RU2313532C1 - Method for preparing trimethylsilane - Google Patents

Abstract

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for synthesis of methylsilanes. Invention proposes a method for reducing trimethylchlorosilane using sodium hydroxide activated with Lewis acids used as suspension in mineral oil and carried out at increased temperature in a mixture of inert hydrocarbon and simple ether. Synthesized methylsilanes are used in synthesis of polymers and rubbers and in manufacturing semiconductors and in microelectronics. Invention provides development of a method for synthesis of trimethylsilane of high purity and the yield of the end product and improved safety and in the simplifying equipment process.

EFFECT: improved method of synthesis.

9 cl, 1 tbl, 22 ex

Description

The invention relates to the field of chemical technology, namely the production of alkyl substituted silanes, in particular to a method for producing methylsilanes. Methylsilanes are used to produce polymers, rubbers, rubbers, in the manufacture of semiconductors and microelectronics, for plasma etching of silicon wafers.

The known method [A. Gilbert, G. Cooper, R. Shade. Jndustr. and Engng. Chem. S 1, 665 (1959)] producing trimethylsilane by reducing trimethylchlorosilane with sodium hydride by passing trimethylchlorosilane vapors through a suspension of finely divided sodium hydride at 250 ° C. At a lower temperature, for example at 200 ° C, the reaction is poor.

The disadvantage of this method is the low yield of the target product and technical difficulties when mixing and maintaining in a loose state of dry sodium hydride, as well as its extreme fire and explosion hazard at such a high temperature.

A known method of activating the reaction of hydrides of alkali and alkaline earth metals with silicon chloride using chloride and other zinc salts [O.E. Ringwald, US Pat. USA 3050366, 1962].

However, this process satisfactorily proceeds only in the environment of a hydrocarbon solvent, and methylchlorosilanes are not restored under these conditions.

The closest in technical essence to the proposed method and adopted as a prototype is a method for producing trimethylsilane by reducing trimethylchlorosilane with lithium aluminum hydride in an inert hydrocarbon solvent [RF Patent No. 2266293, decl. 08/25/04]. The process is carried out at 80-120 ° C, and an alkyl aromatic hydrocarbon selected from the series C _n H _{n + 2} , where n = 7-8, is used as a solvent.

The reaction proceeds according to the following equation:

LiAlH ₄ + 4Me ₃ SiCl → 4 Me ₃ SiH + LiCl + AlCl ₃

The disadvantage of this method is the high cost of lithium aluminum hydride, as well as its high fire and explosion hazard.

The technical task of this invention is to improve the manufacturability of the process by simplifying the hardware design of the process, improving safety and reducing the cost of production of trimethylsilane while maintaining high yields of the product.

In the proposed method, sodium hydride in the form of a suspension in mineral oil is used as a trimethichlorosilane reducing agent. In this form, it is safe to work in the open air and has a much lower cost in terms of hydride equivalent compared to lithium aluminum hydride. However, in this form, sodium hydride exhibits low activity in the reduction reaction of trimethylchlorosilane.

NaH + Me ₃ SiCl → Me ₃ SiH + NaCl

It has been established that if halides of certain metals, which are Lewis acids, in particular aluminum or zinc, are added to sodium hydride, its activity in the reduction reaction of trimethylchlorosilane significantly increases. Chlorides, bromides, iodides can be used as halide. Fluorides in this case do not show activity. In this case, the process proceeds through an intermediate stage of the formation of aluminum hydride or zinc:

I. 3NaH + AlHal ₃ → AlH ₃ + 3NaHal

2 NaH + ZnHal ₂ → ZnH ₂ + 2NaHal, and further

II. AlH ₃ + 3Me ₃ SiCl → 3Me ₃ SiH + AlCl ₃

ZnH ₂ + 2Me ₃ SiCl → 2Me ₃ SiH + ZnCl ₂

The metal halide is added not in stoichiometric, but in catalytic amounts, because, apparently, the metal chloride formed in stage II reacts again with sodium hydride to form metal hydride.

The activation process of sodium hydride is carried out in an inert hydrocarbon solvent, but trimethylsilane yields are low, and not all recovery systems work due to the fact that neither sodium hydride nor aluminum and zinc halides dissolve in hydrocarbons and the reaction reduces to heterophasic processes on the surface of dispersed components.

Carrying out the reduction process in ethers or mixtures of ethers with hydrocarbons qualitatively changes the course of the reaction, since, apparently, at the first stage of reduction, a metal hydride soluble in ether is formed, which binds to the ether and becomes resistant to thermal decomposition and reduction activity with respect to to trimethylchlorosilane. At the same time, the use of pure esters reduces the reduction efficiency, apparently due to the formation of complexes with the starting trimethylchlorosilane, which are more resistant to the action of reducing agents, and also leads to an intensive cleavage of the ester with aluminum and zinc halides with the release of by-products polluting trimethylsilane and the process becomes more expensive due to the higher cost of ether compared to hydrocarbon.

Suitable ester solvents for the proposed process

- ethers selected from the series ROR ′, where R, R ′ = C _n H _{2n + 1} , n = 2-3 (diethyl ether, dipropyl ether);

- ethylene glycol ethers selected from the series ROCH ₂ CH ₂ OR ′, where R, R ′ = C _n H _{2n + 1} , n = 1-2 (dimethoxyethane, diethoxyethane);

- glima CH ₃ O (CH ₂ CH ₂ O) _n CH ₃ , where n = 1-2 (monoglyme, diglyme).

The use of heavier ethers (diisopropyl, dibutyl), higher glymes does not lead to the reduction of trimethylchlorosilane, and such internal esters as tetrahydrofuran, dioxane are cleaved by the reduction system.

Suitable hydrocarbons are saturated hydrocarbons С _n Н _{2n + 2} , n = 7-12 (heptane, octane, nonane, decane, dodecane) or aromatic hydrocarbons С _n Н _2n-6 , n = 6-8 (benzene, toluene, xylene ethylbenzene).

The use of hydrocarbons with a smaller number n is not advisable due to the high volatility, but with a large n leads to viscous, difficult to mix solutions.

The selected ratio of solvents in the mixture from 50: 1 to 1:10 allows to obtain trimethylsilane with a sufficiently high yield at lower cost for hardware design to ensure process safety.

The proposed method is as follows. All operations upon receipt of trimethylsilane are carried out in an atmosphere of dry inert gas.

A mixture of solvents, AlBr ₃ and NaH in the form of a suspension in mineral oil is charged into a four-necked flask equipped with a stirrer, a thermometer, a “bypass” dropping funnel, a reflux condenser with a gas pipe connected to a cooled trap. With stirring, the reaction mixture is heated to 60-120 ° C and maintained at this temperature for 10-30 minutes. Then, trimethylchlorosilane is dosed uniformly and gradually through a dropping funnel. At the end of dosing, the mixture is left to stand for another 0.5 hours at this temperature, and then the trap is disconnected. The composition of trimethylsilane is determined chromatographically. The yield is 75-85%.

The proposed method is illustrated by the following examples, and the results of the examples are shown in the table.

Example 1. A four-necked flask with a volume of 0.5 l, equipped with a stirrer, a thermometer, a dropping funnel and a reflux condenser with a gas outlet pipe, is connected to a trap cooled to a temperature below -70 ° C. Exit from the trap into the atmosphere is carried out through a drain cartridge. 60 ml of dry toluene, 13.5 g (0.05 M) of aluminum bromide, 24 g (0.6 M) of a 60% suspension of sodium hydride in mineral oil, 60 ml of diglyme are loaded into the flask. With stirring, the mixture is heated to 90 ° C and held for 20 minutes. Then, 64 ml (0.5 M) of trimethylchlorosilane are uniformly added over 1 hour. The resulting trimethylsilane is collected in a cooled trap. The yield is 80%.

The remaining examples are performed similarly when changing certain conditions of the process (indicated in the table). Examples 1-16 illustrate the proposed method, examples 17-21 are made according to the proposed method, but with parameter values outside the range of the proposed values, example 22 is made according to the prototype method.

Table Example No. Solvent The ratio of Activator Temperature, ° C Exit, % one toluene - diglyme 1: 1 AlBr ₃ 90 80 2 benzene - diglyme 10: 1 AlBr ₃ 95 79 3 xylene - monoglyme 20: 1 AlBr ₃ 85 78 four ethylbenzene - diglyme 50: 1 AlBr ₃ one hundred 75 5 heptane - diethyl ether 1: 5 AlBr ₃ 90 76 6 octane - dipropyl ether 1:10 AlBr ₃ 110 74 7 dean - glim 1: 1 AlCl ₃ 60 75 8 toluene - dimethoxyethane 1: 1 Ali ₃ 90 79 9 toluene - diglyme 1: 1 ZnCl ₂ one hundred 71 10 heptane - glyme 1: 1 ZnBr ₂ 95 73 eleven benzene - diethoxyethane 1: 1 ZnI ₂ 90 76 12 toluene - diethyl ether 1: 1 ZnCl ₂ + AlBr ₃ one hundred 79 13 xylene - diglyme 1: 1 AlBr ₃ 60 65 fourteen toluene - diethyl ether 1: 1 AlBr ₃ 80 78 fifteen ethylbenzene - diglyme 1: 1 AlBr ₃ one hundred 79 16 toluene - dimethoxyethane 1: 1 AlBr ₃ 120 73 17 toluene - glim 60: 1 AlBr ₃ 90 25 eighteen dodecan - diglyme 1:20 AlBr ₃ 90 29th 19 toluene - diglyme 1: 1 Znf ₂ 90 0 twenty nonan - diglyme 1: 1 AlBr ₃ fifty 7 21 heptane - diglyme 1: 1 AlBr ₃ 130 10 22 ethylbenzene 1-0 - 120 80

Claims (9)

1. A method of producing trimethylsilane, including the recovery of substituted silane chlorides with a metal hydride at an elevated temperature in an organic solvent, characterized in that activated metal hydride is used as a metal hydride in the form of a suspension in mineral oil, and the process of recovering the substituted silane chlorides is carried out in a mixture of hydrocarbon and ether solvent. 2. The method according to claim 1, characterized in that for the activation of sodium hydride use Lewis acids selected from the group: zinc and / or aluminum halides. 3. The method according to claim 1, characterized in that the activation process of sodium hydride is carried out simultaneously with the recovery process of trimethylchlorosilane. 4. The method according to claim 1, characterized in that as a mixture of solvents use a mixture of hydrocarbon and ether in a ratio of 50: 1-1: 10. 5. The method according to claim 4, characterized in that as the hydrocarbon use saturated hydrocarbons selected from the series C _n H _{2n + 2} , where n = 7-12. 6. The method according to claim 4, characterized in that as the hydrocarbon use aromatic hydrocarbons selected from the series C _n H _2n-6 where n = 6-8. 7. The method according to claim 4, characterized in that the ether solvents are ethers selected from the series ROR ′, where R, R ′ = CnH _{2n + 1} , where n = 2-3. 8. The method according to claim 4, characterized in that ethylene glycol ethers selected from the series ROCH ₂ CH ₂ OR ′ are used as the ethereal solvent, where R, R ′ = C _n H _{2n + 1} , where n = 1-2 . 9. The method according to claim 4, characterized in that as an ethereal solvent using glims selected from the range of CH ₃ O (CH ₂ CH ₂ O) _n CH ₃ , where n = 1-2 (monoglyme, diglyme).