High-purity tungsten(VI) oxytetrachloride and method for manufacturing the same

Abstract

The present invention relates to tungsten(VI) oxytetrachloride characterized by high chemical purity and a method for producing the same.

Description

Technology Field

[0001] The present invention relates to tungsten(VI) oxytetrachloride characterized by specific chemical purity and phase purity, and also to a method for manufacturing the same. Background Technology

[0002] Tungsten (VI) oxytetrachloride is an inorganic compound of tungsten in the oxychloride group having the stoichiometric formula WOCl4. Tungsten (VI) oxytetrachloride is primarily used for the production of olefins, particularly as a catalyst for ring-opening reactions. Additional applications of tungsten (VI) oxytetrachloride can be found in the semiconductor industry and as a starting compound in sol-gel processes.

[0003] DE 33 47 918 describes a glass substrate having a thermochromic coating containing VO2 or V2O3, having variable transmittance to solar light, wherein the optical change occurs within a temperature range of 25 to 75°C and the transmittance to all solar energy in the infrared range decreases by at least twofold when the coating is heated over its temperature transition range. The coating containing VO2 or V2O3 is a layer formed by the chemical decomposition and optional reduction of a chemically deposited vanadium compound doped with an oxide of a metal having an ionic radius greater than that of vanadium. A suitable dopant identified is WOCl4, which can lower the transition temperature of the VO2 film upon addition.

[0004] Paper [N. Oezer et al., "Optical and Electrochromic Properties of Sol-Gel Deposited Doped Tungsten Oxide Films" [January 1996] describes the use of WOCl4 as a precursor compound in the manufacture of tungsten oxide-doped films.

[0005] A person skilled in the art is aware of various methods for producing tungsten (VI) oxytetrachloride, for example, by the reaction of tungsten (VI) oxide, tungsten (VI) chloride, or sodium tungstate with thionyl chloride, or by the thermal decomposition of tungsten (VI) diooxide dichloride. Other methods of production include boiling tungsten (VI) oxide in octachlorocyclopentene or reacting stoichiometric amounts of tungsten (VI) oxide with tungsten (VI) chloride in an evacuated ampoule at 200°C.

[0006] Literature [ J. Inorg. Nucl. Chem. [F. Zado, published in the paper [25, 1115 (1963)] "The high yield synthesis of the tungsten(VI) oxyhalides WOCl 4 , WOBr 4 and WO 2 Cl 2 and some observations on tungsten(VI) bromide and tungsten(V) chloride" [] describes the preparation of tungsten (VI) oxytetrachloride by sealing WCl6 and WO3 in an evacuated ampoule and heating the ampoule to 100°C. The temperature was raised to 150°C after 2 hours, and the ampoule was placed so that the deposited product could sublimate over a period of 24 hours.

[0007] Literature [AE Castro Lunar et al., J. Chem. Eng. Data [1983, 26, 349-350] includes a title "Vapour Pressure of WOCl 4 " The preparation of tungsten (VI) oxytetrachloride by the reaction of CCl4 and WO3 at 673 K is described below.

[0008] Examples of other known methods for preparing tungsten(VI) oxytetrachloride include the reaction of WCl6 with an organosilicon compound according to the following formula:

[0009] WCl6+ Me3Si-O-SiMe3→ WOCl4+ 2 Me3SiCl,

[0010] Use of the above-mentioned thionyl chloride according to the following formula:

[0011] WO3 + 2 SOCl2 → WOCl4 + 2 SO2,

[0012] and also a one-step reaction of tungsten heated in oxygen-containing Cl2 gas.

[0013] However, the method described in the prior art has the disadvantage that tungsten(VI) oxytetrachloride typically contains a significant fraction of impurities, such as metallic impurities and other tungsten compounds, which appear as additional crystalline phases, and that the method can only be used on a laboratory scale. Accordingly, the chemical purity of commercially available tungsten(VI) oxytetrachloride is specified as 98% to 99.95% due to metallic impurities. Most of the metallic impurities can, of course, be removed by additional purification steps, such as sublimation. However, sublimation results in increased crystal growth, causing tungsten(VI) oxytetrachloride to take the form of large needle-shaped crystals with low bulk density, which is a disadvantage in a series of applications. To obtain a suitable particle size, the crystals must be appropriately processed, for example, by a grinding method. However, due to the low stability of tungsten(VI) oxytetrachloride, this leads to the introduction of metallic impurities and the formation of unwanted phases. An additional aggravating factor is that the decomposition of tungsten (VI) oxytetrachloride is accompanied by the formation of highly corrosive compounds such as hydrochloric acid. The purification method typically required also has the disadvantage that some impurities, particularly additional tungsten compounds and certain non-metals, cannot be sufficiently removed, even if they are removed.

[0014] Accordingly, the object of the present invention is to provide tungsten(VI) oxytetrachloride that overcomes the disadvantages of the prior art, and also a simple and efficient method of manufacturing the same that can be implemented on an industrial scale and works without additional steps of mechanical post-processing, such as grinding, sieving, or sublimation.

[0015] The above objective is achieved by providing tungsten (VI) oxytetrachloride with high chemical and crystallographic purity and specific morphology. Specific details for implementing the invention

[0016] Accordingly, the first subject of the present application is tungsten(VI) oxytetrachloride having a chemical purity of greater than 99.95%, wherein the tungsten(VI) oxytetrachloride has a fraction of a compound selected from the group consisting of WCl6, WO2Cl2, WO3, and WO2, defined as the ratio of the reflection with maximum intensity (I(P2)100) of one of the compounds with maximum intensity (I(P2)100) in the X-ray diffraction pattern of tungsten(VI) oxytetrachloride in the X-ray diffraction pattern to the reflection with maximum intensity (I(WOCl4)100) of the tungsten(VI) oxytetrachloride in the X-ray diffraction pattern

[0017] The tungsten(VI) oxytetrachloride according to the present invention is, more specifically, the tungsten(VI) oxytetrachloride of the empirical formula WOCl4.

[0018] In relation to the present invention, the chemical purity of a WOCl4 sample refers to the ratio of the cumulative weight ratio of tungsten, chlorine, and oxygen elements to the cumulative weight ratio of all other impurity elements in the sample. The purity of the material is expressed as the quantitative ratio of WOCl4 to the total weight of the composition, wherein if no other elements other than tungsten, chlorine, and oxygen are present, the material has 100% chemical purity. In the context of the present invention, impurities include not only metallic impurities but also non-metallic impurities, in particular silicon, carbon, sulfur, molybdenum, nickel, and their compounds.

[0019] Chemical purity should be distinguished from crystallographic purity. In relation to the present application, the crystallographic purity of a material is the ratio of the crystal phase of an unwanted compound to the crystal phase of the target compound, in the present invention, tungsten(VI) oxytetrachloride. Here, the ratio of the crystal phases can be determined, for example, by the intensity of the various phases in an X-ray diffraction pattern. Suitable recording can be performed on a powder sample using, for example, an instrument from Malvern-PANalytical (semiconductor detector, Cu LFF X-ray tube of 40 KV / 40 mA, X'Pert-MPD with Ni filter).

[0020] Conventional tungsten(VI) oxytetrachloride, in addition to the specified chemical impurities, may contain additional compounds, such as WCl6, and optionally additional tungsten oxides as so-called secondary phases. These oxides are primarily the associated oxides WO2Cl2, WO3, and WO2, which have crystal structures different from tungsten(VI) oxytetrachloride and are detectable via X-ray diffraction. In one particularly preferred embodiment, the tungsten(VI) oxytetrachloride of the present invention substantially does not contain additional tungsten compounds and, in particular, additional tungsten oxide compounds. Preferably, the tungsten(VI) oxytetrachloride of the present invention substantially does not contain compounds selected from the group consisting of WCl6, WO2Cl2, WO3, and WO2. The fraction of such additional compounds as mentioned above may be defined by the intensity ratio of the major tungsten(VI) oxytetrachloride phase to the specified secondary phase. The principal phase and the secondary phase can be identified by their reflection intensity, which is represented as an impulse per angle [°2θ] in the X-ray diffraction pattern. In one particularly preferred embodiment, when determined by X-ray diffraction in each case, the ratio of the reflection having the highest intensity of the secondary phase (I(P2)100) to the reflection having the highest intensity of the principal tungsten (VI) oxytetrachloride phase (I(WOCl4)100), expressed as I(P2)100 / I(WOCl4)100, is preferably less than 0.02, more preferably 0.001 to 0.02, and more particularly 0.001 to 0.01. In relation to the present invention, when the ratio of the major phase and the secondary phase as defined above is 0.001 or less, the tungsten(VI) oxytetrachloride of the present invention is selected from the group consisting of WCl6, WO2Cl2, WO3 and WO2 and is considered to substantially not contain the compound described as the secondary phase in relation to the present invention. In a further preferred embodiment, no secondary phase is detectable.Here, the fraction of additional tungsten compounds is determined by X-ray diffraction, which is used to determine the powder sample using, for example, an instrument from Malvern-Panelistic (X'Pert-MPD with a semiconductor detector, 40 KV / 40 mA Cu LFF X-ray tube, and Ni filter).

[0021] In one preferred embodiment, the tungsten(VI) oxytetrachloride of the present invention has a chemical purity of 99.99% or more, preferably 99.995% or more, more preferably 99.999% or more.

[0022] Conventional tungsten(VI) oxytetrachloride generally contains a series of chemical impurities that may impede further use of tungsten(VI) oxytetrachloride. These chemical impurities, depending on the method of manufacture, are, more specifically, silicon and its compounds, sulfur and its compounds, and also carbon, molybdenum, and iron. In contrast, the tungsten(VI) oxytetrachloride of the present invention is characterized by low levels of impurities. In one preferred embodiment, the tungsten(VI) oxytetrachloride of the present invention contains silicon and / or a compound of silicon in an amount of less than 50 ppm, preferably less than 25 ppm, more preferably less than 5 ppm, wherein the data are based on the total weight of the tungsten(VI) oxytetrachloride in each case.

[0023] In a further preferred embodiment, the tungsten(VI) oxytetrachloride of the present invention contains sulfur and / or a compound of sulfur in an amount of less than 100 ppm, preferably less than 30 ppm, more preferably less than 10 ppm, wherein the data are based on the total weight of the tungsten(VI) oxytetrachloride in each case.

[0024] The fraction of metallic impurities other than silicon is less than 100 ppm overall, preferably less than 70 ppm, more preferably less than 50 ppm, wherein the data is based on the total weight of tungsten(VI) oxytetrachloride in each case. The metallic impurities may be, for example, elements of the second and third main groups, refractory metals, more specifically iron, chromium, nickel, and molybdenum. In one particularly preferred embodiment, the tungsten(VI) oxytetrachloride of the present invention has a fraction of molybdenum and / or its compounds of less than 20 ppm, preferably less than 10 ppm, more preferably less than 5 ppm, based on the total weight of tungsten(VI) oxytetrachloride in each case.

[0025] Likewise, an embodiment in which the tungsten(VI) oxytetrachloride of the present invention contains carbon in an amount of less than 200 ppm, preferably less than 100 ppm, more preferably less than 40 ppm, wherein the data is based on the total weight of the tungsten(VI) oxytetrachloride in each case.

[0026] In addition to its high chemical and crystallographic purity, the tungsten(VI) oxytetrachloride of the present invention is also characterized by its morphology. While conventional tungsten(VI) oxytetrachloride generally takes the form of large needle-shaped crystals, surprisingly, this was not observed in the tungsten(VI) oxytetrachloride of the present invention. Accordingly, in one preferred embodiment, the tungsten(VI) oxytetrachloride of the present invention takes the form of a fine powder, wherein 90% of all powder particles have a particle size of 100 μm or less, preferably 70 μm or less, as determined by optical microscopy, where particle size represents the longest extension of the particle. Here, the percentage figures are based on the total number of powder particles. Surprisingly, as a result of the specific morphology of the tungsten(VI) oxytetrachloride of the present invention, it has been found possible to improve the dissolution kinetics of tungsten(VI) oxytetrachloride in further applications.

[0027] Furthermore, as a result of the specific morphology of the tungsten(VI) oxytetrachloride of the present invention, it is possible to achieve a distinct improvement in bulk density, sometimes also referred to as bulk weight. In one preferred embodiment, the tungsten(VI) oxytetrachloride of the present invention has a density of 0.5 g / cm³ 3 It has excess bulk density. Bulk density ρ b is, food Accordingly, the volume of the occupied bed V b Mass of the bed for m It is defined as the ratio and can be determined by ASTM B329-06.

[0028] Further subject of the present invention is a method for producing tungsten (VI) oxytetrachloride of the present invention. The method of the present invention is characterized by the fact that in step a) a tungsten metal is reacted with chlorine gas and oxygen at temperature T (1), and in step b) a mixture of products is subjected to oxidation at temperature T (2) in the presence of an oxidizing agent to provide tungsten (VI) oxytetrachloride of the present invention.

[0029] The tungsten metal used in step a) is preferably a metal powder having a particle size D90 of less than 300 μm, as determined by ASTM B822, preferably having a particle size D90 of less than 150 μm. Here, particle size D90 represents the fraction of particles having a particle size less than a specified value.

[0030] The reaction in step a) of the method of the present invention is preferably carried out at a temperature T (1) of 600 to 1000°C.

[0031] Although not intended to be bound by any specific theory, in relation to the present invention, the reaction of tungsten metal with chlorine gas and oxygen in step a) of the method of the present invention is thought to produce a mixture of tungsten(VI) oxytetrachloride and tungsten(VI) chloride. In relation to the method of the present invention, surprisingly, it has been found that the obtained tungsten(VI) chloride can be selectively oxidized to tungsten(VI) oxytetrachloride in an additional step to provide tungsten(VI) oxytetrachloride having high purity and a specific morphology.

[0032] Furthermore, the method of the present invention provides the advantage of supplying tungsten(VI) oxytetrachloride of high chemical and crystallographic purity, and thus eliminating the need for additional post-processing steps, such as sublimation. Accordingly, an embodiment of the method of the present invention is preferred in which additional purification and / or processing steps, particularly sublimation and / or grinding, are omitted. Without being bound by any particular theory, it is thought that the omission of additional processing steps, such as sublimation, grinding, or sieving by the method of the present invention contributes to the production of tungsten(VI) oxytetrachloride existing in the form of small particles, in contrast to conventional tungsten(VI) oxytetrachloride.

[0033] The oxidizing agent used in step b) is preferably selected from the group consisting of oxygen, water, and water vapor. A particularly preferred oxidizing agent used in step b) of the method of the present invention is water or water vapor. When water is used as the oxidizing agent in step b) of the method of the present invention, oxidation is preferably carried out at a relative atmospheric humidity of 20% to 80%, more preferably 40% to 60%.

[0034] Oxidation of tungsten chloride compounds typically occurs at temperatures above 300°C. In relation to the method of the present invention, surprisingly, it has been found that oxidation can also be carried out at significantly lower temperatures without the formation of higher oxides or oxychlorides, e.g., WO2Cl2 or WO3, and without any loss in yield. Accordingly, an embodiment of the method is preferred in which the oxidation in step b) is carried out at a temperature T(2) of 0 to 80°C, preferably 0 to 60°C, preferably for a period of 5 minutes to 50 hours.

[0035] Furthermore, contrary to general expectations, it has been proven advantageous to carry out the reaction between tungsten metal and oxygen and chlorine gas under an atmosphere in which oxygen is present in a sub-stoichiometric ratio relative to tungsten metal. Accordingly, an embodiment in which oxygen is used in a sub-stoichiometric ratio in step a) is preferred. In step a) of the method of the present invention, the stoichiometric ratio of oxygen to tungsten metal is preferably 0.85 to 0.97, more preferably 0.85 to 0.9.

[0036] A series of methods known in the prior art for producing tungsten(VI) oxytetrachloride are based on the use of organic compounds, in particular organic sulfur compounds and organosilicon compounds. In connection with the present invention, surprisingly, it has been found that tungsten(VI) oxytetrachloride can be obtained in high purity under mild conditions without the use of these compounds, some of which are harmful to health. Accordingly, an embodiment of the method of the present invention is preferred in which no sulfur compounds and / or silicon compounds and / or chlorinated hydrocarbons are used in the method of the present invention.

[0037] Tungsten(VI) oxytetrachloride produced according to the method of the present invention differs from tungsten(VI) oxytetrachloride produced by conventional methods not only in terms of its purity, but particularly in terms of its morphology. Accordingly, further subject of the present invention is tungsten(VI) oxytetrachloride produced according to the method of the present invention. A characteristic of tungsten(VI) oxytetrachloride produced by the method of the present invention is that 90% of all particles have a particle size of 100 μm or less, preferably 70 μm or less, as determined by optical microscopy. Here, the percentage is based on the total number of particles. Here, particle size refers to the longest dimension of the particle.

[0038] Further objects of the present invention are the use of the tungsten(VI) oxytetrachloride of the present invention or the tungsten(VI) oxytetrachloride obtained according to the method of the present invention as a catalyst in chemical reactions, more particularly in the production of functional hydrocarbons; in the semiconductor industry, and / or in sol-gel processes, particularly for producing electrochromic coatings.

[0039] The present invention is described in more detail by the following examples and drawings, and this should not be understood as limiting the concept of the invention in any way.

[0040] 실시예:

[0041] 1. Comparative Example 1

[0042] Tungsten (VI) oxytetrachloride was prepared according to the following reaction scheme:

[0043] WCl6+ Me3Si-O-SiMe3→ WOCl4+ 2 Me3SiCl (Comp. 1)

[0044] The analysis of the obtained tungsten (VI) oxytetrachloride, including chemical purity, detected crystalline phase, particle size and bulk density, is outlined in Table 1.

[0045] As can be seen from Figure 1, which presents the X-ray diffraction pattern of the obtained tungsten (VI) oxytetrachloride, a significant fraction of WO2Cl2 was present as well as the target compound.

[0046] Figures 2a and 2b present optical microscope images of tungsten (VI) oxytetrachloride prepared according to Formula Comp. 1, where the needle-like shape of the crystals is clearly visible and less than 40% of all particles have a size of less than 100 μm.

[0047] 2. Comparative Example 2

[0048] As an additional comparative example, tungsten (VI) oxytetrachloride was prepared according to the following reaction scheme:

[0049] WO3+ 2 SOCl2→ WOCl4+ 2 SO2 (Comp. 2)

[0050] The analysis of the obtained tungsten (VI) oxytetrachloride, including chemical purity, detected crystalline phase, particle size and bulk density, is outlined in Table 1.

[0051] The X-ray diffraction pattern of the product confirms the presence of WO2Cl2 as a secondary product as well as the target tungsten (VI) oxytetrachloride (Fig. 3).

[0052] Figure 4 presents an optical microscope image of tungsten (VI) oxytetrachloride prepared according to Formula Comp. 2, where the needle-like shape of the crystals is clearly visible and less than 10% of all particles have a size of less than 100 μm.

[0053] 3. Comparative Example 3

[0054] As an additional comparative example, tungsten(VI) oxytetrachloride was prepared by a one-step reaction at 800°C according to the following reaction scheme:

[0055] W + 2 Cl2+ 0.5 O2→ WOCl4 (Comp. 3)

[0056] The analysis of the obtained tungsten (VI) oxytetrachloride, including chemical purity, detected crystalline phase, particle size and bulk density, is outlined in Table 1.

[0057] The obtained tungsten(VI) oxytetrachloride provided an X-ray diffraction pattern (Fig. 5) containing not only the target tungsten(VI) oxytetrachloride but also significant amounts of WCl6 and WO2Cl2. In this experiment, it should be noted that, in fact, WO2Cl2 constitutes the major phase, and tungsten(VI) oxytetrachloride constitutes only the secondary phase. Reproducible tests under the same conditions confirmed, according to X-ray diffraction analysis, that these three compounds occur in varying proportions. It was not possible to prepare pure-phase tungsten(VI) oxytetrachloride by a one-step reaction.

[0058] Optical microscope images of tungsten (VI) oxytetrachloride prepared according to Formula Comp. 3 also clearly show the needle-like shape of the crystals, where less than 50% of all particles have a size of less than 100 μm.

[0059]

[0060] 4. Examples of the present invention

[0061] Tungsten (VI) oxytetrachloride was prepared according to the present invention by a two-step method, wherein in the first step a), tungsten metal powder having a particle size D90 of less than 150 μm was reacted at 800°C in a Cl2 gas stream while adding oxygen at a stoichiometric ratio of 0.85 based on the amount of tungsten used.

[0062] The obtained intermediate reaction product contains a significant amount of WCl6 in addition to the target tungsten(VI) oxytetrachloride due to the substoichiometric addition of oxygen (stoichiometric ratio of 0.85).

[0063] This intermediate was reacted under various oxidation conditions according to step b) to provide the tungsten(VI) oxytetrachloride of the present invention; the oxidation conditions for the powders prepared under experiments 4.1 to 4.8 and all related analytical results are outlined in Table 2. Oxidation was carried out in a conditioning cabinet containing water, where the relative atmospheric humidity and temperature of the cabinet were controlled as shown in Table 2.

[0064] Analysis of the obtained tungsten (VI) oxytetrachloride, including chemical purity, detected crystalline phase, particle size and bulk density, can be seen from Table 2 under Experiment 4.0.

[0065]

[0066] Figure 6 presents the X-ray diffraction pattern of the intermediate from Experiment 4.0 obtained after step a). As can be seen from the pattern, no other tungsten compounds other than the specified compounds WOCl4 and WCl6 are present.

[0067] Figure 7 presents an optical microscope image of the product after step a). In contrast to conventional manufacturing methods, the powder is not in the form of needle-shaped crystals. Instead, more than 95% of the total number of powder particles have a particle size of less than 100 μm based on the longest longitudinal dimension of the particle.

[0068] Figure 8 presents the X-ray diffraction pattern of the product from Experiment 4.2 obtained after step b). As can be seen from the pattern, there was complete oxidation of WCl6 to provide the target WOCl4.

[0069] As shown by the optical microscope image in Fig. 9, the morphology of tungsten (VI) oxytetrachloride was not affected in any way by oxidation. In the final product from Experiment 4.2 as well, tungsten (VI) oxytetrachloride was in the form of small particles with a particle size of less than 100 μm for more than 95% of the total number of powder particles.

[0070] As can be seen from Table 2, in experiments 4.1 to 4.6, the tungsten(VI) oxytetrachloride of the present invention was prepared having a chemical purity of over 99.95% and, in particular, as a result of controlling the oxidation conditions during step b), containing no detectable secondary phase or containing a secondary phase with an I(P2)100 / I(WOCl4)100 ratio of less than 0.03. As in experiments 4.7 and 4.8, when the process window for oxidation is exited, a rapidly increasing amount of WO2Cl2 is formed, which becomes visible as a result of an increase in the I(P2)100 / I(WOCl4)100 ratio.

[0071] The fraction of crystalline tungsten compounds is determined by X-ray diffraction, for example, using an instrument from Malvern-Panelistic (semiconductor detector, Cu LFF X-ray tube of 40 KV / 40 mA, X'Pert-MPD with Ni filter). The reflections identified in the qualitative analysis of the X-ray diffraction pattern were included in the tungsten compound reflections known from the literature.

[0072] Trace analysis of chemical impurities was performed by ICP-OES using the analytical instrument PQ 9000 (Analytik Jena) or Ultima 2 (Horiba). The confirmed chemical purity is obtained arithmetically as the difference between a hypothetical contamination-free sample, represented as 100 wt%, and the total sum of all impurities (in wt% units), including all non-metals and Si.

Claims

Claim 1 Tungsten (VI) oxytetrachloride having a chemical purity of more than 99.95%, wherein the tungsten (VI) oxytetrachloride has a fraction of a compound selected from the group consisting of WCl6, WO2Cl2, WO3, and WO2, defined as the ratio of the reflection having the highest intensity (I(P2)100) of one of the compounds having the highest intensity (I(WOCl4)100) in the X-ray diffraction pattern of tungsten (VI) oxytetrachloride in the X-ray diffraction pattern to the reflection having the highest intensity (I(WOCl4)100) of tungsten (VI) oxytetrachloride in the X-ray diffraction pattern of WCl6, WO2Cl2, WO3, and WO2 in the X-ray diffraction pattern of less than 0.

03. Claim 2 Tungsten (VI) oxytetrachloride according to claim 1, characterized in that the tungsten (VI) oxytetrachloride has a fraction of a secondary phase of less than 0.02, 0.001 to 0.02, or 0.001 to 0.01, defined in each case by X-ray diffraction as the ratio of the reflection having the highest intensity of the secondary phase (I(P2)100) to the reflection having the highest intensity of the tungsten (VI) oxytetrachloride (I(WOCl4)100). Claim 3 Tungsten (VI) oxytetrachloride according to claim 1 or 2, characterized in that the tungsten (VI) oxytetrachloride has a chemical purity of 99.99% or more, 99.995% or more, or 99.999% or more. Claim 4 Tungsten (VI) oxytetrachloride according to claim 1 or 2, characterized in that the tungsten (VI) oxytetrachloride comprises silicon, a silicon compound, or both in an amount of less than 50 ppm, less than 25 ppm, or less than 5 ppm based on the total weight of the tungsten (VI) oxytetrachloride in each case. Claim 5 Tungsten (VI) oxytetrachloride according to claim 1 or 2, characterized in that the tungsten (VI) oxytetrachloride comprises sulfur, a compound of sulfur, or both in an amount of less than 100 ppm, less than 30 ppm, or less than 10 ppm based on the total weight of the tungsten (VI) oxytetrachloride in each case. Claim 6 Tungsten (VI) oxytetrachloride according to claim 1 or 2, characterized in that the tungsten (VI) oxytetrachloride has a fraction of less than 20 ppm, less than 10 ppm, or less than 5 ppm of molybdenum, a compound of molybdenum, or all of these, based on the total weight of the tungsten (VI) oxytetrachloride in each case. Claim 7 Tungsten (VI) oxytetrachloride according to claim 1 or 2, characterized in that the fraction of metallic impurities in the tungsten (VI) oxytetrachloride is less than 100 ppm or less than 70 ppm based on the total weight of the tungsten (VI) oxytetrachloride in each case. Claim 8 Tungsten (VI) oxytetrachloride according to claim 1 or 2, characterized in that the tungsten (VI) oxytetrachloride contains carbon in an amount of less than 200 ppm, less than 100 ppm, or less than 40 ppm based on the total weight of the tungsten (VI) oxytetrachloride in each case. Claim 9 Tungsten (VI) oxytetrachloride according to claim 1 or 2, characterized in that the tungsten (VI) oxytetrachloride is in the form of a powder, wherein 90% of all powder particles have a particle size of 100 μm or less or 70 μm or less when determined by optical microscopy. Claim 10 In claim 1 or 2, tungsten(VI) oxytetrachloride is 0.5 g / cm³ 3 Tungsten (VI) oxytetrachloride characterized by having an excess bulk density. Claim 11 A method for producing tungsten (VI) oxytetrachloride according to claim 1, characterized in that in step a) a tungsten metal is reacted with chlorine gas and oxygen, and in step b) a mixture of products is subjected to oxidation in the presence of an oxidizing agent to provide tungsten (VI) oxytetrachloride. Claim 12 A method according to claim 11, characterized in that the oxidizing agent in step b) is selected from the group consisting of oxygen, water, and water vapor. Claim 13 A method according to claim 11 or 12, characterized in that the oxidation in step b) is performed using water as an oxidizing agent at a relative atmospheric humidity of 20% to 80% or 40% to 60%. Claim 14 A method according to claim 11 or 12, characterized in that the oxidation in step b) is performed at a temperature of 0 to 80°C or 0 to 60°C. Claim 15 A method according to claim 11 or 12, characterized in that in step a), oxygen is used in a substoichiometric ratio, wherein the stoichiometric ratio of oxygen to tungsten metal is 0.8 to 0.97 or 0.85 to 0.

9. Claim 16 Tungsten (VI) oxytetrachloride obtainable by the method according to paragraph 11. Claim 17 A method of using tungsten(VI) oxytetrachloride according to any one of claims 1, 2 and 16 to produce an electrochromic coating in one or more selected from the semiconductor industry and sol-gel processes, as a catalyst in a chemical reaction, as a catalyst in the production of functional hydrocarbons, in one or more selected from the semiconductor industry and sol-gel processes.

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