A short-process preparation method for alkoxysilanes

Abstract

This invention relates to a short-process method for preparing alkoxysilanes. A silicon source and catalyst are added to an alcohol, and after nitrogen purging, the mixture is heated under negative pressure. After the reaction is complete, the mixture is filtered, and the filtrate is then distilled under reduced pressure after nitrogen purging. The resulting solid product is dissolved in an organic solvent, filtered, and the filtrate is then distilled under reduced pressure to remove the organic solvent, yielding the alkoxysilane. This method directly reacts precipitated silica as the silicon source with an alcohol to generate alkoxysilanes. This process has a short synthetic route, is simple to operate, has low energy consumption, low production cost, and is environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of organosilicon synthesis, particularly the synthesis of alkoxysilanes. Background Technology

[0002] Organosilicon materials are not only an important component of the new materials sector within the national strategic emerging industries, but also indispensable supporting materials for other strategic emerging industries. Alkoxysilanes are crucial organosilicon raw materials, serving as fundamental raw materials for the preparation of silane compounds, organosilicon polymers, colloidal silica, silylating agents, and ceramics. They are widely used in precision casting, silica manufacturing, adhesives, coatings, and the preparation of special coatings. They can also be used as catalysts and crosslinking agents for olefin polymerization and have experienced rapid development in recent years.

[0003] To date, there are generally two methods for the industrial preparation of alkoxysilanes: one is the chlorosilane alcoholysis method, and the other is the direct synthesis of alkoxysilanes. The chlorosilane alcoholysis method uses elemental silicon to react with chlorine to produce silicon tetrachloride, which is then alcoholyzed with the corresponding alcohol to synthesize alkoxysilanes. This two-step method has a long process flow, high material loss, low yield, complex recovery process for the generated byproduct HCl, and is prone to equipment corrosion and environmental pollution, and also requires high equipment investment. The direct synthesis of alkoxysilanes utilizes elemental silicon to react with alcohols (mainly highly reactive lower alcohols) in the presence of a catalyst to produce alkoxysilanes. This method has a low silicon utilization rate. Both existing methods require elemental silicon, which is generally produced by reducing silicon dioxide with carbon at high temperatures. This process is energy-intensive and easily generates gases such as carbon monoxide.

[0004] Silica has a stable structure, and the Si-O-Si bonds are difficult to break. Currently, there are only a few reports of directly synthesizing alkoxysilanes by reacting highly reactive silica such as rice husk ash and fumed silica with alcohols under high temperature and pressure. However, rice husk ash is obtained by burning rice husks and has low yield; fumed silica is a product of the organosilicon industry. Existing methods require harsh reaction conditions and the silicon source used is expensive.

[0005] This invention uses precipitated silica and higher alcohols as raw materials. Utilizing the differences in boiling points and volatility of water, higher alcohols, and the products, the water generated during the reaction is removed promptly under vacuum, successfully preparing alkoxysilanes. This method is a direct synthesis method for alkoxysilanes, offering good atom economy, low cost, and environmental friendliness with minimal waste emissions, aligning with the principles of green chemistry. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for synthesizing alkoxysilanes, namely, to directly synthesize alkoxysilanes by using precipitated silica as a silicon source and alcohol in the presence of a catalyst.

[0007] The specific implementation method of this invention is as follows: A short-process preparation method for alkoxysilane includes the following steps: adding a silicon source and a catalyst to an alcohol, purging with nitrogen, heating and reacting under negative pressure, filtering after the reaction is completed, purging the filtrate with nitrogen and distilling under reduced pressure, dissolving the obtained solid product with an organic solvent, filtering, removing the organic solvent from the filtrate by reduced pressure distillation, and obtaining alkoxysilane.

[0008] The silicon source is precipitated silica.

[0009] The catalyst is anhydrous magnesium chloride or anhydrous aluminum chloride.

[0010] The mass ratio of the silicon source to the catalyst is 1:0.4~1.

[0011] The alcohol is a primary alcohol with ≥9 carbon atoms.

[0012] The alcohol mentioned is any one of nonanol, decol, undecylol, and dodecaylol.

[0013] The reduced pressure heating reaction temperature is 120~200 ℃, and the reduced pressure heating reaction time is 5-12 h under -0.05Mpa~-0.1 MPa (gauge pressure).

[0014] The vacuum distillation temperature is 130-200 ℃.

[0015] The organic solvent is any one of ethanol, dimethyl sulfoxide, N,N-dimethylformamide, or tetrahydrofuran.

[0016] The reaction of silicon source and alcohol in the presence of a catalyst to produce alkoxysilane and water is a reversible reaction. The water produced must be removed promptly to allow the reaction to proceed towards the alkoxysilane. This invention utilizes the differences in boiling points and volatility between water, higher alcohols, and their products. Water has a boiling point of 100 °C, while higher alcohols and their products have boiling points above 200 °C. Under vacuum, the boiling points of substances decrease, and water evaporates at a lower temperature. However, higher alcohols and their products have higher boiling points than water and will not evaporate simultaneously with water.

[0017] After the reaction is complete, the mixture is filtered, and the filtrate is replaced with nitrogen and then distilled under reduced pressure to remove unreacted alcohol. The distilled alcohol can be recycled. The distillation residue is dissolved in an organic solvent, filtered, and the organic solvent is removed by distillation under reduced pressure to obtain alkoxysilane.

[0018] The beneficial effects of this invention are as follows: 1. This invention uses inexpensive silicon sources such as precipitated silica and primary alcohols with 9 or more carbon atoms as raw materials to synthesize alkoxysilanes in a one-step process. The raw materials are inexpensive and readily available, the reaction operation is simple, and the production cost is low; 2. This invention avoids the process of high-temperature reduction of silicon dioxide to generate elemental silicon, which can significantly reduce energy consumption, reduce by-products, and alleviate environmental pressure; 3. The preparation method of this invention is a short-process technology with good atom economy. Attached Figure Description

[0019] Figure 1 The infrared spectrum of tetranonyl orthosilicate prepared in Example 1 is shown.

[0020] Figure 2 The infrared spectrum of tetradecyl orthosilicate prepared in Example 5. Specific implementation methods

[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below.

[0022] Example 1

[0023] 1.95 g of 2000-mesh precipitated silica and 1.31 g of aluminum chloride were added to excess n-nonyl alcohol. After nitrogen purging, the mixture was reacted at 130 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. After the reaction was complete, the mixture was filtered. The filtrate was then purified by nitrogen purging and distilled under reduced pressure at 140 °C until dry. The distilled n-nonyl alcohol was collected and refluxed. The resulting solid was dissolved in ethanol and filtered. The ethanol was removed by rotary evaporation at 60 °C to obtain oily tetranonyl orthosilicate, with a yield of 65.2%. Its infrared spectrum is shown below. Figure 1 As shown, 1455cm -1 The peak at 2924 cm⁻¹ represents the methylene bending vibration. -1 The peak at 2854 cm⁻¹ represents the asymmetric stretching vibration of the methylene group. -1 The peak at 1086 cm⁻¹ represents the methylene symmetric stretching vibration. -1 and 880 cm -1 The peak value for the stretching vibration of Si-OC is 1044 cm⁻¹. -1 The peak value for CO stretching vibration is 3234 cm⁻¹. -1 The peak at this point is the OH stretching vibration peak, which is the hydroxyl peak of the residual alcohol, proving that the product is tetranonyl orthosilicate.

[0024] Example 2

[0025] 1.95 g of 150-mesh precipitated silica and 1.15 g of anhydrous magnesium chloride were added to excess n-nonyl alcohol. After nitrogen purging, the mixture was reacted at 135 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. After the reaction was complete, the mixture was filtered, and the filtrate was distilled to dryness under reduced pressure at 140 °C after nitrogen purging. The distilled n-nonyl alcohol could be recovered. The resulting solid was dissolved in ethanol by ultrasonication and then filtered. The ethanol was removed from the filtrate by rotary evaporation at 50 °C to obtain oily tetranonyl orthosilicate, with a yield of 67.1%.

[0026] Example 3

[0027] 1.5 g of 150-mesh precipitated silica and 1.2 g of anhydrous magnesium chloride were added to excess n-nonyl alcohol. After nitrogen purging, the mixture was reacted at 130 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. After the reaction was complete, the mixture was filtered, and the filtrate was distilled to dryness under reduced pressure at 140 °C after nitrogen purging. The distilled n-nonyl alcohol could be recovered. The resulting solid was dissolved in ethanol by ultrasonication and then filtered. The ethanol was removed from the filtrate by rotary evaporation at 60 °C to obtain oily tetranonyl orthosilicate, with a yield of 63.3%.

[0028] Example 4

[0029] 1.5 g of 800-mesh precipitated silica and 1.2 g of anhydrous magnesium chloride were added to excess n-nonyl alcohol. After nitrogen purging, the mixture was reacted at 135 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. After the reaction was complete, the mixture was filtered. The filtrate was then purified by nitrogen purging and distilled under reduced pressure at 140 °C until dry. The distilled n-nonyl alcohol could be recovered. The resulting solid was dissolved by sonication in dimethyl sulfoxide and filtered. The filtrate was then distilled under reduced pressure at 80 °C to remove the dimethyl sulfoxide, yielding oily tetranonyl orthosilicate with a yield of 66.2%.

[0030] Example 5

[0031] 1.95 g of 150-mesh precipitated silica and 1.11 g of anhydrous magnesium chloride were added to excess n-decanol. After nitrogen purging, the mixture was reacted at 140 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. After the reaction was complete, the mixture was filtered, and the filtrate was distilled under reduced pressure at 150 °C until dry. The distilled n-decanol was recovered, and the residual solid was dissolved in ethanol by ultrasonication and filtered. The filtrate was rotary evaporated at 70 °C to obtain tetradecyl orthosilicate, with a yield of 68.2%. The solid was cooled to room temperature and solidified to obtain a waxy solid. Its infrared spectrum is shown below. Figure 2 As shown, 1448 cm -1 The peak at 2926 cm⁻¹ represents the methylene bending vibration. -1 The peak at 2965 cm⁻¹ represents the asymmetric stretching vibration of the methylene group. -1 The peak at 2855 cm⁻¹ represents the asymmetric stretching vibration of methyl groups. -1The peak at 1087 cm⁻¹ represents the methylene symmetric stretching vibration. -1 and 877 cm -1 The peak at 1043 cm⁻¹ represents the stretching vibration of Si-OC. -1 The peak at this point corresponds to the CO stretching vibration. This confirms that the product is tetradecyl orthosilicate.

[0032] Example 6

[0033] 1.5 g of 150-mesh precipitated silica and 1.01 g of anhydrous magnesium chloride were added to excess n-decanol. After nitrogen purging, the mixture was reacted at 160 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. The mixture was filtered, and the filtrate was distilled under reduced pressure at 150 °C until dry. The distilled n-decanol was recovered, and the residual solid was dissolved in ethanol by ultrasonication and filtered. The filtrate was rotary evaporated at 70 °C to obtain an oily tetradecyl orthosilicate. After cooling to room temperature, the solid solid solid solidified to obtain a waxy solid with a yield of 64.8%.

[0034] Example 7

[0035] 1.5 g of 800-mesh precipitated silica and 0.95 g of anhydrous magnesium chloride were added to excess n-decanol. After nitrogen purging, the mixture was reacted at 160 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. After the reaction was complete, the mixture was filtered, and the filtrate was distilled under reduced pressure at 150 °C until dry. The distilled n-decanol was recovered, and the residual solid was dissolved in dimethyl sulfoxide by sonication and filtered. The filtrate was distilled under reduced pressure at 70 °C to obtain an oily tetradecyl orthosilicate with a yield of 68.7%. The solid was cooled to room temperature and solidified to obtain a waxy solid.

[0036] Example 8

[0037] 1.61 g of 2000-mesh precipitated silica and 0.94 g of anhydrous magnesium chloride were added to excess dodecyl alcohol (preheated to a liquefied state). After nitrogen purging, the mixture was reacted at 200 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. The mixture was filtered, and the filtrate was distilled under reduced pressure at 210 °C until dry. The distilled dodecyl alcohol was recovered, and the residual solid was dissolved in anhydrous ethanol by ultrasonication and filtered. The filtrate was rotary evaporated at 70 °C to obtain oily dodecyl orthosilicate, which was then cooled to room temperature to solidify, yielding a solid with a yield of 58.9%.

[0038] Example 9

[0039] 1.5 g of 150-mesh precipitated silica and 0.98 g of anhydrous magnesium chloride were added to excess dodecyl alcohol (preheated to a liquefied state). After nitrogen purging, the mixture was reacted at 205 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. The mixture was filtered, and the filtrate was distilled under reduced pressure at 210 °C until dry. The distilled dodecyl alcohol was recovered, and the residual solid was dissolved in anhydrous ethanol by ultrasonication and filtered. The filtrate was rotary evaporated at 70 °C to obtain oily dodecyl orthosilicate, which was then cooled to room temperature to solidify, yielding a solid with a yield of 54.3%.

[0040] Example 10

[0041] 1.49 g of 800-mesh precipitated silica and 1.00 g of anhydrous magnesium chloride were added to excess dodecyl alcohol (preheated to a liquefied state). After nitrogen purging, the mixture was reacted at 200 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 11 h. The mixture was filtered, and the filtrate was distilled under reduced pressure at 210 °C until dry. The distilled dodecyl alcohol was recovered, and the residual solid was dissolved in anhydrous ethanol by ultrasonication and filtered. The filtrate was rotary evaporated at 60 °C to obtain oily dodecyl orthosilicate, which was then cooled to room temperature to solidify, yielding a solid with a yield of 56.4%.

[0042] Example 11

[0043] 1.95 g of 150-mesh precipitated silica and 1.32 g of aluminum chloride were added to excess dodecyl alcohol (preheated to a liquefied state). After nitrogen purging, the mixture was reacted at 200 °C under -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. The mixture was filtered, and the filtrate was distilled under reduced pressure at 210 °C until dry. The distilled dodecyl alcohol was recovered, and the residual solid was dissolved in anhydrous ethanol by ultrasonication and filtered. The filtrate was rotary evaporated at 70 °C to obtain oily dodecyl orthosilicate, which was then cooled to room temperature to solidify, yielding a solid with a yield of 53.2%.

[0044] Comparative Example 1

[0045] 1.48 g of 150-mesh precipitated silica and 1.00 g of anhydrous magnesium chloride were added to excess n-octanol. After nitrogen purging, the mixture was reacted at 180 °C at -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. The mixture was filtered, and the filtrate was distilled under reduced pressure at 210 °C until dry. The distilled dodecanol was recovered, and the remaining solid was dissolved in anhydrous ethanol by ultrasonication and filtered. The filtrate was rotary evaporated at 70 °C, but no product was obtained.

[0046] Comparative Example 2

[0047] 1.50-150 mesh precipitated silica and 0.99 g anhydrous magnesium chloride were added to excess n-pentanol. After nitrogen purging, the mixture was reacted at 120 °C at -0.05 MPa to -0.1 MPa (gauge pressure) for 12 h. The mixture was filtered, and the filtrate was distilled under reduced pressure at 210 °C until dry. The distilled dodecanol was recovered, and the remaining solid was dissolved in anhydrous ethanol by ultrasonication and then filtered. The filtrate was rotary evaporated at 70 °C, but no product was obtained.

Claims

1. A short-process preparation method for alkoxysilanes, characterized in that, The process includes the following steps: adding a silicon source and a catalyst to an alcohol, purging with nitrogen, and heating the mixture under negative pressure. After the reaction is complete, the mixture is filtered, and the filtrate is purged with nitrogen and then distilled under reduced pressure. The resulting solid product is dissolved in an organic solvent and filtered. The filtrate is then distilled under reduced pressure to remove the organic solvent, yielding an alkoxysilane. The alcohol is any one of nonanol, decanol, undecylol, and dodecanol. The reaction temperature under reduced pressure is 120-200℃, and the reaction time under reduced pressure at -0.05 MPa to -0.1 MPa is 5-12 h. The organic solvent is any one of ethanol, dimethyl sulfoxide, N,N-dimethylformamide, or tetrahydrofuran. The catalyst is anhydrous magnesium chloride or anhydrous aluminum chloride.

2. The short-process preparation method of alkoxysilane according to claim 1, characterized in that, The silicon source is precipitated silica, and the particle size of precipitated silica is 120-2000 mesh.

3. The short-process preparation method of alkoxysilane according to claim 1, characterized in that, The mass ratio of silicon source to catalyst is 1:0.4~1.

4. The short-process preparation method of alkoxysilane according to claim 1, characterized in that, The vacuum distillation temperature is 130-200 ℃.

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