HIGH PURITY TUNGSTEN (VI) OXYTETRACHLORIDE AND PROCESS FOR PREPARING IT

Abstract

The present invention relates to tungsten(VI) oxytetrachloride, which is notable for its particular chemical purity, and also to a method for its production.

Description

HIGH PURITY TUNGSTEN (VI) OXYTETRACHLORIDE AND PROCESS FOR PREPARING IT DESCRIPTION OF THE INVENTION The present invention relates to tungsten(VI) oxytetrachloride, which is notable for its particular chemical purity and phase purity, and also to a method for its production. Tungsten(VI) oxytetrachloride is an inorganic tungsten compound belonging to the oxychloride group, with the stoichiometric formula WOCl4. It is primarily used as a catalyst in olefin production, particularly in ring-opening reactions. Additional applications include the semiconductor industry and its use as a starting material in sol-gel processes. Document DE 33 47 918 describes a glass substrate having a thermochromic coating containing VO2 or V2O3, with variable transmissibility to solar rays, where an optical change takes place within a temperature range of 25 to 75°C and the transmissibility to full solar energy in the infrared range decreases by a factor of at least two when the coating is heated through its transition range. Ref. 334487 temperature. The coating containing VC>2 or V2O3 is a layer produced by the chemical decomposition and optionally the reduction of a chemically deposited vanadium compound doped with metal oxides having an ionic radius larger than vanadium. Among the suitable doping agents identified is WOCl4, which, when added, is able to lower the transformation temperature of the VO2 film. N. Ózer and colleagues, in their essay Optical and Electrochromic Properties of Sol-Gel Deposited Doped Tungsten Oxide Films of January 1996, describe the use of WOCI4 as a precursor compound in the production of tungsten oxide doped films. The expert is familiar with several methods for producing tungsten(VI) oxytetrachloride, such as by reacting tungsten(VI) oxide, tungsten(VI) chloride, or sodium tungstate with thionyl chloride, or by thermally decomposing tungsten(VI) dioxide dichloride. Other production methods 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. F. Zado, in his essay "The high yield synthesis of the tungsten (VI) oxyhalides WOCl4, WOBr4 and WO2Cl2 and some observations on tungsten(VI) bromide and tungsten(V) chloride", published in J. Inorg. Nuci. Chem. 25, 1115 (1963), describes the preparation of tungsten (VI) oxytetrachloride by sealing WClg and WO3 in an evacuated ampoule and heating the ampoule to 100°C. The temperature was raised after two hours to 150°C and the ampoule was positioned so that the deposited product could be sublimated over a period of 24 hours. AE Castro Lunar and collaborators, in J. Chem. Eng. Data 1983, 26, 349-350, under the title Vapour Pressure of WOCI4, describe the preparation of tungsten (VI) oxytetrachloride by means of the reaction of CCI4 with WO3 at 400°C (673°K). Examples of other known preparation methods for tungsten(VI) oxytetrachloride are the reaction of WClg with an organosilicon compound according to the equation WC16+ Me3Si-O-SiMe3-» WOC14+ 2 Me3SiCl, the above-mentioned use of thionyl chloride according to the equation WO3 + 2 SOCI2 -> WOCI4 + 2 SO2, and also the reaction of a heated tungsten step in a CI2 gas containing oxygen. The methods described in the previous technique have The disadvantage, however, is that tungsten(VI) oxytetrachloride usually has a significant fraction of impurities, such as metallic impurities and other tungsten compounds, which manifest as additional crystal phases, and the methods can only be employed on a laboratory scale. Therefore, the chemical purity of commercially available tungsten(VI) oxytetrachloride is stated to be 98% to 99.95%, based on metallic impurities. Of course, most of the metallic impurities can be removed by means of additional purification steps, such as sublimation. However, sublimation results in increased crystal growth, and thus tungsten(VI) oxytetrachloride takes the form of large, acicular crystals that have a low apparent density, which is a disadvantage for a number of applications.To obtain suitable particle sizes, the crystals must be properly processed by methods such as crushing. However, due to the low stability of tungsten(VI) oxytetrachloride, this leads to the introduction of metallic impurities and the formation of undesirable phases. An additional exacerbating factor is that the decomposition of tungsten(VI) oxytetrachloride is accompanied by the formation of highly corrosive compounds such as hydrochloric acid. Conventionally required purification methods also have the disadvantage that some impurities, especially additional tungsten compounds and certain non-metallic materials, cannot be sufficiently removed. Therefore, an objective 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 for its production, which can be implemented even on an industrial scale and which works without additional final mechanical treatment steps, such as crushing, sieving or sublimation, for example. The objective is achieved through the provision of tungsten(VI) oxytetrachloride which has high chemical and crystallographic purity and a specific morphology. A first subject of the present application is therefore a tungsten (VI) oxytetrachloride having a chemical purity greater than 99.95% and wherein the tungsten (VI) oxytetrachloride has a fraction of compounds selected from the group consisting of WClg, WO2CI2, WO3 and WO2, defined as the ratio of the reflection having the highest intensity of one of these compounds (I(P2)100) in the X-ray diffraction pattern to the reflection having the highest intensity of tungsten (VI) oxytetrachloride (I(WOC14)100) in the X-ray diffraction pattern, expressed as I(P2)100 / 1(WOC14)100, less than 0.03. Tungsten(VI) oxytetrachloride according to the present invention is more particularly tungsten(VI) oxytetrachloride of the empirical formula WOCI4. In the context of the present invention, the chemical purity of a sample of WOCl₄ refers to the ratio of the cumulative weight proportions of the elements tungsten, chlorine, and oxygen to the cumulative weight proportions of all other impurities in the sample. The purity of the substance is expressed as a quantitative ratio of WOCl₄ to the overall weight of the composition, with a substance having a chemical purity of 100% if no other elements are present except tungsten, chlorine, and oxygen. Impurities within the meaning of the present invention comprise not only metallic impurities but also non-metallic impurities, in particular silicon, carbon, sulfur, molybdenum, and nickel, and components thereof. Chemical purity must be distinguished from crystallographic purity. In the context of this application, the crystallographic purity of a substance is the ratio of the crystal phase of an undesired compound to the crystal phase of the desired compound, currently tungsten(VI) oxytetrachloride. The ratio of the crystal phases can be determined here, for example, by means of the intensities of the various phases in an X-ray diffraction pattern. Suitable recordings can be made on powder samples by means of, for example, a Malvern-PANalytical instrument (X'Pert-MPDMR with a semiconductor detector, Cu LFF X-ray tube with 40 kV / 40 mA, Ni filter). In addition to the established chemical impurities, conventional tungsten(VI) oxytetrachloride may comprise additional compounds, such as, for example, WCle and optionally additional tungsten oxides as what are called secondary phases. These oxides are primarily the related oxides WO2Cl2, WO3, and WO2, which have a different crystal structure from tungsten(VI) oxytetrachloride and are detectable by X-ray diffractometry. In a particularly preferred embodiment, the tungsten(VI) oxytetrachloride of the invention substantially does not comprise additional tungsten compounds and, in particular, does not comprise additional tungsten oxide compounds. Preferably, the tungsten(VI) oxytetrachloride of the invention is substantially free of compounds selected from the group consisting of WCle, WO2Cl2, WO3, and WO2.The fraction of additional compounds mentioned above can be defined by the ratio of the intensity of the main phase of tungsten(VI) oxytetrachloride to that of the established secondary phases. The main and secondary phases can be determined by their reflection intensities in the X-ray diffraction pattern, indicated as impulses per angle [°2theta]. In a particularly preferred embodiment, the ratio of the reflection having the highest intensity of a secondary phase (I(P2)100) to the reflection having the highest intensity of the main phase of tungsten (VI) oxytetrachloride (I(WOCI4)100), expressed as I(P2)100 / 1(WOCI4)100, is preferably less than 0.02, more preferably from 0.001 to 0.02, more particularly from 0.001 to 0.01, determined in each case by means of X-ray diffractometry.The tungsten(VI) oxytetrachloride of the invention is considered, in the context of the present invention, to be substantially free of compounds selected from the group consisting of WC16, WO2CI2, WO3, and WO2, and declared as secondary phases in the context of the present invention if the ratio of the primary and secondary phases defined above is 0.001 or less. In a further preferred embodiment, no secondary phase is detectable. The fractions of additional tungsten compounds are determined herein by means of X-ray diffractometry, performed, for example, on powder samples using an instrument. Malvern-PANalytical (X'Pert-MPDMRcon semiconductor detector, Cu LFF x-ray tube with 40 KV / 40 mA, Ni filter). In a preferred embodiment, the tungsten(VI) oxytetrachloride of the invention has a chemical purity of 99.99% or more, preferably 99.995% or more and more preferably 99.999% or more. Conventional tungsten(VI) oxytetrachloride generally contains a number of chemical impurities that can disrupt its potential applications. These impurities, depending on the production method, are primarily silicon and its compounds, sulfur and its compounds, and also carbon, molybdenum, and iron. In contrast, the tungsten(VI) oxytetrachloride of the invention is notable for its low impurity content. In a preferred embodiment, the tungsten(VI) oxytetrachloride of the invention comprises silicon and / or silicon compounds in amounts less than 50 ppm, preferably less than 25 ppm, and more preferably less than 5 ppm, these figures being based on the total weight of the tungsten(VI) oxytetrachloride. In a further preferred embodiment, the tungsten(VI) oxytetrachloride of the invention comprises sulfur and / or sulfur compounds in an amount less than ML / a / ZUZZ / UU l OU l 100 ppm, preferably in an amount less than 30 ppm and more preferably in an amount less than 10 ppm, the data being based in each case on the total weight of tungsten(VI) oxytetrachloride. The overall fraction of metallic impurities, other than silicon, is less than 100 ppm, preferably less than 70 ppm, and more preferably less than 50 ppm, where the data are based in each case on the total weight of tungsten(VI) oxytetrachloride. The metallic impurities may be, for example, elements from main groups 2 and 3, refractory metals, and more particularly iron, chromium, nickel, and molybdenum. In a particularly preferred embodiment, the tungsten(VI) oxytetrachloride of the invention has a fraction of molybdenum and / or its compounds of less than 20 ppm, preferably less than 10 ppm, and more preferably less than 5 ppm, based in each case on the total weight of tungsten(VI) oxytetrachloride. A preferred embodiment is one in which the tungsten (VI) oxytetrachloride of the invention comprises carbon in an amount less than 200 ppm, preferably in an amount less than 100 ppm and more preferably in an amount less than 40 ppm, the data being based in each case on the total weight of the tungsten (VI) oxytetrachloride. In addition to its high chemical and crystallographic purity, the tungsten(VI) oxytetrachloride of the invention is notable for its morphology. While conventional tungsten(VI) oxytetrachloride generally takes the form of large acicular crystals, this is not surprisingly the case with the tungsten(VI) oxytetrachloride of the invention. In a preferred embodiment, the tungsten(VI) oxytetrachloride of the 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, and where particle size refers to the longest extent of the particle. The percentage figure is based on the total number of powder particles.It has been surprisingly discovered that as a result of the specific morphology of the tungsten (VI) oxytetrachloride of the invention, it has been possible to improve the dissolution kinetics of the tungsten (VI) oxytetrachloride in the additional application. As a result of the specific morphology of the tungsten(VI) oxytetrachloride of the invention, it has been possible to achieve a distinct improvement in apparent density, sometimes also referred to as apparent weight. In a preferred embodiment, the tungsten(VI) oxytetrachloride of the invention has an apparent density greater than 0.5 g / cm³. The apparent density pb is defined as the ratio of the mass m of the bed to the volume of bed occupied, according to the formula Pb = V& and can be determined by means of ASTM B329-06. An additional theme of the present invention is a method for producing the tungsten(VI) oxytetrachloride of the invention. The method of the invention is notable in that in a first step a) tungsten metal is reacted with chlorine gas and oxygen at a temperature T(1), and the resulting product mixture is subjected in a further step b) to oxidation at a temperature T(2) in the presence of an oxidizing agent to provide the tungsten(VI) oxytetrachloride of the invention. The tungsten metal used in step a) is preferably a metal powder having a D90 particle size less than 300 pm, preferably having a D90 particle size less than 150 pm, as determined by ASTM B822. The D90 particle size here indicates the fraction of particles which have a particle size smaller than the specified value. The reaction in step a) of the method of the invention is conducted at a temperature T(l) of 600 to 1000°C, preferably. ινΐΛ / a / zuzz / uu í ou i Without being linked to any particular theory, it is assumed in the context of the present invention that in step a) of the method of the invention, the reaction of tungsten metal with chlorine gas and oxygen produces a mixture of tungsten(VI) oxytetrachloride and tungsten(VI) chloride. In the context of the method of the invention, it has been surprisingly discovered that in a further step, the tungsten(VI) chloride obtained can be selectively oxidized to tungsten(VI) oxytetrachloride, yielding tungsten(VI) oxytetrachloride that has high purity and a specific morphology. Furthermore, the method of the invention offers the advantage of providing tungsten(VI) oxytetrachloride with high chemical and crystallographic purity, thus eliminating the need for additional final treatment steps such as sublimation. Therefore, a preferred embodiment of the method of the invention omits purification steps and / or additional operating steps, particularly sublimation and / or grinding. While not bound by any particular theory, it is assumed that omitting additional operating steps such as sublimation, grinding, or sieving contributes to the production, under the method of the invention, of tungsten(VI) oxytetrachloride. ML / a / ZUZZ / UU l OU l which is present in the form of small particles, in contrast to conventional tungsten (VI) oxytetrachloride. The oxidizing agent used in step b) is preferably selected from the group consisting of oxygen, water, and steam. A particularly preferred oxidizing agent used in step b) of the method of the invention is water or steam. When water is used as the oxidizing agent in step b) of the method of the invention, the oxidation is preferably carried out at a relative atmospheric humidity of 20% to 80%, more preferably 40% to 60%. The oxidation of tungsten chloride compounds conventionally takes place at temperatures of 300°C or higher. In the context of the method of the invention, it has been surprisingly discovered that the oxidation can also be carried out at significantly lower temperatures without the formation of higher oxides or oxychlorides, such as WO2Cl2 or WO3, for example, and without any field deduction, especially when water is used as the oxidizing agent. Therefore, a preferred embodiment of the method is one in which the oxidation in step b) is carried out at a temperature T(2) of 0 to 80°C, preferably from 0 to 60°C, preferably for a period of 5 minutes to 50 hours. Furthermore, it has proven advantageous, contrary to general expectations, to carry out the reaction of tungsten metal with oxygen and chlorine gas in an atmosphere where the oxygen is present in a substoichiometric ratio to the tungsten metal. Therefore, an embodiment in which the oxygen in step a) is used in a substoichiometric ratio is preferred. The stoichiometric ratio of oxygen to tungsten metal in step a) of the method of the invention is preferably from 0.85 to 0.97, more preferably from 0.85 to 0.9. Several prior art methods for producing tungsten(VI) oxytetrachloride rely on the use of organic compounds, particularly organosulfur compounds and organosilicon compounds. In the context of the present invention, it has been surprisingly discovered that tungsten(VI) oxytetrachloride can be obtained with high purity under moderate conditions even without the use of these compounds, some of which are harmful to health. Therefore, a preferred embodiment of the method of the invention is one in which sulfur compounds, silicon compounds, and / or chlorinated hydrocarbons are not used. Tungsten(VI) oxytetrachloride produced according to the method of the invention differs not only in its purity but also, in particular, in its morphology from tungsten(VI) oxytetrachloride produced by conventional methods. Therefore, a further subject of the present invention is tungsten(VI) oxytetrachloride produced according to the method of the invention. One feature of tungsten(VI) oxytetrachloride produced by the method of the invention is that 90% of all particles have a particle size of 100 pm or less, preferably 70 pm or less, as determined by optical microscopy. The percentages herein are based on the total number of particles. Particle size herein refers to the longest dimension of the particle. An additional theme of the present invention is the use of tungsten (VI) oxytetrachloride of the invention or of tungsten (VI) oxytetrachloride obtained according to the method of the invention as a catalyst in chemical reactions, more particularly in the preparation of functional hydrocarbons; in the semiconductor industry and / or in sol-gel processes, especially for producing electrochromic coatings. The present invention is clarified in greater detail by the following examples and figures, which in no way should be understood as limiting the concept of the invention. Examples: 1. Comparative Example 1 Tungsten(VI) oxytetrachloride was prepared according to the following reaction equation: WC16+ Me3Si-O-SiMe3WOC14+ 2 Me3SiCl (Comp. 1) An analysis of the obtained tungsten(VI) oxytetrachloride, including chemical purity, detected crystalline phases, particle size, and apparent density, is compiled in Table 1. As is apparent from Figure 1, which shows an X-ray diffraction pattern of the obtained tungsten(VI) oxytetrachloride, there were significant fractions of WO2CI2 as well as the desired compound. Figures 2a and 2b show optical micrographs of tungsten(VI) oxytetrachloride prepared according to the Compound of formula 1, wherein the acicular shape of the crystals is clearly apparent and less than 40% of all particles are smaller than 100 pm. 2. Comparative Example 2 For further comparison, tungsten(VI) oxytetrachloride was prepared according to the following reaction equation: WO3+ 2 SOC12-> WOCI4 + 2 SO2(Comp. 2) An analysis of the obtained tungsten(VI) oxytetrachloride, including chemical purity, detected crystalline phases, particle size, and apparent density, is compiled in Table 1. An X-ray diffraction pattern of the product demonstrates the presence of WO2C12 as a byproduct, as well as the desired tungsten (VI) oxytetrachloride (Figure 3). Figure 4 shows an optical micrograph of tungsten(VI) oxytetrachloride prepared according to the Compound of formula 2, wherein the acicular shape of the crystals is clearly apparent and less than 10% of all particles are smaller than 100 pm. 3. Comparative Example 3 For further comparison, tungsten(VI) oxytetrachloride was prepared according to the following reaction equation in a one-step reaction at 800°C: W + 2 Cl2+ 0.5 O2-> WOCI4 (Comp. 3) An analysis of the obtained tungsten(VI) oxytetrachloride, including chemical purity, detected crystalline phases, particle size, and apparent density, is compiled in Table 1. The tungsten(VI) oxytetrachloride obtained yielded an X-ray diffraction pattern (Figure 5) which, like the desired tungsten(VI) oxytetrachloride, also contained significant amounts of WClg and WO₂Cl₂. It should be noted that in this experiment, WO₂Cl₂ actually constituted the main phase, and tungsten(VI) oxytetrachloride was only a secondary phase. Reproduction tests under identical conditions confirmed the presence of these three compounds in varying proportions, based on X-ray diffraction analysis. It was not possible to produce pure tungsten(VI) oxytetrachloride via the one-step reaction. Optical micrographs of tungsten(VI) oxytetrachloride prepared according to Compound of formula 3 also clearly showed an acicular shape of the crystals, where less than 50% of all particles were smaller than 100 pm. Table 1 X-ray Diffractometry Experiment Particle Size (Optical Microscopy) Chemical Trace Analysis Qualitative Phase Composition Quantitative Phase Composition l(P2)100 / l(WOCI4)100 Percentage of Particle Number <100 μη Si SC Mo Fe Total sum of all metallic impurities Total sum of all impurities including all non-metals and Si Chemical Purity Apparent Density Main Phase MP Secondary Phases SP [%1 [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm / % by weight] [%] [g / cm3] Comp. 1 WOCI4(MP), WO2Cl2(SP) 0.052 <40% 55 21 981 10 71 135 1192 / 0.1192 99.8808 0.43 Comp. 2 WOCI4(MP), WO2CI2(SP) 0.108 <10% 15 352 240 11 80 104 711 / 0.0711 99.9289 0.33 Comp. 3 W02CI2(MP)W0CI4(SP), WCI6(SP) 1.19 <50% 6 11 21 9 10 68 106 / 0.0106 99.9894 0.39 OS¿OO / ZW / XIAI 4. Inventive example Tungsten(VI) oxytetrachloride was prepared according to the invention by means of a two-step process, considering that in a first step a) tungsten metal powder having a particle size D90 less than 150 pm was brought to the reaction at 800°C in a Cl2y gas stream with the addition of oxygen in a stoichiometric ratio of 0.85, based on the amount of tungsten used. The intermediate reaction product received contains, due to the substoichiometric addition of oxygen (stoichiometric ratio of 0.85), in addition to the desired tungsten(VI) oxytetrachloride, significant amounts of WClg. This intermediate product was reacted according to step b) under various oxidation conditions to provide the tungsten(VI) oxytetrachloride of the invention; the oxidation conditions and also the relevant analytical results for the powders produced according to experiments 4.1 to 4.8 were compiled in Table 2. The oxidation took place in a water conditioning cabinet, wherein the cabinet controlled the relative atmospheric humidity and temperature as indicated in Table 2. An analysis of the tungsten oxytetrachloride i ou i (VI) obtained, including chemical purity, crystalline phases detected, particle size and apparent density, is evident from Table 2 according to experiment 4.0. 4.2 60 25 0.5 WOCI4 Without sec. >95% 4 9 12 9 5 63 88 99.9912 0.58 4.3 60 25 1 WOCI4 No sec. >95% 4 8 17 7 g 67 96 99.9904 0.58 4.4 40 60 0.5 WOCI4 No sec. >95% 2 9 16 9 θ 65 92 99.9908 0.61 4.5 60 60 0.5 WOCI4 No sec. >95% 4 6 19 6 7 68 97 99.9903 0.58 4.6 80 60 0.5 WOCI4(MP), WO2CI2(SP) 0.0025 >95% 4 7 11 9 6 61 83 99.9912 0.63 4.7 60 90 0.2 WOCI4(MP), WO2CI2(SP) 0.097 >95% 4 9 15 5 4 68 96 99.9904 0.65 4.8 60 90 0.5 WOCI4(MP), WO2CI2(SP), 0.471 >95% 3 5 15 8 5 65 88 99.9912 0.64 Figure 6 shows an X-ray diffraction pattern of the intermediate product of experiment 4.0, obtained after step a). As is apparent from the pattern, there are no tungsten compounds other than the established compounds WOC14 and WCle. Figure 7 shows an optical micrograph of the product after step a). In contrast to conventional production methods, the powder is not in the form of acicular crystals. Instead, the particle size of more than 95% of the total number of powder particles is less than 100 µm, based on the longest longitudinal dimension of the particles. Figure 8 shows an X-ray diffraction pattern of the product of experiment 4.2, obtained after step b). As is apparent from the pattern, there was complete oxidation of the WCle to provide the desired WOC14. As shown by the optical micrograph in Figure 9, the morphology of tungsten(VI) oxytetrachloride was not affected in any way by oxidation. Also, in the final product of Experiment 4.2, tungsten(VI) oxytetrachloride was in the form of small particles, with a particle size less than 100 pm, comprising more than 95% of the total number of powder particles. As is apparent from Table 2, in experiments 4.1 to 4.6, tungsten(VI) oxytetrachlorides of the invention were prepared that had a chemical purity greater than 99.95% and contained no detectable secondary phases or secondary phases with an I(P2)100 / 1(WOCI4) 100 ratio less than 0.03, as a result, in particular, of the control over the oxidation conditions during step b). If the process window for oxidation is deviated from, as in experiments 4.7 and 4.8, rapidly increasing amounts of WO2C12 are formed, which become visible as a result of an increase in the I(P2)100 / 1(WOCI4) 100 ratio. The fractions of crystalline tungsten compounds were confirmed by X-ray diffractometry, determined, for example, in powder samples using a Malvern-PANalytical instrument (X' Pert-MPDMR with semiconductor detector, Cu LFF X-ray tube with 40 kV / 40 mA, Ni filter). In the qualitative analysis of the X-ray diffraction patterns, the confirmed reflections were assigned to reflections of known tungsten compounds from the literature. Trace analysis of chemical impurities was carried out by ICP-OES using the analytical instruments PQ 9000MR (Analytik Jena) or Ultima 2MR ML / a / ZUZZ / UU l ÓU l (Horiba). The confirmed chemical purity is obtained arithmetically as the difference between the hypothetical contamination-free sample at 100% by weight and the sum total of all impurities, including all non-metals and Si, in % by weight. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. Tungsten(VI) oxytetrachloride, characterized in that the tungsten(VI) oxytetrachloride has a chemical purity greater than 99.95% and wherein the tungsten(VI) oxytetrachloride has a fraction of compounds selected from the group consisting of WCle, WO2CI2, WO3 and WO2, defined as the ratio of the reflection having the highest intensity of one of these compounds (I(P2)100) in the X-ray diffraction pattern to the reflection having the highest intensity of tungsten(VI) oxytetrachloride (I(WOCI4) 100) in the X-ray diffraction pattern, expressed as I (P2)100 / 1 (WOCI4) 100 , less than 0.

03.

2. Tungsten(VI) oxytetrachloride according to claim 1, characterized in that the tungsten(VI) oxytetrachloride has a fraction of secondary phases, defined as the ratio of the reflection having the highest intensity of a secondary phase (I(P2)100) to the reflection having the highest intensity of tungsten(VI) oxytetrachloride (I(WOCI4) 100 ), expressed as I (P2 ) 100 / 1 (WOCI4) 100 , less than 0.02, preferably from 0.001 to 0.02, more preferably from 0.001 to 0.01, in each case by means of X-ray diffraction.

3. Tungsten(VI) oxytetrachloride according to at least one of claims 1 and 2, characterized in that the tungsten(VI) oxytetrachloride has a chemical purity of 99.99% or more, preferably 99.995% or more, more preferably 99.999% or more.

4. Tungsten(VI) oxytetrachloride according to at least one of claims 1 to 3, characterized in that the tungsten(VI) oxytetrachloride comprises silicon and / or silicon compounds in an amount less than 50 ppm, preferably less than 25 ppm, more preferably less than 5 ppm, based in each case on the total weight of the tungsten(VI) oxytetrachloride.

5. Tungsten(VI) oxytetrachloride according to at least one of claims 1 to 4, characterized in that the tungsten(VI) oxytetrachloride comprises sulfur and / or sulfur compounds in an amount less than 100 ppm, preferably less than 30 ppm, more preferably less than 10 ppm, based in each case on the total weight of the tungsten(VI) oxytetrachloride.

6. Tungsten(VI) oxytetrachloride according to at least one of claims 1 to 5, characterized in that the tungsten(VI) oxytetrachloride has a molybdenum fraction and / or its compounds less than 20 ppm, preferably less than 10 ppm, more preferably less than 5 ppm, based in each case on the total weight of the tungsten(VI) oxytetrachloride.

7. Tungsten(VI) oxytetrachloride according to at least one of claims 1 to 6, characterized in that the fraction of metallic impurities in the tungsten(VI) oxytetrachloride is less than 100 ppm, preferably less than 70 ppm, based in each case on the total weight of the tungsten(VI) oxytetrachloride.

8. Tungsten(VI) oxytetrachloride according to at least one of claims 1 to 7, characterized in that the tungsten(VI) oxytetrachloride comprises carbon in an amount less than 200 ppm, preferably less than 100 ppm, more preferably less than 40 ppm, based in each case on the total weight of the tungsten(VI) oxytetrachloride.

9. Tungsten(VI) oxytetrachloride according to at least one of claims 1 to 8, 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 pm or less, preferably 70 pm or less, as determined by optical microscopy.

10. Tungsten(VI) oxytetrachloride according to at least one of claims 1 to 9, characterized in that the tungsten(VI) oxytetrachloride has an apparent density greater than 0.5 g / cm3.

11. A method for producing tungsten(VI) oxytetrachloride according to at least one of claims 1 to 10, characterized in that in a first step a) the tungsten metal is reacted with chlorine gas and oxygen and the resulting product mixture is subjected in a further step b) to oxidation in the presence of an oxidizing agent to provide tungsten(VI) oxytetrachloride.

12. The method according to claim 11, characterized in that the oxidizing agent in step b) is selected from the group consisting of oxygen, water, and steam.

13. The method according to at least one of claims 11 and 12, characterized in that the oxidation in step b) is carried out at a relative atmospheric humidity of 20% to 80%, preferably 40% to 60% with water as the oxidizing agent.

14. The method according to at least one of claims 11 to 13, characterized in that the oxidation in step b) is carried out at a temperature of 0 to 80°C, preferably 0 to 60°C.

15. The method according to at least one of claims 11 to 14, characterized in that the oxygen in step a) is used in a substoichiometric ratio, wherein the stoichiometric ratio of oxygen to tungsten metal is preferably from 0.8 to 0.97 and more preferably from 0.85 to 0.

9.

16. Tungsten(VI) oxytetrachloride, characterized in that it can be obtained by a method in accordance with at least one of claims 11 to 15.

17. The use of tungsten(VI) oxytetrachloride according to at least one of claims 1 to 10 or 16 as a catalyst in chemical reactions, more particularly in the preparation of functional hydrocarbons; in the semiconductor industry and / or in sol-gel processes, especially for producing electrochromic coatings.