CN115634718A - Preparation method and application of graphene oxide/chitosan/polyvinyl alcohol composite microsphere solid-supported copper catalyst - Google Patents
Preparation method and application of graphene oxide/chitosan/polyvinyl alcohol composite microsphere solid-supported copper catalyst Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 106
- 239000010949 copper Substances 0.000 title claims abstract description 98
- 229920001661 Chitosan Polymers 0.000 title claims abstract description 72
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 61
- 229910021389 graphene Inorganic materials 0.000 title claims abstract description 56
- 229910052802 copper Inorganic materials 0.000 title claims abstract description 52
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 title claims abstract description 51
- 239000004372 Polyvinyl alcohol Substances 0.000 title claims abstract description 44
- 229920002451 polyvinyl alcohol Polymers 0.000 title claims abstract description 44
- 239000004005 microsphere Substances 0.000 title claims abstract description 39
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- 238000002360 preparation method Methods 0.000 title claims abstract description 20
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 claims abstract description 73
- 238000006243 chemical reaction Methods 0.000 claims abstract description 53
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 46
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- 238000000034 method Methods 0.000 claims abstract description 27
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- 239000000654 additive Substances 0.000 claims abstract description 19
- 238000003756 stirring Methods 0.000 claims abstract description 18
- 230000000996 additive effect Effects 0.000 claims abstract description 17
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- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 6
- HGTBZFMPHBAUCQ-KHZPMNTOSA-N cyclopentane;dicyclohexyl-[(1r)-1-(2-diphenylphosphanylcyclopentyl)ethyl]phosphane;iron Chemical compound [Fe].[CH]1[CH][CH][CH][CH]1.[C]1([C@@H](C)P(C2CCCCC2)C2CCCCC2)[CH][CH][CH][C]1P(C=1C=CC=CC=1)C1=CC=CC=C1 HGTBZFMPHBAUCQ-KHZPMNTOSA-N 0.000 claims description 6
- -1 o-methylphenyl Chemical group 0.000 claims description 6
- 239000003208 petroleum Substances 0.000 claims description 6
- 239000012286 potassium permanganate Substances 0.000 claims description 6
- 238000009210 therapy by ultrasound Methods 0.000 claims description 6
- SXRSQZLOMIGNAQ-UHFFFAOYSA-N Glutaraldehyde Chemical compound O=CCCCC=O SXRSQZLOMIGNAQ-UHFFFAOYSA-N 0.000 claims description 5
- 238000004440 column chromatography Methods 0.000 claims description 5
- 229910000365 copper sulfate Inorganic materials 0.000 claims description 5
- ARUVKPQLZAKDPS-UHFFFAOYSA-L copper(II) sulfate Chemical compound [Cu+2].[O-][S+2]([O-])([O-])[O-] ARUVKPQLZAKDPS-UHFFFAOYSA-L 0.000 claims description 5
- 229910002804 graphite Inorganic materials 0.000 claims description 5
- 239000010439 graphite Substances 0.000 claims description 5
- 125000001997 phenyl group Chemical group [H]C1=C([H])C([H])=C(*)C([H])=C1[H] 0.000 claims description 5
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- 239000000126 substance Substances 0.000 claims description 4
- 125000000094 2-phenylethyl group Chemical group [H]C1=C([H])C([H])=C(C([H])=C1[H])C([H])([H])C([H])([H])* 0.000 claims description 3
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 3
- 239000012043 crude product Substances 0.000 claims description 3
- 238000000227 grinding Methods 0.000 claims description 3
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- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 3
- 125000001544 thienyl group Chemical group 0.000 claims description 3
- BMIBJCFFZPYJHF-UHFFFAOYSA-N 2-methoxy-5-methyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine Chemical compound COC1=NC=C(C)C=C1B1OC(C)(C)C(C)(C)O1 BMIBJCFFZPYJHF-UHFFFAOYSA-N 0.000 claims description 2
- UNXISIRQWPTTSN-UHFFFAOYSA-N boron;2,3-dimethylbutane-2,3-diol Chemical compound [B].[B].CC(C)(O)C(C)(C)O UNXISIRQWPTTSN-UHFFFAOYSA-N 0.000 claims description 2
- 238000004140 cleaning Methods 0.000 claims description 2
- 238000004108 freeze drying Methods 0.000 claims description 2
- 125000003854 p-chlorophenyl group Chemical group [H]C1=C([H])C(*)=C([H])C([H])=C1Cl 0.000 claims description 2
- PTVDYARBVCBHSL-UHFFFAOYSA-N copper;hydrate Chemical compound O.[Cu] PTVDYARBVCBHSL-UHFFFAOYSA-N 0.000 claims 1
- 238000012360 testing method Methods 0.000 abstract description 16
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- 238000002474 experimental method Methods 0.000 description 4
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- 238000005481 NMR spectroscopy Methods 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 150000001639 boron compounds Chemical class 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
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- NLFBCYMMUAKCPC-KQQUZDAGSA-N ethyl (e)-3-[3-amino-2-cyano-1-[(e)-3-ethoxy-3-oxoprop-1-enyl]sulfanyl-3-oxoprop-1-enyl]sulfanylprop-2-enoate Chemical compound CCOC(=O)\C=C\SC(=C(C#N)C(N)=O)S\C=C\C(=O)OCC NLFBCYMMUAKCPC-KQQUZDAGSA-N 0.000 description 2
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- 238000000926 separation method Methods 0.000 description 2
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- 238000005303 weighing Methods 0.000 description 2
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- 229910021591 Copper(I) chloride Inorganic materials 0.000 description 1
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 description 1
- KFVREYFOFOLMIE-UHFFFAOYSA-N O.O.O.O.[Na+].[Na+].[Na+].[O-]B([O-])[O-] Chemical compound O.O.O.O.[Na+].[Na+].[Na+].[O-]B([O-])[O-] KFVREYFOFOLMIE-UHFFFAOYSA-N 0.000 description 1
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- 235000005513 chalcones Nutrition 0.000 description 1
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- MXOAEAUPQDYUQM-UHFFFAOYSA-N chlorphenesin Chemical group OCC(O)COC1=CC=C(Cl)C=C1 MXOAEAUPQDYUQM-UHFFFAOYSA-N 0.000 description 1
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- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
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Images
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/584—Recycling of catalysts
Abstract
The invention discloses a preparation method and application of a graphene oxide/chitosan/polyvinyl alcohol composite microsphere solid-supported copper catalyst, and relates to the field of graphene oxide composite materials. By using the CS-GO-PVA-Cu catalyst, toluene, ether or methanol is selected as an additive, then water is added for stirring reaction, and an asymmetric boron addition test is carried out, so that the prepared chiral organic boride has the advantages of high product yield, high enantioselectivity, small catalyst dosage, mild reaction conditions and the like; the method is carried out at room temperature, is simple and easy to operate, saves cost and is environment-friendly; and the catalytic material can be repeatedly used, and has potential industrial application value.
Description
Technical Field
The invention relates to the field of graphene oxide composite materials, in particular to a preparation method and application of a graphene oxide/chitosan/polyvinyl alcohol composite microsphere solid-supported copper catalyst.
Background
Organic borides, an important organic compound, can be easily and conveniently converted to other organic compounds. Therefore, how to construct chiral organic borides efficiently is becoming a hot spot for chemists to study. Transition metal catalyzed conjugation of α, β -unsaturated compounds has been studied by many scientists, for example, catalytic systems constructed from metals such as platinum, rhodium, copper, nickel, etc., all achieve β -position boronation of α, β -unsaturated compounds. Among them, copper-catalyzed conjugate boronization of α, β -unsaturated compounds has also been widely studied due to its mild reaction conditions, cheap and easily available catalyst, low ligand usage, good substrate universality, and the like.
To date, copper-catalyzed α -substitution of α, β -unsaturated substrates has presented serious challenges such as poor reactivity of tri-substituted olefin substrates catalyzed by existing catalytic methods, complicated enantioselective control by non-stereospecific protonation, and lack of mild neutral conditions to avoid or reduce epimerization and byproduct formation. Therefore, very few cases of success for such reactions are known. To date, work on asymmetric catalytic β -boronation of α, β unsaturated substrates has focused primarily on the use of copper catalysts under alkaline conditions. In 2014, documents (org, lett, 2014,16, 1426-1429) report that Cu catalyzes an asymmetric conjugate hydroboration reaction of a β -substituted α -dehydroamino acid derivative, cuprous chloride is used as a copper source, (S, sp) -ip-FOXAP is used as a ligand, sodium tert-butoxide is used as a base, methanol is used as a proton source, a molecular sieve is used as an additive, tetrahydrofuran is used as a solvent, and the asymmetric conjugate hydroboration reaction of a plurality of α -dehydroamino acid derivatives is realized at normal temperature. However, the reaction process in the document must be performed in an argon atmosphere, and the experimental operation is complex and the conditions are harsh; the dosage of the ligand is large, and the cost is high; a large amount of alkali is needed in the reaction process, so that the environment pollution is easily caused, and the method is not suitable for industrial production.
Therefore, it is urgently needed to develop a preparation method of chiral organic boride based on asymmetric boronation reaction of alpha, beta-unsaturated ester, which is simple, convenient, feasible, mild in condition, low in cost, green, environment-friendly and high in yield.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a preparation method and application of a graphene oxide/chitosan/polyvinyl alcohol composite microsphere solid supported copper catalyst, which solves the problems that in the prior art, a large amount of alkali is required for reaction, and environmental pollution is caused to a certain extent; the reaction needs an anhydrous and anaerobic environment and a large amount of chiral ligands, the cost is high, the catalyst cannot be recycled, and the method is not suitable for industrial production; the copper-supported composite material has the advantages that the unique compatibility and spatial structure of the copper-supported composite microsphere of Graphene Oxide (GO)/Chitosan (CS)/polyvinyl alcohol (PVA) are utilized, the specific surface area is larger, the complexing capability to copper is obviously enhanced, and the catalytic activity is higher when the chiral organic boride is prepared; in addition, the chitosan contains a large amount of amino groups, so that an alkaline environment is provided for the reaction, the catalytic reaction can be realized in pure water, no alkali is required to be added, and the concept of green chemistry is met; meanwhile, the catalyst is convenient to recycle for many times, and the method is very suitable for industrial application. Specifically, the following technique is used.
The invention also provides a preparation method of the graphene oxide/chitosan/polyvinyl alcohol composite microsphere solid supported copper catalyst, which comprises the following steps:
s1, preparing graphene oxide, adding the graphene oxide into a chitosan solution, and carrying out normal-temperature ultrasonic treatment (the common power is 50-100W, and the frequency is 28-40 kHz) for 15-60min; then adding polyvinyl alcohol and glutaraldehyde, and then carrying out normal-temperature ultrasound (parameters are the same as above) for 30-60min to prepare a first system with the mass fraction of graphene oxide being 1-5%; adding absolute ethyl alcohol into a saturated sodium hydroxide aqueous solution, uniformly mixing, and cooling to room temperature to obtain a second system; in general, the volume ratio of the saturated aqueous sodium hydroxide solution to the absolute ethyl alcohol can be selected to be 4 (3-8).
S2, dripping the first system prepared in the step S1 into the second system to form microspheres, filtering, cleaning and drying at room temperature;
and S3, soaking the product prepared in the step S2 in water at the temperature of 40-80 ℃ for 1-2h, adding an excessive copper sulfate aqueous solution, stirring for reaction, filtering to obtain filter residue, drying at the temperature of 40-60 ℃ for 12-24h, and grinding to obtain the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst.
In the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst (CS-GO-PVA-Cu catalyst for short) prepared by adopting the method, chitosan is used for Cu 2+ The adsorption of (2) is mainly based on amino group coordination, and the main adsorption reaction comprises:
protonating amino groups:
matching:
hydrogen bond adsorption:
electrostatic attraction:
when the pH of the reaction system is lower, the-NH formed by the protonation reaction is participated in 3+ A large number of Cu ions for co-absorption of Cu 2+ Of (C-NH) 2 Less, cu 2+ The complexation with chitosan is reduced.
The chitosan has excellent chelating and adsorbing capacity, can load metal to prepare the catalyst, and has good catalytic effect. Copper is a powerful catalyst, but it is almost insoluble in water and other organic solvents, so to prepare such catalysts, the chitosan must be chemically modified before it can be loaded with the metal. The graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst provided by the invention is prepared by compounding Chitosan (CS) serving as a matrix, glutaraldehyde serving as a cross-linking agent and general CS serving as a matrix material with GO, adding a small amount of polyvinyl alcohol (PVA) into the composite microsphere to perform cross-linking modification, and loading copper ions. The preparation method improves the acid resistance of the chitosan, and has stronger complexing effect on copper ions through chemical adsorption and physical adsorption. Structural morphology, thermal stability and component analysis are carried out on the prepared graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst (CS-GO-PVA-Cu catalyst) through various characterization means such as XRD, SEM and TGA, and the fact that when the GO mass fraction in the first system is 4%, the residual copper ions are the highest, and the prepared copper-loaded catalytic material has the best copper loading effect is found.
Preferably, in step S1, the preparation method of graphene oxide includes the following steps:
s11, uniformly mixing graphite pieces, concentrated phosphoric acid (mass fraction is 83-98%) and concentrated sulfuric acid (mass fraction is 98%), and quantitatively adding potassium permanganate in batches; the mass ratio of the graphite flake to the potassium permanganate is 1;
s12, stirring the mixed system prepared in the step S11 at 40-60 ℃ for 12-24H, cooling to room temperature, pouring ice blocks until the ice blocks are dissolved, and adding H into the solution system 2 O 2 And (3) washing the aqueous solution (the mass fraction is generally more than or equal to 20%) until the solution is bright yellow, and freeze-drying to obtain the solid graphene oxide.
Preferably, in step S1, the chitosan solution is prepared by mixing, stirring and dissolving chitosan with a purity of 100-200mpa.s and an acetic acid aqueous solution with a mass fraction of 6-8%, wherein the concentration of chitosan is 1-2g/mL.
Preferably, in step S3, the concentration of the copper sulfate aqueous solution is 3-5mol/L.
The invention also provides a method for further preparing the chiral organic boride by utilizing the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst prepared by any one of the preparation methods, wherein the chemical formula of the chiral organic boride is as follows:
wherein R is phenyl, p-chlorophenyl, 2-phenylethyl, o-methylphenyl or thienyl;
the preparation method comprises the following steps:
p1, taking alpha, beta-unsaturated ester (namely a compound I in the reaction formula of the step P1), pinacol diboron, graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst and ligand (R, S) -josiphos according to the mass proportion of 1 (1.2-2) (0.01-0.02) (0.01-0.03), adding an additive for pre-dissolving, adding water, mixing at room temperature, and stirring for reacting for 2.5-6h; filtering after the reaction is finished, and reserving filtrate and filter residue for later use; the additive is at least one of methanol, ether and toluene;
p2, taking the filtrate obtained in the step P1, purifying and drying to obtain pure chiral organic boride (namely a product II of the reaction formula in the step P1); and (4) washing and drying the filter residue obtained in the step (P1), and recovering the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst for recycling.
It should be noted that, in step P1, α, β -unsaturated esters are a broad class of organic compounds having the following formula:
the α, β -unsaturated ester used in step P1, except that the R group can be phenyl, P-chlorophenyl, 2-phenylethyl, o-methylphenyl, or thienyl. Corresponding chiral organic borides can be obtained by using the above method of the invention as long as the alpha, beta-unsaturated esters are used as raw materials. The additive used in step P1 is any one or more of methanol, diethyl ether or toluene. The ratio of the volume of methanol, diethyl ether or toluene to the volume of water to be subsequently added is preferably 1 (9-20).
The synthetic procedure for α, β -Unsaturated Esters can be carried out with reference to the literature (Catalytic Asymmetric catalysis of Acyclic α, β -unreacted Esters and Nitriles Angew. Chem.2008,120, 151-153); the reaction is as follows, and the product is characterized by its structure by means of Nuclear Magnetic Resonance (NMR).
Taking the case where the additive is toluene and the volume ratio of toluene to subsequently added water is 1:
in the above process of the present invention, pinacol ester diboron [ B ] is provided 2 (pin) 2 ]The intermediate and active center copper in a CS-GO-PVA-Cu catalyst generate a copper boron intermediate, the intermediate and alpha, beta-unsaturated ester generate a boron addition reaction to generate an enol copper intermediate, and the intermediate is quickly protonated under the action of proton source water to generate a boron addition product (namely chiral organic boride). In the reaction, water provides a proton source effect, so that the copper enol intermediate is subjected to a protonation process to generate a target product, and the regeneration of a catalytic material is realized.
The ligand (R, S) -josiphos used in step P1, specifically named (R) - (-) -1[ (S) -2- (diphenylphosphino) ferrocene ] ethyldicyclohexylphosphine, is a commercially available product (e.g. commercially available from ann, nagly) and has the following structural formula:
wherein Ph refers to phenyl and Cy refers to cyclohexane.
Preferably, the additive used in step P1 is toluene, and the ratio of water to toluene in the copper supported on the graphene oxide/chitosan/polyvinyl alcohol composite microspheres to copper contained in the copper supported catalyst is 0.002mmol (1.8-2) mL (0.1-0.2) mL.
It should be noted that, in the above dosage ratio, the mmol and the mL are relative concepts, and the use of 0.002mmol, (1.8-2) mL and (0.1-0.2) mL is not limited as long as the relationship between the amount of the copper in the CS-GO-PVA-Cu catalyst and the volume of the additive (toluene) is ensured to satisfy the above requirement. Therefore, the above ratio of the amounts to be actually expressed specifically means that when toluene is used as the additive in step P1, the volume ratio of toluene to (subsequently added) water is 1 (9-20), while also ensuring that the copper concentration in the CS-GO-PVA-Cu catalyst is 0.002mmol/2mL,1mmol/L, i.e., 1mM.
Preferably, in the step P1, the mass ratio of the α, β -unsaturated ester I, pinacol diborate, copper in the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst, and the ligand (R, S) -josiphos is 1.
Preferably, in step P1, the reaction time for mixing and stirring at room temperature is 3h.
Preferably, step P2 is specifically: after the reaction is finished, filtering the reaction solution after the reaction is finished, and extracting the filtrate by using ethyl acetate to obtain an organic phase containing the chiral organic boride; the organic phase is treated with anhydrous Na 2 SO 4 Drying, filtering, removing ethyl acetate, and purifying the obtained crude product by column chromatography to obtain chiral organic boride; and (4) washing and drying the filter residue obtained in the step P1, and then recovering the CS-GO-PVA-Cu catalyst.
As a conventional method, the recovery process of the CS-GO-PVA-Cu catalyst can be specifically selected as follows: and (3) washing the filter residue obtained in the step (P1) by using an organic solvent (such as petroleum ether) for three times (3X 10 mL), drying to remove the organic solvent, and recycling the CS-GO-PVA-Cu catalyst for recycling.
More preferably, in the step P2, the developing solvent used for column chromatography is petroleum ether and ethyl acetate in a volume ratio of (4-9): 1.
In order to perform the performance detection of the finally prepared chiral organic boride, the chiral organic boride (i.e. the product II of the following reaction formula) is further oxidized by the conventional method in the field to prepare the corresponding chiral hydroxy compound (i.e. the compound III of the following reaction formula), and the enantioselectivity determination is performed to determine the stereochemical configuration by comparing the optical rotation of the chiral hydroxy compound with that in the literature, wherein the reaction formula is as follows.
Compared with the prior art, the invention has the advantages that:
1. the graphene oxide/chitosan/polyvinyl alcohol composite microsphere copper-immobilized catalyst provided by the invention has good biocompatibility, is green and environment-friendly, can be used for participating in a pure water reaction, and has good effect of immobilizing metal copper and longer service life; the method is simple and convenient to operate, can be very conveniently separated from other components in a reaction system by means of a solid-liquid separation method after the reaction is finished, greatly reduces the production cost, realizes repeated recycling of the CS-GO-PVA-Cu catalyst, and can also obviously reduce various environmental pollution problems;
2. by using the graphene/chitosan/polyvinyl alcohol composite microspheres provided by the invention as a catalyst, higher conversion rate of reactants can be realized only by using lower dosage; the reaction condition is mild, no alkali is needed to be added, the reaction is carried out at room temperature, and the method is simple and easy to operate.
Drawings
FIG. 1 is an SEM spectrogram of CS powder raw material, wherein the left image is magnified 2000 times, and the right image is magnified 3000 times;
FIG. 2 is an SEM spectrogram of a CS-GO-PVA-Cu catalyst (GO content is 0 wt%), wherein the left image is magnified by 2000 times, and the right image is magnified by 3000 times;
FIG. 3 is an SEM spectrogram of a CS-GO-PVA-Cu catalyst (GO content is 2 wt%), with the left image being 2000 times and the right image being 5000 times;
FIG. 4 is an SEM spectrogram of CS-GO-PVA-Cu catalyst (GO content is 4 wt%), with a left magnification of 2000 times and a right magnification of 5000 times;
FIG. 5 is an XRD spectrum of CS-GO-PVA-Cu catalyst; in the figure, a curve is a chitosan raw material, b, c and d curves are XRD spectrograms of solid powder loaded with copper when the GO content in the first system is 0%, 2% and 4% respectively;
FIG. 6 is a TGA spectrum of a CS-GO-PVA-Cu catalyst;
FIG. 7 is a schematic representation of a CS-GO-PVA-Cu catalyst.
Detailed Description
The technical solutions of the present invention will be described clearly and completely below, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the following embodiments, if not specifically described, the preparation method of the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst (CS-GO-PVA-Cu catalyst) is performed according to the following method:
s1, preparing Graphene Oxide (GO), weighing 1.0g of Chitosan (CS), 0.18mL of acetic acid and 100mL of distilled water, putting into a flask, uniformly mixing, and magnetically stirring for 12 hours at room temperature; adding graphene oxide into a chitosan solution, and carrying out normal-temperature ultrasonic treatment (power of 50-100W and frequency of 28-40 kHz) for 20min to obtain a GO/CS homogeneous phase blending system;
then adding 50mg of polyvinyl alcohol and 1mL of glutaraldehyde, and then carrying out normal-temperature ultrasonic treatment (power of 50-100W and frequency of 28-40 kHz) for 30min to prepare a GO/CS/PVA homogeneous phase blending system (namely a first system) containing graphene oxide with a specific mass fraction;
adding 60mL of absolute ethyl alcohol, 12g of sodium hydroxide and 40mL of distilled water into a 250mL beaker, stirring until the mixture is colorless and transparent, and then cooling to room temperature to prepare a second system;
s2, dropwise adding the first system prepared in the step S1 into the second system by using a syringe with the volume of 5mL to form microspheres; filtering, washing the microspheres with anhydrous ethanol for three times, then washing with distilled water for three times, and drying at room temperature;
s3, adding the product prepared in the step S2 into a 100mL flask filled with 15mL of distilled water, soaking at 50 ℃ for 1h, adding an excessive copper sulfate aqueous solution (prepared from 1g of copper sulfate pentahydrate and 10mL of distilled water), stirring and reacting for 6h, and adsorbing copper ions; and finally, filtering and separating filter residues, washing the filter residues with distilled water to remove free copper ions and sulfate ions, drying the filter residues for 12 hours at 50 ℃, and grinding the dried filter residues to obtain the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst.
The preparation method of the graphene oxide used in the step S1 comprises the following steps:
s11, uniformly mixing 4.0g of graphite flake, 35mL of concentrated phosphoric acid (98% in mass fraction) and 350mL of concentrated sulfuric acid (98% in mass fraction), adding 5g of potassium permanganate every 10min for 4 times, namely adding 20g of potassium permanganate;
s12, magnetically stirring the mixed system prepared in the step S11 at a constant temperature of 50 ℃ for 12 hours, cooling to room temperature, pouring ice blocks until the ice blocks are dissolved, and adding H with the mass fraction of 30% into the solution system 2 O 2 And (3) washing and drying the aqueous solution until the solution is bright yellow to obtain solid Graphene Oxide (GO). H 2 O 2 The amount of aqueous solution added was such that the final solution was bright yellow.
Test example 1: influence of content of graphene oxide in first system on performance of CS-GO-PVA-Cu catalyst
Two groups of CS-GO-PVA-Cu catalysts are prepared, and the differences are as follows: in the first system prepared in the step S1, the mass fractions of the graphene oxide are respectively 2wt% and 4wt%, and are respectively recorded as a first test group and a second test group.
In addition, a CS powder raw material and a catalyst without any graphene oxide (namely a CS-PVA-Cu catalyst) are taken as a control group and a control group. The only difference of the specific preparation method is that the step S1 specifically comprises the following steps: weighing 1.0g of Chitosan (CS), 0.18mL of acetic acid and 100mL of distilled water, putting into a flask, uniformly mixing, and magnetically stirring at room temperature for 12h; then adding 50mg of polyvinyl alcohol and 1mL of glutaraldehyde, and carrying out ultrasonic treatment at normal temperature for 30min to prepare a CS/PVA homogeneous blending system without graphene oxide;
60mL of absolute ethanol, 12g of sodium hydroxide and 40mL of distilled water were added to a 250mL beaker, stirred until colorless and transparent, and then cooled to room temperature, to prepare a second system. Subsequent processes such as preparation of microspheres and the like are kept unchanged, and finally the CS-PVA-Cu catalyst used for comparison is prepared.
By comparing the SEM characterization patterns of the CS powder raw material (figure 1) and the CS-PVA-Cu catalyst without GO (figure 2); an SEM characterization of the CS-GO-PVA-Cu catalyst with 2wt% GO (FIG. 3), and an SEM characterization of the CS-GO-PVA-Cu catalyst with 4wt% GO (FIG. 4), it can be found that:
(1) In fig. 1, the phases of the CS powder raw materials of the control group formed at the operating voltage of 5kv and the magnification of 500 and 5000 times, the chitosan powder was in a flat state.
(2) In FIG. 2, the phases of the CS-PVA-Cu catalyst powders of the control group at a working voltage of 5kv and a magnification of 2000 and 5000 times without GO are slightly coarser than those of the chitosan raw material; the surface has few attached micro particles, which shows that the copper ion loading is successful, but the loading effect is poor.
(3) In fig. 3, when GO content of the first system was 2%, the phases formed by solid powders of CS-GO-PVA-Cu catalyst of one experimental group at working voltage of 5kv and magnification of 2000 and 5000 times were significantly coarser than the chitosan feedstock; the surface adhesion of the fine particles was slightly larger than that of FIG. 2, and it was demonstrated that the copper ion loading was successful, but the loading effect was general.
(4) In fig. 4, when GO content of the first system is 4%, phases formed by solid powders of CS-GO-PVA-Cu catalysts of the experimental two groups at a working voltage of 5kv and a magnification of 2000 and 5000 times are significantly coarse compared to chitosan raw material; compared with the figure 2, the surface has more attached micro particles, which indicates that the copper ion loading is successful; by comparison, the chitosan surface white particles are successfully loaded with copper, and the loading effect is optimal.
As shown in fig. 5, by comparing the XRD characterization patterns of the products of the test group one, group two and the control group one, group two, it can be found that: compared with chitosan powder, the diffraction peaks of graphene/chitosan/polyvinyl alcohol copper-loaded catalytic material at the same positions are relatively low and wide as shown by XRD curves b-d, because hydrogen bonds in molecules are changed after the material is complexed with copper, the crystallization performance of the material is weakened, and the success of loading bivalent copper is shown. The d curve (two experimental groups) has the highest GO content, so that excessive GO can be coordinated with copper ions, and more sharp crystallization peaks appear, so that the effect of loading copper on CS-GO-PVA-Cu-2 is relatively good.
As shown in fig. 6, by comparing the TGA characterization profiles of the products of test one, two and control one, two groups it can be found that: the CS-GO-PVA-Cu catalyst in the test group and the test group has two weight losses probably in the range from room temperature to 700 ℃, the first weight loss at 30-100 ℃ is caused by the separation of water molecules from the body, and the second weight loss at 200-400 ℃ is the oxidative degradation of the macromolecular chain skeleton of the polymer. The highest residual copper ion in the CS-GO-PVA-Cu catalysts prepared by the two groups of experiments proves that the loaded copper content in the CS-GO-PVA-Cu catalysts prepared finally is the highest when the GO mass fraction in the first system is 4%.
Test example 2: performance study of organic boride prepared by CS-GO-PVA-Cu catalyst
The specific preparation method of the organic boride comprises the following steps:
p1, taking 41mg chalcone (compound I) and 60mg B2 (pin) 2 5mg of CS-GO-PVA-Cu catalyst prepared in the experiment example 1 in two groups and 5.0mg of ligand (R, S) -josiphos, wherein the four substances are added into 0.2mL of toluene for pre-dissolving, and then 1.8mL of distilled water is added and stirred for 3 hours at room temperature, so that asymmetric boronation reaction of alpha, beta-unsaturated ester is carried out, and the reaction equation is as follows:
wherein R is phenyl;
filtering after the reaction is finished, and reserving filtrate and filter residue for later use;
and P2, taking the filtrate obtained in the step P1, purifying and drying to obtain pure chiral organic boride (product II), wherein the specific method comprises the following steps: after the reaction is finished, filtering the reaction solution, extracting the filtrate for three times (3X 10 mL) by using ethyl acetate to obtain an organic phase containing the chiral organic boride; the organic phase is treated with anhydrous Na 2 SO 4 Drying, filtering, rotary steaming, removing redundant ethyl acetate, and purifying the obtained crude product by column chromatography to obtain chiral organic boride; washing the filter residue obtained in the step P1 with petroleum ether for three times (3X 10 mL), drying to remove the petroleum ether, and recovering the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst for recycling;
the chiral organic boron compound (product II) obtained in the step P2 is further converted into a corresponding chiral hydroxyl compound (compound III) through oxidation, and the chiral hydroxyl compound is used for determining enantioselectivity and determining stereochemical configuration. The specific method comprises the following steps: adding 244mg of sodium borate tetrahydrate and 5mL of a mixed solvent containing tetrahydrofuran and water into the chiral organic boride obtained in the step P2, wherein the volume ratio of the tetrahydrofuran to the distilled water is 3; after 4 hours of reaction, the whole reaction system was filtered and extracted three times with ethyl acetate (3X 10 mL), the organic phase was separated and then purified with anhydrous Na 2 SO 4 Drying, filtering and rotary evaporating to remove solvent. Purifying the residue by using a petroleum ether/ethyl acetate mixed solvent (volume ratio is 5; the reaction formula is as follows:
1. effect of different additives on the boron addition reaction in step P1
Preparing a CS-GO-PVA-Cu catalyst by using the two experimental methods of the experimental example 1, and preparing corresponding chiral organic boride according to the methods, wherein the stirring reaction time of the step P1 is 3 hours; the only difference is that: the additives used in step P1 were 0.2mL of methanol, ether, toluene, acetone, respectively, and the amount of distilled water added subsequently was 1.8mL. In addition, a control group of 2mL of distilled water without any additive was used. The yield and enantioselectivity (expressed in ee value) of the finally prepared chiral organic boride are shown in the following table 1.
TABLE 1 results of investigation of the influence of different solvents on the boron addition reaction
From Table 1 above, it can be seen that when the reaction time is 3 hours and the amount of catalyst is 5mg, the effect of the change in the reaction solvent on the yield and the enantioselectivity (ee) is significant. When toluene and water are used as solvents, the yield and the ee value both reach over 90 percent, which indicates that the reaction effect is good; when methanol and water, ether and water are used as solvents, the yield and the ee value are both more than 80 percent, which indicates that the reaction effect is good; when only distilled water is added, although the ee value reaches more than 80 percent, the yield is low and the conversion effect is poor; when acetone and water are used as solvents, the yield and ee value are both low. This indicates that toluene and water are the best reaction solvents for the five aqueous solutions tested, with the same reaction time and catalyst amount.
2. Influence of different CS-GO-PVA-Cu catalyst dosages on boron addition reaction in step P1
Preparing a CS-GO-PVA-Cu catalyst by using the method of the two groups of experiments in the experimental example 1, preparing corresponding chiral organic boride according to the method, wherein the stirring reaction time in the step P1 is 3h, the additive is 0.2mL of methylbenzene, and then adding 1.8mL of distilled water; the only difference is that: the dosages of the CS-GO-PVA-Cu catalyst added in the step P1 are 1mg, 2.5mg, 5mg and 7.5mg respectively. In addition, no CS-GO-PVA-Cu catalyst was added in step P1 as a control. The yield and enantioselectivity (expressed in ee value) of the finally prepared chiral organic boride are shown in Table 2 below.
TABLE 2 investigation results of the effect of CS-GO-PVA-Cu catalyst loading on boron addition reaction
As can be found from the above table 2, when toluene and water are used as solvents and the reaction time is 3 hours, the yield of the chiral organic boride is obviously influenced by changing the using amount of the catalyst, but the influence on the ee value is very small, and the ee values of the five tests reach more than 90%. When the catalyst is used in an amount of 0, the yield is only 37 percent; when the dosage of the catalyst is 1mg, the yield is only 43 percent; when the dosage of the catalyst is 2.5mg, the yield is only 47 percent; when the dosage of the catalyst is 5mg, the yield is 98 percent; the yield was only 98% with a catalyst amount of 7.5mg. When the amount is 5mg, the yield is not obviously improved by adding 7.5mg of the catalyst. Therefore, for economic reasons, an optimum catalyst dosage of 5mg is chosen.
3. Influence of the time of the stirring reaction on the boron addition reaction in step P1
The CS-GO-PVA-Cu catalyst was prepared using the two-group test method of test example 1, with an addition of 5mg, with the additive used in step P1 being 0.2mL of toluene, followed by 1.8mL of distilled water; the corresponding chiral organic boride is prepared according to the method, and the only difference is that: in the step P1, the reaction time after the CS-GO-PVA-Cu catalyst is added is 0h, 1h, 2h, 3h and 4h respectively. The yield and enantioselectivity (expressed in ee value) of the finally prepared chiral organic boride are shown in Table 3 below.
TABLE 3 results of investigation of the influence of reaction time on boron addition reaction
It can be seen from Table 3 that when the same amount of catalyst used was 5mg in the same solvent of 0.2mL of toluene and 1.8mL of water, the length of reaction time significantly affected the yield of organic boron compound, but the effect on the ee value was small, and the ee values of the five tests reached 90% or more. When the reaction time is 0h, the reaction does not occur; when the reaction time is 1h, the yield is only 25 percent, and the reaction is not complete; when the reaction time is 2 hours, the yield is 58 percent; when the reaction time is 3 hours, the yield is rapidly improved to 98 percent; by continuing to increase the reaction time to 4h, the yield reached 99% and almost complete conversion was achieved. The yield did not increase significantly for a reaction time of 4h relative to a reaction time of 3h. Therefore, to save time and cost, 3h was chosen as the optimal reaction time.
According to the reaction results, the optimal conditions for applying the prepared catalyst in the boron addition reaction are determined, namely 0.2mL of toluene is added as an additive, 1.8mL of distilled water is added subsequently, the reaction time is 3h, and the dosage of the catalyst is 5mg. The catalytic material is applied to boron addition reaction, under the optimal reaction condition, the yield is up to 98%, and the enantioselectivity value is also up to 95%, which shows that the catalytic effect of the graphene oxide/chitosan/polyvinyl alcohol composite copper catalyst is remarkable under the condition.
4. Influence of the number of catalyst cycles on the boron addition reaction in step P1
The CS-GO-PVA-Cu catalyst was prepared using the method of test two sets of test example 1, and the recycled catalyst was recovered in step P2 of test 2, and the addition was 5mg, the additive used in step P1 was toluene 0.2mL, followed by distilled water 1.8mL; the reaction time is 3h, and the corresponding chiral organic boride is prepared according to the method; the only difference is that: in the step P1, the CS-GO-PVA-Cu catalyst is added to be recycled in the step P2 in the test 2, the recycling times are respectively 0 time, 1 time, 2 times, 3 times, 4 times and 5 times, and the performance of the recycled catalyst is inspected. The yield and enantioselectivity (expressed in ee value) of the finally prepared chiral organic boride are shown in Table 4 below.
TABLE 4 investigation result of influence of number of catalyst cycles on boron addition reaction
As can be seen from Table 4, when 0.2mL of toluene and 1.8mL of water are used as the solvent, the same amount of the catalyst is used as 5mg, and the same reaction time is 3 hours, the number of times of recycling the catalyst has little influence on the yield and enantioselectivity of the boron addition reaction. The catalyst which is not recycled and the catalyst which is recycled for 5 times have the yield and the enantioselectivity value of more than 90 percent, and almost complete conversion is realized. The catalyst recycled and reused still has obvious catalytic effect, the performance of the recycled catalyst is good, and the purposes of recycling, saving cost and green chemistry are achieved.
The practice of the present invention has been described in detail in the foregoing detailed description, however, the present invention is not limited to the specific details in the foregoing embodiment. Within the scope of the claims and the technical idea of the invention, a number of simple modifications and changes can be made to the technical solution of the invention, and these simple modifications are within the scope of protection of the invention.
Claims (10)
1. The preparation method of the graphene oxide/chitosan/polyvinyl alcohol composite microsphere solid supported copper catalyst is characterized by comprising the following steps:
s1, preparing graphene oxide, adding the graphene oxide into a chitosan solution, and carrying out ultrasonic treatment at normal temperature for 15-60min; then adding polyvinyl alcohol and glutaraldehyde, and performing normal-temperature ultrasonic treatment for 30-60min to prepare a first system with the mass fraction of graphene oxide being 1-5%; adding absolute ethyl alcohol into a saturated sodium hydroxide aqueous solution, uniformly mixing, and cooling to room temperature to prepare a second system; the volume ratio of the saturated sodium hydroxide aqueous solution to the absolute ethyl alcohol is 4 (3-8).
S2, dripping the first system prepared in the step S1 into the second system to form microspheres, filtering, cleaning and drying at room temperature;
and S3, soaking the product prepared in the step S2 in water at the temperature of 40-80 ℃ for 1-2h, adding an excessive copper sulfate aqueous solution, stirring for reaction, filtering to obtain filter residue, drying at the temperature of 40-60 ℃ for 12-24h, and grinding to obtain the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst.
2. The method for preparing the graphene oxide/chitosan/polyvinyl alcohol composite microsphere copper-supported catalyst according to claim 1, wherein in the step S1, the method for preparing the graphene oxide comprises the following steps:
s11, uniformly mixing graphite pieces, concentrated phosphoric acid and concentrated sulfuric acid, and quantitatively adding potassium permanganate in batches; the mass ratio of the graphite flake to the potassium permanganate is 1;
s12, stirring the mixed system prepared in the step S11 at 40-60 ℃ for 12-24H, cooling to room temperature, pouring ice blocks until the ice blocks are dissolved, and adding H into the solution system 2 O 2 And (3) washing the aqueous solution until the solution is bright yellow, and freeze-drying to obtain solid graphene oxide.
3. The preparation method of the graphene oxide/chitosan/polyvinyl alcohol composite microsphere copper-supported catalyst according to claim 1, wherein in the step S1, the chitosan solution is prepared by mixing, stirring and dissolving chitosan with the purity of 100-200mpa.s and an acetic acid aqueous solution with the mass fraction of 6-8%, and the concentration of the chitosan is 1-2g/mL.
4. The method for preparing the graphene oxide/chitosan/polyvinyl alcohol composite microsphere copper-supported catalyst according to claim 1, wherein in the step S3, the concentration of the copper sulfate aqueous solution is 3-5mol/L.
5. The application of the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst prepared by the preparation method of claim 1 is characterized in that the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst is used for preparing chiral organic borides, and has the chemical formula:
wherein R is phenyl, p-chlorophenyl, 2-phenylethyl, o-methylphenyl or thienyl;
the preparation method comprises the following steps:
p1, taking alpha, beta-unsaturated ester, polyboronate pinacol ester, graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst and ligand (R, S) -josiphos according to the mass ratio of 1 (1.2-2) to 0.01-0.02 (0.01-0.03), adding an additive for pre-dissolving, adding water for mixing at room temperature, and stirring for reacting for 2.5-6 hours; filtering after the reaction is finished, and reserving filtrate and filter residue for later use; the additive is at least one of methanol, ether and toluene;
p2, taking the filtrate obtained in the step P1, purifying and drying to obtain pure chiral organic boride; and (3) washing and drying the filter residue obtained in the step P1, and recovering the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst for recycling.
6. The use of claim 5, wherein the additive used in step P1 is toluene, and the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst contains copper water, toluene =0.002mmol, (1.8-2) mL, (0.1-0.2) mL.
7. The use according to claim 5, wherein in the step P1, the mass ratio of the alpha, beta-unsaturated ester, pinacol diboron, copper in the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst, the ligand (R, S) -josiphos is 1.
8. The use according to claim 5, wherein in step P1, the water is added and mixed at room temperature and the reaction time is 3h.
9. The use according to claim 5, wherein step P2 is specifically: after the reaction is finished, filtering the reaction solution, taking the filtrate, and extracting the filtrate by using ethyl acetate to obtain an organic phase containing chiral organic boride; the organic phase is treated with anhydrous Na 2 SO 4 Drying, filtering, removing ethyl acetate, and purifying the obtained crude product by column chromatography to obtain chiral organic boride; and D, washing and drying the filter residue obtained in the step P1, and recovering the graphene oxide/chitosan/polyvinyl alcohol composite microsphere immobilized copper catalyst.
10. The use according to claim 8, characterized in that, in step P2, the developing solvent used for column chromatography is petroleum ether and ethyl acetate in the volume ratio of (4-9): 1.
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