A method for carbon dioxide-assisted catalytic synthesis of alkoxysilanes

Abstract

This invention relates to a method for the carbon dioxide-assisted catalytic synthesis of alkoxysilanes. The method utilizes the reaction of carbon dioxide with an alcohol to generate a trace amount of dialkyl carbonate, which then reacts with a silicon source to produce alkoxysilanes. This reduces the activation energy required for the reaction, shortens the reaction time, and increases the yield. This method features a short synthetic route, low energy consumption, and is environmentally friendly, representing a breakthrough in the field of organosilicon synthesis, particularly for the synthesis of alkoxysilanes.

Description

Technical Field

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

[0002] Organoalkoxysilanes are important intermediates in the preparation of silicone oils, silicone rubbers, and silicone resins, second only to organochlorosilanes in usage. Long-chain organoalkoxysilanes, due to their excellent hydrothermal stability, can be used as special media, suitable for use as heat transfer fluids, working oils, and lubricants. They can also be used as surface treatment agents for inorganic fillers (hydrophobic, anti-sticking) and coating modifiers.

[0003] Alkoxysilanes, such as tetranonyl orthosilicate, are generally prepared from halosilanes and their corresponding alcohols. Existing methods often require first reducing silicon dioxide to elemental silicon, then reacting it with hydrogen chloride and hydrogen at 200-350°C under a catalyst to produce chlorosilanes. These chlorosilanes are then reacted with alcohols to yield organoalkoxysilanes. This method is lengthy, complex, energy-intensive, and costly.

[0004] This invention utilizes the effect of carbon dioxide-assisted catalysis to reduce the activation energy of the reaction, and provides a method for the direct reaction of precipitated silica with primary alcohols to prepare alkoxysilanes with a short process, short reaction time, and low energy consumption. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to develop a method for the synthesis of alkoxysilanes using carbon dioxide-assisted catalysis. This method utilizes carbon dioxide, an inexpensive and readily available co-catalyst, to directly prepare organoalkoxysilanes from precipitated silica and primary alcohols with ≥9 carbon atoms under the action of a catalyst and a co-catalyst.

[0006] The specific implementation method of this invention is as follows: A dehydration device is installed, excess alcohol is added to a reaction flask, and after nitrogen purging, precipitated silica and a catalyst are added sequentially under nitrogen protection. After three carbon dioxide purgings, the reaction is heated and stirred for 2-6 hours under a carbon dioxide atmosphere. The mixture is then cooled to 30-40 °C and filtered. Unreacted alcohol is removed by vacuum distillation of the filtrate. An organic solvent is added to the residue, stirred, and then filtered. The organic solvent is removed by vacuum distillation of the filtrate to obtain alkoxysilanes.

[0007] In the above scheme, the heating reaction temperature is 210~250 ℃.

[0008] In the above scheme, the alcohol is a primary alcohol with ≥9 carbon atoms. As a preferred embodiment, the alcohol is n-nonanol or n-decanol.

[0009] In the above scheme, the catalyst is anhydrous magnesium chloride or anhydrous aluminum chloride.

[0010] In the above scheme, the organic solvent is methanol, ethanol, isopropanol or n-butanol.

[0011] Appendix Figure 3 The dehydration apparatus, from top to bottom, consists of a condenser, a dehydration tube, and a reaction flask. The desiccant in the dehydration tube can be 3A molecular sieve, alumina, anhydrous sodium sulfate, or anhydrous magnesium sulfate. Under a carbon dioxide atmosphere, carbon dioxide reacts with the primary alcohol to produce trace amounts of dialkyl carbonate and water. The water and primary alcohol azeotropically vaporize, rise to the condenser, and liquefy upon cooling. The mixed liquid drips into the straight dehydration tube, directly contacting the desiccant. The water is adsorbed and removed by the desiccant, and the remaining liquid returns to the reaction flask. This external adsorption dehydration coupled with the chemical reaction effectively removes the water produced in the reaction, promoting the forward reaction. The newly generated trace amounts of dialkyl carbonate are unstable and can decompose on the silicon source surface to generate alkoxy radicals, which combine with silicon atoms to form alkoxysilanes and carbon dioxide.

[0012] The beneficial effects of this invention are: 1) This invention utilizes carbon dioxide-assisted catalysis to reduce the activation energy required for the reaction, shorten the reaction time, and reduce energy consumption; 2) This invention uses an external dehydration device for dehydration; 3) This invention uses inexpensive silicon sources such as precipitated silica, which is low in cost and environmentally friendly. Attached Figure Description

[0013] Figure 1 The infrared spectrum of tetranonyl orthosilicate prepared in Example 1 is shown.

[0014] Figure 2 The infrared spectrum of tetradecyl orthosilicate prepared in Example 7.

[0015] Figure 3 This is a diagram of the reflux reaction apparatus of the present invention. Detailed Implementation

[0016] 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.

[0017] Example 1

[0018] As attached Figure 3The experimental setup was constructed, with a dehydration tube (a straight glass tube) connecting the reflux condenser and the reaction flask. The desiccant in the dehydration tube was 3A molecular sieve. Excess n-nonyl alcohol was added to the reaction flask, purged with nitrogen, and then 1.50 g of 150-mesh precipitated silica and 0.95 g of anhydrous magnesium chloride were added under nitrogen protection. The mixture was purged with carbon dioxide three times, refluxed at 220 °C for 4 h under a carbon dioxide atmosphere, cooled to 40 °C, and the filtrate was purged with nitrogen and then distilled under reduced pressure at 140 °C to remove the n-nonyl alcohol. The distilled n-nonyl alcohol was collected and recycled. The residue was added to ethanol and stirred vigorously for 2 hours, then filtered. The ethanol was removed by rotary evaporation at 60 °C to obtain oily tetranonyl orthosilicate with a yield of 90%. Its infrared spectrum is shown below. Figure 1 As shown, 1456 cm -1 The peak at 2924 cm⁻¹ represents the bending vibration of the methylene group. -1 The peak at 2956 cm⁻¹ represents the asymmetric stretching vibration of the methylene group. -1 The peak at 2855 cm⁻¹ represents the asymmetric stretching vibration of the methyl group. -1 The peak at 1088 cm⁻¹ represents the symmetric stretching vibration of the methylene group. -1 and 881 cm -1 The peak value for the stretching vibration of Si-OC is 1045 cm⁻¹. -1 The peak at this point corresponds to the stretching vibration of CO. Preliminary evidence suggests the product is tetranonyl orthosilicate.

[0019] Example 2

[0020] The experimental setup was the same as in Example 1, with 3A molecular sieve used as the desiccant in the dehydration tube. Excess n-nonyl alcohol was added to the reaction flask, purged with nitrogen, and then 1.50 g of 325-mesh precipitated silica and 0.98 g of anhydrous magnesium chloride were added under nitrogen protection. The mixture was purged with carbon dioxide three times, refluxed at 217 °C for 5 h under a carbon dioxide atmosphere, cooled to 40 °C, and the filtrate was purged with nitrogen and then distilled under reduced pressure at 140 °C to remove the n-nonyl alcohol. The distilled n-nonyl alcohol was collected and recycled. The residue was added to methanol and stirred vigorously for 2 hours, then filtered. The filtrate was rotary evaporated at 40 °C to remove the methanol, yielding oily tetranonyl orthosilicate in 89% yield.

[0021] Example 3

[0022] The experimental setup was the same as in Example 1, with 3A molecular sieve used as the desiccant in the dehydration tube. Excess n-nonyl alcohol was added to the reaction flask, purged with nitrogen, and then 1.64 g of 800-mesh precipitated silica and 1.01 g of anhydrous magnesium chloride were added under nitrogen protection. The mixture was purged with carbon dioxide three times, refluxed at 218 °C for 5 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen and then distilled under reduced pressure at 150 °C to remove the n-nonyl alcohol. The distilled n-nonyl alcohol was collected and recycled. The residue was added to isopropanol and stirred vigorously for 2 hours, then filtered. The isopropanol was removed by rotary evaporation at 80 °C to obtain oily tetranonyl orthosilicate with a yield of 88%.

[0023] Example 4

[0024] The experimental setup was the same as in Example 1, with 3A molecular sieve used as the desiccant in the dehydration tube. Excess n-nonyl alcohol was added to the reaction flask, purged with nitrogen, and then 1.7 g of 2000-mesh precipitated silica and 0.96 g of anhydrous magnesium chloride were added under nitrogen protection. The mixture was purged with carbon dioxide three times, refluxed at 222 °C for 5 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen and then distilled under reduced pressure at 140 °C to remove the n-nonyl alcohol. The distilled n-nonyl alcohol was collected and recycled. The residue was added to ethanol and stirred vigorously for 2 hours, then filtered. The filtrate was rotary evaporated at 60 °C to remove the ethanol, yielding oily tetranonyl orthosilicate with a yield of 91%.

[0025] Example 5

[0026] The experimental setup was the same as in Example 1, with anhydrous sodium sulfate as the desiccant in the dehydration tube. Excess n-nonyl alcohol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 1.45 g of 150-mesh precipitated silica and 0.99 g of anhydrous magnesium chloride were added. The mixture was purged with carbon dioxide three times, refluxed at 220 °C for 6 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen, and then distilled under reduced pressure at 145 °C to remove the n-nonyl alcohol. The distilled n-nonyl alcohol was collected and recycled. The residue was added to ethanol, stirred vigorously for 2 hours, and then filtered. The filtrate was rotary evaporated at 60 °C to remove the ethanol, yielding oily tetranonyl orthosilicate with a yield of 92%.

[0027] Example 6

[0028] The experimental setup was the same as in Example 1, with anhydrous sodium sulfate as the desiccant in the dehydration tube. Excess n-nonyl alcohol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 2.00 g of 800-mesh precipitated silica and 0.95 g of anhydrous magnesium chloride were added. The mixture was purged with carbon dioxide three times, refluxed at 218 °C for 6 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen and then distilled under reduced pressure at 140 °C to remove the n-nonyl alcohol. The distilled n-nonyl alcohol was collected and recycled. The residue was added to isopropanol and stirred vigorously for 2 hours, then filtered. The filtrate was rotary evaporated at 80 °C to remove the isopropanol, yielding oily tetranonyl orthosilicate with a yield of 90%.

[0029] Example 7

[0030] The experimental setup was the same as in Example 1, with anhydrous magnesium sulfate as the desiccant in the dehydration tube. Excess n-decanol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 1.80 g of 150-mesh precipitated silica and 0.95 g of anhydrous magnesium chloride were added. The mixture was purged with carbon dioxide three times, refluxed at 235 °C for 6 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen and then distilled under reduced pressure at 160 °C to remove the n-decanol. The distilled n-decanol was collected and recycled. The residue was added to ethanol and stirred vigorously for 2 hours, then filtered. The ethanol was removed by rotary evaporation at 60 °C to obtain oily tetradecyl orthosilicate, which solidified at 25 °C, with a yield of 87%. Its infrared spectrum is shown below. Figure 2 As shown, its infrared spectrum is as follows Figure 2 As shown, 1456 cm -1 The peak at 2924 cm⁻¹ represents the methylene bending vibration. -1 The peak at 2957 cm⁻¹ represents the asymmetric stretching vibration of the methylene group. -1 The peak at 2854 cm⁻¹ represents the asymmetric stretching vibration peak of the methyl group. -1 The peak at 1086 cm⁻¹ represents the methylene symmetric stretching vibration. -1 and 879 cm -1 The peak at 1042 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.

[0031] Example 8

[0032] The experimental setup was the same as in Example 1, with anhydrous magnesium sulfate as the desiccant in the dehydration tube. Excess n-decanol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 1.52 g of 800-mesh precipitated silica and 1.01 g of anhydrous magnesium chloride were added. The mixture was purged with carbon dioxide three times, refluxed at 240 °C for 6 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen and then distilled under reduced pressure at 170 °C to remove the n-decanol. The distilled n-decanol was collected and recycled. The residue was added to methanol and stirred vigorously for 2 hours, then filtered. The filtrate was rotary evaporated at 45 °C to remove the methanol, yielding oily tetradecyl orthosilicate, which solidified at 25 °C, with a yield of 88%.

[0033] Example 9

[0034] The experimental setup was the same as in Example 1, with anhydrous sodium sulfate as the desiccant in the dehydration tube. Excess n-decanol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 1.91 g of 325-mesh precipitated silica and 0.98 g of anhydrous magnesium chloride were added. The mixture was purged with carbon dioxide three times, refluxed at 230 °C for 6 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen and then distilled under reduced pressure at 160 °C to remove the n-decanol. The distilled n-decanol was collected and recycled. The residue was added to isopropanol and stirred vigorously for 2 hours, then filtered. The isopropanol was removed by rotary evaporation at 80 °C to obtain oily tetradecyl orthosilicate, which solidified at 25 °C, with a yield of 85%.

[0035] Example 10

[0036] The experimental setup was the same as in Example 1, with anhydrous sodium sulfate as the desiccant in the dehydration tube. Excess n-decanol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 1.71 g of 2000-mesh precipitated silica and 0.96 g of anhydrous magnesium chloride were added. The mixture was purged with carbon dioxide three times, refluxed at 235 °C for 5 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen and then distilled under reduced pressure at 160 °C to remove the n-decanol. The distilled n-decanol was collected and recycled. The residue was added to ethanol and stirred vigorously for 2 hours, then filtered. The ethanol was removed by rotary evaporation at 60 °C to obtain oily tetradecyl orthosilicate, which solidified at 25 °C, with a yield of 86%.

[0037] Example 11

[0038] The experimental setup was the same as in Example 1, with anhydrous sodium sulfate as the desiccant in the dehydration tube. Excess n-decanol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 1.75 g of 150-mesh precipitated silica and 0.95 g of anhydrous magnesium chloride were added. The mixture was purged with carbon dioxide three times, refluxed at 230 °C for 5 h under a carbon dioxide atmosphere, cooled to 40 °C, and filtered. The filtrate was purged with nitrogen and then distilled under reduced pressure at 165 °C to remove the n-decanol. The distilled n-decanol was collected and refluxed. The residue was added to methanol and stirred vigorously for 2 hours, then filtered. The filtrate was rotary evaporated at 50 °C to remove the methanol, yielding oily tetradecyl orthosilicate. This was cooled to 25 °C to solidify, with a yield of 87%.

[0039] Example 12

[0040] The experimental setup was the same as in Example 1, with 3A molecular sieve used as the desiccant in the dehydration tube. Excess n-nonyl alcohol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 1.49 g of 325-mesh precipitated silica and 0.99 g of anhydrous magnesium chloride were added. The reaction was refluxed at 217 °C for 5 h under a nitrogen atmosphere, then cooled to 40 °C. After purging the filtrate with nitrogen, the n-nonyl alcohol was removed by vacuum distillation at 140 °C. The distilled n-nonyl alcohol was collected and recycled. The residue was added to methanol and stirred vigorously for 2 hours, then filtered. The methanol was removed by rotary evaporation of the filtrate at 40 °C to obtain oily tetranonyl orthosilicate, with a yield of 59%.

[0041] Example 13

[0042] The experimental setup was the same as in Example 1, with 3A molecular sieve used as the desiccant in the dehydration tube. Excess n-decyl alcohol was added to the reaction flask, purged with nitrogen, and under nitrogen protection, 1.51 g of 325-mesh precipitated silica and 1.00 g of anhydrous magnesium chloride were added. The reaction was refluxed at 217 °C for 5 h under a nitrogen atmosphere, then cooled to 40 °C. After purging the filtrate with nitrogen, n-nonyl alcohol was removed by vacuum distillation at 140 °C. The distilled n-nonyl alcohol was collected and recycled. The residue was added to methanol and stirred vigorously for 2 hours, then filtered. The filtrate was rotary evaporated at 40 °C to remove methanol, yielding oily tetradecyl orthosilicate in 60% yield.

Claims

1. A method for the carbon dioxide-assisted catalytic synthesis of alkoxysilanes, characterized in that, The specific steps are as follows: A dehydration apparatus is set up, excess alcohol is added to the reaction flask, and precipitated silica and catalyst are added sequentially under nitrogen protection. After several carbon dioxide replacements, the reaction is heated under a carbon dioxide atmosphere. After the reaction is complete, the mixture is filtered, and the filtrate is distilled under reduced pressure to remove unreacted alcohol. An organic solvent is added to the residue, and after stirring and mixing evenly, the mixture is filtered. The organic solvent is then distilled under reduced pressure to obtain alkoxysilane. The alcohol is n-nonanol or n-decanol. The reaction temperature is maintained at 210~250 ℃, and the reaction time is 2-6 h. The catalyst is anhydrous aluminum chloride or anhydrous magnesium chloride.

2. The method for carbon dioxide-assisted catalytic synthesis of alkoxysilanes according to claim 1, characterized in that, The organic solvent is any one of methanol, ethanol, isopropanol or n-butanol.

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