Preparation method of 2, 3, 5-trimethylbenzoquinone capable of reducing chlorinated impurities

Abstract

The invention provides a preparation method of 2, 3, 5-trimethylbenzoquinone capable of reducing chlorinated impurities. The preparation method comprises the following steps: reacting chlorinated 1-butyl-3-methylimidazolium salt with Lewis acid in a solvent A under the action of acid to obtain an ionic liquid catalyst; in a solvent B, under the action of an ionic liquid catalyst and acid, 2, 3, 6-trimethylphenol is oxidized to prepare the 2, 3, 5-trimethylbenzoquinone. The preparation method disclosed by the invention is simple, simple and convenient to operate, low in discharge amount of three wastes, green, safe, environment-friendly, low in cost, high in product yield, purity and content, free of chlorinated impurities and suitable for industrial production, and process conditions are easy to realize;

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology of vitamins, and specifically relates to a method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities. Background Technology

[0002] 2,3,5-Trimethylbenzoquinone is an important intermediate in the preparation of vitamin E, mainly prepared by the oxidation of 2,3,6-trimethylphenol. The hydrogenation of 2,3,5-trimethylbenzoquinone yields 2,3,5-trimethylhydroquinone, which is the main ring of vitamin E. Vitamin E is a fat-soluble vitamin. Vitamin E acetate is one of the ester derivatives of vitamin E, possessing antioxidant, moisturizing, immune-boosting, and free radical scavenging functions. Therefore, it is widely used in food, medicine, feed, and cosmetics. The demand for vitamin E in domestic and international markets is rapidly increasing, and the production and quality of 2,3,5-trimethylbenzoquinone have become key factors restricting the cost of vitamin E.

[0003] Existing technology: Chinese patent document CN101113131A discloses an ionic liquid composed of imidazole, quaternary ammonium, and pyridine cations and anions as the reaction medium, copper halide as the catalyst, and the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethylbenzoquinone using pure oxygen or oxygen-enriched gas. This method has a low yield of the target product and does not provide data on purity. After the reaction, the product is distilled off; the distilled ionic liquid reaction medium can be reused, but the copper halide catalyst needs to be added back before the reaction can proceed.

[0004] Chinese patent document CN102633614A discloses a composite catalyst composed of copper chloride (and / or cobalt chloride), ferric chloride, and triethylamine hydrochloride. Using this composite catalyst, 2,3,6-trimethylphenol is synthesized from it via hydrogen peroxide oxidation. However, the molar ratio of hydrogen peroxide to 2,3,6-trimethylphenol in this method is over 30, resulting in high raw material costs for hydrogen peroxide; the yield of the target product needs further improvement; and no data on product purity are provided.

[0005] Chinese patent document CN102108047A discloses a method for preparing 2,3,5-trimethylbenzoquinone by adding a phase transfer catalyst and using water as the reaction medium, under the catalysis of copper halide and lithium halide, and by using pure oxygen or oxygen-enriched gas for oxidation reaction. However, the high cost of lithium halide increases production costs. Furthermore, the poor solubility of the reactant 2,3,6-trimethylphenol in the system makes the system viscous, which is detrimental to mass and heat transfer. The yield of the target product needs further improvement.

[0006] In summary, current methods for preparing 2,3,5-trimethylbenzoquinone suffer from problems such as high product cost, low yield, and low purity. To address these issues, this invention is proposed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities. The method is simple, easy to operate, and the process conditions are readily achievable. It saves energy, produces minimal waste, is environmentally friendly and safe, and has low cost. The product has high yield and purity, high content, and is free of chlorinated impurities, making it suitable for industrial production.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities, comprising the steps of: (1) In solvent A, under the action of acid, 1-butyl-3-methylimidazolium chloride reacts with Lewis acid to obtain an ionic liquid catalyst; (2) In solvent B, 2,3,6-trimethylphenol is oxidized to prepare 2,3,5-trimethylbenzoquinone under the action of ionic liquid catalyst and acid.

[0009] According to a preferred embodiment of the present invention, in step (1), solvent A is ethanol or methanol; the molar ratio of 1-butyl-3-methylimidazolium chloride to the volume ratio of solvent A is 1-3 mol / L.

[0010] According to a preferred embodiment of the present invention, in step (1), the acid is an aqueous solution of hydrochloric acid with a mass concentration of 30-38%; the pH of the reaction solution is adjusted to 1-2 using the acid.

[0011] According to a preferred embodiment of the present invention, in step (1), the molar ratio of 1-butyl-3-methylimidazolium chloride to Lewis acid is (1-2):1.

[0012] According to a preferred embodiment of the present invention, in step (1), the Lewis acid is one or a combination of two or more of cobalt chloride, copper chloride, ferric chloride or magnesium chloride.

[0013] According to a preferred embodiment of the present invention, in step (1), the preparation method of 1-butyl-3-methylimidazolium chloride includes the following steps: N-methylimidazolium and 1-chlorobutane are dissolved in acetonitrile, reacted, the solvent is removed by vacuum distillation, washed with ether, and dried to obtain 1-butyl-3-methylimidazolium chloride.

[0014] Preferably, the molar ratio of N-methylimidazole to 1-chlorobutane is 1:1-2; the molar ratio of N-methylimidazole to acetonitrile is 1:1-5 mol / L; the reaction temperature is 60-100℃; the reaction time is 20-30 h; and the reaction is carried out under inert gas protection, reflux, and stirring conditions. Preferably, the inert gas is nitrogen or argon.

[0015] According to a preferred embodiment of the present invention, in step (1), the reaction temperature is room temperature, the reaction time is 4 to 6 hours, and the reaction is carried out under stirring conditions.

[0016] According to a preferred embodiment of the present invention, in step (1), the post-treatment method of the reaction solution obtained from the reaction includes the steps of: removing the solvent by vacuum distillation, washing the obtained product with acetone, and drying to obtain the ionic liquid catalyst.

[0017] According to a preferred embodiment of the present invention, in step (1), the preparation method of the ionic liquid catalyst includes the following steps: dissolving 1-butyl-3-methylimidazolium chloride and Lewis acid in solvent A, adding acid dropwise, reacting, removing the solvent by vacuum distillation, washing the obtained product with acetone, and drying to obtain the ionic liquid catalyst.

[0018] According to a preferred embodiment of the present invention, in step (2), solvent B is a mixed solvent of water and alcohol, wherein the alcohol is dodecanol, undecylol, n-decylol, n-nonylol or n-octanol, and the mass ratio of water to alcohol is 1:3-5; the mass ratio of 2,3,6-trimethylphenol to solvent B is 1:2-5.

[0019] According to a preferred embodiment of the present invention, in step (2), the acid is an aqueous solution of hydrochloric acid with a mass concentration of 30-32%; the mass of the acid is 0.1-10% of the mass of 2,3,6-trimethylphenol, preferably 0.1-1%.

[0020] According to a preferred embodiment of the present invention, in step (2), the mass of the ionic liquid catalyst is 5-40% of the mass of 2,3,6-trimethylphenol, preferably 20-40%.

[0021] According to a preferred embodiment of the present invention, in step (2), the oxidation reaction temperature is 30-80°C, the reaction time is 1-10 hours, the reaction is carried out under air and stirring conditions, and the gauge pressure of the reaction is 10-20 kPa. Preferably, the oxidation reaction temperature is 40-60°C, and the reaction time is 5-10 hours.

[0022] According to a preferred embodiment of the present invention, in step (2), the post-treatment method of the reaction solution obtained by the oxidation reaction includes the following steps: the reaction solution is allowed to stand and separate into phases, the upper organic phase is taken, and the organic phase is washed with water and distilled to obtain 2,3,5-trimethylbenzoquinone; the lower aqueous phase is an aqueous solution of an ionic liquid catalyst, which can be directly reused.

[0023] The method of this invention is described by the following synthetic route:

[0024] This invention relates to the preparation of 2,3,5-trimethylbenzoquinone under ionic liquid catalyst and air oxidation. The main reaction produces the product 2,3,5-trimethylbenzoquinone. However, due to the addition of hydrochloric acid, the reaction continues to react with hydrogen chloride to generate the impurity chlorotrimethylbenzoquinone. Chlorotrimethylbenzoquinone has extremely similar properties to 2,3,5-trimethylbenzoquinone, making it difficult to separate them by distillation. This chlorotrimethylbenzoquinone is eventually introduced into the final product, vitamin E acetate, forming corresponding derivative impurities. This results in a decrease in the purity of the final product.

[0025] The use of imidazole-based ionic liquid catalysts in this invention significantly reduces the amount of hydrochloric acid used, preventing 2,3,5-trimethylbenzoquinone from further reacting with hydrogen chloride to form chlorotrimethylbenzoquinone, thus reducing byproduct generation and improving the purity and content of the target product 2,3,5-trimethylbenzoquinone.

[0026] Technical features and beneficial effects of the present invention: 1. The preparation method of 2,3,5-trimethylbenzoquinone of the present invention is simple, easy to operate, easy to achieve process conditions, saves energy, involves fewer separation processes, produces less wastewater, is green, safe and environmentally friendly, has high atom economy, low cost, and is suitable for industrial production.

[0027] 2. This invention utilizes the catalytic activation effect of ionic liquid catalysts, reducing the amount of hydrochloric acid used and achieving highly selective preparation of 2,3,5-trimethylbenzoquinone, while lowering the content of chlorinated impurities. The method of this invention exhibits high reaction selectivity, high yield and purity of the target product, and effectively reduces the content of chlorinated trimethylbenzoquinone impurities in the product.

[0028] 3. In the synthesis of 2,3,5-trimethylbenzoquinone, methyl butylimidazolium ionic liquid, as a catalyst, effectively solves the problems of poor catalyst selectivity, poor catalytic activity, and inability to be recycled. The ionic liquid catalyst preparation method of this invention is simple, low-cost, green, safe, and environmentally friendly. It requires a small amount of catalyst, exhibits good catalytic selectivity and activity, and can be recycled and reused, thus showing broad application prospects in the synthesis of 2,3,5-trimethylbenzoquinone.

[0029] 4. The ionic liquid formed by 1-butyl-3-methylimidazolium chloride and a Lewis acid has a 1-methyl-3-butylimidazolium cation ([BMIM)). +The anion is a Lewis acid complex anion. The catalyst has an imidazole ring structure with a methyl group attached to the nitrogen atom at position 1 and a butyl group attached to the nitrogen atom at position 3, forming an asymmetric organic cation. This structure endows the ionic liquid with good solubility and stability, while also affecting its physicochemical properties. The cation and anion are stably bonded together by ionic bonds. Compared to a simple mixture of 1-butyl-3-methylimidazolium chloride and a Lewis acid, this structure is more stable, exhibiting better catalytic activity and stability. Attached Figure Description

[0030] Figure 1 This is the HPLC chromatogram of 2,3,5-trimethylbenzoquinone prepared in Example 3; Figure 2 This is the HPLC chromatogram of 2,3,5-trimethylbenzoquinone prepared in Example 4; Figure 3 This is the HPLC chromatogram of 2,3,5-trimethylbenzoquinone prepared in Example 5; Figure 4 This is the HPLC chromatogram of 2,3,5-trimethylbenzoquinone prepared in Example 6; Figure 5 The HPLC chromatogram of 2,3,5-trimethylbenzoquinone prepared in Comparative Example 1 is shown below. Figure 6 This is the HPLC chromatogram of 2,3,5-trimethylbenzoquinone prepared in Comparative Example 2. Detailed Implementation

[0031] The present invention has been described in detail below with reference to embodiments, but the present invention is not limited thereto.

[0032] All raw materials and reagents used in the examples are commercially available products. The yields in the examples are molar yields, unless otherwise specified.

[0033] Example 1: Preparation of ionic liquid catalysts N-methylimidazole (82.1 g, 1 mol) and 1-chlorobutane (111.08 g, 1.2 mol) were dissolved in 400 mL of acetonitrile. The mixture was refluxed and stirred at 80 °C for 24 hours under a nitrogen atmosphere. After the reaction was completed, the solvent was removed by vacuum distillation, and the mixture was washed several times with diethyl ether to remove excess halogenated hydrocarbons. The mixture was then dried under vacuum to obtain a white solid [BMIM]Cl for later use.

[0034] [BMIM]Cl (174.67 g, 1 mol) and CoCl2•6H2O (237.93 g, 1 mol) were dissolved in 500 mL of ethanol. The pH was adjusted to 1–2 by adding 32% concentrated hydrochloric acid, and the mixture was stirred until completely dissolved. The reaction was carried out at room temperature for 5 hours. After the reaction was complete, the ethanol was removed by vacuum distillation. The resulting product was washed several times with acetone and dried under vacuum (40–60 °C, 12 hours) to obtain the target ionic liquid catalyst [BMIM]. + [CoCl3 - ].

[0035] Example 2: Preparation of ionic liquid catalysts N-methylimidazole (82.1 g, 1 mol) and 1-chlorobutane (111.08 g, 1.2 mol) were dissolved in 400 mL of acetonitrile. The mixture was refluxed and stirred at 80 °C for 24 hours under a nitrogen atmosphere. After the reaction was completed, the solvent was removed by vacuum distillation, and the mixture was washed several times with diethyl ether to remove excess halogenated hydrocarbons. The mixture was then dried under vacuum to obtain a white solid [BMIM]Cl for later use.

[0036] [BMIM]Cl (174.67 g, 1 mol) and CuCl2•2H2O (170.48 g, 1 mol) were dissolved in 500 mL of ethanol. The pH was adjusted to 1–2 by adding 32% hydrochloric acid, and the mixture was stirred until completely dissolved. The reaction was carried out at room temperature for 5 hours. After the reaction was complete, the ethanol was removed by vacuum distillation. The resulting product was washed several times with acetone and dried under vacuum (40–60 °C, 12 hours) to obtain the target ionic liquid catalyst [BMIM]. + [CuCl3 - ].

[0037] Example 3: Preparation of 2,3,5-trimethylbenzoquinone In a 500 mL four-necked flask, 10 g of the methylbutylimidazolium ionic liquid catalyst prepared by the method in Example 1, 200 g of dodecanol, and 50 g of water were first added. 50.0 g of 2,3,6-trimethylphenol was weighed and added to the flask, followed by 0.5 g of 32% concentrated hydrochloric acid. The stirring and air pump (compressed air was initially introduced) were turned on, and the temperature was raised to 60 °C. The gauge pressure of the reaction system was controlled at 10 kPa, and the reaction was allowed to proceed for 8 hours. After the reaction was completed, the mixture was allowed to stand and separate into layers. The lower layer was an aqueous layer of the methylbutylimidazolium ionic liquid, which could be recycled and reused as a catalyst for the oxidation reaction. The upper organic phase was a dodecanol solution of 2,3,5-trimethylbenzoquinone. The organic phase was washed twice with 100 g of water until the pH of the washings reached 7.0. The organic phase was then separated by distillation to separate dodecanol and 2,3,5-trimethylbenzoquinone. The yield of 2,3,5-trimethylbenzoquinone was 98.5%, the impurity content of chloro-2,3,5-trimethylbenzoquinone was 0.11%, and the purity was 99.14%. The HPLC chromatogram is shown below. Figure 1 As shown.

[0038] Example 4: Preparation of 2,3,5-trimethylbenzoquinone In a 500 mL four-necked flask, 10 g of the methylbutylimidazolium ionic liquid catalyst prepared by the method in Example 2, 200 g of dodecanol, and 50 g of water were first added. 50.0 g of 2,3,6-trimethylphenol was weighed and added to the flask, followed by 0.5 g of 32% concentrated hydrochloric acid. The stirring and air pump (compressed air was initially introduced) were turned on, and the temperature was raised to 60 °C. The gauge pressure of the reaction system was controlled at 10 kPa, and the reaction was allowed to proceed for 8 hours. After the reaction was completed, the mixture was allowed to stand and separate into layers. The lower layer was an aqueous layer of the methylbutylimidazolium ionic liquid, which could be recycled and reused as a catalyst for the oxidation reaction. The upper organic phase was a dodecanol solution of 2,3,5-trimethylbenzoquinone. The organic phase was washed twice with 100 g of water until the pH of the washings reached 7.0. The organic phase was then separated by distillation to separate dodecanol and 2,3,5-trimethylbenzoquinone. The yield of 2,3,5-trimethylbenzoquinone was 98.3%, the impurity content of chloro-2,3,5-trimethylbenzoquinone was 0.11%, and the purity was 99.04%. The HPLC chromatogram is shown below. Figure 2 As shown.

[0039] Example 5: Preparation of 2,3,5-trimethylbenzoquinone In a 500 mL four-necked flask, 20 g of the methylbutylimidazolium ionic liquid catalyst prepared by the method in Example 2, 200 g of dodecanol, and 50 g of water were first added. 50.0 g of 2,3,6-trimethylphenol was weighed and added to the flask, followed by 0.5 g of 32% concentrated hydrochloric acid. The stirring and air pump (compressed air was initially introduced) were turned on, and the temperature was raised to 60 °C. The gauge pressure of the reaction system was controlled at 10 kPa, and the reaction was allowed to proceed for 8 hours. After the reaction was completed, the mixture was allowed to stand and separate into layers. The lower layer was an aqueous layer of the methylbutylimidazolium ionic liquid, which could be recycled and reused as a catalyst for the oxidation reaction. The upper organic phase was a dodecanol solution of 2,3,5-trimethylbenzoquinone. The organic phase was washed twice with 100 g of water until the pH of the washings reached 7.0. The organic phase was then separated by distillation to separate dodecanol and 2,3,5-trimethylbenzoquinone. The yield of 2,3,5-trimethylbenzoquinone was 98.9%, the impurity content of chloro-2,3,5-trimethylbenzoquinone was 0.06%, and the purity was 99.20%. The HPLC chromatogram is shown below. Figure 3 As shown.

[0040] Example 6: Preparation of 2,3,5-trimethylbenzoquinone In a 500 mL four-necked flask, 10 g of the methylbutylimidazolium ionic liquid catalyst prepared in Example 2, 200 g of dodecanol, and 50 g of water were first added. 50.0 g of 2,3,6-trimethylphenol was weighed and added to the flask, followed by 5 g of 32% concentrated hydrochloric acid. The stirring and air pump were turned on (compressed air was initially introduced), and the temperature was raised to 60 °C. The gauge pressure of the reaction system was controlled at 10 kPa, and the reaction was allowed to proceed for 8 hours. After the reaction, the mixture was allowed to stand and separate into layers. The lower layer was an aqueous layer of the methylbutylimidazolium ionic liquid, which could be recycled and reused as a catalyst for the oxidation reaction. The upper organic phase was a dodecanol solution of 2,3,5-trimethylbenzoquinone. The organic phase was washed twice with 100 g of water until the pH of the washings reached 7.0. The organic phase was then separated by distillation to separate dodecanol and 2,3,5-trimethylbenzoquinone. The yield of 2,3,5-trimethylbenzoquinone was 95.8%, the impurity content of chloro-2,3,5-trimethylbenzoquinone was 0.19%, and the purity was 99.02%. The HPLC chromatogram is shown below. Figure 4 As shown.

[0041] Comparative Example 1: Preparation of 2,3,5-trimethylbenzoquinone In a 500 mL four-necked flask, add 200 g of dodecanol, 50 g of deionized water, 5.0 g of 32% concentrated hydrochloric acid, 50 g of 2,3,6-trimethylphenol, and 5.11 g of copper chloride dihydrate. After starting the stirrer and air pump, heat to 60 °C and begin purging with compressed air, maintaining the gauge pressure of the reaction system at 10 kPa. React for 8 hours. After the reaction, allow the mixture to stand and separate into layers. Discard the lower layer. The upper organic phase is a dodecanol solution of 2,3,5-trimethylbenzoquinone. Wash the organic phase twice with 100 g of water until the pH of the eluent reaches 7.0. Separate the organic phase and perform distillation to separate dodecanol and 2,3,5-trimethylbenzoquinone. The yield of 2,3,5-trimethylbenzoquinone is 90.5%, the impurity content of chloro-2,3,5-trimethylbenzoquinone is 0.46%, and the purity is 98.81%. HPLC chromatogram is shown below. Figure 5 As shown.

[0042] Comparative Example 2: Preparation of 2,3,5-trimethylbenzoquinone In a 500 mL four-necked flask, 46.81 g of [BMIM]Cl prepared by the method in Example 2, 200 g of dodecanol, 50 g of water, 5.11 g of copper chloride dihydrate (the molar ratio of [BMIM]Cl to copper chloride dihydrate is 8:1), and 50.0 g of 2,3,6-trimethylphenol were first added to the flask. Then, 5 g of concentrated hydrochloric acid with a mass concentration of 32% was added, and the mixture was thoroughly mixed and dispersed. After turning on the stirrer and air pump (compressed air was initially introduced), the temperature was raised to 60 °C, and the gauge pressure of the reaction system was controlled at 10 kPa. The reaction was carried out for 8 h. After the reaction was completed, the mixture was allowed to stand and separate into layers. The upper organic phase was a dodecanol solution of 2,3,5-trimethylbenzoquinone. The organic phase was washed twice with 100 g of water until the pH of the washings was 7.0. The organic phase was separated by distillation to separate dodecanol and 2,3,5-trimethylbenzoquinone. The yield of 2,3,5-trimethylbenzoquinone was 91.8%, the impurity content of chloro-2,3,5-trimethylbenzoquinone was 0.50%, and the purity was 98.43%. The HPLC chromatogram is shown below. Figure 6 As shown.

[0043] Comparative Example 3: Preparation of 2,3,5-trimethylbenzoquinone In a 500 mL four-necked flask, 10 g of methyl butylimidazolium ionic liquid catalyst [BMIM] was first added. + [MgCl3 - (The preparation method is the same as in Example 1, except that CoCl2•6H2O is replaced with 1 mol MgCl2•6H2O) and 200g dodecanol, 50g water, and 50.0g 2,3,6-trimethylphenol were weighed and added to a four-necked flask, followed by 0.5g of concentrated hydrochloric acid with a mass concentration of 32%. After turning on the stirrer and air pump (compressed air was initially introduced), the temperature was raised to 60℃, and the gauge pressure of the reaction system was controlled at 10kPa. The reaction was carried out for 8 hours. After the reaction was completed, the mixture was allowed to stand and separate into layers. The upper organic phase was a dodecanol solution of 2,3,5-trimethylbenzoquinone. The organic phase was washed twice with 100g of water until the pH of the washing liquid was 7.0. The organic phase was separated by distillation to separate dodecanol and 2,3,5-trimethylbenzoquinone. The yield of 2,3,5-trimethylbenzoquinone was 50.3%, the impurity content of chlorinated 2,3,5-trimethylbenzoquinone was 0.83%, and the purity was 98.24%.

Claims

1. A method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities, comprising the steps of: (1) In solvent A, under the action of acid, 1-butyl-3-methylimidazolium chloride reacts with Lewis acid to obtain an ionic liquid catalyst; (2) In solvent B, 2,3,6-trimethylphenol is oxidized to prepare 2,3,5-trimethylbenzoquinone under the action of ionic liquid catalyst and acid.

2. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, Step (1) includes one or more of the following conditions: i. Solvent A is ethanol or methanol; the molar ratio of 1-butyl-3-methylimidazolium chloride to the volume ratio of solvent A is 1-3 mol / L; ii. The acid is a 30-38% hydrochloric acid aqueous solution; adjust the pH of the reaction solution to 1-2 using the acid; iii. The molar ratio of 1-butyl-3-methylimidazolium chloride to Lewis acid is (1-2):

1.

3. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, In step (1), Lewis acid is one or a combination of two or more of cobalt chloride, copper chloride, ferric chloride or magnesium chloride.

4. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, In step (1), the preparation method of 1-butyl-3-methylimidazolium chloride includes the following steps: N-methylimidazolium and 1-chlorobutane are dissolved in acetonitrile, reacted, the solvent is removed by vacuum distillation, washed with diethyl ether, and dried to obtain 1-butyl-3-methylimidazolium chloride; Preferably, the molar ratio of N-methylimidazole to 1-chlorobutane is 1:1-2; the molar amount of N-methylimidazole and the volume ratio of acetonitrile are 1:1-5 mol / L; the reaction temperature is 60~100℃, the reaction time is 20-30h, and the reaction is carried out under inert gas protection, reflux, and stirring conditions; preferably, the inert gas is nitrogen or argon.

5. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, In step (1), the reaction temperature is room temperature, the reaction time is 4 to 6 hours, and the reaction is carried out under stirring conditions.

6. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, In step (1), the preparation method of the ionic liquid catalyst includes the following steps: dissolving 1-butyl-3-methylimidazolium chloride and Lewis acid in solvent A, adding acid dropwise, reacting, removing the solvent by vacuum distillation, washing the obtained product with acetone, and drying to obtain the ionic liquid catalyst.

7. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, In step (2), solvent B is a mixed solvent of water and alcohol, wherein the alcohol is dodecanol, undecylol, n-decylol, n-nonylol or n-octanol, and the mass ratio of water to alcohol is 1:3-5; the mass ratio of 2,3,6-trimethylphenol to solvent B is 1:2~5.

8. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, In step (2), the acid is an aqueous solution of hydrochloric acid with a mass concentration of 30-32%; the mass of the acid is 0.1-10% of the mass of 2,3,6-trimethylphenol, preferably 0.1-1%.

9. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, In step (2), the mass of the ionic liquid catalyst is 5-40% of the mass of 2,3,6-trimethylphenol, preferably 20-40%.

10. The method for preparing 2,3,5-trimethylbenzoquinone with reduced chlorinated impurities according to claim 1, characterized in that, In step (2), the oxidation reaction temperature is 30-80℃, the reaction time is 1-10 hours, the reaction is carried out under air and stirring conditions, and the gauge pressure of the reaction is 10-20 kPa; preferably, the oxidation reaction temperature is 40-60℃ and the reaction time is 5-10 hours.

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