaperiodate precipitates.

Depending on the intended use of the periodate, it is not essential to subject the desired periodate to a purification step. In many cases it is sufficient to evaporate the water from the aqueous medium obtained after neutralization, especially when periodate is used as oxidizing agent. In some cases, the water does not even need to be evaporated (ie the aqueous medium obtained from the anode compartment can be used as is in the subsequent oxidation step), or at least not dried.

The exact composition of the periodate obtained by the process of the invention depends on the reaction and workup conditions. For example, if the anodic oxidation is carried out under neutral pH and if no basic or acidic workup is carried out after the reaction to introduce a cation different from the counter cation in the iodide used as starting material, The result is a periodate whose countercation matches that of iodide. If the anodic oxidation is carried out under basic conditions and the base used is an inorganic basic salt whose countercation matches that of iodide, then starting with further basic or acidic workup If no cations different from the countercations of the iodide used as material are introduced, again periodates are obtained whose countercations match those of the iodide.

For example, an alkali metal iodide is reacted in the presence of an alkali metal basic salt having the same alkali metal as the counter cation. When a basic workup follows the reaction, this uses the same base as the base used in the reaction, or at least a base with the same alkali metal cation. When an acidic workup is applied, the acid is either not a metal salt or a salt containing the same alkali metal as the iodide, such as alkali metal hydrogen sulfate, alkali metal hydrogen phosphate, or alkali metal dihydrogen phosphate. .

However, the metal iodides are reacted in the presence of bases containing different cations (e.g. CuI/NaOH combinations) and/or work up with bases or acids that introduce cations different from those of the iodides. In general, different periodates with different countercations can be formed. If desired, they can be separated from each other such as by fractional crystallization. However, for most applications, the periodates can be subjected to further use as obtained, ie without further separation from one another.

The process of the present invention produces periodate of a quality suitable for certain demanding applications such as pharmaceuticals, cosmetics and nutritionals, starting from iodide which is readily available, economical, problem-free and easy to handle. , allowing it to be manufactured in a single step. In addition to high atom economy, this process is particularly attractive due to its high conversion and space-time yields and its lack of need for promoters and additives.

The method is now further illustrated by the following examples.

Example 1: Anodic oxidation of sodium iodide to sodium periodate in a semi-continuous process via 0.5 mm Teflon spacer-tethered cation exchange membranes (Nafion™ from DuPont) The flow cell with anode and cathode compartments separated from each other and with an electrode surface of 12 cm ² was connected per compartment to two Ritmo™ 033 pumps from Fink (Germany). A boron-doped diamond electrode (DIACHEM™ electrode from Condias GmbH; 10 μm BDD on a silicon substrate (3 mm thick); ~800 ppm boron) was used as the anode and stainless steel as the cathode. NaI (1.49 g, 10.0 mmol, 0.4 M) was dissolved in 25 mL aqueous NaOH (4 M) and the solution was circulated through the anode chamber (flow rate = 7.5 L/h).

An aqueous NaOH solution (4M) was circulated through the cathode chamber. A current density j of 100 mA cm ⁻² and a charge Q=10 F=9649° C. were applied. The reaction was allowed to proceed for about 2.2 hours at room temperature. After electrolysis, the suspension formed in the anode chamber was removed therefrom and the flow system was flushed with aqueous _NaHSO4 solution and water.

For analytical purposes, a sample of the suspension was mixed with an aqueous NaHSO ₄ solution until the precipitate was completely dissolved and the resulting solution was subjected to liquid chromatography equipped with a photodiode array (LC-PDA; LC stationary phase: C18 reverse phase). Sodium paraperiodate gave a yield of 94%. The suspension was mixed with aqueous NaOH to complete the precipitation, the precipitate was filtered, washed with cold water and dried to give the desired sodium paraperiodate with 97% purity (isolated 90% yield of paraperiodate).

A portion of the precipitated sodium paraperiodate is converted to metaperiodate by acidifying with nitric acid, concentrating the resulting solution, and recrystallizing the precipitate in water (130° C.→room temperature), Sodium metaperiodate was obtained with a yield of 65%.

Example 2: Anodic oxidation of sodium iodide to sodium periodate in a semi-continuous process The process was carried out as in Example 1, but using 0.3 mol NaI and 5 mol NaOH, Q = 9F. bottom. Yield was 93% by LC-PDA.

Example 3: Anodic oxidation of sodium iodide to sodium periodate in a semi-continuous process The process was carried out as in Example 1, but using 0.1 mol NaI and 3 mol NaOH. The flow rate was 4 L/h, j was 90 mA cm ⁻² and Q=12F. Yield was 90% by LC-PDA.

Example 4: Anodic Oxidation of Potassium Iodide to Potassium Periodate in a Semi-Continuous Process The process was similar to Example 1, except potassium iodide was substituted for sodium iodide and hydroxide was substituted for sodium hydroxide. Performed with potassium. Yield was 89% by LC-PDA.

Example 5: Anodic oxidation of Cu(I) iodide to Cu(I) periodate in a semi-continuous process was carried out using Sodium hydroxide was used as base. Yield was 76% by LC-PDA.

Example 6: Anodic Oxidation of Sodium Iodide to Sodium Periodate in a Batch Process A split beaker cell with a Nafion™ membrane, a BDD anode and a stainless cathode (both 3×1 cm ² ) was used. Both chambers were filled with aqueous NaOH (3.0 M, 6 mL). NaI (640 μmol, 0.33 M) was added to the anode chamber and electrolysis was initiated using a charge Q=9 F=1719 C (t=1.59 h) and a current density j=100 mA/cm ² . After electrolysis was completed, the contents of the anode chamber were acidified with aqueous NaHSO ₄ solution and the solution was analyzed by LC-PDA. A yield of 90% was shown.

Comparative Example: Anodic Oxidation of Sodium Iodide in a Batch Process with Pb or _PbO2 Anode The process was carried out as in Example 6, but with a Pb or _PbO2 anode. A PbO ₂ anode was prepared from a Pb anode by subjecting the Pb anode to electrolytic oxidation at 100 mA/cm ² at 3000° C. in 30% H ₂ SO ₄ . Anodization of sodium iodide with a Pb or PbO ₂ anode, otherwise under the same conditions as in Example 6, formed 53% or <54% sodium periodate, respectively.

Claims (21)

1. A method of preparing a metal periodate by anodic oxidation of a metal iodide in an electrolytic cell comprising one or more anodes and one or more cathodes, comprising:
A method, wherein said one or more anodes are carbon-containing electrodes. 2. The method of claim 1, wherein the one or more anodes comprises a diamond layer doped with one or more elements of Groups 13, 15 or 16 of the IUPAC Periodic Table. 3. The method of claim 2, wherein said one or more anodes comprises a boron-doped diamond layer. A doped diamond layer is connected to a support material, the support material comprising elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the aforementioned eight elements, graphite, vitreous carbon, carbon fiber, and combinations of these materials. A process according to any one of claims 1 to 4, wherein the metal iodides are selected from the group consisting of alkali metal iodides, alkaline earth metal iodides and transition metal iodides. the metal iodide is selected from the group consisting of alkali metal iodides, alkaline earth metal iodides, Cu(I) iodide and Zn(II) iodide; preferably lithium iodide, sodium iodide, iodide selected from potassium, cesium iodide, magnesium iodide, calcium iodide, Cu(I) iodide and Zn(II) iodide; especially selected from sodium iodide, potassium iodide and Cu(I) iodide in particular selected from sodium iodide and potassium iodide. the periodate is paraperiodate, metaperiodate, orthoperiodate, or a mixture of two or three of these periodates; preferably paraperiodate, A process according to any one of the preceding claims, which is metaperiodate or a mixture of paraperiodate and metaperiodate. for preparing sodium paraperiodate, sodium metaperiodate, or a mixture of sodium paraperiodate and sodium metaperiodate by anodic oxidation of sodium iodide; or by anodic oxidation of potassium iodide, for preparing potassium paraperiodate, potassium metaperiodate, or a mixture of potassium paraperiodate and potassium metaperiodate; Process according to any one of claims 1 to 7 for preparing sodium iodate or a mixture of sodium paraperiodate and sodium metaperiodate. subjecting an aqueous solution containing a metal iodide to anodic oxidation, wherein the aqueous solution contains 0.001 to 12 mol/l, preferably 0.01 to 5 mol/l, more preferably 0.05 to 2 mol/l of the metal iodide. , in particular from 0.1 to 1 mol/l, in particular from 0.2 to 0.6 mol/l, and quite particularly from 0.3 to 0.5 mol/l (concentration refers to the amount of iodide ). 10. Process according to any one of the preceding claims, wherein the anodic oxidation is carried out at a pH of at least 8, preferably a pH of at least 10, especially a pH of at least 12, especially a pH of at least 14. Anodization is carried out in the presence of a base,
11. The method of Claim 10, wherein the base is selected from the group consisting of metal hydroxides, metal oxides, and metal carbonates. 12. The method of claim 11, wherein when the base is a metal hydroxide and the metal iodide is an alkali metal iodide, the metal of the base matches the metal of the metal iodide. subjecting an aqueous solution comprising a metal iodide and a base to anodization;
metal iodide and base in a molar ratio of 1:2 to 1:30, preferably a molar ratio of 1:2 to 1:20, more preferably a molar ratio of 1:5 to 1:15, more preferably 1:8 A molar ratio of ~1:12, especially a molar ratio of about 1:10 (the molar ratio being the number of moles of iodide present in the metal iodide and the number of moles of hydroxide present in or obtained from the base). 13. A method according to claim 11 or 12, used in relation to the number of moles. 14. Any of claims 1-13, wherein the anodization is carried out at a current density of 10-500 mA/cm ² , preferably 50-150 mA/cm ² , especially 80-120 mA/cm ² , especially about 100 mA/cm ² . or the method described in paragraph 1. an electrolytic cell in which anodization is performed comprises one or more anodes in one or more anode compartments and one or more cathodes in one or more cathode compartments;
A method according to any one of claims 1 to 14, wherein the anode and cathode compartments are separate. 16. A method according to claim 15, wherein said one or more cathode compartments comprise an aqueous medium having a pH of at least 8, preferably a pH of at least 10, especially a pH of at least 12, especially a pH of at least 14. 17. A method according to claim 15 or 16, comprising the steps of:
- introducing into said one or more anode compartments an aqueous solution comprising a metal iodide and optionally a base;
- subjecting the aqueous solution to electrolysis to achieve anodic oxidation of iodide; and
- Separating the metal periodate formed from the anodic oxidation of iodide from said one or more anode compartments. The aqueous solution has a concentration of 0.01 to 5 mol/l, preferably a concentration of 0.01 to 5 mol/l, more preferably a concentration of 0.05 to 2 mol/l, particularly a concentration of 0.1 to 1 mol/l, specifically contains an alkali metal iodide in a concentration of 0.2 to 0.6 mol/l, quite particularly in a concentration of 0.3 to 0.5 mol/l, and furthermore a base which is an alkali metal hydroxide,
the alkali metal of the base matches the alkali metal of the alkali metal iodide,
Alkali metal iodide and base in a molar ratio of 1:2 to 1:30, preferably a molar ratio of 1:2 to 1:20, more preferably a molar ratio of 1:5 to 1:15, more preferably 1: 18. Process according to claim 17, comprising a molar ratio of 8 to 1:12, in particular a molar ratio of about 1:10. 19. The method of claim 17 or 18, wherein 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. A method according to any one of the preceding claims, wherein the anodization is carried out in the absence of accelerators and additives. A method according to any one of the preceding claims, carried out as a semi-continuous process or as a continuous process.