Method for synthesizing 1, 2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate under assistance of microwaves

Abstract

The invention discloses a method for synthesizing 1, 2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate under the assistance of microwaves, and belongs to the technical field of organic synthesis. The method comprises the following steps: firstly, adding 1-butyl-3-methylimidazolium hydrogen sulfate into a microwave reactor, then adding a raw material cyclohexene and an oxidant hydrogen peroxide, and carrying out a heating reaction; after the reaction is finished, the obtained reaction liquid is extracted, the reaction liquid obtained after extraction is separated through silica gel column chromatography, then dichloromethane is used for elution, the solvent is removed, and the product 1, 2-cyclohexanediol is obtained. The 1, 2-cyclohexanediol is synthesized by oxidizing cyclohexene with hydrogen peroxide under the conditions of microwave heating and taking the ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate as a solvent and a catalyst, and the method is a green and efficient synthesis process; and the method has the advantages of low production cost, short reaction time, easy separation of the reacted product, energy saving, consumption reduction and environmental protection.

Description

I. Technical Field:

[0001] This invention relates to the field of organic synthesis technology, specifically to a method for synthesizing 1,2-cyclohexanediol using microwave-assisted ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate. II. Background Technology:

[0002] 1,2-Cyclohexanediol is an important organic synthesis raw material, mainly used in pharmaceuticals, pesticides, high-grade coatings, surfactants, and rubber additives. It is an organic synthesis intermediate with very broad application prospects. With its application in industries such as epoxy resins and polyurethanes, 1,2-cyclohexanediol is attracting increasing attention, and its application value is gradually increasing. Therefore, researching the production process of 1,2-cyclohexanediol is of great significance. Currently, in addition to existing methods such as the hydrolysis of cyclohexane oxide and the oxidation of cyclohexene, some new synthetic methods have also emerged, such as the direct hydrogenation of catechol to 1,2-cyclohexanediol, and the hydrogenolysis of o-hydroxycyclohexanol methyl ether (obtained from lignin derivatives through hydrogenation) to 1,2-cyclohexanediol. However, this method is currently only in the pilot-scale stage. To achieve efficient and green production of 1,2-cyclohexanediol, technicians have been conducting unremitting research. However, there are still some problems to be solved in the synthesis of 1,2-cyclohexanediol, such as poor catalyst stability, the need to add toxic solvents during the preparation process, and relatively low synthesis efficiency. With the gradual deterioration of the global environment, environmental protection issues have received high attention, so there is an urgent need to develop an efficient and green production process for 1,2-cyclohexanediol.

[0003] Currently, there are numerous reported methods for preparing 1,2-cyclohexanediol from cyclohexene via oxidation, which generally fall into the following categories: cyclohexene is directly oxidized to 1,2-cyclohexanediol using catalysts such as potassium permanganate, osmium tetroxide, m-chloroperoxybenzoic acid, and tert-butyl hydroperoxide. While H₂O₂ is a commonly used oxidant in cyclohexene epoxidation reactions, the yield of direct epoxidation is low, necessitating the selection of a suitable catalytic system. Reported catalytic systems include phosphotungsten heteropolysalt systems, transition metal systems, and metalloporphyrin systems, but these often involve long reaction times and high energy consumption. Relevant literature is as follows:

[0004] 1. Rosatella et al. (Rosatella AA, Afonso CAM, Branco L C. Oxidation of cyclohexene to trans-1,2-cyclohexanediol promoted by ptoluenesulfonic acid without organic solvents[J]. Journal of Chemical Education, 2011, 88(7):1002-1003.) used cyclohexene as a raw material to directly oxidize cyclohexene in H2O2 solution with p-toluenesulfonic acid as a catalyst to synthesize trans-1,2-cyclohexanediol. After reacting at 75℃ for 4 h, the cyclohexene conversion rate reached 97.9%, and the yield of 1,2-cyclohexanediol reached 79%.

[0005] 2. Antonetti et al. (Antonetti C, Galletti AMR, Accorini P, et al. Two alter-native routes for 1,2-cyclohexanediol synthesis by means of green processes: Cyclohexene dihydroxylation and cate-chol hydrogenation[J]. Applied Catalysis A General, 2013, 466:21-31.) proposed two methods for synthesizing 1,2-cyclohexanediol: one method involves the dihydroxylation of cyclohexene in H2O2 solution under tungstic acid / phosphoric acid catalysis to synthesize 1,2-cyclohexanediol; the other method involves the hydrogenation of catechol under Ru(OH)x / Al2O3 catalyst to prepare 1,2-cyclohexanediol. Studies have shown that the addition of a phase transfer agent (PTA) during the dihydroxylation of cyclohexene significantly affects the synthesis of 1,2-cyclohexanediol, achieving a target product yield of 97.4%. This may be because the addition of PTA improves the dispersion of the reaction system and increases the effective contact between the catalyst and the reactants. However, the catalyst is subject to significant loss and is difficult to recover and reuse. Hydrogenation of catechol in aqueous solution yields 1,2-cyclohexanediol at a rate of 90%, with good catalyst stability and recyclability, while also having a minimal environmental impact.

[0006] 3. Jiang et al. (Jiang Y, Zhao Y, Xu X, et al. Mesoporous titanosilicate nanoparticles: facile preparation and application in heterogeneous epoxidation of cyclohexene[J]. Rsc Advances, 2016, 6(81):77481-77488.) disclosed the synthesis of 40-75 nm mesoporous titanosilicate molecular sieve nanoparticles (Nano-Ti-MCM-41) using titanosilicate as raw material and hexadecyltrimethylammonium bromide (CTAB) as template via hydrothermal method. Compared with other titanosilicate molecular sieve nanoparticles, Nano-Ti-MCM-41 showed better catalytic effect on cyclohexene oxidation reaction in H2O2 solution, with higher cyclohexene conversion rate and higher selectivity for 1,2-cyclohexanediol. The improved catalytic performance is mainly attributed to the smaller particle size, increased surface area, and shorter channels of the Nano-Ti-MCM-41 prepared by this method, which allows for timely diffusion of reactants and cyclohexene epoxide on the nanoparticle surface and reduces residence time. Simultaneously, Nano-Ti-MCM-41 effectively prevents titanium loss and exhibits good stability and recyclability.

[0007] 4. Noh et al. (Noh H, Cui Y, Peters AW, et al. An exceptionally stable metal-organic framework supported molybdenum(VI)oxide catalyst for cyclohexene epoxidation[J]. Journal of the American Chemical Society, 2016, 138(44):14720-14726.). This paper discloses the preparation of a porous Mo-SIM catalyst by grafting Mo(VI) onto the Zr6 nodes of the mesoporous metal-organic framework NU-1000 via an impregnation method. The catalytic effect of Mo-SIM on the epoxidation of cyclohexene was investigated using tert-butyl hydroperoxide as the oxidant. The conversion rate of cyclohexene reached 93%, and the selectivity (epoxycyclohexane and 1,2-cyclohexanediol) reached 99%, significantly higher than that of Mo-ZrO2. Furthermore, Mo-SIM showed better stability than Mo-ZrO2, and no Mo(VI) loss was observed before and after the cyclohexene epoxidation reaction catalyzed by Mo-SIM.

[0008] 5. Ahn et al. (Ahn S, Thornburg NE, Li Z, et al. Stable metal-organic framework-supported niobium catalysts[J]. Inorganic Chemistry, 2016, 55(22):11954-11961.). The method disclosed in this paper is to use NU-1000 as a support to load Nb(V) by atomic layer deposition and impregnation methods, and the loading amount was measured to reach 1.6 mmol·g. -1 Compared with traditional Nb-ZrO2 catalysts, the NU-1000 supported Nb(V) catalyst exhibits higher selectivity for the epoxidation of cyclohexene.

[0009] 6. Santoro et al. (Santoro S, Santi C, Sabatini M, et al. Eco-friendly olefin dihydroxylation catalyzed by diphenyl diselenide[J]. Adv. Synth. Catal., 2005, 350(18): 2881-2884.). This literature discloses that hydrogen peroxide can oxidize olefins to vicinal diols under diselenide catalysis. This reaction uses hydrogen peroxide as the oxidant, produces no byproducts, has high atom economy, and has broad industrial application prospects. Inspired by this, Yu Lei's research group in China applied it to the oxidation of cyclohexene and developed a clean synthesis method for the industrial intermediate 1,2-cyclohexanediol. In acetonitrile solvent, diphenyl diselenide can catalyze the oxidation of cyclohexene by hydrogen peroxide to produce 1,2-cyclohexanediol. The catalyst dosage can be reduced to 1%, while the yield of 1,2-cyclohexanediol can reach 96%. This reaction does not require any other additives, produces no byproducts, and is clean and environmentally friendly.

[0010] 7. Gao Fei et al. (Gao Fei, Jia Yingping, Cui Yingna, et al. Catalytic effect of ionic liquids on the oxidation of cyclohexene by H2O2 to prepare trans-1,2-cyclohexanediol [J]. 2011, 28(6): 662-666.), This literature discloses that in seven imidazole ionic liquids, the cyclohexene feed was 3.0 mmol, the H2O2 dosage was 3.3 mmol, the ionic liquid c dosage was 0.60 g (2.1 mmol), the reaction temperature was 100℃, and the reaction time was 5 h. The reaction results showed that the yield and selectivity of trans-1,2-cyclohexanediol were 95% and 97%, respectively; the catalytic effect of ionic liquid f was also good, with the yield and selectivity of trans-1,2-cyclohexanediol reaching 84% and 90%, respectively.

[0011] In summary, there are many existing literature reports on the preparation of 1,2-cyclohexanediol from cyclohexene by oxidizing peroxide, but no literature reports on the preparation of 1,2-cyclohexanediol using microwave-assisted ionic liquids. III. Summary of the Invention:

[0012] The technical problem this invention aims to solve is: Based on existing methods for preparing 1,2-cyclohexanediol from cyclohexene by oxidizing cyclohexene with peroxide, this invention provides a microwave-assisted method for synthesizing 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate. This invention utilizes microwave heating and the ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate as both solvent and catalyst to synthesize 1,2-cyclohexanediol from cyclohexene by oxidizing cyclohexene with peroxide. This method is a green and efficient synthetic process. The preparation of 1,2-cyclohexanediol using this method is simple, easy to recover, and has a short reaction time. The preparation of 1,2-cyclohexanediol using this invention results in low production costs, a short reaction time, easy separation of the product after the reaction, energy saving, and environmental benefits.

[0013] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0014] This invention provides a microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate, the method comprising the following steps:

[0015] a. Using cyclohexene as raw material, 1-butyl-3-methylimidazolium hydrogen sulfate as solvent and catalyst, and hydrogen peroxide as oxidant, wherein the amount of 1-butyl-3-methylimidazolium hydrogen sulfate added accounts for 150-200% of the mass of cyclohexene, and the molar ratio of hydrogen peroxide to cyclohexene is 0.8-1.5:1;

[0016] b. First, add 1-butyl-3-methylimidazolium hydrogen sulfate to the microwave reactor, then add the raw material cyclohexene and the oxidant hydrogen peroxide for heating reaction, controlling the reaction temperature at 30-80℃ and the reaction time at 20-50min;

[0017] c. After the reaction is complete, the resulting reaction solution is extracted. The extracted reaction solution is then separated by silica gel column chromatography and eluted with dichloromethane to remove the solvent, yielding the product 1,2-cyclohexanediol.

[0018] According to the above-described microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate, the amount of 1-butyl-3-methylimidazolium hydrogen sulfate added in step a is 160-180% of the mass of cyclohexene.

[0019] According to the above-described microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate, step b describes controlling the reaction temperature at 40–60°C and the reaction time at 25–45 min.

[0020] According to the above method for microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate, the power of the microwave reactor in step b is controlled to be 160-480W.

[0021] According to the above method for the microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate, the solvent used for extraction of the reaction solution obtained in step c is ethyl acetate or methyl acetate.

[0022] According to the above-described microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate, the reaction solutions obtained after extraction in step c are sequentially combined, separated by silica gel column chromatography, eluted with dichloromethane, and concentrated to remove the solvent, to obtain the product 1,2-cyclohexanediol.

[0023] According to the above method for synthesizing 1,2-cyclohexanediol with microwave-assisted 1-butyl-3-methylimidazolium hydrogen sulfate, the solvent removed in step c is recycled, and the recycled solvent 1-butyl-3-methylimidazolium hydrogen sulfate is reused.

[0024] The microwave technology employed in this invention offers significant advantages in organic synthesis, including rapid reaction rates, high yields, fewer byproducts, and energy efficiency. Compared to traditional heating methods, microwave heating achieves "internal heating" through the absorption of energy by polar molecules, resulting in more uniform heating of reactants and rapid temperature rise. This can shorten reaction times from hours to minutes or even seconds. Microwave radiation, through dipole polarization and ion conduction mechanisms, is highly efficient at converting microwave energy into heat for strongly polar ionic liquids, achieving instantaneous temperature rise within the reaction system and significantly reducing the activation energy. It effectively improves reaction selectivity and product purity, reduces solvent usage, lowers energy consumption and environmental pollution, and aligns with green chemistry principles.

[0025] Ionic liquids, as a class of salts that are liquid at or near room temperature, possess unique physicochemical properties such as low volatility and high stability. They have virtually no vapor pressure, allowing reactions to proceed under normal pressure, in open or closed conditions, avoiding the need for autoclaves. The products can often be recovered through simple phase separation or distillation, maintaining their activity even after multiple cycles, achieving "zero" volatile organic solvent emissions. Ionic liquids can not only replace traditional solvents but also serve as catalysts or catalyst supports. In organic synthesis, they create safer and more environmentally friendly reaction environments, effectively improving reaction rates, conversion rates, and selectivity. They exhibit superior performance in various organic synthesis reactions and are widely regarded as a new generation of "green solvents."

[0026] Microwave-assisted ionic liquid (MAIL) technology is a cutting-edge and highly efficient technique in modern chemistry. MAIL utilizes microwaves to directly act on the ionic liquid, generating endogenous heat and rapidly raising the temperature. This reduces reaction times to minutes or even seconds, while allowing for precise control of product structure. MAIL technology primarily addresses the problems of slow reaction times and numerous byproducts found in traditional methods. Ionic liquid catalytic systems are easy to separate, simplifying subsequent product separation and purification. Ionic liquids can be recycled multiple times without significant deactivation. Their advantages in catalytic efficiency and process sustainability have been widely validated, making them an important tool for promoting green chemistry.

[0027] The positive and beneficial effects of this invention are as follows:

[0028] 1. The technical solution of this invention uses 1-butyl-3-methylimidazolium hydrogen sulfate as a solvent and catalyst, cyclohexene as a raw material, and hydrogen peroxide as an oxidant to synthesize 1,2-cyclohexanediol in one step. The product obtained by this invention contains only 1,2-cyclohexanediol and water, with no toxic byproducts and no pollution. Therefore, this invention is a green and efficient synthetic process. The method of preparing 1,2-cyclohexanediol using this invention is simple, easy to separate and purify, and has a short reaction time. The technical solution of this invention for preparing 1,2-cyclohexanediol has low production costs, mild reaction conditions, and the product is easy to separate after the reaction, resulting in energy saving and reduced consumption.

[0029] 2. The solvent and catalyst used in this invention, 1-butyl-3-methylimidazolium hydrogen sulfate, is an ionic liquid. Ionic liquids have advantages such as good thermal stability, non-volatility, high conductivity, and a wide electrochemical window. 1-Butyl-3-methylimidazolium ionic liquids have been extensively studied due to their low viscosity, relatively high conductivity, and ease of synthesis. 1-Butyl-3-methylimidazolium hydrogen sulfate exhibits good catalytic effect, a simple reaction system, short reaction time, and convenient synthesis process. The reaction is carried out under normal pressure, saving energy and reducing consumption. It also provides good product selectivity and convenient subsequent product separation, significantly reducing product separation costs. After extraction, washing, and vacuum distillation, 99% high-purity 1,2-cyclohexanediol can be obtained, which is superior to existing synthesis processes.

[0030] 3. The microwave-assisted synthesis of 1,2-cyclohexanediol using ionic liquids in this invention significantly shortens the reaction time, thereby effectively reducing production costs and yielding significant economic and social benefits.

[0031] 4. The technical solution of this invention uses hydrogen peroxide as an oxidant. Hydrogen peroxide is widely available and inexpensive, which helps to reduce production costs. After the reaction, the only byproduct is water, which is pollution-free. It is an environmentally friendly and clean route that can be industrialized.

[0032] 5. This invention utilizes microwave-assisted ionic liquid technology (MAIL technology) to synthesize 1,2-cyclohexanediol using 1-butyl-3-methylimidazolium hydrogen sulfate as a catalyst. Compared with existing ionic liquid catalytic synthesis technology for 1,2-cyclohexanediol, the synthesis time is shortened from 5 hours to tens of minutes, and the reaction temperature is reduced from 100℃ to below 60℃, greatly saving energy consumption and improving the yield. Furthermore, the ionic liquid can be recycled more than 5 times.

[0033] In summary, the technical solution of this invention has significant economic and social benefits. IV. Description of the attached drawings:

[0034] Figure 1 A schematic diagram of the process route for the microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate according to the present invention.

[0035] Figure 2 Infrared spectra of the product prepared by this invention and 1,2-cyclohexanediol standard;

[0036] The self-made product of this invention and the 1,2-cyclohexanediol standard were subjected to infrared detection respectively, and the infrared absorption spectra of the two were obtained, as follows: Figure 2 As shown. By Figure 2 It can be seen that the infrared absorption spectra of the product synthesized in this invention are basically consistent with those of the 1,2-cyclohexanediol standard. Specifically, the infrared absorption spectrum at 3337 cm⁻¹ is... -1 The absorption peak at 2936 cm⁻¹ should correspond to the OH structure in the molecule. -1 The absorption peak at 2857 cm⁻¹ should be due to the asymmetric stretching vibration of the methylene-CH₂ group -CH in the molecule; -1 Attributable to the symmetric stretching vibration of the methylene-CH2 group (-CH); in the range of 500-1500 cm⁻¹ -1 The bending vibrations of the -CC- bond and the stretching vibrations of the covalent bond involving heavier atoms are present. All the functional groups mentioned above correspond to the molecular structure of 1,2-cyclohexanediol, and the absorption spectra compared with those of the standard show good agreement. This proves that the product obtained in this invention is indeed 1,2-cyclohexanediol.

[0037] Figure 3 Typical gas chromatograms for analyzing the products synthesized in this invention;

[0038] The final determined chromatographic conditions are as follows: The yield of 1,2-cyclohexanediol, the product of this invention, was determined by gas chromatography. An HP-5 column was selected, and the gas chromatograph method was as follows: initial temperature 50℃, held for 4 min, then increased at 20℃·min. -1 Heat to 150℃ and hold for 3 minutes; then increase the temperature by 20℃·min. -1 The temperature was raised to 260℃ and held for 2 min; the injection volume was 0.5 μl. The 1,2-cyclohexanediol product of this invention was analyzed under these chromatographic conditions, and the gas chromatogram is shown below. Figure 3 As shown.

[0039] Depend on Figure 3 It can be seen that the retention time of 2.366 min is for acetonitrile, the retention time of 3.135 min is for ethyl acetate, and the retention time of 9.535 min is for 1,2-cyclohexanediol. This demonstrates that the process for synthesizing 1,2-cyclohexanediol using 1-butyl-3-methylimidazolium hydrogen sulfate catalyzed by this invention produces no other byproducts, and subsequent product separation and purification are simple. V. Detailed Implementation Methods:

[0040] The present invention will be further illustrated below with reference to the embodiments, but this does not limit the scope of protection of the technical solution of the present invention.

[0041] In the following embodiments of the present invention, cyclohexene is used as raw material, 1-butyl-3-methylimidazolium hydrogen sulfate is used as solvent and catalyst, and hydrogen peroxide is used as oxidant; the power of the microwave reactor is controlled to be 160-480W.

[0042] Example 1:

[0043] The detailed steps of the microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazol hydrogen sulfate are as follows:

[0044] a. Using cyclohexene as raw material, 1-butyl-3-methylimidazolium hydrogen sulfate as solvent and catalyst, and hydrogen peroxide as oxidant; wherein the mass fraction of 1-butyl-3-methylimidazolium hydrogen sulfate added accounts for 150% of cyclohexene, and the molar ratio of hydrogen peroxide to cyclohexene is 1.5:1;

[0045] b. First, weigh 10g of 1-butyl-3-methylimidazolium hydrogen sulfate and add it to the microwave reactor. Then add 10mL (0.1mol) of β-cyclohexene and 14.2mL (0.15mol) of hydrogen peroxide. The power of the microwave reactor is 320W. Heat the reactor to 50℃ and stir for 30min under these conditions.

[0046] c. After the reaction is complete, the resulting reaction solution is poured into a pear-shaped separatory funnel and extracted with ethyl acetate. The resulting reaction solution (i.e., the organic phase) is separated by silica gel column chromatography and eluted with dichloromethane to remove the solvent. The resulting filtrate is evaporated under reduced pressure to remove the solvent, and the solid obtained is the product of this invention, 1,2-cyclohexanediol.

[0047] In this embodiment, the removed solvent is vacuum distilled to obtain solvent 1-butyl-3-methylimidazolium hydrogen sulfate for reuse.

[0048] The product 1,2-cyclohexanediol prepared in this embodiment was analyzed by gas chromatography, and its yield was 92.86%.

[0049] Example 2:

[0050] The detailed steps of the microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazol hydrogen sulfate are as follows:

[0051] a. Using cyclohexene as raw material, 1-butyl-3-methylimidazolium hydrogen sulfate as solvent and catalyst, and hydrogen peroxide as oxidant; wherein the mass fraction of 1-butyl-3-methylimidazolium hydrogen sulfate accounts for 200% of cyclohexene, and the molar ratio of hydrogen peroxide to cyclohexene is 0.8:1;

[0052] b. First, weigh 16.4g of 1-butyl-3-methylimidazolium hydrogen sulfate and add it to the microwave reactor. Then add 10mL (0.1mol) of β-cyclohexene and 7.6mL (0.08mol) of hydrogen peroxide. The power of the microwave reactor is 480W. Heat the reactor to 60℃ and stir for 20min under these conditions.

[0053] c. After the reaction is complete, the resulting reaction solution is poured into a pear-shaped separatory funnel and extracted with ethyl acetate. The resulting reaction solution (i.e., the organic phase) is separated by silica gel column chromatography and eluted with dichloromethane to remove the solvent. The solvent in the resulting filtrate is removed by vacuum distillation, and the solid obtained is the product of this invention, 1,2-cyclohexanediol.

[0054] In this embodiment, the removed solvent is vacuum distilled to obtain solvent 1-butyl-3-methylimidazolium hydrogen sulfate for reuse.

[0055] The product 1,2-cyclohexanediol obtained in this embodiment was analyzed by gas chromatography, and its yield was 91.01%.

[0056] Example 3:

[0057] The detailed steps of the microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazol hydrogen sulfate are as follows:

[0058] a. Using cyclohexene as raw material, 1-butyl-3-methylimidazolium hydrogen sulfate as solvent and catalyst, and hydrogen peroxide as oxidant; wherein the mass fraction of 1-butyl-3-methylimidazolium hydrogen sulfate accounts for 160% of cyclohexene, and the molar ratio of hydrogen peroxide to cyclohexene is 1:1;

[0059] b. First, weigh 13.1g of 1-butyl-3-methylimidazolium hydrogen sulfate and add it to the microwave reaction vessel. Then add 10mL (0.1mol) of β-cyclohexene and 10mL (0.1mol) of hydrogen peroxide. The power of the microwave reactor is 240W. Heat the temperature to 40℃ and stir the reaction for 40min under these conditions.

[0060] c. After the reaction is complete, the resulting reaction solution is poured into a pear-shaped separatory funnel and extracted with ethyl acetate. The resulting reaction solution (i.e., the organic phase) is separated by silica gel column chromatography and eluted with dichloromethane to remove the solvent. The solvent in the resulting filtrate is removed by vacuum distillation, and the solid obtained is the product of this invention, 1,2-cyclohexanediol.

[0061] In this embodiment, the removed solvent is vacuum distilled to obtain solvent 1-butyl-3-methylimidazolium hydrogen sulfate for reuse.

[0062] The product obtained in this embodiment was analyzed by gas chromatography, and its yield was 94.53%.

[0063] Example 4:

[0064] The detailed steps of the microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazol hydrogen sulfate are as follows:

[0065] a. Using cyclohexene as raw material, 1-butyl-3-methylimidazolium hydrogen sulfate as solvent and catalyst, and hydrogen peroxide as oxidant; wherein the mass fraction of 1-butyl-3-methylimidazolium hydrogen sulfate accounts for 150% of cyclohexene, and the molar ratio of hydrogen peroxide to cyclohexene is 1.3:1;

[0066] b. First, weigh 12.3g of 1-butyl-3-methylimidazolium hydrogen sulfate and add it to the microwave reaction vessel. Then add 10mL (0.1mol) of β-cyclohexene and 12mL (0.13mol) of hydrogen peroxide. The power of the microwave reactor is 480W. Heat the mixture to 35℃ and stir for 20min under these conditions.

[0067] c. After the reaction is complete, the resulting reaction solution is poured into a pear-shaped separatory funnel and extracted with ethyl acetate. The resulting reaction solution (i.e., the organic phase) is separated by silica gel column chromatography and eluted with dichloromethane to remove the solvent. The solvent in the resulting filtrate is removed by vacuum distillation, and the solid obtained is the product of this invention, 1,2-cyclohexanediol.

[0068] In this embodiment, the removed solvent is vacuum distilled to obtain solvent 1-butyl-3-methylimidazolium hydrogen sulfate for reuse.

[0069] The product 1,2-cyclohexanediol obtained in this embodiment was analyzed by gas chromatography, and its yield was 90.22%.

[0070] Example 5:

[0071] The detailed steps of the microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazol hydrogen sulfate are as follows:

[0072] a. Using cyclohexene as raw material, 1-butyl-3-methylimidazolium hydrogen sulfate as solvent and catalyst, and hydrogen peroxide as oxidant; wherein the mass fraction of 1-butyl-3-methylimidazolium hydrogen sulfate accounts for 180% of cyclohexene, and the molar ratio of hydrogen peroxide to cyclohexene is 1:1;

[0073] b. First, weigh 12.3g of 1-butyl-3-methylimidazolium hydrogen sulfate and add it to the microwave reaction vessel. Then add 10mL (0.1mol) of β-cyclohexene and 10mL (0.1mol) of hydrogen peroxide. The power of the microwave reactor is 160W. Heat the mixture to 30℃ and stir for 50min under these conditions.

[0074] c. After the reaction is complete, the resulting reaction solution is poured into a pear-shaped separatory funnel and extracted with methyl acetate. The resulting reaction solution (i.e., the organic phase) is separated by silica gel column chromatography and eluted with dichloromethane to remove the solvent. The solvent in the resulting filtrate is removed by vacuum distillation, and the solid obtained is the product of this invention, 1,2-cyclohexanediol.

[0075] In this embodiment, the removed solvent is vacuum distilled to obtain solvent 1-butyl-3-methylimidazolium hydrogen sulfate for reuse.

[0076] The product 1,2-cyclohexanediol obtained in this embodiment was analyzed by gas chromatography, and its yield was 92.48%.

[0077] Example 6:

[0078] The detailed steps of the microwave-assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazol hydrogen sulfate are as follows:

[0079] a. Using cyclohexene as raw material, 1-butyl-3-methylimidazolium hydrogen sulfate as solvent and catalyst, and hydrogen peroxide as oxidant; wherein the mass fraction of 1-butyl-3-methylimidazolium hydrogen sulfate accounts for 170% of cyclohexene, and the molar ratio of hydrogen peroxide to cyclohexene is 1.5:1;

[0080] b. First, weigh 12.3g of 1-butyl-3-methylimidazolium hydrogen sulfate and add it to the microwave reaction vessel. Then add 10mL (0.1mol) of β-cyclohexene and 14.2mL (0.15mol) of hydrogen peroxide. The power of the microwave reactor is 320W. Heat the mixture to 40℃ and stir for 40min under these conditions.

[0081] c. After the reaction is complete, the resulting reaction solution is poured into a pear-shaped separatory funnel and extracted with methyl acetate. The resulting reaction solution (i.e., the organic phase) is separated by silica gel column chromatography and eluted with dichloromethane to remove the solvent. The solvent in the resulting filtrate is removed by vacuum distillation, and the solid obtained is the product of this invention, 1,2-cyclohexanediol.

[0082] In this embodiment, the extracted solvent was vacuum distilled to obtain solvent 1-butyl-3-methylimidazolium hydrogen sulfate for reuse.

[0083] The product 1,2-cyclohexanediol obtained in this embodiment was analyzed by gas chromatography, and its yield was 96.53%.

[0084] The present invention conducted the following experimental analysis on the obtained product 1,2-cyclohexanediol:

[0085] The product of this invention was analyzed by infrared analysis using a NExus-470 Fourier transform infrared spectrometer (FT-IR).

[0086] The content of the product synthesized in this invention was determined using an Agilent 7890B gas chromatograph. The gas chromatographic conditions were as follows:

[0087] The yield of 1,2-cyclohexanediol was determined by gas chromatography. An HP-5 column was selected. The gas chromatography method was as follows: initial temperature 50℃, held for 4 min, then increased to 150℃ at a rate of 20℃·min⁻¹ and held for 3 min; then increased to 260℃ at a rate of 20℃·min⁻¹ and held for 2 min. The injection volume was 0.5 μl.

Claims

1. A process for the microwave assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate, characterized in that, The method comprises the following steps: a. taking cyclohexene as raw material, 1-butyl-3-methylimidazole hydrogen sulfate as solvent and catalyst, and hydrogen peroxide as oxidant, the addition amount of 1-butyl-3-methylimidazole hydrogen sulfate accounts for 150-200% of the mass of cyclohexene, and the molar ratio of hydrogen peroxide to cyclohexene is 0.8-1.5:1; b. first, 1-butyl-3-methylimidazole hydrogen sulfate is added into a microwave reactor, then raw material cyclohexene and oxidant hydrogen peroxide are added for heating reaction, and the reaction temperature is controlled at 30-80℃ and the reaction time is 20-50 min; c. after the reaction is completed, the obtained reaction liquid is extracted, the obtained reaction liquid after extraction is separated by silica gel column chromatography, then eluted with dichloromethane, and the solvent is removed to obtain product 1,2-cyclohexanediol.

2. The process for the microwave assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate according to claim 1, characterized in that: In step a, the addition amount of 1-butyl-3-methylimidazole hydrogen sulfate accounts for 160-180% of the mass of cyclohexene.

3. The process for the microwave assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate according to claim 1, characterized in that: In step b, the reaction temperature is controlled at 40-60℃ and the reaction time is 25-45 min.

4. The process for the microwave assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate according to claim 1, characterized in that: In step b, the power of the microwave reactor is controlled at 160-480 W.

5. The process for the microwave assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate according to claim 1, characterized in that: In step c, when the obtained reaction liquid is extracted, the solvent used is ethyl acetate or methyl acetate.

6. The process for the microwave assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate according to claim 1, characterized in that: In step c, after extraction, the obtained reaction liquid is successively subjected to combination, separation by silica gel column chromatography, elution with dichloromethane, and concentration to remove the solvent, to obtain product 1,2-cyclohexanediol.

7. The process for the microwave assisted synthesis of 1,2-cyclohexanediol from 1-butyl-3-methylimidazolium hydrogen sulfate according to claim 1, characterized in that: In step c, the removed solvent is subjected to recovery treatment, and the recovered 1-butyl-3-methylimidazole hydrogen sulfate is reused.

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