KR20220110770A - Method for preparing periodate - Google Patents

Abstract

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

Description

Method for preparing periodate

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

Periodate is a powerful oxidizing agent widely used in chemical synthesis. There is a constant need for economical methods for producing them and for production methods that comply with specific regulations, especially when periodates are used at a certain point in the synthesis of products for use in the pharmaceutical, cosmetic or nutritional fields.

Periodates or periodic acids can be produced electrochemically by anodic oxidation starting from elemental iodine or iodine salts in which the iodine has an oxidation state below +VII.

For example, the anodization of iodine to periodic acid using a PbO ₂ anode is described in US 2,830,941 or Y. It is described in Journal of the Electrochemical Society 1962, 109, 419 by Y. Aiya et al.

Anodizing of iodic acid or iodate to periodate or periodate is for example Y. by Y. Aiya et al. (Journal of the Electrochemical Society 1962, 109, 419), H.H. Trans. by HH Willard et al. Electrochem. Soc. 1932, 62, 239], a. Hickling et al. by A. Hickling et al. [J. Chem. Soc. 1940, 256] or by CW Nam et al. [Journal of the Korean Chemical Society 1971, 16, 324]. Oxidation is carried out at the PbO ₂ anode.

However, metal-based electrodes such as lead dioxide, ruthenium dioxide, iridium dioxide, etc. can dissolve in anodic conditions and can be a source of metallic impurities in the desired product. In particular, the lead-based positive electrode is disclosed in C.W. Nam et al. [Journal of the Korean Chemical Society 1974, 18, 373] or Y. As reported by Y. Aiya et al. (Journal of the Electrochemical Society 1962, 109, 419), dissolved in anodic conditions, 0.05 g/Ah or even 2.5 g/Ah It is well known that mass loss can occur. However, the presence of these metallic impurities is unacceptable for certain applications such as medicine, cosmetics or nutrients. For example, to comply with pharmaceutical directive regulations, these impurities must be removed, which is cumbersome and uneconomical.

Another disadvantage of the above-mentioned method is that iodine or iodate is used as the starting material. Iodine readily sublimes at room temperature to produce harmful vapors. Also, it is poorly soluble in water (a common medium for such electrolysis). In comparison, iodate is safe to handle, but has a fairly high molar cost.

Iodide as a starting material is of interest both from an economic point of view as well as from a handling point of view.

Direct electrochemical oxidation of iodide (I ⁻ ) to periodate was investigated for lead dioxide as a cathode material by Kim and Nam (CW Nam and HJ Kim, Journal of the Korean Chemical Society). 1974, 18, 373-380). Here, an aqueous solution of 1 mole of potassium iodide was electrolyzed at 60° C. in an unseparated cell by applying a 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 in anodic conditions and create metallic impurities in the desired product, which is unacceptable for certain applications. In addition, the presence of chromium is unacceptable in certain applications such as health, personal care products and nutrients.

US 5,520,793 relates to an electrochemical process for the production of high purity grades of hydrogen iodide by cathodic reduction of solubilized iodine. Incidentally, the anode is used to produce a valuable product selected from periodic acid, oxygen or protons. To this end, the anode compartment contains an aqueous solution comprising an oxidizing agent. The aqueous solution is preferably acidic. The positive electrode may be any commercially available one. Among many others, graphite is mentioned as a suitable cathode material. However, the process at the anode is not used to provide the metal periodate. Indeed, the presence of any external cations such as sodium and potassium is undesirable because of the potential for back migration or contamination of the catholyte through the cell separator.

WO 2004/055243 discloses the electrolytic production of inorganic peroxide compounds such as perhalogen acids, perhalates or permanganates starting from halogens or magnesium compounds in a lower oxidation state using an electrode with a doped diamond layer as an anode it's about how What has been specifically described is the oxidation of sodium chlorate or chlorine to sodium perchlorate. Oxidation of chlorine is carried out at pH 0 using an electrolyte comprising NaCl. It was stated that NaCl is oxidized first to chlorine and then to perchlorate. A current efficiency of 65% is not satisfactory.

Janssen et al. [Electrochimica Acta 2003, 48, 3959] and [NL1013348C2] described the electrochemical synthesis of lithium periodate from lithium iodate using a boron-doped diamond (BDD) anode. explained about it. The importance of using lithium salts with respect to starting materials and products was emphasized.

However, as already explained, iodate is a rather expensive starting material, much more expensive when used as a lithium salt. In general, lithium salts are more expensive.

It is an object of the present invention to provide an electrochemical process for the preparation of periodates which avoids the disadvantages of the prior art processes. More precisely, the process of the present invention should produce periodate free of undesirable metals and in particular lead free for certain applications such as medicine, cosmetics or nutrients, starting at a low cost, readily available and easy to handle. It must be initiated from the material. This method should allow for high current efficiency and should be suitable for scale-up. In addition, the use of toxic anti-reducing agents should be avoided.

Summary of the invention

The above object is achieved by an electrochemical method using a metal iodide as a starting material and using a carbon-based anode.

Accordingly, the present invention relates to a method for the preparation of metal periodate by anodizing of metal iodide in an electrolysis cell comprising at least one anode and at least one cathode, said one The above anode is characterized in that it is an electrode containing carbon.

DETAILED DESCRIPTION OF THE INVENTION

The content set forth below in connection with the preferred embodiments of the present invention is effective not only in itself, but preferably in combination with each other.

Embodiments of the invention (E.x)

General and preferred embodiments E.x are summarized in the following non-exhaustive list. Further preferred embodiments become apparent from the paragraphs following this list.

E.1. A method for preparing a metal periodate by anodization of a metal iodide in an electrolysis cell comprising at least one anode and at least one cathode, wherein the at least one anode is an electrode comprising carbon.

E.2. The method as defined in embodiment E.1, characterized in that at least one anode comprises a diamond layer doped with at least one IUPAC group 13, 15 or 16 element of the periodic table.

E.3. The method as defined in embodiment E.2, characterized in that at least one anode comprises a boron doped diamond layer.

E.4. The method as defined in any one of embodiments E.2 or E.3, wherein the doped diamond layer is connected to a support material, said support material comprising the elements silicon, germanium, zirconium, niobium, a method selected from the group consisting of titanium, tantalum, molybdenum, tungsten, carbides of the aforementioned eight elements, graphite, glassy carbon, carbon fibers and combinations of the aforementioned materials.

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

E.6. The method as defined in embodiment E.5, wherein the metal iodide is selected from the group consisting of alkali metal iodide, alkaline earth metal iodide, Cu(I) iodide and Zn(II) iodide.

E.7. The method as defined in embodiment E.6, wherein 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. How to become.

E.8. The method as defined in embodiment E.7, wherein the metal iodide is selected from the group consisting of sodium iodide, potassium iodide and Cu(I) iodide.

E.9. The method as defined in embodiment E.8, wherein the metal iodide is selected from the group consisting of sodium iodide and potassium iodide.

E.10. The method as defined in any one of the preceding embodiments, wherein the periodate salt is para-periodate, meta-periodate, ortho-periodate or a mixture of two or three of these periodates. .

E.11. The method as defined in embodiment E.10, wherein the periodate salt is para-periodate, meta-periodate or a mixture of para-periodate and meta-periodate.

E.12. The process as defined in any one of the preceding embodiments, wherein sodium para-periodate, sodium meta-periodate or a mixture of sodium para-periodate and sodium meta-periodate is prepared by anodizing of sodium iodide. manufacture; or a method 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.

E.13. The process as defined in embodiment E.12, wherein sodium para-periodate, sodium meta-periodate or a mixture of sodium meta-periodate with sodium para-periodate is prepared by anodizing of sodium iodide how to do it.

E.14. A method as defined in any one of the preceding embodiments, comprising the step of anodizing an aqueous solution comprising metal iodide, wherein the aqueous solution comprises metal iodide in a concentration of 0.001 to 12 mol/l, wherein the concentration How to refer to the amount of iodide.

E.15. The method as defined in embodiment E.14, wherein the aqueous solution comprises metal iodide in a concentration of from 0.05 to 2 mol/l, wherein the concentration refers to the amount of iodide.

E.16. The method of embodiment E.15, wherein the aqueous solution comprises metal iodide in a concentration of 0.1 to 1 mol/l, wherein the concentration refers to the amount of iodide.

E.17. The method of embodiment E.16, wherein the aqueous solution comprises metal iodide in a concentration of 0.2 to 0.6 mol/l, wherein the concentration refers to the amount of iodide.

E.18. The method of embodiment E.17, wherein the aqueous solution comprises metal iodide in a concentration of 0.3 to 0.5 mol/l, wherein the concentration refers to the amount of iodide.

E.19. The method as defined in any one of the preceding embodiments, wherein the anodizing is carried out at a pH of at least 8.

E.20. The method as defined in embodiment E.19, wherein the anodizing is carried out at a pH of at least 10.

E.21. The method as defined in embodiment E.20, wherein the anodizing is carried out at a pH of at least 12.

E.22. The method as defined in embodiment E.21, wherein the anodizing is carried out at a pH of at least 14.

E.23. The method as defined in any one of embodiments E.19 to E.22, wherein the anodizing is carried out in the presence of a base, wherein the base is selected from the group consisting of metal hydroxides, metal oxides and metal carbonates.

E.24. The method as defined in embodiment E.23, wherein the base is a metal hydroxide and, when the metal iodide is an alkali metal iodide, the metal of the base corresponds to the metal in the metal iodide.

E.25. The method as defined in any one of embodiments E.23 or E.24, comprising the step of anodizing an aqueous solution comprising a metal iodide and a base, wherein the metal iodide and the base are from 1:2 to 1: a molar ratio of 30, wherein the molar ratio is to moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base.

E.26. The method as defined in embodiment E.25, comprising the step of anodizing an aqueous solution comprising a metal iodide and a base, wherein the metal iodide and the base are used in a molar ratio of 1:2 to 1:20, wherein wherein the molar ratio is to moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base.

E.27. The method as defined in embodiment E.26, wherein the metal iodide and the base are used in a molar ratio of 1:5 to 1:15, wherein the molar ratio is in the moles of the iodide present in the metal iodide and in the base or in the base. for the moles of hydroxide obtainable from

E.28. The method as defined in embodiment E.27, wherein the metal iodide and the base are used in a molar ratio of 1:8 to 1:12, wherein the molar ratio is in the moles of the iodide present in the metal iodide and in the base or in for the moles of hydroxide obtainable from

E.29. The method as defined in embodiment E.28, wherein the metal iodide and the base are used in a molar ratio of approximately 1:10, wherein the molar ratio is the moles of iodide present in the metal iodide and the moles of iodide present in or obtainable from the base. per moles of hydroxide.

E.30. The method as defined in any one of the preceding embodiments, wherein the anodizing is performed at a current density in the range of 10 to 500 mA/cm 2 .

E.31. The method as defined in embodiment E.30, wherein the anodizing is performed at a current density in the range of 50 to 150 mA/cm 2 .

E.32. The method as defined in embodiment E.31, wherein the anodizing is performed at a current density in the range of 80 to 120 mA/cm 2 .

E.33. The method as defined in embodiment E.32, wherein the anodizing is performed at a current density of about 100 mA/cm 2 .

E.34. The method as defined in any one of the preceding embodiments, wherein the electrolysis cell in which the anodic oxidation is carried out comprises at least one anode in at least one anode compartment and at least one cathode in at least one cathode compartment, wherein the anode compartment comprises a cathode compartment and separate, and in particular the electrolysis cell is a separation cell in which the anode compartment(s) are separated from the cathode compartment(s) by a common separation means (separator) such as a semipermeable membrane or a diaphragm.

E.35. The method as defined in embodiment E.34, wherein the at least one negative electrode compartment comprises an aqueous medium having a pH of at least 8.

E.36. The method as defined in embodiment E.35, wherein the at least one negative electrode compartment comprises an aqueous medium having a pH of at least 10.

E.37. The method as defined in embodiment E.36, wherein the at least one negative electrode compartment comprises an aqueous medium having a pH of at least 12.

E.38. The method as defined in embodiment E.37, wherein the at least one negative electrode compartment comprises an aqueous medium having a pH of at least 14.

E.39. A method as defined in any one of the preceding embodiments,

introducing an aqueous solution containing metal iodide and optionally a base into the at least one anode compartment;

· anodizing the iodide by electrolyzing the aqueous solution; and

separating the metal periodate formed in the anodization of the iodide from the at least one anode compartment;

Way.

E.40. The method as defined in embodiment E.39, wherein the aqueous solution contains alkali metal iodide in a concentration of 0.01 to 5 mol/l; It further contains a base which is an alkali metal hydroxide, wherein the alkali metal of the base corresponds to the alkali metal in the alkali metal iodide; wherein the alkali metal iodide and the base are contained in a molar ratio of 1:2 to 1:30.

E.41. The process as defined in embodiment E.40, wherein the aqueous solution contains alkali metal iodide in a concentration of 0.05 to 2 mol/l.

E.42. The process as defined in embodiment E.41, wherein the aqueous solution contains alkali metal iodide in a concentration of 0.1 to 1 mol/l.

E.43. The process as defined in embodiment E.42, wherein the aqueous solution contains alkali metal iodide in a concentration of 0.2 to 0.6 mol/l.

E.44. The process as defined in embodiment E.43, wherein the aqueous solution contains alkali metal iodide in a concentration of 0.3 to 0.5 mol/l.

E.45. The process as defined in any one of embodiments E.39 to E.44, wherein the alkali metal iodide and the base are contained in a molar ratio of 1:2 to 1:20.

E.46. The process as defined in embodiment E.45, wherein the alkali metal iodide and the base are contained in a molar ratio of 1:5 to 1:15.

E.47. The method as defined in embodiment E.46, wherein the alkali metal iodide and the base are contained in a molar ratio of 1:8 to 1:12.

E.48. The method as defined in embodiment E.47, wherein the alkali metal iodide and the base are contained in a molar ratio of approximately 1:10.

E.49. The method as defined in any one of embodiments 39 to 48, wherein the alkali metal iodide is sodium iodide and the base is sodium hydroxide; or wherein the alkali metal iodide is potassium iodide and the base is potassium hydroxide.

E.50. The method as defined in any one of the preceding embodiments, wherein the anodizing is carried out in the absence of an accelerator and an additive.

E.51. The process as defined in any one of the preceding embodiments, which is carried out in a semi-continuous process.

E.52. The method as defined in any one of embodiments E.1 to E.50, which is carried out as a continuous process.

E.53. The method as defined in any one of embodiments E.1 to E.50, which is carried out as a batch process.

Metal periodates are metal salts of various periodic acids. In periodic acid, the corresponding anion consists of iodine and oxygen in the +VII oxidation state. Periodates are in particular ortho-periodates (IO ₆ ⁵ - ; thus metal ortho-periodates with formula M ₅ IO ₆ ), meta-periodates (IO ₄ ⁻ , thus metal meta with formula MIO ₄ ) -periodate), dimesoperiodate (I ₂ O ₉ ^4- , hence metal dimesoperiodate having the formula M ₄ I ₂ O ₉ ), mesoperiodate (IO ₅ ^3- ; hence the formula M ₃ IO ₅ ) metal mesoperiodates having a) and para-periodate salts. Para-periodate is a salt of the formula M ₃ H ₂ IO ₆ and is also known as the corresponding double salt MIO ₄ *2 MOH. where M is the metal equivalent [(M ⁿ⁺ ) _1/n , where n is the number of charges]; Thus, for example, for alkali metal periodates, M is an alkali metal cation; For alkaline earth metal periodates, M is (M ²⁺ ) _1/2 . In periodates having multiple negative charges, multiple metal equivalents M may have the same or different meanings. By way of example, the three metal equivalents M in para-periodate M ₃ H ₂ IO ₆ or MIO ₄ *2 MOH may all have the same meaning or may be derived from different metals; Situations may arise where, for example, the counter cation of iodide used as the starting material is selectively present during anodization or differs from the counter cation present in the base used during work-up of the reaction product. See below for details.

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

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

Suitable alkaline earth metal iodides 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 that are stable under atmospheric conditions (air, moisture) and are at least partially soluble at the desired concentration in the reaction medium. Generally, the reaction medium for anodization is aqueous. However, since the reaction (anodic oxidation) can also be carried out, for example, under acidic or -preferably basic conditions which can significantly improve the solubility in the reaction medium, the low solubility in pure water does not necessarily mean that the transition metal iodide is It's not that it's not suitable. For example, CuI, which is essentially insoluble in water at a pH of about 7, contains an inorganic basic salt in which the reaction medium is basic and in particular the reaction medium is a base and the cation forms a water-soluble iodide, as in the case of, for example, NaOH or KOH. , it is a suitable starting compound.

Suitable transition metal iodides are Sc(III), Y(III), La(III), Co(II), Ni(II), Cu(I) and Zn(II) iodides. Among them, Cu(I) (CuI) iodide and Zn(II) iodide (ZnI ₂ ) are preferable in terms of economical efficiency and availability.

Thus, the process of the present invention prepares metal periodates by anodizing an alkali metal iodide, alkaline earth metal iodide or transition metal iodide, which is stable under atmospheric conditions (air, moisture) and soluble at the desired concentration in the reaction medium. wherein the transition metal iodide is preferably Sc(III), Y(III), La(III), Co(II), Ni(II), Cu(I) and Zn(II) selected from iodides.

The process of the present invention is more preferably provided for preparing a metal periodate by anodizing an alkali metal iodide, alkaline earth metal iodide, Cu(I) iodide or Zn(II) iodide.

Even more preferably, the method of the present invention is provided for preparing a metal periodate by anodizing an alkali metal iodide or alkaline earth metal iodide. As mentioned above, suitable alkali metal iodides are iodides of lithium, sodium, potassium or cesium. Of these, iodides of lithium, sodium or potassium are preferred. More preferred are iodides of sodium or potassium. Suitable alkaline earth metal iodides are iodides of magnesium or calcium. Among these, calcium iodide is preferable.

The process of the present invention is particularly provided for the production of alkali metal periodates by anodic oxidation of alkali metal iodides. Suitable and preferred alkali metal iodides are listed above. Suitable alkali metal periodates are the periodates of lithium, sodium, potassium or cesium. Among these, the periodate salts of lithium, sodium or potassium are preferable. Periodates of sodium or potassium are more preferred. Specifically, the method of the present invention is provided for preparing sodium periodate by anodizing sodium iodide or preparing potassium periodate by anodizing potassium iodide. Very particularly, the process of the invention provides for the preparation of sodium periodate by anodizing of sodium iodide.

The periodate salts prepared according to the present invention are preferably para-periodates, meta-periodates, ortho-periodates or mixtures of two or three of these periodates. Thus, in a preferred embodiment, the process of the invention comprises (by anodizing of course metal iodide) metal para-periodates, meta-periodates, ortho-periodates or two or three of these periodates. provided for preparing a mixture of species. Suitable and preferred metal iodides are listed above. More preferably, the method of the present invention comprises para-periodate, meta-periodate, ortho- by anodic oxidation of alkali metal iodide, alkaline earth metal iodide, Cu(I) iodide or Zn(II) iodide. provided for preparing a periodate salt or a mixture of two or three periodate salts thereof. Even more preferably, the method of the present invention comprises para-periodate salt, meta-periodate salt, ortho-periodate salt or peroxides of two or three kinds thereof by anodic oxidation of alkali metal iodide or alkaline earth metal iodide. provided for preparing a mixture of iodates. Particularly preferably, the method of the present invention comprises an alkali metal para-periodate, meta-periodate, ortho-periodate salt or a mixture of two or three periodates thereof by anodizing an alkali metal iodide. provided for manufacturing. In particular, the method of the present invention prepares sodium para-periodate, sodium meta-periodate, sodium ortho-sodium periodate or a mixture of two or three kinds of periodate salts by anodic oxidation of sodium iodide, or , or potassium iodide by anodic oxidation of potassium iodide, potassium meta-periodate, potassium ortho-potassium periodate, or a mixture of two or three kinds of these periodates. Specifically, the method of the present invention prepares sodium para-periodate, sodium meta-sodium periodate, ortho-sodium periodate or a mixture of two or three types of periodate salts by anodizing sodium iodide. provided to do

The periodate salts prepared according to the invention are more preferably para-periodate salts, meta-periodate salts or a mixture of para-periodate and meta-periodate salts. Thus, in a more preferred embodiment, the process of the invention comprises a metal para-periodate, or a metal meta-periodate or a metal para-periodate and a metal meta-periodate (by anodizing of the metal iodide, of course) provided for preparing a mixture of acid salts. Suitable and preferred metal iodides are listed above. Even more preferably, the process of the present invention comprises metal para-periodates, metal meta-periodates or metal para-periodates by anodization of alkali metal iodides, earth metal iodides, Cu(I) iodide or Zn(II) iodide. Provided for preparing a mixture of metal para-periodate and metal meta-periodate. Even more preferably, the method of the present invention comprises metal para-periodate, metal meta-periodate or metal para-periodate and metal meta-periodate by anodization of an alkali metal iodide or alkaline earth metal iodide. provided for preparing a mixture of acid salts. Particularly preferably, the process of the present invention comprises the formation of an alkali metal para-periodate, an alkali metal meta-periodate or an alkali metal para-periodate and an alkali metal meta-periodate by anodization of an alkali metal iodide. provided for preparing a mixture. In particular, the method of the present invention prepares sodium para-periodate, sodium meta-periodate or a mixture of sodium para-periodate and sodium meta-periodate by anodizing sodium iodide, or potassium iodide is provided for preparing potassium para-periodate, potassium meta-periodate or a mixture of potassium para-periodate and potassium meta-periodate by anodization of Specifically, the method of the present invention is provided for preparing sodium para-periodate, sodium meta-periodate or a mixture of sodium para-periodate and sodium meta-periodate by anodization of sodium iodide. .

Anodes comprising carbon (or electrodes more generally speaking) or carbon based anodes/electrodes are well known in the art, as also mentioned below, for example graphite electrodes, vitreous carbon (vitreous carbon) electrodes, reticulated vitreous carbon electrodes, carbon fiber electrodes, carbide-based composites-based electrodes, carbon-silicon composite-based electrodes, graphene-based electrodes, and diamond-based electrodes.

The anode comprising carbon is not necessarily entirely composed of carbonaceous material. Graphite electrodes are often composed of graphite alone or as the main material, but other carbonaceous materials may be present as the outer layer of the electrode, ie the part in direct contact with the electrolyte, or as part of it. More details are given below.

Among the anodes, a diamond-based electrode is preferable. These electrodes are characterized by very high overpotentials for both oxygen and hydrogen evolution leading to a wide potential window.

Due to the large bandgap exceeding 5 eV, diamond itself is generally an electrical insulator and therefore not suitable as an electrode material. However, diamond can be made conductive by doping with certain elements. Another alternative to making diamond conductive is annealing the undoped diamond thin film in vacuum at temperatures above 1550 °C. Under these harsh conditions, a network of conductive carbon phases may be formed in the diamond film.

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

Suitable dopants are selected from IUPAC group 13, 15 or 16 elements of the periodic table.

Accordingly, in a preferred embodiment, the at least one anode used in the method of the present invention comprises diamond doped with at least one IUPAC 13, 15 or 16 element of the Periodic Table.

A suitable dopant of group 13 is boron. Suitable dopants of Group 15 are nitrogen and phosphorus. A suitable dopant for Group 16 is sulfur. Boron doping leads to p-type semiconductors, while nitrogen-, phosphorus- and sulfur-doping leads to n-type conductivity. It is also possible to use, for example, two or more different dopants followed by boron-nitrogen-co-doping or boron-sulfur-co-doping. If the conductivity of two or more dopants is different, as in the case of B-N- or B-S-co-doping in the case of co-doping, the type of conductivity produced in the co-doped diamond is particularly dependent on the concentration of a single dopant and can be tuned to the desired type.

Among the dopants, boron doping is preferable. Accordingly, in a more preferred embodiment, the at least one anode used in the method of the present invention comprises boron doped diamond.

The boron-doped diamond preferably contains boron in an amount of 0.02 to 1% by weight (200 to 10,000 ppm), more preferably 0.04 to 0.2% by weight, in particular 0.06 to 0.09% by weight, relative to the total weight of the doped diamond. do.

As already mentioned above, these electrodes generally do not consist of doped diamond alone. Rather, the doped diamond is adhered to the substrate. Most often, doped diamond is present as a layer on a conductive substrate, although diamond particle electrodes in which doped diamond particles are embedded in a conductive or non-conductive substrate are also suitable. However, an anode in which doped diamond is present as a layer on a conductive substrate is preferred.

Accordingly, in particular, the at least one anode used in the method of the present invention comprises a boron doped diamond layer.

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

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

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

Preferably, the support material is from the group consisting of the elements silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the eight aforementioned metals, graphite, glassy carbon, carbon fibers and combinations (especially composites) thereof. is selected from

More preferred are the elements silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten and a combination of each of the metal carbides with one of the above-mentioned seven metals.

Doped diamond electrodes and methods for making them are known in the art and are described, for example, in the aforementioned Janssen, Electrochimica Acta 2003, 48, 3959, NL1013348C2 and references cited therein. . Suitable fabrication methods include, for example, chemical vapor deposition (CVD), such as high temperature filament CVD or microwave plasma CVD for producing electrodes with doped diamond films; and a high temperature high pressure (HTHP) method for making electrodes with doped diamond particles. Doped diamond electrodes are commercially available.

Suitably, the electrochemical oxidation of iodide is carried out in an aqueous medium. Accordingly, the method of the present invention comprises the step of anodizing an aqueous solution comprising a metal iodide.

The aqueous solution contains metal iodide, 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 1 mol/l, especially from 0.2 to 0.6 mol/l, very particularly in concentrations of 0.3 to 0.5 mol/l; Here, the concentration refers to the amount of iodide. "Concentration refers to the amount of iodide" means, for example, that 1 mol/l of iodide (M ⁺ )(I ^- ) is used to obtain an aqueous solution containing 1 mol/l of iodide, (M ²⁺ )(I ⁻ ) ₂ is only 0.5 mol/l and iodide (M ³⁺ )(I ⁻ ) ³ is only 0.33 mol/l.

Since the concentration of iodide naturally decreases in the course of conversion to periodate when the reaction is carried out in batch mode, the above concentration, of course, represents the concentration at the beginning of the reaction. For a continuous reaction design, the concentration refers to the concentration in the aqueous medium that is continuously introduced into the reaction. For semi-continuous reaction designs, the concentration refers to the concentration in the aqueous medium introduced during the course of the reaction.

In principle, it is possible to carry out anodization in acidic, neutral or basic media. However, iodine formed in the middle under neutral or acidic conditions is not immediately further oxidized, and may evaporate or precipitate to avoid further reaction. In acidic media, this is compounded by the presence of three additional reaction pathways for iodine formation, which certainly enhances the iodine elution problem.

In contrast, in a basic medium, the iodine phase reacts directly with hypoiodic acid and iodide further by disproportionation with OH ⁻ (I ₂ + OH ⁻ → I ⁻ + HIO). Therefore, basic reaction conditions are preferred. Another advantage of alkaline pH is a lower open circuit voltage and thus a higher electrolysis efficiency.

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

Therefore, the anodization is preferably carried out in the presence of a base. Suitable bases are those that 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 any separation problems, the counter cations in these bases preferably correspond to the metal cations in the iodide used. Given the general use of aqueous media for anodization, an exception to this preferred setting is necessary if the base of the cation corresponding to the metal cation in the iodide is not (sufficiently) water-soluble. By way of example, CuO, Cu(OH) ₂ and CuCO ₃ are essentially water insoluble. Therefore, when CuI is used as the iodide, it is appropriate to use a water-soluble base that is not based on Cu, such as NaOH or KOH. The same applies when certain alkaline earth metal iodides are used, in particular MgI ₂ or CaI ₂ , since the corresponding hydroxides, oxides and carbonates are almost insoluble in water. Again in this case, it is appropriate to use a water-soluble base that is not Mg- or Ca-based, such as NaOH or KOH. By "not sufficiently water soluble" it is meant that the base is not soluble at the desired iodide to base ratio (at a given iodide concentration) or at the concentration necessary to obtain the desired pH.

Preferably, the base is a metal hydroxide. More preferably, the base is a metal hydroxide, wherein the metal of the base corresponds to the metal in the metal iodide used; Cases where the corresponding base is not (sufficiently) water-soluble are excluded here. Preference is given to using alkali metal iodides, alkaline earth metal iodides and certain transition metal iodides as starting materials, and considering the solubility of the corresponding hydroxides in the aqueous reaction medium, preference is given to using alkali metal hydroxides as bases. When an alkali metal iodide is used as a starting material, it is preferable that the metal of the base corresponds to the metal of the alkali metal iodide to be used.

Preferably, the metal iodide and the base are from 1:2 to 1:30, more preferably from 1:2 to 1:20, even more preferably from 1:5 to 1:15, particularly preferably from 1:8 to 1:12, in particular from 1:10 to 1:11, wherein the molar ratio is based on the moles of iodide present in the metal iodide and the moles of hydroxide present or obtainable therefrom in the base. Calculated. In metal iodides, when the metal cations form water-soluble hydroxides (eg alkali metal iodides), the molar ratio is very particularly around 1:10, whereas in iodides the metal cations are hardly soluble or insoluble in water hydroxide. (eg alkaline earth metal iodide, Cu(I) iodide and Zn(II) iodide), the molar ratio is very particularly about 1:11.

Accordingly, the method of the present invention preferably comprises the step of anodizing an aqueous solution comprising a metal iodide and a base, wherein the metal iodide and the base are 1:2 to 1:30, more preferably 1:2 to 1:20, even more preferably from 1:5 to 1:15, particularly preferably from 1:8 to 1:12, in particular from 1:10 to 1:11, wherein the molar ratio is metal iodine to moles of iodide present in the cargo and moles of hydroxide present in or obtainable from the base. In metal iodides, when the metal cations form water-soluble hydroxides (eg alkali metal iodides), the molar ratio is very particularly around 1:10, whereas in iodides the metal cations are hardly soluble or insoluble in water hydroxide. (eg alkaline earth metal iodide, Cu(I) iodide and Zn(II) iodide), the molar ratio is very particularly about 1:11.

"The molar ratio calculated based on the moles of iodide present in the metal iodide and the moles of hydroxide present in or obtainable from the base" is to be understood as follows: x moles of iodide M ^a+ (I ^- ) _a and y moles of base M ^b+ (OH ⁻ ) _b are used, the relevant molar ratio is calculated as (x·a):(y·b). x moles of iodide M ^a+ (I ^- ) _a and y moles of base (M ⁺ ) ₂ (CO ₃ ^2- ) or (M ⁺ ) ₂ (O ² - ), if used, 1 mole of oxide or Since carbonate forms 2 moles of hydroxide, the corresponding molar ratio is calculated as (x·a ):(y·2). Similarly, 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, the molar ratio is calculated as (x·a):(y·2). If 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 are used, corresponding moles The ratio is calculated as (x·a):(y·6).

A molar ratio of "approximately" 1:10 or 1:11 is meant to include uncertainty due to weighing errors, etc., and generally includes a deviation of ±15%.

A specific 1:10 ratio corresponds to the theoretical optimal stoichiometry for para-periodate formation as seen in the reaction at the electrode under basic conditions:

Therefore, 8 equivalents of OH ⁻ are required for optimal conversion at the anode. Another 2 OH ⁻ is required to obtain para-periodate, a particularly desired target periodate salt to be produced by the process of the present invention.

When using an iodide, which forms a hydroxide in which the metal cation is poorly soluble or insoluble in water, it forms a salt that is hardly soluble or insoluble in water with the cation to compensate for the hydroxyl ion that precipitates out and is excluded from the reaction. Another hydroxyl equivalent per equivalent of iodide is required for this purpose, and therefore a specific 1:11 ratio is required for optimal stoichiometry for this type of iodide.

Electrolysis can be performed under constant current control (applied current is controlled; voltage can be measured but not controlled) or potentiostatic control (applied voltage is controlled; current can be measured but not controlled) and , the former is preferred.

For preferred constant current control, the observed voltage is generally in the range of 0 to 30 V, more frequently 1 to 20 V, in particular 1 to 10 V.

In the case of constant potential control, the applied voltage is generally in the same range, ie from 1 to 30 V, preferably from 1 to 20 V, in particular from 2 to 10 V.

The anodization is preferably carried out at a current density in the range of 10 to 500 mA/cm 2 , more preferably 50 to 150 mA/cm 2 , in particular 80 to 120 mA/cm 2 , especially about 100 mA/cm 2 .

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

The anodization is preferably carried out at a temperature of 5 to 80 °C, more preferably 10 to 60 °C, in particular 20 to 30 °C, in particular 20 to 25 °C.

The reaction pressure is not critical. Therefore, anodization is usually carried out at ambient pressure. However, to avoid boiling, higher pressures may be appropriate if the reaction is to be carried out at a temperature higher than the normal boiling point of the aqueous medium.

The electrolysis cell in which the anodic oxidation is carried out comprises at least one anode in at least one anode compartment and at least one cathode in at least one cathode compartment, wherein the anode compartment is preferably separate from the cathode compartment.

Separation of the anode compartment(s) from the cathode compartment(s) may be achieved by using different electrolysis cells for the cathode(s) and anode(s) and connecting these cells by salt bridges for charge equalization; However, it is preferred to use a common electrolysis cell in which the anode compartment(s) is separated from the cathode compartment(s) by a semipermeable membrane or conventional separation means (separator) such as a diaphragm or frit. In other words, the electrolysis cell is a separate cell. The separator separates the anolyte [the liquid medium in the anode compartment(s)] and the catholyte [the liquid medium in the cathode compartment(s)] but allows for charge equalization. A diaphragm is a separator comprising a porous structure of an oxidizing material such as silicate, for example in the form of a porcelain or ceramic. Semipermeable membranes are generally preferred because of the susceptibility of the diaphragm material to harsh conditions, especially when the reaction is carried out at basic pH. The semipermeable membrane is preferably one that withstands these conditions, in particular basic pH. Suitable semipermeable membranes are in particular cation exchange membranes, ie membranes composed of a material that passes cations (and fluids (usually water)) but not anions. More particularly, the semipermeable membrane is a proton exchange membrane (PEM). Membrane materials that withstand harsh conditions, especially basic pH, are based on fluorinated polymers. Examples of suitable materials for this type of membrane are the Nafion® brand from DuPont de Nemours or W.L. sulfonated tetrafluoroethylene based fluoropolymer-copolymers such as the Gore-Select® brand from Gore & Associates, Inc. When using iodides having divalent or higher counter cations, it is preferable to use different semipermeable separators that are permeable only to monovalent cations. A diaphragm is preferred in this case.

The reaction at the cathode(s) depends of course on the catholyte present in the cathode compartment(s). As already mentioned above, the at least one negative electrode compartment typically comprises an aqueous medium as the catholyte. The reaction taking place at the cathode in this case is the reduction of water to hydrogen (under the formation of hydroxyl anions, see equation above). Preferably, the at least one negative electrode compartment comprises an aqueous medium having a pH of at least 8, preferably at least 10, in particular at least 12, in particular at least 14.

Suitably, an inorganic base is used to obtain a basic pH in the aqueous medium of the negative electrode compartment. Suitable and preferred inorganic bases have already been described above with respect to the medium of the anode compartment; That is, they are preferably selected from metal hydroxides, metal oxides and metal carbonates. Hydroxide is preferred. More preferred are alkali metal hydroxides, especially sodium hydroxide and potassium hydroxide.

The material of the anode 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 present invention comprises

- introducing an aqueous solution containing metal iodide and optionally a base into the at least one anode compartment;

- anodic oxidation of iodide by electrolyzing said aqueous solution; and

- separating the metal periodate formed in the anodization of the iodide from the at least one anode compartment.

The aqueous solution introduced into the at least one anode compartment preferably contains metal iodide 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, in particular from 0.1 to 1 mol/l, especially 0.2 to 0.6 mol/l, very particularly 0.3 to 0.5 mol/l; where concentration refers to the amount of iodide; See description above. As regards preferred metal iodides, reference is made to the above. As already mentioned above, when the reaction is carried out batchwise, the concentration refers of course to the concentration at the beginning of the reaction, since the concentration of iodide naturally decreases in the course of conversion to periodate. Where the reaction is designed to be continuous or semi-continuous, the concentration refers to the concentration in the aqueous medium introduced continuously or partially in the course of the reaction.

The aqueous solution preferably contains a base. As regards preferred bases, reference is made to those mentioned above. Preferably, the counter cation in the base corresponds to the metal cation in the iodide; This preferred setting is excluded if the base in question is not (sufficiently) water-soluble; See description above.

The aqueous solution introduced into the at least one anode compartment preferably contains the metal iodide and the base from 1:2 to 1:30, more preferably from 1:2 to 1:20, even more preferably from 1:5 to 1:15. , particularly preferably in a molar ratio of 1:8 to 1:12, in particular 1:10 to 1:11. When the metal cations in the metal iodides form water-soluble hydroxides (eg alkali metal iodides), the molar ratio is very particularly about 1:10, whereas in the iodides the metal cations form hydroxides that are hardly soluble or insoluble in water. In the case of formation (eg alkaline earth metal iodide, Cu(I) iodide and Zn(II) iodide) the molar ratio is very particularly about 1:11. The molar ratio relates to the moles of iodide present in the metal iodide and the moles of hydroxide present in or obtainable from the base; See description above.

More preferably, the aqueous solution contains alkali metal iodide, preferably 0.01 to 5 mol/l, more preferably 0.05 to 2 mol/l, in particular 0.1 to 1 mol/l, especially 0.2 to 0.6 mol/l, very especially in concentrations of 0.3 to 0.5 mol/l; It further contains a base which is an alkali metal hydroxide, wherein the alkali metal of the base corresponds to the alkali metal in the alkali metal iodide; wherein the alkali metal iodide and the base are preferably 1:2 to 1:30, more preferably 1:2 to 1:20, even more preferably 1:5 to 1:15, particularly preferably 1: It is contained in a molar ratio of 8 to 1:12, in particular in a molar ratio of approximately 1:10.

Even more preferably, the aqueous solution contains sodium or potassium iodide from 0.01 to 5 mol/l, preferably from 0.05 to 2 mol/l, in particular from 0.1 to 1 mol/l, especially from 0.2 to 0.6 mol/l, very particularly from 0.3 to Contained in a concentration of 0.5 mol/l; It further contains a base which is sodium hydroxide or potassium hydroxide, wherein the alkali metal of the base corresponds to 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) lim); 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, even more preferably 1:5 to 1:15; Particularly preferably it is contained in a molar ratio of 1:8 to 1:12, in particular in a molar ratio of approximately 1:10. Specifically, the aqueous solution contains sodium iodide from 0.01 to 5 mol/l, preferably from 0.05 to 2 mol/l, in particular from 0.1 to 1 mol/l, especially from 0.2 to 0.6 mol/l, very particularly from 0.3 to 0.5 mol/l. concentration; It further contains sodium hydroxide, wherein sodium iodide and sodium hydroxide are preferably 1:2 to 1:30, more preferably 1:2 to 1:20, even 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 approximately 1:10.

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

Even 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, in particular 0.05 to 0.5 mol/l; It further contains a base which is sodium hydroxide; Calcium iodide and sodium hydroxide are preferably 1:4 to 1:60, more preferably 1:4 to 1:40, even more preferably 1:10 to 1:30, particularly preferably 1:16 to It is contained in a molar ratio of 1:24, in particular in a molar ratio of approximately 1:22.

In another more preferred embodiment, the aqueous solution contains Cu(I) iodide, 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, especially from 0.2 to 0.6 mol /l, very particularly in concentrations of 0.3 to 0.5 mol/l; It 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, even more preferably 1:5 to 1:15, particularly preferably 1 It is contained in a molar ratio of :8 to 1:12, in particular in a molar ratio of approximately 1:11.

The anodization in the process of the invention is preferably carried out without accelerators and additives. Promoters in the sense of the present invention are understood to be anti-reducing agents and oxidation promoters, for example polarizing substances. Additives are understood to refer to any substance other than the starting compound, products formed in the course of the reaction, acids, bases, electrolyte medium (usually water) and accelerators. In the processes of the prior art, the presence of accelerators or additives is often required to obtain periodate in satisfactory yield. For example, the method described in [Journal of the Korean Chemical Society 1974, 18, 373] by Nam et al. requires the presence of potassium dichromate as an anti-reducing agent. Chromium should be avoided in certain applications such as health, personal care or nutrition. Fluorides such as lithium fluoride or silicon fluoride are also often used; They are said to improve the overpotential of oxygen at the anode and improve the oxidation efficiency. In particular, the anodization in the process of the invention is preferably carried out in the absence of any accelerators, in particular in the absence of any chromium salts and any fluorides, such as lithium fluoride or silicon fluoride.

When a plurality of anodes are used, two or more anodes may be arranged in the same anode compartment or in separate compartments. When two or more anodes are present in the same compartment, they may be arranged side by side or in tiers. When a plurality of anode compartments are used, they may also be arranged side by side or in tiers.

The same applies if more than one negative electrode is used.

Alternatively, where the electrolysis device comprises a plurality of anodes and a plurality of cathodes, the electrolysis device may comprise a plurality of electrolysis cells, each cell comprising an anode and a cathode compartment. The electrolysis cells may be arranged side by side or in tiers.

Suitable geometries and arrangements of electrolysis devices comprising a plurality of anodes and/or cathodes are known to those skilled in the art.

The method of the present invention is suitable for reaction on an industrial scale as well as on a laboratory scale.

The process of the present 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 or continuous process.

In the batch (or discontinuous, time-lapse) method, the electrolyte containing iodide is electrolyzed and the product is separated from the anode compartment after a certain period of time is stopped, whereas in the continuous process design the electrolyte passes through the cell continuously, i.e., iodine The electrolyte containing the cargo is continuously added and reacted and the resulting reaction mixture is continuously removed from the process. Semicontinuous process design involves both types of elements. The process is in principle continuous, but at a certain point in time an electrolyte containing iodide is added and the resulting reaction mixture is removed at a certain point.

When the reaction is carried out batchwise, the anode and cathode compartments are generally designed as batch cells. When the reaction is carried out semi-continuously or continuously, the anode and cathode compartments are generally designed as flow cells.

Various designs and geometries of batches and flow cells are known in the art and can be applied to the present methods.

The appropriate design of an electrolysis device depends on whether the reaction is carried out as a batch, continuous or semi-continuous process and can be determined by the skilled person. In general, the electrolysis apparatus is equipped with a heat exchanger, a thermometer, mixing means and gas outlets of the cathode and anode compartment(s). For continuous or semi-continuous processes, continuous feeding and removal means are provided, for example in the form of a recirculation loop equipped with a pump.

After the anodization is performed, the periodate is separated from the anode compartment. If necessary, the periodate is separated from the aqueous medium removed from the anode compartment. The separation method and work-up depend in particular on the desired product and reaction conditions and are known in principle to the person skilled in the art.

For example, in order to obtain para-periodate salts which are not highly soluble in water, they can be simply precipitated from the aqueous reaction medium after concentration if necessary if they are sufficiently basic. Concentration can be carried out by general methods such as partial evaporation of the solvent under reduced pressure, partial freeze drying, partial reverse osmosis, and the like, if necessary. The precipitated product can be separated by general methods such as filtration or decantation of the supernatant. The precipitate is then optionally subjected to further purification steps such as washing with water or a solvent mixture containing water, digestion with water or a solvent mixture containing water, or recrystallization to remove unreacted iodide, excess base, unwanted by-products, etc. if present. can be rough Alternatively, water can be removed from the aqueous reaction medium, for example by evaporation of the solvent under reduced pressure, freeze-drying, reverse osmosis, if necessary, evaporation of the remaining water, etc., if necessary, and, if necessary, the residue is a precipitate. can be purified as mentioned above for If the reaction medium is not sufficiently basic, para-periodate is obtained after addition of additional base to the reaction medium. Subsequent operations may be performed as described above.

To obtain meta-periodate, the reaction medium must be neutralized if it is sufficiently basic to form para-periodate. In principle, any acid can be used provided that the anion in question is poorly oxidized. Suitable acids are, for example, sulfuric acid, hydrogen sulfate, phosphoric acid, dihydrogen phosphate, hydrogen phosphate, nitric acid, silicic acid and the like. When hydrogen sulfate, dihydrogen phosphate or hydrogen phosphate is used, the counter cation is preferably the same as that of the iodide used as the starting product, or the counter cation in the base and the iodide are different, but the corresponding hydrogen sulfate, dihydrogen phosphate or Hydrogen phosphate is the same as that of a base when it is water-soluble. The meta-periodate can then be separated from the aqueous medium by the usual means as described above. However, given the good aqueous solubility of meta-periodate, it is generally necessary to concentrate the aqueous medium before meta-periodate is precipitated.

Depending on the intended use of the periodate salt, the desired periodate salt may not undergo a purification step. In many cases, it is sufficient to evaporate water from the aqueous medium obtained after neutralization, especially when periodates are used as oxidizing agents. In some cases, it is not even necessary to evaporate the water (ie, the aqueous medium obtained from the anode compartment can be used as such in the subsequent oxidation process), or at least not to be dried.

The exact composition of the periodate salt obtained in the process of the present invention depends on the reaction and work-up conditions. For example, if the anodization is carried out at neutral pH and the reaction is not followed by a basic or acidic work-up in which a cation different from the counter cation in the iodide used as the starting material is introduced, the counter cation is a period corresponding to that of iodide. acid is obtained. The anodic oxidation is carried out under basic conditions, the base used is an inorganic basic salt corresponding to the counter cation in the iodide, and the counter cation is an inorganic basic salt corresponding to the counter cation in the iodide, and no further basic or acidic work-up introduces a cation different from the counter cation in the iodide used as the starting material If not, periodate is again obtained in which the counter cation corresponds to that of iodide. This is the case, for example, when an alkali metal iodide is reacted in the presence of an alkali metal basic salt having the same alkali metal as the countercation. When the reaction is followed by a basic work-up, the same base as used in the reaction or a base having at least the same alkali metal cation is used. When acidic post-treatment is applied, the acid is not a metal salt or is a salt containing the same alkali metal as the iodide, such as alkali metal hydrogen sulphate, hydrogen phosphate or dihydrogen phosphate. However, if the metal iodide is carried out in the presence of a base comprising a different cation (e.g. CuI/NaOH combination) and/or the work-up is carried out with a base or acid that introduces a different cation than the cation of the iodide, In general, various periodates with different counter cations can be formed. If necessary, they can be separated from each other by fractional crystallization, but for most application purposes the periodates can be further used as obtained, ie without further separation from each other.

The process of the present invention allows the production of periodate salts of a quality suitable for specific stringent applications such as pharmaceuticals, cosmetics and nutrients in a single step starting from iodide, which is readily available, economical, trouble free and easy to handle. The high conversion and construction yields combined with high atomic economy and the need for accelerators and additives make the process particularly attractive.

The method will now be further described through the following examples.

Example

Example 1 - Anodization of sodium iodide to sodium periodate in a semi-continuous process

A flow cell with anode and anode compartments separated from each other via a cation exchange membrane (Nafion® from DuPont) connected by 0.5 mm Teflon spacers as compartments containing a 12 cm 2 electrode surface was constructed with two Ritmo from Fink (Germany) for each compartment. Connected to the ®033 pump. A boron-doped diamond electrode (DIACHEM® electrode from Condias GmbH, 10 μm BDD on a silicon support (3 mm thick); about 800 ppm of 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 of aqueous NaOH (4 M) and the solution was circulated through the anode chamber (flow rate = 7.5 L/h). An aqueous NaOH (4 M) solution was circulated through the cathode chamber. A current density j of 100 mAcm ^-2 and a charge amount of Q = 10F = 9649 C were applied. The reaction was carried out at room temperature for about 2.2 hours. After electrolysis, the suspension formed in the anode compartment was removed and the flow system was washed with aqueous NaHSO ₄ and water. For analytical purposes, the suspension sample is mixed with aqueous NaHSO ₄ until the precipitate is completely dissolved, and the resulting solution is analyzed by liquid chromatography (LC-PDA; LC stationary phase: C18 reverse phase) coupled with a photodiode array. A % yield of para-sodium periodate was confirmed. The suspension was mixed with aqueous NaOH to complete precipitation, the precipitate was filtered, washed with cold water and dried to obtain the desired sodium para-periodate with a purity of 97% (isolated para-periodate yield 90%) was obtained with

A portion of the precipitated sodium para-periodate was acidified with nitric acid, the resulting solution was concentrated, and the precipitate was recrystallized from water (130 ° C → room temperature) to convert sodium meta-periodate to sodium meta-periodate. It was obtained in a yield of 65%.

Example 2 - Anodization of Sodium Iodide to Sodium Periodate in a Semi-Continuous Process

The same procedure as in Example 1 was performed except that 0.3 mol of NaI and 5 mol of NaOH were used; Q was 9F. The yield according to LC-PDA was 93%.

Example 3 - Anodization of Sodium Iodide to Sodium Periodate in a Semi-Continuous Process

The same procedure as in Example 1 was performed except that 0.1 mol of NaI and 3 mol of NaOH were used. The flow rate was 4 L/h, j was 90 mAcm ^-2 , Q = 12F. The yield according to LC-PDA was 90%.

Example 4 - Anodization of Potassium Iodide to Potassium Periodate in a Semi-Continuous Process

The process was performed in the same manner as in Example 1, except that potassium iodide was used instead of sodium iodide and potassium hydroxide was used instead of sodium hydroxide. The yield according to LC-PDA was 89%.

Example 5 - Anodization of Cu(I) iodide to Cu(I) periodate in a semi-continuous process

The process was performed in the same manner as in Example 1, except that Cu(I) iodide was used instead of sodium iodide. The yield according to LC-PDA was 76%.

Example 6: Anodization of Sodium Iodide to Sodium Periodate in a Batch Process

A separate beaker cell equipped with a Nafion® membrane, a BDD anode and a stainless steel cathode (both 3 x 1 cm 2 ) was used. Both chambers were charged with aqueous NaOH solution (3.0 M, 6 mL). NaI (640 μmol, 0.33 M) was added to the anode chamber and electrolysis was initiated using a charge of Q = 9 F = 1719 C (t = 1.59 h) and a current density of j = 100 mA/cm 2 . After the electrolysis was completed, the contents of the anode chamber were acidified with an aqueous NaHSO ₄ solution, and the solution was analyzed by LC-PDA, showing a yield of 90%.

Comparative Example - Anodization of sodium iodide by batch process on Pb or PbO ₂ anode

The process was performed in the same manner as in Example 6 except that a Pb or PbO ₂ positive electrode was used. The PbO ₂ anode was prepared by electrolytic oxidation of the Pb anode at 100 mA/cm 2 and 3000 C in 30% H ₂ SO ₄ . Anodization of sodium iodide using a Pb or PbO ₂ anode and the others under the same conditions as in Example 6 resulted in the formation of 53% or <54% sodium periodate, respectively.

Claims (21)

metal periodate by anodic oxidation of metal iodide in an electrolysis cell comprising at least one anode and at least one cathode A method of manufacturing, wherein the at least one positive electrode is an electrode comprising carbon. The method of claim 1, wherein the at least one anode comprises a diamond layer doped with at least one IUPAC 13, 15 or 16 element of the periodic table. 3. The method of claim 2, wherein at least one anode comprises a boron-doped diamond layer. 4. A doped diamond layer as claimed in claim 2 or 3, wherein the doped diamond layer is connected to a support material, said support material comprising elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, said a method selected from the group consisting of carbides of the eight mentioned elements, graphite, glassy carbon, carbon fibers and combinations of the aforementioned materials. 5. The method according to any one of claims 1 to 4, wherein the metal iodide is selected from the group consisting of alkali metal iodides, alkaline earth metal iodides and transition metal iodides. 6. The metal iodide according to claim 5, wherein the metal iodide is selected from alkali metal iodide, alkaline earth metal iodide, Cu(I) iodide and Zn(II) iodide; Preferably lithium iodide, sodium iodide, potassium iodide, cesium iodide, magnesium iodide, calcium iodide, Cu(I) iodide and Zn(II) iodide; in particular sodium iodide, potassium iodide and Cu(I) iodide; in particular selected from the group consisting of sodium iodide and potassium iodide. 7. The method according to any one of claims 1 to 6, wherein the periodate is para-periodate, meta-periodate, ortho-periodate or a mixture of two or three of these periodates, in particular Para-periodate, meta-periodate or a mixture of para-periodate and meta-periodate. 8. The sodium meta-periodate according to any one of claims 1 to 7, wherein sodium para-periodate, sodium meta-periodate or a mixture of sodium para-periodate and sodium meta-periodate by anodization of sodium iodide is carried out. manufacture of; or preparation of potassium para-periodate, potassium meta-periodate or a mixture of potassium para-periodate and potassium meta-periodate by anodic oxidation of potassium iodide; A process for the preparation of sodium para-periodate, sodium meta-periodate or a mixture of sodium para-periodate and sodium meta-periodate, in particular by the anodization of sodium iodide. 9. The method according to any one of claims 1 to 8, comprising the step of anodizing an aqueous solution comprising metal iodide, wherein the aqueous solution produces metal iodide by 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, especially from 0.2 to 0.6 mol/l, very particularly from 0.3 to 0.5 mol/l; wherein concentration refers to the amount of iodide. 10 . The method according to claim 1 , wherein the anodization is carried out at a pH of at least 8, preferably at least 10, in particular at least 12, in particular at least 14. The method of claim 10 , wherein the anodization is carried out in the presence of a base, wherein the base is selected from the group consisting of metal hydroxides, metal oxides and metal carbonates. The method of claim 11 , wherein the base is a metal hydroxide, and when the metal iodide is an alkali metal iodide, the metal of the base corresponds to the metal in the metal iodide. 13. The method according to claim 11 or 12, comprising the step of anodizing an aqueous solution comprising metal iodide and a base, wherein the metal iodide and base are from 1:2 to 1:30, preferably from 1:2 to used in a molar ratio of 1:20, more preferably 1:5 to 1:15, even more preferably 1:8 to 1:12, in particular a molar ratio of approximately 1:10; wherein the molar ratio is to moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base. 14. The anodic oxidation according to any one of claims 1 to 13, wherein the anodization is in the range of 10 to 500 mA/cm, preferably 50 to 150 mA/cm, in particular 80 to 120 mA/cm, in particular about 100 mA/cm The method is performed at a current density of 15. The electrolysis cell according to any one of claims 1 to 14, wherein the electrolysis cell in which the anodic oxidation is carried out comprises at least one anode in at least one anode compartment and at least one cathode in at least one cathode compartment, wherein the anode compartment is separate from the cathode compartment. 16. The method according to claim 15, wherein the at least one negative electrode compartment comprises an aqueous medium having a pH of at least 8, preferably at least 10, in particular at least 12, in particular at least 14. 17. The method of claim 15 or 16,
- introducing an aqueous solution containing metal iodide and optionally a base into the at least one anode compartment;
- anodic oxidation of iodide by electrolyzing said aqueous solution; and
- separating the metal periodate formed in the anodization of the iodide from the at least one anode compartment,
Way. 18. The aqueous solution according to claim 17, wherein the aqueous solution contains 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, especially Contain in concentrations of 0.2 to 0.6 mol/l, very particularly 0.3 to 0.5 mol/l; It further contains a base which is an alkali metal hydroxide, wherein the alkali metal of the base corresponds to the alkali metal in the alkali metal iodide; The alkali metal iodide and the base are 1:2 to 1:30, preferably 1:2 to 1:20, more preferably 1:5 to 1:15, even more preferably 1:8 to 1: 12, in particular in a molar ratio of approximately 1:10. 19. The method according to any one of claims 17 to 18, wherein the alkali metal iodide is sodium iodide and the base is sodium hydroxide; wherein the alkali metal iodide is potassium iodide and the base is potassium hydroxide. 20. The method according to any one of claims 1 to 19, wherein the anodization is carried out in the absence of accelerators and additives. 21. The process according to any one of claims 1 to 20, carried out as a semi-continuous or continuous process.