Process for the preparation of mixtures of chlorinated silanes with increased proportions of Si4Cl10 and / or Si5Cl12

Abstract

Process for producing a mixture of chlorinated polysilanes with an increased proportion of Si4Cl 10 and / or Si5Cl 12 from mixtures with a higher mass of long-chain chlorinated polysilanes, in which a) to a mixture containing more than 40% long-chain chlorinated polysilanes containing more than six directly or indirectly linked silicon atoms, b) in exactly one chlorination step, elemental chlorine is added in an amount such that a total composition of the original long-chain portion is achieved which corresponds to 2.3 to 2.7 chlorine atoms per silicon atom, and c) chlorination takes place at a temperature greater than 0°C and less than 160°C and a pressure greater than 200 hPa and less than 2000 hPa.

Description

[0001] The present invention relates to a process for the preparation of mixtures of chlorinated silanes with increased proportions of Si4Cl 10 and / or Si5Cl 12 by adding defined amounts of elemental chlorine to long-chain chlorinated polysilanes or their mixtures under suitable conditions.

[0002] From the state of the art, for example, according to R. Schwarz, U. Gregor, Journal of Inorganic and General Chemistry 1939, 241, 395-415 or M. Schmeisser, P. Voss, Journal of Inorganic and General Chemistry 1964, 334, 50-56, it is known that the thermal decomposition of long-chain chlorinated polysilanes under suitable temperature and pressure conditions yields a mixture of short-chain chlorinated silanes, which also contains decachlorotetrasilane Si4Cl 10 and dodecachloropentasilane Si5Cl 12These compounds can then be separated from the mixture by fractional distillation, yielding 8.06% Si4Cl 10 and 10.33% Si5Cl 10 based on the weight of the starting material.

[0003] For example, from M. Schmeisser, P. Voss, Zeitschrift für anorganische und allgemeine Chemie 1964, 334, 50-56 it is further known that after passing a mixture of chlorine gas and nitrogen in the ratio 1 : 1 for three days at temperatures of up to 60°C over a material of the composition [SiCl2] x a mixture of chlorosilanes can be separated by distillation, that 8.17% Si4Cl 10 and 4.30% Si5Cl 10 based on the weight of the starting material.

[0004] For example, WO 2011 / 067415 A1 discloses that by chlorine cleavage of long-chain chlorinated polysilanes, mixtures of kinetically stable short-chain chlorosilanes can be obtained, which also contain iso-Si4Cl 10 and neo-Si5Cl 12 However, the yields of tetrasilane and pentasilane based on the amount of long-chain chlorinated polychlorosilanes used are low, since the other isomers of the two homologues are not sufficiently stable kinetically. Therefore, depending on the chlorination conditions and the mixture of chlorinated polysilanes used, they are no longer present in the resulting mixture of substances. 29 Si NMR spectroscopy. However, it is observed that signals of the isomers n-Si4Cl 10 , n-Si5Cl 12 and iso-Si5Cl 12are detectable in the reaction mixture before the mixture of kinetically stable short-chain chlorosilanes is reached. These isomers appear to be somewhat more stable against cleavage with chlorine than their longer-chain homologues with more than five Si atoms.

[0005] The process according to the invention fulfils the task of providing a process for the production of mixtures of chlorinated silanes with increased proportions of Si4Cl 10 and / or Si5Cl 12 compared to the state of the art.

[0006] The object is achieved by producing a mixture of chlorinated silanes from long-chain chlorinated polysilanes or mixtures thereof by adding elemental chlorine in a suitable amount in relation to the mass of the long-chain chlorinated polysilanes used and under suitable reaction conditions, in which Si4Cl 10 -isomers and / or Si5Cl 12-Isomers are contained in increased proportions in relation to the mass of long-chain chlorinated polysilanes used.

[0007] The amount of elemental chlorine is chosen so that, on the one hand, larger amounts of Si4Cl 10 - and Si5Cl 12 -isomer mixtures are produced, but on the other hand the cleavage of the isomers that are less stable towards chlorine on the way to the mixture of kinetically stable chlorosilanes has not yet progressed far.

[0008] Chlorinated silanes within the meaning of the invention are compounds of the composition SiCl o H p(0 less than o less than or equal to 4, 0 less than or equal to p less than 4, 0.2 less than or equal to o+p less than or equal to 4). This includes both molecular compounds with 1 less than o+p less than or equal to 4 and extended and highly cross-linked solid structures with 0.2 less than or equal to o+p less than or equal to 1.

[0009] Chlorinated polysilanes within the meaning of the invention are chlorinated silanes with at least two directly bonded Si atoms in the molecular structure.

[0010] Chlorosilanes in the sense of the invention are compounds of the type Si n Cl 2n or Si n Cl 2n+2 (n greater than or equal to 1).

[0011] Mixtures of chlorinated polysilanes within the meaning of the invention can also be compounds of the type SiCl x H 4-x (x = 1 - 4) are included.

[0012] For the purposes of the invention, chlorinated silanes are those which have more than six silicon atoms linked directly or indirectly to one another, without any other chemical element being involved in the linkage.

[0013] For the purposes of the invention, chlorinated silanes are those which have two to six silicon atoms directly linked to one another without any other chemical element being involved in the linkage or which contain only one silicon atom.

[0014] In a first embodiment of the process according to the invention, sufficient elemental chlorine is added to long-chain chlorinated polysilanes or mixtures thereof to achieve a total composition of the originally long-chain portion corresponding to 2.3 to 2.7 chlorine atoms per silicon atom, preferably 2.4 to 2.6 chlorine atoms per silicon atom. For example, starting from a mixture of long-chain chlorinated polysilanes with an average composition of SiCl 0,2 This means an addition of 211.6% to 252.0% of elemental chlorine relative to the starting mass of long-chain chlorinated polysilanes, preferably 221.7% to 241.9%. For example, starting from a mixture of long-chain chlorinated polysilanes with an average composition of SiCl 1,0This means an addition of 72.5% to 94.9% of elemental chlorine relative to the starting mass of long-chain chlorinated polysilanes, preferably 78.1% to 89.3%. For example, starting from a mixture of long-chain chlorinated polysilanes with an average composition of SiCl 2,0 This means an addition of 11.1% to 25.1% of elemental chlorine relative to the starting mass of long-chain chlorinated polysilanes, preferably 14.3% to 21.5%. This embodiment of the process according to the invention contains exactly one chlorination step.

[0015] In a second embodiment of the process according to the invention, a plurality of chlorination steps are carried out and after each chlorination step a fractional distillation is carried out in which Si4Cl 10 or Si4Cl 10 and Si5Cl 12is partially or completely separated from the respective product mixture. The respective distillation residue is subjected to a further chlorination step. The advantage of this procedure is that the concentration of isomers that are comparatively easily cleaved by chlorine remains lower in the respective reaction mixtures than towards the end of the reaction period in a reaction mixture according to the first embodiment of the process according to the invention. Therefore, a smaller total amount of these isomers is further degraded.

[0016] The reaction conditions of successive chlorination steps may be the same. On the other hand, the reaction conditions of successive chlorination steps may differ. For example, the reaction temperature of one chlorination step may be higher than that of the previous chlorination step.

[0017] In the second embodiment of the process according to the invention, the mass of elemental chlorine added for the first chlorination step is between 5% and 25% based on the mass of long-chain chlorinated polysilanes used, preferably between 8% and 18%, particularly preferably between 10% and 17%. The mass of elemental chlorine added for each subsequent chlorination step is between 0.5% and 10% based on the mass of long-chain chlorinated polysilanes used in the first chlorination step, preferably between 1% and 5%.

[0018] The series of successive chlorination steps is terminated when no Si4Cl 10 or Si4Cl 10 and Si5Cl 12 more can be obtained from the final fractional distillation or if the last isolated amount of the two chlorosilanes falls below a previously defined limit.

[0019] In each of the two embodiments of the process according to the invention, the material used can be diluted before each chlorination step with suitable substances that, for example, reduce the viscosity of the mixture to be chlorinated. Examples of suitable diluents are short-chain chlorinated silanes, in particular SiCl4 or Si2Cl6, or inert organic solvents or mixtures of short-chain chlorinated silanes and / or inert organic solvents. Furthermore, inert organic solvents that are readily distinguishable from Si4Cl are preferred. 10 and / or Si5Cl 12 can be separated, especially by fractional distillation.

[0020] Compounds that do not react with elemental chlorine and / or chlorinated silanes contained in the reaction mixture under the reaction conditions are referred to as inert.

[0021] The distillative workup of the mixture of chlorinated silanes obtained from a chlorination according to the process of the invention is preferably carried out at bottom temperatures of less than 220°C, more preferably less than 180°C, particularly preferably less than 165°C, and at final pressures of less than 20 hPa, preferably less than 10 hPa, particularly preferably less than 5 hPa. The distillation can be carried out with a stepwise or continuously increasing bottom temperature and / or a stepwise or continuously decreasing pressure profile. The distillation can also be carried out at a constant bottom temperature and / or constant distillation pressure.

[0022] The chlorination of a mixture of chlorinated polysilanes or a mixture of chlorinated silanes is carried out at a reaction mixture temperature of greater than 0°C, preferably greater than 15°C and less than 160°C, more preferably less than 130°C, particularly preferably less than 100°C, and at a pressure of 200 hPa to 2000 hPa, more preferably 700 hPa to 1500 hPa, particularly preferably 900 hPa to 1300 hPa. The chlorination can be carried out with a stepwise or continuously increasing reaction mixture temperature. The chlorination can also be carried out at a constant reaction mixture temperature.

[0023] Macroscopically liquid, long-chain chlorinated polysilanes or mixtures thereof, or macroscopically liquid mixtures of long-chain chlorinated polysilanes and diluents, are preferred for the process according to the invention. Macroscopically liquid, within the meaning of the invention, are those mixtures of components for which a stationary mixture of components exhibits a smooth, uninterrupted, and liquid-appearing phase boundary with the gas space.

[0024] The macroscopically liquid reaction mixture can be stirred or otherwise mixed during chlorination for improved temperature control and more homogeneous reaction.

[0025] Elemental chlorine can be fed to the reaction apparatus as a liquid mixture consisting of elemental chlorine dissolved in at least one suitable solvent. Examples of suitable solvents are short-chain chlorinated silanes, in particular SiCl4 or Si2Cl6, or inert organic solvents or mixtures of short-chain chlorinated silanes and / or inert organic solvents. Furthermore, inert organic solvents that are readily distinguishable from Si4Cl are preferred. 10 and / or Si5Cl 12 can be separated, especially by fractional distillation.

[0026] For the addition of chlorine solutions, the mass of elemental chlorine added is determined via the amount of chlorine solution added, taking into account the chlorine concentration in mass of chlorine per mass of chlorine solution or in mass of chlorine per volume of chlorine solution.

[0027] Elemental chlorine can be fed into the reaction apparatus during chlorination in pure form or diluted with an inert gas. Examples of inert gases include N2, Ar, or He, or mixtures thereof. The reaction gas can be introduced directly into the liquid reaction mixture, for example, through one or more gas inlet tubes. These can be equipped with fritted structures or other components with a plurality of smaller openings to achieve better distribution and smaller bubble size of the introduced gas. The reaction gas can also be introduced through one or more inlet openings into the gas space adjacent to the liquid reaction mixture.

[0028] Chlorination can also take place in a downward-flowing reaction column through which a mixture of chlorinated polysilanes flows downward while being brought into contact with the reaction gas. The reaction column can contain packing to increase the liquid surface area. The mixture of chlorinated silanes can be distributed and / or mixed on the inner surface of the reaction column by movable components. The movable components can be inserted into the reaction column and / or the reaction column itself can be set in rotation about its longitudinal axis. This procedure can preferably be used for mixtures of chlorinated polysilanes which, under reaction conditions, contain no or only small amounts of solid components, preferably less than 5% based on the weight of the mixture of chlorinated polysilanes used.

[0029] Chlorination can be carried out in such a way that residual reaction gas leaves the chlorination reactor during chlorination. This is particularly necessary if the reaction gas contains inert gas.

[0030] A better conversion of the chlorine gas used can be achieved by introducing undiluted chlorine gas into a reaction apparatus with a closed exhaust side in such a quantity that the pressure in the apparatus does not rise or only rises slowly. Pressure relief then only occurs if the pressure in the apparatus reaches a predetermined value. A further advantage of the closed apparatus is the improved control of the amount of chlorine gas introduced into the reaction mixture, since the determination of the quantity is not distorted by discharged chlorine gas.

[0031] The mass of the introduced chlorine gas can be determined, for example, by repeatedly weighing a chlorine gas cylinder or by summing a chlorine gas flow through a flow meter or mass flow controller over the flow time.

[0032] Various mixtures of chlorinated silanes can be used for the process according to the invention. Preference is given to mixtures that consist of more than 40% long-chain components with more than six directly or indirectly bonded silicon atoms in the molecular structure. The individual components can be solid or liquid, or soluble in one another.

[0033] The method according to the invention will be explained in more detail below using non-limiting comparative and exemplary embodiments.

[0034] Comparison example 1: 546.7 g of a mixture of chlorinated polysilanes obtained by plasma-chemical reaction of SiCl4 with H2 with an average composition of SiCl 2,1 are diluted with 297.4 g of Si2Cl6 and reacted with 180 g of Cl2 (32.9% based on the mixture of chlorinated polysilanes used) in a closed-off-gas reaction apparatus within 41 h at reaction temperatures of 70-80°C and a pressure between 1000 hPa and 1300 hPa. 829.8 g of the product mixture are first purified by short-path distillation to a bath temperature of 140°C at 10 -2 hPa, and the 727.5 g of isolated volatile components are then fractionally distilled. A total of 716.1 g of SiCl4, Si2Cl6, and Si3Cl8 are separated. Only 11.4 g of higher-boiling material remains (corresponding to a yield of 2.58% based on the mixture of chlorinated polysilanes used), which is not further processed.

[0035] Comparison example 2: 13.446 kg of a mixture of chlorinated polysilanes obtained by plasma-chemical reaction of SiCl4 with H2 with an average composition of SiCl 2,1 are diluted with 10.246 kg of a mixture of Si3Cl8 and Si2Cl6 and reacted in a closed-off reaction apparatus at 60°C to 120°C and a pressure between 950 hPa and 1350 hPa with a total of 3.3 kg of Cl2 (24.5% based on the mixture of chlorinated polysilanes used). The total reaction time is 10 h. By fractional distillation, 682.9 g of mainly Si4Cl are obtained. 10 containing fraction with small residues of Si3Cl8 was isolated. The Si4Cl 10 -Yield is thus about 5.1% based on the mixture of chlorinated polysilanes used.

[0036] Example 1: 558.4 g of a mixture of chlorinated polysilanes obtained by plasma-chemical reaction of SiCl4 with H2 with an average composition of SiCl 2,1 are diluted with 303.8 g of Si2Cl6 and reacted with 110 g of Cl2 (19.7% based on the mixture of chlorinated polysilanes used) in a reaction apparatus closed on the exhaust side within 19 h at reaction temperatures of 40-50°C and a pressure between 1000 hPa and 1300 hPa. 932.5 g of the product mixture are first purified by short-path distillation to a bath temperature of 160°C and 10 -2 hPa pressure and the volatile components are then fractionally distilled. 71.6 g of a mixture consisting mainly of Si4Cl 10 A fraction with small amounts of Si3Cl8 was obtained. This corresponds to a yield of approximately 12.8% based on the mixture of chlorinated polysilanes used.

[0037] Example 2: A total of 81.422 kg of a mixture of chlorinated polysilanes obtained by plasma-chemical conversion of SiCl4 with H2 with an average composition of SiCl 2,1 are diluted with a total of 38.330 kg of Si2Cl6 and reacted in several portions at reaction temperatures of 40-65°C and pressures of 950-1350 hPa in exhaust-side sealed apparatuses with a total of 16.3 kg of chlorine gas (20.02% based on the mixture of chlorinated polysilanes used). Fractional distillation of the product mixtures yields 6.275 kg, mainly consisting of Si4Cl. 10 existing fraction with small residues of Si3Cl8 (7.71% based on the mixture of chlorinated polysilanes used).

[0038] The collected 37.671 kg of fractionation residues are diluted with 10.814 kg of Si2Cl6 and reacted with a total of 4.1 kg of chlorine gas (5.04% based on the originally used mixture of chlorinated polysilanes) at reaction temperatures of 55-65°C and pressures of 1000-1350 hPa in a closed-off-gas apparatus. Fractional distillation of the product mixtures yields 3.014 kg, mainly Si4Cl. 10 existing fraction with small residues of Si3Cl8 (3.70% based on the originally used mixture of chlorinated polysilanes). Overall, the combination of two chlorination steps followed by fractional distillation results in a yield of 11.41% of Si4Cl. 10 based on the originally used mixture of chlorinated polysilanes.

[0039] This embodiment demonstrates, in comparison with Comparative Example 2, that with similar amounts of elemental chlorine based on the starting mass of chlorinated polysilanes, significantly increased yields of Si4Cl can be achieved by interposed distillation steps in multi-stage chlorination processes. 10 are accessible.

Claims

[1] Process for preparing a mixture of chlorinated polysilanes with an increased proportion of Si4Cl 10 and / or Si5Cl 12 from mixtures with a higher mass of long-chain chlorinated polysilanes, in which a) to a mixture containing more than 40% long-chain chlorinated polysilanes containing more than six directly or indirectly linked silicon atoms, b) in exactly one chlorination step, elemental chlorine is added in an amount such that a total composition of the original long-chain portion is achieved which corresponds to 2.3 to 2.7 chlorine atoms per silicon atom, and c) chlorination takes place at a temperature greater than 0°C and less than 160°C and a pressure greater than 200 hPa and less than 2000 hPa. [2] Process for preparing a mixture of chlorinated polysilanes with an increased proportion of Si4Cl 10 and / or Si5Cl 12from mixtures with a higher mass of long-chain chlorinated polysilanes, in which a) to a mixture containing more than 40% long-chain chlorinated polysilanes containing more than six directly or indirectly linked silicon atoms, b) in several chlorination steps, a mass of elemental chlorine for a first chlorination step between 5% and 25% based on the mass of long-chain chlorinated polysilanes used and for each further step a mass of elemental chlorine between 0.5% and 10% based on the mass of long-chain chlorinated polysilanes used in the first chlorination step is added, wherein after each chlorination step a fractional distillation is carried out in which Si4Cl 10 and / or Si5Cl 12 separated and the distillation residue is subjected to a further chlorination step, and c) chlorination takes place at a temperature greater than 0°C and less than 160°C and a pressure greater than 200 hPa and less than 2000 hPa. [3] Method according to claim 1 or 2, characterized by that the mixture of long-chain chlorinated polysilanes is diluted with SiCl4 and / or Si2Cl6 and / or at least one inert organic solvent before a chlorination step. [4] Method according to claim 1 and 3 or 2 and 3, characterized by that chlorination takes place at a temperature greater than 15°C and less than 130°C and a pressure greater than 700 hPa and less than 1500 hPa. [5] Method according to claim 1 and 3 to 4 or 2 and 3 to 4, characterized by that elemental chlorine is added as chlorine gas in pure form or diluted with inert gases. [6] Method according to claim 1 and 3 to 5 or 2 and 3 to 5, characterized bythat the distillative treatment takes place at bottom temperatures below 220°C and at final pressures below 20 hPa.