Preparation method and application of chiral copper heterogeneous catalyst based on attapulgite

Abstract

The invention provides a preparation method and application of an attapulgite-based chiral copper heterogeneous catalyst. The preparation method comprises the following specific preparation steps: (1) carrying out surface modification on attapulgite; (2) preparing a chiral copper catalyst solution; (3) soaking attapulgite in a chiral copper catalyst solution for catalyst loading to obtain a chiral copper heterogeneous catalyst; and (4) carrying out catalytic reaction test on the catalyst. The heterogeneous catalyst prepared by the invention can realize catalytic conversion of CO2, can greatly increase the catalytic reaction rate and the product yield, has excellent mass transfer kinetics performance and catalytic effect, and has the advantage of convenience in recovery.

Description

Technical Field

[0001] This invention relates to a method for preparing a chiral copper heterogeneous catalyst supported on attapulgite, specifically a method for preparing a heterogeneous catalyst for CO2 catalytic conversion. Background Technology

[0002] As a significant component of greenhouse gases, CO2 levels are rapidly increasing, becoming a major global issue. However, due to its non-toxicity, abundance, and sustainability, CO2 can also serve as an ideal carbon source for synthesizing high-value fuels, pharmaceuticals, or fine chemicals. Chiral compounds are often structural units in pharmaceuticals, pesticides, and fragrances, and their synthesis is relatively difficult, requiring expensive catalysts, thus making them valuable and ideal targets for CO2 conversion. However, CO2's high thermodynamic stability and kinetic inertness make its reactions challenging, resulting in limited research on asymmetric catalytic conversion of CO2 into chiral compounds. Furthermore, most catalysts currently used in the asymmetric catalytic conversion of CO2 are homogeneous catalysts, which suffer from difficulties in recovery and high costs, hindering the practical application of asymmetric catalytic conversion reactions of CO2.

[0003] Attapulgite (ATP), also known as palygorskite, is a hydrous magnesium aluminum silicate mineral with a layered, chain-like transitional structure. Its theoretical chemical formula is Si8Mg5O. 20 Attapulgite (OH)₂(OH₂)₄·4H₂O is a rare non-metallic mineral raw material. Its crystals are rod-shaped or fibrous, with a crystal structure containing both silicon-oxygen tetrahedra and longitudinal side chains. The chain units are connected by Si-O-Si bonds, forming zeolite-like channels with a cross-sectional size of 0.37 nm × 0.64 nm. Due to its rod-shaped crystal morphology, unique porous structure, and large specific surface area, attapulgite possesses excellent adsorption, purification, and decolorization properties, and is widely used in chemical, environmental protection, agricultural, and metallurgical fields. Attapulgite is inexpensive, has a large specific surface area, and is rich in surface silanol groups, making it an excellent adsorbent and adsorbent carrier. Furthermore, studies have found that there is a charge imbalance on the surface of attapulgite, which is beneficial to improving its adsorption performance. Therefore, loading chiral homogeneous catalysts onto attapulgite to prepare chiral heterogeneous catalysts can fully utilize the adsorption capacity and Lewis acid sites of attapulgite to activate CO₂, and is easy to recover, making it highly practical. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for preparing a chiral copper heterogeneous catalyst using attapulgite as a support, and its application in the asymmetric catalytic conversion reaction of CO2. This invention is based on the asymmetric conjugate addition-CO2 capture tandem reaction of α,β-unsaturated amides. The chiral copper catalyst used in this reaction is supported on attapulgite to obtain a chiral heterogeneous catalyst, which is then applied to the reaction.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted in this invention is: a method for preparing a chiral copper heterogeneous catalyst using attapulgite as a support, which can be applied to the asymmetric conjugate addition-CO2 capture tandem reaction of α,β-unsaturated amides, as shown in the following reaction formula:

[0006] The method includes the following steps:

[0007] (1) Disperse the attapulgite in hydrochloric acid solution by ultrasonication, then add surfactant, stir and soak at room temperature for 20 hours, and filter.

[0008] The surfactants mentioned therein include one of stearyl polyoxyethylene (2) ether, stearyl polyoxyethylene (10) ether, stearyl polyoxyethylene (20) ether, stearyl polyoxyethylene (21) ether, oil-based polyoxyethylene (2) ether, oil-based polyoxyethylene (10) ether, oil-based polyoxyethylene (20) ether, cetyl polyoxyethylene (2) ether, cetyl polyoxyethylene (10) ether, cetyl polyoxyethylene (20) ether, lauryl polyoxyethylene (4) ether, and lauryl polyoxyethylene (23) ether.

[0009] (2) The filtered attapulgite was calcined under vacuum to obtain activated attapulgite.

[0010] The calcination temperature is 200–400°C.

[0011] (3) Dissolve the chiral ligand and copper salt in an organic solvent and stir for 1 hour to obtain a chiral copper catalyst solution.

[0012] The organic solvent is one of acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, methyl tert-butyl ether, dioxane, dichloromethane, toluene, n-hexane, and cyclohexane.

[0013] The chiral ligand L is selected from any one of compounds L1 to L5, and its structural formula is as follows:

[0014] Furthermore, in the structural formulas of compounds L1 to L5, R 1 It is any one of methyl, ethyl, isopropyl, and phenyl; R2 R 3 All are any one of cyclohexyl, phenyl, tert-butyl, 3,5-dimethylphenyl, 2-methylphenyl, 3,5-ditrifluoromethylphenyl, and 2-furanyl; R 4 It is any one of phenyl, 4-methylphenyl, and 3,5-dimethylphenyl; R 5 It is any one of phenyl, 3,5-dimethylphenyl, and 4-methoxy-3,5-di-tert-butylphenyl.

[0015] The copper salt is any one of cuprous chloride, cuprous bromide dimethyl sulfide complex, cuprous iodide, cuprous thiophene-2-carboxylate, cuprous acetate, cuprous trifluoromethanethiol, and cuprous trifluoromethanesulfonate toluene complex.

[0016] (4) The modified attapulgite was impregnated in a chiral copper catalyst solution, stirred for 1 hour, centrifuged, and dried under reduced pressure in a vacuum oven to obtain a chiral copper heterogeneous catalyst.

[0017] (5) Under an inert gas atmosphere, chiral copper heterogeneous catalyst and (E)-N,N-dimethyl-2-butenamide were added to the reaction tube, and then an organic solvent was added and stirred to dissolve. After cooling the reaction solution to -40°C, Lewis acid was added, and after stirring for 20 min, ethyl magnesium bromide was added to carry out an asymmetric conjugate addition reaction. After reacting for 2 h, CO2 was introduced, and the temperature was raised to room temperature to continue the CO2 capture reaction. After reacting for 24 h, the reaction was quenched with 1M hydrochloric acid, and N,N-dimethyl-2-carboxy-3-methylpentanamide was obtained by extraction with methyl tert-butyl ether, vacuum distillation, and purification.

[0018] The organic solvent is selected from acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, diethyl ether, methyl tert-butyl ether, dioxane, dichloromethane, toluene, n-hexane, and cyclohexane.

[0019] The Lewis acid is any one of boron trifluoride diethyl ether complex, boron trichloride, boron tribromide, boron triiodide, trimethylchlorosilane, trimethylbromosilane, trimethyliodosilane, trimethylsilyl trifluoromethanesulfonate, tert-butyldimethylsilyltrifluoromethanesulfonate, and tert-butyldiphenylsilyltrifluoromethanesulfonate.

[0020] The beneficial effects of this invention are as follows:

[0021] In our previous research, we reported an asymmetric conjugate addition-CO2 capture tandem reaction of α,β-unsaturated amides, which can convert CO2 into α-carboxyamide compounds with continuous chiral centers (Qiuxin Zhang, et al. Green transformation of CO2 into γ-amino alcohols with continuous stereocenters[J]. Chemical Communications, 2024, 60, 2062-2065). However, this reaction has a low yield due to the low reactivity of CO2, and the catalyst is a homogeneous catalyst, making it difficult to recycle. Based on this, this invention supports the chiral ketone catalyst used in this reaction in the pores of modified attapulgite to prepare a chiral copper heterogeneous catalyst, which is then used to catalyze the asymmetric conjugate addition-CO2 capture tandem reaction of α,β-unsaturated amides, yielding α-carboxyamide compounds containing two continuous chiral centers. Compared with the prior art, this invention has the following advantages:

[0022] (1) Attapulgite has a rich pore structure. After modification, its pores are released, which can adsorb chiral copper catalysts into the pores and enhance the catalytic effect of the catalyst through the confinement effect of the pores.

[0023] (2) Attapulgite can adsorb CO2 in its pores, accelerate its mass transfer rate, and activate CO2 by utilizing its Lewis acid sites, which can greatly increase the reactivity of CO2.

[0024] (3) After the chiral copper catalyst is loaded onto attapulgite, it is easy to recycle and reuse, which can greatly reduce the cost of the catalyst and facilitate its industrial application. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention will be described in detail below, but the following embodiments do not limit the scope of protection of the present invention.

[0026] In the embodiments of the present invention, unless otherwise described, conventional experimental methods were used. The processes involved in the embodiments are all understandable and easily implemented by those skilled in the art based on the product manual or basic knowledge in the field.

[0027] In the following embodiments, all processes and methods not described in detail are conventional methods known in the art. The source, trade name, and components of the reagents used are indicated upon their first appearance unless otherwise specified. Subsequent use of the same reagents will be based on the same information as the first appearance. Unless otherwise specified, all reagents and materials involved are commercially available.

[0028] Example 1:

[0029] (1) Add 10g of attapulgite and 500mL of 10% hydrochloric acid to a round-bottom flask, sonicate for 10min, then add 500mg of stearyl polyoxyethylene (20) ether, stir and soak for 20h, and filter. After the reaction is complete, wash with ethanol and water, and finally dry in a vacuum oven at 50℃ to obtain attapulgite with dopamine coating.

[0030] (2) The filtered attapulgite clay was calcined for 4 hours under a vacuum of 50 mmHg, with the temperature controlled at around 200℃.

[0031] (3) Under argon protection, 2.06 mg (0.01 mmol) of cuprous bromide-dimethyl sulfide complex and 9.61 mg (0.015 mmol) of chiral diphosphorus ligand (R,S) were added to a dry Shrek tube. Fe )-L3(R 2 = Cyclohexyl, R 3 =Phenyl) and 10 mL of acetonitrile were stirred and reacted for 1 h to obtain a chiral copper catalyst solution.

[0032] (4) Under argon protection, 50 mg of modified attapulgite was impregnated in a chiral copper catalyst solution, stirred for 1 h, centrifuged, and dried under reduced pressure in a vacuum oven to obtain a chiral copper heterogeneous catalyst.

[0033] (5) Under argon protection, the above-mentioned chiral copper heterogeneous catalyst and 22.63 mg (0.2 mmol) (E)-N,N-dimethyl-2-butenamide were added to a dry Shrek tube, followed by 2 mL of anhydrous dichloromethane and stirring to dissolve. The reaction solution was cooled to -40°C, and 88.90 mg (0.4 mmol) of trimethyl trifluoromethanesulfonate was added. The mixture was stirred for 20 min, and then 0.133 mL of Grignard reagent ethyl magnesium bromide (0.4 mmol, 3.0 M in Et2O) was added to initiate the reaction. After 2 h of reaction, CO2 at a pressure of 1 atm was introduced into the reaction system, and the mixture was transferred to room temperature for 24 h of reaction. After the reaction was complete, 5 mL of hydrochloric acid solution (1 M) and 20 mL of methyl tert-butyl ether were added to quench the reaction. The mixture was stirred at room temperature for 10 min, and the catalyst was recovered by centrifugation. The supernatant was extracted with methyl tert-butyl ether (3*20). The organic layers were combined (mL), dried over anhydrous magnesium sulfate, filtered, and evaporated to dryness to obtain the crude product. Using a mixture of dichloromethane and methanol (volume ratio 10:1) as eluent, column chromatography was performed to obtain a colorless, oily liquid pure product in 83% yield. Spectroscopic data are as follows: 1H NMR (400MHz, DMSO-d6): δ3.44(minor)and3.42(major)(d,J=9.1Hz,1H),3.04(minor)and 3.03(major)(s,3H),2.83(s,3H),2.07-1.95(m,1H),1.54-1.41(minor)and1.38-1.26(major)(m,1H),1.17-0.97(m,1H),0.92-0.77(m,6H); 13 C NMR (100MHz, DMSO-d6): δ170.72(minor)and170.62(major),168.00(major)and 167.97(minor),53.96(major)and 53.85(minor),37.35(minor)and 37.23(major),35.34(major)and 35.33(minor),34.47(minor)and34.40(major),26.43,16.35(major)and 16.20(minor),11.34(major)and 11.29(minor); HRMS(ESI+,m / Z): theoretical value 188.1281, measured value 188.1280.

[0034] Example 2

[0035] (1) Add 10g of attapulgite clay and 500mL of 10% hydrochloric acid to a round-bottom flask, sonicate for 10min, then add 500mg of oil-based polyoxyethylene (2) ether, stir and soak for 20h, and filter.

[0036] (2) The filtered attapulgite clay was calcined for 4 hours under a vacuum of 50 mmHg, with the temperature controlled at around 400℃.

[0037] (3) Under argon protection, 1.91 mg (0.01 mmol) of cuprous thiophene-2-carboxylate and 7.60 mg (0.015 mmol) of chiral ligand (R,R)-L1 (R) were added to a dry Shrek tube. 1 =phenyl) and 10 mL of tetrahydrofuran were stirred and reacted for 1 h to prepare a chiral copper catalyst solution.

[0038] (4) Under argon protection, 50 mg of modified attapulgite was impregnated in a chiral copper catalyst solution, stirred for 1 h, centrifuged, and dried under reduced pressure in a vacuum oven to obtain a chiral copper heterogeneous catalyst.

[0039] (5) Under argon protection, the above-mentioned chiral copper heterogeneous catalyst and 22.63 mg (0.2 mmol) (E)-N,N-dimethyl-2-butenamide were added to a dry Shrek tube, followed by 2 mL of anhydrous methyl tert-butyl ether (MTBE) solvent and stirred to dissolve. The reaction solution was cooled to -40°C, and 61.24 mg (0.4 mmol) of trimethylbromosilane was added. The mixture was stirred for 20 min, and then 0.133 mL of Grignard reagent ethyl magnesium bromide (0.4 mmol, 3.0 M in Et2O) was added to initiate the reaction. After 2 h of reaction, CO2 at a pressure of 1 atm was introduced into the reaction system, and the mixture was transferred to room temperature for 24 h of reaction. After the reaction was complete, 5 mL of hydrochloric acid solution (1 M) and 20 mL of MTBE were added to quench the reaction. The mixture was stirred at room temperature for 10 min, and the catalyst was recovered by centrifugation. The supernatant was extracted with MTBE (3*20 mL). The organic layers were combined (mL), dried over anhydrous magnesium sulfate, filtered, and evaporated to dryness to obtain the crude product. Using a mixture of dichloromethane and methanol (10:1 v / v) as eluent, column chromatography was performed to obtain a colorless, oily liquid pure product in 78% yield. Spectroscopic data are as follows: 1 H NMR (400MHz, DMSO-d6): δ3.44(minor)and3.42(major)(d,J=9.1Hz,1H),3.04(minor)and 3.03(major)(s,3H),2.83(s,3H),2.07-1.95(m,1H),1.54-1.41(minor)and1.38-1.26(major)(m,1H),1.17-0.97(m,1H),0.92-0.77(m,6H); 13 C NMR (100MHz, DMSO-d6): δ170.72(minor)and170.62(major),168.00(major)and 167.97(minor),53.96(major)and 53.85(minor),37.35(minor)and 37.23(major),35.34(major)and 35.33(minor),34.47(minor)and34.40(major),26.43,16.35(major)and 16.20(minor),11.34(major)and 11.29(minor); HRMS(ESI+,m / Z): theoretical value 188.1281, measured value 188.1280.

[0040] Example 3

[0041] (1) Add 10g of attapulgite and 500mL of 10% hydrochloric acid to a round-bottom flask, sonicate for 10min, then add 500mg of lauryl polyoxyethylene (4) ether, stir and soak for 20h, and filter.

[0042] (2) The filtered attapulgite clay was calcined for 4 hours under a vacuum of 50 mmHg, with the temperature controlled at around 300℃.

[0043] (3) Under argon protection, add 0.99 mg (0.01 mmol) cuprous chloride and 10.18 mg (0.015 mmol) chiral ligand (R)-L4 (R) to a dry Shrek tube. 4 =4-methylphenyl) and 10 mL of dichloromethane were stirred and reacted for 1 h to obtain a chiral copper catalyst solution.

[0044] (4) Under argon protection, 50 mg of modified attapulgite was impregnated in a chiral copper catalyst solution, stirred for 1 h, centrifuged, and dried under reduced pressure in a vacuum oven to obtain a chiral copper heterogeneous catalyst.

[0045] (5) Under argon protection, the above-mentioned chiral copper heterogeneous catalyst and 22.63 mg (0.2 mmol) (E)-N,N-dimethyl-2-butenamide were added to a dry Shrek tube, followed by 2 mL of anhydrous toluene and stirring to dissolve. The reaction solution was cooled to -40°C, and 75.16 mg (0.4 mmol) of boron trifluoride diethyl ether complex was added. The mixture was stirred for 20 min, and then 0.133 mL of Grignard reagent ethyl magnesium bromide (0.4 mmol, 3.0 M in Et2O) was added to initiate the reaction. After 2 h of reaction, CO2 at a pressure of 1 atm was introduced into the reaction system, and the mixture was transferred to room temperature for 24 h of reaction. After the reaction was complete, 5 mL of hydrochloric acid solution (1 M) and 20 mL of methyl tert-butyl ether were added to quench the reaction. The mixture was stirred at room temperature for 10 min, and the catalyst was recovered by centrifugation. The supernatant was extracted with methyl tert-butyl ether (3*20). The organic layers were combined (mL), dried over anhydrous magnesium sulfate, filtered, and evaporated to dryness to obtain the crude product. Using a mixture of dichloromethane and methanol (volume ratio 10:1) as eluent, column chromatography was performed to obtain a colorless, oily liquid pure product in 75% yield. Spectroscopic data are as follows: 11H NMR (400 MHz, DMSO-d6): δ 3.44 (minor) and 3.42 (major) (d, J = 9.1 Hz, 1H), 3.04 (minor) and 3.03 (major) (s, 3H), 2.83 (s, 3H), 2.07 - 1.95 (m, 1H), 1.54 - 1.41 (minor) and 1.38 - 1.26 (major) (m, 1H), 1.17 - 0.97 (m, 1H), 0.92 - 0.77 (m, 6H); 13 13C NMR (100 MHz, DMSO-d6): δ 170.72 (minor) and 170.62 (major), 168.00 (major) and 167.97 (minor), 53.96 (major) and 53.85 (minor), 37.35 (minor) and 37.23 (major), 35.34 (major) and 35.33 (minor), 34.47 (minor) and 34.40 (major), 26.43, 16.35 (major) and 16.20 (minor), 11.34 (major) and 11.29 (minor); HRMS (ESI+, m / z): calcd for 188.1281, found 188.1280.

Claims

1. A process for the preparation of chiral copper heterogeneous catalyst based on attapulgite and its application, characterized in that, The method comprises the following steps: (1) dispersing attapulgite in 10% hydrochloric acid solution under ultrasonic, then adding a surfactant, stirring and soaking for 20 hours, and filtering; (2) calcining the filtered attapulgite under vacuum to obtain activated attapulgite; (3) dissolving a chiral ligand and a copper salt in an organic solvent, stirring for 1 hour to obtain a chiral copper catalyst solution; (4) immersing the modified attapulgite in the chiral copper catalyst solution, stirring for 1 hour, centrifuging, and drying in a vacuum oven under reduced pressure to obtain a chiral copper heterogeneous catalyst; (5) under an inert gas atmosphere, adding the chiral copper heterogeneous catalyst and (E)-N,N-dimethyl-2-butenamide into a reaction tube, then adding an organic solvent to stir and dissolve; cooling the reaction solution to-40℃, adding a Lewis acid, stirring for 20 minutes, adding ethyl magnesium bromide to perform asymmetric conjugate addition reaction, reacting for 2 hours, introducing CO2, increasing the temperature to room temperature to continue the CO2 capture reaction; after reacting for 24 hours, quenching the reaction with 1M hydrochloric acid, extracting with methyl tert-butyl ether, distilling under reduced pressure, and purifying to obtain N,N-dimethyl-2-carboxy-3-methyl valeramide.

2. The production method according to claim 1, characterized by, In step (1), the surfactant includes one of stearic polyoxyethylene (2) ether, stearic polyoxyethylene (10) ether, stearic polyoxyethylene (20) ether, stearic polyoxyethylene (21) ether, oleyl polyoxyethylene (2) ether, oleyl polyoxyethylene (10) ether, oleyl polyoxyethylene (20) ether, cetyl polyoxyethylene (2) ether, cetyl polyoxyethylene (10) ether, cetyl polyoxyethylene (20) ether, lauryl polyoxyethylene (4) ether, and lauryl polyoxyethylene (23) ether.

3. The preparation method according to claim 1, characterized in that, In step (2), the calcination temperature is 200-400℃.

4. The method of claim 1, wherein, In step (3), the organic solvent is one of acetonitrile, tetrahydrofuran, 2-methyl tetrahydrofuran, diethyl ether, methyl tert-butyl ether, dioxane, dichloromethane, toluene, n-hexane, and cyclohexane.

5. The preparation method according to claim 1, characterized in that, In step (3), the chiral ligand L is selected from any one of compounds L1-L5, and the structural formula is: wherein, in the structural formula of compounds L1 to L5, R 1 is any one of a methyl group, an ethyl group, an isopropyl group, and a phenyl group; R 2 , R 3 are each any one of a cyclohexyl group, a phenyl group, a tert-butyl group, a 3,5-dimethylphenyl group, a 2-methylphenyl group, a 3,5-ditrifluoromethylphenyl group, and a 2-furyl group; R 4 is any one of a phenyl group, a 4-methylphenyl group, and a 3,5-dimethylphenyl group; and R 5 is any one of a phenyl group, a 3,5-dimethylphenyl group, and a 4-methoxy-3,5-di-tert-butylphenyl group.

6. The preparation method according to claim 1, characterized in that, In step (3), the copper salt is any one of cuprous chloride, cuprous bromide dimethyl sulfide complex, cuprous iodide, cuprous thiophene-2-carboxylate, cuprous acetate, cuprous trifluoromethanethiol, and cuprous trifluoromethanesulfonate toluene complex.

7. The preparation method according to claim 1, characterized in that, In step (5), the organic solvent is one of acetonitrile, tetrahydrofuran, 2-methyl tetrahydrofuran, diethyl ether, methyl tert-butyl ether, dioxane, dichloromethane, toluene, n-hexane, and cyclohexane.

8. The method of claim 1, wherein, In step (5), the Lewis acid is any one of boron trifluoride diethyl ether complex, boron trichloride, boron tribromide, boron triiodide, trimethylchlorosilane, trimethylbromosilane, trimethyliodosilane, trimethylsilyl trifluoromethanesulfonate, tert-butyldimethylsilyl trifluoromethanesulfonate, and tert-butyldiphenylsilyl trifluoromethanesulfonate.

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