A method for efficiently catalyzing the epoxidation of olefins to produce epoxides

Abstract

The application relates to a method for efficiently catalyzing olefin epoxidation to prepare an epoxide compound, belonging to the technical field of organic chemical industry and catalytic synthesis. The method adopts a one-pot process, directly adds heteropoly acid and quaternary ammonium salt into a reaction kettle containing deionized water, does not need to pre-synthesize a catalyst, subsequently adds an organic solvent, an olefin substrate and hydrogen peroxide, reacts at 5 DEG C to 70 DEG C, and obtains a product after standing and layering. The molar ratio of the heteropoly acid to the quaternary ammonium salt is 1:(1-10). The application forms an active catalytic system through in-situ self-assembly at a two-phase interface, the process is simple and the condition is mild, the conversion rate can reach 97.20% when cyclohexene is used as a substrate, the selectivity of cyclohexene oxide reaches 96.50%, the catalytic system can be recycled, is safe and environment-friendly, and is suitable for industrial production.

Description

Technical Field

[0001] A highly efficient catalytic method for preparing epoxides by epoxidation of olefins belongs to the field of organic chemical engineering and catalytic synthesis technology. Background Technology

[0002] Epoxides, as a highly valuable class of organic synthetic intermediates, have found extremely wide applications in pharmaceuticals, pesticides, fine chemicals, and polymer materials. For example, cyclohexane oxide is an important raw material for the synthesis of pharmaceutical intermediates, fragrances, and specialty epoxy resins. Traditional olefin epoxidation methods often use organic peroxy acids such as m-chloroperoxybenzoic acid or peracetic acid as oxidants, but these processes are often accompanied by high raw material costs and the generation of large amounts of organic acid byproducts, placing significant pressure on the environment.

[0003] In recent years, the assembly of phase transfer catalysts using clean oxidant hydrogen peroxide and heteropoly acids (such as phosphotungstic acid) combined with quaternary ammonium salts has become a research hotspot. However, several technical shortcomings still exist in existing related patents and literature: One existing method involves first reacting phosphotungstic acid and quaternary ammonium salt, precipitating, filtering, washing, and drying to prepare a supported catalyst, which is then added to the epoxidation reaction. However, the complex pre-synthesis and separation steps required for the catalyst lead to a cumbersome process, long production cycle, and the loss of heteropolyacid components during catalyst salt formation and washing, reducing economic efficiency.

[0004] Another existing conventional process for olefin epoxidation in a two-phase system uses phosphotungsten as a catalyst, but the reaction temperature often needs to be maintained above 75°C. This makes low-boiling-point olefins or heat-sensitive materials prone to side reactions, resulting in a significant decrease in the selectivity of the target product, the epoxide compound. Furthermore, high concentrations of hydrogen peroxide pose safety hazards at higher temperatures.

[0005] Existing technologies can also synthesize cyclohexane oxide using specific mixed metal heteropolyacids in conjunction with long-chain quaternary ammonium salt catalysts. Although this process reduces the reaction temperature to some extent, its catalyst-to-substrate molar ratio is relatively high, and it requires specific organic solvents at extremely high stirring rates to achieve satisfactory conversion. The selectivity of the target product, cyclohexane oxide, is often difficult to stabilize above 95%, and the separation and recovery of the catalytic system in post-processing is extremely cumbersome.

[0006] Therefore, developing a one-step olefin epoxidation process that does not require complex catalyst pre-synthesis steps, has mild and safe reaction conditions, high catalytic efficiency, and excellent product selectivity is of great practical significance for realizing the large-scale industrial production of such products. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a one-pot method for the efficient catalytic epoxidation of olefins to prepare epoxides, which has a simple and efficient process, mild and safe reaction conditions, excellent catalytic activity and selectivity, and a recyclable catalytic system.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for preparing epoxides by efficient catalytic epoxidation of olefins, using a one-pot reaction process, including the following steps: adding heteropolyacid, quaternary ammonium salt, and deionized water sequentially to a reaction vessel, stirring evenly, then adding organic solvent, olefin substrate, and hydrogen peroxide, controlling the reaction temperature to carry out the epoxidation reaction; after the reaction is completed, allowing the mixture to stand and separate into layers, separating the organic phase and purifying it to obtain the target epoxide; wherein, the molar ratio of the heteropolyacid to the quaternary ammonium salt is 1:(1~10).

[0009] This invention eliminates the pre-synthesis step of traditional supported catalysts. After heteropolyacids and quaternary ammonium salts come into contact in the aqueous phase, they can spontaneously migrate to the two-phase interface to form active peroxyheteropolyacid species with phase transfer function, realizing in-situ activation and transfer of hydrogen peroxide from the aqueous phase to the organic phase. The catalytic efficiency is improved by more than 15% compared with pre-synthesized catalysts. The molar ratio is controlled within the range of 1:(1~10), which can ensure that the quaternary ammonium salt fully combines with the heteropolyacid anions, avoiding the activity loss caused by the dissolution of free heteropolyacids in the aqueous phase, and also prevent emulsification caused by excessive quaternary ammonium salt, ensuring the efficiency of subsequent static stratification.

[0010] Preferably, in the above-mentioned method for the efficient catalytic epoxidation of olefins to prepare epoxides, the heteropolyacid is selected from at least one of phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, silicotungstic acid, phosphotungstic acid, silicotungstic acid, cobalt tungstic acid, and iron tungstic acid. This type of heteropolyacid is the core active component of this catalytic system. The central atom and coordinating polyatoms in its molecular structure are connected by bridging oxygen, which can effectively enrich hydrogen peroxide and activate its peroxy bond, significantly reducing the activation energy of the epoxidation reaction. Specifically, tungsten-based heteropolyacids (such as phosphotungstic acid and silicotungstic acid) exhibit excellent low-temperature catalytic activity due to the strong polarization effect of the tungsten-oxygen double bond; molybdenum-based heteropolyacids have relatively high redox potentials, suitable for deep oxidation regulation of specific substrates; while transition metal-substituted heteropolyacids such as cobalt and iron can introduce variable-valence redox centers, further enhancing catalytic efficiency through a multi-electron transfer mechanism.

[0011] Preferably, in the above-mentioned method for the efficient catalytic epoxidation of olefins to prepare epoxides, the quaternary ammonium salt is selected from at least one of hexadecylpyridine chloride, hexadecyltrimethylammonium bromide, tetrabutylammonium bromide, benzyltriethylammonium chloride, dodecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, quaternary ammonium chitosan, and trioctylmethylammonium chloride. The quaternary ammonium salts have different carbon chain lengths and molecular structures, allowing for precise control of the oil-water partition coefficient of the catalytic system: long-chain quaternary ammonium salts (such as octadecyltrimethylammonium chloride) have stronger lipophilicity and are suitable for catalyzing low-polarity olefin substrates; short-chain quaternary ammonium salts (such as tetrabutylammonium bromide) have better water solubility and can improve the stability of the catalyst in the aqueous phase; quaternary ammonium chitosan, as a natural high-molecular-weight quaternary ammonium salt, possesses both biodegradability and multiple active sites, which can reduce the environmental impact of the process. The ion pairs formed by the cations of the quaternary ammonium salt and the anions of heteropolyacids can effectively carry active oxygen species into the organic phase, increasing the epoxidation reaction rate by 2-3 times, while stabilizing the selectivity of the target product at over 90%.

[0012] Preferably, in the above-mentioned method for the efficient catalytic epoxidation of olefins to prepare epoxides, the reaction temperature is 5℃~70℃. This temperature range aims to achieve an optimal match between catalytic activity, product selectivity, and process safety. Setting the lower limit of the temperature to 5℃ effectively avoids the problem of limited mass transfer caused by increased viscosity of the reaction system at low temperatures; while controlling the upper limit at 70℃ is for strict control of the thermal stability of high-concentration hydrogen peroxide, which is significantly lower than the reaction threshold of 75℃ or above in traditional processes, fundamentally reducing the safety hazards caused by the violent decomposition of the oxidant. Within this range, the active catalytic interface constructed in situ by the heteropolyacid and the quaternary ammonium salt remains stable, providing sufficient molecular kinetic energy to overcome the activation energy barrier of the epoxidation reaction, and effectively inhibiting side reactions such as ring-opening hydrolysis of epoxides in acidic media, ensuring the efficient generation of the target product under mild conditions, which meets the dual requirements of green chemical engineering for energy conservation, emission reduction, and safety control.

[0013] Preferably, in the above-mentioned method for preparing epoxy compounds by efficient catalytic epoxidation of olefins, the olefin substrate is selected from at least one of cyclohexene, propylene, cyclopentene, cyclooctene, 1-octene, and styrene. The above substrates cover mainstream industrial categories such as cyclic olefins, linear α-olefins, and aromatic olefins, verifying the broad applicability of this catalytic system: cyclic olefins such as cyclohexene and cyclopentene have moderate reactivity, achieving a conversion rate of over 95% at 30℃~45℃, and the products are key raw materials for the synthesis of special epoxy resins and pharmaceutical intermediates; linear olefins such as propylene and 1-octene have low polarity, and by matching with long-chain quaternary ammonium salt catalysts, a conversion rate of over 90% can be achieved under mild conditions, and the products propylene oxide and 1,2-epoxyoctane are core monomers of polyether polyols; conjugated olefins such as styrene can effectively avoid polymerization side reactions by reacting in the high-temperature range, maintaining a selectivity of over 91%.

[0014] Preferably, in the above-mentioned method for the efficient catalytic epoxidation of olefins to prepare epoxides, the organic solvent is selected from at least one of 1,2-dichloroethane, dichloromethane, and chloroform. These halogenated hydrocarbon solvents form a stable biphase system with the aqueous phase, exhibiting good solubility for both the olefin substrate and the epoxidation product. Furthermore, the distribution of active species between the two phases can be controlled by the solvent polarity: 1,2-dichloroethane has a high boiling point, suitable for medium-high temperature reactions of 45℃ to 70℃, reducing the volatilization loss of low-boiling-point solvents; dichloromethane has a low boiling point, making it more suitable for low-temperature ranges of 5℃ to 30℃, facilitating subsequent product separation by vacuum distillation; chloroform's polarity is intermediate between the two, optimizing the reaction selectivity of certain specific olefin substrates. None of the three solvents react violently with hydrogen peroxide, ensuring process safety, and they can be recovered and reused through simple distillation, reducing waste emissions.

[0015] Preferably, in the above-mentioned method for the efficient catalytic epoxidation of olefins to prepare epoxy compounds, the molar ratio of heteropolyacid to quaternary ammonium salt is 1:(2.5~3.5). This ratio range is a core optimization range determined based on the interfacial catalysis mechanism, aiming to construct an appropriate number and structurally stable active phase transfer centers. Within this range, the heteropolyacid anion and the quaternary ammonium salt cation can form a homogeneous ion-pair pair in a near-stoichiometric manner, ensuring sufficient catalytic active sites at the two-phase interface to achieve in-situ efficient activation of hydrogen peroxide, while effectively avoiding problems such as emulsion stabilization and increased phase separation energy consumption caused by excessive quaternary ammonium salt.

[0016] More preferably, in the above-mentioned method for the efficient catalytic epoxidation of olefins to prepare epoxy compounds, the molar ratio of heteropolyacid to quaternary ammonium salt is 1:3. 1:3 is the most preferred molar ratio, at which point the anionic sites of the heteropolyacid can form ion-pair structures with the quaternary ammonium salt cations with the optimal stoichiometric ratio, and the mass transfer efficiency of the active species at the two-phase interface reaches its peak. Experiments show that the utilization rate of heteropolyacid is increased by 10%~15% compared to other ratios, and the catalytic activity half-life is extended to over 200 hours. When cyclohexene is used as a substrate, the conversion rate can reach 97.20%, and the selectivity for cyclohexane oxide reaches 96.50%, an improvement of approximately 2 percentage points compared to the 1:2.5 ratio and approximately 4.4 percentage points compared to the 1:10 ratio. Simultaneously, it avoids the emulsification problem caused by excessive quaternary ammonium salt, and the settling time is shortened to less than 10 minutes, significantly improving production efficiency.

[0017] Preferably, in the above-mentioned method for preparing epoxides by efficient catalytic epoxidation of olefins, the hydrogen peroxide has a mass fraction of 20% to 50%. Using a 20% to 50% mass fraction of hydrogen peroxide as the oxidant ensures a sufficient supply of active oxygen while avoiding the safety hazards caused by the thermal instability of high-concentration hydrogen peroxide. 20% hydrogen peroxide is suitable for low-temperature reactions at 5℃ to 30℃, with a controllable reaction rate; 30% to 50% hydrogen peroxide reduces the water content in the reaction system, suppressing hydrolysis side reactions of the epoxide, and is particularly suitable for substrates sensitive to moisture, such as styrene and cyclooctene. Within this concentration range, the decomposition rate of hydrogen peroxide is less than 5%, and the atom economy is improved by more than 40% compared to traditional organic peroxyacid oxidants. The only byproduct is water, meeting the requirements of green chemistry.

[0018] Preferably, in the above-mentioned method for the efficient catalytic epoxidation of olefins to prepare epoxides, the amount of heteropolyacid used is 0.1% to 5% of the olefin substrate. Controlling the amount of heteropolyacid at 0.1% to 5% of the olefin substrate achieves an optimal balance between catalytic efficiency and economy: the low amount of 0.1% is suitable for highly active substrates and optimized 1:3 molar ratio systems, reducing catalyst costs by 60%; the higher amount of 5% is used for substrates with lower reactivity, such as 1-octene, ensuring complete conversion of all substrates.

[0019] Preferably, in the above-mentioned method for the efficient catalytic epoxidation of olefins to prepare epoxy compounds, the heteropolyacid-quaternary ammonium salt catalytic system after the reaction is directly recycled to the next round of reaction. After the reaction, the heteropolyacid and quaternary ammonium salt remain stable as active ion pairs and can be directly recycled to the next round of reaction without additional treatment. Experiments show that this catalytic system can be reused more than 100 times continuously without significant decrease in activity. The cyclohexene conversion rate remains above 95%, and the selectivity of cyclohexane oxide is maintained at around 96%. This characteristic completely solves the problems of difficult separation and easy deactivation of traditional supported catalysts, eliminates the catalyst regeneration process, reduces solid waste emissions, and reduces the cost of waste treatment by more than 70%, making it highly valuable for industrial application.

[0020] Compared with existing technologies, this invention has the following advantages: This invention utilizes heteropolyacids and quaternary ammonium salts to directly generate active catalytic species in the reaction system, eliminating the traditional catalyst pre-synthesis process and achieving a true "one-pot" process, significantly shortening the production cycle and avoiding the loss of active components. This system exhibits excellent catalytic efficiency under mild conditions of 5℃~70℃, achieving a conversion rate of 97.20% and a selectivity of 96.50% for cyclohexene as a substrate. The low-temperature environment effectively suppresses side reactions and significantly reduces the risk of hydrogen peroxide thermal decomposition. The process constructs a two-phase system using water / halogenated hydrocarbons, uses low-toxicity hydrogen peroxide as the oxidant, and the only byproduct is water. Combined with the recycling of the aqueous catalyst, this reduces waste at the source, offering advantages of high safety, excellent economic benefits, and green environmental protection. Detailed Implementation

[0021] The present invention will be specifically described below through examples. Unless otherwise stated, all raw materials used are commercially available. In this application, the molar mass of heteropoly acids is expressed in their anhydrous acid form; for quaternary ammonium salts of polymers such as quaternary ammonium chitosan, the amount of substance is expressed as repeating units containing quaternary ammonium groups.

[0022] Example 1 To a 500 mL four-necked glass reactor equipped with a mechanical stirrer, thermometer, constant-pressure dropping funnel, and reflux condenser, 3.60 g of phosphotungstic acid, 1.37 g of hexadecyltrimethylammonium bromide, and 50 mL of deionized water were added sequentially, with the molar ratio of heteropoly acid to quaternary ammonium salt precisely controlled at 1:3. The stirrer was started and set to 400 rpm, and the mixture was continuously stirred and premixed at room temperature for 30 min to ensure complete dissolution of the solid materials and the formation of a homogeneous, pale yellow, transparent catalytic aqueous solution. Subsequently, 100 mL of 1,2-dichloroethane, 10.0 g of cyclohexene substrate, and 20.8 g of 30% hydrogen peroxide were added to the system. At this point, the amount of phosphotungstic acid added was approximately 1.02% of the molar amount of cyclohexene. The reaction mixture was heated to 60 °C and reacted for 4 h under constant temperature and continuous stirring at 500 rpm, with reflux condensation used to prevent solvent evaporation during the reaction. After the reaction was complete, heating was stopped, and the mixture was allowed to cool naturally to room temperature and stand in a separatory funnel for 10 minutes. The system automatically separated into two layers: an upper organic phase containing the target product and a lower aqueous phase rich in heteropolyacid-quaternary ammonium salts. The organic phase was separated and washed twice with deionized water, dried over anhydrous sodium sulfate for 2 hours, and purified by vacuum distillation. The fraction collected at 128℃~130℃ / 101kPa yielded a colorless, transparent liquid cyclohexane oxide. Gas chromatography analysis showed a cyclohexene conversion of 97.20% and a cyclohexane oxide selectivity of 96.50%. The catalytic system was retained in the reactor and directly used in the next reaction. After 100 cycles, the cyclohexene conversion remained above 95%, and the cyclohexane oxide selectivity remained around 96%, demonstrating excellent stability.

[0023] Example 2 4.12 g of silicotungstic acid, 0.33 g of benzyltriethylammonium chloride, and 40 mL of deionized water were added to a 500 mL four-necked reactor equipped with a mechanical stirrer, thermometer, and reflux condenser, maintaining a molar ratio of heteropoly acid to quaternary ammonium salt of 1:1. The mixture was stirred and premixed for 25 min at room temperature and 350 rpm to form a clear and transparent catalytic aqueous solution. Subsequently, 80 mL of dichloromethane, 6.81 g of cyclopentene, and 17.0 g of 20% hydrogen peroxide were added to the system. The reactor was placed in a cryogenic bath and slowly cooled to 5 °C, where it was kept at a constant temperature with stirring for 8 h. During the reaction, the stirring speed was maintained at 450 rpm to ensure good mass transfer. After the reaction, the cooling source was removed, and the system was allowed to return to room temperature. The mixture was then allowed to stand in a separatory funnel for 25 min to separate into layers. The separated organic phase was successively washed with water, dried over anhydrous sodium sulfate, and subjected to atmospheric distillation to remove the solvent. Finally, the cyclopentane oxide fraction was collected by vacuum distillation. Gas chromatography analysis showed that the cyclopentene conversion rate reached 88.5%, and the selectivity for cyclopentane oxide was 91.2%. The catalytic system was reserved for subsequent batches and can maintain high catalytic activity without the need for additional catalyst.

[0024] Example 3 Add 5.00 g of phosphomolybdic acid and 2.16 g of tetrabutylammonium bromide (molar ratio approximately 1:2.5) sequentially to a pressure-resistant high-pressure reactor, followed by 60 mL of deionized water. Start stirring and premix at room temperature for 30 min to form a stable catalytic aqueous solution. Then, inject 100 mL of chloroform into the reactor, seal the reactor, and slowly introduce 4.20 g of propylene gas through the inlet valve. After the gas has been introduced, slowly add 9.7 g of 35% hydrogen peroxide through a dropping funnel, while simultaneously raising the temperature to 40 °C. Under sealed conditions, maintain the stirring speed at 500 rpm and react at a constant temperature for 5 h. After the reaction is complete, cool the reactor to room temperature using an ice-water bath, slowly depressurize, and transfer the reaction mixture to a separating funnel to allow for separation. Separate the upper organic phase, remove acidic impurities by alkali washing, and then purify by water washing, drying, and distillation to obtain propylene oxide. Gas chromatography analysis showed that the propylene conversion rate was 89.7% and the propylene oxide selectivity was 96.5%. The reaction process was stable and no violent exothermic phenomenon was observed.

[0025] Example 4 To a 500 mL four-necked reactor equipped with a mechanical stirrer, thermometer, and reflux condenser, add 4.88 g of phosphotungstic molybdate and 2.53 g of octadecyltrimethylammonium chloride, with a molar ratio of 1:3.5. Add 120 mL of chloroform, 13.61 g of cyclooctene, and 17.0 g of 50% hydrogen peroxide. Start the stirrer at 450 rpm and simultaneously turn on the condenser to heat the reaction system to 70 °C. Maintain this temperature for 3 hours. During the reaction, the reaction mixture appears as a homogeneous emulsion through the observation window, and after standing, clear phase separation occurs. After the reaction is complete, stop heating and allow it to cool naturally to room temperature. Transfer the reaction mixture to a separatory funnel and let it stand for 10 minutes until the two phases are clear before separating the liquid. The separated organic phase is first washed with water to remove residual acid and inorganic salts, then dried with anhydrous magnesium sulfate for 1.5 hours. After filtration, chloroform is first removed by atmospheric distillation, and finally, the epoxide cyclooctane fraction is collected by vacuum distillation. Gas chromatography analysis showed that the conversion rate of cyclooctene was 96.3% and the selectivity was 94.6%. The catalyst enrichment solution was directly used in the next batch of reaction, and after 100 consecutive runs, no significant decrease in catalytic activity was observed.

[0026] Example 5 5.44 g of cobalt tungstic acid and 1.01 g of quaternary ammonium chitosan were added to the reactor at a molar ratio of 1:3, with the amount of quaternary ammonium chitosan calculated based on repeating sugar units containing quaternary ammonium groups. 100 mL of 1,2-dichloroethane, 11.22 g of 1-octene, and 20.4 g of 30% hydrogen peroxide were added. Stirring was started at 400 rpm, and the temperature was raised to 50°C for a total reaction time of 6 hours. Due to the flocculation and sedimentation characteristics of quaternary ammonium chitosan, after the reaction, the mixture was allowed to stand in a separatory funnel for 30 minutes. Obvious flocculent aggregation of the catalyst in the lower aqueous phase was observed, which facilitated phase separation. The upper clear organic phase was carefully separated, washed with water until neutral, dried overnight with anhydrous sodium sulfate, filtered, and collected by vacuum distillation. Gas chromatography analysis showed that the conversion rate of 1-octene was 85.6%, and the selectivity for 1,2-epoxyoctane was 91.2%. The catalyst can be directly absorbed back into the reactor, demonstrating good operational convenience.

[0027] Example 6 0.29 g of ferrotungstic acid (0.1% of the molar amount of styrene) was added to a 250 mL four-necked reactor equipped with a mechanical stirrer, thermometer, and reflux condenser. 0.08 g of dodecyltrimethylammonium chloride was then added, in a molar ratio of 1:3. Subsequently, 80 mL of 1,2-dichloroethane, 10.4 g of styrene, and 13.6 g of 25% hydrogen peroxide were added. The stirrer was started at 500 rpm, and the temperature was raised to 30 °C and maintained for 7 hours. During the reaction, the color of the reaction solution darkened slightly as the reaction proceeded. After the reaction was complete, the mixture was allowed to cool naturally to room temperature and allowed to stand for 20 minutes in a separatory funnel to separate into layers. The organic phase was separated and successively washed with 5% sodium carbonate solution, washed with deionized water until neutral, dried over anhydrous sodium sulfate, and purified by vacuum distillation to finally obtain the epoxy phenyl ethane product. Gas chromatography analysis showed that despite the extremely low catalyst dosage, the styrene conversion rate reached 82.5%, with a selectivity of 92.1%. After the catalyst system is slightly concentrated by a rotary evaporator to compensate for volatilization losses, it can be used for subsequent reactions, demonstrating the high efficiency of the catalyst system.

[0028] Example 7 Using cyclohexene as a substrate, this study focuses on the reaction performance under optimized process window. 3.60 g of phosphotungstic acid, 1.37 g of hexadecyltrimethylammonium bromide, and 50 mL of deionized water were added to a 500 mL four-necked reactor, maintaining a heteropolyacid to quaternary ammonium salt molar ratio of 1:3. After premixing with stirring at room temperature for 30 min, 100 mL of 1,2-dichloroethane, 10.0 g of cyclohexene, and 20.8 g of 30% hydrogen peroxide were added. The amount of phosphotungstic acid used was 1.02% of the molar amount of cyclohexene. The system was heated to 60 °C and stirred for 4 h. During the reaction, the reaction solution was homogeneous and emulsion-like, with good heat transfer. After the reaction, the mixture was cooled to room temperature and allowed to stand for 10 min to separate into layers. The organic phase was separated, washed with water, dried, and distilled under reduced pressure, collecting the fraction from 128 °C to 130 °C. Gas chromatography analysis showed a cyclohexene conversion of 97.80% and a selectivity of 96.20% for cyclohexane oxide. The catalyst system is used directly in the next round of reaction.

[0029] Example 8 Styrene was selected as the substrate, and the reaction was carried out under optimized catalyst ratios and temperature conditions. 4.12 g of silicotungstic acid, 0.98 g of benzyltriethylammonium chloride, and 50 mL of deionized water were added to the reactor, with the molar ratio of heteropolyacid to quaternary ammonium salt controlled at 1:3. After thorough stirring, 80 mL of dichloromethane, 10.4 g of styrene, and 20.4 g of 30% hydrogen peroxide were added. The reaction system was heated to 40 °C and stirred at this temperature for 5 h. No significant material surge was observed during the reaction, and the system remained stable. After the reaction, the system was cooled and allowed to stand for 15 min to separate the layers, separating the upper organic phase. The organic phase was washed with alkali to remove acidic byproducts, then washed with water, dried with anhydrous sodium sulfate, and purified by vacuum distillation to obtain epoxide phenyl ethane. The styrene conversion rate was 94.5%, and the selectivity for epoxide phenyl ethane was 93.2%. The catalyst system was reserved for subsequent batches, and no significant emulsification was observed.

Claims

1. A method for preparing epoxides by efficient catalytic epoxidation of olefins, characterized in that, One-pot reaction process is adopted. The process includes the following steps: adding heteropoly acid, quaternary ammonium salt, and deionized water sequentially to a reaction vessel, stirring until homogeneous, then adding organic solvent, olefin substrate, and hydrogen peroxide, and controlling the reaction temperature to carry out the epoxidation reaction; after the reaction is completed, allowing the mixture to stand and separate into layers, separating the organic phase and purifying it to obtain the target epoxide compound; wherein, the molar ratio of the heteropoly acid to the quaternary ammonium salt is 1:(1~10).

2. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, The heteropolyacid is selected from at least one of phosphotungstic acid, silicotungstic acid, phosphotomolybdic acid, silicotomolybdic acid, phosphotungmolybdic acid, silicotomolybdic acid, cobalt tungstic acid, and ferrotungstic acid.

3. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, The quaternary ammonium salt is selected from at least one of hexadecylpyridine chloride, hexadecyltrimethylammonium bromide, tetrabutylammonium bromide, benzyltriethylammonium chloride, dodecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, quaternary ammonium chitosan, and trioctylmethylammonium chloride.

4. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, The reaction temperature is 5℃~70℃.

5. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, The olefin substrate is selected from at least one of cyclohexene, propylene, cyclopentene, cyclooctene, 1-octene, and styrene.

6. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, The organic solvent is selected from at least one of 1,2-dichloroethane, dichloromethane, and chloroform.

7. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, The molar ratio of the heteropolyacid to the quaternary ammonium salt is 1:(2.5~3.5).

8. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, The hydrogen peroxide has a mass fraction of 20% to 50%.

9. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, The amount of the heteropolyacid used is 0.1% to 5% of the amount of the olefin substrate.

10. The method for preparing epoxides by efficient catalytic epoxidation of olefins according to claim 1, characterized in that, After the reaction is complete, the heteropolyacid-quaternary ammonium salt catalytic system in the system is directly recycled for the next round of reaction.