RU2436788C1 - Method of producing alkyl silanes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: in order to simplify the process of producing alkyl silanes and their further purification, synthesis of alkylchloro silanes is carried out in the medium of aromatic hydrocarbons in the presence of a catalyst - tetrakis(diethylamido)-phosphonium salts, more preferably bromides and chlorides, at temperature ranging from 20°C to 250°C. The activator is used in amount of 0.005-1 mol, more preferably 0.01-0.05 mol for each substituted halogen atom in the initial alkylchloro silane.

EFFECT: disclosed method enables to obtain the end product with high purity and high output.

3 cl, 1 tbl, 8 ex

Description

The invention relates to organoelemental chemistry, in particular to the chemistry of silicon compounds and, in particular, to a technology for producing alkylsilanes of the general formula:

SiH _n R _4-n , where

R is the aliphatic radical C _k H _{2k + 1} , at k = 1-4, and n = 1-3, based on the reductive dehalogenation of the corresponding alkyl chlorosilanes with lithium hydride in the presence of aromatic hydrocarbons in the presence of an activator.

State of the art

There are many methods for producing alkylsilanes by reaction of alkylchlorosilanes with lithium aluminum hydride in an organic solvent (RU 2177946, RU 2266293, JP 2005154336).

A feature that is common to the known and claimed methods is the use of alkaline hydrides in an organic solvent medium.

The reason that prevents obtaining the required technical result in the known method is the use of a dangerous reagent - lithium aluminum hydride, which has a relatively high price in the market of chemical products.

A known method of producing alkylsilanes, which consists in the reaction of alkylchlorosilanes with sodium hydride in the presence of an organic solvent (US 3535092).

Signs that are common to the known and claimed methods consist in carrying out the reaction in an organic solvent medium and using hydride (sodium) as a reducing agent.

The reason that prevents obtaining the required technical result in the known method is the use of an extremely explosive reagent sodium hydroxide as a reducing agent, which can be operated only in an inert gas atmosphere.

The closest analogue (prototype) is a method for producing alkylsilanes by reaction of alkylchlorosilanes with lithium hydride in tetrahydrofuran medium (US 4824657).

Signs that are common to the known and claimed methods are to carry out the reaction with lithium hydride in an organic solvent medium.

The reason that prevents obtaining the required technical result in the known method is the use of tetrahydrofuran (hereinafter THF) as a solvent, which easily forms peroxide during storage and requires thorough cleaning before use. THF has a low boiling point (57 ° C), which leads to significant contamination of the target products and complicates their purification. In addition, after the synthesis, the resulting lithium halide is dissolved in THF, which makes it difficult to purify and return to the process.

SUMMARY OF THE INVENTION

The problem to which the invention is directed, is to reduce the cost of the target product, simplify the process of synthesis of alkylsilanes and their further purification.

The technical result that mediates the solution of this problem is that the production of alkylsilanes of the General formula:

SiH _n R _4-n , where

R is an aliphatic radical C _k H _{2k + 1} , at k = 1-4, and n = 1-3, carried out by the reaction of alkylchlorosilanes of the general formula:

SiCl _n R _4-n ,

with lithium hydride, in the presence of an activator, ensuring its good reactivity.

The technical result is achieved by the fact that the process is carried out in an organic solvent medium, which is used as an aromatic hydrocarbon, while the initial alkyl chlorosilane is dosed to a suspension of lithium hydride in an organic solvent in the presence of an activator. The resulting alkylsilane as it forms is distilled off from the reaction mass and collected in a trap.

The technical result is also achieved by the fact that as activators use salts of tetrakis (diethylamido) phosphonium, preferably its bromides and chlorides.

The technical result is also achieved by the fact that the said activator is taken in an amount of from 0.005 to 1 mol, preferably from 0.01 to 0.05 mol for each substituted halogen atom in the original alkyl chlorosilane.

The technical result is also achieved by the fact that the process is carried out at a temperature of from 20 ° C to 250 ° C, preferably 50-100 ° C.

The technical result is also achieved by the fact that after the reaction, the organic solvent is separated from salts and reused in the synthesis of alkylsilanes without the addition of an activator.

New (relative to the prototype) features of the claimed method are the reaction of alkylchlorosilane with lithium hydride in the presence of an activator.

Signs are also new regarding:

- the chemical nature of the activator;

- the possibility of reuse in the reaction of the solvent and activator;

- said molar ratio of starting reagents.

Information confirming the possibility of carrying out the invention

Synthesis of alkylsilanes of the general formula:

SiH _n R _4-n , where

R is an aliphatic radical C _k H _{2k + 1} , at k = 1-4, and n = 1-3, carried out in a reactor with stirring. Moreover, any alkylchlorosilane having at least one replaceable halogen atom connected to silicon is used as the main starting material for the reductive dehalogenation reaction. As another source of the reaction reagent serving as a source of hydride ion, lithium hydride is used as the safest and most affordable hydrogen-containing agent.

Typically, lithium hydride is added in a molar ratio with substituted halogen (0.8-5): 1, more preferably (0.9-1.2): 1.

It should be taken into account that an excess of lithium hydride leads to complications in the disposal of the residual reaction mass. In this regard, an important part of this invention is the use of an activator.

The activator forms an active complex with lithium hydride, capable of replacing a halogen atom with a hydride ion in a medium of a low-polar solvent. In the absence of an activator, the reaction begins only at a high temperature (more than 250 ° C) or in the presence of aluminum compounds forming aluminum hydrides with lithium hydride. The activator allows you to reduce the reaction temperature to 60-100 ° C and to eliminate the use of aluminum compounds that cause the formation of by-products.

As an activator in the described invention, tetrakis (diethylamido) phosphonium salts are used, preferably bromides and chlorides thereof.

The amount of activator in the reaction is from 0.005 to 1 mol, preferably from 0.01 to 0.05 mol for each substituted halogen atom in the starting alkyl chlorosilane.

The use of low concentrations of activator leads to a slowdown of the reaction and a decrease in the yield of target products, and an increase in its amount in excess of 30 mol% is not economically feasible.

The process is carried out in the presence of a solvent. As a solvent, any liquids that do not interact with a hydride ion, in particular non-polar aprotic liquids, are suitable. Commonly used non-polar aprotic solvents are aromatic hydrocarbons, for example: benzene, toluene, xylenes and their technical mixture, ethylbenzene, mesitylene, etc. These solvents may be used in admixture with each other. Aliphatic and alicyclic hydrocarbons also fall into this category.

Solvents serve to improve the mixing of the reaction mass and to stabilize the thermal regime of the reaction mass.

Aprotic solvents can be used in any quantity, for example from 50 to 500 mass%, more preferably from 100 to 250 mass% with respect to a compound containing a halogen that is changed to hydrogen.

The following examples illustrate the invention.

General part of examples

Equipment used

The laboratory plant for the production of alkylsilanes from alkylchlorosilanes consists of a reactor - a 150 ml four-necked flask equipped with a high-speed stirrer, thermometer, dropping funnel with a siphon for dosing alkylchlorosilane and a reflux condenser. To collect the reaction product, a low-temperature trap is installed at the outlet of the reflux condenser, which is cooled by the refrigerant to a temperature of minus 20 ÷ minus 30 ° С. At the exit of the low-temperature trap, a toluene bubbler is installed. To purge the system, argon is supplied from the cylinder through an additional bubbler with toluene.

Enlarged synthesis was carried out in a capacitive type reactor with a volume of 40 dm ³ made of stainless steel. The reactor is equipped with: a turbine stirrer with a rotation speed of 200 rpm, a reverse heat exchanger, which is cooled with antifreeze, a siphon for dosing alkylchlorosilane, a jacket for heating and cooling, a vacuum gauge, a thermocouple, shutoff valves for unloading liquid products and supplying an inert gas, a loading hatch for loading activator, solvent and suspension of lithium hydride in a solvent. The dosage of alkylsilane was carried out by a metering pump. The reactor was heated and cooled with water using a water heater and a circulation pump.

All synthesis steps were carried out only with argon purge.

Process

A suspension of lithium hydride in 1 / 5-1 / 2 parts of toluene was loaded into a dry reactor with stirring, and then the remaining part of toluene and an activator. After that, the reactor was closed, checked for leaks and with vigorous stirring, the suspension was heated to 60-65 ° C. Then, alkylchlorosilane (10% of the total) was slowly dosed. If the reaction after a dosage of 10% alkylchlorosilane did not start, the reaction mixture was heated and kept at a temperature of 75-85 ° C. After the start of the reaction, the dosage of alkylchlorosilane was continued, maintaining the synthesis temperature in the range of 65-75 ° C. The resulting product was condensed in the collector at a temperature of minus 10 ÷ minus 30 ° C. After dosing, exposure was carried out at a temperature of 75-100 ° C. At the end of the synthesis, the resulting product from the collection was unloaded into cylinders and analyzed for GLC. Lithium chloride salts, an activator, as well as toluene and alkylchlorosilane, which were then returned to recycling, were isolated from the bottom residue of the synthesis.

Example 1. 0.8 g of lithium hydride (excess 11%), 15 ml of toluene and 0.8 g of tetrakis (diethylamido) phosphonium bromide activator were charged into a 150 ml flask. The mixture was heated to 65-74 ° C and 9.8 g of trimethylchlorosilane was dosed for 5 minutes at this temperature. Then the reaction mass was kept at a temperature of 80 ° C for 20 minutes In a low-temperature trap, 5 g of trimethylsilane with a basic substance content of 77.3% was condensed. The yield of trimethylsilane in terms of lithium hydride was 51.7%.

Example 2. 0.8 g of lithium hydride (5.2% excess), 15 ml of toluene and 0.8 g of tetrakis (diethylamido) phosphonium bromide activator were charged into a 150 ml flask. The mixture was warmed to 70-80 ° C and 10.4 g of trimethylchlorosilane was dosed for 10 minutes at this temperature. After which the reaction mass was kept at a temperature of 80-95 ° C for 75 minutes 6.1 g of trimethylsilane with a basic substance content of 89.8% were condensed in a low temperature trap. The yield of trimethylsilane in terms of lithium hydride was 73.6%.

Example 3. In a flask with a volume of 150 ml was charged 1.2 g of lithium hydride (excess 0.6%), 15 ml of toluene and 1.1 g of activator - tetrakis (diethylamido) phosphonium chloride. The mixture was heated to 76-97 ° C and 9.7 g of dimethyldichlorosilane was dosed for 5 minutes at this temperature. After which the reaction mass was kept at a temperature of 83-97 ° C for 50 minutes 3 g of dimethylsilane with a basic substance content of 90.0% was condensed in a low temperature trap. The yield of dimethylsilane in terms of lithium hydride was 60.0%.

Example 4. 2.8 g of lithium hydride (excess 1%), 45 ml of toluene and 2.8 g of tetrakis (diethylamido) phosphonium bromide activator were charged into a 150 ml flask. The mixture was heated to 78-85 ° C and 38.7 g of trimethylchlorosilane was dosed for 15 minutes at this temperature. After which the reaction mass was kept at a temperature of 78-105 ° C for 20 minutes 27 g of trimethylsilane with a basic substance content of 82.05% were condensed in a low temperature trap. The yield of trimethylsilane in terms of lithium hydride was 84.5%.

Example 5. A 1000 ml flask was charged with 18.5 g of lithium hydride (2% excess), 390 ml of toluene and 18.5 g of tetrakis (diethylamido) phosphonium bromide activator. The mixture was warmed to 85-97 ° C and 259.4 g of trimethylchlorosilane was dosed for 80 minutes at this temperature. Then the reaction mass was kept at a temperature of 86-102 ° C for 60 minutes In a low-temperature trap, 148.7 g of trimethylsilane with a basic substance content of 94.2% were condensed. The yield of trimethylsilane in terms of lithium hydride was 80.9%.

Example 6. In a 40-liter stainless steel reactor, 1134 g of lithium hydride (1% excess), 16 L of toluene and 1134 g of tetrakis (diethylamido) phosphonium bromide activator were charged. The mixture was warmed to 68-75 ° C and 15.64 kg of trimethichlorosilane was dosed for 12 hours at this temperature. Then the reaction mass was kept at a temperature of 83 ° C for 3 hours. 9.32 kg of trimethylsilane with a basic substance content of 80.0% were condensed in the collection. The yield of trimethylsilane in terms of lithium hydride was 71.1%.

Example 7. In a 200 ml flask, 4.0 g of lithium hydride (without excess), 71.4 ml of toluene and 5 g of tetrakis (diethylamido) phosphonium bromide activator were charged. The mixture was heated to 60 ° C and at a temperature of 65-85 ° C, 28.9 g of methyl dichlorosilane was dosed over 90 minutes. After which the reaction mass was kept at a temperature of 80-85 ° C for 30 minutes. In a low-temperature trap, 10.14 g of methylsilane with a basic substance content of 95.7% was condensed. The yield of methylsilane in terms of lithium hydride was 84.4%.

Example 8. Into a 200 ml flask were charged 4.0 g of lithium hydride (without excess), 71.4 ml of toluene and 2 g of tetrakis (diethylamido) phosphonium bromide activator. The mixture was heated to 60 ° C and 28.9 g of methyl dichlorosilane were dosed for 90 minutes at a temperature of 65-75 ° C. After which the reaction mass was kept at a temperature of 80-85 ° C for 30 minutes. In the low-temperature trap, 7.19 g of methylsilane with a basic substance content of 90.9% was condensed. The yield of methylsilane in terms of lithium hydride was 56.9%.

The experimental results are presented in table 1.

Claims (3)

1. The method of producing alkylsilanes of the General formula:
SiH _n R _4-n , where
R is the aliphatic radical C _k H _{2k + 1} , when k = 1-4, and n = 1-3, which consists in the interaction of alkylchlorosilanes of the general formula:
SiCl _n R _4-n ,
with lithium hydride in an organic solvent medium, characterized in that the reaction is carried out in the presence of an activator - salts of tetrakis (diethylamido) phosphonium, preferably bromide or chloride, and an aromatic hydrocarbon is used as an organic solvent. 2. The method of producing alkylsilanes according to claim 1, characterized in that the activator uses tetrakis (diethylamido) phosphonium salts in an amount of from 0.005 to 1 mol, preferably from 0.01 to 0.05 mol, for each substituted halogen atom in starting alkylchlorosilane. 3. The method of producing alkylsilanes according to any one of claims 1 and 2, characterized in that the process is carried out at a temperature of from 20 ° C to 250 ° C, preferably 50-100 ° C.