A bifunctional heterogeneous catalyst and its preparation method and application

Abstract

The present application provides a bifunctional heterogeneous catalyst and its preparation method and application, which belongs to the technical field of polymer compounds. Amino-functionalized imidazolium ionic liquid, AIBN, etc. are synthesized to obtain polyaminovinyl imidazolium hydrobromide ionic liquid, which is deprotonated to obtain amino-modified polyvinyl imidazole, and 2,4,6-trichloro-1,3,5-triazine is added to react to obtain a bifunctional heterogeneous catalyst. The above-mentioned bifunctional heterogeneous catalyst can achieve high selectivity and high yield cyclization of epoxides.

Description

Technical Field

[0001] The present application relates to a bifunctional heterogeneous catalyst and a preparation method and application thereof, belonging to the technical field of polymer compounds. Background Art

[0002] In recent years, the use of fossil fuels has released a large amount of carbon dioxide, causing serious environmental and energy problems. The "greenhouse effect" has become a hot issue in the world, posing a potential threat to the human ecological environment, such as global warming, climate anomalies, and rising sea levels caused by melting glaciers. Among them, excessive carbon dioxide emissions are considered to be the main greenhouse gas. Therefore, it is considered a feasible method to directly use technology to develop C1 resources to deal with excess carbon dioxide in the atmosphere and obtain high value-added chemical products. Among them, the preparation of five-membered cyclic carbonates by coupling addition of carbon dioxide and epoxides is considered to be one of the most effective methods. In addition, as an atom-economical green chemical reaction, this reaction is the best choice to overcome the inert thermodynamic problem of carbon dioxide. However, the coupling reaction of carbon dioxide and epoxide is an exothermic reaction (ΔHr = –144KJ mo1 –1 ), mainly because the ternary ring opening process in epoxides is a non-spontaneous process, so the reaction requires catalyst activation. However, in order to promote the coupling reaction (or cycloaddition reaction) of epoxides and carbon dioxide, especially the efficient conversion of carbon dioxide under atmospheric pressure conditions. The development of highly active catalysts remains a huge challenge.

[0003] In addition to using metal Lewis acid sites to activate epoxides, hydrogen bond donors (such as –OH, –COOH, –NH2) are often used to activate epoxides through hydrogen bonding. In addition, hydrogen bonding can also stabilize transition states and intermediates during the catalytic reaction, thereby significantly promoting the cycloaddition reaction of carbon dioxide and epoxides. At the same time, polymers containing hydrogen bond donors and nucleophilic groups are considered to be the most promising bifunctional heterogeneous catalysts, which can play a synergistic catalytic role in CO2 cycloaddition reactions. Polyionic liquids (PILs) combine the functional properties of ionic liquids and polymers, especially the inherent nucleophilic halogen anions and polar imidazolium cations in imidazolium-based polyionic liquids, which provide a broad platform for adjusting the physicochemical properties of materials and designing effective catalytic processes, providing ideal catalytic ability for carbon dioxide cycloaddition reactions, but the above catalysts introduce corrosive metals, which have a very adverse impact on the environment. Summary of the invention

[0004] In view of this, the present application first provides a bifunctional heterogeneous catalyst, in which the organic triazine group can promote the adsorption and activation of carbon dioxide, and the hydrogen bond donor as a key active site can activate the epoxide by forming hydrogen bonds, thereby improving the catalytic activity while avoiding the negative impact of the use of corrosive metals on the environment.

[0005] Specifically, the present application is implemented through the following scheme:

[0006] A bifunctional heterogeneous catalyst with the structural formula:

[0007]

[0008] The structure of the bifunctional heterogeneous catalyst includes hydrogen bonds, hydrogen bond donors, triazine rings and imidazolium salts. The imidazolium salts and hydrogen bond donors activate epoxides through hydrogen bonds. The hydrogen bond donors also stabilize the intermediates generated during the reaction. The basic triazine ring increases the concentration of carbon dioxide around the catalytic center and activates carbon dioxide through interaction, thereby improving the catalytic activity. The organic triazine group in the bifunctional catalyst can promote the adsorption and activation of carbon dioxide, and the hydrogen bond donor, as a key active site, can activate the epoxide by forming hydrogen bonds.

[0009] The second object of the present application is to provide a method for preparing the above-mentioned bifunctional heterogeneous catalyst, comprising the following steps:

[0010] (1) Synthesis of polyaminovinyl imidazolium hydrobromide ionic liquid: dissolving amino-functionalized imidazolium ionic liquid and AIBN in a methanol solution, reflux reacting at 70° C. for 24 h under a nitrogen atmosphere, cooling to room temperature after the reaction, filtering, washing, and drying to obtain polyaminovinyl imidazolium hydrobromide ionic liquid;

[0011] (2) Synthesis of polyvinyl imidazole: After the polyaminovinyl imidazole hydrobromide ionic liquid is deprotonated with an equimolar amount of NaOH aqueous solution, it is dried to obtain amino-modified polyvinyl imidazole;

[0012] (3) Synthesis of bifunctional heterogeneous catalyst: Polyvinyl imidazole was dispersed in anhydrous DMF, and an anhydrous DMF solution of 2,4,6-trichloro-1,3,5-triazine was added under N2 atmosphere. The reaction was carried out at 100°C for 12 h. After the reaction was stopped and cooled to room temperature, the mixture was filtered, rinsed, and dried to obtain a bifunctional heterogeneous catalyst.

[0013] Further, as a preference:

[0014] In step (1), the synthesis method of the amino-functionalized imidazolium hydrobromide ionic liquid is as follows: N-vinyl imidazole and 2-bromoethylamine hydrobromide are dissolved in an ethanol solution, and the mixture is refluxed at 80° C. for 12 hours under a nitrogen atmosphere to obtain the obtained ionic liquid.

[0015] In step (1), the molar ratio of the amino-functionalized imidazolium ionic liquid to AIBN is 30-35:1.

[0016] The drying temperature is 80°C.

[0017] Step (2) is drying at room temperature.

[0018] In step (3), the drying temperature is 80°C.

[0019] The above preparation method utilizes the Lewis acidic molecular characteristics of carbon dioxide to introduce basic sites into PILs to meet the effective activation of carbon dioxide. Based on this, imidazolium alkaline polyionic liquid is selected as the polymer backbone, and triazine ring is used as a cross-linking agent to functionalize the polyionic liquid to prepare a hydrogen bond donor / triazine ring cross-linked polyionic liquid bifunctional heterogeneous catalyst (Tri-PAVImBr).

[0020] The third purpose of the present application is to provide the application of the above-mentioned bifunctional heterogeneous catalyst in the cycloaddition reaction of epoxides, wherein 0.5-6 mg of bifunctional heterogeneous catalyst is added for every mole of epoxide, the carbon dioxide pressure is 0.1 MPa, the reaction temperature is 80-100°C, and the reaction time is 24-36 hours.

[0021] Further, preferably:

[0022] The epoxide is Any of .

[0023] In the above applications, the organic triazine group in the bifunctional heterogeneous catalyst can promote the adsorption and activation of carbon dioxide, and the hydrogen bond donor as a key active site can activate the epoxide by forming hydrogen bonds. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The solid state of Tri-PAVImBr in this application 13 C NMR;

[0025] Figure 2 is the gas adsorption isotherm curve of Tri-PAVImBr at 273K and 298K in this application;

[0026] Figure 3 is the isosteric heat of adsorption of CO2 (Q st );

[0027] Figure 4 TGA curves of PAVImBr and Tri-PAVImBr;

[0028] Figure 5 This is the CO2-TPD curve of Tri-PAVImBr. DETAILED DESCRIPTION

[0029] In the following examples, the reagents and experimental instruments used are shown in Table 1 and Table 2, respectively.

[0030] Table 1: Experimental reagent names, specifications and manufacturers

[0031]

[0032]

[0033] Table 2: Experimental equipment name and manufacturer

[0034]

[0035] Example 1

[0036] In this example, an amino-functionalized imidazolium cationic alkaline polyionic liquid was selected as the main chain, and a hydrogen bond donor / triazine ring functionalized polyionic liquid bifunctional heterogeneous catalyst (Tri-PAVImBr) was prepared by using a triazine ring functionalized imidazolium polyionic liquid. The specific process is as follows:

[0037] (1) Synthesis of amino-functionalized imidazolium hydrobromide ionic liquid (AVImBr·HBr): In a 250 mL round-bottom flask, N-vinylimidazole (VIm) (4.71 g, 5 mmol) and 2-bromoethylamine hydrobromide (12.28 g, 6 mmol) were dissolved in 50 mL of ethanol solution and refluxed at 80°C for 12 h under nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, and the crude product was recovered by filtration, washed three times with ethanol to remove unreacted monomers, and dried in a vacuum oven at 30°C overnight to obtain a white solid (yield: 13.3 g, 89%).

[0038] 1 H NMR (400MHz, D2O): δ9.15(N-CH=N,1H),7.79-7.63(-NCH=CH-N + ,2H),7.09(C=CH-,1H),5.77-5.40(H2=C-,2H),4.57(N + -CH2-,2H),3.52(-CH2-,2H). 13 C NMR (101MHz, D2O) δ133.23,125.91,120.75,118.23,108.17,44.50,36.51.

[0039] (2) Synthesis of polyaminovinyl imidazolium hydrobromide ionic liquid (PAVImBr·HBr): Dissolve amino-functionalized imidazolium ionic liquid (AVImBr·HBr) (10.4 g, 34.5 mmol) and AIBN (0.17 g, 1 mmol) in an appropriate amount of methanol solution and transfer to a 150 mL round-bottom flask. Reflux at 70°C for 24 h under a nitrogen atmosphere and cool to room temperature after the reaction. Collect the solid polymer by filtration, wash three times with methanol, and dry the product at 80°C overnight to obtain white solid PAVImBr·HBr (yield: 9.2 g, 92%).

[0040] 1 H NMR (400MHz, D2O): 9.58~9.33(N-CH=N,1H), 8.14~7.54(vinyl-N-CH andethyl-N-CH,2H), 4.73~4.38(N-CH2-CH2,2H), 3.83~3.53(CH2-NH2,2H), 3.53~3.38(N-CH,1H), 3.08~2.33(NC-CH2,2H).

[0041] (3) Synthesis of bifunctional heterogeneous catalyst (Tri-PAVImBr): Polyaminovinyl imidazole hydrobromide ionic liquid (9.2 g, 31 mmol) was deprotonated with an equimolar amount of NaOH aqueous solution and dried to obtain amino-modified polyvinyl imidazole PAVImBr (6.43 g). PAVImBr (3.2 g) was dispersed in anhydrous DMF and transferred to a round-bottom flask, evacuated and filled with N2. Under N2 atmosphere, an anhydrous DMF solution of 2,4,6-trichloro-1,3,5-triazine (0.85 g, 4.5 mmol) was added to the round-bottom flask. The mixture was reacted in an oil pan at 100°C for 12 h. After stopping the reaction and cooling to room temperature, the mixture was filtered, rinsed with CH2Cl2 several times, and the solid was collected. After drying, the target product Tri-PAVImBr (3.97 g) was obtained.

[0042] The above process can be expressed by the following reaction formula:

[0043]

[0044] The target product prepared by the above method was tested, and the results are as follows:

[0045] 1) Solid-state NMR carbon spectroscopy analysis ( 13 C NMR)

[0046] Through solid state 13 C NMR further analyzed the polymer skeleton. Figure 1 Shown: In solid state 13The characteristic vibration signal peaks at 40-54 ppm in the C NMR spectrum are attributed to the polymerized double bond carbon and methylene bridge. The obvious signals at 120, 125 and 133 ppm are attributed to the unsaturated -C=C- and -C=N on the imidazole ring. + The characteristic peak of -C=N- belonging to the triazine ring can be observed at 165ppm, indicating that 2,4,6-trichloro-1,3,5-triazine can form a covalent bond with the amino group. 13 C NMR spectroscopy further confirmed the successful preparation of Tri-PAVImBr.

[0047] 2) CO2 adsorption curve and isosteric adsorption heat

[0048] To study the interaction between Tri-PAVImBr and CO2, their CO2 adsorption isotherms were measured at 273 K and 298 K, respectively. The CO2 adsorption isotherms were fitted using a two-site Langmuir curve, and the isosteric heat of adsorption (Q st ),like Figure 2 , 3 As shown: At 273K and 0.1MPa CO2 pressure, the CO2 absorption of Tri-PAVImBr is 2.58cm 3 g -1 When the temperature rises to 298K, the absorption of CO2 drops to 0.95cm 3 g -1 .Q st It is usually considered a rough estimate of the interaction energy. At low CO2 coverage, the Q of Tri-PAVImBr to CO2 is st 16.5 kJ·mol -1 , indicating that there is a good interaction between it and the CO2 molecule.

[0049] 3) Thermogravimetric analysis (TGA)

[0050] The thermal stability of PAVImBr and Tri-PAVImBr was studied by thermogravimetric analysis. Figure 4 As shown: in the range of room temperature to 100°C, due to the evaporation of absorbed water, the weight loss of PAVImBr is about 10%, and that of Tri-PAVImBr is about 8%; when the temperature is further increased to about 270°C, the PAVImBr polymer skeleton begins to decompose; when the temperature continues to rise to 290°C, Tri-PAVImBr begins to decompose, and the thermal stability of the cross-linked polymer skeleton is slightly increased after the introduction of triazine rings.

[0051] 4) Carbon dioxide temperature programmed desorption analysis (CO2-TPD)

[0052] The strength of the basic sites in the bifunctional catalyst was analyzed by carbon dioxide temperature programmed desorption (CO2-TPD). Figure 5 As shown in Figure 2, two carbon dioxide desorption peaks appeared in Tri-PAVImBr at 98°C and 250°C, indicating that there are two basic sites with different basic strengths in Tri-PAVImBr, namely, the imidazole ring and the triazine ring. In addition, the triazine ring with a relatively high CO2 desorption temperature (212°C) exhibits stronger basicity than the imidazole ring with a relatively low desorption temperature (118°C). Therefore, the introduction of triazine rings with significantly increased basicity in polyionic liquids is expected to greatly improve the activity of CO2 cycloaddition reactions.

[0053] Example 2

[0054] In this example, Tri-PAVImBr prepared by the method of Example 1 was used as a catalyst. 60 mg (n (Br – ) =0.25mmol) catalyst, and then add 10mmol epichlorohydrin (ECH) into the Schlenk tube, and react at 100°C under 0.1MPa CO2 pressure for 24h. After the reaction is completed, the catalyst is separated by filtration, washed with dichloromethane, and dried at 60°C in vacuum, and then the next catalytic cycle can be continued.

[0055] Replacement Example 1

[0056] The configuration of this embodiment is the same as that of embodiment 2, except that: the catalysts used are PAVImBr-HBr, PAVImBr, Trichloro-Triazine, PAVImBr / Trichloro-Triazine (0.25 mmol PAVImBr and 0.082 mmol Trichloro-Triazine are physically mixed), and a blank group is formed with no catalyst added.

[0057] The reaction products of Example 2 and Alternative Example 1 were tested respectively. 1 H NMR was used to determine the effect of the catalyst on the reaction selectivity and conversion rate of the substrate. The results are shown in Table 3.

[0058] Table 3: Effects of different catalysts on ECH cycloaddition reaction

[0059] Serial number catalyst Conversion rate, % Selectivity, % 1 Blank group Trace - 2 PAVImBr-HBr 65.03 99 3 PAVIM 75.31 99 4 Trichloro-Triazine Trace - 5 PAVImBr / Trichloro-Triazine 79.72 99 6 Tri-PAVImBr 94.33 99 .

[0060] It can be seen from Table 3 that the highest conversion rate of ECH is 79.72% when the imidazolium salt homopolymer modified by 2-bromoethylamine and the physical blend of triazine ring are used as catalysts (sequence numbers 1-5 in Table 3). The catalytic activity is higher than that of the imidazolium salt homopolymer modified by 2-bromoethylamine as a catalyst for ECH. This is because: the electron-rich N atom in the triazine organic group has a strong interaction with CO2 and exhibits good carbon dioxide adsorption performance, thereby increasing the CO2 concentration near the PAVImBr catalyst and further promoting the cycloaddition reaction. After the imidazolium salt homopolymer modified by bromoethylamine and 2,4,6-trichloro-1,3,5-triazine are cross-linked by covalent bonds to form a cross-linked polymer (Tri-PAVImBr), the conversion rate of ECH reaches 94.33% (ie, Example 2). Compared with the physically mixed catalyst system (sequence number 5 in Table 3), the activity of the cross-linked catalyst is greatly improved. This is because the integration of multiple sites in the same skeleton is conducive to the intramolecular synergy between each site. The selectivity of the above catalysts to chloropropane cyclic carbonate is basically above 99%.

[0061] Example 3

[0062] The configuration of this embodiment is the same as that of embodiment 2, except that: the epoxide is as shown in Table 4, and the reaction is carried out at 100° C. under 0.1 MPa CO 2 pressure for 36 hours.

[0063] Table 4: Comparison of the catalytic effects of the bifunctional heterogeneous catalysts on different epoxides

[0064]

[0065] Combined with Table 4, it can be seen that when the bifunctional heterogeneous catalyst prepared in this case is used for catalytic cyclization, the highly electronegative heteroatoms existing on the side chains of epoxides such as allyl glycidyl ether, butyl glycidyl ether, phenyl glycidyl ether and methacrylate glycidyl ether can effectively promote the ring opening of epoxides, and show good reaction activity in the cycloaddition reaction, and the conversion rate can reach more than 80%. When the bifunctional heterogeneous catalyst is used to catalyze the reaction of styrene oxide, it has a good conversion rate for the conjugated aromatic substrate coordinated with the aromatic substituted epoxide, and is easier to activate, so a conversion rate of 80% can be obtained. Tri-PAVImBr has a low catalytic activity in the cycloaddition reaction of 1,2-epoxyhexane and carbon dioxide, and the conversion rate of 1,2-epoxyhexane is only 31.51%.

Claims

1. A bifunctional heterogeneous catalyst, characterized in that: Its structural formula is: 。 2. A method for preparing the bifunctional heterogeneous catalyst according to claim 1, characterized in that: The following steps are involved: (1) Synthesis of polyaminovinyl imidazolium hydrobromide ionic liquid: N-vinyl imidazole and 2-bromoethylamine hydrobromide were dissolved in ethanol solution, and refluxed at 80 °C for 12 h under nitrogen atmosphere to obtain amino-functionalized imidazolium hydrobromide ionic liquid; amino-functionalized imidazolium hydrobromide ionic liquid and AIBN were dissolved in methanol solution, and refluxed at 70 °C for 24 h under nitrogen atmosphere. After the reaction, the solution was cooled to room temperature, filtered, washed, and dried to obtain polyaminovinyl imidazolium hydrobromide ionic liquid. (2) Synthesis of polyvinyl imidazole: The polyaminovinyl imidazole hydrobromide ionic liquid is deprotonated with an equimolar amount of NaOH aqueous solution and then dried to obtain amino-modified polyvinyl imidazole; (3) Synthesis of bifunctional heterogeneous catalyst: Polyvinyl imidazole was dispersed in anhydrous DMF, and an anhydrous DMF solution of 2,4,6-trichloro-1,3,5-triazine was added under N2 atmosphere. The reaction was carried out at 100°C for 12 h. After the reaction was stopped and cooled to room temperature, the catalyst was filtered, rinsed, and dried to obtain a bifunctional heterogeneous catalyst.

3. The method for preparing a bifunctional heterogeneous catalyst according to claim 2, characterized in that: In step (1), the molar ratio of the amino-functionalized imidazolium ionic liquid to AIBN is 30-35:

1.

4. The method for preparing a bifunctional heterogeneous catalyst according to claim 2, characterized in that: In step (1), the drying temperature is 80°C.

5. The method for preparing a bifunctional heterogeneous catalyst according to claim 2, characterized in that: Step (2) is drying at room temperature.

6. The method for preparing a bifunctional heterogeneous catalyst according to claim 2, characterized in that: In step (3), the drying temperature is 80°C.

7. Use of the bifunctional heterogeneous catalyst according to claim 1 in an epoxide cycloaddition reaction, characterized in that: 0.5-6 mg of bifunctional heterogeneous catalyst is added for each mole of epoxide, the carbon dioxide pressure is 0.1 MPa, the reaction temperature is 80-100° C., and the reaction time is 24-36 h.

8. Use of a bifunctional heterogeneous catalyst according to claim 7 in an epoxide cycloaddition reaction, characterized in that: The epoxide is , , , , , Any of .

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