WO2021110928A1 - Method for preparing periodates - Google Patents
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- WO2021110928A1 WO2021110928A1 PCT/EP2020/084659 EP2020084659W WO2021110928A1 WO 2021110928 A1 WO2021110928 A1 WO 2021110928A1 EP 2020084659 W EP2020084659 W EP 2020084659W WO 2021110928 A1 WO2021110928 A1 WO 2021110928A1
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- iodide
- periodate
- metal
- sodium
- anodic oxidation
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/24—Halogens or compounds thereof
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/28—Per-compounds
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/042—Electrodes formed of a single material
- C25B11/043—Carbon, e.g. diamond or graphene
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
- C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
- C25B11/083—Diamond
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
- C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
- C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
Definitions
- the present invention relates to a method for preparing a metal periodate by anodic oxidation of a metal iodide using carbon-based anodes.
- Periodates are powerful oxidizing agents widely used in chemical syntheses. There is a constant need for economic methods for producing them and for production methods complying with certain regulations, especially if the periodates are used at some point in the synthesis of products for use in the pharmaceutical, cosmetic or nutrition field.
- the periodates or periodic acid can be produced electrochemically by anodic oxidation starting from elemental iodine or from iodine salts in which iodine has an oxidation state of below +VII.
- Metal-based electrodes such as lead dioxide, ruthenium dioxide, iridium dioxide, etc. may however dissolve under anodic conditions and may contribute to metal impurities in the desired product.
- lead-based anodes are well known to dissolve under anodic conditions and mass losses of 0.05 g/Ah or even 2.5 g/Ah may occur, as reported by C.W. Nam et al. in Journal of the Korean Chemical Society 1974, 18, 373 or by Y. Aiya et al. in Journal of the Electrochemical Society 1962, 109, 419.
- the presence of such metal impurities is however not acceptable in certain applications, such as pharmaceutics, cosmetics or nutrition. To comply, for example, with pharmaceutical guideline regulations, it is thus necessary to remove these impurities, which is cumbersome and non-economic.
- Iodine sublimes readily at ordinary temperatures and generates hazardous vapors. Moreover, it is poorly soluble in water (the usual medium for such electrolyses) lodate in comparison is safe to handle, but the molar cost is significantly higher.
- Iodides as starting material are interesting both from an economic and handling view.
- the lead dioxide electrode may dissolve under anodic conditions and lead to metal impurities in the desired product, which for certain applications is not acceptable.
- the presence of chromium is not acceptable in certain applications, such as health, personal care and nutrition.
- US 5,520,793 relates to an electrochemical process for producing high purity grades of hydrogen iodide by cathodic reduction of solubilized iodine.
- the anode is used for generating a product of value selected from periodic acid, oxygen or protons.
- the anodic compartment contains and aqueous solution comprising an oxidation agent.
- the aqueous solution is preferably acidic.
- the anode may be any of those commercially used. Among many others, graphite is mentioned as suitable anode material.
- the process at the anode is however not used for providing metal periodates. Actually, the presence of any foreign cations, such as sodium and potassium, is undesired, since this would have the potential for contaminating the catholyte by back-migration or passing through the cell divider.
- WO 2004/055243 relates to a process for electrolytic production of inorganic peroxy compounds, such as perhalogenic acids, perhalogenates or permanganates starting from halogen or magnesium compounds in a lower oxidation state using an electrode with a doped diamond layer as anode. Specifically described is only the oxidation of sodium chlorate or chlorine to sodium perchlorate. The oxidation of chlorine is carried out at pH 0 using an electrolyte containing NaCI. NaCI is said to be oxidized first to chlorine and then to perchlorate. The current efficiency of 65% is not satisfactory.
- Lithium salts in general are rather expensive.
- the method should yield the periodates devoid of metals undesired in certain applications, such as pharmaceutics, cosmetics or nutrition, and especially devoid of lead, and should start from low-priced, readily available and easy-to-handle starting materials.
- the method should allow high current efficiency and should be suitable for scale-up. Moreover, it should be possible to avoid the use of toxic anti-reducing agents.
- the object is achieved by an electrochemical method using metal iodides as starting material and a carbon-based anode.
- the present invention thus relates to a method for preparing a metal periodate by anodic oxidation of a metal iodide in an electrolysis cell comprising one or more anodes and one or more cathodes, characterised in that the one or more anodes are carbon-comprising electrodes.
- Embodiments (E.x) of the invention Embodiments (E.x) of the invention
- E.1 A method for preparing a metal periodate by anodic oxidation of a metal iodide in an electrolysis cell comprising one or more anodes and one or more cathodes, characterised in that the one or more anodes are carbon-comprising electrodes.
- E.2. The method as defined in embodiment E.1 , characterised in that the one or more anodes comprise a diamond layer doped with one or more lUPAC group 13, 15 or 16 elements of the periodic table.
- E.4 The method as defined in any of embodiments E.2 or E.3, where the doped diamond layer is connected to a support material, where the support material is selected from the group consisting of elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the eight afore-mentioned elements, graphite, glassy carbon, carbon fibre and combinations of the afore-mentioned materials.
- the support material is selected from the group consisting of elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the eight afore-mentioned elements, graphite, glassy carbon, carbon fibre and combinations of the afore-mentioned materials.
- metal iodide is selected from the group consisting of alkali metal iodides, earth alkaline metal iodides and transition metal iodides.
- metal iodide is selected from the group consisting of alkali metal iodides, earth alkaline metal iodides, Cu(l) iodide and Zn(ll) iodide.
- metal iodide is selected from the group consisting of lithium iodide, sodium iodide, potassium iodide, caesium iodide, magnesium iodide, calcium iodide, Cu(l) iodide and Zn(ll) iodide.
- periodate is a para-periodate, meta-periodate, ortho-periodate or a mixture of two or three of these periodates.
- E.14 The method as defined in any of the preceding embodiments, comprising subjecting an aqueous solution comprising the metal iodide to anodic oxidation, where the aqueous solution comprises the metal iodide in a concentration of from 0.001 to 12 mol/l, where the concentration refers to the amount of iodide.
- E.15 The method as defined in embodiment E.14, where the aqueous solution comprises the metal iodide in a concentration of from 0.05 to 2 mol/l, where the concentration refers to the amount of iodide.
- E.25 The method as defined in any of embodiments E.23 or E.24, where the method comprises subjecting an aqueous solution comprising the metal iodide and a base to anodic oxidation, where the metal iodide and the base are used in a molar ratio of from 1 :2 to 1 :30, where the molar ratio relates to moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base.
- E.26 The method as defined in embodiment E.25, where the method comprises subjecting an aqueous solution comprising the metal iodide and a base to anodic oxidation, where the metal iodide and the base are used in a molar ratio of from 1 :2 to 1 :20, where the molar ratio relates to moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base.
- E.34 The method as defined in any of the preceding embodiments, where the electrolysis cell in which the anodic oxidation is carried out comprises one or more anodes in one or more anode compartments and one or more cathodes in one or more cathode compartments, where the anode compartments are separated from the cathode compartments, where in particular the electrolysis cell is a divided cell in which the anode compartment(s) is/are separated from the cathode compartment(s) by usual dividing means (separators), such as semipermeable membranes or diaphragmas.
- dividing means such as semipermeable membranes or diaphragmas.
- aqueous solution contains an alkali metal iodide in a concentration of from 0.01 to 5 mol/l; and further contains a base which is an alkali metal hydroxide, where the alkali metal of the base corresponds to the alkali metal in the alkali metal iodide; where the alkali metal iodide and the base are contained in a molar ratio of from 1 :2 to 1 :30.
- Metal periodates are the metal salts of the various periodic acids.
- the corresponding anions are composed of iodine in oxidation state +VII and oxygen.
- Periodates include i.a. ortho-periodates (ICV ; the metal ortho-periodate thus having the formula M d IOb), meta-periodates (ICV; the metal meta-periodate thus having the formula MICU), dimesoperiodates (I 2 O 9 4 ; the metal dimesoperiodate thus having the formula M 4 I 2 O 9 ), mesoperiodates (IO 5 3 ; the metal mesoperiodate thus having the formula M 3 IO 5 ) and para- periodates.
- Para-periodates are salts of the formula M3H2IO6 and are also known as the corresponding double salt MIC> 4* 2 MOH.
- M in the above formulae is a metal equivalent [(M n+ )i /n , where n is the charge number]; in case of, for example, an alkali metal periodate M is thus an alkali metal cation; and in case of an earth alkaline metal periodate M is (M 2+ ) I/ 2.
- the more than one metal equivalents M can have the same or different meanings.
- all three metal equivalents M can have the same meaning or can be derived from different metals; a situation which can for example occur if the counter cation of the iodide used as starting material differs from the counter cation present in the base optionally present during anodic oxidation or used during workup of the reaction product.
- the counter cation of the iodide used as starting material differs from the counter cation present in the base optionally present during anodic oxidation or used during workup of the reaction product.
- the metal iodide is preferably selected from the group consisting of alkali metal iodides, earth alkaline metal iodides and transition metal iodides.
- Suitable alkali metal iodides to be used as starting materials in the method of the present invention are for example lithium, sodium, potassium or cesium iodide.
- Suitable earth alkaline metal iodides to be used as starting materials in the method of the present invention are for example magnesium or calcium iodide.
- Suitable transition metal iodides to be used as starting materials in the method of the present invention are those which are stable under atmospheric conditions (air, moisture) and are at least partly soluble at the desired concentration in the reaction medium.
- the reaction medium for the anodic oxidation is aqueous.
- a low solubility in pure water does however not necessarily disqualify a transition metal iodide, since the reaction (anodic oxidation) can for example be carried out under acidic or - preferably - basic conditions which may drastically enhance solubility in the reaction medium.
- Cul which is essentially non-soluble in water at a pH of ca. 7, is nevertheless a suitable starting compound if the reaction medium is basic and especially if the reaction medium contains as base an inorganic basic salt in which the cation forms water-soluble iodides, such as is the case, for example, for NaOH or KOH.
- Suitable transition metal iodides are the Sc(lll), Y(lll), La(lll), Co(ll), Ni(ll), Cu(l) and Zn(ll) iodides. Among these, in view of their economic efficiency and availability, preference is given to Cu(l) iodide (Cul) and Zn(ll) iodide (Znh).
- the method of the invention thus serves preferably for preparing a metal periodate by anodic oxidation of an alkali metal iodide, an earth alkaline metal iodide or a transition metal iodide which is stable under atmospheric conditions (air, moisture) and is soluble at the desired concentration in the reaction medium, where the transition metal iodide is preferably selected from the Sc(lll), Y(lll), La(lll), Co(ll), Ni(ll), Cu(l) and Zn(ll) iodides.
- the method of the invention serves more preferably for preparing a metal periodate by anodic oxidation of an alkali metal iodide, an earth alkaline metal iodide, Cu(l) iodide or Zn(ll) iodide.
- the method of the invention serves for preparing a metal periodate by anodic oxidation of an alkali metal iodide or an earth alkaline metal iodide.
- suitable alkali metal iodides are those of lithium, sodium, potassium or cesium. Among these, preference is given to the iodides of lithium, sodium or potassium. More preference is given to the iodides of sodium or potassium.
- Suitable earth alkaline metal iodides are those of magnesium or calcium. Among these, preference is given to calcium iodide.
- the method of the invention serves in particular for preparing an alkali metal periodate by anodic oxidation of an alkali metal iodide.
- Suitable and preferred alkali metal iodides are listed above.
- Suitable alkali metal periodates are those of lithium, sodium, potassium or cesium. Among these, preference is given to the periodates of lithium, sodium or potassium. More preference is given to the periodates of sodium or potassium.
- the method of the invention serves for preparing a sodium periodate by anodic oxidation of sodium iodide, or for preparing a potassium periodate by anodic oxidation of potassium iodide.
- the method of the invention serves for preparing a sodium periodate by anodic oxidation of sodium iodide.
- the periodate to be prepared according to the invention is preferably a para-periodate, meta periodate, ortho-periodate or a mixture of two or three of these periodates.
- the method of the invention serves for preparing a metal para- periodate, meta-periodate, ortho-periodate or a mixture of two or three of these periodates (of course by anodic oxidation of a metal iodide). Suitable and preferred metal iodides are listed above.
- the method of the invention serves for preparing a para- periodate, meta-periodate, ortho-periodate or a mixture of two or three of these periodates by anodic oxidation of an alkali metal iodide, an earth alkaline metal iodide, Cu(l) iodide or Zn(ll) iodide.
- the method of the invention serves for preparing a para- periodate, meta-periodate, ortho-periodate or a mixture of two or three of these periodates by anodic oxidation of an alkali metal iodide or earth alkaline metal iodide.
- the method of the invention serves for preparing an alkali metal para-periodate, meta-periodate, ortho-periodate or a mixture of two or three of these periodates by anodic oxidation of an alkali metal iodide.
- the method of the invention serves for preparing sodium para-periodate, sodium meta-periodate, sodium ortho-periodate or a mixture of two or three of these periodates by anodic oxidation of sodium iodide, or for preparing potassium para-periodate, potassium meta-periodate, potassium ortho-periodate or a mixture of two or three of these periodates by anodic oxidation of potassium iodide.
- the method of the invention serves for preparing sodium para-periodate, sodium meta-periodate, sodium ortho-periodate or a mixture of two or three of these periodates by anodic oxidation of sodium iodide.
- the periodate to be prepared according to the invention is more preferably a para-periodate, a meta-periodate or a mixture of a para-periodate and a meta-periodate.
- the method of the invention serves for preparing a metal para- periodate, or a metal meta-periodate or a mixture of a metal para-periodate and a metal meta-periodate (of course by anodic oxidation of a metal iodide). Suitable and preferred metal iodides are listed above.
- the method of the invention serves for preparing a metal para-periodate, a metal meta-periodate or a mixture of a metal para- periodate and a metal meta-periodate by anodic oxidation of an alkali metal iodide, an earth alkaline metal iodide, Cu(l) iodide or Zn(ll) iodide.
- the method of the invention serves for preparing a metal para-periodate, a metal meta-periodate or a mixture of a metal para-periodate and a metal meta-periodate by anodic oxidation of an alkali metal iodide or earth alkaline metal iodide.
- the method of the invention serves for preparing an alkali metal para-periodate, an alkali metal meta-periodate or a mixture of an alkali metal para-periodate and an alkali metal meta-periodate by anodic oxidation of an alkali metal iodide.
- the method of the invention serves for preparing sodium para-periodate, sodium meta-periodate or a mixture of sodium para- periodate and sodium meta-periodate by anodic oxidation of sodium iodide, or for preparing potassium para-periodate, potassium meta-periodate or a mixture of potassium para- periodate and potassium meta-periodate by anodic oxidation of potassium iodide.
- the method of the invention serves for preparing sodium para-periodate, sodium meta-periodate or a mixture of sodium para-periodate and sodium meta-periodate by anodic oxidation of sodium iodide.
- Carbon-comprising anodes or electrodes, more generally speaking) or carbon-based anodes/electrodes, as they are also termed in the following, are well known in the art and include for example graphite electrodes, vitreous carbon (glassy carbon) electrodes, reticulated vitreous carbon electrodes, carbon fiber electrodes, electrodes based on carbonized composites, electrodes based on carbon-silicon composites, graphene-based electrodes and diamond-based electrodes.
- the carbon-comprising anodes are not necessarily composed entirely of the carbonaceous material. While graphite electrodes are often composed of graphite as only or as main material, other carbonaceous materials may be present just as or as a part of the outer layer of the electrode, i.e. of that part which is in direct contact with the electrolyte. Further details are given below.
- Such electrodes are characterized by a very high overpotential for both oxygen and hydrogen evolution leading to a wide potential window.
- diamond perse is normally an electric insulator and thus not suitable as electrode material.
- diamond can be made conductive by doping with certain elements.
- Another alternative of making diamond conductive is annealing thin undoped diamond films in vacuum at temperatures above 1550°C. These drastic conditions presumably result in the formation of a network of conducting carbon phases within the diamond film.
- diamond-based electrodes are preferably electrodes comprising electroconductively-doped diamond.
- Suitable dopants are selected from lUPAC groups 13, 15 or 16 elements of the periodic table.
- the one or more anodes used in the method of the present invention comprise diamond doped with one or more lUPAC group 13, 15 or 16 elements of the periodic table.
- a suitable dopant of group 13 is boron.
- Suitable dopants of group 15 are nitrogen and phosphorus.
- a suitable group 16 dopant is sulfur. Boron doping leads to p-type semiconductors, whereas nitrogen-, phosphorus- and sulfur-doping results in n-type conductivity. It is also possible to use two or more different dopants, resulting in, for example, boron-nitrogen-co-doping or boron-sulfur-co-doping.
- the type of the resulting conductivity in the co-doped diamond depends inter alia on the concentration of the single dopants and can be tuned to the desired type.
- the one or more anodes used in the method of the invention comprise boron- doped diamond.
- the boron-doped diamond comprises boron in an amount of preferably 0.02 to 1% by weight (200 to 10,000 ppm), more preferably of 0.04 to 0.2% by weight, in particular of 0.06 to 0.09% by weight, relative to the total weight of the doped diamond.
- such electrodes are generally not composed of doped diamond alone. Rather, the doped diamond is attached to a substrate. Most frequently, the doped diamond is present as a layer on a conducting substrate, but diamond particle electrodes, in which doped diamond particles are embedded into a conducting or non-conducting substrate are suitable as well. Preference is however given to anodes in which the doped diamond is present as a layer on a conducting substrate.
- the one or more anodes used in the method of the invention comprise a boron-doped diamond layer.
- Suitable support materials for electrodes comprising a boron-doped diamond layer are silicon, self-passivating metals, metal carbides, graphite, glassy carbon, carbon fibers and combinations thereof.
- Suitable self-passivating metals are for example germanium, zirconium, niobium, titanium, tantalum, molybdenum and tungsten.
- Suitable combinations are for example metal carbide layers on the corresponding metal (such an interlayer may be formed in situ when a diamond layer is applied to the metal support), composites of two or more of the above-listed support materials and combinations of carbon and one or more of the other elements listed above.
- Examples for composites are siliconized carbon fiber carbon composites (CFC) and partially carbonized composites.
- the support material is selected from the group consisting of elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten, carbides of the eight aforementioned metals, graphite, glassy carbon, carbon fibers and combinations (in particular composites) thereof. More preference is given to elemental silicon, germanium, zirconium, niobium, titanium, tantalum, molybdenum, tungsten and a combination of one of the seven afore-mentioned metals with the respective metal carbide.
- Doped diamond electrodes and methods for preparing them are known in the art and described, for example, in the above-mentioned Janssen article in Electrochimica Acta 2003, 48, 3959, in NL1013348C2 and the references cited therein. Suitable preparation methods include, for example, chemical vapour deposition (CVD), such as hot filament CVD or microwave plasma CVD, for preparing electrodes with doped diamond films; and high temperature high pressure (HTHP) methods for preparing electrodes with doped diamond particles. Doped diamond electrodes are commercially available.
- CVD chemical vapour deposition
- HTHP high temperature high pressure
- the electrochemical oxidation of the iodide is carried out in aqueous medium.
- the method of the invention comprises subjecting an aqueous solution comprising the metal iodide to anodic oxidation.
- the aqueous solution comprises the metal iodide in a concentration of 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, in particular from 0.1 to 1 mol/l, specifically from 0.2 to 0.6 mol/l, and very specifically from 0.3 to 0.5 mol/l; where the concentration refers to the amount of iodide.
- the concentration refers to the amount of iodide means to express that in order to obtain an aqueous solution containing, for example, of 1 mol/l of iodide, 1 mol/l of the iodide (M + )(l _ ) are used, but only 0.5 mol/l of the iodide (M 2+ )(l ' )2 and only 0.33 mol/l of the iodide (M 3+ )(l )3.
- the above concentrations refer of course to the concentrations at the beginning of the reaction, since, as a matter of course, the concentration of the iodide decreases in the course of its conversion into the periodate.
- the above concentrations refer to the concentration in the aqueous medium continually introduced into the reaction.
- the above concentrations refer to the concentration in the aqueous medium introduced in the course of the reaction.
- the anodic oxidation is carried out at a pH of at least 8, preferably of at least 10, in particular of at least 12 and specifically of at least 14.
- the anodic oxidation is preferably carried out in the presence of a base.
- Suitable bases are all those which are water-soluble and form hydroxyl ions in aqueous phase.
- Preferred are inorganic bases, such as metal hydroxides, metal oxides and metal carbonates.
- the counter cation corresponds preferably to the metal cation in the iodide used.
- the base the cation of which corresponds to the metal cation in the iodide is not (sufficiently) water soluble.
- CuO, Cu(OH)2 and CuCCh are essentially insoluble in water. Therefore, if Cul is used as iodide, it is indicated to use a water-soluble base which is not Cu-based; such as NaOH or KOH.
- the base is a metal hydroxide. More preferably, the base is a metal hydroxide, where the metal of the base corresponds to the metal in the metal iodide used; except for the above-described case where the corresponding base is not (sufficiently) water-soluble.
- the metal of the base corresponds to the metal in the metal iodide used; except for the above-described case where the corresponding base is not (sufficiently) water-soluble.
- the metal of the base corresponds preferably to the metal in the alkali metal iodide used.
- the metal iodide and the base are used in a molar ratio of 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 and in particular in a molar ratio of from 1:10 to 1:11, where the molar ratio is calculated based on moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base.
- the metal cation of which forms water-soluble hydroxides such as the alkali metal iodides
- the molar ratio is very specifically approximately 1:10
- the metal cation of which forms scarcely water-soluble or insoluble hydroxides such as the earth alkaline metal iodides
- the molar ratio is very specifically approximately 1:11.
- the method of the invention thus preferably comprises subjecting an aqueous solution comprising the metal iodide and a base to anodic oxidation, where the metal iodide and the base are used in a molar ratio of from 1:2 to 1:30, 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 and specifically in a molar ratio of from 1 : 10 to 1 : 11 , where the molar ratio relates to moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base.
- the molar ratio is very specifically approximately 1:10, whereas in case of iodides the metal cation of which forms scarcely water-soluble or insoluble hydroxides (such as the earth alkaline metal iodides, Cu(l) iodide and Zn(ll) iodide), the molar ratio is very specifically approximately 1:11.
- Molar ratio calculated based on moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base is to be understood as follows: In case x moles of the iodide M a+ (l ) a and y moles of the base M b+ (OH ) b are used, the relevant molar ratio is calculated as (x a):(y b).
- a molar ratio of “approximately” 1:10 or 1:11 means to include uncertainties, such as due to weighing errors and the like and generally includes a deviation of ⁇ 15%.
- the specific 1:10 ratio corresponds to the theoretical optimum stoichiometry for the formation of the para-periodate, as can be seen from the reaction at the electrodes under basic conditions:
- the electrolysis can be carried out under galvanostatic control (applied current is controlled; voltage may be measured, but is not controlled) or potentiostatic control (applied voltage is controlled; current may be measured, but is not controlled), the former being preferred.
- the observed voltage is generally in the range of from 0 to 30 V, more frequently from 1 to 20 V and in particular from 1 to 10 V.
- the applied voltage is generally in the same range, i.e. from 1 to 30 V, preferably from 1 to 20 V, in particular from 2 to 10 V.
- the anodic oxidation is preferably carried out at a current density in the range of from 10 to 500 mA/cm 2 , more preferably from 50 to 150 mA/cm 2 , in particular from 80 to 120 mA/cm 2 and specifically of ca. 100 mA/cm 2 .
- a charge amount of preferably at least 660,000 C ( ⁇ 7 F), more preferably of at least 772,000 C (-8 F), in particular of at least 868,000 C (-9 F), and specifically of at least 964,000 (-10 F) per mol of iodide anions to be oxidized is applied; e.g. a charge amount of preferably from 660,000 to 1,928,000C (-7-20 F), more preferably from 772,000 to 1,446,000 C (-8-15 F), in particular from 868,000 to 1,156,000 C (-9-12 F), and specifically from 964,000 to 1,060,000 C (-10-11 F) per mol of
- the anodic oxidation is preferably carried out at a temperature of from 5 to 80°C, more preferably from 10 to 60°C, in particular from 20 to 30°C and specifically from 20 to 25°C.
- the reaction pressure is not critical.
- the anodic oxidation is therefore generally carried out at ambient pressure. Higher pressures can however be indicated if the reaction is to be carried out at a temperature above the normal boiling point of the aqueous medium in order to avoid ebullition.
- the electrolysis cell in which the anodic oxidation is carried out comprises one or more anodes in one or more anode compartments and one or more cathodes in one or more cathode compartments, where the anode compartments are preferably separated from the cathode compartments.
- the separation of the anode compartment(s) from the cathode compartment(s) can be accomplished by using different electrolysis cells for cathode(s) and anode(s) and connecting these cells by a salt bridge for charge equalization; preference is however given to using a common electrolysis cell in which the anode compartment(s) is/are separated from the cathode compartment(s) by usual dividing means (separators), such as semipermeable membranes or diaphragmas or frits. Alternatively expressed, the electrolysis cell is a divided cell.
- the separators separate the anolyte [liquid medium in the anode compartment(s)] from the catholyte [liquid medium in the cathode compartment(s)], but allow charge equalization.
- Diaphragmas are separators comprising porous structures of an oxidic material, such as silicates, e.g. in the form of porcelain or ceramics. Due to the sensitivity of diaphragma materials to harsher conditions, semipermeable membranes are however generally preferred, especially if the reaction is carried out at basic pH, as it is preferred.
- the semipermeable membrane is preferably one which resists such conditions, especially basic pH.
- Suitable semipermeable membranes are in particular cation exchange membranes, i.e. membranes composed of materials which allow the passage of cations [and the fluid (which is generally water)], but not of anions. More specifically, the semipermeable membrane is a proton exchange membrane (PEM).
- PEM proton exchange membrane
- Membrane materials which resist harsher conditions, especially basic pH, are based on fluorinated polymers.
- suitable materials for this type of membranes are sulfonated tetrafluoroethylene based fluoropolymer-copolymers, such as the Nafion® brand from DuPont de Nemours or the Gore-Select® brand from W.L. Gore & Associates, Inc..
- iodides with bi- or higher valent counter cations preference is however given to the use of separators different semipermeable membranes which are permeable only for monovalent cations. In this case, preference is given to diaphragmas.
- the reaction at the cathode(s) depends of course on the catholyte present in the cathode compartment(s).
- the one or more cathode compartments typically comprise an aqueous medium as catholyte.
- the reaction taking place at the cathode is in this case the reduction of water to hydrogen (under formation of hydroxyl anions; see above equation).
- the one or more cathode compartments comprise an aqueous medium with a pH of at least 8, preferably of at least 10, in particular of at least 12 and specifically of at least 14.
- an inorganic base is used to obtain the basic pH in the aqueous medium in the cathode compartment.
- Suitable and preferred inorganic bases have already been described above in context with the medium in the anode compartments; i.e. they are preferably selected from metal hydroxides, metal oxides and metal carbonates. Preference is given to the hydroxides. More preference is given to alkali metal hydroxides, in particular to sodium and potassium hydroxide.
- the cathode material is not very critical, and any material commonly used is suitable, such as stainless steel, chromium-nickel steel, platinum, nickel, bronze, tin, zirconium or carbon.
- a stainless steel electrode is used as cathode.
- the method of the invention comprises
- the aqueous solution which is introduced into the one or more anode compartments preferably contains the metal iodide in a concentration of 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, specifically from 0.2 to 0.6 mol/l, and very specifically from 0.3 to 0.5 mol/l; where the concentration refers to the amount of iodide; see above explanation.
- preferred metal iodides reference is made to what has been said above.
- the concentrations refer of course to the concentrations at the beginning of the reaction, since, as a matter of course, the concentration of the iodide decreases in the course of its conversion into the periodate.
- the above concentrations refer to the concentration in the aqueous medium continually or portion-wise introduced in the course of the reaction.
- the aqueous solution preferably contains a base.
- a base As regards preferred bases, reference is made to what has been said above.
- the counter cation in the base corresponds to the metal cation in the iodide; exception from this preference being the case where the corresponding base is not (sufficiently) water-soluble; see above explanations.
- the aqueous solution as introduced into the one or more anode compartments preferably contains the metal iodide and the base in a molar ratio of 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 and in particular in a molar ratio of from 1:10 to 1:11.
- the molar ratio is very specifically approximately 1:10, whereas in case of iodides the metal cation of which forms scarcely water-soluble or insoluble hydroxides (such as the earth alkaline metal iodides, Cu(l) iodide and Zn(ll) iodide), the molar ratio is very specifically approximately 1:11.
- the molar ratio relates to moles of iodide present in the metal iodide and moles of hydroxide present in or obtainable from the base; see above explanation.
- the aqueous solution contains an alkali metal iodide in a concentration of preferably from 0.01 to 5 mol/I, more preferably from 0.05 to 2 mol/l, in particular from 0.1 to 1 mol/l, specifically from 0.2 to 0.6 mol/l, and very specifically from 0.3 to 0.5 mol/l; and further contains a base which is an alkali metal hydroxide, where the alkali metal of the base corresponds to the alkali metal in the alkali metal iodide; where the alkali metal iodide and the base are contained in a molar ratio of preferably 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 and in particular in a molar ratio of approximately 1:10.
- the aqueous solution contains sodium or potassium iodide in a concentration of from 0.01 to 5 mol/l, preferably from 0.05 to 2 mol/l, in particular from 0.1 to 1 mol/l, specifically from 0.2 to 0.6 mol/l, and very specifically from 0.3 to 0.5 mol/l; and further contains a base which is sodium or potassium hydroxide, where the alkali metal of the base corresponds to the alkali metal in the alkali metal iodide (i.e.
- the aqueous solution contains sodium iodide in a concentration of from 0.01 to 5 mol/l, preferably from 0.05 to 2 mol/l, in particular from 0.1 to 1 mol/l, specifically from 0.2 to 0.6 mol/l, and very specifically from 0.3 to 0.5 mol/l; and further contains sodium hydroxide, where sodium iodide and sodium hydroxide are contained in a molar ratio of preferably 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 and in particular in a molar ratio of approximately 1:10.
- the aqueous solution contains an earth alkaline metal iodide in a concentration of preferably from 0.005 to 2.5 mol/l, more preferably from 0.025 to 1 mol/l and in particular from 0.05 to 0.5 mol/l; and further contains a base which is an alkali metal hydroxide; where the earth alkaline metal iodide and the base are contained in a molar ratio of preferably from 1:4 to 1:60, more preferably from 1:4 to 1:40, even more preferably from 1:10 to 1:30, particularly preferably from 1:16 to 1:24 and in particular in a molar ratio of approximately 1:22.
- the aqueous solution contains calcium iodide in a concentration of from 0.005 to 2.5 mol/l, preferably from 0.025 to 1 mol/l and in particular from 0.05 to 0.5 mol/l; and further contains a base which is sodium hydroxide; where the calcium iodide and sodium hydroxide are contained in a molar ratio of preferably from 1:4 to 1:60, more preferably from 1:4 to 1:40, even more preferably from 1:10 to 1:30, particularly preferably from 1:16 to 1:24 and in particular in a molar ratio of approximately 1:22.
- the aqueous solution contains Cu(l) iodide in a concentration of preferably from 0.01 to 5 mol/l, more preferably from 0.05 to 2 mol/l, in particular from 0.1 to 1 mol/l, specifically from 0.2 to 0.6 mol/l, and very specifically from 0.3 to 0.5 mol/l; and further contains a base which is an alkali metal hydroxide; where the Cu(l) iodide and the base are contained in a molar ratio of preferably 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 and in particular in a molar ratio of approximately 1:11.
- the anodic oxidation is preferably carried out in the absence of promoters and additives.
- Promoters in terms of the present invention are understood as anti-reducing agents and oxidation promoters, such as polarizing substances.
- Additives are understood to refer to any substance different from the starting compounds, products formed in the course of reaction, acids, bases, the electrolyte medium (generally water) and promoters.
- the presence of promoters or additives is often necessary for obtaining periodates in satisfactory yields. For instance, the method of Nam et al. as described in Journal of the Korean Chemical Society 1974, 18, 373 requires the presence of potassium dichromate as anti-reducing agent.
- chromium is to be avoided in certain applications, such as health, personal care or nutrition.
- Fluorides such as lithium fluoride or silicium fluoride are also often used; they are said to enhance the overpotential of oxygen at the anode and improve the oxidation efficiency.
- the anodic oxidation is preferably carried out in the absence of any promoters, and especially in the absence of any chromium salts and any fluorides such as lithium fluoride or silicium fluoride.
- the two or more anodes can be arranged in the same anode compartment or in separate compartments. If the two or more anodes are present in the same compartment, they can be arranged next to each other or on top of each other. If one or more anode compartments are used, they, too, can be arranged next to each other or on top of each other.
- the electrolysis apparatus may comprise more than one electrolysis cell, each cell comprising an anode and a cathode compartment.
- the electrolysis cells can be arranged next to each other or on top of each other.
- the method of the invention is suitable for reactions on laboratory scale as well as on industrial scale.
- 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 or continuous process.
- the electrolyte containing the iodide is subjected to electrolysis and after a certain time this is stopped and the product is isolated from the anode compartment
- in a continuous process design the electrolyte is passed continuously through the cell, i.e. the electrolyte containing the iodide is continually added and reacted and the resulting reaction mixture is continually removed from the process.
- the semi-continuous process design contains elements of both forms. The process is principally continuous, but the electrolyte containing the iodide is added at a certain point of time and the resulting reaction mixture is removed at a certain point of time.
- the anode and cathode compartments are generally designed as batch cells. If the reaction is carried out semi-continuously or continuously, the anode and cathode compartments are generally designed as flow cells.
- the suitable design of the electrolysis apparatus depends on whether the reaction is carried out as batch, continuous or semi-continuous process and can be determined by the skilled person.
- the electrolysis apparatus is equipped with a heat exchanger, a thermometer, a mixing means and a gas outlet off the cathode and also the anode compartment(s).
- means for continuous supply and removal e.g. in the form of recirculation loops equipped with pumps, are provided.
- the periodate is isolated from the anodic compartment. If desired, the periodate is then isolated from the aqueous medium removed from the anodic compartment. Isolation methods and work-up depend inter alia on the desired product and the reaction conditions and are principally known to those skilled in the art.
- the water-solubility of which is not high this can simply be precipitated from the aqueous reaction medium if the latter has been sufficiently basic; if necessary after concentration.
- Concentration if required, can be carried out by usual means, such as evaporation of a part of the solvent, if desired under reduced pressure, partial freeze-drying, partial reverse osmosis etc.
- the precipitated product can be isolated by usual means, such as filtration or decantation of the supernatant.
- the precipitate can then be subjected to further purification steps in order to remove non-reacted iodide, excess base, undesired side products etc., if any, such as washing with water or water- containing solvent mixtures, digestion with water or water-containing solvent mixtures or recrystallization.
- water can be removed from the aqueous reaction medium, for example by evaporation of the solvent, if desired under reduced pressure, freeze-drying, reverse osmosis, if necessary followed by evaporation of residual water, etc., and, if desired, the residue can be purified as described above for the precipitate.
- the reaction medium has not been sufficiently basic, the para-periodate is obtained after further base has been added to the reaction medium. Subsequent workup can be carried out as described above.
- the reaction medium needs to be neutralized if the reaction medium has been sufficiently basic to form the para-periodate.
- any acid can be used if the corresponding anion is not susceptible to oxidation. Suitable acids are for example sulfuric acid, hydrogensulfates, phosphoric acid, dihydrogenphosphates, hydrogenphosphates, nitric acid, silicic acid and the like.
- the counter cation thereof is preferably the same as that of the iodide used as starting product or the same as that of the base, if counter cations in base and iodide differ - provided the corresponding hydrogensulfate, dihydrogenphosphate or hydrogenphosphate is water-soluble.
- the meta-periodate can then be isolated from the aqueous medium by usual means, such as described above. Given the good water solubility of meta-periodates, it is however generally necessary to concentrate the aqueous medium before the meta-periodate precipitates.
- the periodate it is not compulsory to submit the desired periodate to purification steps. In many cases, especially if the periodate is to be used as oxidizing agent, it is sufficient to evaporate the water from the aqueous medium obtained after neutralization. In some cases, it is not even necessary to evaporate water (i.e. the aqueous medium obtained from the anodic compartment can be used as such in subsequent oxidation processes), or at least not to dryness.
- the exact composition of the periodate obtained in the method of the invention depends on the reaction and work-up conditions. If for example anodic oxidation is carried out under neutral pH and if the reaction is not followed by basic or acidic work-up in which a cation different from the counter cation in the iodide used as starting material is introduced, then a periodate is obtained in which the counter cation corresponds to that of the iodide.
- a basic work-up follows the reaction, this uses the same base as that used in the reaction or at least a base with the same alkali metal cation.
- the acid is either not a metal salt or is a salt containing the same alkali metal as the iodide, such as alkali metal hydrogensulfate, hydrogenphosphate or dihydrogenphosphate. If however a metal iodide is reacted in the presence of a base which contains a different cation (e.g.
- the combination Cul/NaOH) and/or the work-up is carried out with a base or an acid which introduces a cation different from the cation of the iodide, generally various periodates differing in their counter cations may form. If desired, these can be separated from each other, e.g. by fractionated crystallization, but for most application purposes the periodates can be subjected to further use as obtained; i.e. without further separation from each other.
- the method of the present invention allows the production of periodates in a quality suitable for certain demanding applications, such as pharmacy, cosmetics and nutrition, starting from readily available, economic and non-problematic, easy-to-handle iodides in a single step.
- Example 1 Anodic oxidation of sodium iodide to sodium periodate in a semi-continuous process
- An aqueous solution of NaOH (4 M) was circulated through the cathodic chamber.
- the reaction was carried out at room temperature for ca. 2.2 h. After electrolysis, the suspension formed in the anodic compartment was removed therefrom and the flow system was rinsed with aqueous NaHSCU and water.
- a sample of the suspension was mixed with aqueous NaHSCU until complete dissolution of the precipitate and the resulting solution was analyzed by liquid chromatography with a photo diode array (LC-PDA; LC stationary phase: C18 reversed phase), showing a yield of 94% of sodium para-periodate.
- the suspension was mixed with aqueous NaOH to complete precipitation and the precipitate was filtered, washed with cold water and dried to yield the desired sodium para-periodate in a purity of 97% (90% yield of isolated para-periodate).
- a part of the precipitated sodium para-periodate was converted into the meta-periodate by acidification with nitric acid, concentration of the obtained solution and recrystallization of the precipitate in water (130°C room temperature) to obtain sodium meta-periodate in a yield of 65%.
- Example 2 Anodic oxidation of sodium iodide to sodium periodate in a semi-continuous process
- Example 3 Anodic oxidation of sodium iodide to sodium periodate in a semi-continuous process
- Example 4 Anodic oxidation of potassium iodide to potassium periodate in a semi- continuous process
- Example 5 Anodic oxidation of Cu(l) iodide to Cu(l) periodate in a semi-continuous process The process was carried out in analogy to example 1 , using however Cu(l) iodide instead of sodium iodide. Sodium hydroxide was used as a base. The yield according to LC-PDA was 76%.
- Example 6 Anodic oxidation of sodium iodide to sodium periodate in a batch process
- the PbC>2 anode was prepared from a Pb anode by subjecting the same to electrolytical oxidation in 30% H2SO4 at 100 mA/cm 2 and 3000 C.
- Anodic oxidation of sodium iodide using a Pb or PbC>2 anode and otherwise under the same conditions as in example 6 resulted in the formation of 53% or ⁇ 54% of sodium periodate, respectively.
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US17/756,429 US20230053763A1 (en) | 2019-12-06 | 2020-12-04 | Method for preparing periodates |
EP20816492.1A EP4069889A1 (en) | 2019-12-06 | 2020-12-04 | Method for preparing periodates |
JP2022533555A JP2023504839A (en) | 2019-12-06 | 2020-12-04 | Method for preparing periodate |
CN202080094512.2A CN115003860A (en) | 2019-12-06 | 2020-12-04 | Preparation method of periodate |
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Citations (5)
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US2830941A (en) | 1958-04-15 | mehltretter | ||
EP0021826A2 (en) * | 1979-06-26 | 1981-01-07 | Chlorine Engineers Corp., Ltd. | Apparatus for electrolyzing an aqueous solution |
US5520793A (en) | 1995-04-03 | 1996-05-28 | Benham Electrosynthesis Company, Inc. | Methods of producing hydrogen iodide electrochemically |
NL1013348C2 (en) | 1999-10-20 | 2001-04-23 | Univ Eindhoven Tech | Periodate preparation by electrolytic oxidation of iodate, comprises use of lithium iodate as electrolyte and electrode comprising lead, lead alloy or electrically conducting diamond |
WO2004055243A1 (en) | 2002-12-13 | 2004-07-01 | Degussa Ag | Process for the electrolytic production of inorganic peroxy compounds |
-
2020
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- 2020-12-04 US US17/756,429 patent/US20230053763A1/en active Pending
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US2830941A (en) | 1958-04-15 | mehltretter | ||
EP0021826A2 (en) * | 1979-06-26 | 1981-01-07 | Chlorine Engineers Corp., Ltd. | Apparatus for electrolyzing an aqueous solution |
US5520793A (en) | 1995-04-03 | 1996-05-28 | Benham Electrosynthesis Company, Inc. | Methods of producing hydrogen iodide electrochemically |
NL1013348C2 (en) | 1999-10-20 | 2001-04-23 | Univ Eindhoven Tech | Periodate preparation by electrolytic oxidation of iodate, comprises use of lithium iodate as electrolyte and electrode comprising lead, lead alloy or electrically conducting diamond |
WO2004055243A1 (en) | 2002-12-13 | 2004-07-01 | Degussa Ag | Process for the electrolytic production of inorganic peroxy compounds |
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WO2023194432A1 (en) | 2022-04-05 | 2023-10-12 | Pharmazell Gmbh | Method for preparing periodates via anodic oxidation in a steady state reactor |
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