Vanillyl butyl ether, its preparation method and application

Abstract

The present application relates to the technical field of organic fine chemical industry, in particular to a kind of geranial butyl ether and its preparation method and application.The present application is tri-block copolymer as template agent, tetraethyl orthosilicate is used as silicon source to form mesoporous silica precursor, titanium species is introduced in template retention state, and chloro-trimethylsilane end-capping and decyltrichlorosilane hydrophobic modification are carried out in turn;After template removal, graft 3-mercaptopropyl trimethoxysilane and oxidation, obtain the solid catalyst;The catalyst is used for etherification reaction of geranial and n-butanol, and geranial butyl ether is obtained by vacuum alcohol distillation and vacuum rectification.The present application is conducive to reducing side reaction, improving target product selectivity and improving catalyst cycle stability.

Description

Technical Field

[0001] This invention relates to the field of organic fine chemical technology, specifically to vanillin butyl ether, its preparation method, and its application. Background Technology

[0002] Vanillyl butyl ether (3-methoxy-4-hydroxybenzyl butyl ether) is an important flavor and fragrance intermediate, widely used in the preparation of food additives, daily chemical fragrances, and temperature-sensitive functional materials. This compound is typically prepared by the dehydration and etherification reaction of vanillyl and n-butanol under acid catalysis. Mechanistically, this process involves the nucleophilic substitution of the benzylic hydroxyl group of vanillyl with the hydroxyl group of n-butanol under acidic conditions, accompanied by the formation of a water molecule. Since this reaction is a reversible equilibrium reaction, if the water generated during the reaction cannot be removed from the catalytically active site in time, it will significantly inhibit the forward etherification reaction, leading to a decrease in the reaction rate and limited equilibrium conversion.

[0003] To overcome the aforementioned equilibrium limitations, existing technologies often employ homogeneous acid catalysts, such as p-toluenesulfonic acid, sulfuric acid, and phosphoric acid, combined with azeotropic dehydration devices. This involves continuously removing water from the reaction system to propel the reaction to the right. However, homogeneous acid catalysis systems have significant drawbacks: firstly, strong acid conditions easily trigger side reactions such as vanillin condensation and resinification, generating dark-colored polymeric byproducts that deepen the color of the reaction solution and increase the difficulty of post-treatment decolorization and purification; secondly, after the reaction, the homogeneous acid requires neutralization and washing processes for removal, generating large amounts of saline wastewater and preventing catalyst recovery and recycling, which is detrimental to continuous industrial production.

[0004] To overcome the shortcomings of homogeneous acids, researchers have attempted to prepare solid acid catalysts for vanillin etherification by loading sulfonic acid groups and phosphate groups onto porous solid supports. These catalysts can be easily separated from the reaction products and have the potential for recycling. However, in practical applications, solid acid catalysts still face many challenges in vanillin etherification. First, vanillin molecules contain phenolic hydroxyl and methoxy groups, exhibiting strong polarity and high reactivity. They are prone to non-specific adsorption on conventional solid acid surfaces, leading to disordered occupation of active sites and affecting catalytic efficiency. Second, solid acid supports typically possess abundant microporous structures, while vanillin molecules are relatively large, making diffusion within the micropores restricted. This results in insufficient utilization of active sites within the pores, and the generated water molecules are also easily trapped inside the pores, further inhibiting the etherification reaction. Third, if the acid centers on the solid acid surface lack spatial arrangement, the strong acid sites on the outer surface and pore openings can easily become initiation points for condensation and resinification side reactions, leading to decreased reaction selectivity, higher product color, and increased burden on subsequent distillation purification.

[0005] In recent years, some studies have attempted to optimize the performance of solid acid catalysts through hydrophobic modification or the construction of gradient acid site distributions. For example, organosilanes are used to hydrophobically modify the outer surface of the catalyst to enhance its affinity for organic substrates and promote rapid water desorption. However, these modification methods are often relatively simple and fail to fully consider the entire process of activation, transformation, and product desorption of vanillin molecules in different regions inside and outside the pores, and it is also difficult to precisely control the spatial distribution of acid sites at the pore opening and inside the pores.

[0006] Therefore, in the existing technology, the etherification reaction of vanillin and n-butanol still generally suffers from problems such as a narrow reaction temperature window, parallel etherification and side reactions, heavy post-processing burden, and significant batch fluctuations during scale-up. It is difficult to simultaneously achieve yield, purity, and industrial continuous stability. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a vanillyl butyl ether, its preparation method and application, in order to solve the problem in the prior art that it is impossible to simultaneously improve the reaction conversion rate, main product selectivity and catalyst recycling stability in the preparation process of vanillyl butyl ether without significantly increasing the reaction temperature and adding post-processing steps.

[0008] To achieve the above objectives, the present invention provides a method for preparing vanillin butyl ether, comprising the following steps: in the presence of anhydrous n-butanol, catalyzing the reaction of vanillin with n-butanol using a solid catalyst for vanillin butyl ether to obtain crude vanillin butyl ether product; subjecting the crude vanillin butyl ether product to vacuum distillation to remove n-butanol and vacuum distillation to obtain vanillin butyl ether.

[0009] The preparation steps of the solid catalyst for vanillin butyl ether are as follows:

[0010] (1) Under acidic conditions, using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer as template agent and tetraethyl orthosilicate as silicon source, a carrier precursor with template still retained inside the pores was obtained by hydrolysis, polycondensation and aging.

[0011] (2) The carrier precursor is subjected to dewatering treatment to obtain a carrier precursor with low water content;

[0012] (3) Disperse the low-water-content carrier precursor in anhydrous toluene to form a carrier dispersion. Separately, disperse tetrabutyl titanate in anhydrous toluene to form a titanium precursor solution. Add the titanium precursor solution dropwise to the carrier dispersion. After the reaction is complete, add short-chain end-capping solution and long-chain end-capping solution in sequence to perform surface silanization end-capping treatment to obtain a composite carrier precursor. The composite carrier precursor is refluxed with anhydrous ethanol to remove the template to obtain a composite carrier.

[0013] (4) The composite support was grafted with 3-mercaptopropyltrimethoxysilane to form a mercaptopropyl-containing composite support, which was then oxidized to obtain a solid catalyst for vanillin butyl ether.

[0014] Preferably, the acidic condition in step (1) is a 2 mol / L hydrochloric acid aqueous solution.

[0015] Preferably, the weight ratio of tetraethyl orthosilicate and polyethylene oxide-polyethylene oxide-polyethylene oxide triblock copolymer in step (1) is 34-38:15-17.

[0016] Preferably, the aging temperature in step (1) is 98-102℃ and the aging time is 23-25h.

[0017] Preferably, the hydrolysis-condensation temperature in step (1) is 39-41℃ and the hydrolysis-condensation time is 23-25h.

[0018] Preferably, the desorption water treatment temperature in step (2) is 110-112℃, and the desorption water treatment time is 5-7h.

[0019] Preferably, the ratio of the low-water-content carrier precursor, tetrabutyl titanate, short-chain capping liquid and long-chain capping liquid in step (3) is 11-13:3.6-4.4:18-22:18-22.

[0020] Preferably, the short-chain end-capping liquid in step (3) is obtained by dispersing trichloromethylsilane in anhydrous toluene, wherein the mass ratio of trichloromethylsilane to anhydrous toluene is 1:20.

[0021] Preferably, the long-chain end-capping liquid in step (3) is obtained by dispersing decyltrichlorosilane in anhydrous toluene, wherein the mass ratio of decyltrichlorosilane to anhydrous toluene is 1:10.

[0022] Preferably, the tetrabutyl titanate solution in step (3) is added dropwise over 18-20 minutes at 0-5°C, and after the addition is completed, the reaction continues at 0-5°C for 40 minutes, then at 25°C for 2 hours, and finally at 68-72°C for 4-4.5 hours.

[0023] Preferably, after the short-chain end-capping liquid in step (3) is added dropwise within 15 minutes, it is reacted at 0-5℃ for 30 minutes, and then reacted at 25℃ for 2 hours.

[0024] Preferably, after the long-chain end-capping liquid in step (3) is added dropwise within 15 minutes, it is first reacted at 25°C for 1 hour, and then reacted at 68-72°C for 5-5.5 hours.

[0025] Preferably, the anhydrous ethanol reflux in step (3) is carried out at 78-79°C, the reflux extraction time is 8-9 hours, and the reflux is repeated 3 times.

[0026] Preferably, the grafting treatment in step (4) is performed at a temperature of 104-106°C and a reaction time of 10-11 h.

[0027] Preferably, the oxidation in step (4) is carried out using hydrogen peroxide solution at 25-26°C. During the dropwise addition of hydrogen peroxide solution, the system temperature is controlled to be no higher than 30°C. After the dropwise addition is completed, the reaction continues at 25-26°C for 4 hours, and then the temperature is raised to 40-42°C for another 4 hours.

[0028] Preferably, the weight ratio of the solid catalyst for vanillin butyl ether, anhydrous n-butanol, and vanillin is 4.8-5.5:393-407:48-52.

[0029] Preferably, the vacuum distillation is carried out at 50°C and 10 kPa, the purpose of which is to distill off most of the n-butanol under reduced pressure.

[0030] Furthermore, the present invention also provides vanillyl butyl ether.

[0031] Furthermore, the present invention also provides an application of vanillyl butyl ether for the preparation of food additives, daily chemical fragrances, or temperature-sensitive functional materials.

[0032] The beneficial effects of this invention are:

[0033] The method for preparing vanillin butyl ether provided by this invention introduces Lewis acidic titanium sites into the pore region of the mesoporous silica support by constructing a partitioned solid acid catalyst. These sites can preferentially adsorb and moderately activate vanillin molecules, enabling them to form an orientation conducive to directional etherification before entering the pores. This effectively avoids non-specific adsorption and condensation side reactions of vanillin on the outer surface and near the pores, thereby enabling the main reaction pathway to be initiated at a lower temperature. This significantly reduces the tendency to form high-boiling byproducts, resulting in a lighter color of the reaction solution and a lighter post-processing burden.

[0034] The present invention further constructs a short-chain trimethylsilyl end-capping layer and a long-chain decyl hydrophobic layer sequentially under the template retention state, forming a two-level surface structure with distinct inner and outer layers. The spatial division of labor and temporal limitation of the two hydrophobic structures enable the catalyst to maintain the accessibility of the pores and the clear partition between the pore opening and the acid site inside the pore during the reaction process.

[0035] This invention introduces propyl sulfonic acid sites inside the pores after template removal. Vanillin is activated at the pore opening and enters the pores in an orderly manner. The directional etherification reaction with n-butanol is completed at the internal sulfonic acid sites. The resulting product then leaves the pores and is propelled by water molecules discharged with the assistance of the hydrophobic layer on the outer surface. This continuous reaction path of pore opening activation - etherification inside the pores - drainage from the outer layer comprehensively improves the conversion efficiency, selectivity and recycling stability of the catalyst, and is especially suitable for the industrial continuous preparation of fragrance intermediates and temperature-sensitive functional raw materials. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0037] The raw materials and specifications used in this embodiment are as follows:

[0038] Polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer: Sigma-Aldrich, catalog number 435465, average number-average molecular weight 5800; Tetrabutyl titanate, Aladdin, catalog number T104105, purity not less than 99%.

[0039] Example 1: A method for preparing vanillin butyl ether, the specific steps of which are as follows:

[0040] S1: Add 520g of 2mol / L hydrochloric acid aqueous solution to a three-necked flask equipped with a mechanical stirrer. Add 16g of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer at 40℃ and stir at 40℃ until completely dissolved to obtain a homogeneous and transparent template solution. Then, add 36g of tetraethyl orthosilicate in three portions with a 10min interval between each addition while stirring continuously. After all the copolymer is added, continue stirring at 40℃ for 24h. After the reaction is completed, transfer the solution to a polytetrafluoroethylene-lined sealed container and age it at 100℃ for 24h. After aging, filter the solution and wash it twice each with deionized water and anhydrous ethanol until the filtrate is nearly neutral. Then, vacuum dry it at 80℃ for 12h to obtain the carrier precursor.

[0041] S2: Weigh 12g of the carrier precursor and add it to 120g of anhydrous toluene. Stir at room temperature for 30min, filter, and then vacuum dry at 110℃ for 6h to obtain a carrier precursor with low water content.

[0042] S3: Add 160g of anhydrous toluene to a three-necked flask containing 12g of low-water-content carrier precursor, and disperse under nitrogen protection at 25°C with mechanical stirring for 30min to form a carrier dispersion; separately dissolve 4g of tetrabutyl titanate in 20g of anhydrous toluene to prepare a titanium precursor solution; add the titanium precursor solution dropwise to the carrier dispersion at 0-5°C over 20min, and after the addition is complete, continue stirring at 0-5°C for 40min, then raise the temperature to 25°C and react for 2h, and finally raise the temperature to 70°C and react for 4h.

[0043] S4: Keep the S3 reaction system under nitrogen protection and cool it to 0-5℃. Add 4g of triethylamine to the reaction solution and stir for 10min. Then, dissolve 1g of trichlorotrimethylsilane in 20g of anhydrous toluene to prepare a short-chain end-capping solution. Add the short-chain end-capping solution dropwise to the reaction system over 15min. After the dropwise addition is complete, stir at 0-5℃ for 30min and then raise the temperature to 25℃ and react for 2h.

[0044] S5: Keeping the reaction system of S4 unchanged, 2g of decyltrichlorosilane was pre-dissolved in 20g of anhydrous toluene to prepare a long-chain end-capping solution; the long-chain end-capping solution was added dropwise to the system over 15min at 0-5℃. After the addition was completed, the mixture was stirred at 25℃ for 1h, and then the temperature was increased to 70℃ for 5h. After the reaction was completed, the mixture was filtered while hot. The filter cake was washed twice each with anhydrous toluene and anhydrous ethanol to remove unreacted silane, the generated triethylamine hydrochloride and oligomer condensate. Then, it was vacuum dried at 60℃ for 8h to obtain the composite carrier precursor.

[0045] S6: Add 400g of anhydrous ethanol to the system obtained in S5, reflux and extract at 78℃ for 8h, filter and repeat the extraction twice, for a total of 3 extractions. After the extraction is completed, filter, wash the filter cake twice with anhydrous ethanol, and then vacuum dry at 60℃ for 10h to obtain the composite carrier.

[0046] S7: Add 160g of anhydrous toluene to the system obtained in S6, and stir and disperse at room temperature for 30min under nitrogen protection. Then, dissolve 3g of 3-mercaptopropyltrimethoxysilane in 20g of anhydrous toluene and add it dropwise to the system over 20min at 25℃. After the addition is complete, reflux at 105℃ for 10h. After the reaction is complete, filter the mixture and wash the filter cake twice each with anhydrous toluene and anhydrous ethanol. Then, dry it under vacuum at 60℃ for 6h to obtain a composite carrier containing mercaptopropyl groups.

[0047] S8: Add 240g of anhydrous ethanol and 60g of deionized water to the system obtained in S7, stir at room temperature to form a suspension system, and then add 40g of hydrogen peroxide solution (30%) dropwise over 30min at 25℃. During the dropwise addition, control the system temperature to not exceed 30℃. After the dropwise addition is completed, continue the reaction at 25℃ for 4h, and then raise the temperature to 40℃ for 4h. After the reaction is completed, filter the solution. Wash the filter cake with deionized water until the filtrate is nearly neutral, then wash it once with anhydrous ethanol, and finally dry it under vacuum at 60℃ for 10h to obtain a solid catalyst for vanillin butyl ether.

[0048] Preparation of vanillin butyl ether: 5g of solid catalyst for vanillin butyl ether and 250g of anhydrous n-butanol were added to a three-necked flask equipped with a mechanical stirrer and a reflux condenser. The mixture was stirred at 60°C for 30min under nitrogen protection, allowing the n-butanol to preferentially wet the long-chain hydrophobic layer on the outer surface and enter the pore region. Separately, 50g of vanillin was dissolved in 150g of anhydrous n-butanol to obtain a vanillin feed solution. Maintaining the temperature of the main reaction system at 65°C, the vanillin feed solution was added dropwise to the main reaction system at a uniform rate over 40min. After the addition was completed... The temperature was raised to 85℃ and the reaction was maintained for 10 hours. Samples were taken every 2 hours during the reaction, and the conversion of vanillin was detected by high performance liquid chromatography. The reaction was stopped when the vanillin mass fraction was less than 2%. After the reaction was completed, the system was cooled to 50℃, and the catalyst was recovered by hot filtration. The filter cake was washed once with hot n-butanol, and the filtrate and washings were combined. Most of the n-butanol was distilled off under reduced pressure at 50℃ and 10 kPa to obtain the crude product. The crude product was then subjected to reduced pressure distillation below 200 Pa to obtain a colorless to light yellow liquid vanillin butyl ether.

[0049] Example 2: A method for preparing vanillin butyl ether, the specific steps of which are as follows:

[0050] S1: Add 500g of 2mol / L hydrochloric acid aqueous solution to a three-necked flask equipped with a mechanical stirrer. Add 15g of polyethylene oxide-polyethylene oxide-polyethylene oxide triblock copolymer at 39℃ and maintain mechanical stirring at 380r / min until completely dissolved to obtain a homogeneous and transparent template solution. Then, add 34g of tetraethyl orthosilicate in three portions with a 10min interval between each addition while continuously stirring. After all the copolymer is added, continue stirring at 39℃ for 23h. After the reaction is completed, transfer the solution to a polytetrafluoroethylene-lined sealed container and age it at 98℃ for 23h. After aging, filter the solution and wash it twice each with deionized water and anhydrous ethanol until the filtrate is nearly neutral. Then, vacuum dry it at 80℃ for 12h to obtain the carrier precursor.

[0051] S2: Weigh 11g of the carrier precursor and add it to 110g of anhydrous toluene. Stir at 320r / min for 30min at room temperature, filter, and then vacuum dry at 110℃ for 5h to obtain a carrier precursor with low water content.

[0052] S3: Add 150g of anhydrous toluene to a three-necked flask containing 11g of low-water-content carrier precursor. Under nitrogen protection, mechanically stir at 500r / min at 25℃ for 30min to form a carrier dispersion. Separately, dissolve 3.6g of tetrabutyl titanate in 18g of anhydrous toluene to prepare a titanium precursor solution. Add the titanium precursor solution dropwise to the carrier dispersion at 0℃ over 18min. After the addition is complete, continue stirring at 0℃ for 40min, then raise the temperature to 25℃ and react for 2h, and finally raise the temperature to 68℃ and react for 4h.

[0053] S4: Keep the reaction solution obtained in step S3 under nitrogen protection and cool it to 0°C. Add 3.8g of triethylamine to the reaction solution and stir for 10min. Then, dissolve 0.9g of trichlorotrimethylsilane in 18g of anhydrous toluene to prepare a short-chain end-capping solution. Add the short-chain end-capping solution dropwise to the reaction system over 15min. After the dropwise addition is completed, stir at 0°C for 30min and then raise the temperature to 25°C to react for 2h.

[0054] S5: Keeping the reaction system of S4 unchanged, 1.8g of decyltrichlorosilane was pre-dissolved in 18g of anhydrous toluene to prepare a long-chain end-capping solution. The long-chain end-capping solution was added dropwise to the system at 0℃ over 15min. After the addition was completed, the mixture was stirred at 25℃ for 1h, and then the temperature was increased to 68℃ for 5h. After the reaction was completed, the mixture was filtered while hot. The filter cake was washed twice each with anhydrous toluene and anhydrous ethanol, and then dried under vacuum at 60℃ for 8h to obtain the composite carrier precursor.

[0055] S6: Add 390g of anhydrous ethanol to the system obtained in S5, reflux and extract at 78℃ for 8h, filter and repeat the extraction twice, for a total of 3 extractions. After the extraction is completed, filter, wash the filter cake twice with anhydrous ethanol, and then vacuum dry at 60℃ for 10h to obtain the composite carrier.

[0056] S7: Add 160g of anhydrous toluene to the system obtained in S6, and stir and disperse at room temperature for 30min under nitrogen protection. Then, dissolve 2.8g of 3-mercaptopropyltrimethoxysilane in 18g of anhydrous toluene and add it dropwise to the system over 20min at 25℃. After the addition is complete, reflux at 104℃ for 10h. After the reaction is complete, filter the mixture and wash the filter cake twice each with anhydrous toluene and anhydrous ethanol. Then, dry it under vacuum at 60℃ for 6h to obtain a composite support containing mercaptopropyl groups.

[0057] S8: Add 235g of anhydrous ethanol and 55g of deionized water to the system obtained in S7, stir at room temperature to form a suspension system, and then add 38g of hydrogen peroxide solution (30%) dropwise over 30min at 25℃. During the dropwise addition, control the system temperature to not exceed 30℃. After the dropwise addition is completed, continue the reaction at 25-26℃ for 4h, and then raise the temperature to 40℃ for 4h. After the reaction is completed, filter the solution. Wash the filter cake with deionized water until the filtrate is nearly neutral, then wash it once with anhydrous ethanol, and finally dry it under vacuum at 60℃ for 10h to obtain a solid catalyst for vanillin butyl ether.

[0058] Preparation of vanillin butyl ether: 4.8 g of solid catalyst for vanillin butyl ether and 245 g of anhydrous n-butanol were added to a three-necked flask equipped with a mechanical stirrer and a reflux condenser. The mixture was stirred and pre-wetted at 550 r / min for 30 min at 58 °C under nitrogen protection. Separately, 48 g of vanillin was dissolved in 148 g of anhydrous n-butanol to obtain a vanillin feed solution. Maintaining the temperature of the main reaction system at 64 °C, the vanillin feed solution was added dropwise to the main reaction system at a uniform rate over 35 min. After the addition was completed, the temperature was raised to 84 °C. The reaction was carried out at ℃ for 10 hours. Samples were taken every 2 hours during the reaction, and the conversion of vanillin was detected by high performance liquid chromatography. The reaction was stopped when the mass fraction of vanillin was less than 2%. After the reaction was completed, the system was cooled to 50℃, and the catalyst was recovered by hot filtration. The filter cake was washed once with hot n-butanol. The filtrate and washings were combined, and most of the n-butanol was distilled off under reduced pressure at 50℃ and 10 kPa to obtain the crude product. The crude product was then subjected to reduced pressure distillation below 200 Pa to obtain colorless to light yellow liquid vanillin butyl ether.

[0059] Example 3: A method for preparing vanillin butyl ether, the specific steps of which are as follows:

[0060] S1: Add 540g of 2mol / L hydrochloric acid aqueous solution to a three-necked flask equipped with a mechanical stirrer. Add 17g of polyethylene oxide-polyethylene oxide-polyethylene oxide triblock copolymer at 41℃ and maintain mechanical stirring at 430r / min until completely dissolved to obtain a homogeneous and transparent template solution. Then, add 38g of tetraethyl orthosilicate in three portions with a 10min interval between each addition while continuously stirring. After all the copolymer is added, continue stirring at 41℃ for 25h. After the reaction is completed, transfer the copolymer to a polytetrafluoroethylene-lined sealed container and age it at 102℃ for 25h. After aging, filter the solution and wash it twice each with deionized water and anhydrous ethanol until the filtrate is nearly neutral. Then, vacuum dry it at 80℃ for 12h to obtain the carrier precursor.

[0061] S2: Weigh 13g of the carrier precursor and add it to 130g of anhydrous toluene. Stir at 380r / min for 30min at room temperature, filter, and then vacuum dry at 112℃ for 7h to obtain a carrier precursor with low water content.

[0062] S3: Add 170g of anhydrous toluene to a three-necked flask containing 13g of low-water-content carrier precursor. Under nitrogen protection, mechanically stir at 550r / min at 25℃ for 30min to form a carrier dispersion. Separately, dissolve 4.4g of tetrabutyl titanate in 22g of anhydrous toluene to prepare a titanium precursor solution. Add the titanium precursor solution dropwise to the carrier dispersion at 5℃ over 20min. After the addition is complete, continue stirring at 5℃ for 40min, then raise the temperature to 25℃ and react for 2h. Finally, raise the temperature to 72℃ and react for 4.5h.

[0063] S4: Keep the reaction solution obtained in step S3 under nitrogen protection and cool it to 5°C. Add 4.2g of triethylamine to the reaction solution and stir for 10min. Then, dissolve 1.1g of trichlorotrimethylsilane in 22g of anhydrous toluene to prepare a short-chain end-capping solution. Add the short-chain end-capping solution dropwise to the reaction system over 15min. After the dropwise addition is completed, stir at 5°C for 30min and then raise the temperature to 25°C to react for 2h.

[0064] S5: Keeping the reaction system of S4 unchanged, 2.2g of decyltrichlorosilane was pre-dissolved in 22g of anhydrous toluene to prepare a long-chain end-capping solution. The long-chain end-capping solution was added dropwise to the system at 5°C over 15min. After the addition was completed, the mixture was stirred at 25°C for 1h, and then the temperature was increased to 72°C for 5.5h. After the reaction was completed, the mixture was filtered while hot. The filter cake was washed twice each with anhydrous toluene and anhydrous ethanol, and then dried under vacuum at 60°C for 8h to obtain the composite carrier precursor.

[0065] S6: Add 410g of anhydrous ethanol to the system obtained in S5, reflux and extract at 79℃ for 9h, filter and repeat the extraction twice, for a total of 3 extractions. After extraction, filter, wash the filter cake twice with anhydrous ethanol, and then vacuum dry at 60℃ for 10h to obtain the composite carrier.

[0066] S7: Add 160g of anhydrous toluene to the system obtained in S6, and stir and disperse at room temperature for 30min under nitrogen protection. Then, dissolve 3.2g of 3-mercaptopropyltrimethoxysilane in 22g of anhydrous toluene and add it dropwise to the system over 20min at 25℃. After the addition is complete, reflux at 106℃ for 11h. After the reaction is complete, filter the mixture and wash the filter cake twice each with anhydrous toluene and anhydrous ethanol. Then, dry it under vacuum at 60℃ for 6h to obtain a composite support containing mercaptopropyl groups.

[0067] S8: Add 245g of anhydrous ethanol and 65g of deionized water to the system obtained in S7, stir at room temperature to form a suspension system, and then add 42g of hydrogen peroxide solution (30%) dropwise over 30min at 26℃. During the dropwise addition, control the system temperature to not exceed 30℃. After the dropwise addition is completed, continue the reaction at 25-26℃ for 4h, and then raise the temperature to 42℃ for 4h. After the reaction is completed, filter the solution. Wash the filter cake with deionized water until the filtrate is nearly neutral, then wash it once with anhydrous ethanol, and finally dry it under vacuum at 60℃ for 10h to obtain a solid catalyst for vanillin butyl ether.

[0068] Preparation of vanillin butyl ether: 5.5 g of solid catalyst for vanillin butyl ether and 255 g of anhydrous n-butanol were added to a three-necked flask equipped with a mechanical stirrer and a reflux condenser. The mixture was stirred and pre-wetted at 650 r / min for 35 min at 62 °C under nitrogen protection. Separately, 52 g of vanillin was dissolved in 152 g of anhydrous n-butanol to obtain a vanillin feed solution. Maintaining the temperature of the main reaction system at 66 °C, the vanillin feed solution was added dropwise to the main reaction system at a uniform rate over 40 min. After the addition was completed, the temperature was raised to 86 °C. The reaction was carried out at ℃ for 11 hours. Samples were taken every 2 hours during the reaction, and the conversion of vanillin was detected by high performance liquid chromatography. The reaction was stopped when the vanillin mass fraction was less than 2%. After the reaction was completed, the system was cooled to 50℃, and the catalyst was recovered by hot filtration. The filter cake was washed once with hot n-butanol. The filtrate and washings were combined, and most of the n-butanol was distilled off under reduced pressure at 50℃ and 10 kPa to obtain the crude product. The crude product was then subjected to reduced pressure distillation below 200 Pa to obtain colorless to light yellow liquid vanillin butyl ether.

[0069] Comparative Example 1: The difference from Example 1 is that in step S3, tetrabutyl titanate is not added, but anhydrous toluene is used as the equal mass compensation drop solution; the other conditions are the same as in Example 1.

[0070] Comparative Example 2: The difference from Example 1 is that in step S4, chlorotrimethylsilane is not added, but anhydrous toluene is used as the equal mass compensation drop solution; the other conditions are the same as in Example 1.

[0071] Comparative Example 3: The difference from Example 1 is that in step S5, decyltrichlorosilane is not added, but anhydrous toluene is used as the equal mass compensation drop solution; the other conditions are the same as in Example 1.

[0072] Comparative Example 4: The difference from Example 1 is that the order of steps S5 and S4 is reversed. That is, decyltrichlorosilane is added first while the template is retained, and then chlorotrimethylsilane is added to complete the short chain end capping; the other conditions are the same as in Example 1.

[0073] Comparative Example 5: The difference from Example 1 is that in step S7, 3-mercaptopropyltrimethoxysilane is not added, but anhydrous toluene is used as the equal mass compensation drop solution, and the oxidation treatment in step S8 is not performed. After step S7 is completed, it is directly used to prepare vanillin butyl ether; the other conditions are the same as in Example 1.

[0074] Comparative Example 6: The difference from Example 1 is that step S6 is performed first to remove the template, and then steps S3, S4 and S5 of Example 1 are performed sequentially to construct the titanium site at the orifice, perform the first short chain end capping and the second long chain shell construction, and then the subsequent steps are performed; the remaining conditions are the same as those of Example 1.

[0075] Performance testing

[0076] Specific surface area characterization: In accordance with GB / T 19587-2017, 150 mg of each sample was weighed, and after vacuum degassing at 160℃ for 6 h, nitrogen adsorption-desorption test was performed at liquid nitrogen temperature, and the specific surface area was calculated according to the BET method.

[0077] Vanillin conversion, vanillin butyl ether selectivity, total by-products and finished product purity were tested according to GB / T16631-2008. A C18 reversed-phase column with dimensions of 250 mm × 4.6 mm and a particle size of 5 μm was used. The mobile phase was methanol / water at a volume ratio of 68:32. The flow rate was 1.0 mL / min. The column temperature was 30 °C. The detection wavelength was 280 nm. The injection volume was 10 μL. Vanillin and vanillin butyl ether reference solutions were prepared separately, and a 5-point external standard curve was established. 0.100 g of the reaction endpoint sample was taken, diluted to 25 mL with methanol, filtered, and injected. 0.050 g of the distillate fraction sample was taken, diluted to 25 mL with methanol, filtered, and injected. Vanillin conversion was calculated based on the initial and endpoint molar amounts of vanillin. Vanillin butyl ether selectivity was calculated as the ratio of the endpoint molar amount of vanillin butyl ether to the total converted vanillin. The total amount of byproducts was calculated as the normalized sum of the peak areas of all chromatographic components except vanillin and vanillin butyl ether. The purity of the finished product was calculated using the external standard method.

[0078] Moisture content of finished product: The determination shall be carried out in accordance with GB / T 6283-2008. 1.000g of the main distillate obtained shall be accurately weighed and tested by Karl Fischer coulometric method. Anhydrous methanol shall be used as the titration solvent. The endpoint shall be determined by automatic potentiometric method. Each sample shall be tested in parallel 3 times and the arithmetic mean shall be taken.

[0079] Colorimetric test of finished product: The test shall be conducted in accordance with GB / T 3143-1982. Take 50 mL of the obtained distillate main fraction and place it in a 50 mL colorimetric tube. Visually compare it with the platinum-cobalt standard color series at 25℃. The result shall be expressed in Hazen units. If the colorimetric value of the sample exceeds the upper limit of the standard color series, dilute it with colorless anhydrous ethanol at a mass ratio of 1:1 and retest. Then, calculate the value according to the dilution factor.

[0080] Catalyst cycle stability test: The repeated reaction method was used for determination. After each reaction, the catalyst was recovered, washed, and dried according to the method described in the sample preparation section before reuse. After each cycle, the vanillin conversion rate and vanillin butyl ether selectivity were determined according to the method in test item six, and the data of the 5th cycle were recorded; the above test results are shown in Table 1.

[0081] Table 1 Performance Test Results

[0082]

[0083] Data Analysis: As can be seen from the data in Table 1 of the examples, the vanillin butyl ether prepared by this invention exhibits good overall balance in terms of reaction efficiency, main product orientation, finished product purity, color control, and recyclability stability. This indicates that the catalyst does not rely on a single acid site to drive the reaction, but rather forms a continuous complex through the Lewis acidic titanium sites at the pore opening, the two-stage hydrophobic layers on the outer surface, and the propylsulfonic acid sites inside the pores. This is mainly because vanillin is first directionally activated in the pore opening region, and then undergoes etherification conversion inside the pores. Simultaneously, the long-chain hydrophobic layer on the outer surface promotes the enrichment of n-butanol and reduces the retention of by-product water, ensuring that the acid sites remain in a favorable reaction environment. This not only facilitates the continuous progress of the main reaction but also reduces the tendency for condensation and resinification on the outer surface, thus balancing the burden of post-processing and recyclability stability, making it suitable for the continuous preparation of fragrance intermediates and temperature-sensitive functional raw materials.

[0084] As can be seen from the data in Table 1 for Example 1 and Comparative Example 1, the main reaction proceeded significantly slower and side reactions accumulated more easily after the absence of Lewis acidic titanium sites at the pore opening. The main reason for this is that vanillin lacks pre-activation in the pore opening region before entering the pore channel, resulting in a longer residence time of the molecule on the outer surface and near the pore opening, making it more prone to condensation and resinification, thus increasing the burden on subsequent purification.

[0085] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 2 and 3, when either the short-chain trimethylsilyl group is pre-capped or the long-chain decyl group is missing from the shell structure, the catalyst can still maintain a certain reactivity, but the overall balance is significantly reduced. This suggests that the short-chain trimethylsilyl group and the long-chain decyl group do not simply exist side-by-side, but rather play different roles in pore confinement and outer drainage, respectively. Only when they work together can a clear internal and external partitioning and spatial division of labor be formed, and their effect is significantly greater than that of either group acting alone.

[0086] As can be seen from the data in Example 1 and Comparative Example 4 in Table 1, simply changing the order of addition of the short-chain trimethylsilyl group and the long-chain decyl group causes a simultaneous deterioration in multiple properties. The main reason is that when the long-chain decyl group preferentially contacts the outer surface and orifice while the template is retained, it is more likely to form a volume occupation first. Subsequently, the short-chain trimethylsilyl group has difficulty completing uniform and light end-capping, resulting in the orifice area being neither unobstructed nor able to maintain clear partitioning. It can be inferred that the limitation of the addition sequence is not a simple adjustment, but a key condition that determines whether the spatial structure can be established.

[0087] As can be seen from the data in Table 1 for Example 1 and Comparative Example 5, even with the Lewis acidic titanium sites at the pore opening and the two-level hydrophobic layer on the outer surface retained, the specific surface area is not low if the propylsulfonic acid sites inside the pores formed after template removal are lacking, but the main reaction conversion is still significantly insufficient. The main reason is that a larger accessible pore does not equate to higher reaction efficiency. What truly determines performance is the complete coordination of pore opening activation, in-pore reaction, and external drainage. The improvement brought about by this coordination cannot be replaced by a single structural change.

[0088] As can be seen from the data in Table 1 for Example 1 and Comparative Example 6, after removing the template and then introducing the titanium sites at the pore openings and the hydrophobic layer on the outer surface, the pore accessibility, reaction efficiency, and recycling stability of the catalyst all decreased significantly. The main reason is that after template removal, the subsequently introduced titanium components, short-chain trimethylsilyl groups, and long-chain decyl groups are no longer confined to the outer surface and the vicinity of the pore openings, but can more easily and indiscriminately enter the interior of the pores, causing the effective space inside the pores to be occupied, and making it difficult to form a clear pre-activation structure in the pore opening region.

[0089] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing vanillin butyl ether, characterized in that, The process includes the following steps: in the presence of anhydrous n-butanol, vanillin and n-butanol are reacted with a solid catalyst for vanillin butyl ether to obtain crude vanillin butyl ether; the crude vanillin butyl ether is subjected to vacuum distillation to remove n-butanol and vacuum fractionation to obtain vanillin butyl ether. The preparation steps of the solid catalyst for vanillin butyl ether are as follows: (1) Under acidic conditions, using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer as template agent and tetraethyl orthosilicate as silicon source, a carrier precursor with template still retained inside the pores was obtained by hydrolysis, polycondensation and aging. (2) The carrier precursor is subjected to dewatering treatment to obtain a carrier precursor with low water content; (3) Disperse the low-water-content carrier precursor in anhydrous toluene to form a carrier dispersion. Separately, disperse tetrabutyl titanate in anhydrous toluene to form a titanium precursor solution. Add the titanium precursor solution dropwise to the carrier dispersion. After the reaction is complete, add short-chain end-capping solution and long-chain end-capping solution in sequence to perform surface silanization end-capping treatment to obtain a composite carrier precursor. The composite carrier precursor is refluxed with anhydrous ethanol to remove the template to obtain a composite carrier. (4) The composite support was grafted with 3-mercaptopropyltrimethoxysilane to form a mercaptopropyl-containing composite support, which was then oxidized to obtain a solid catalyst for vanillin butyl ether. The short-chain end-capping solution in step (3) is obtained by dispersing trichloromethylsilane in anhydrous toluene, wherein the mass ratio of trichloromethylsilane to anhydrous toluene is 1:20; The long-chain end-capping liquid in step (3) is obtained by dispersing decyltrichlorosilane in anhydrous toluene, wherein the mass ratio of decyltrichlorosilane to anhydrous toluene is 1:

10.

2. The preparation method according to claim 1, characterized in that, The weight ratio of tetraethyl orthosilicate and polyethylene oxide-polyethylene oxide-polyethylene oxide triblock copolymer in step (1) is 34-38:15-17.

3. The preparation method according to claim 1, characterized in that, The aging temperature in step (1) is 98-102℃ and the aging time is 23-25h; the hydrolysis condensation temperature is 39-41℃ and the hydrolysis condensation time is 23-25h.

4. The preparation method according to claim 1, characterized in that, The desorption water treatment temperature in step (2) is 110-112℃, and the desorption water treatment time is 5-7h.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the low-water-content carrier precursor, tetrabutyl titanate, short-chain capping liquid and long-chain capping liquid in step (3) is 11-13:3.6-4.4:18-22:18-22.

6. The preparation method according to claim 1, characterized in that, The anhydrous ethanol reflux in step (3) is carried out at 78-79℃, the reflux extraction time is 8-9h, and the reflux is repeated 3 times.

7. The preparation method according to claim 1, characterized in that, The grafting treatment in step (4) is performed at a temperature of 104-106℃ and a reaction time of 10-11h.

8. The preparation method according to claim 1, characterized in that, The weight ratio of the solid catalyst for vanillin butyl ether, anhydrous n-butanol, and vanillin is 4.8-5.5:393-407:48-52.

9. A vanillyl butyl ether, characterized in that, It is prepared according to any one of claims 1-8.

10. An application of vanillyl butyl ether according to claim 9, characterized in that, Used in the preparation of food additives, daily chemical flavorings, or temperature-sensitive functional materials.

Images