Synthesis method of dromethicone

Abstract

The invention belongs to the technical field of synthesis of organic compounds, and relates to a synthesis method of drometrisiloxane, which comprises the following steps: carrying out Williamson etherification reaction on an ultraviolet light absorber UV-P and methyl allyl chloride to obtain an intermediate I; carrying out Claisen rearrangement reaction on the intermediate I to obtain an intermediate II; and carrying out hydrosilylation reaction on the intermediate II and heptamethyltrisiloxane to obtain dromethicone, the Williamson etherification reaction comprises the following steps: dissolving an ultraviolet light absorber UV-P in an alcohol ether solvent, and reacting with methyl allyl chloride under the condition of an acid-binding agent. According to the synthesis method of the drometrisiloxane, the etherification reaction is efficient, simple and convenient, the hydrosilylation reaction catalyst is high in efficiency, the solvent system is green and economical, the overall process is high in yield and purity, and the product quality is excellent.

Description

A method for synthesizing trisiloxanes Technical Field

[0001] This invention belongs to the field of organic compound synthesis technology, and relates to a method for synthesizing trisiloxane. Background Technology

[0002] Tris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(methyltris(s(mcg))))))))))))))))))))))))))))))))"" ⇌ DTS) DTS) DTS DTS) DTS DTS))"" DTS DTS DTS)) DTS DTS DTS))"" DTS ... Trisiloxane is a novel sunscreen agent containing an organosilicon structure. It exhibits good tolerability, low sensitization, and is suitable for sensitive skin. As a lipid-soluble sunscreen agent, trisiloxane can perfectly blend with the oily components of sunscreen products, thus showing broad application prospects, particularly suitable for waterproof sunscreen formulations. Studies have shown that trisiloxane can interact with another sunscreen agent, Mexoryl... ® SX)TDSA work together to provide photostable UVA and UVB protection without breaking down in sunlight and losing its sun protection capabilities, thus providing long-lasting protection.

[0003] Currently, the mainstream synthetic route for trisiloxanes typically involves three steps: Williamson etherification, Claisen rearrangement, and hydrosilylation, as shown in WO 2012055063A1 and CN. The methods disclosed in patents such as 202411657859.X and CN202410234129.2 generally have the following shortcomings: First, in the etherification reaction, since the reaction system is a solid-liquid heterogeneous reaction system, a large amount of phase transfer agent (such as tetrabutylammonium halide, tetrabutylammonium hydrogen sulfate, etc.) and high-boiling-point solvent (such as benzyl alcohol, diphenyl ether) are usually added to promote the reaction. The reaction efficiency is low, the reaction time is more than 17 hours, and the post-processing is cumbersome, which increases the complexity and cost of post-processing and may introduce impurities. Second, in the hydrosilylation reaction, a homogeneous Karstedt catalyst is usually used. The triazole structure of the reactant is easy to deactivate the catalyst, resulting in a high amount of platinum metal and a reduced reaction selectivity. Alternatively, a palladium catalyst is used. When the catalytic cycle slows down, Pd(0) atoms will attract each other and form palladium black precipitate, which leads to the deactivation of part of the catalyst and thus greatly reduces the catalytic effect.

[0004] Therefore, it is of great significance to develop a simple, low-cost, catalyst-efficient, and environmentally friendly method for the synthesis of trisiloxanes. Summary of the Invention

[0005] The main objective of this invention is to overcome the deficiencies in the prior art and provide a method for synthesizing trisiloxane.

[0006] To achieve the above objectives, the specific technical solution is as follows: This invention provides a method for synthesizing trisiloxane, comprising: reacting ultraviolet absorber UV-P with methyl allyl chloride via a Williamson etherification reaction to obtain intermediate I; reacting intermediate I with a Claisen rearrangement reaction to obtain intermediate II; and reacting intermediate II with heptamethyltrisiloxane via a hydrosilylation reaction to obtain trisiloxane; wherein the Williamson etherification reaction step comprises: dissolving ultraviolet absorber UV-P in an alcohol ether solvent, and reacting it with methyl allyl chloride under acid-binding conditions.

[0007] The structural formulas of intermediate I and intermediate II are as follows: Intermediate I Intermediate II In the synthesis method provided by this invention, the Williamson etherification reaction uses an alcohol ether solvent. This solvent system can simultaneously dissolve polar raw materials (UV-P, acid-binding agent) and non-polar reagents (methylallyl chloride), enhancing the compatibility of the system, increasing the contact area of ​​the reactants, achieving a highly efficient etherification reaction with high yield and fast reaction, and significantly shortening the reaction time; at the same time, it avoids the use of phase transfer catalysts and the post-processing problems they bring.

[0008] Furthermore, the structural formula of the alcohol ether solvent is shown in formula (1): Formula (1) wherein R1 is selected from C2-C3 straight-chain or branched alkyl groups, and R2 is selected from C1-C3 straight-chain or branched alkyl groups; preferably, the alcohol ether solvent is selected from one or more of propylene glycol monoethyl ether, ethylene glycol monopropyl ether or ethylene glycol monomethyl ether; and / or, the acid-binding agent is selected from at least one of potassium carbonate, potassium phosphate, sodium hydroxide, and potassium hydroxide.

[0009] This invention utilizes the aforementioned alcohol ether solvents, whose hydroxyl groups can interact with the nitrogen atoms on the benzotriazole ring in UV-P, enhancing its solubility. Simultaneously, the ether bonds in the alcohol ether solvents provide a nonpolar environment, which can dissolve the weakly polar methyl allyl chloride, thereby enhancing the miscibility of the first-step reaction system, reducing the solid-liquid heterogeneous interface, and making the etherification reaction more complete and efficient. Furthermore, the aforementioned alcohol ether solvents exhibit good stability, not reacting with reactants and products, reducing the introduction of impurities and resulting in higher product purity. Moreover, this reaction system does not require the use of phase transfer catalysts and high-boiling-point solvents, simplifying the reaction and post-processing procedures.

[0010] Furthermore, in the Williamson etherification reaction, the total mass of the ultraviolet absorber UV-P and methyl allyl chloride in the alcohol ether solvent is 30-46 wt%; furthermore, the molar ratio of the ultraviolet absorber UV-P to methyl allyl chloride is 1:(1.2-1.5).

[0011] Furthermore, the Williamson etherification reaction is carried out at a temperature of 90-100°C for a time of 3-6 hours.

[0012] This invention can complete the Williamson etherification reaction in a short time with high yield.

[0013] Furthermore, after the Williamson etherification reaction is completed, the solvent is cooled, filtered, and the filtrate is subjected to vacuum distillation to recover the alcohol ether solvent, yielding intermediate I. The vacuum distillation is carried out at a temperature of 60-110°C and a pressure of -0.08-0.1 MPa.

[0014] This invention uses alcohol ether solvents instead of high-boiling-point solvents such as benzyl alcohol and diphenyl ether in the Williamson etherification reaction. The resulting system exhibits a very small amount of fine suspended matter dispersed in a yellowish-brown liquid, unlike existing technologies where solids settle at the bottom, resulting in a stratified solid-liquid phase state or a large amount of suspended matter. This demonstrates that alcohol ether solvents not only dissolve the reactants but also enhance the miscibility between them, thus avoiding the post-processing problems associated with phase transfer catalysts and high-boiling-point solvents. After the reaction, only cooling, filtration to remove inorganic salts, and distillation to recover the alcohol ether solvent are required to obtain high-purity intermediate I, simplifying post-processing steps and reducing complexity. Furthermore, the recovered alcohol ether solvent can be reused.

[0015] Further, the hydrosilylation reaction step is as follows: intermediate II is dissolved in an alkane solvent and subjected to a hydrosilylation reaction with heptamethyltrisiloxane under the conditions of a supported platinum catalyst or a nitrogen heterocyclic carbene platinum complex catalyst to obtain trisiloxane.

[0016] In the hydrosilylation reaction of this invention, a supported platinum catalyst is used, which facilitates recovery and reuse. The catalyst can be recovered by simple filtration after the reaction, significantly reducing platinum consumption and cost. Furthermore, its easy separation properties ensure a low platinum residue in the product; the content of this catalyst in the trisiloxane product is <3 × 10⁻⁶. -6 (3 ppm) is beneficial for application in cosmetics; or the use of nitrogen heterocyclic carbene platinum complex catalysts can significantly reduce the amount of platinum used and improve the selectivity and catalytic efficiency of hydrosilylation reactions.

[0017] Furthermore, the support for the supported platinum catalyst is selected from activated carbon, silica, molecular sieve, or alumina, and the platinum loading is 0.1%-10%; or, the structural formula of the nitrogen heterocyclic carbene platinum complex catalyst is shown in formula (2): In formula (2), R is selected from H or a group shown in formula (3) below: Formula (3) wherein R1 is selected from H, CH3, CN, OMe, CF3 or branched C3~C4 alkyl, and R2 and R3 are selected from H, CH3 or branched C3~C4 alkyl; preferably R1 is CN, R2 and R3 are H or R1, R2 and R3 are CH3.

[0018] Furthermore, the nitrogen-heterocyclic carbene platinum complex catalyst is synthesized by reacting a benzoxazole complex with a Karstedt catalyst, as shown in the following general reaction formula: Among them, X - Selected from Cl - Or BF4 - .

[0019] Specifically, the preparation method of the nitrogen heterocyclic carbene platinum complex catalyst includes the following steps: mixing Karstedt catalyst, benzoxazole complex, potassium tert-butoxide and xylene, stirring and reacting at room temperature for 10-15 h, and after the reaction is completed, filtering, crystallizing and drying to obtain the nitrogen heterocyclic carbene platinum complex catalyst.

[0020] The nitrogen-heterocyclic carbene platinum complex catalyst of this invention exhibits strong electron feedback capability of Pt. By incorporating benzoxazole complexes onto the Pt in the Karstedt catalyst, the weak π-acceptance of the benzoxazole complexes can stabilize Pt through feedback bonds. This allows the nitrogen-heterocyclic carbene platinum complex catalyst obtained above to exist stably in hydrosilylation reactions, maximizing its catalytic activity and significantly reducing the amount of platinum required. Furthermore, the benzoxazole complexes also incorporate R1, R2, and R3 groups, which can significantly improve the selectivity of the catalyst and increase the yield of the hydrosilylation reaction.

[0021] Furthermore, the mass ratio of the supported platinum catalyst to intermediate II is (1-5):20.

[0022] Furthermore, based on the total mass of intermediate II and heptamethyltrisiloxane, the mass fraction of Pt in the nitrogen-heterocyclic carbene platinum complex catalyst is 6 × 10⁻⁶. -6 -8×10 -6 (6-8ppm).

[0023] This invention uses the aforementioned nitrogen-heterocyclic carbene platinum complex catalyst as a homogeneous catalyst, which exhibits ultra-high catalytic efficiency and stability, reducing the amount of platinum required to the ppm level. Compared with the traditional Karstedt catalyst, the amount of platinum required can be reduced by two orders of magnitude. At the same time, this catalyst has high selectivity, and its unique electronic and steric effects can effectively regulate the reaction pathway, significantly suppress side reactions (such as isomerization and over-addition), and improve the purity and yield of the target product.

[0024] Furthermore, the alkane solvent is selected from at least one of cyclohexane, n-heptane, isoheptane, n-octane, and isooctane, with cyclohexane being preferred.

[0025] This invention uses alkane solvents to replace traditional toluene and xylene, resulting in lower toxicity, a more stable system, and a suitable boiling point, which is beneficial for safe production and environmental protection.

[0026] Furthermore, in the hydrosilylation reaction, the amount of the alkane solvent used is 1-1.2 times the mass of intermediate II.

[0027] Furthermore, the molar ratio of intermediate II to heptamethyltrisiloxane is 1:(1.1-1.3).

[0028] Furthermore, the hydrosilylation reaction is carried out at a temperature of 60-85°C for a time of 4-6 hours.

[0029] The advantages of the hydrosilylation reaction of this invention are high catalyst efficiency, mild conditions, less waste, and simple post-treatment.

[0030] Furthermore, after the hydrosilylation reaction is completed, the alkane solvent is recovered by vacuum distillation, and the remaining material to be crystallized is recrystallized in a mixed alcohol solvent to obtain trisiloxane. The vacuum distillation is carried out at a temperature of 30-80℃ and a pressure of -(0.08-0.1) MPa.

[0031] Specifically, the mixed alcohol solvent is selected from at least two of methanol, ethanol, and isopropanol; further, the mass of the mixed alcohol solvent is 2.5-3.5 times the mass of the remaining material to be crystallized.

[0032] Further, the Claisen rearrangement reaction steps are as follows: intermediate I is heated to 180-200°C under solvent-free conditions, and the Claisen rearrangement reaction time is 8-12 hours to obtain intermediate II; after the Claisen rearrangement reaction is completed, isopropanol is added for dissolution, followed by cooling crystallization and vacuum drying to obtain high-purity intermediate II.

[0033] After the Claisen rearrangement reaction described in this invention is completed, crystallization can be avoided, and the reaction can be directly carried out in the next step after decolorization with activated carbon.

[0034] Compared with the prior art, the present invention has the following significant advantages: the etherification reaction of the present invention is efficient and simple. By selecting alcohol ether solvents, the solvent system has both polarity and solubility. Under the condition of not using a phase transfer catalyst, a high-yield and short-time efficient etherification reaction of UV-P and methyl allyl chloride can be achieved. The reaction time can be shortened to 3-6 hours. Moreover, the post-processing is simple, requiring only filtration and distillation, avoiding the separation and purification difficulties caused by using a phase transfer catalyst.

[0035] The hydrosilylation reaction catalyst of this invention has high efficiency. It adopts a supported platinum catalyst, which can realize simple filtration and recovery of the catalyst, reducing platinum metal loss, lowering costs and environmental pollution. It uses a nitrogen heterocyclic carbene platinum complex synthesized by Karstedt and benzoxazole complex as a homogeneous catalyst. Its excellent electronic properties and steric hindrance can significantly improve catalytic activity and stability, reducing the amount of platinum used by two orders of magnitude, while improving the selectivity of the reaction and effectively suppressing side reactions.

[0036] The solvent system of this invention is green and economical. In the hydrosilylation step, alkane solvents such as cyclohexane are used to replace traditional toluene, xylene, etc., which are less toxic and more stable, thus contributing to safe production and environmental protection.

[0037] The overall process of this invention has high yield, high purity, and excellent product quality. Attached Figure Description

[0038] Figure 1 is a state diagram of the Williamson etherification reaction system in Example 3 of the present invention; Figure 2 is a state diagram of the Williamson etherification reaction system in Comparative Example 1 of the present invention; Figure 3 is a state diagram of the Williamson etherification reaction system in Comparative Example 2 of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Unless otherwise specified in the embodiments of the present invention, the techniques or conditions described in the literature in this field or the product instructions shall be followed; if the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased through legitimate channels.

[0041] Example 1: Synthesis of Intermediate I: UV absorber UV-P (50.0 g, 1.0 equiv), 150 mL propylene glycol monoethyl ether, and potassium carbonate (49.0 g, 1.6 equiv) were added sequentially to a reaction vessel and stirred for 1 h. Then, 87.1 g of methyl allyl chloride solution (molar ratio of methyl allyl chloride to UV absorber UV-P was 1.3) was added dropwise over 1 h. The solvent for this solution was propylene glycol monoethyl ether, with a concentration of 30 wt%. After the addition was complete, the mixture was heated to 95 °C and reacted for 4 h, with the reaction progress monitored by liquid chromatography. After the reaction was complete, the reaction solution was cooled to room temperature and filtered to obtain a yellow solution, which was then... Intermediate I was obtained by vacuum distillation under -0.09 MPa pressure conditions at ℃. Synthesis of Intermediate II: Intermediate I was added to a reaction vessel and replaced three times with N2. The mixture was heated to 180℃ and reacted for 8 hours. The reaction progress was monitored using the liquid phase. After the reaction was completed, the reaction solution was cooled to 90℃, dissolved in isopropanol, cooled to 20℃ to crystallize, and dried to obtain 58.6 g of Intermediate II with a purity of 99.68% and UV-P < 0.01%. The overall yield of the first two steps was 94.51%.

[0042] Example 2: Synthesis of Intermediate I: UV absorber UV-P (50.0 g, 1.0 equiv), 150 mL of ethylene glycol monopropyl ether, and potassium carbonate (49.0 g, 1.6 equiv) were sequentially added to a reaction vessel and stirred for 1 h. Then, 66.97 g of methyl allyl chloride solution (molar ratio of methyl allyl chloride to UV absorber UV-P was 1.5) was added dropwise over 1 h. The solvent for this solution was ethylene glycol monopropyl ether, with a concentration of 45 wt%. After the addition was complete, the mixture was heated to 95 °C and reacted for 4 h, with the reaction progress monitored by liquid chromatography. After the reaction was complete, the reaction solution was cooled to room temperature and filtered to obtain a yellow solution. Then, the solution was subjected to a 110°C test. Intermediate I was obtained by vacuum distillation under -0.09 MPa pressure conditions at ℃. Synthesis of Intermediate II: Intermediate I was added to a reaction vessel and replaced three times with N2. The mixture was heated to 200℃ and reacted for 8 hours. The reaction progress was monitored using a liquid phase. After the reaction was complete, the reaction solution was cooled to 90℃, dissolved in isopropanol, cooled to 20℃ to crystallize, and dried to obtain 57.9 g of Intermediate II with a purity of 99.73% and UV-P < 0.01%. The overall yield of the first two steps was 93.38%.

[0043] Example 3: Synthesis of Intermediate I: UV absorber UV-P (50.0 g, 1.0 equiv), 150 mL of ethylene glycol monomethyl ether, and potassium carbonate (49.0 g, 1.6 equiv) were sequentially added to a reaction vessel and stirred for 1 h. Then, 60.28 g of methyl allyl chloride solution (molar ratio of methyl allyl chloride to UV absorber UV-P was 1.2) was added dropwise over 1 h. The solvent for this solution was ethylene glycol monomethyl ether, and the concentration of the solution was 40 wt%. After the addition was complete, the mixture was heated to 95 °C. The reaction was carried out for 4 hours, and the reaction progress was monitored by liquid chromatography. After the reaction was completed, the reaction solution was cooled to room temperature and filtered to obtain a yellow solution. Then, it was distilled under reduced pressure at 80℃ and -0.09MPa to obtain intermediate I. Synthesis of intermediate II: Intermediate I was added to the reaction vessel and replaced with N2 three times. The mixture was heated to 190℃ and reacted for 8 hours, and the reaction progress was monitored by liquid chromatography. After the reaction was completed, the reaction solution was cooled to 90℃, dissolved in isopropanol, cooled to 20℃ to crystallize, and dried to obtain 59.3g of intermediate II with a purity of 99.80% and UV-P < 0.01%. The overall yield of the first two steps was 95.63%.

[0044] Figure 1 shows the state diagram of the Williamson etherification reaction system in this embodiment. It can be seen that the reaction system is a clear yellow-brown liquid with only a small amount of suspended matter. The reaction system is relatively homogeneous, and there is no yellow solid adhering to the bottle wall.

[0045] Conclusion: Propylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monomethyl ether can all be used to complete the reaction efficiently, with the overall yield of the first two steps exceeding 93%.

[0046] Example 4: Hydrosilylation using a supported platinum catalyst. Intermediate II (58.6 g, 1.0 equiv) prepared in Example 1 was dissolved in 70.3 g of cyclohexane. The mixture was heated to 65°C, and then 2.93 g of 10% platinum-carbon catalyst was added and stirred for 30 min. Then, 56.0 g of heptamethyltrisiloxane (1.2 equiv) was added dropwise. After the addition was complete, the temperature was raised to 80°C, and the reaction was allowed to proceed for 4 h. The reaction was monitored using a liquid phase. After the reaction was complete, the reaction solution was cooled to room temperature, filtered, and then reacted with 5 g of cyclohexane. The catalyst can be recovered by rinsing the filter cake with alkyl. Then, the filtrate is subjected to vacuum distillation at 40℃ and -0.09MPa to recover the cyclohexane solvent. 234g of a mixed solvent of isopropanol and methanol in a ratio of 1:1 is added and heated to dissolve. After slowly cooling to -5℃, a large amount of white solid precipitates. After crystallization and stirring for 3 hours, it is filtered and vacuum dried to obtain 93.7g of white solid. The yield of the third step reaction is 89.00%, the purity is 97.5%, and the content of platinum-carbon catalyst in the white solid is 2.1ppm.

[0047] Example 5: Hydrosilylation using a supported platinum catalyst. Intermediate II (50.0 g, 1.0 equiv) prepared in Example 1 was dissolved in 60 g of n-heptane. The mixture was heated to 65°C, and 8 g of alumina-supported platinum catalyst with a loading of 3% was added and stirred for 30 min. Then, 47.8 g of heptamethyltrisiloxane (1.2 equiv) was added dropwise. After the addition was complete, the temperature was raised to 80°C, and the reaction was carried out for 5 h. The reaction progress was monitored using a liquid phase. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and then reacted with 5 g of cyclohexane. The catalyst can be recovered by rinsing the filter cake with alkane; then the filtrate is concentrated under reduced pressure at 50℃ and -0.09MPa to recover the n-heptane solvent. 200g of a 1:1 mixture of isopropanol and methanol is added and heated to dissolve. After slowly cooling to -5℃, a large amount of white solid precipitates. After crystallization and stirring for 3h, it is filtered and vacuum dried to obtain 79.2g of white solid. The yield of the third step is 88.17%, the purity is 99.81%, and the content of alumina-supported platinum catalyst in the white solid is 2.4ppm.

[0048] Conclusion: Using a supported platinum catalyst, the yield of the third step is over 88%, and the catalyst can be recovered by filtration, making post-processing simple.

[0049] Example 6 Synthesis of Nitrogen Heterocyclic Carbene Platinum Complex Solid Catalyst I: A Karstedt catalyst concentrate containing 0.5 mmol Pt (20 wt%, solvent: tetramethyldivinylsiloxane), 1-m-trimethylphenylbenzoxazole chloride (342 mg, 1.25 mmol), potassium tert-butoxide (168 mg, 1.5 mmol), and 5 ml of cyclohexane were added to a reaction vessel. The mixture was stirred at 20 °C for 15 h. After the reaction was complete, the mixture was filtered, then concentrated under vacuum. 20 ml of ethanol was added to crystallize the catalyst. After filtration and drying, 658 mg of solid catalyst I was obtained, with a yield of 85%. Its structural formula is shown below: Solid catalyst I uses a nitrogen-heterocyclic carbene platinum complex for hydrosilylation: Intermediate II (50.0 g, 1.0 equiv) prepared in Example 1 was dissolved in 60 g of cyclohexane, heated to 65 °C, and then 5 g of cyclohexane was added. mg of solid catalyst I (which, after conversion, contains 0.737 mg of platinum, with a platinum concentration of approximately 7.54 ppm relative to the total reactant mass of 97.8 g) was stirred for 30 min, and 47.8 g of heptamethyltrisiloxane (1.2 equiv) was added dropwise. After the addition was complete, the temperature was raised to 80 °C, and the reaction was carried out for 5 h. The reaction progress was monitored by liquid phase. After the reaction was completed, the temperature of the reaction solution was lowered to room temperature, filtered, and then the filtrate was subjected to vacuum distillation at 40 °C and -0.09 MPa to recover the cyclohexane solvent. Then, 200 g of a mixed solvent of isopropanol and methanol in a ratio of 1:1 was added, heated to dissolve, and then slowly cooled to -5 °C, after which a large amount of white solid precipitated. After crystallization and stirring for 3 h, the mixture was filtered, dried under vacuum, and 82.7 g of white solid was obtained, indicating that the yield of the third step of the hydrosilylation reaction was 92.07%, and the purity was 99.70%.

[0050] Example 7 Synthesis of Nitrogen Heterocyclic Carbene Platinum Complex Solid Catalyst II: A Karstedt catalyst concentrate containing 0.5 mmol Pt, 1-p-cyanophenylbenzoxazole chloride (321 mg, 1.25 mmol), potassium tert-butoxide (168 mg, 1.5 mmol), and 5 ml of xylene were added to a 10 ml flask. The mixture was stirred at 20 °C for 15 h. After the reaction was complete, the mixture was filtered, concentrated under vacuum, and crystallized by adding 20 ml of ethanol. After filtration and drying, 686 mg of solid catalyst II was obtained, with a yield of 91%. Its structural formula is shown below: Solid catalyst II utilizes the hydrosilylation of a nitrogen-heterocyclic carbene platinum complex: Intermediate II (50.0 g, 1.0 equiv) prepared in Example 1 was dissolved in 60 g of n-heptane, heated to 65 °C, and then 5 g of... mg of solid catalyst II (which, after conversion, contains 0.71 mg of platinum, with a platinum concentration of approximately 7.2 ppm relative to the total reactant mass of 97.8 g) was stirred for 30 min, and 47.8 g of heptamethyltrisiloxane (1.2 equiv) was added dropwise. After the addition was complete, the temperature was raised to 80 °C, and the reaction was carried out for 5 h. The reaction progress was monitored by liquid phase. After the reaction was completed, the temperature of the reaction solution was lowered to room temperature, filtered, and then the filtrate was subjected to vacuum distillation at 50 °C and -0.09 MPa to recover the n-heptane solvent. Then, 200 g of a mixed solvent of isopropanol and methanol in a ratio of 1:1 was added, heated to dissolve, and then slowly cooled to -5 °C, after which a large amount of white solid precipitated. After crystallization and stirring for 3 h, the mixture was filtered, dried under vacuum, and 83.4 g of white solid was obtained, indicating that the yield of the third step of the hydrosilylation reaction was 92.84%, with a purity of 99.56%.

[0051] Conclusion: The use of trace amounts (milligram level) of nitrogen heterocyclic carbene platinum complexes can efficiently catalyze the reaction with a yield of over 92% and extremely high product purity, demonstrating its excellent catalytic efficiency.

[0052] Comparative Example 1: This comparative example uses the phase transfer catalyst tetrabutylammonium bromide and solvent benzyl alcohol disclosed in Example 2 of existing patent CN201080069734.5 to synthesize intermediates I and II. The specific steps are as follows: UV absorber UV-P (50.0 g, 1.0 equiv), 150 mL benzyl alcohol, 2.86 g tetrabutylammonium bromide, and potassium carbonate (49.0 g, 1.6 equiv) are added sequentially to a reaction vessel and stirred for 1 h. Then, 87.1 g of a benzyl alcohol solution of methyl allyl chloride (30 wt%) is added dropwise over 1 h. After the addition is complete, the mixture is heated to 95 °C and reacted for 17 hours. h, the reaction process was monitored by liquid phase; after the reaction was completed, the reaction solution was cooled to room temperature and filtered, and then distilled under reduced pressure at 110℃ and -0.09MPa to obtain intermediate I; the synthesis of intermediate II is described in Example 3, and finally 55.56g of intermediate II was obtained with a purity of 99.2% and UV-P < 0.5%, and the overall yield of the first two steps was 89.6%.

[0053] Figure 2 shows the state diagram of the Williamson etherification reaction system in this comparative example. It can be seen that the reaction system is a viscous, brownish-black liquid, not as clear as in Figure 1, and contains a large amount of suspended matter, with yellow solids adhering to the bottle walls. This indicates that when using benzyl alcohol and the phase transfer catalyst tetrabutylammonium bromide, the miscibility between the reactants is poor, thus affecting the reaction rate.

[0054] Comparative Example 2: This comparative example uses the phase transfer catalyst tetrabutylammonium chloride and solvent xylene disclosed in Example 5 of the existing patent CN202411657859.X to synthesize intermediate I and intermediate II. For specific steps, please refer to paragraphs 0083-0085 of the patent specification. The purity of intermediate II disclosed therein is 99.6%, and the yield of the first two steps is 84%.

[0055] Figure 3 shows the state diagram of the Williamson etherification reaction system in step 1) of this comparative example. It can be seen that a large amount of yellow solid is deposited at the bottom of the three-necked round-bottom flask, indicating a solid-liquid two-phase separation. The upper liquid layer is yellowish-brown, and the flask walls are adhered to the yellow solid. This demonstrates that when using xylene and the phase transfer catalyst tetrabutylammonium chloride, the reactants exhibit solid-liquid separation, and contact between the reactants only occurs at the interfaces between the phases.

[0056] Comparative Example 3: The preparation method provided in this comparative example differs from that in Example 3 only in that butanediol monopropyl ether is used instead of propylene glycol monoethyl ether solvent. This comparative example yielded 53.26 g of intermediate II with a purity of 99.5% and UV-P < 0.5%, with a combined yield of 85.9% for the first two steps.

[0057] Comparative Example 4: The preparation method provided in this comparative example differs from that in Example 3 only in that ethylene glycol monobutyl ether is used instead of propylene glycol monoethyl ether solvent. This comparative example yielded 51.90 g of intermediate II with a purity of 99.1% and UV-P < 0.5%, and the overall yield of the first two steps was 83.7%.

[0058] In Comparative Example 5, Karstedt catalyst concentrate (0.5 mmol Pt), 1,3-dicyclohexylimidazolium tetrafluoroborate (230 mg, 1.25 mmol), potassium tert-butoxide (168 mg, 1.5 mmol), and 5 ml of xylene were added to a 10 ml flask. The mixture was stirred at 20 °C for 15 h. After the reaction was completed, the mixture was filtered, concentrated under vacuum, and 20 ml of isopropanol was added to crystallize the mixture. After filtration and drying, 245 mg of solid catalyst III was obtained, with a yield of 76.1%.

[0059] Solid catalyst III was used in the hydrosilylation reaction, with the same dosage and steps as in Example 6. This comparative example ultimately yielded 69.9 g of a white solid, representing a yield of 77.82% and a purity of 99.50% for the third step of the hydrosilylation reaction.

[0060] Comparative Example 6 directly used a Karstedt catalyst to catalyze the hydrosilylation reaction. Specifically, 0.5 g of a Karstedt catalyst with a concentration of 7600 ppm was added (after conversion, the platinum concentration in this catalyst is approximately 389 ppm relative to the total reactant mass of 97.8 g). The other steps were the same as in Example 6. This comparative example ultimately yielded 74.6 g of a white solid, indicating a yield of 83.1% and a purity of 99.56% for the third step of the hydrosilylation reaction.

[0061] A comparison of Examples 1-3 and Comparative Examples 1-2 shows that in the first step of the etherification reaction, this invention uses alcohol ether solvents instead of the high-boiling-point solvents benzyl alcohol and xylene used in the prior art. Alcohol ether solvents can act as solvents and also improve the compatibility between the reactants in the etherification reaction, thereby avoiding the use of phase transfer catalysts in the prior art and achieving a highly efficient etherification reaction. This not only shortens the reaction time from 17 hours in the prior art to 3-6 hours, but also increases the overall yield of the first two steps by about 10%. A comparison of Examples 1-3 and Comparative Examples 3-4 shows that only by using the alcohol ether solvents specified in this invention can the above-mentioned excellent effects be obtained.

[0062] A comparison of Example 6 and Comparative Example 6 shows that in the third step of the hydrosilylation reaction, the nitrogen-heterocyclic carbene platinum complex catalyst specified in this invention can maximize the yield of the reaction with minimal dosage. Compared with the Karstedt catalyst in Comparative Example 6, the amount of platinum is reduced by two orders of magnitude, but the yield of the third step is increased by about 10%. A comparison of Example 6 and Comparative Example 5 shows that only the nitrogen-heterocyclic carbene platinum complex specified in this invention can significantly improve its catalytic effect. When the ligand salt is an imidazole, the catalytic effect is greatly reduced with the same amount of catalyst.

[0063] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for synthesizing trisiloxane, characterized in that, include: The ultraviolet absorber UV-P was subjected to a Williamson etherification reaction with methyl allyl chloride to obtain intermediate I; Intermediate I was subjected to a Claisen rearrangement reaction to obtain intermediate II; And intermediate II is subjected to a hydrosilylation reaction with heptamethyltrisiloxane to obtain trimetrisiloxane; wherein the Williamson etherification reaction step includes: dissolving ultraviolet absorber UV-P in an alcohol ether solvent and reacting it with methyl allyl chloride under acid-binding conditions.

2. The method for synthesizing trisiloxane according to claim 1, characterized in that, The structural formula of the alcohol ether solvent is shown in formula (1): Formula (1) wherein R1 is selected from C2-C3 straight-chain or branched alkyl groups, and R2 is selected from C1-C3 straight-chain or branched alkyl groups; and / or, the total mass of the ultraviolet absorber UV-P and methyl allyl chloride in the alcohol ether solvent is 30-46 wt%; and / or, the molar ratio of the ultraviolet absorber UV-P to methyl allyl chloride is 1:(1.2-1.5).

3. The method for synthesizing trisiloxane according to claim 2, characterized in that, The alcohol ether solvent is selected from at least one of propylene glycol monoethyl ether, ethylene glycol monopropyl ether, or ethylene glycol monomethyl ether; and / or, the acid-binding agent is selected from at least one of potassium carbonate, potassium phosphate, sodium hydroxide, or potassium hydroxide.

4. The method for synthesizing trisiloxane according to any one of claims 1-3, characterized in that, The Williamson etherification reaction is carried out at a temperature of 90-100°C for 3-6 hours; and / or, after the Williamson etherification reaction is completed, the solvent is recovered by cooling, filtration and vacuum distillation of the filtrate to obtain intermediate I, wherein the vacuum distillation is carried out at a temperature of 60-110°C and a pressure of -(0.08-0.1) MPa.

5. The method for synthesizing trisiloxane according to any one of claims 1-3, characterized in that, The steps of the hydrosilylation reaction include: dissolving intermediate II in an alkane solvent, and reacting it with heptamethyltrisiloxane under the conditions of a supported platinum catalyst or a nitrogen heterocyclic carbene platinum complex catalyst to obtain trisiloxane.

6. The method for synthesizing trisiloxane according to claim 5, characterized in that, The support for the supported platinum catalyst is selected from activated carbon, silica, molecular sieve, or alumina, and the platinum loading is 0.1%-10%; or, the structural formula of the nitrogen heterocyclic carbene platinum complex catalyst is shown in formula (2): In formula (2), R is selected from H or a group shown in formula (3) below: Formula (3) wherein R1 is selected from H, CH3, CN, OMe, CF3 or branched C3~C4 alkyl, and R2 and R3 are selected from H, CH3 or branched C3~C4 alkyl; preferably R1 is CN, R2 and R3 are H or R1, R2 and R3 are CH3.

7. The method for synthesizing trisiloxane according to claim 6, characterized in that, In the hydrosilylation reaction, the mass ratio of the supported platinum catalyst to intermediate II is (1-5):20; or, based on the total mass of intermediate II and heptamethyltrisiloxane, the mass fraction of Pt in the nitrogen-heterocyclic carbene platinum complex catalyst is 6 × 10⁻⁶. -6 -8×10 -6 .

8. The method for synthesizing trisiloxane according to claim 5, characterized in that, The alkane solvent is selected from at least one of cyclohexane, n-heptane, isoheptane, n-octane, and isooctane, preferably cyclohexane; and / or, the amount of the alkane solvent is 1-1.2 times the mass of intermediate II; and / or, the molar ratio of intermediate II to heptamethyltrisiloxane is 1:(1.1-1.3).

9. The method for synthesizing trisiloxane according to claim 5, characterized in that, The hydrosilylation reaction is carried out at a temperature of 60-85℃ for 4-6 hours; and / or, after the hydrosilylation reaction is completed, the alkane solvent is recovered by vacuum distillation, and the remaining material to be crystallized is recrystallized in a mixed alcohol solvent to obtain trisiloxane. The vacuum distillation is carried out at a temperature of 30-80℃ and a pressure of -(0.08-0.1) MPa.

10. The method for synthesizing trisiloxane according to claim 9, characterized in that, The mixed alcohol solvent is selected from at least two of methanol, ethanol, and isopropanol; and / or, the mass of the mixed alcohol solvent is 2.5-3.5 times the mass of the remaining material to be crystallized.

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