Preparation method capable of improving conversion rate in aryl chlorosilane reduction to prepare aryl silane

Abstract

A preparation method capable of improving the conversion rate in aryl chlorosilane reduction to prepare aryl silane, which comprises: forming a reduction reaction system of aryl chlorosilane, a reducing agent and a phase transfer catalyst in an ether solvent, heating the reduction reaction system to react, and performing vacuum distillation so as to obtain an aryl silane, the reducing agent comprising an alkali metal hydride, and the phase transfer catalyst comprising alkali metal borohydride. The present preparation method uses alkali metal borohydride as the phase transfer catalyst to improve the reduction capability of the alkali metal hydride reducing agent, and further promote the progress of the chemical reaction of reducing aryl chlorosilane to prepare aryl silane, thus driving the reaction towards complete reaction. Therefore, the method remarkably reduces the content of intermediate products, in particular aryl monochlorosilane, in the final product, thus obtaining high-purity aryl silane with an extremely low chlorine content.

Description

Preparation method for improving conversion rate of aromatic silane by reducing aromatic chlorosilane

[0001] The present invention claims priority to Chinese patent application No. 202311599850.3, filed with the Patent Office of China on November 28, 2023, entitled “Method for Improving the Conversion Rate of Aromatic Silanes Prepared by Reduction of Aromatic Chlorosilanes”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to the technical field of organic compound preparation, and in particular to a preparation method for improving the conversion rate of aromatic silane prepared by reducing aromatic chlorosilane. Background Art

[0003] Aromatic silanes, particularly phenylsilane, are important organosilicon intermediates. They can be used as reducing agents, as raw materials for the synthesis of polysilanes, and as a raw material for the preparation of diiodosilane. Diiodosilane is a new silicon-based precursor material suitable for forming silicon-containing thin films via atomic layer deposition (ALD) at relatively low temperatures, enabling the production of high-end semiconductor chips. Diiodosilane can be prepared through the iodination reaction of elemental iodine and phenylsilane.

[0004] The production of diiodosilane requires high-purity phenylsilane, particularly one free of chloride impurities, as these can contaminate the diiodosilane, causing excessive levels of chlorine. Chlorine impurities can cause numerous problems in semiconductor chip manufacturing, including corrosion of equipment and shortening chip lifespan.

[0005] Phenylsilane is traditionally prepared by reducing phenyltrichlorosilane with a metal hydride. During this reduction, phenyldichlorosilane and phenylmonochlorosilane intermediates are formed. Under common production conditions, due to the steric hindrance of the benzene ring, even with an excess of metal hydride, these intermediates cannot be completely reduced. Consequently, industrially produced phenylsilane products contain a certain amount of phenylchlorosilane impurities.

[0006] The industry is aware that using LiH2 to reduce phenyltrichlorosilane does not achieve complete reduction. To address this issue, U.S. Patent No. 4,629,801 reports an improved method using a tertiary amine to improve the reduction efficiency of LiH2 on phenyltrichlorosilane, thereby increasing the degree of the reduction reaction. However, the tertiary amine in this implementation is difficult to prepare and poses significant risks to equipment and personnel. Furthermore, the implementation method is complex, and the introduced tertiary amine acts as an impurity, affecting the purity of the phenylsilane product. Consequently, industrial operability is limited, and an alternative solution is urgently needed.

[0007] Summary of the Invention

[0008] In view of the shortcomings of the prior art, the object of the present invention is to provide a preparation method for improving the conversion rate of aromatic silanes prepared by reducing aromatic chlorosilanes.

[0009] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0010] In a first aspect, the present invention provides a method for improving the conversion rate of aromatic silanes prepared by reducing aromatic chlorosilanes, comprising:

[0011] Aromatic chlorosilane, a reducing agent and a phase transfer catalyst are formed into a reduction reaction system in an ether solvent;

[0012] After heating the reduction reaction system to react, aromatic silane is obtained by distillation under reduced pressure;

[0013] Wherein, the reducing agent comprises an alkali metal hydride, and the phase transfer catalyst comprises an alkali metal borohydride.

[0014] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least:

[0015] The preparation method provided by the present invention uses alkali metal borohydride as a phase transfer catalyst to enhance the reducing ability of an alkali metal hydride reducing agent, thereby improving the chemical reaction process of reducing aromatic chlorosilane to prepare aromatic silane, thereby allowing the reaction to proceed toward completion, significantly reducing the content of intermediates in the final product, especially aromatic monochlorosilane, and obtaining high-purity aromatic silane with an extremely low chlorine content.

[0016] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of this application and implement them according to the contents of the specification, the following is an explanation of the preferred embodiments of the present invention. DETAILED DESCRIPTION

[0017] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The following will further explain this technical solution, its implementation process and principles.

[0018] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0019] Moreover, relational terms such as “first” and “second” are merely used to distinguish one component or method step from another with the same name, but do not necessarily require or imply any actual relationship or order between these components or method steps.

[0020] The embodiment of the present invention provides a method for improving the conversion rate of preparing aromatic silane by reducing aromatic chlorosilane, which comprises the following steps:

[0021] Aromatic chlorosilane, a reducing agent and a phase transfer catalyst are formed into a reduction reaction system in an ether solvent;

[0022] After heating the reduction reaction system to react, aromatic silane is obtained by distillation under reduced pressure;

[0023] Wherein, the reducing agent comprises an alkali metal hydride, and the phase transfer catalyst comprises an alkali metal borohydride.

[0024] Common metal hydrides used in reduction methods, including lithium hydride, generally have low solubility due to poor compatibility with solvents. Even in excess, they lack the desired reducing efficiency, a major cause of the formation of phenylchlorosilane impurities. The solution provided by the present invention is to use a metal hydride with good compatibility with both the solvent and lithium hydride, such as an alkali metal borohydride such as sodium borohydride, to act as a phase transfer catalyst, improving the solubility and reactivity of the primary reducing agent, LiH. This improves the reducing efficiency and the speed of the reaction, resulting in a significant reduction in phenylchlorosilane impurities while using the same amount of metal hydride.

[0025] Based on the above scheme, the present invention creatively adds sodium borohydride at a certain mass ratio of lithium hydride, which can improve the conversion rate of aromatic trichlorosilane during the reaction and obtain higher-purity phenylsilane. The purity of the aromatic silane prepared and purified in the laboratory under the same experimental conditions and the same experimental equipment can reach 99.994%, the proportion of phenyl monochlorosilane is about 0.006%, and the chlorine content in the pure phenylsilane is about 15 ppm. The chlorine content is significantly reduced after the addition of borohydride in the synthesis reaction.

[0026] In the current prior art, relevant technical solutions, such as the technical method mentioned in the background art for improving the degree of reduction of phenyltrichlorosilane by using tertiary amines, point out that conventional reducing agents such as lithium hydride cannot achieve the technical effect of complete reduction. This is mainly due to the excessive steric hindrance effect of the aromatic group in the reactant. The present invention, by finding a catalyst to replace the tertiary amine, not only improves the thoroughness of the reaction and reduces the chlorine content, but also achieves the technical goal of improving industrial operability, thus making significant progress.

[0027] Some related existing technologies, such as the Chinese invention patent with publication number CN 108530477 A, also mention a technical solution for reducing chloroalkylchlorosilanes by combining catalysts such as lithium hydride and sodium borohydride. Although both involve the reduction of Si-Cl bonds, the specific technical objectives and effects are significantly different from those of the present invention.

[0028] The technical problem solved by this prior art is how to improve the reaction selectivity. The role of the added borohydride catalyst is to reduce the content of lithium hydride to avoid the reduction of chlorine atoms connected to the alkyl group. The difference between aromatic chlorosilanes and alkyl chlorosilanes is that the phenyl group has a higher steric hindrance effect than the alkyl group. Therefore, the reduction of phenyl chlorosilane is more difficult than the reduction of alkyl chlorosilane. This also results in the above-mentioned prior art. As long as the selectivity is well controlled, the chlorine in the alkyl chlorosilane can be easily and almost completely reduced. However, in the present invention, due to the effect of steric hindrance, it is difficult to achieve complete reduction. That is, the purpose and role of the above-mentioned prior art is to selectively obtain a specific product in which the chlorosilane is reduced but the alkyl chloride is not reduced. The present invention does not involve the selectivity issue of alkyl chloride and silyl chloride. The main problem is that the silyl chloride cannot be completely reduced.

[0029] In short, the above-mentioned related prior art addresses the issues of reduction reaction rate and reduction reaction selectivity, which are issues of reaction kinetic rate, while the present invention addresses the issue of the extent of the reduction reaction, which is an issue of reaction thermodynamic equilibrium. The two are not identical technical issues. It is also worth noting that the so-called improvement of reducing ability encompasses multiple situations. Promoting the rate of the reduction reaction is one kinetic situation, while increasing the reducing property of the reducing agent to change the extent of chemical equilibrium is one thermodynamic situation. The two should not be confused. Increasing the reaction rate does not necessarily mean changing the chemical equilibrium; it simply means that equilibrium can be reached quickly.

[0030] More specifically, these prior arts also mention the invention in the background art of the present invention for improving the reduction efficiency of phenyltrichlorosilane by LiH. Therefore, these prior arts recognize the problem that needs to be solved in the reduction of phenyltrichlorosilane, but do not point out that their invention can be used to better solve this problem.

[0031] Secondly, the present invention aims to reduce the content of a partial reduction byproduct, namely phenylmonochlorosilane, in the phenylsilane product, rather than selectively reducing either alkyl chloride or silicon chloride. Furthermore, the 100% yield of alkylsilane mentioned in several of the embodiments is sufficient to demonstrate that due to the low steric hindrance of the alkyl group, the reaction progress can naturally be achieved completely after controlling the selectivity. Therefore, the above-mentioned prior art does not actually face the technical problem of incomplete reduction of the three chlorine atoms connected to the silicon atom. However, for the aromatic chlorosilanes to be reduced in the present invention, it is generally accepted in the industry that conventional reduction methods are impossible to achieve a 100% reduction effect (i.e., the product has a chlorine content of 0 ppm). The claim of a 100% yield in the above-mentioned prior art precisely demonstrates that its goal is not to address the problem of chlorine content in the product caused by insufficient reaction progress after the reduction reaction reaches equilibrium.

[0032] In some embodiments, the aromatic chlorosilane includes any one or a combination of two or more of phenyltrichlorosilane, phenyldichlorosilane, phenylmonochlorosilane, o-tolyltrichlorosilane, m-tolyltrichlorosilane, p-tolyltrichlorosilane, o-tolyldichlorosilane, m-tolyldichlorosilane, p-tolyldichlorosilane, o-tolylmonochlorosilane, m-tolylmonochlorosilane, and p-tolylmonochlorosilane, but is not limited thereto.

[0033] In some embodiments, the alkali metal hydride includes any one or a combination of two or more of LiH, NaH, KH, LiAlH4, NaAlH4 and KAlH4, but is not limited thereto.

[0034] In some embodiments, the alkali metal borohydride includes any one or a combination of two or more of NaBH4, LiBH4 and KBH4, but is not limited thereto.

[0035] In some embodiments, the ether solvent is selected from a high-boiling-point ether solvent having a boiling point higher than that of the aromatic silane by more than 100° C., preferably in some embodiments, a high-boiling-point ether solvent higher than 150° C.;

[0036] In some embodiments, the ether solvent has a boiling point of at least 270°C.

[0037] In some embodiments, the high boiling point ether solvent includes any one of tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether and diethylene glycol dibutyl ether, or a combination of two or more thereof.

[0038] Based on this, the present invention creatively uses a high-boiling point solvent, such as tetraethylene glycol dimethyl ether, as the solvent for the reduction reaction. By utilizing the boiling point difference of 155 degrees between the solvent and the aromatic silane, a high-purity phenylsilane product can be quickly separated by vacuum distillation after the reduction reaction is completed.

[0039] In some embodiments, in the reduction reaction system, the molar ratio of the chlorine atoms in the aromatic chlorosilane to the hydrogen atoms in the reducing agent is (0.5-1):1;

[0040] In some embodiments, in the reduction reaction system, the content of the phase transfer catalyst is 1-10% of the total mass of the reducing agent;

[0041] In some embodiments, in the reduction reaction system, the mass ratio of the reducing agent to the ether solvent is 1:(5-100).

[0042] In some embodiments, the preparation method specifically comprises the following steps:

[0043] The reducing agent, phase transfer catalyst and ether solvent are fully mixed and then heated to the reaction temperature to form a reaction system;

[0044] Slowly adding the aromatic chlorosilane to the reaction system, controlling the temperature to be stable, and maintaining the reaction temperature after the addition is completed to complete the reduction reaction;

[0045] In some embodiments, the reaction temperature is 80-120° C., and the reduction reaction time is 1-24 h.

[0046] In some embodiments, the following steps are also included:

[0047] The reduced pressure distillation is performed while maintaining the reaction temperature.

[0048] Based on the above embodiment, the purity of the aromatic silane obtained in the typical implementation case of the present invention is above 99.99%, the mass ratio of the intermediate product aromatic monochlorosilane is below 0.01%, and the chlorine content is below 25 ppm.

[0049] The present invention improves the method for reducing phenyltrichlorosilane with a metal hydride. By addressing the low solubility of commonly used metal hydrides, a small amount of a highly soluble metal hydride is used to achieve an effect similar to that of a phase transfer catalyst, enhancing the reduction efficiency of the primary metal hydride and significantly reducing the phenylchlorosilane impurity content in the phenylsilane product. Furthermore, the present invention utilizes a high-boiling-point ether solvent, with a boiling point at least 100 degrees Celsius higher than that of phenylsilane, enabling rapid separation of a high-purity phenylsilane product via vacuum distillation after the reduction reaction is complete.

[0050] The technical solution of the present invention is further described in detail below through several embodiments. However, the selected embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0051] In the following examples and comparative examples, unless otherwise specified, the compounds and reagents used are conventional reagents and are commercially available; unless otherwise specified, the pressure is at normal pressure and temperature; and the analytical testing methods involved include:

[0052] Before purification, take 1 ml of phenylsilane synthesis crude product, add 10 ml of dehydrated n-hexane to the crude product, filter and take 1 ml of filtrate sample into a chromatographic glass bottle, use a syringe to draw 0.5 μl of sample, inject the sample and test to obtain the chromatographic composition of the crude product.

[0053] After purification, 1 ml of the pure phenylsilane obtained after distillation was taken, 0.5 μl of the sample was drawn with an injection needle, and the sample was injected for testing to obtain the chromatographic composition of the pure phenylsilane.

[0054] Example 1

[0055] 38.0 g (4.77 mol) of lithium hydride and 2.0 g (0.053 mol) of sodium borohydride were weighed and added to 638 ml of tetraethylene glycol dimethyl ether solvent. The atmosphere in the reaction apparatus was replaced with a protective atmosphere, such as argon. After the mixture was heated to 80°C, 255 g (1.21 mol) of phenyltrichlorosilane was added dropwise to the lithium hydride and tetraethylene glycol dimethyl ether mixture. The reaction temperature was controlled within the range of 100 ± 2°C using cold oil cooling. After the addition of phenyltrichlorosilane was complete, the reaction was continued for 12 hours. A 1 ml sample of the mixture was taken and diluted with 10 ml of n-hexane, filtered, and sampled for chromatographic analysis to monitor the progress of the reaction.

[0056] After the reaction reaches its maximum, the heating temperature is maintained at 100±2°C, and phenylsilane is separated by vacuum distillation to obtain pure phenylsilane with a purity of 99.994%, which contains 0.006% phenylmonochlorosilane and a chlorine content of 15 ppm.

[0057] Comparative Example 1

[0058] 39.7 g (4.99 mol) of lithium hydride was weighed and added to 630 ml of tetraethylene glycol dimethyl ether solvent. The atmosphere of the reaction apparatus was replaced and the mixture was heated to 80°C. 252 g (1.19 mol) of phenyltrichlorosilane was added dropwise to the lithium hydride and tetraethylene glycol dimethyl ether mixture. The reaction temperature was controlled within the range of 100 ± 2°C using cold oil cooling. After the addition of phenyltrichlorosilane was complete, the reaction was continued for 12 hours. A 1 ml sample of the mixture was taken and diluted with 10 ml of n-hexane, filtered, and sampled for chromatographic analysis to monitor the progress of the reaction.

[0059] After the reaction reaches its maximum, the heating temperature is maintained at 100±2°C, and phenylsilane is separated by vacuum distillation to obtain pure phenylsilane with a purity of 99.649%, which contains 0.351% of phenylmonochlorosilane and a chlorine content of 865ppm.

[0060] Comparison of the above examples with the comparative examples reveals that the addition of sodium borohydride (about 5% by weight of lithium hydride) to the reduction of phenyltrichlorosilane with lithium hydride to produce phenylsilane improves the conversion rate of phenylsilane and significantly reduces the content of the phenylchlorosilane byproduct, thereby significantly reducing the chlorine content of the purified phenylsilane. Furthermore, the use of high-boiling-point tetraethylene glycol dimethyl ether as a solvent in the reduction reaction allows for simple and rapid isolation of the high-purity phenylsilane product by vacuum distillation after completion of the reaction.

[0061] Example 2

[0062] This embodiment is substantially the same as embodiment 1, with the main difference being that the content of sodium borohydride is adjusted to 1% and 10% by weight of the lithium hydride, respectively, and both embodiments can obtain phenylsilane with a chlorine content that meets the requirements.

[0063] Example 3

[0064] This embodiment is substantially the same as embodiment 1, with the main difference being that the reducing agent and the catalyst are replaced. The reducing agent is replaced with sodium hydride, and the phase transfer catalyst is replaced with potassium borohydride. Phenylsilane with a chlorine content that meets the requirements can still be obtained.

[0065] Example 4

[0066] This embodiment is substantially the same as embodiment 1, with the main difference being that p-tolyltrichlorosilane is used instead of phenyltrichlorosilane, and the obtained p-tolylsilane contains only 0.01% of p-tolylchlorosilane, and the chlorine content is 22 ppm.

[0067] In addition, based on the above description, the embodiments of the present invention replace various feasible aromatic chlorosilanes, reducing agents and phase transfer catalysts, all of which can achieve equivalent technical effects, significantly improve the conversion rate and significantly reduce the chlorine content.

[0068] Based on the above examples and comparative examples, it can be clearly seen that the preparation method provided by the present invention uses alkali metal borohydride as a phase transfer catalyst to improve the reducing ability of the alkali metal hydride reducing agent, thereby improving the chemical reaction process of reducing aromatic chlorosilane to prepare aromatic silane, thereby allowing the reaction to proceed in the direction of complete reaction, significantly reducing the content of intermediates in the final product, especially aromatic monochlorosilane, and being able to obtain high-purity aromatic silane with extremely low chlorine content.

[0069] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications made in accordance with the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A preparation method for improving the conversion rate of preparing arylsilane by reducing arylchlorosilane, characterized in that, it includes: forming a reduction reaction system of arylchlorosilane, a reducing agent and a phase transfer catalyst in an ether solvent; after heating the reduction reaction system for reaction, obtaining arylsilane by vacuum distillation; wherein, the reducing agent includes alkali metal hydride, and the phase transfer catalyst includes alkali metal borohydride.

2. The preparation method according to claim 1, characterized in that, the arylchlorosilane includes any one or a combination of two or more of phenyltrichlorosilane, phenyldichlorosilane, phenylmonochlorosilane, o-tolyltrichlorosilane, m-tolyltrichlorosilane, p-tolyltrichlorosilane, o-tolyldichlorosilane, m-tolyldichlorosilane, p-tolyldichlorosilane, o-tolylmonochlorosilane, m-tolylmonochlorosilane, p-tolylmonochlorosilane.

3. The preparation method according to claim 1, characterized in that, The alkali metal hydride includes any one or a combination of two or more of LiH, NaH, KH, LiAlH 4 , NaAlH 4 and KAlH 4 ; and / or, the alkali metal borohydride includes NaBH 4 , LiBH 4 and KBH 4 or any combination of two or more thereof.

4. The preparation method according to claim 1, characterized in that, the ether solvent is selected from high-boiling ether solvents with a boiling point 100 °C higher than that of the arylsilane, preferably higher than 150 °C; preferably, the boiling point of the ether solvent is at least 270 °C.

5. The preparation method according to claim 4, characterized in that, the high-boiling ether solvent includes any one or a combination of two or more of tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether and diethylene glycol dibutyl ether.

6. The preparation method according to claim 1, characterized in that, in the reduction reaction system, the molar ratio of the chlorine atom in arylchlorosilane to the hydrogen atom of the reducing agent is (0.5 - 1):1; and / or, in the reduction reaction system, the content of the phase transfer catalyst is 1 - 10% of the total mass of the reducing agent; and / or, in the reduction reaction system, the mass ratio of the reducing agent to the ether solvent is 1:(5 - 100).

7. The preparation method according to claim 1, characterized in that, specifically includes: fully mixing the reducing agent, the phase transfer catalyst and the ether solvent and then heating to the reaction temperature; slowly adding the arylchlorosilane to the precursor system and controlling the reaction temperature to be stable, and maintaining the reaction temperature to complete the reduction reaction after the addition is completed.

8. The preparation method according to claim 7, characterized in that, the reaction temperature is 80 - 120 °C, and the reduction reaction time is 1 - 24 h.

9. The preparation method according to claim 7, characterized in that, it further includes: maintaining the reaction temperature for the vacuum distillation.

10. The preparation method according to claim 1, characterized in that, the purity of the obtained arylsilane is above 99.99%, the mass ratio of the intermediate arylmonochlorosilane is below 0.01%, and the chlorine content is below 25 ppm.