CN101875662B - Method for preparing pentamethyl disiloxane - Google Patents

Abstract

The invention discloses a method for preparing pentamethyl disiloxane. In a reaction formula below, R may be methyl, ethyl, propyl, phenyl or ethenyl; and X may be a chlorine atom or bromine atom; n is an integer ranging from 4 to 100. Reaction steps include: (1) adding high-hydrogen silicone oil represented by a formula III into a Grignard reagent to perform a Grignard reaction in the presence of an ether solvent and a cosolvent; and (2) adding water to perform a hydrolysis reaction to prepare the pentamethyl disiloxane represented by a formula I. The method has high reaction yield and high product quality and is suitable for industrial preparation.

Description

A kind of method for preparing pentamethyldisiloxane

technical field

The invention belongs to the field of organosilicon chemical synthesis, and in particular relates to a method for preparing pentamethyldisiloxane.

Background technique

Pentamethyldisiloxane is an extremely important organosilicon intermediate. This compound has active silicon-hydrogen bonds and can be used as a monomer for the synthesis of organosilicon polymers. It can also be added to carbon compounds to form silicon-carbon Polymers can also link silicone rubber, silicone oil, and silicone resin to modify their properties, and are also raw materials for synthesizing special surfactants. Therefore, pentamethyldisiloxane plays an extremely important role in synthetic silicone products.

The methods for preparing pentamethyldisiloxane disclosed in the prior art all use dimethylchlorosilane or its derivatives as raw materials and prepare by hydrolysis method: Japanese Patent Publication JP64031791 uses dimethylethoxysilane and Trimethylchlorosilane is used as a raw material, Japanese Patent Publication JP3002188 uses dimethylchlorosilane and hexamethyldisilazane as raw materials, and Japanese Patent Publication JP2157285 reports that trimethylsilanol and dimethylchlorosilane are used as raw materials . The common disadvantages of these three routes are: expensive raw materials lead to higher costs, low product yield (less than 20%), and are not suitable for large-scale industrial production.

Contents of the invention

In order to overcome the shortcomings of high product cost and low yield in the existing preparation method, the present invention devotes itself to developing a new preparation method. Through a large number of tests and comparisons, the inventor proposed a Grignard reagent method for preparing pentamethyldisiloxane.

Technical scheme of the present invention is as follows:

A method for preparing pentamethyldisiloxane, the reaction formula is as follows:

In the formula: R is selected from methyl, ethyl, propyl, phenyl or vinyl;

X is selected from a chlorine atom or a bromine atom;

n is an integer from 4 to 100;

The reaction steps are as follows:

1) adding the high hydrogen-containing silicone oil shown in formula III to the Grignard reagent, and carrying out the Grignard reaction in the presence of an ether solvent and a cosolvent;

2) adding water to carry out hydrolysis reaction to prepare pentamethyldisiloxane shown in formula I.

In order to facilitate those skilled in the art to better understand the present invention, the following step-by-step chemical reaction formula is used for further detailed description, and the definition of each group in the formula is the same as before.

In the formula: III-1 is the main content fragment of high hydrogen-containing silicone oil III.

Reaction formula (1) is the preparation of Grignard reagent, which is a well-known conventional reaction. Usually, halogenated hydrocarbons are used in solvents to react with metal magnesium to generate alkylmagnesium halide RMgX. This organic magnesium compound is called Grignard Reagent. Grignard reagents can undergo addition reactions with compounds such as aldehydes and ketones, and generate alcohols after hydrolysis. This type of reaction is called a Grignard reaction (Grignard Reaction). Grignard reagents are one of the most widely used reagents in organic synthesis. Grignard reagents are very sensitive to water. In fact, all compounds with active hydrogen can react with Grignard reagents, such as alcohols, terminal alkynes, primary amines, and carboxylic acids. Therefore, when preparing Grignard reagents, anhydrous reagents and dry instruments should be used. Generally, various halogenated hydrocarbons react with magnesium to generate Grignard reagents. However, different halogenated hydrocarbons have different reactivity with magnesium. Generally speaking, when the alkyl groups are the same, iodoalkanes are the most reactive, and fluorocarbons are the least reactive (actually no one has used fluorocarbons to make Grignard reagents). Haloalkane activity RI>RBr>RCI>RF. In the preparation of Grignard reagents, the choice of solvent is also a key factor. Conventional solvents are ethers and tetrahydrofuran, because the oxygen atoms in the molecules of these compounds have lone pairs of electrons, which can form solvent-soluble complexes with Grignard reagents. The Grignard reagent of the present invention can be selected from common solvents such as absolute diethyl ether, tert-butyl methyl ether, diethylene glycol dimethyl ether, isobutyl ether, n-butyl ether, and tetrahydrofuran. More preferred solvents are diethyl ether and tetrahydrofuran. The amount of solvent used is preferably 5-20:1 by weight ratio of solvent to magnesium powder, preferably 10-16:1.

The reaction temperature and reaction time have a great influence on the yield of the prepared Grignard reagent. In this unit reaction, the higher the reaction temperature, the faster the reaction speed and the shorter the reaction cycle, but the more corresponding impurities are produced; the lower the reaction temperature, the less likely the reaction will be initiated, and the longer the reaction time, the greater the reaction rate. period time. It is advisable to control the temperature at 30-70°C, and the preferred reaction temperature is 45-60°C; in this unit reaction, the time for controlling the preparation of the Grignard reagent is 8-24 hours, and the preferred reaction time is 12-18 hours.

According to the preparation method of the present invention, the preparation of the Grignard reagent (reaction 1), the Grignard reaction (reaction 2) and the hydrolysis reaction (reaction 3) are all carried out in the same reactor. The test finds that suitable solvent consumption in the reaction (1) is unfavorable for the carrying out of the reaction (2), and this is mainly because the solubility of the raw material III in the ether solvent in the reaction (2) is low, thereby affecting the reaction effect; As the amount of ether solvent increases, the amount of raw material III dissolved in the solvent increases, and the amount of reaction products II-1 and II-2 generated in this step increases, and the yield of the final target product also increases accordingly. However, too much solvent will inevitably increase the cost of raw materials and the cost of post-treatment separation, so it is necessary to control the amount of solvent within a reasonable range. Through a large number of tests, the inventor adopts the mode of adding a certain proportion of cosolvent in reaction (2) to increase the solubility of raw material III, which not only can avoid using a large amount of ether solvents, but also obviously improves the final target product (shown in formula I) Pentamethyldisiloxane) yield. The cosolvent used in the present invention is selected from cyclohexane, n-hexane, benzene, toluene, xylene, etc., and the preferred cosolvent is benzene or toluene. The appropriate ratio between the added co-solvent and the ether solvent is 0.5-10:1 by weight to ensure the smooth progress of the reaction, and the preferred ratio is 0.8-2:1.

In the Grignard reaction shown in reaction (2), controlling the appropriate material ratio can not only ensure the complete reaction of raw material III, but also reduce the occurrence of side reactions and avoid generating a large amount of alcohol. The suitable feeding ratio is that the molar ratio of the III-1 segment in the raw material III to the methylmagnesium halide is 0.8-10:1, especially 1-5:1. In this unit reaction, the Grignard reaction temperature is a key factor controlling the amount and ratio of compounds II-1 and II-2, and has a crucial impact on the yield of the final target product. The higher the reaction temperature, the easier the side reactions are to carry out, and the relative amount of compound II-1 and II-2 is less; when the temperature is lower, it is only conducive to the formation of compound II-2, not conducive to the formation of compound II-1 , leading to the final hydrolysis product mainly generating compound I-1. Experiments have found that it is advisable to control the Grignard reaction temperature between 10-30°C, and the preferred reaction temperature is 20-30°C. Generally, it is advisable to control the Grignard reaction time to 5-8 hours.

In reaction (3), factors such as hydrolysis temperature, hydrolysis time, and hydrolysis medium also have a crucial influence on the yield of product compounds. In this unit reaction, the hydrolysis process is that the compounds with two structures of compounds II-1 and II-2 undergo autohydrolysis and isohydrolysis, and the hydrolyzed products are three structures of I, I-1, and I-2. Due to steric hindrance, the amount of generating I-2 is usually relatively small, so controlling the temperature is conducive to hydrolysis between compounds II-1 and II-2 (i.e. carrying out different hydrolysis), and limiting compound II-2 to carry out self hydrolysis is The essential. It is advisable to control the hydrolysis temperature at 0-50°C, and the preferred hydrolysis temperature is 10-15°C. In this unit reaction, the longer the hydrolysis time is, the more impurities will be generated. Generally, it is advisable to control the hydrolysis time for 6-15 hours, and preferably the hydrolysis reaction time is 7-8 hours. The hydrolysis reaction can be carried out in an acidic medium such as sulfuric acid, hydrochloric acid, etc., a neutral medium such as water, and an alkaline medium such as sodium carbonate and sodium hydroxide. When hydrolyzed in water or alkaline medium, it is easy to produce a large amount of white solid to form an emulsified state with the reaction solution, which is difficult to separate; while hydrolyzed in acidic medium, the solution becomes a transparent layered solution when the reaction is completed, which is easy to extract and separate. Therefore, it is recommended to choose hydrolysis under acidic medium conditions.

The final target product is obtained by rectifying the hydrolyzate. Selecting a rectifying tower with 40 plates and a reflux ratio of 15:1 can obtain the final product compound I (pentamethyldisiloxane) with a purity of more than 98%, and can also obtain a small amount of the other two compounds through rectification. Important silicone intermediates I-1 (1,1,3,3-tetramethyldisiloxane) and I-2 (hexamethyldisiloxane).

Compared with the traditional organosilicon monomer hydrolysis method, the preparation method of the present invention has the following advantages:

(1) Avoid the disadvantages of the traditional organosilicon monomer hydrolysis method: due to the difference in the degree of hydrolysis of chloride ions in the organosilicon monomer, it is difficult to control the degree of hydrolysis, that is, it is difficult to control the self-hydrolysis and degradation of the organosilicon monomer. The speed of different hydrolysis results in more by-products.

(2) The yield and the purity of the product pentamethyldisiloxane are greatly improved.

(3) The raw materials used in the present invention are low in price, high in hydrolysis purity, easy to separate product compounds, and have good industrial value.

Detailed ways

The following examples are used to further describe and illustrate the present invention for a better understanding of the present invention, but are not intended to limit the claims stated in the present invention. All reagents used are commercially available.

Example 1

Add 7.2 grams (0.3 mol) of magnesium powder and 108 grams of ether into a 500 ml four-neck flask equipped with a thermometer, agitator, and condenser, and feed methyl bromide gas under nitrogen protection to control the reaction temperature at 50°C until the magnesium powder All gone. After reacting for 14 hours, 45 g (0.47 mol) of methyl bromide was introduced. Chemical analysis determined that the Grignard reagent content was 96%. Add 100 grams of toluene to the above-mentioned four-necked bottle, cool to about 20°C, add n=20 (molecular weight is about 1300), and 30 grams of high hydrogen-containing silicone oil (hydrogen content 1.56%) with n=20 (molecular weight is about 1300) and both ends are methyl groups (mainly The molar number of content fragments is 0.46 moles), and the reaction was carried out at 20° C. for 5 hours. Then, the temperature was controlled at 15° C., and 200 grams of 20% dilute sulfuric acid was added dropwise to the reactant in the above-mentioned four-neck flask, and the addition was completed and kept for 7 hours until the solution was transparent, and the hydrolysis reaction was completed. The reaction solution was separated into an oil layer, washed with water until neutral, dried and rectified to collect fractions at 83-84°C to obtain 7 g of the target compound as a colorless transparent liquid with a purity of over 98% and a yield of 50% by gas chromatography.

Target compound IR (KBr) (Impact 400 produced by Nicolet, USA): 2966cm-1 (C-H stretching vibration of methyl silane), 2131cm-1 (Si-H stretching vibration of silane), 1261cm-1 (C-H stretching vibration of methyl silane C-H in-plane symmetric deformation vibration), 1072cm-1 (Si-O stretching vibration in siloxane);

Target compound NMR (using CHCl ₃ =7.264ppm in CDCl ₃ as internal standard) (Mercury300 (UX) produced by Varian, USA): δH, ppm (DMSO): 0.196 (s, 9H, CH3), 0.172 (bs, 6H , CH3), 4.68 (m, 1H, Si-H).

Example 2

Add 7.2 grams (0.3 mol) of magnesium powder and 108 grams of ether into a 500 ml four-necked bottle equipped with a thermometer, agitator, and condenser, and feed in methyl chloride gas under nitrogen protection, and control the reaction temperature at 50°C until the magnesium powder disappears completely. . The reaction time was 18 hours, 25 g (0.5 mol) of methyl chloride was introduced, and the content of the Grignard reagent was determined to be 95% by chemical analysis. Add 120 grams of toluene to the above-mentioned four-necked bottle, and add 38.4 grams of high hydrogen-containing silicone oil (hydrogen content 1.56%) with n=20 (molecular weight is about 1300) and methyl groups at both ends (main content fragment) dropwise at 30 ° C. The number of moles is 0.6 mol), and the reaction was incubated for 8 hours. Then, the temperature was lowered to 15° C., and 200 grams of 20% dilute sulfuric acid was added dropwise to the above-mentioned four-necked flask. After the addition, the reaction was incubated at 15° C. for 7 hours until the solution was transparent, and the hydrolysis reaction was completed. The separated oil layer was washed with water until neutral, dried, and the fraction at 83-84°C was collected by rectification to obtain 6 g of the target compound as a colorless transparent liquid with a purity of over 98% and a yield of 45% by gas chromatography.

Target compound IR (KBr) (Impact 400 produced by Nicolet, USA): 2966cm-1 (C-H stretching vibration of methyl silane), 2131cm-1 (Si-H stretching vibration of silane), 1261cm-1 (C-H stretching vibration of methyl silane C-H in-plane symmetric deformation vibration), 1072cm-1 (Si-O stretching vibration in siloxane);

Target compound NMR (using CHCl ₃ =7.264ppm in CDCl ₃ as internal standard) (Mercury300 (UX) produced by Varian, USA): δH, ppm (DMSO): 0.196 (s, 9H, CH3), 0.172 (bs, 6H , CH3), 4.68 (m, 1H, Si-H).

Claims (2)

1. method for preparing pentamethyl disiloxane, reaction formula is following:

In the formula: R is selected from methyl, ethyl, propyl group, phenyl or vinyl;

X is selected from chlorine atom or bromine atoms;

N is from 4 to 100 integer;

Reactions step is following:

1) in Grignard reagent, adds the high containing hydrogen silicone oil shown in the formula III, in the presence of ether solvent and solubility promoter, carry out the grignard reaction;

2) add the water pentamethyl disiloxane shown in the prepared in reaction formula I that is hydrolyzed, hydrolysising reacting temperature 10-15 ℃, the time is 7-8 hour;

The main content fragment of raw material III and the mol ratio of methylmagnesium-halide are 1-5 in the grignard reaction: 1; Temperature of reaction is 20-30 ℃; Described solubility promoter is selected from benzene or toluene, and the ratio of solubility promoter and ether solvent is 1-2 by weight: 1;

Described main content fragment structure is

2. according to the described preparation method of claim 1, it is characterized in that: the reaction that in acidic medium, is hydrolyzed, 15 ℃ of temperature of reaction.