High-purity oxytetrachlorotungsten(VI) and its manufacturing method

Abstract

The present invention relates to oxytetrachlorotungsten(VI) which is characterized by its particular chemical purity and to a method for producing the same.

Description

[Technical field]

[0001] The present invention relates to tungsten(VI) oxytetrachloride, which is characterized in particular by its chemical and phase purity, and to a method for its preparation.

[0002] Tungsten(VI) oxytetrachloride is an inorganic compound of tungsten from the group of oxychlorides with the stoichiometric formula WOCl4. Tungsten(VI) oxytetrachloride is primarily used as a catalyst for the production of olefins, especially in ring-opening reactions. Further areas of use of tungsten(VI) oxytetrachloride are as a starting compound for the semiconductor industry and sol-gel processes.

[0003] DE 3347918 A1 describes a glass substrate with a thermochromic coating containing VO2 or V2O3, the optical change of which occurs within a temperature range of 25-75°C, and the transmittance of the entire solar energy in the infrared range is reduced by at least half when the coating is heated through the temperature transition range, the coating containing VO2 or V2O3 being produced by chemical decomposition and optional reduction of a chemically deposited vanadium compound, the layer being doped with an oxide of a metal having a larger ionic radius than vanadium. WOCl4 is mentioned as a suitable dopant, the addition of which makes it possible to lower the transformation temperature of the VO2 film.

[0004] N. Ozer et al., in their January 1996 article, “Optical and Electrochromic Properties of Sol-Gel Deposited Doped Tungsten Oxide Films,” describe the use of WOCl4 as a precursor compound in the production of tungsten oxide doped films.

[0005] Various methods are known to those skilled in the art for the preparation of oxytetrachlorotungsten(VI), for example by reacting tungsten(VI) oxide, tungsten(VI) chloride or sodium tungstate with thionyl chloride, or by pyrolysis of dioxotungsten(VI) chloride. Other preparation methods include boiling tungsten(VI) oxide in octachlorocyclopentene, or reacting stoichiometric amounts of tungsten(VI) oxide with tungsten(VI) chloride in a vacuum ampoule at 200°C.

[0006] F. Zado, in his article "The high yield synthesis of the Tungsten(VI) oxyhalides WOCl4, WOBr4and WO2Cl2and some observations on tungsten(VI) bromide and tungsten(V) chloride" in J. Inorg. Nucl. Chem. 25, 1115 (1963), describes the production of tungsten(VI) oxytetrachlorotungsten by placing WCl6 and WO3 in a vacuum ampoule and heating it to 100 °C. After 2 hours, the ampoule was placed in a position to allow the temperature to rise to 150 °C and the precipitate to sublime for 24 hours.

[0007] AE Castro Lunar et al., in J. Chem. Eng. Data 1983, 26, 349-350, entitled "Vapour Pressure of WOCl4", describe the preparation of oxytetrachlorotungsten(VI) by the reaction of CCl4 with WO3 at 673K.

[0008] Other known methods for preparing oxytetrachlorotungsten(VI) include, for example: WCl6+Me3Si-O-SiMe3→WOCl4+2Me3SiCl Reaction of WCl6 with organosilicon compounds by the reaction of WO3+2SOCl2→WOCl4+2SO2 and the one-step reaction of heated tungsten in oxygen-containing Cl2 gas.

[0009] However, the methods described in the prior art have the disadvantage that tungsten oxytetrachloro(VI) usually has a significant proportion of impurities, such as metal impurities and other tungsten compounds, which are manifested by further crystalline phases, and the methods can only be carried out on a laboratory scale. Therefore, the chemical purity of commercially available tungsten oxytetrachloro(VI) is 98% to 99.95% with respect to metal impurities. Indeed, most of the metal impurities can be removed by further purification steps, for example by sublimation. However, sublimation leads to increased crystal growth, so that tungsten oxytetrachloro(VI) is present in the form of large needle-like crystals with a low bulk density, which is a drawback for a range of applications. In order to obtain a suitable particle size, the crystals must be properly treated, for example by grinding methods. However, due to the low stability of tungsten oxytetrachloro(VI), this leads to the introduction of metal impurities and the formation of undesirable phases. This is also exacerbated by the formation of highly corrosive compounds, such as hydrochloric acid, during the decomposition of tungsten oxytetrachloro(VI). Furthermore, the previously required purification methods have the drawback that some impurities, in particular further tungsten compounds and some non-metals, can only be removed insufficiently or not at all.

[0010] It is therefore an object of the present invention to provide tungsten(VI) oxytetrachloride which overcomes the disadvantages of the prior art and a simple and efficient process for its preparation which can be carried out on an industrial scale and which does not require additional steps of mechanical post-treatment, such as, for example, grinding, sieving or sublimation.

[0011] This objective is achieved by providing tungsten(VI) oxytetrachloride having high chemical and crystallographic purity and specific morphology.

[0012] A first subject of the present application is therefore oxytetrachlorotungsten(VI) having a chemical purity of more than 99.95%, which oxytetrachlorotungsten(VI) has a proportion of compounds selected from the group consisting of WCl6, WO2Cl2, WO3 and WO2 of less than 0.03, this proportion being defined as the ratio of the most intense reflections of these compounds in the X-ray diffraction pattern (I(P2)100) to the most intense reflection of oxytetrachlorotungsten(VI) in the X-ray diffraction pattern (I(WOCl4)100), expressed as I(P2)100 / I(WOCl4)100.

[0013] The tungsten(VI) oxytetrachloride according to the present invention is in particular tungsten(VI) oxytetrachloride having the molecular formula WOCl4.

[0014] In the present invention, the chemical purity of a WOCl4 sample refers to the ratio of the cumulative weight percentage of the elements tungsten, chlorine and oxygen to the cumulative weight percentage of all other impurity elements in the sample. Here, the purity of a substance is expressed as the ratio of the amount of WOCl4 to the total weight of the sample, and if no other elements other than tungsten, chlorine and oxygen are detected in the sample, the chemical purity is 100%. Impurities in the sense of the present invention refer not only to metallic impurities, but also to non-metallic impurities, in particular silicon, carbon, sulfur, molybdenum, iron, chromium and nickel and their compounds.

[0015] Chemical purity must be distinguished from crystallographic purity. In the present application, crystallographic purity means the ratio of the crystalline phases of the unwanted compound to the crystalline phase of the desired compound, here tungsten(VI) oxytetrachloro. Here, the ratio of the crystalline phases can be determined, for example, using the intensities of the various phases in an X-ray diffraction pattern. Suitable recordings can be made on powder samples, for example, using an apparatus from Malvern-PANalytical (X'Pert-MPD with semiconductor detector, 40 KV / 40 mA, Cu LFF X-ray tube with Ni filter).

[0016] Besides the aforementioned chemical impurities, conventional oxytetrachlorotungsten(VI) may have further compounds, such as WCl6, and optionally further tungsten oxides as so-called secondary phases. These oxides are mainly the similar oxides WO2Cl2, WO3 and WO2, which have a different crystal structure from oxytetrachlorotungsten(VI) and are detectable by X-ray diffraction. In a particularly preferred embodiment, the oxytetrachlorotungsten(VI) according to the invention is substantially free of further tungsten compounds, in particular free of further tungsten oxide compounds. Preferably, the oxytetrachlorotungsten(VI) according to the invention is substantially free of compounds selected from the group consisting of WCl6, WO2Cl2, WO3 and WO2. The proportion of such further compounds can be defined by the intensity ratio of the oxytetrachlorotungsten(VI) main phase and the aforementioned secondary phases. The main and secondary phases can be identified by their reflection intensities in the X-ray diffraction pattern, which are shown as impulses per angle [2θ°] in the X-ray diffraction pattern. In a particularly preferred embodiment, the ratio of the reflection with the highest intensity of the secondary phase (I(P2)100) to the reflection with the highest intensity of the tungsten(VI) main phase (I(WOCl4)100), expressed as I(P2)100 / I(WOCl4)100, is preferably less than 0.02, particularly preferably 0.001 to 0.02, in particular 0.001 to 0.01, each measured by X-ray diffraction. The tungsten(VI) oxytetrachloromethane according to the invention is considered to be substantially free of compounds selected from the group consisting of WCl6, WO2Cl2, WO3 and WO2 and referred to in the present invention as secondary phases, if the ratio of the main phase to the secondary phase, as defined above, is less than or equal to 0.001. In a further preferred embodiment, no secondary phases are detectable. The proportion of further tungsten compounds is determined here by X-ray diffraction methods and is measured, for example, on powder samples using an apparatus from Malvern-PANalytical (X'Pert-MPD with semiconductor detector, 40 KV / 40 mA, Cu LFF X-ray tube with Ni filter).

[0017] In a preferred embodiment, the tungsten(VI) oxytetrachloride according to the invention has a chemical purity of 99.99% or more, preferably 99.995% or more, particularly preferably 99.999% or more.

[0018] Conventional tungsten oxytetrachloride (VI) generally has a series of chemical impurities that may adversely affect the further use of tungsten oxytetrachloride (VI). These chemical impurities are, depending on the production method, in particular silicon and its compounds, sulfur and its compounds, as well as carbon, molybdenum and iron. In contrast, tungsten oxytetrachloride (VI) according to the present invention is characterized by a low impurity level. In a preferred embodiment, tungsten oxytetrachloride (VI) according to the present invention contains silicon and / or silicon compounds in an amount of less than 50 ppm, preferably less than 25 ppm, particularly preferably less than 5 ppm, where these data are each based on the total weight of tungsten oxytetrachloride (VI).

[0019] In a further preferred embodiment, the tungsten(VI) oxytetrachloride according to the invention comprises sulfur and / or sulfur compounds in an amount of less than 100 ppm, preferably less than 30 ppm, particularly preferably less than 10 ppm, where these data are each based on the total weight of the tungsten(VI) oxytetrachloride.

[0020] The proportion of metal impurities other than silicon is generally less than 100 ppm, preferably less than 70 ppm, particularly preferably less than 50 ppm, where each of these data is based on the total weight of tungsten oxytetrachloro(VI).Metal impurities can be, for example, elements of the second and third main groups, refractory metals, in particular iron, chromium, nickel and molybdenum.In a particularly preferred embodiment, the tungsten oxytetrachloro(VI) according to the invention has a proportion of molybdenum and / or its compounds of less than 20 ppm, preferably less than 10 ppm, particularly preferably less than 5 ppm, respectively, based on the total weight of tungsten oxytetrachloro(VI).

[0021] Also preferred is an embodiment in which the tungsten(VI) oxytetrachloromethane according to the invention comprises carbon in an amount of less than 200 ppm, preferably less than 100 ppm, particularly preferably less than 40 ppm, where these data are each based on the total weight of the tungsten(VI) oxytetrachloromethane.

[0022] In addition to its high chemical and crystallographic purity, the tungsten oxytetrachloride (VI) according to the present invention is further characterized by its morphology. Conventional tungsten oxytetrachloride (VI) generally exists in the form of large needle-like crystals, whereas this morphology is surprisingly not observed in the tungsten oxytetrachloride (VI) according to the present invention. Thus, in a preferred embodiment, the tungsten oxytetrachloride (VI) according to the present invention exists in the form of a fine powder, and 90% of all powder particles have a particle size of 100 μm or less, preferably 70 μm or less, as measured by optical microscopy, where the particle size represents the longest dimension of the particle. Here, the percentage is relative to the total number of powder particles. Surprisingly, it has been found that the specific morphology of the tungsten oxytetrachloride (VI) according to the present invention makes it possible to improve the dissolution kinetics of the tungsten oxytetrachloride (VI) in further applications.

[0023] Due to the specific morphology of the tungsten(VI) oxytetrachloride according to the invention, it was further possible to achieve a distinct improvement in bulk density (also sometimes called bulk specific gravity). In a preferred embodiment, the tungsten(VI) oxytetrachloride according to the invention has a bulk density of 0.5 g / cm 3 where the bulk density ρ Sch is the formula ρ Sch = m / V Sch According to the bulk weight m and the bulk occupied volume V Sch It is defined as the ratio of β-aminobutyric acid to β-aminobutyric acid and can be measured in accordance with ASTM B329-06.

[0024] A further subject of the invention is a method for producing oxytetrachlorotungsten (VI) according to the invention, characterized in that in a first step a) metallic tungsten is reacted with chlorine gas and oxygen at a temperature T(1) and the resulting product mixture is oxidized in a further step b) in the presence of an oxidizing agent at a temperature T(2) to obtain oxytetrachlorotungsten (VI) according to the invention.

[0025] The metallic tungsten used in step a) is preferably a metal powder having a particle size D90 of less than 300 μm, preferably less than 150 μm, as measured according to ASTM B822. Note that the D90 value of the particle size refers to the proportion of particles having a particle size less than a specified value.

[0026] The reaction of step a) of the process according to the invention is preferably carried out at a temperature T(1) between 600 and 1000°C.

[0027] Without being bound by any particular theory, it is assumed in the present invention that in step a) of the method according to the present invention, a mixture of tungsten oxytetrachlorotungsten (VI) and tungsten chloride (VI) is produced by the reaction of tungsten metal with chlorine gas and oxygen. In the method according to the present invention, it has surprisingly been found that in a further step, the obtained tungsten chloride (VI) can be selectively oxidized to tungsten oxytetrachlorotungsten (VI), thereby obtaining tungsten oxytetrachlorotungsten (VI) with high purity and specific morphology.

[0028] The method according to the invention further provides the advantage that tungsten(VI) oxytetrachloride can be obtained with high chemical and crystallographic purity, and therefore further post-treatment steps, such as sublimation, can be omitted. Therefore, preferred are embodiments of the method according to the invention in which further purification and / or processing steps, in particular sublimation and / or grinding, are omitted. Without being bound to a particular theory, it is assumed that the omission of additional processing steps, such as sublimation, grinding or sieving, contributes to the fact that the method according to the invention provides tungsten(VI) oxytetrachloride that is present in the form of small particles, in contrast to conventional tungsten(VI) oxytetrachloride.

[0029] The oxidizing agent used in step b) is preferably selected from the group consisting of oxygen, water and water vapor. Particularly preferred oxidizing agents used in step b) of the method according to the invention are water or water vapor. Preferably, when using water as oxidizing agent in step b) of the method according to the invention, the oxidation is carried out at a relative atmospheric humidity of 20% to 80%, preferably 40% to 60%.

[0030] The oxidation of tungsten chloride compounds is conventionally carried out at temperatures of 300 ° C or higher. It has surprisingly been found in the process according to the invention that the oxidation can also be carried out at significantly lower temperatures without the formation of higher oxides or oxychlorides, such as, for example, WO2Cl2 or WO3, and without loss of yield, especially when using water as oxidizing agent. Therefore, preferred is an embodiment of the process, in which the oxidation in step b) is carried out at a temperature T(2) between 0 and 80 ° C, preferably between 0 and 60 ° C, for a period preferably between 5 min and 50 h.

[0031] Furthermore, contrary to common expectations, it has been demonstrated that it is advantageous to carry out the reaction of tungsten metal with oxygen and chlorine gas in an atmosphere with a substoichiometric ratio of oxygen to tungsten metal. Therefore, preferred are embodiments in which oxygen in step a) is used in a substoichiometric ratio. Preferably, the stoichiometric ratio of oxygen to tungsten metal in step a) of the method according to the invention is between 0.85 and 0.97, particularly preferably between 0.85 and 0.9.

[0032] A series of methods for preparing oxytetrachlorotungsten(VI) known in the prior art are based on the use of organic compounds, in particular organosulfur compounds and organosilicon compounds.In the present invention, it has surprisingly been found that it is possible to obtain high purity oxytetrachlorotungsten(VI) under mild conditions without using such compounds, some of which are harmful to health.Therefore, preferred are embodiments of the method according to the present invention that do not use sulfur compounds and / or silicon compounds and / or chlorinated hydrocarbons in the method according to the present invention.

[0033] The tungsten oxytetrachloro(VI) produced by the method according to the invention differs from the tungsten oxytetrachloro(VI) produced by the conventional methods not only in terms of its purity but also in particular in terms of its morphology. Therefore, a further subject of the invention is the tungsten oxytetrachloro(VI) produced by the method according to the invention. The tungsten oxytetrachloro(VI) produced by the method according to the invention is characterized in that 90% of all particles have a particle size of 100 μm or less, preferably 70 μm or less, as measured by optical microscopy, where the percentage is based on the total number of particles. Here, the particle size refers to the longest dimension of the particle.

[0034] A further subject of the invention is the use of the tungsten(VI) oxytetrachloromethane according to the invention or obtainable by the process according to the invention as a catalyst in chemical reactions, in particular as a catalyst in the preparation of functionalized hydrocarbons, in the semiconductor industry and / or in sol-gel processes, in particular for the preparation of electrochromic coatings.

[0035] The present invention will be described in more detail with reference to the following examples and drawings, but it should be understood that these do not limit the concept of the invention in any way. [Brief description of the drawings]

[0036] [Figure 1] FIG. 2 is a diagram showing an X-ray diffraction pattern of oxytetrachlorotungsten (VI) of Comparative Example 1. [Diagram 2] FIG. 2 is an optical microscope photograph of oxytetrachlorotungsten (VI) of Comparative Example 1. [Diagram 3] FIG. 2 shows an X-ray diffraction pattern of oxytetrachlorotungsten (VI) of Comparative Example 2. [Figure 4] FIG. 2 is an optical microscope photograph of oxytetrachlorotungsten (VI) of Comparative Example 2. [Diagram 5]FIG. 2 shows an X-ray diffraction pattern of oxytetrachlorotungsten (VI) of Comparative Example 3. [Figure 6] FIG. 2 shows the X-ray diffraction pattern of the intermediate of Test 4.0 according to the present invention. [Figure 7] FIG. 2 shows an optical microscope photograph of an intermediate of Test 4.0 according to the present invention. [Figure 8] FIG. 2 shows the X-ray diffraction pattern of the product of test 4.2 according to the present invention. [Figure 9] FIG. 2 shows an optical microscope photograph of the product of test 4.2 according to the invention.

[0037] Working Example 1. Comparative Example 1 Tungsten oxytetrachloride (VI) was produced according to the following reaction scheme.

[0038] WCl6+Me3Si-O-SiMe3→WOCl4+2Me3SiCl (Comparative Example 1)

[0039] The analyses of the obtained oxytetrachlorotungsten(VI) including chemical purity, detected crystal phases, particle size, and bulk density are summarized in Table 1.

[0040] As is clear from FIG. 1, which shows the X-ray diffraction pattern of the obtained oxytetrachlorotungsten(VI), not only the target compound but also a significant proportion of WO2Cl2 was present.

[0041] 2a and 2b show optical micrographs of tungsten(VI) oxytetrachloride prepared according to the formula of Comparative Example 1, in which the needle-like morphology of the crystals is clearly visible, and less than 40% of the total particles have a size of less than 100 μm.

[0042] 2. Comparative Example 2 As a further comparative example, oxytetrachlorotungsten (VI) was produced according to the following reaction scheme.

[0043] WO3 + 2SOCl2 → WOCl4 + 2SO2 (Comparative Example 2)

[0044] The analyses of the obtained oxytetrachlorotungsten(VI) including chemical purity, detected crystal phases, particle size, and bulk density are summarized in Table 1.

[0045] The X-ray diffraction pattern of the product shows the presence of the desired oxytetrachlorotungsten(VI) as well as WO2Cl2 as a by-product (Figure 3).

[0046] FIG. 4 shows an optical microscope photograph of oxytetrachlorotungsten(VI) prepared according to the formula of Comparative Example 2, in which the needle-like morphology of the crystals is clearly visible, and less than 10% of the total particles have a size of less than 100 μm.

[0047] 3. Comparative Example 3 As a further comparison, tungsten(VI) oxytetrachloro was produced in a single step at 800°C according to the following reaction scheme:

[0048] W+2Cl2+0.5O2→WOCl4 (Comparative example 3)

[0049] The analyses of the obtained oxytetrachlorotungsten(VI) including chemical purity, detected crystal phases, particle size, and bulk density are summarized in Table 1.

[0050] The resulting oxytetrachlorotungsten(VI) shows an X-ray diffraction pattern (Figure 5) containing not only the desired oxytetrachlorotungsten(VI) but also significant amounts of WCl6 and WO2Cl2. It should be noted that in this test, WO2Cl2 is the main phase, and oxytetrachlorotungsten(VI) is only a secondary phase. In a reproduction test under the same conditions, X-ray diffraction analysis confirmed the appearance of varying amounts of these three compounds. Pure oxytetrachlorotungsten(VI) could not be produced in the one-step reaction.

[0051] Optical micrographs of oxytetrachlorotungsten(VI) prepared according to the formula of Comparative Example 3 also clearly show the needle-like morphology of the crystals, with less than 50% of the total particles having a size less than 100 μm.

[0052] [Table 1]

[0053] 4. Examples of the Present Invention Tungsten(VI) oxytetrachloride was prepared according to the invention in a two-stage process, in which in the first step a) tungsten metal powder having a particle size D90 of less than 150 μm was reacted in a Cl2 gas stream at 800 ° C with the addition of oxygen in a stoichiometric ratio of 0.85 relative to the amount of tungsten used.

[0054] The reaction product obtained contained a significant amount of WCl6 in addition to the desired tungsten(VI) oxytetrachloromethane due to the substoichiometric addition of oxygen (stoichiometric ratio 0.85).

[0055] This product mixture of WOCl4 and WCl6 was reacted according to step b) of the method according to the invention under different oxidation conditions to obtain tungsten oxytetrachloride(VI) according to the invention, where the oxidation conditions and all the relevant analytical results of the powders produced in tests 4.1 to 4.8 are summarized in Table 2. The oxidation was carried out in an air-conditioned cabinet filled with water, in which the relative atmospheric humidity and temperature were controlled as shown in Table 2.

[0056] The analysis of the obtained oxytetrachlorotungsten(VI) including chemical purity, crystal phases detected, particle size and bulk density are evident from Table 2, Test 4.0 et seq.

[0057] [Table 2]

[0058] Figure 6 shows the X-ray diffraction pattern of the intermediate obtained after step a) of test 4.0. As is evident from this pattern, no further tungsten compounds are present other than the aforementioned compounds WOCl4 and WCl6.

[0059] Figure 7 shows an optical microscope photograph of the product after step a). Unlike conventional manufacturing methods, the powder is not in the form of needle-like crystals. More than 95% of the total number of powder particles have a particle size of less than 100 μm with respect to the longest longitudinal dimension of the particle.

[0060] Figure 8 shows the X-ray diffraction pattern of the product obtained after step b) of test 4.2, which clearly shows that complete oxidation of WCl6 has occurred to give the desired WOCl4.

[0061] As shown in the optical micrograph of Figure 9, the morphology of tungsten(VI) oxytetrachloromethane was not affected by oxidation. In the final product of Test 4.2, tungsten(VI) oxytetrachloromethane was also present in the form of small particles, with more than 95% of the total number of powder particles having a particle size of less than 100 μm.

[0062] As is evident from Table 2, in tests 4.1 to 4.6, by controlling the oxidation conditions, especially in the second step of the method according to the invention, it was possible to produce oxytetrachlorotungsten (VI) according to the invention with a chemical purity of more than 99.95% and with no secondary phases detected or with a ratio of I(P2)100 / I(WOCl4)100 of less than 0.03. When departing from the favorable process range of oxidation, as in tests 4.7 and 4.8, a rapidly increasing amount of WO2Cl2 is formed, which can be seen by an increase in the ratio of I(P2)100 / I(WOCl4)100.

[0063] The proportion of crystalline tungsten compounds is confirmed by X-ray diffraction, e.g. measured on powder samples using a Malvern-PANalytical device (X'Pert-MPD with semiconductor detector, 40 KV / 40 mA, Cu LFF X-ray tube with Ni filter). In the qualitative analysis of the X-ray diffraction patterns, the confirmed reflections are assigned to those of tungsten compounds known from the literature.

[0064] Trace analysis of chemical impurities was performed by ICP OES using the following analytical instruments: PQ 9000 (Analytik Jena) or Ultima 2 (Horiba). The determination of chemical purity is mathematically determined as the difference in weight percent between a hypothetical 100% impurity-free sample containing only the elements tungsten, chlorine and oxygen and the sum of all impurities including all metals, nonmetals and all remaining elements including Si.

Claims

1. Tungsten(VI) oxytetrachloride, said oxytetrachloride having a chemical purity of greater than 99.95% and an X-ray diffraction pattern with a ratio I(P2)100 / I(WOCl4)100 of less than 0.03, where I(P2)100 is the reflection with the highest intensity of a secondary phase and the most intense reflection of either WCl6, WO2Cl2, WO3 or WO2, and I(WOCl4)100 is the most intense reflection of oxytetrachloride in the X-ray diffraction pattern.

2. The ratio I(P2)100 / I(WOCl ４ 2. The tungsten (VI) oxytetrachloride according to claim 1, wherein the tungsten (VI) oxide is 0.02 or less.

3. The tungsten (VI) oxytetrachloromethane according to claim 1 or 2, wherein the tungsten (VI) oxytetrachloromethane has a chemical purity of 99.99% or more.

4. The tungsten oxytetrachlorotungsten (VI) according to any one of claims 1 to 3, wherein the tungsten oxytetrachlorotungsten (VI) contains silicon and / or silicon compounds in an amount of less than 50 ppm, each based on the total weight of the tungsten oxytetrachlorotungsten (VI).

5. The tungsten (VI) oxytetrachlorotungsten (VI) according to any one of claims 1 to 4, wherein the tungsten (VI) oxytetrachlorotungsten (VI) contains sulfur and / or sulfur compounds in an amount of less than 100 ppm each based on the total weight of the tungsten (VI) oxytetrachlorotungsten (VI).

6. 6. The tungsten oxytetrachloromethane (VI) of claim 1, wherein the tungsten oxytetrachloromethane (VI) has a molybdenum content of less than 20 ppm and / or its compounds, based on the total weight of the tungsten oxytetrachloromethane (VI).

7. The tungsten oxytetrachloromethane (VI) according to any one of claims 1 to 6, wherein the proportion of metal impurities in the tungsten oxytetrachloromethane (VI) is less than 100 ppm each based on the total weight of the tungsten oxytetrachloromethane (VI).

8. The tungsten (VI) oxytetrachloromethane according to any one of claims 1 to 7, wherein the tungsten (VI) oxytetrachloromethane contains carbon in an amount of less than 200 ppm, based on the total weight of the tungsten (VI) oxytetrachloromethane.

9. The tungsten (VI) oxytetrachloride according to any one of claims 1 to 8, wherein the tungsten (VI) oxytetrachloride is present in the form of a powder, and 90% of all powder particles have a particle size of 100 μm or less as measured by optical microscopy.

10. The tungsten oxytetrachloride (VI) is 0.5 g / cm ３ The tungsten oxytetrachloride (VI) of any one of claims 1 to 9, having a bulk density of more than

11. 11. A method for producing oxytetrachlorotungsten (VI) according to any one of claims 1 to 10, characterized in that in a first step a) metallic tungsten is reacted with chlorine gas and oxygen, and in a further step b) the resulting product mixture is oxidized in the presence of an oxidizing agent to obtain oxytetrachlorotungsten (VI).

12. The method of claim 11 , wherein the oxidant in step b) is selected from the group consisting of oxygen, water, and water vapor.

13. 13. The method according to claim 11 or 12, wherein the oxidation in step b) is carried out using water as oxidant at a relative atmospheric humidity of between 20% and 80%.

14. The process according to any one of claims 11 to 13, wherein the oxidation in step b) is carried out at a temperature of from 0 to 80°C.

15. The method according to any one of claims 11 to 14, wherein the oxygen in step a) is used in a sub-stoichiometric ratio.

16. 11. Use of tungsten(VI) oxytetrachloride according to any one of claims 1 to 10 as a catalyst in chemical reactions.

Images