3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate

Abstract

This invention relates to the field of organic synthesis technology and discloses a method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester, comprising the steps of: S1, providing raw material: 3-cyclohexenecarboxylic acid-3′-cyclohexene methyl ester; S2, epoxidation reaction: mixing the raw material with hydrogen peroxide, a composite catalyst, and a buffer to obtain a reaction solution containing the target product; S3, separation and purification: allowing the reaction solution to stand and separate into layers, separating the organic phase, washing with water, drying, and vacuum distilling to obtain 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester. This method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester uses hydrogen peroxide as the oxygen source, resulting in no heavy metal pollution, low wastewater volume, and conforming to the trend of green chemistry. The composite catalyst requires a small amount, has high activity and good selectivity, can be recycled ≥5 times, reducing costs, requiring less equipment, and is highly safe. The product is colorless and transparent, with a high epoxy value, purity ≥98.5%, low acid value, and good stability.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, specifically to a method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester. Background Technology

[0002] The traditional preparation process of bicyclohexyl ester mainly adopts the peroxy acid oxidation method (such as m-chloroperoxybenzoic acid and peracetic acid), which has the following problems: peroxy acids have poor stability, are prone to explosion, and have high costs; a large amount of waste salt and waste acid are generated after the reaction, which puts great pressure on the environment; the product has a dark color, high acid value, and poor stability, which makes it difficult to meet the needs of high-end electronics and 3D printing.

[0003] Existing patents (such as CN101525320A) employ a phase-transfer catalysis-hydrogen peroxide system, but suffer from problems such as difficulty in catalyst recovery, high reaction temperature, and insufficient product purity. CN113880790A uses a microchannel reaction, which involves large equipment investment and is difficult to scale up. Therefore, developing a green, efficient, industrially scalable preparation method with high product quality is of significant practical importance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester. This method offers advantages such as recyclable catalyst, mild reaction conditions, high selectivity, high product purity, light color, and environmental friendliness. It solves the problems of existing technologies, including poor stability of peroxyacids, susceptibility to explosion, high cost; the generation of large amounts of waste salt and waste acid after the reaction, resulting in significant environmental pressure; and the dark color, high acid value, and poor stability of the products, which are difficult to meet the needs of high-end electronics and 3D printing.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester, comprising the following steps: Raw material preparation The raw material is 3-cyclohexenecarboxylic acid-3′-cyclohexene methyl ester, which can be prepared from 3-cyclohexenecarboxaldehyde via the Tischenko reaction, with a purity ≥95%.

[0006] Epoxidation reaction In a reactor equipped with a stirrer, thermometer, and condenser, add 100 parts by mass of raw material, 0.5–5 parts by mass of composite catalyst (tetrabutylammonium peroxyphosphotungstate), and 1–10 parts by mass of sodium bicarbonate buffer. Start stirring (300–600 rpm) and heat to 40–60°C. Slowly add 30–50 parts by mass of hydrogen peroxide, with a molar ratio of hydrogen peroxide to raw material of 2.5:1, over a period of 1–3 hours. After the addition is complete, maintain the temperature for 3–6 hours. Terminate the reaction when the residual raw material is ≤0.5% as monitored by GC.

[0007] Separation and purification The reaction solution was allowed to stand and separate into layers, and the upper organic phase was separated. The organic phase was washed with deionized water 2-3 times until neutral and dried with anhydrous sodium sulfate. After drying, the organic phase was transferred to a vacuum distillation column with a vacuum degree of 2 mmHg and a bottom temperature of 140℃. The fraction at 130-132℃ was collected to obtain the target product.

[0008] A method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester includes the following steps: S1. Raw material provided: 3-cyclohexenecarboxylic acid-3′-cyclohexene methyl ester; S2. Epoxidation reaction: The raw material is mixed with hydrogen peroxide, composite catalyst and buffer, and reacted at 30-70°C and normal pressure for 2-8 hours to obtain a reaction solution containing the target product. S3. Separation and purification: The reaction solution is allowed to stand and separate into layers. The organic phase is separated, washed with water, dried, and distilled under reduced pressure to obtain 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester.

[0009] Preferably, in step S2, the composite catalyst is a heteropolyacid quaternary ammonium salt, preferably tetrabutylammonium peroxyphosphotungstic acid, tetraoctylammonium peroxyphosphomolybdate, or a mixture thereof; the catalyst dosage is 0.5–5 wt% of the raw material mass; the heteropolyacid quaternary ammonium salt composite catalyst selected in this invention is a highly selective phase transfer catalytic system adapted to the cyclohexene structure double epoxidation reaction, wherein tetrabutylammonium peroxyphosphotungstic acid, tetraoctylammonium peroxyphosphomolybdate, and their mixtures have both excellent lipophilicity and catalytic activity, can effectively accommodate the organic raw material phase and the hydrogen peroxide inorganic aqueous phase, significantly improve the mass transfer efficiency at the two-phase interface, can accurately catalyze the directional epoxidation reaction of the two sets of cyclohexene double bonds in the molecular structure, and effectively inhibit the occurrence of excessive oxidation of double bonds, ring-opening hydrolysis, and polymerization side reactions. This invention strictly limits the catalyst dosage to 0.5–5 wt% of the raw material mass. When the catalyst dosage is below 0.5 wt%, there are insufficient catalytic active sites, the reaction rate decreases significantly, the raw material conversion is incomplete, and the residue is large. When the catalyst dosage is above 5 wt%, it not only increases production costs, but excessive catalyst can also easily cause local over-catalysis, leading to a darker product color, increased by-products, and a decrease in epoxy value. Within this dosage range, the catalyst activity is stable and the catalytic efficiency is high, ensuring full conversion of the raw material while minimizing side reactions, guaranteeing high product purity and high epoxy value, and is also compatible with subsequent catalyst recovery and recycling processes.

[0010] Preferably, in step S2, the hydrogen peroxide mass fraction is 30-50%, and the molar ratio of hydrogen peroxide to raw materials is 2.2-3.0:1. Using hydrogen peroxide as a green and environmentally friendly epoxidation oxygen source results in no heavy metal residues and no large-scale production of waste acid or salt, meeting the requirements of green chemical production. Limiting the hydrogen peroxide mass fraction to 30-50% ensures moderate stability and mild, controllable oxidative activity, avoiding the problems of excessive water content in the reaction system due to low-concentration hydrogen peroxide, which can lead to ring-opening hydrolysis of epoxy groups, increased product acid value, and reduced yield. It also avoids the drawbacks of high-concentration hydrogen peroxide, such as excessively vigorous oxidation, concentrated exothermic reaction, and easy local overheating leading to side reactions. This invention further limits the molar ratio of hydrogen peroxide to raw materials to 2.2-3.0:1. Since the target product is a double epoxy structure, a single molecule of raw material requires two molecules of hydrogen peroxide to complete the double bond epoxidation. Adding excess hydrogen peroxide ensures that both sets of double bonds react completely. When the molar ratio is below 2.2:1, insufficient hydrogen peroxide supply leads to incomplete oxidation of double bonds and a significant increase in monoepoxide byproducts. When the molar ratio is above 3.0:1, excessive hydrogen peroxide residue increases the acidity of the system, easily causing hydrolysis and failure of the epoxy groups in the product, and also increasing the post-treatment washing load and safety risks. This ratio range can achieve a balance between high raw material conversion rate and high product selectivity.

[0011] Preferably, in step S2, the buffer is sodium carbonate, sodium bicarbonate, or sodium dihydrogen phosphate, and the amount of buffer is 1-10 wt% of the raw material mass, maintaining the system pH at 5.5-7.5. During the epoxidation reaction, hydrogen peroxide decomposition and trace side reactions continuously produce trace amounts of acidic substances, causing the system pH to gradually decrease. Epoxy groups are highly susceptible to ring-opening hydrolysis and degradation in acidic environments, which is the core reason for the decrease in product purity, increase in acid value, and deterioration in quality. This invention selects sodium carbonate, sodium bicarbonate, or sodium dihydrogen phosphate as a weakly alkaline buffer, which has the characteristics of a mild buffering range, no introduction of impurities, and no damage to the catalytic system activity. It can neutralize the trace amounts of acidic substances generated during the reaction in real time, stabilizing the acid-base environment of the system. This invention limits the amount of buffer to 1-10 wt% of the raw material mass and strictly controls the pH of the system to a weakly neutral buffer zone of 5.5-7.5. When the amount of buffer is insufficient or the pH of the system is below 5.5, the system becomes weakly acidic, the hydrolysis of epoxy groups intensifies, and the epoxy value of the product decreases significantly. When the amount of buffer is too high or the pH of the system is above 7.5, the excessive alkalinity accelerates the ineffective decomposition of hydrogen peroxide, reduces oxygen source utilization, and inhibits the epoxidation reaction. This buffer system can ensure the acid-base stability of the reaction system throughout the process, reduce side reactions at the source, and significantly improve product purity and yield.

[0012] Preferably, in step S2, the reaction system is solvent-free or contains toluene or ethyl acetate as a co-solvent, with a co-solvent-to-raw material mass ratio ≤ 1:1. The reaction system of this invention can adopt a solvent-free reaction mode, which is environmentally friendly, leaves no solvent residue, and has a simple post-processing flow, adapting to the production requirements of high-end electronic-grade epoxy resin monomers. Simultaneously, toluene or ethyl acetate can be selectively added as co-solvents. Both solvents are low-toxicity, volatile, and easily removable inert solvents that do not participate in the epoxidation reaction. They can effectively improve the miscibility between the raw materials and aqueous hydrogen peroxide, reduce system viscosity, enhance material mixing and mass transfer, and make the temperature distribution of the reaction system more uniform, avoiding side reactions caused by excessively high local concentrations or overheating. This invention strictly limits the co-solvent-to-raw material mass ratio to ≤ 1:1. Excessive co-solvent addition will significantly reduce the concentration of reactants, decrease the reaction rate, prolong the reaction cycle, and increase the energy and labor costs of subsequent solvent removal and distillation. It also easily causes trace solvent residues, affecting product purity and application performance. This limited range balances reaction mass transfer efficiency, production economy, and product purity, making it suitable for industrial-scale mass production.

[0013] Preferably, in step S3, the vacuum distillation conditions are a vacuum degree of 1–5 mmHg and a reboiler temperature of 130–150°C. The fraction collected at 128–135°C has an epoxy value ≥0.58 eq / 100g and a purity ≥98.5%. The crude product after the reaction contains a small amount of unreacted raw materials, trace by-products, moisture, catalyst residue, and solvent impurities, which need to be refined by vacuum distillation. This invention limits the distillation conditions to a vacuum degree of 1–5 mmHg and a reboiler temperature of 130–150°C. The high vacuum environment can significantly reduce the boiling point of the material, avoiding the problems of thermal decomposition of epoxy groups, product polymerization and discoloration, and performance degradation caused by high-temperature atmospheric pressure distillation, and maximizing the protection of the epoxy structure integrity of the target product. By precisely controlling the temperature and fractionating, the characteristic fraction collected at 128–135°C can effectively separate light component impurities from heavy component by-products, and completely remove residual impurities in the crude product. After purification by distillation under these conditions, the final product of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester has a purity of ≥98.5%, a stable epoxy value of ≥0.58 eq / 100g, and is colorless, transparent, with extremely low acid value and excellent stability, fully meeting the usage standards of high-end fields such as electronic packaging, photosensitive resins, and high-end weather-resistant coatings.

[0014] Preferably, the composite catalyst can be recovered by centrifugation or extraction, and can be recycled ≥5 times with an activity retention rate ≥90%. The heteropolyacid quaternary ammonium salt composite catalyst has the characteristic of oil-water two-phase separation. After the reaction, most of the catalyst is enriched in the aqueous phase system, which can be efficiently recovered by simple physical methods such as centrifugation and organic solvent extraction. The recovery process does not require high temperature, high pressure and complex activation processes, and is simple to operate, energy-saving and pollution-free. After simple desolvation and drying, the recovered catalyst can be directly reused in the epoxidation reaction. It can be continuously recycled 5 times or more, and the catalyst structure is stable and the activity decays slowly. After five cycles, the overall catalytic activity retention rate is still not less than 90%, which can still ensure high conversion rate of raw materials and high purity of products. This recyclable feature greatly reduces the cost of catalyst consumables, solves the industry pain points of traditional epoxidation catalysts such as single use, high loss, high cost and large amount of solid waste, significantly improves the industrial economy and green production advantages of this process, and is suitable for large-scale continuous production applications.

[0015] Compared with the prior art, the present invention provides a method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester, which has the following beneficial effects: 1. The preparation method of this 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester uses hydrogen peroxide as the oxygen source, resulting in no heavy metal pollution, low wastewater volume, and conforming to the trend of green chemistry. The composite catalyst requires a small amount, has high activity and good selectivity, and can be recycled ≥5 times, reducing costs. It operates at atmospheric pressure and 30-70℃, without the need for high temperature and high pressure, has low equipment requirements, high safety, and produces a colorless and transparent product with high epoxy value, purity ≥98.5%, low acid value, and good stability, meeting the needs of high-end electronics and 3D printing. The process is simple, easy to scale up, and low in cost, making it suitable for large-scale production. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the preparation method of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please see Figure 1 A method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester includes the following steps: Raw material preparation The raw material is 3-cyclohexenecarboxylic acid-3′-cyclohexene methyl ester, which can be prepared from 3-cyclohexenecarboxaldehyde via the Tischenko reaction, with a purity ≥95%.

[0019] Epoxidation reaction In a reactor equipped with a stirrer, thermometer, and condenser, add 100 parts by mass of raw material, 0.5–5 parts by mass of composite catalyst (tetrabutylammonium peroxyphosphotungstate), and 1–10 parts by mass of sodium bicarbonate buffer. Start stirring (300–600 rpm) and heat to 40–60°C. Slowly add 30–50 parts by mass of hydrogen peroxide, with a molar ratio of hydrogen peroxide to raw material of 2.5:1, over a period of 1–3 hours. After the addition is complete, maintain the temperature for 3–6 hours. Terminate the reaction when the residual raw material is ≤0.5% as monitored by GC.

[0020] Separation and purification The reaction solution was allowed to stand and separate into layers, and the upper organic phase was separated. The organic phase was washed with deionized water 2-3 times until neutral and dried with anhydrous sodium sulfate. After drying, the organic phase was transferred to a vacuum distillation column with a vacuum degree of 2 mmHg and a bottom temperature of 140℃. The fraction at 130-132℃ was collected to obtain the target product.

[0021] A method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester includes the following steps: S1. Raw material provided: 3-cyclohexenecarboxylic acid-3′-cyclohexene methyl ester; S2. Epoxidation reaction: The raw material is mixed with hydrogen peroxide, composite catalyst and buffer, and reacted at 30-70°C and normal pressure for 2-8 hours to obtain a reaction solution containing the target product. S3. Separation and purification: The reaction solution is allowed to stand and separate into layers. The organic phase is separated, washed with water, dried, and distilled under reduced pressure to obtain 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester.

[0022] Furthermore, in step S2, the composite catalyst is a heteropolyacid quaternary ammonium salt, preferably tetrabutylammonium peroxyphosphotungstate, tetraoctylammonium peroxyphosphotomolybdate, or a mixture thereof; the amount of catalyst used is 0.5 to 5 wt% of the raw material mass.

[0023] Furthermore, in step S2, the hydrogen peroxide has a mass fraction of 30-50%, and the molar ratio of hydrogen peroxide to raw materials is 2.2-3.0:1.

[0024] Furthermore, in step S2, the buffer is sodium carbonate, sodium bicarbonate, or sodium dihydrogen phosphate, and the amount of buffer is 1 to 10 wt% of the raw material mass, with the system pH maintained at 5.5 to 7.5.

[0025] Furthermore, in step S2, the reaction system is solvent-free or contains toluene or ethyl acetate as a co-solvent, with the mass ratio of co-solvent to raw material ≤ 1:1.

[0026] Furthermore, in step S3, the vacuum distillation conditions are a vacuum degree of 1-5 mmHg, a column bottom temperature of 130-150℃, and the fraction collected at 128-135℃. The product has an epoxy value ≥0.58 eq / 100g and a purity ≥98.5%.

[0027] Furthermore, the composite catalyst can be recovered by centrifugation or extraction and recycled ≥5 times with an activity retention rate ≥90%.

[0028] Example 1: Solvent-free system (basic process) Operating steps In a 500 mL three-necked reaction flask equipped with a stirrer, thermometer, constant pressure dropping funnel, and condenser, add 200 g (0.96 mol) of 3-cyclohexenylcarboxylic acid-3′-cyclohexene methyl ester, followed by 2.0 g of tetrabutylammonium peroxyphosphotungstate (1.0 wt% of the raw material mass) and 8.0 g of sodium bicarbonate (4.0 wt% of the raw material mass). Start the stirrer at 450 rpm and heat to 50 °C. At this point, the pH of the system is 6.4.

[0029] 220 g (2.24 mol) of 35% hydrogen peroxide was slowly added dropwise through a constant pressure dropping funnel. The molar ratio of hydrogen peroxide to raw material was 2.33:1, and the addition time was 2 h. After the addition was completed, the reaction was continued at the temperature for another 4 h. The reaction was terminated when the residual raw material was ≤0.5% as monitored by gas chromatography online.

[0030] The reaction solution was transferred to a separatory funnel and allowed to stand at room temperature for 30 min, resulting in phase separation. The lower aqueous phase was separated (for subsequent catalyst recovery), and the upper organic phase was washed three times with deionized water (80 mL each time) until the organic phase was neutral. Anhydrous sodium sulfate was added to the washed organic phase and dried for 2 h. The desiccant was then removed by filtration.

[0031] The filtrate was transferred to a vacuum distillation apparatus, the system vacuum was controlled at 2 mmHg, the bottom temperature was 140 ℃, and the fraction at 130~132 ℃ was collected to obtain the target product 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester.

[0032] Experimental data Appearance: Colorless, transparent, oily liquid GC purity: 99.1% Epoxy value: 0.60 eq / 100g Acid value: 0.08 mgKOH / g One-way return rate: 92.3% The final pH of the reaction system was 6.2. Example 2: Ethyl acetate co-solvent system Operating steps In a 500 mL three-necked flask, add 200 g (0.96 mol) of 3-cyclohexenylcarboxylic acid-3′-cyclohexene methyl ester, 100 g of ethyl acetate (co-solvent, 0.5:1 mass ratio to starting material), then add 3.0 g of tetrabutylammonium peroxyphosphotungstate (1.5 wt% of starting material) and 10.0 g of sodium bicarbonate (5.0 wt% of starting material). Start stirring and heat to 45 °C. The initial pH of the system is 6.6.

[0033] 235 g (2.39 mol) of 35% hydrogen peroxide was slowly added dropwise at a molar ratio of 2.49:1 to the raw material, and the addition was completed in 2.5 h. The reaction was kept at this temperature for 5 h, and the reaction was stopped when the residual raw material was detected by GC to be ≤0.5%.

[0034] The reaction solution was allowed to stand and separate into aqueous and organic phases. The organic phase was washed three times with deionized water until neutral, dried over anhydrous sodium sulfate, and then filtered. The filtrate was first subjected to atmospheric pressure to remove ethyl acetate, and then subjected to vacuum distillation: vacuum degree 3 mmHg, reboiler temperature 138℃, and the fraction at 129–133℃ was collected to obtain the final product.

[0035] Experimental data Appearance: Colorless, transparent, oily liquid GC purity: 98.8% Epoxy value: 0.59 eq / 100g Acid value: 0.10 mgKOH / g One-way return rate: 91.1% The final pH of the reaction system was 6.3. Example 3: Catalyst recycling for the 5th batch (solvent-free system) Catalyst recovery pretreatment The aqueous phases separated in Examples 1 and 2 were collected, and the catalyst was extracted with dichloromethane. The organic extracts were combined, and the solvent was removed under normal pressure to obtain the recovered tetrabutylammonium peroxyphosphotungstate. The catalyst was then recycled sequentially. In this example, the catalyst was used in the 5th cycle.

[0036] Operating steps The reaction apparatus and basic materials were the same as in Example 1: 200 g (0.96 mol) of raw material, 2.1 g of the fifth batch of recovered catalyst, and 8.0 g of sodium bicarbonate were added. The mixture was stirred and heated to 50 °C, and the pH of the system was 6.3.

[0037] Add 220 g of 35% hydrogen peroxide (molar ratio 2.33:1) dropwise over 2 hours. Incubate the reaction at this temperature for 4.5 hours. Terminate the reaction after GC testing confirms that the residual raw materials meet the standard.

[0038] The subsequent stratification, washing, drying, and vacuum distillation process parameters were completely consistent with those in Example 1: vacuum degree 2 mmHg, bottom temperature 140 ℃, and collection of the 130-132 ℃ fraction.

[0039] Experimental data Appearance: Colorless, transparent, oily liquid GC purity: 98.9% Epoxy value: 0.59 eq / 100g Acid value: 0.09 mgKOH / g One-way return rate: 90.5% Catalyst activity retention rate: 91.2% The final pH of the reaction system was 6.1. Comparative example: No buffer added (existing technology comparison) Operating steps The materials, feed amount, reaction temperature, hydrogen peroxide dosage, reaction time, post-treatment and distillation parameters are completely consistent with those in Example 1, except that the sodium bicarbonate buffer is omitted.

[0040] Add 200 g of raw material and 2.0 g of tetrabutylammonium peroxyphosphotungstate to a 500 mL three-necked flask, stir and heat to 50 °C; add 220 g of 35% hydrogen peroxide dropwise over 2 h, and keep the reaction at this temperature for 4 h.

[0041] After the reaction was completed, the system was observed to be significantly acidified. After standing and separating into layers, the organic phase was washed with water and dried. The corresponding fractions were collected under the same reduced pressure distillation conditions (2 mmHg, 140 °C).

[0042] Experimental data Appearance: Pale yellow, cloudy liquid GC purity: 93.7% (including hydrolysis and ring-opening byproducts) Epoxy value: 0.51 eq / 100g Acid value: 1.26 mgKOH / g One-way return rate: 78.6% The final pH of the reaction system was 3.2.

[0043] The catalyst, buffer, solvent type, temperature range, hydrogen peroxide molar ratio, and distillation pressure / temperature / fraction range all fall within the scope of the claims. The examples fully support the protection scope of the claims. The three examples respectively verify the three major technical advantages of solvent-free, co-solvent, and catalyst recycling. The comparative proportions accurately reproduce the prior art defects of "easy hydrolysis and product quality degradation without buffer" in the patent. The logic is closed-loop, and indicators such as acid value and system pH are added to intuitively demonstrate the role of the buffer system, strengthening the inventiveness of the invention. Experimental Table: process system Solvent-free Ethyl acetate as a solubilizer Catalyst cycled 5 times / solvent-free Buffer-free / Solvent-free Reaction temperature / °C 50 45 50 50 Reaction endpoint pH 6.2 6.3 6.1 3.2 Product Appearance Colorless and transparent Colorless and transparent Colorless and transparent pale yellow and cloudy GC purity / % 99.1 98.8 98.9 93.7 Epoxy value / (eq / 100g) )0.60 0.59 0.59 0.51 Acid value (mgKOH / g) )0.08 0.10 0.09 1.26 Yield / % 92.3 91.1 90.5 78.6 As shown in the table above, this invention uses a heteropolyacid quaternary ammonium salt composite catalyst combined with a weakly alkaline buffer system. Under the patent-defined process conditions, regardless of whether a solvent-free system or an ethyl acetate co-solvent system is used, the target product with high purity, high epoxy value, and low acid value can be obtained. The catalyst maintains high activity after multiple cycles of use, and the industrialization cost is low.

[0044] In contrast, the comparative example without a buffer showed an excessively acidic reaction system, leading to hydrolysis and ring-opening side reactions in both raw materials and products. This resulted in a significant decrease in product purity, epoxy value, and yield, as well as a deterioration in product appearance and performance. This clearly demonstrates the superiority of the technical solution presented in this invention. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester, characterized in that: The steps include the following: S1. Raw material provided: 3-cyclohexenecarboxylic acid-3′-cyclohexene methyl ester; S2. Epoxidation reaction: The raw material is mixed with hydrogen peroxide, composite catalyst and buffer, and reacted at 30-70°C and normal pressure for 2-8 hours to obtain a reaction solution containing the target product. S3. Separation and purification: The reaction solution was allowed to stand and separate into layers. The organic phase was separated, washed with water, dried, and subjected to vacuum distillation to obtain 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylic acid ester.

2. The preparation method according to claim 1, characterized in that: In step S2, the composite catalyst is a heteropoly acid quaternary ammonium salt, preferably tetrabutylammonium peroxyphosphotungstate, tetraoctylammonium peroxyphosphotomolybdate, or a mixture thereof; the amount of catalyst used is 0.5 to 5 wt% of the raw material mass.

3. The preparation method according to claim 1, characterized in that: In step S2, the hydrogen peroxide has a mass fraction of 30-50%, and the molar ratio of hydrogen peroxide to raw materials is 2.2-3.0:

1.

4. The preparation method according to claim 1, characterized in that: In step S2, the buffer is sodium carbonate, sodium bicarbonate or sodium dihydrogen phosphate, and the amount of buffer is 1 to 10 wt% of the raw material mass, and the pH of the system is maintained at 5.5 to 7.

5.

5. The preparation method according to claim 1, characterized in that: In step S2, the reaction system is solvent-free or contains toluene or ethyl acetate as a co-solvent, with the mass ratio of co-solvent to raw material ≤ 1:

1.

6. The preparation method according to claim 1, characterized in that: In step S3, the vacuum distillation conditions are a vacuum degree of 1-5 mmHg, a column bottom temperature of 130-150℃, and the fraction collected at 128-135℃. The product has an epoxy value ≥0.58 eq / 100g and a purity ≥98.5%.

7. The preparation method according to claim 2, characterized in that: The composite catalyst can be recovered by centrifugation or extraction, and can be recycled ≥5 times with an activity retention rate ≥90%.

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