Multi-acid-group complex catalyst for Baeyer-Villiger oxidation reaction of cyclohexanone as well as preparation method and application of multi-acid-group complex catalyst

Abstract

The invention discloses a polyacid-based complex catalyst for a cyclohexanone Baeyer-Villiger oxidation reaction as well as a preparation method and application of the polyacid-based complex catalyst. The structural formula of the complex is as follows: [Cu3 (4-atrz) 8 (H2O) 2 (PW12O40) 2], wherein the 4-atrz is 4-amino-1, 2, 4-triazole, and the 4-atrz is 4-amino-1, 2, 4-triazole. The average particle size of the complex is 0.145 [mu] m to 0.500 [mu] m. The method comprises the following steps: putting phosphotungstic acid, soluble copper salt and 4-amino-1, 2, 4-triazole into a high-pressure reaction kettle with a polytetrafluoroethylene lining, adding deionized water for dissolving, adjusting the pH value, reacting at 120 DEG C, and carrying out ball milling to obtain the copper complex. The multi-acid-group copper complex catalyst has the advantages of low cost, high catalytic reaction speed, high conversion rate and good stability, and can be used as a thermal reaction catalyst in a cyclohexanone Baeyer-Villiger oxidation reaction.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of cyclohexanone catalytic material preparation, and particularly relates to a polyacid-based complex catalyst for Baeyer-Villiger oxidation of cyclohexanone and a preparation method and application thereof. BACKGROUND

[0002] In the field of organic synthesis, Baeyer-Villiger (B-V) oxidation reaction occupies an important position, which can convert ketones into esters, and plays a key role in the production of lactones. Lactones, as key intermediates in many industries such as agricultural chemicals, dyes, fragrances, spices, pharmaceutical industries, are self-evident in importance. Taking ε-caprolactone monomer as an example, it is an important intermediate of poly-caprolactone, a drug carrier in the field of biopharmaceuticals. However, the traditional Baeyer-Villiger oxidation reaction usually uses organic peroxide as an oxidant, which has many drawbacks, such as high cost, high risk, and a large amount of waste liquid generated during the reaction, causing serious environmental pollution. With the increasing awareness of environmental protection and the demand for sustainable development, researchers urgently need to find a more green and environmentally friendly catalytic system to replace the traditional method. The Mukaiyama method uses oxygen as an oxidant and aldehyde as a sacrificial agent, which has the advantages of high safety, green environmental protection, no pollution, and high yield, and shows great attraction in industrial production, providing a new way to solve the problem of traditional Baeyer-Villiger oxidation reaction.

[0003] At present, there are many reports on Baeyer-Villiger oxidation reaction catalysts based on the Mukaiyama method, including complex, hydrotalcite, transition metal ion / metal oxide, and metal supported on various carriers. For example, WO2021047292A1 uses Fe(NO3)3 as a catalyst and oxygen as an oxidant to achieve 72% conversion of cyclohexanone. The published literature (Inorg Chem, 2024, 63, 23577) reports that the iron complex based on metal porphyrin ligand as a catalyst, with air as an oxidant, the conversion rate of cyclohexanone reaches 99%. In the published literature (Catal Commun, 2020, 139, 105985), copper nitrate and tin chloride are supported on a metal-organic framework composed of Cr 3+ and terephthalic acid to prepare Cu II -Sn IV @MIL-101(Cr) catalyst, which shows high catalytic effect for the oxidation of cyclohexanone to ε-caprolactone. However, these catalysts usually have the problems of unsatisfactory catalytic effect, high cost of catalyst, easy loss of catalytically active components, or difficulty in recycling of catalyst.

[0004] As an inorganic polynuclear anion metal-oxygen cluster with unique oxidation-reduction properties and Bronsted acidity, polyoxometalate (abbreviated as polyacid) exhibits excellent catalytic effect in various acid catalysis and oxidation catalysis reactions. In particular, the combination of polyacid and noble metal complex to form polyacid-based complex can combine the better catalytic effect of polyacid and complex, and show stronger structural stability, but the cost is high. Therefore, it is of great significance to design and synthesize a polyacid-based transition metal complex catalyst with fast catalytic speed, high conversion rate and low cost to realize the efficient oxidation of cyclohexanone to epsilon-caprolactone. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a polyacid-based complex catalyst for cyclohexanone Baeyer-Villiger oxidation reaction with fast catalytic speed, high conversion rate and low cost, and a preparation method and application thereof.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A polyacid-based complex catalyst for cyclohexanone Baeyer-Villiger oxidation reaction, the structure formula of the complex is as follows:

[0008] [Cu3(4-atrz)8(H2O)2(PW 12 O 40 )2];

[0009] Wherein, 4-atrz is 4-amino-1,2,4-triazole.

[0010] Further, the average particle size of the complex is 0.145-0.500 μm.

[0011] A preparation method of a polyacid-based complex catalyst for cyclohexanone Baeyer-Villiger oxidation reaction, the specific steps are as follows:

[0012] Phosphotungstic acid, soluble copper salt and 4-amino-1,2,4-triazole are placed in a high-pressure reaction kettle with a polytetrafluoroethylene lining in a molar ratio of 0.5:1.45:1, dissolved after adding deionized water, the pH value is adjusted to 3.6, heated, reacted at 120℃ for 4 days, cooled to room temperature, washed and dried to obtain a polyacid-based copper complex single crystal constructed by amino triazole ligand.

[0013] Further, the phosphotungstic acid is H3PW 12 O 40 , and the soluble copper salt is copper chloride hexahydrate.

[0014] Further, the amino triazole ligand structured polyacid based copper complex single crystal is ball milled in deionized water for 1 hour to obtain the amino triazole ligand structured polyacid based copper complex.

[0015] Further, the amino triazole ligand structured polyacid based copper complex single crystal is ball milled in deionized water for 1 hour to obtain the amino triazole ligand structured polyacid based copper complex.

[0016] Further preferably, the mass-volume ratio of the amino triazole ligand structured polyacid based copper complex single crystal to deionized water is 5 g / mL.

[0017] Application of a polyacid based complex catalyst as a thermal reaction catalyst in a cyclohexanone Baeyer-Villiger oxidation reaction.

[0018] Further, the temperature of the oxidation reaction is 50 DEG C.

[0019] Further, the conversion rate of the cyclohexanone Baeyer-Villiger oxidation reaction is 99%.

[0020] The beneficial effects of the present application are:

[0021] (1) The 4-amino-1,2,4-triazole with amino sites has alkaline amino sites as an organic ligand, and the polyacid based copper complex is constructed, which is low in cost; the polyacid with Bronsted acidity and redox property, the metal ion with Lewis acidity, and the organic ligand with Lewis basicity are integrated together to form a bifunctional catalytic system with acid-base catalytic active sites.

[0022] (2) Compared with the complex material, the polyacid based copper complex catalyst exhibits higher stability, fast catalytic reaction speed, short catalytic reaction time, and can be recycled multiple times without significant decay of catalytic activity compared with the polyacid catalyst. The prepared polyacid based copper complex single crystal 1-HT exhibits a cyclohexanone conversion rate of 86% and an epsilon-caprolactone selectivity of 99%. Through submicronization treatment, the crystal surface has more accessible catalytic active sites, and exhibits more excellent catalytic activity compared with traditional single crystal materials. The micronized polyacid based copper complex exhibits higher catalytic effect, the conversion rate can reach 99%, the epsilon-caprolactone selectivity can reach 99%, and excellent recyclability is exhibited. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A schematic diagram of the coordination structure of the amino triazole ligand structured polyacid based copper complex prepared in the present application (corresponding to Example 1);

[0024] Figure 2Schematic diagram of three-dimensional supramolecular structure of polyacid-based copper complex constructed by amino-triazole ligand of the present application (corresponding to Example 1);

[0025] Figure 3 Scanning electron microscope image of 1-DBM prepared by dry ball milling method of the present application (corresponding to Example 2);

[0026] Figure 4 Scanning electron microscope image of 1-SBM prepared by solvent-assisted ball milling method of the present application (corresponding to Example 3);

[0027] Figure 5 PXRD pattern of polyacid-based copper complex constructed by amino-triazole ligand of the present application (corresponding to Example 1, Example 2 and Example 3);

[0028] Figure 6 Comparison chart of catalytic effect of polyacid-based copper complex constructed by amino-triazole ligand of the present application (corresponding to Example 1, Example 2 and Example 3) on oxidation reaction of cyclohexanone B-V;

[0029] Figure 7 Conversion rate-time curve of 1-SBM of the present application (corresponding to Example 3) catalyzing oxidation reaction of cyclohexanone B-V. DETAILED DESCRIPTION

[0030] In order to make the above objectives, features and advantages of the present application more apparent and comprehensible, the specific embodiments of the present application will be described in detail below with reference to the description and examples.

[0031] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, therefore the present application is not limited by the specific embodiments disclosed below.

[0032] Example 1

[0033] (1) Synthesis of polyacid-based copper complex single crystal constructed by amino-triazole ligand

[0034] Phosphotungstic acid H3PW 12 O 40(1.45g, 0.50mmol), copper chloride hexahydrate (0.35g, 1.45mmol) and 4-amino-1, 2, 4-triazole (0.085g, 1.01mmol) were placed in a high-pressure reaction kettle with a polytetrafluoroethylene liner, dissolved in 10mL of deionized water, adjusted to pH 3.6 with a 1 mol / L sodium hydroxide solution, then warmed to 120°C for 4 days, cooled to room temperature, washed and dried to obtain blue block-shaped crystals, which were amino triazole ligand-structured polyacid-based copper complexes ([Cu3(4-atrz)8(H2O)2(PW 12 O 40 )2]) single crystals (1-HT).

[0035] Example 2

[0036] (1) Synthesis of amino triazole ligand-structured polyacid-based copper complex single crystals 12 O 40 , copper chloride hexahydrate and 4-amino-1, 2, 4-triazole and deionized water were expanded by 10 times;

[0037] (2) Synthesis of submicron amino triazole ligand-structured polyacid-based copper complexes

[0038] 5g of high-aluminum ball milling medium and 10g of the amino triazole ligand-structured polyacid-based copper complex single crystals prepared in step (1) were placed in a ball mill, dry ball milled at a speed of 300 rpm for 1 hour to obtain submicron amino triazole ligand-structured polyacid-based copper complexes (1-DBM) with an average particle size of 0.50μm.

[0039] Example 3

[0040] (1) Synthesis of amino triazole ligand-structured polyacid-based copper complex single crystals 12 O 40 , copper chloride hexahydrate and 4-amino-1, 2, 4-triazole and deionized water were expanded by 10 times;

[0041] (2) Synthesis of amino triazole ligand-structured polyacid-based copper complexes

[0042] 5g of high-aluminum ball milling medium and 10g of the amino triazole ligand-structured polyacid-based copper complex single crystals prepared in step (1) were placed in a ball mill, dry ball milled at a speed of 300 rpm for 1 hour to obtain submicron amino triazole ligand-structured polyacid-based copper complexes (1-DBM) with an average particle size of 0.50μm.

[0043] Crystal structure analysis of the amino-triazole ligand constructed polyoxometalate-based copper complex single crystal material (1-HT) prepared in Example 1

[0044] The crystal results of 1-HT prepared in Example 1 are shown in Table 1:

[0045] Table 1 X-ray single crystal diffraction structure data table of 1-HT prepared in Example 1 of the present application

[0046]

[0047] The X-ray single crystal diffraction analysis of Table 1 shows that the amino-triazole ligand constructed polyoxometalate-based copper complex single crystal material (1-HT) prepared in Example 1 has a molecular formula of C 16 H 36 Cu3N 32 O 82 P2W 24 There are two crystallographically independent Cu(II) ions in its structure (denoted as: Cu1 and Cu2), wherein Cu1 is in a five-coordinated mode and Cu2 is in a six-coordinated mode, and their coordination structures are shown in Figure 1 Cu1 is coordinated with nitrogen atoms in four ligands and one water molecule, and Cu2 is coordinated with nitrogen atoms in four ligands and two end oxygen atoms in the polyoxometalate, thereby forming a [Cu3(4-atrz)8(H2O)2(PW 12 O 40 )2] building unit; these building units are constructed into a three-dimensional supramolecular structure through hydrogen bonding between oxygen atoms in the polyoxometalate and amino groups in the ligands, and the structure is shown in Figure 2 Physicochemical characterization of the amino-triazole ligand constructed polyoxometalate-based copper complex prepared in the inventive example

[0048] Figure 3 The scanning electron microscope image of the polyoxometalate-based copper complex 1-DBM prepared in Example 2 is shown in Figure 2, and according to Figure 3 The average crystal size of 1-DBM is measured to be 0.50 μm.

[0049] Figure 4 The scanning electron microscope image of the polyoxometalate-based copper complex 1-SBM prepared in Example 3 is shown in Figure 3, and according to Figure 4 The average particle size of 1-SBM is measured to be 145 nm.

[0050] From the powder X-ray diffraction (PXRD) characterization of Figure 5 , it can be seen that the diffraction peaks of the three different sizes of amino-triazole ligand constructed polyoxometalate-based copper complexes prepared in Examples 1-3 are consistent with the diffraction peaks simulated from the single crystal data Figure 5 ), indicating that the compounds obtained by the three methods are the same substance and are pure phases.​

[0051] Third, the catalytic cyclohexanone B-V oxidation of different amino triazole ligand constructed polyacid base copper complexes prepared in the embodiments 1-3 of the present application

[0052] (I) Conversion rate and selectivity of different amino triazole ligand constructed polyacid base copper complexes

[0053] (1) The amino triazole ligand constructed polyacid base copper complex single crystal material (1-HT) prepared in the embodiment 1 of the present application catalyzes the cyclohexanone B-V oxidation reaction, which comprises the following steps:

[0054] The prepared amino triazole ligand constructed polyacid base copper complex single crystal material (1-HT) 0.75 μmol, 1,2-dichloroethane 3 mL and cyclohexanone 1 mmol are added into a reaction tube, the reaction tube is placed into a parallel reactor preheated to 50°C, 2 mmol of benzaldehyde is added into the reaction tube after heating for 10 minutes, an oxygen balloon is connected, and the reaction is carried out for 6 hours under stirring, then the reaction tube is transferred into an ice water bath for cooling to stop the reaction. The conversion rate of cyclohexanone and the selectivity of ε-caprolactone are detected by gas chromatography, and the reaction is taken as a biphenyl internal standard. The results show that the conversion rate of cyclohexanone is 86% and the selectivity of ε-caprolactone reaches 99% at this time.

[0055] (2) The submicron amino triazole ligand constructed polyacid base copper complex (1-DBM) prepared in the embodiment 2 catalyzes the cyclohexanone B-V oxidation reaction, which comprises the following steps:

[0056] The prepared submicron amino triazole ligand constructed polyacid base copper complex (1-DBM) 0.75 μmol, 1,2-dichloroethane 3 mL and cyclohexanone 1 mmol are added into a reaction tube, the reaction tube is placed into a parallel reactor preheated to 50°C, 2 mmol of benzaldehyde is added into the reaction tube after heating for 10 minutes, an oxygen balloon is connected, and the reaction is carried out for 6 hours under stirring, then the reaction tube is transferred into an ice water bath for cooling to stop the reaction. The conversion rate of cyclohexanone and the selectivity of ε-caprolactone are detected by gas chromatography, and the reaction is taken as a biphenyl internal standard. The results show that the conversion rate of cyclohexanone is 95% and the selectivity of ε-caprolactone reaches 99% at this time.

[0057] (3) The amino triazole ligand constructed polyacid base copper complex (1-SBM) prepared in the embodiment 3 catalyzes the cyclohexanone B-V oxidation reaction, which comprises the following steps:

[0058] The prepared amino-triazole ligand-constructed polyacid-based copper complex 1-SBM 0.75 μmol, 1,2-dichloroethane 3 mL and cyclohexanone 1 mmol were added into a reaction tube, the reaction tube was placed into a parallel reactor preheated to 50°C, 2 mmol of benzaldehyde was added into the reaction tube after heating for 10 minutes, an oxygen balloon was connected, and the reaction was carried out under stirring for 6 hours, then the reaction tube was transferred into an ice water bath to cool to stop the reaction, the conversion rate of cyclohexanone and the selectivity of ε-caprolactone were detected by gas chromatography, and biphenyl was used as an internal standard. The results show that the conversion rate of cyclohexanone is 99% and the selectivity of ε-caprolactone reaches 99% at this time.

[0059] Figure 6 The amino-triazole ligand-constructed polyacid-based copper complexes 1-HT, 1-DBM and 1-SBM prepared for Examples 1-3 were compared in terms of the catalytic effect on the oxidation reaction of cyclohexanone B-V. The conversion rates of cyclohexanone were 86%, 95% and 99% respectively and the selectivities of ε-caprolactone were all 99% after the reaction for 6 h at 50°C. It is shown that the catalytic effect is obviously improved with the decrease of the crystal size of the polyacid-based copper complex 1.

[0060] Figure 7 The conversion rate of cyclohexanone B-V oxidation reaction catalyzed by 1-SBM was plotted against time. The conversion rate of cyclohexanone was significantly improved to 95% in the first 4 h, and then the improvement tended to be flat. The conversion rate of cyclohexanone reached 99% when the reaction time was further extended to 6 h.

[0061] (II) Catalyst recovery

[0062] After the completion of the catalytic reaction, the catalyst was recovered and utilized. The experimental method was as follows: after the completion of the catalytic reaction, the reaction liquid containing the catalyst was centrifuged to collect the lower layer catalyst. After being washed with ethanol for three times, the recovered catalyst was dried in a vacuum oven at 80°C, and then was repeatedly used in the reaction of cyclohexanone oxidation to ε-caprolactone, and the catalytic effect was not obviously weakened.

[0063] (1) Catalytic effect of the recovered 1-HT catalyst on the reaction of cyclohexanone oxidation to ε-caprolactone

[0064] Reaction steps: the recovered 1-HT 0.75 μmol, 1,2-dichloroethane 3 mL and cyclohexanone 1 mmol were added into a reaction tube, the reaction tube was placed into a parallel reactor preheated to 50°C, 2 mmol of benzaldehyde was added into the reaction tube after heating for 10 minutes, an oxygen balloon was connected, and the reaction was carried out under stirring for 6 hours, then the reaction tube was transferred into an ice water bath to cool to stop the reaction. The conversion rate of cyclohexanone and the selectivity of ε-caprolactone were detected by gas chromatography, and biphenyl was used as an internal standard.

[0065] The catalyst used was the catalyst prepared in Example 1 which was recovered after the first time of reuse according to the above method. Gas chromatographic analysis showed that the conversion of cyclohexanone was 84% and the selectivity of ε-caprolactone was 99%. After reuse for five times, the conversion of cyclohexanone was 82% and the selectivity of ε-caprolactone was still 99%.

[0066] (2) Catalytic effect of recovered 1-DBM catalyst on the reaction of oxidation of cyclohexanone to ε-caprolactone

[0067] Reaction procedure: The recovered 1-DBM 0.75 μmol, 1,2-dichloroethane 3 mL and cyclohexanone 1 mmol were added into a reaction tube. The reaction tube was placed in a parallel reactor preheated to 50°C. After heating for ten minutes, 2 mmol of benzaldehyde was added into the reaction tube and an oxygen balloon was connected. After stirring for 6 hours, the reaction tube was transferred into an ice water bath to cool down to stop the reaction. The conversion of cyclohexanone and the selectivity of ε-caprolactone were detected by gas chromatography with biphenyl as an internal standard.

[0068] The catalyst used was the catalyst prepared in Example 2 which was recovered after the first time of reuse according to the above method. Gas chromatographic analysis showed that the conversion of cyclohexanone was 94% and the selectivity of ε-caprolactone was 99%. After reuse for five times, the conversion of cyclohexanone was 90% and the selectivity of ε-caprolactone was still 99%.

[0069] (3) Catalytic effect of recovered 1-SBM catalyst on the reaction of oxidation of cyclohexanone to ε-caprolactone

[0070] Reaction procedure: The recovered 1-DBM 0.75 μmol, 1,2-dichloroethane 3 mL and cyclohexanone 1 mmol were added into a reaction tube. The reaction tube was placed in a parallel reactor preheated to 50°C. After heating for ten minutes, 2 mmol of benzaldehyde was added into the reaction tube and an oxygen balloon was connected. After stirring for 6 hours, the reaction tube was transferred into an ice water bath to cool down to stop the reaction. The conversion of cyclohexanone and the selectivity of ε-caprolactone were detected by gas chromatography with biphenyl as an internal standard.

[0071] The catalyst used was the catalyst prepared in Example 3 which was recovered after the first time of reuse according to the above method. Gas chromatographic analysis showed that the conversion of cyclohexanone was 97% and the selectivity of ε-caprolactone was 99%. After reuse for five times, the conversion of cyclohexanone was 95% and the selectivity of ε-caprolactone was still 99%.

[0072] In summary, the polyacid-based copper complex catalyst prepared has low cost, fast catalytic reaction speed, high conversion rate and good stability. It can be used as a thermal reaction catalyst in the Baeyer-Villiger oxidation reaction of cyclohexanone. The conversion of cyclohexanone and the selectivity of ε-caprolactone can both reach 99%.

Claims

1. A polyacid-based complex catalyst for the Baeyer-Villiger oxidation of cyclohexanone, characterized in that: The structural formula of the complex is as follows: [Cu3(4-atrz)8(H2O)2(PW 12 O 40 )2]; Wherein, 4-atrz is 4-amino-1,2,4-triazole.

2. The polyacid-based complex catalyst for the Baeyer-Villiger oxidation of cyclohexanone according to claim 1, wherein: The average particle size of the complex is 0.145 μm-0.500 μm.

3. A method for preparing a polyacid-based complex catalyst for Baeyer-Villiger oxidation of cyclohexanone as claimed in claim 1 or 2, characterized in that: The specific steps are as follows: Phosphotungstic acid, soluble copper salt and 4-amino-1,2,4-triazole were placed in a polytetrafluoroethylene-lined autoclave at a molar ratio of 0.5:1.45:

1. After deionized water was added to dissolve them, the pH value was adjusted to 3.6, the temperature was raised, and the reaction was carried out at 120°C for 4 days. The reaction was then cooled to room temperature, washed and dried to obtain a single crystal of a polyacid-based copper complex constructed with an aminotriazole ligand.

4. The method for preparing a polyacid-based complex catalyst for Baeyer-Villiger oxidation of cyclohexanone according to claim 3, wherein: The phosphotungstic acid is H3PW 12 O 40 , the soluble copper salt is copper chloride hexahydrate.

5. The method for preparing a polyacid-based complex catalyst for Baeyer-Villiger oxidation of cyclohexanone according to claim 3, wherein: The single crystal of the polyoxo copper complex constructed with aminotriazole ligands was dry-milled for 1 hour to obtain a submicron polyoxo copper complex constructed with aminotriazole ligands.

6. The method for preparing a polyacid-based complex catalyst for Baeyer-Villiger oxidation of cyclohexanone according to claim 3, wherein: The polyacid-based copper complex single crystal constructed with aminotriazole ligands was added into deionized water and ball-milled for 1 hour to obtain the polyacid-based copper complex constructed with aminotriazole ligands.

7. The method for preparing a polyacid-based complex catalyst for Baeyer-Villiger oxidation of cyclohexanone according to claim 6, wherein: The mass volume ratio of the polyacid-based copper complex single crystal constructed by the aminotriazole ligand to deionized water is 5 g / mL.

8. Use of the polyacid-based complex catalyst according to claim 1 or 2 as a thermal reaction catalyst in the Baeyer-Villiger oxidation reaction of cyclohexanone.

9. The use according to claim 8, characterized in that: The temperature of the oxidation reaction is 50°C.

10. The use according to claim 8, characterized in that: The conversion rate of the Baeyer-Villiger oxidation of cyclohexanone was 99%.

Images