Imidazole cobalt complex as well as preparation method and application thereof

Abstract

The invention provides an imidazole cobalt complex and a preparation method and application thereof, and the preparation method of the imidazole cobalt complex comprises the following steps: step 1, adding substituted imidazole and 1, 2-dibromoethane into a first solvent, carrying out water bath heating reaction to obtain a turbid liquid, filtering to obtain a precipitate, and recrystallizing the precipitate; step 2, mixing the precipitate with cobalt salt, adding a second solvent into the mixture, and carrying out heating reflux reaction; and after the reaction is finished, filtering, washing and drying to obtain the imidazole cobalt complex. The imidazole cobalt complex has the advantages of stable steric configuration, mild reaction conditions, high catalytic performance and the like, the synthesis process is simple, the central metal is cheap and easy to obtain, and industrial production is easy to realize. The imidazole cobalt complex disclosed by the invention has a good application prospect and large-scale popularization potential in the field of catalytic oxidation of dimethylnaphthalene reaction.

Description

Technical Field

[0001] This invention relates to materials technology, and more particularly to an imidazole cobalt complex, its preparation method, and its application. Background Technology

[0002] β-Menadione is an important fine chemical raw material, mainly used to synthesize vitamin K derivatives, especially vitamin K3, which has wide applications in pharmaceuticals, pesticides, and feed additives. Currently, industrial production in my country primarily uses liquid-phase oxidation, with most processes involving the oxidation of 2-methylnaphthalene with CrO3 in an acidic medium. This method achieves a β-menadione yield of 40-50%, but it suffers from several drawbacks, such as corrosion of equipment by strong acids, low catalytic oxidation yield, and the generation of large amounts of chromium-containing wastewater causing severe environmental pollution. Therefore, finding a green, safe, and effective method for the catalytic oxidation of 2-methylnaphthalene to synthesize β-menadione using low-toxicity raw materials, reaction solvents, and catalysts has been a key focus for chemical researchers.

[0003] In recent years, with the advent of the concept of green chemistry, hydrogen peroxide, as a green oxidant, has received widespread attention for its use in the oxidation of 2-methylnaphthalene to prepare β-menaquinone. Japanese scholars Yamaguchi S et al. reported a method using palladium acetate or palladium sulfate as a catalyst in an acetic acid system, with 60% H₂O₂ as the oxidant. This method yielded β-menaquinone at a yield of 50-64%. However, excessively high hydrogen peroxide concentrations can easily lead to explosions, limiting the application of this method in industrial production.

[0004] Yang Jianguo et al. applied for a patent for the synthesis of 2-methyl-1,4-naphthoquinone using ionic liquid as a catalyst (patent application number: 200310053091.4). This method is the first to use a phosphorylated ionic liquid as a catalyst for the catalytic oxidation of 2-methylnaphthalene, with glacial acetic acid as the reaction solvent and hydrogen peroxide as the oxidant. The reaction was carried out at 90°C for 2 hours, achieving a yield of 61% for β-naphthoquinone. This method avoids the problems of chromium contamination and excessively high hydrogen peroxide concentrations. However, the acidic reaction system still causes equipment corrosion and environmental pollution, and the high cost of ionic liquids inevitably increases production costs.

[0005] Florea et al. synthesized a V2O5 / Al2O3 catalyst via a chemical precipitation-adsorption method, using 30% H2O2 as the oxidant, a reaction temperature of 80℃, and a reaction time of 24 h, achieving a conversion rate of 76% for 2-methylnaphthalene. While the process conditions were mild, the catalyst stability needs improvement, and it produced numerous byproducts and required an excessively long reaction time. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned problems by proposing an imidazole cobalt complex that has advantages such as stable spatial configuration, mild reaction conditions, and high catalytic performance. Its synthesis process is simple, the central metal is inexpensive and readily available, and it is easy to achieve industrial production.

[0007] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," "consisting of," etc., and similar meanings.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: an imidazole cobalt complex, with the general formula as follows:

[0009]

[0010] In Equation I, R 1 Selected from hydrogen, C1-C4 hydrocarbon groups and their derivatives, C6-C 13 One of the aryl groups and their derivatives; R 2 Selected from hydrogen, C1-C4 hydrocarbon groups and their derivatives, C6-C 13 One of the aryl groups and their derivatives; each X may be the same or different, and each is independently selected from NO3. - SO4 - or Cl - .

[0011] Furthermore, in Equation I, R 1 R 2 Each is independently selected from hydrogen, methyl, ethyl, isopropyl, or benzyl.

[0012] Another object of the present invention discloses a method for preparing an imidazole cobalt complex, comprising the following steps:

[0013] Step 1: Add the substituted imidazole and 1,2-dibromoethane to the first solvent, heat the mixture in a water bath to obtain a suspension, filter to obtain a precipitate, and recrystallize the precipitate to obtain crystals;

[0014] Step 2: Mix the crystals and cobalt salt, add a second solvent, and heat under reflux to react; after the reaction is complete, filter, wash, and dry to obtain the imidazole cobalt complex.

[0015] Furthermore, the substituted imidazole is a methyl-substituted imidazole, an ethyl-substituted imidazole, an isopropyl-substituted imidazole, or a benzyl-substituted imidazole.

[0016] Furthermore, the first solvent is petroleum ether and / or tetrahydrofuran.

[0017] Furthermore, the molar ratio of the substituted imidazole to 1,2-dibromoethane is 1:1.5-3.

[0018] Furthermore, the water bath heating reaction temperature in step 1 is 60-80℃, and the reaction time is 2-4h.

[0019] Further, the recrystallization of the precipitate to obtain crystals includes the following steps: adding the precipitate (crystals containing impurities) to a solvent, heating to dissolve, filtering and cooling, and recrystallizing to obtain crystals. The solvent is acetonitrile and / or dichloromethane. Recrystallization can purify the product, thereby purifying the impure product.

[0020] Furthermore, the cobalt salt is one or more of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, and cobalt sulfate.

[0021] Furthermore, the molar ratio of the crystal to the cobalt salt is 1:0.5-2.

[0022] Furthermore, the second solvent is one or more of acetonitrile, methanol, and ethanol.

[0023] Furthermore, the heating reflux reaction temperature in step 2 is 60-80℃, and the reaction time is 1.5-6h.

[0024] Furthermore, the washing in step 2 is an alcohol washing, and the alcohols include, but are not limited to, ethanol and methanol.

[0025] Furthermore, the drying temperature in step 2 is 80-100℃; the drying time is 0.5-2h.

[0026] The synthetic route for the imidazole cobalt complexes of this invention is shown below:

[0027]

[0028] Another object of the present invention is to disclose the application of an imidazole cobalt complex in the catalytic oxidation of dimethylnaphthalene.

[0029] Furthermore, the method for catalytic oxidation of dimethylnaphthalene using the imidazole cobalt complex is as follows: the catalytic oxidation of dimethylnaphthalene is carried out under normal pressure, without the need for anhydrous, oxygen-free, or inert gas protection such as nitrogen; the amount of imidazole cobalt complex used is 1%-10% of the substrate.

[0030] Furthermore, the amount of the imidazole cobalt complex is 3%-8% of the substrate.

[0031] Furthermore, the reaction requires reflux heating in a water bath at a temperature of 60-90℃ for a duration of 2-6 hours.

[0032] The imidazole cobalt complex is used in the catalytic oxidation of dimethylnaphthalene, and the reaction formula is as follows:

[0033]

[0034] The imidazole cobalt complexes, their preparation method, and applications of this invention have the following advantages compared with existing technologies:

[0035] 1) Imidazoles belong to nitrogen-containing heterocyclic compounds. Their nitrogen atoms possess lone pairs of electrons and σ bonds, endowing them with overall electron-donating properties, making them excellent ligands. These ligands have advantages such as structural stability, high electron cloud density, strong coordination ability, and low toxicity, and are widely used in coordination chemistry. The presence of two nitrogen atoms in the imidazole structure allows it to bind to acceptors (such as metal ions) through various mechanisms such as hydrogen bonding and coordination, easily forming diverse functional compounds.

[0036] Cobalt, as a transition metal, has advantages such as high natural abundance, rich reserves, low price, and environmental friendliness. Cobalt also possesses multiple variable valence states and good structural tunability, making it excellent in fields such as catalysis.

[0037] Based on the above advantages, this invention synthesizes a series of imidazole-cobalt complexes using substituted imidazoles and cobalt salts as raw materials. In these complexes, the imidazole ligand (providing high electron cloud density and dual nitrogen coordination sites) synergistically interacts with the cobalt center to form a spatially stable complex. Studies have shown that this series of imidazole-cobalt complexes exhibits excellent catalytic performance in the catalytic oxidation of dimethylnaphthalene.

[0038] 2) The imidazole cobalt complexes provided by this invention exhibit catalytic performance (especially for the catalytic oxidation of dimethylnaphthalene) that can be significantly altered by changes in substituents. By controlling the type of substituents, highly efficient catalytic oxidation of dimethylnaphthalene can be achieved. Under optimal reaction conditions, the conversion rate of dimethylnaphthalene can reach 85.6%.

[0039] 3) The raw materials for imidazole cobalt complexes provided by this invention are inexpensive, readily available, safe and low in toxicity; the reaction synthesis process is simple, the central metal is inexpensive and readily available, and it is easy to realize industrial production.

[0040] In summary, the imidazole cobalt complexes of this invention have advantages such as stable spatial configuration, mild reaction conditions, and high catalytic performance, and have good application prospects and large-scale promotion potential in the field of catalytic oxidation of dimethylnaphthalene. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the molecular structure of the methylimidazolium cobalt complex obtained from a single crystal in Example 1;

[0042] Figure 2 This is a schematic diagram of the molecular structure of the ethylimidazolium cobalt complex obtained from a single crystal in Example 2;

[0043] Figure 3 This is a schematic diagram of the molecular structure of the isopropyl imidazolium cobalt complex obtained from a single crystal in Example 3;

[0044] Figure 4 This is a schematic diagram of the molecular structure of the benzylimidazolium cobalt complex obtained from a single crystal in Example 4;

[0045] Figure 5 The HPLC chromatogram shows the oxidation of dimethylnaphthalene under the catalytic conditions of Example 8. Detailed Implementation

[0046] The present invention will be further described below with reference to embodiments. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0047] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0048] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0049] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0050] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0051] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0052] In this instruction manual, when "room temperature" or "room temperature" is used, the temperature can be 15-25℃.

[0053] Unless otherwise specified, all reagents or instruments used in this instruction manual are commercially available products.

[0054] Example 1:

[0055] This embodiment discloses an imidazole cobalt complex—methylimidazolium cobalt complex, the structural formula of which is as follows:

[0056]

[0057] The preparation method of the methylimidazolium cobalt complex includes the following steps:

[0058] Add 2.0 mL of methylimidazole to 15 mL of petroleum ether. After the methylimidazole dissolves in the petroleum ether, add 1.1 mL of 1,2-dibromoethane. Reflux and stir at 60 °C for 2 h. Filter, and purify the precipitate by recrystallization with 20 mL of CH₂Cl₂. Add the purified crystals and 5.56 g of cobalt chloride hexahydrate to 10 mL of acetonitrile solvent. Add a stir bar and reflux and stir at 60 °C for 3 h in a water bath. After the reaction is complete, allow to stand and cool, filter under reduced pressure to obtain the crude product, recrystallize with 25 mL of CH₂Cl₂, filter under reduced pressure, evaporate the solvent to obtain the pure product. Figure 1 The single-crystal analytical diagrams demonstrate the successful synthesis of the methylimidazolium cobalt complex.

[0059] Example 2:

[0060] This embodiment discloses an imidazole cobalt complex—the ethylimidazole cobalt complex, whose structural formula is as follows:

[0061]

[0062] The preparation method of the ethylimidazolium cobalt complex includes the following steps:

[0063] Take 2.0 mL of ethylimidazole and add it to 15 mL of petroleum ether. After the ethylimidazole dissolves in the petroleum ether, add 0.89 mL of 1,2-dibromoethane. Reflux and stir at 60 °C for 2 h. Filter, and purify the precipitate by recrystallization with 20 mL of CH₂Cl₂. Add 4.75 g of cobalt chloride hexahydrate and 10 mL of acetonitrile solvent to the purified crystals. Place a stir bar in a water bath and reflux and stir at 60 °C for 3 h. After the reaction is complete, allow to stand and cool, filter under reduced pressure to obtain the crude product, recrystallize with 25 mL of CH₂Cl₂, filter under reduced pressure, evaporate the solvent, and obtain the pure product. Figure 2 The single-crystal analytical diagrams demonstrate the successful synthesis of the ethylimidazolium cobalt complex.

[0064] Example 3:

[0065] This embodiment discloses an imidazole cobalt complex—isopropylimidazolium cobalt complex, the structural formula of which is as follows:

[0066]

[0067] The preparation method of the isopropyl imidazolium cobalt complex includes the following steps:

[0068] Take 2.0 mL of isopropyl imidazole and add it to 15 mL of petroleum ether. After the isopropyl imidazole dissolves in the petroleum ether, add 0.76 mL of 1,2-dibromoethane. Reflux and stir at 60 °C for 2 h. Filter, and purify the precipitate by recrystallization with 20 mL of CH₂Cl₂. Add 4.14 g of cobalt chloride hexahydrate and 10 mL of acetonitrile solvent to the purified crystals. Place a stir bar in a water bath and reflux and stir at 60 °C for 3 h. After the reaction is complete, allow to stand and cool, filter under reduced pressure to obtain the crude product, recrystallize with 25 mL of CH₂Cl₂, filter under reduced pressure, evaporate the solvent, and obtain the pure product. Figure 3 The single-crystal analytical diagrams demonstrate the successful synthesis of the isopropylimidazolium cobalt complex.

[0069] Example 4:

[0070] This embodiment discloses an imidazole cobalt complex—benzylimidazolium cobalt complex, the structural formula of which is as follows:

[0071]

[0072] The preparation method of the benzylimidazolium cobalt complex includes the following steps:

[0073] Take 2.0 g of benzylimidazole and add it to 15 mL of petroleum ether. After the benzylimidazole dissolves in the petroleum ether, add 0.54 mL of 1,2-dibromoethane. Reflux and stir at 60 °C for 2 h. Filter, and purify the precipitate by recrystallization with 20 mL of CH2Cl2. Add 2.87 g of cobalt chloride hexahydrate and 10 mL of acetonitrile solvent to the purified crystals. Place a stir bar in a water bath and reflux and stir at 60 °C for 3 h. After the reaction is complete, allow to stand and cool, filter under reduced pressure to obtain the crude product, recrystallize with 25 mL of CH2Cl2, filter under reduced pressure, evaporate the solvent, and obtain the pure product. Figure 4 Single-crystal analytical diagrams demonstrate the successful synthesis of the benzylimidazolium cobalt complex.

[0074] The imidazole cobalt complexes of Examples 1-4 were applied to the catalytic oxidation of 2-methylnaphthalene, resulting in the following application examples 1-8.

[0075] Application Example 1:

[0076] This application example provides a method for the catalytic oxidation of 2-methylnaphthalene by the methylimidazolium cobalt complex prepared in Example 1 under high temperature conditions, specifically including the following steps:

[0077] 1. Selection of High Performance Liquid Chromatography Conditions

[0078] 2-Methylnaphthalene and β-menaquinone were detected using HPLC. The mobile phase was initially selected as acetonitrile / water at a volume ratio of 7:3, with a flow rate of 0.85 mL / min and a detection wavelength of 236 nm. The HPLC system, pump, detector, and incubator used were E-2659, LC-6AD, SPD-M20A 230V, and CTO-10AVP, respectively. The column type, particle size, and column length were C18-WR, 5 μm, and 4.6 × 250 mm, respectively.

[0079] 2.2-Methylnaphthalene standard curve plotting

[0080] Accurately weigh 0.0514 g of 2-methylnaphthalene standard using an electronic analytical balance, quantitatively transfer it to a 250 mL volumetric flask, dilute to volume with acetonitrile, and mix well to obtain a standard solution with a mass concentration of 205.60 μg / mL. Seal and store the solution. Then, accurately pipette different volumes of the 2-methylnaphthalene standard solution into 25 mL volumetric flasks, dilute to volume with acetonitrile, and mix well to obtain a series of standard solutions with mass concentrations of 16.45, 20.56, 25.70, 51.40, 102.80, and 205.60 μg / mL. Filter the solutions through 0.22 μm organic filter paper and analyze them by HPLC. Record the peak time and peak area for each mass concentration, and plot the 2-methylnaphthalene standard curve. The linear equation is y = 19371x + 88940, with a correlation coefficient of 0.9990.

[0081] 3. Plotting the standard curve for β-menaquinone

[0082] 0.0273 g of β-menaquinone standard was accurately weighed using an electronic analytical balance and quantitatively transferred to a 250 mL volumetric flask. The solution was diluted to volume with acetonitrile and shaken well to obtain a standard solution with a mass concentration of 109.20 μg / mL. This solution was then sealed and stored. Different volumes of 2-methylnaphthalene standard solution were then accurately pipetted into 25 mL volumetric flasks and diluted to volume with acetonitrile. This yielded a series of standard solutions with mass concentrations of 6.825, 13.65, 27.30, 54.60, and 109.2 μg / mL. The solutions were filtered through 0.22 μm organic filter paper and analyzed by HPLC. The peak times and peak areas for the corresponding mass concentrations were recorded, and a standard curve for β-menaquinone was plotted. The linear equation was y = 108862x + 521, with a correlation coefficient of 0.9993.

[0083] 1. Catalytic performance evaluation of methylimidazolium cobalt complex

[0084] Add 0.1 g of 2-methylnaphthalene, 10 mL of acetonitrile solvent, and 0.01 g of methylimidazolium cobalt complex. Set the magnetic stirrer temperature to 80 °C and add 2 mL of 30% hydrogen peroxide solution dropwise over 5 min using a constant pressure separatory funnel. Let the reaction proceed for 2 h until the reaction is complete. After cooling and standing, take a 100 mL clean conical flask and a regular funnel, filter the solution, and quantitatively transfer it to a 50 mL clean volumetric flask. Make up to volume with acetonitrile solvent. Accurately transfer 1 mL of the solution and dilute it 50 times with acetonitrile solvent for HPLC analysis.

[0085] In this application example, the conversion rate of dimethylnaphthalene was 48.6%.

[0086] Application Example 2:

[0087] This application example provides a method for the catalytic oxidation of 2-methylnaphthalene using the ethylimidazolium cobalt complex prepared in Example 2 under high temperature conditions, specifically including the following steps:

[0088] The selection of high performance liquid chromatography conditions, the preparation of the 2-methylnaphthalene standard curve, and the preparation of the β-menaquinone standard curve are the same as in Application Example 1.

[0089] The catalytic performance of the ethylimidazolium cobalt complex was investigated as follows: 0.1 g of 2-methylnaphthalene was added, followed by 10 mL of acetonitrile solvent and 0.01 g of the ethylimidazolium cobalt complex. The magnetic stirrer was set to 80 °C. 2 mL of 30% hydrogen peroxide solution was added dropwise over 5 min using a constant pressure separatory funnel. The reaction was allowed to proceed for 2 h. After complete reaction, the mixture was cooled and allowed to stand. A 100 mL clean, dry conical flask and a regular funnel were used for filtration. The solution was quantitatively transferred to a 50 mL clean, dry volumetric flask and diluted to volume with acetonitrile solvent. 1 mL of the solution was accurately transferred and diluted 50 times with acetonitrile solvent for HPLC analysis.

[0090] In this application example, the conversion rate of dimethylnaphthalene was 54.7%.

[0091] Application Example 3:

[0092] This application example provides a method for the catalytic oxidation of 2-methylnaphthalene using the isopropyl imidazolium cobalt complex prepared in Example 3 under high temperature conditions, specifically including the following steps:

[0093] The selection of high performance liquid chromatography conditions, the preparation of the 2-methylnaphthalene standard curve, and the preparation of the β-menaquinone standard curve are the same as in Application Example 1.

[0094] The catalytic performance of the isopropylimidazolium cobalt complex was investigated as follows: 0.1 g of 2-methylnaphthalene was added, followed by 10 mL of acetonitrile solvent and 0.01 g of the isopropylimidazolium cobalt complex. The magnetic stirrer was set to 80 °C. 2 mL of 30% hydrogen peroxide solution was added dropwise over 5 min using a constant pressure separatory funnel. The reaction was allowed to proceed for 2 h. After complete reaction, the mixture was cooled and allowed to stand. A 100 mL clean, dry conical flask and a regular funnel were used for filtration. The solution was quantitatively transferred to a 50 mL clean, dry volumetric flask and diluted to volume with acetonitrile solvent. 1 mL of the solution was accurately transferred and diluted 50 times with acetonitrile solvent for HPLC analysis.

[0095] In this application example, the conversion rate of dimethylnaphthalene was 53.3%.

[0096] Application Example 4:

[0097] This application example provides a method for the catalytic oxidation of 2-methylnaphthalene by the benzylimidazolium cobalt complex prepared in Example 4 under high temperature conditions, specifically including the following steps:

[0098] The selection of high performance liquid chromatography conditions, the preparation of the 2-methylnaphthalene standard curve, and the preparation of the β-menaquinone standard curve are the same as in Application Example 1.

[0099] The catalytic performance of the benzylimidazolium cobalt complex was investigated as follows: 0.1 g of 2-methylnaphthalene was added, followed by 10 mL of acetonitrile solvent and 0.01 g of the benzylimidazolium cobalt complex. The magnetic stirrer was set to 80 °C. 2 mL of 30% hydrogen peroxide solution was added dropwise over 5 min using a constant pressure separatory funnel. The reaction was allowed to proceed for 2 h. After complete reaction, the mixture was cooled and allowed to stand. A 100 mL clean, dry conical flask and a regular funnel were used for filtration. The solution was quantitatively transferred to a 50 mL clean, dry volumetric flask and diluted to volume with acetonitrile solvent. 1 mL of the solution was accurately transferred and diluted 50 times with acetonitrile solvent for HPLC analysis.

[0100] In this application example, the conversion rate of dimethylnaphthalene was 65.1%.

[0101] Application Example 5:

[0102] This application example provides a method for the catalytic oxidation of 2-methylnaphthalene using the benzylimidazolium cobalt complex prepared in Example 4 with different amounts of catalyst, specifically including the following steps:

[0103] The selection of high performance liquid chromatography conditions, the preparation of the 2-methylnaphthalene standard curve, and the preparation of the β-menaquinone standard curve are the same as in Application Example 1.

[0104] The procedure for investigating the effect of the amount of benzylimidazolium cobalt complex on catalytic performance is as follows: Take three dry and clean three-necked flasks, add 0.1 g of 2-methylnaphthalene and 10 mL of acetonitrile solvent to each flask, and weigh out 0.01 g, 0.02 g, and 0.03 g of benzylimidazolium cobalt complex respectively. Set the temperature of the magnetic stirrer to 80℃, and add 2 mL of 30% hydrogen peroxide solution dropwise over 5 min using a constant pressure separatory funnel. After the reaction is complete for 2 h, cool and let stand. Take 100 mL of dry and clean conical flask and ordinary funnel, filter, and quantitatively transfer to 50 mL of dry and clean volumetric flask. Make up to volume with acetonitrile solvent, accurately transfer 1 mL of solution, dilute 50 times with acetonitrile solvent, and analyze by HPLC.

[0105] In this application example, the conversion rate of 2-methylnaphthalene was 75.0% when the catalyst dosage was 0.01g; 79.1% when the catalyst dosage was 0.02g; and 77.8% when the catalyst dosage was 0.03g.

[0106] Application Example 6:

[0107] This application example provides a method for catalytic oxidation of 2-methylnaphthalene using the benzylimidazolium cobalt complex prepared in Example 4 with different amounts of hydrogen peroxide as the oxidant, specifically including the following steps:

[0108] The selection of high performance liquid chromatography conditions, the preparation of the 2-methylnaphthalene standard curve, and the preparation of the β-menaquinone standard curve are the same as in Application Example 1.

[0109] The steps for investigating the effect of hydrogen peroxide dosage on catalytic performance are as follows: Take three dry and clean three-necked flasks, and add 0.1 g of 2-methylnaphthalene, 10 mL of acetonitrile solvent, and 0.02 g of benzylimidazolium cobalt complex to each flask. Set the magnetic stirrer temperature to 80℃, and add 2 mL, 3 mL, and 4 mL of 30% hydrogen peroxide solution respectively using a constant pressure separatory funnel at a controlled flow rate. The addition is completed within 5 min, and the reaction is allowed to proceed for 2 h. After the reaction is complete, the mixture is cooled and allowed to stand. Take 100 mL of dry and clean conical flask and a regular funnel, filter the solution, and quantitatively transfer it to a 50 mL dry and clean volumetric flask. Make up to volume with acetonitrile solvent, accurately transfer 1 mL of the solution, dilute it 50 times with acetonitrile solvent, and analyze it by HPLC.

[0110] In this application example, the conversion rate of 2-methylnaphthalene was 79.1% when the amount of oxidant was 2 mL; 80.8% when the amount of oxidant was 3 mL; and 81.3% when the amount of oxidant was 4 mL.

[0111] Application Example 7:

[0112] This application example provides a method for the catalytic oxidation of 2-methylnaphthalene using the benzylimidazolium cobalt complex prepared in Example 4 at different reaction temperatures, specifically including the following steps:

[0113] The selection of high performance liquid chromatography conditions, the preparation of the 2-methylnaphthalene standard curve, and the preparation of the β-menaquinone standard curve are the same as in Application Example 1.

[0114] The steps for investigating the effect of reaction temperature on catalytic performance are as follows: Take three dry and clean three-necked flasks, and add 0.1 g of 2-methylnaphthalene, 10 mL of acetonitrile solvent, and 0.02 g of benzylimidazolium cobalt complex to them respectively. Set the temperature of the magnetic stirrer to 70℃, 80℃, and 90℃ respectively. Use a constant pressure separatory funnel to control the flow rate and add 4 mL of 30% hydrogen peroxide solution dropwise over 5 min. After the reaction is complete for 2 h, cool and let stand. Take 100 mL of dry and clean conical flask and ordinary funnel, filter, and quantitatively transfer to 50 mL of dry and clean volumetric flask. Make up to volume with acetonitrile solvent, accurately transfer 1 mL of solution, dilute 50 times with acetonitrile solvent, and analyze by HPLC.

[0115] In this application example, the conversion rate of 2-methylnaphthalene was 79.2% at a reaction temperature of 70°C, 82.6% at a reaction temperature of 80°C, and 77.9% at a reaction temperature of 90°C.

[0116] Application Example 8:

[0117] This application example provides a method for catalytic oxidation of 2-methylnaphthalene using the benzylimidazolium cobalt complex prepared in Example 4 at different reaction times, specifically including the following steps:

[0118] The selection of high performance liquid chromatography conditions, the preparation of the 2-methylnaphthalene standard curve, and the preparation of the β-menaquinone standard curve are the same as in Application Example 1.

[0119] The steps for investigating the effect of reaction time on catalytic performance are as follows: Take three dry and clean three-necked flasks, and add 0.1 g of 2-methylnaphthalene, 10 mL of acetonitrile solvent, and 0.02 g of benzylimidazolium cobalt complex to each flask. Set the temperature of the magnetic stirrer to 80℃. Use a constant pressure separatory funnel to control the flow rate and add 4 mL of 30% hydrogen peroxide solution dropwise over 5 min. Set the reaction time to 2 h, 3 h, and 4 h respectively. After the reaction is complete, cool and let stand. Take 100 mL of dry and clean conical flask and ordinary funnel, filter, and quantitatively transfer to 50 mL of dry and clean volumetric flask. Make up to volume with acetonitrile solvent. Accurately transfer 1 mL of solution, dilute 50 times with acetonitrile solvent, and analyze by HPLC.

[0120] In this application example, the conversion rate of 2-methylnaphthalene was 79.1% when the reaction time was 2 hours; 83.2% when the reaction time was 3 hours; and 85.9% when the reaction time was 4 hours.

[0121] Application Example 8 shows that when the catalyst dosage is 0.02 g, the oxidant dosage is 4 mL, the reaction temperature is 80 °C, and the reaction time is 4 h, the benzylimidazolium cobalt complex exhibits the best catalytic performance, with a conversion rate of 85.9% and a separation rate of 72.14% for 2-methylnaphthalene.

[0122] like Figure 5 It is evident that, using benzylimidazolium cobalt complex as a catalyst, under optimal catalytic conditions, 2-methylnaphthalene can be catalyzed and oxidized efficiently. The conversion rate of 2-methylnaphthalene was quantified as 85.9% by HPLC-DAD method.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An imidazole cobalt complex, characterized in that, Its general formula is as follows: In Equation I, R 1 Selected from hydrogen, C1-C4 hydrocarbon groups and their derivatives, C6-C 13 One of the aryl groups and their derivatives; R 2 Selected from hydrogen, C1-C4 hydrocarbon groups and their derivatives, C6-C 13 One of the aryl groups and their derivatives; each X may be the same or different, and each is independently selected from NO3. - SO4 - or Cl - .

2. A method for preparing the imidazole cobalt complex according to claim 1, characterized in that, Includes the following steps: Step 1: Add the substituted imidazole and 1,2-dibromoethane to the first solvent, heat the mixture in a water bath to obtain a suspension, filter to obtain a precipitate, and recrystallize the precipitate to obtain crystals; Step 2: Mix the crystals and cobalt salt, add a second solvent, and heat under reflux to react; after the reaction is complete, filter, wash, and dry to obtain the imidazole cobalt complex.

3. The method for preparing the imidazole cobalt complex according to claim 2, characterized in that, The substituted imidazole is a methyl-substituted imidazole, an ethyl-substituted imidazole, an isopropyl-substituted imidazole, or a benzyl-substituted imidazole; And / or, the first solvent is petroleum ether and / or tetrahydrofuran; And / or, the molar ratio of the substituted imidazole to 1,2-dibromoethane is 1:1.5-3.

4. The method for preparing the imidazole cobalt complex according to claim 2, characterized in that, The water bath heating reaction in step 1 is carried out at a temperature of 60-80℃ for 2-4 hours.

5. The method for preparing the imidazole cobalt complex according to claim 2, characterized in that, The process of recrystallizing the precipitate to obtain crystals includes the following steps: adding the precipitate to a solvent, heating to dissolve, filtering and cooling, and recrystallizing to obtain crystals.

6. The method for preparing the imidazole cobalt complex according to claim 2, characterized in that, The cobalt salt is one or more of cobalt nitrate hexahydrate, cobalt chloride hexahydrate, and cobalt sulfate; And / or, the molar ratio of the crystal to the cobalt salt is 1:0.5-2; And / or, the second solvent is one or more of acetonitrile, methanol and ethanol.

7. The method for preparing the imidazole cobalt complex according to claim 2, characterized in that, The heating and reflux reaction temperature in step 2 is 60-80℃, and the reaction time is 1.5-6h.

8. The application of the imidazole cobalt complex of claim 1 in the field of catalytic oxidation of dimethylnaphthalene.

9. The application according to claim 8, characterized in that, The method for catalytic oxidation of dimethylnaphthalene using imidazole cobalt complexes is as follows: the catalytic oxidation of dimethylnaphthalene is carried out under normal pressure, without the need for anhydrous, oxygen-free, or inert gas protection such as nitrogen; the amount of imidazole cobalt complex used is 1%-10% of the substrate.

10. The application according to claim 9, characterized in that, The reaction requires reflux heating in a water bath at a temperature of 60-90℃ for 2-6 hours.

Images