Preparation of iron-based dipolar super-crosslinked polymer and application of iron-based dipolar super-crosslinked polymer in green oxidation of alpha-hydroxyacetophenone

Abstract

The invention belongs to the field of catalytic application of high polymer materials, and discloses preparation of an iron-based dipolar super-crosslinked polymer and application of the iron-based dipolar super-crosslinked polymer in green oxidation of alpha-hydroxyacetophenone. The preparation method comprises the following steps: forming a monomer with a pyrrole ring on the basis of a precursor containing various functional groups, the multiple functional groups comprise amino groups and other functional groups, and the other functional groups are hydroxyl groups, methoxyl groups, sulfonyl groups, nitro groups, sulfoxide groups and amide; then, in a polar aprotic solvent, mixing a monomer with a cross-linking agent, adding a Lewis acid catalyst, and carrying out heating reflux; and after the reaction is finished, filtering, pickling, washing with alcohol and drying to obtain the iron-based dipolar super-crosslinked polymer. The preparation method is improved, an iron element is immobilized on HCP in situ, and the correspondingly obtained iron-based dipolar super-crosslinked polymer not only contains dipolar fragments, but also contains the iron element, and especially can realize green oxidation of alpha-hydroxyacetophenone in a green solvent in an air atmosphere.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic applications of polymer materials. More specifically, it relates to the preparation of an iron-based dipolar hypercrosslinked polymer and its application in the green oxidation of α-hydroxyacetophenone. This hypercrosslinked polymer can be used as an adjuvant to achieve the green oxidation of α-hydroxyacetophenone to 2,2-dialkoxyacetophenone. Background Art

[0002] α-Hydroxyacetophenone is a lignin model compound. Its molecule contains a carbonyl group and a hydroxyl group, and 2,2-dialkoxyacetophenone can be synthesized by oxidation. 2,2-Dialkoxyacetophenone is an important class of organic synthesis intermediates, which can be used to synthesize various drug molecules, as well as polymer materials and composite materials. These materials have wide applications in fields such as aerospace, electronics and electrical appliances, and automotive manufacturing.

[0003] Generally, 2,2-dialkoxyacetophenone is obtained by oxidative condensation from acetophenone or α-hydroxyacetophenone. In this process, an excessive amount of oxidant usually needs to be added or oxygen is activated by a transition metal complex (for example, it has been reported in the prior art that in an atmosphere of pure oxygen, with pyridine as a ligand, copper tetraacetonitrile hexafluorophosphate is used to activate oxygen). The above methods have high costs and low atom economy. At the same time, a large amount of high-boiling-point and highly toxic dipolar aprotic solvents (such as DMF, DMSO, NMP, and 1,4-dioxane; even low-boiling-point tetrahydrofuran is still toxic and harmful) need to be used, which cannot meet the basic requirements of sustainable green development.

[0004] As a novel organic porous material, hypercrosslinked polymer (HCP) exhibits unique catalytic potential due to its high specific surface area, adjustable pore structure, and excellent chemical stability. Currently, the hypercrosslinked polymer (HCP) is mainly polymerized from some aromatic ring-containing compounds and crosslinking agents such as dimethoxymethane (FDA) or p-dichlorobenzyl (PXC), and is mainly used for adsorbing gases such as methane and carbon dioxide, or introducing some catalytic active sites through post-modification for heterogeneous catalysis. Currently, there are few studies on in-situ immobilization of iron on HCP for oxidation reactions. Summary of the Invention

[0005] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide the preparation of an iron-based dipolar hypercrosslinked polymer and its application in the green oxidation of α-hydroxyacetophenone. By improving the preparation method, iron elements are in-situ immobilized on HCP, and the corresponding iron-based dipolar hypercrosslinked polymer contains both dipolar fragments and iron elements. By using the dipolar fragments and the loaded iron elements in the iron-based dipolar hypercrosslinked polymer, the green oxidation of α-hydroxyacetophenone can be achieved especially in a green solvent and under an air atmosphere.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a method for preparing an iron-based dipolar hypercrosslinked polymer, which is characterized in that a precursor containing multiple functional groups is first pretreated to form a monomer having a pyrrole ring, wherein the multiple functional groups include an amino functional group and other functional groups, and the other functional groups are at least one of a hydroxyl group, a methoxy group, a sulfone group, a nitro group, a sulfoxide group, and an amide group; then, in a polar aprotic solvent, the monomer is mixed with a crosslinking agent, and a Lewis acid catalyst is added, and a heating reflux reaction is carried out; after the reaction is completed, filtration, pickling, alcohol washing, and drying are carried out to obtain the iron-based dipolar hypercrosslinked polymer; wherein, the Lewis acid catalyst is a Lewis acid iron salt, or a mixture of a Lewis acid iron salt and a Lewis acid catalyst without iron element.

[0007] As a further preference of the present invention, in the reaction system, the molar ratio of the monomer to the crosslinking agent is 1:1 to 1:50;

[0008] When the Lewis acid catalyst is a Lewis acid iron salt, the molar ratio of the monomer to the Lewis acid iron salt is 1:1 to 1:80;

[0009] When the Lewis acid catalyst is a mixture of a Lewis acid iron salt and a Lewis acid catalyst without iron element, the molar ratio of the monomer to the Lewis acid iron salt is 1:1 to 1:40, and the molar ratio of the monomer to the Lewis acid catalyst without iron element is 1:1 to 1:40.

[0010] As a further preference of the present invention, the pretreatment is to react the precursor with 2,5-dimethoxytetrahydrofuran in an acetic acid sodium / acetic acid mixed system to obtain the monomer.

[0011] As a further preference of the present invention, the crosslinking agent is one or more of trimethyl orthoformate, p-dichlorobenzyl, p-dibromobenzyl, dimethoxymethane, glyoxal, glyoxal dimethyl acetal, and 1,1,3,3-tetramethoxypropane;

[0012] The polar aprotic solvent is one or more of dichloromethane, dibromomethane, chloroform, 1,2-dichloroethane, acetonitrile, and nitromethane.

[0013] As a further preference of the present invention, the Lewis acid iron salt is one or more of iron bromide and iron chloride; the Lewis acid catalyst without iron element is one or more of aluminum chloride, manganese chloride, copper chloride, zinc bromide, tin tetrachloride, and zirconium chloride.

[0014] As a further preference of the present invention, the acid used in the pickling is one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid, phosphoric acid, formic acid, acetic acid, and the concentration of the acid is 0.1-5 mol / L; the pickling temperature is 40-80 °C, and the pickling time is 2-12 h;

[0015] The alcohol used in the alcohol washing is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol; the alcohol washing temperature is 60-140 °C, and the alcohol washing time is 12-48 h.

[0016] According to another aspect of the present invention, the present invention provides the application of the iron-based dipolar hypercrosslinked polymer prepared by the above preparation method in the oxidation reaction of α-hydroxyacetophenone to produce 2,2-dialkoxyacetophenone, which is characterized in that the reaction is carried out in an air atmosphere with α-hydroxyacetophenone as the raw material, the iron-based dipolar hypercrosslinked polymer as the auxiliary agent, in two or more green mixed solvents and in the presence of an acid catalyst, without the participation of other oxidants; the reaction temperature is 60-120 °C, and the reaction time is 6-12 h;

[0017] Among them, the two or more green mixed solvents at least include a first green solvent and a second green solvent. Among them, the first green mixed solvent is one of methanol, ethanol, isopropanol, n-butanol, and the second green solvent is one of ethyl acetate, butyl acetate, dimethyl carbonate, diethyl carbonate, anisole, cyclopentyl methyl ether, 2-methyltetrahydrofuran, and the volume ratio of the first green solvent to the second green solvent is 1:1-3:1.

[0018] As a further preference of the present invention, the acid catalyst is an acid catalyst, preferably one or more of hydrochloric acid, hydrobromic acid, sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, formic acid, acetic acid, benzoic acid.

[0019] As a further preference of the present invention, the mass ratio of the iron-based dipolar hypercrosslinked polymer to the α-hydroxyacetophenone is 1:10-1:100, and the molar ratio of the acid catalyst to the α-hydroxyacetophenone is 1:1-1:10.

[0020] As a further preference of the present invention, the iron-based dipolar hypercrosslinked polymer in the reaction system can be recovered by filtration and reused as an auxiliary agent in the oxidation reaction of α-hydroxyacetophenone to produce 2,2-dialkoxyacetophenone.

[0021] Through the above technical solution conceived by the present invention, compared with the prior art, the dipolar fragment is introduced into the polymer in a simple manner, and at the same time, iron element is in-situ loaded (Lewis acid iron salt serves as both a polymerization catalyst and can provide iron element; the optionally used Lewis acid catalyst without iron element serves as a co-catalyst), obtaining an iron-based dipolar hypercrosslinked polymer. This iron-based dipolar hypercrosslinked polymer can be particularly used for the green oxidation of α-hydroxyacetophenone, that is, taking this iron-based dipolar hypercrosslinked polymer as an adjuvant, and acid (i.e., protonic acid) to form a composite catalytic system. In a green solvent, α-hydroxyacetophenone is oxidized by air to obtain 2,2-dialkoxyacetophenone (as shown in the examples below, the yield of 2,2-dialkoxyacetophenone can reach more than 90%), and the iron-based dipolar hypercrosslinked polymer after the reaction can be reused after filtration.

[0022] In the oxidation reaction of α-hydroxyacetophenone, the iron-based dipolar hypercrosslinked polymer + acid forms a composite catalytic system, avoiding the use of harmful polar aprotic solvents during the oxidation process. At the same time, the oxidation process can be carried out under an oxygen-containing atmosphere (such as air), without adding an additional oxidant, avoiding the addition of an equivalent or even excessive amount of oxidant, thereby reducing the generation of waste. The present invention provides a new implementation method for the oxidation reaction of α-hydroxyacetophenone to produce 2,2-dialkoxyacetophenone, which has the characteristics of mild reaction conditions, environmental friendliness, high industrialization potential, etc., and is suitable for the efficient conversion of biomass resources.

[0023] Some dipolar groups, such as sulfone group, sulfoxide, nitro group, amide, etc., are often electron-withdrawing groups on the aromatic ring, which play a passivating role on the aromatic ring and are not conducive to the occurrence of hypercrosslinking polymerization based on Friedel-Crafts reaction. Therefore, it is not easy to introduce these polar groups into hypercrosslinked polymers. The present invention innovatively proposes to construct a pyrrole ring unit with polymerization activity relying on the amino functional group in the precursor, thus avoiding the problem of difficult hypercrosslinking polymerization on the previously passivated aromatic ring. Regarding the types of dipolar groups, many hypercrosslinked polymers with different dipolar functional groups are synthesized in the present invention. Finally, it is found that several functional groups such as hydroxyl group, methoxy group, sulfone group, nitro group, sulfoxide, and amide have a promoting effect on the green oxidation of α-hydroxyacetophenone. The main manifestation is that in the presence of these functional groups, the yield of the target product 2,2-dialkoxyacetophenone is significantly improved compared with the control group without functional groups. And based on the present invention, the content of dipolar functional groups and the content of iron element can also be preferably set. In particular, the molar ratio of monomer to crosslinking agent can be preferably controlled to be 1:1 to 1:50, and the molar ratio of monomer to Lewis acid catalyst can be controlled (when the Lewis acid catalyst is only Lewis acid iron salt, the molar ratio of monomer to Lewis acid iron salt is 1:1 to 1:80; when the Lewis acid catalyst is a mixture of Lewis acid iron salt and Lewis acid catalyst without iron element, the molar ratio of monomer to Lewis acid iron salt is 1:1 to 1:40, and the ratio of monomer to Lewis acid catalyst without iron element is 1:1 to 1:40). The content of iron element is preferably controlled to be 0.01 to 1.0 mmol / g, and the corresponding iron-based dipolar hypercrosslinked polymer has the best effect in the reaction of oxidizing α-hydroxyacetophenone to 2,2-dialkoxyacetophenone.

[0024] Specifically, the present invention can achieve the following beneficial effects:

[0025] (1) The iron-based dipolar hypercrosslinked polymer provided by the present invention has good chemical stability, low cost, and simple preparation method. Through inexpensive precursors, hypercrosslinked polymers with dipolar microenvironments are synthesized, and iron elements are in-situ immobilized during the polymerization process, successfully introducing oxygen activation sites into the hypercrosslinked polymers.

[0026] (2) The iron-based dipolar hypercrosslinked polymer obtained by the present invention can be used as an auxiliary agent in particular to realize the oxidation of α-hydroxyacetophenone in a green solvent, and the auxiliary agent can be reused by simple filtration and separation. The oxidation process does not require the use of high-boiling solvents and equivalent oxidants, reduces the amount of waste production, is green and environmentally friendly, and is convenient for industrial production.

[0027] The iron-based dipolar hypercrosslinked polymer obtained in the present invention contains one or more dipolar segments and a certain amount of iron element (the content is 0.01-1.0 mmol / g). In particular, in the present invention, the molar ratio of the monomer to the crosslinking agent used in the synthesis process of the iron-based dipolar hypercrosslinked polymer is preferably 1:1-1:50, so that the content of the dipolar segment can be preferably controlled to construct a strong dipolar environment; at the same time, the molar ratio of the monomer to the Lewis acid catalyst is preferably controlled. When the Lewis acid catalyst is only the iron salt of Lewis acid, the molar ratio of the monomer to the iron salt of Lewis acid is preferably 1:1-1:80; when the Lewis acid catalyst is a mixture of the iron salt of Lewis acid and a Lewis acid catalyst without iron element, the molar ratio of the monomer to the iron salt of Lewis acid is preferably 1:1-1:40, and the ratio of the monomer to the Lewis acid catalyst without iron element is preferably 1:1-1:40. This ratio and the molar ratio of the monomer to the crosslinking agent control the iron content at the same time. The iron element content in the obtained iron-based dipolar hypercrosslinked polymer is 0.01-1.0 mmol / g (that is, each gram of the iron-based dipolar hypercrosslinked polymer contains 0.01-1.0 mmol of iron element). The dipolar segment can provide a strong dipolar microenvironment in a weakly polar green solvent to stabilize the reactive intermediate of the reaction; the supported iron element can well activate oxygen and reduce the energy barrier of the oxidation reaction, so as to further promote the yield increase of the product when the iron-based dipolar hypercrosslinked polymer is used as an auxiliary in the oxidation reaction of α-hydroxyacetophenone. The iron-based dipolar hypercrosslinked polymer prepared in the present invention has dipolar segments, which can well construct a strong polar environment in a weakly polar green solvent. At the same time, the supported iron element has a certain activation effect on oxygen, and the green oxidation of α-hydroxyacetophenone can be realized in an air atmosphere. Detailed implementation manners

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Example 1

[0030] Preparation of HCP-1-PXC iron-based dipolar additive: The preparation process of the iron-based dipolar hypercrosslinked polymer is as follows: Add 1.38 g of 4-nitroaniline (10 mmol) to a round-bottom flask containing 15 mL of acetic acid, and then add 4.51 g of sodium acetate (5.5 equiv., 55 mmol) and 1.98 g of 2,5-dimethoxytetrahydrofuran (1.5 equiv., 15 mmol) to the solution. Reflux the reaction mixture at 120 °C for 8 h, and after neutralization and extraction, separate the target monomer by column chromatography.

[0031] The structural formula of the monomer (monomer 1) obtained in this example is as follows:

[0032]

[0033] Then, weigh 0.94 g (5 mmol) of the monomer into 30 mL of dichloroethane, add 8.75 g (3 equiv., 15 mmol) of p-xylene dichloride (PXC, as a crosslinking agent), 6.67 g of aluminum chloride (10 equiv., 50 mmol), and 8.1 g of iron chloride (10 equiv., 50 mmol) thereto, and reflux the reaction at 90 °C for 24 h. After filtration, the solid is washed with a mixed solution of hydrochloric acid and acetic acid (V / V = 1:1, where hydrochloric acid is commercially available concentrated hydrochloric acid with a concentration of 37 wt% and acetic acid is commercially available pure acetic acid) and ethanol, and vacuum-dried at 90 °C for 12 h to obtain the iron-based dipolar hypercrosslinked polymer HCP-1-PXC.

[0034] Examples 2-4

[0035] The procedures of Examples 2-4 are substantially the same as those of Example 1, except that the types of precursors and crosslinking agents used are different (the molar amounts of precursors, the molar amounts of crosslinking agents, and the types and amounts of Lewis acid catalysts are the same as those in Example 1), and different iron-based dipolar hypercrosslinked polymer products are obtained accordingly, as shown in the following table (the numbers in the naming represent monomers, and FDA\PXC represents crosslinking agents):

[0036]

[0037]

[0038] The structural formula of monomer 2 is as follows:

[0039]

[0040] Examples 5-8

[0041] [[ID= 33]]Examples 5-8 respectively use different iron-based dipolar hypercrosslinked polymers to participate in the oxidation of α-hydroxyacetophenone.

[0042] Oxidation of α-hydroxyacetophenone: Add 1.36 g (10 mmol) of α-hydroxyacetophenone, 50 mg of solid iron-based dipolar hypercrosslinked polymer, 5 mmol (0.5 equiv.) of concentrated hydrochloric acid (commercially available concentrated hydrochloric acid with a concentration of 37 wt%), and add 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1) to a 100 mL round-bottom flask. The reaction solution reacts in an air atmosphere at 80 °C for 12 h. After the reaction is completed, the solid iron-based dipolar hypercrosslinked polymer is recovered by filtration, and the product is obtained by preparative thin-layer chromatography separation. The yields are shown in the following table.

[0043] Iron-based dipolar hypercrosslinked polymer Yield of 2,2-diethoxyacetophenone HCP-1-FDA 92％ HCP-1-PXC 85％ HCP-2-FDA 80％ HCP-2-PXC 86％

[0044] Examples 9 - 12

[0045] Examples 9 - 12 use different proton acids to participate in the oxidation of α-hydroxyacetophenone.

[0046] Oxidation of α-hydroxyacetophenone: Add 1.36 g of α-hydroxyacetophenone, 50 mg of HCP-1-FDA, 5 mmol (0.5 equiv.) of proton acid, and add 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1) to a 100 mL round-bottom flask. The reaction solution reacts in an air atmosphere at 80 °C for 12 h. After the reaction is completed, HCP-1-FDA is recovered by filtration, and the product is obtained by preparative thin-layer chromatography separation. The yields are shown in the following table.

[0047] Protic acid Yield of 2,2-diethoxyacetophenone Hydrobromic acid 95％ p-Toluenesulfonic acid 89％ Formic acid 50％ Acetic acid 52％

[0048] Examples 13 - 15

[0049] Examples 13 - 15 use different mixed solvents to participate in the oxidation of α-hydroxyacetophenone.

[0050] Oxidation of α-hydroxyacetophenone: Add 1.36 g of α-hydroxyacetophenone, 50 mg of HCP-1-FDA, 5 mmol (0.5 equiv.) of hydrobromic acid, and add 10 mL of a mixed solvent (V / V = 1:1) to a 100 mL round-bottom flask. The reaction solution reacts in an air atmosphere at 80 °C for 12 h. After the reaction is completed, HCP-1-FDA is recovered by filtration, and the product is obtained by preparative thin-layer chromatography separation. The yields are shown in the following table.

[0051] Mixed solvent (volume ratio 1:1) Yield of 2,2-diethoxyacetophenone Ethanol + dimethyl carbonate 92％ Ethanol + isopropyl acetate 75％ Ethanol + cyclopentyl methyl ether 95％

[0052] Example 16

[0053] This example discusses the reuse of the recovered iron-based dipolar hypercrosslinked polymer.

[0054] Oxidation of α - hydroxyacetophenone: Add 1.36 g of α - hydroxyacetophenone, 50 mg of HCP - 1 - FDA recovered from Example 5, 5 mmol (0.5 equiv.) of hydrobromic acid into a 100 mL round - bottom flask, and then add 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1). The reaction solution reacts in an air atmosphere at 80 °C for 12 h. After the reaction is completed, filter to recover HCP - 1 - FDA, and the product is obtained by preparative thin - layer chromatography separation, with a yield of 94%.

[0055] Examples 17 - 19

[0056] This example discusses the effect of the molar ratio of monomer 1 to the cross - linker (FDA) on the oxidation yield of α - hydroxyacetophenone. The material preparation method is generally the same as that of Example 2, except that the amount of the cross - linker (FDA) is adjusted to make the molar ratio of monomer 1 to the cross - linker (FDA) different, and the molar ratio of monomer 1 to aluminum chloride and iron chloride remains unchanged at 1:10:10.

[0057] Oxidation of α - hydroxyacetophenone: Add 1.36 g of α - hydroxyacetophenone, 50 mg of an iron - based dipolar hyper - crosslinked polymer obtained by polymerizing monomer 1 with a cross - linker in different molar ratios, 5 mmol (0.5 equiv.) of hydrobromic acid into a 100 mL round - bottom flask, and then add 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1). The reaction solution reacts in an air atmosphere at 80 °C for 12 h. After the reaction is completed, filter to recover the iron - based dipolar hyper - crosslinked polymer, and the product is obtained by preparative thin - layer chromatography separation. The yields are shown in the following table.

[0058] Molar ratio of monomer to crosslinker Yield of 2,2-diethoxyacetophenone 1：1 80％ 1：20 93％ 1：50 78％

[0059] Examples 20 - 22

[0060] This example discusses the effect of the molar ratio of monomer 1 to the Lewis acid iron salt (iron chloride) on the oxidation yield of α - hydroxyacetophenone. The material preparation method is generally the same as that of Example 2, except that the amount of the Lewis acid iron salt (iron chloride) is adjusted to make the molar ratio of monomer 1 to iron chloride different. The molar ratio of monomer 1 to the cross - linker FDA is fixed at 1:20, and the molar ratio of monomer 1 to the non - iron Lewis acid aluminum chloride is fixed at 1:10.

[0061] Oxidation of α-hydroxyacetophenone: Add 1.36 g of α-hydroxyacetophenone, 50 mg of the prepared monomer 1 and an iron-based dipolar hypercrosslinked polymer with different molar ratios of Lewis acid iron salt (ferric chloride), 5 mmol (0.5 equiv.) of hydrobromic acid into a 100 mL round-bottom flask, and add 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1). The reaction solution reacts in an air atmosphere at 80 °C for 12 h. After the reaction, the iron-based dipolar hypercrosslinked polymer is recovered by filtration, and the product is obtained by preparative thin-layer chromatography separation. The yields are shown in the following table.

[0062] Molar ratio of monomer to Lewis acid iron salt Yield of 2,2-diethoxyacetophenone 1：1 75％ 1：20 95％ 1：40 70％

[0063] Examples 23 - 25

[0064] This example discusses the effect of the molar ratio of monomer 1 to iron-free Lewis acid catalyst aluminum chloride on the oxidation yield of α-hydroxyacetophenone. The material preparation method is generally the same as that in Example 2, except that the amount of iron-free Lewis acid catalyst aluminum chloride is adjusted to make the molar ratio of monomer 1 to iron-free Lewis acid catalyst aluminum chloride different, the molar ratio of monomer 1 to crosslinking agent FDA is fixed at 1:20, and the molar ratio of monomer to Lewis acid iron salt (ferric chloride) is fixed at 1:10.

[0065] Oxidation of α-hydroxyacetophenone: Add 1.36 g of α-hydroxyacetophenone, 50 mg of the prepared monomer 1 and an iron-based dipolar hypercrosslinked polymer with different molar ratios of iron-free Lewis acid catalyst aluminum chloride, 5 mmol (0.5 equiv.) of hydrobromic acid into a 100 mL round-bottom flask, and add 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1). The reaction solution reacts in an air atmosphere at 80 °C for 12 h. After the reaction, the iron-based dipolar hypercrosslinked polymer is recovered by filtration, and the product is obtained by preparative thin-layer chromatography separation. The yields are shown in the following table.

[0066]

[0067] Comparative Example 1

[0068] In this comparative example, the harmful polar aprotic solvent THF is used to replace the second green solvent, and the oxidation reaction of α-hydroxyacetophenone is carried out under air conditions without adding an additional oxidant.

[0069] Oxidation of α-hydroxyacetophenone: 1.36 g of α-hydroxyacetophenone was added to a 100 mL round-bottom flask. Without adding the iron-based dipolar hypercrosslinked polymer, 5 mmol (0.5 equiv.) of hydrobromic acid was added, and 10 mL of a mixed solvent of ethanol and THF (V / V = 1:1) was added. The reaction solution was reacted at 80 °C in an air atmosphere for 12 h. After the reaction was completed, the product was obtained by preparative thin-layer chromatography separation, and the yield was 40%.

[0070] Comparative Example 2

[0071] In this comparative example, in a green mixed solvent, 50 mg of the polymer HCP-3-FDA without dipolar segments (3 represents the monomer, and the structure is shown in the following formula. The material preparation method is generally the same as that of Example 2, except that the monomers are different; the molar amount of the monomers remains the same) was added, and the oxidation reaction of α-hydroxyacetophenone was carried out under air conditions.

[0072]

[0073] Oxidation of α-hydroxyacetophenone: 1.36 g of α-hydroxyacetophenone was added to a 100 mL round-bottom flask. 50 mg of HCP-3-FDA, 5 mmol (0.5 equiv.) of hydrobromic acid was added, and 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1) was added. The reaction solution was reacted at 80 °C in an air atmosphere for 12 h. After the reaction was completed, HCP-3-FDA was recovered by filtration, and the product was obtained by preparative thin-layer chromatography separation, and the yield was 23%.

[0074] Comparative Example 3

[0075] In this comparative example, in a green mixed solvent, without adding any polymer, the oxidation reaction of α-hydroxyacetophenone was carried out under air conditions.

[0076] Oxidation of α-hydroxyacetophenone: 1.36 g of α-hydroxyacetophenone was added to a 100 mL round-bottom flask. Without adding any polymer, 5 mmol (0.5 equiv.) of hydrobromic acid was added, and 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1) was added. The reaction solution was reacted at 80 °C in an air atmosphere for 12 h. After the reaction was completed, the product was obtained by preparative thin-layer chromatography separation, and the yield was 25%.

[0077] Comparative Example 4

[0078] In this comparative example, a green mixed solvent was used, without adding any polymer, and ferric chloride and monomer 1 (the structure is shown in Example 1) were added as co-catalysts, and the oxidation reaction of α-hydroxyacetophenone was carried out under air conditions.

[0079] Oxidation of α-hydroxyacetophenone: 1.36 g of α-hydroxyacetophenone was added to a 100 mL round-bottom flask without adding any polymer. 0.05 mmol of FeCl3 and 50 mg of monomer 1 were added as co-catalysts (equivalent to an iron content of 1 mmol / g in the co-catalyst, with a total of 50 mg of co-catalyst), 5 mmol (0.5 equiv.) of hydrobromic acid, and 10 mL of a mixed solvent of ethanol and diethyl carbonate (V / V = 1:1) were added. The reaction solution was reacted in an air atmosphere at 80 °C for 12 h. After the reaction, the product was separated by pre-coated thin-layer chromatography, and the yield was 55%.

[0080] In this comparative example, monomer 1 and ferric chloride were mechanically mixed, and the catalytic effect was far inferior to that of HCP-1-FDA prepared in Example 2, and it could not be recovered and reused.

[0081] The above examples are only for illustration. For example, the precursor for synthesizing the target monomer can also be other substances, as long as the precursor contains multiple functional groups and can form a monomer with a pyrrole ring (these multiple functional groups must contain an amino functional group, and the other functional groups can be at least one of a hydroxyl group, a methoxy group, a sulfone group, a nitro group, a sulfoxide group, and an amide group); in addition, for the sodium acetate / acetic acid mixed system used in synthesizing the monomer, the ratio of sodium acetate to acetic acid can also be other ratios used in the prior art.

[0082] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of an iron-based dipolar hypercrosslinked polymer, characterized in that, First, a precursor containing multiple functional groups is pre-treated to form a monomer with a pyrrole ring. Among them, the multiple functional groups include an amino functional group and other functional groups, and the other functional groups are at least one of a hydroxyl group, a methoxy group, a sulfone group, a nitro group, a sulfoxide group, and an amide group. Then, in a polar aprotic solvent, the monomer is mixed with a cross-linking agent, and a Lewis acid catalyst is added, followed by heating under reflux for reaction. After the reaction is completed, filtration, pickling, alcohol washing, and drying are carried out to obtain an iron-based dipolar hypercrosslinked polymer. Among them, the Lewis acid catalyst is a Lewis acid iron salt or a mixture of a Lewis acid iron salt and a Lewis acid catalyst without iron element.

2. The preparation method according to claim 1, characterized in that, In the reaction system, the molar ratio of the monomer to the cross-linking agent is 1:1 to 1:

50. When the Lewis acid catalyst is a Lewis acid iron salt, the molar ratio of the monomer to the Lewis acid iron salt is 1:1 to 1:

80. When the Lewis acid catalyst is a mixture of a Lewis acid iron salt and a Lewis acid catalyst without iron element, the molar ratio of the monomer to the Lewis acid iron salt is 1:1 to 1:40, and the molar ratio of the monomer to the Lewis acid catalyst without iron element is 1:1 to 1:

40.

3. The preparation method according to claim 1, characterized in that, The pre-treatment is to react the precursor with 2,5-dimethoxytetrahydrofuran in an acetic acid sodium / acetic acid mixed system to obtain the monomer.

4. The preparation method according to claim 1, characterized in that, The cross-linking agent is one or more of trimethyl orthoformate, p-dichlorobenzyl, p-dibromobenzyl, dimethoxymethane, glyoxal, dimethyl acetal of glyoxal, 1,1,3,3-tetramethoxypropane. The polar aprotic solvent is one or more of dichloromethane, dibromomethane, chloroform, 1,2-dichloroethane, acetonitrile, and nitromethane.

5. The preparation method according to claim 1, characterized in that, The Lewis acid iron salt is one or more of iron bromide and iron chloride; the Lewis acid catalyst without iron element is one or more of aluminum chloride, manganese chloride, copper chloride, zinc bromide, tin tetrachloride, and zirconium chloride.

6. The preparation method according to claim 1, wherein, The acid used for pickling is one or more of hydrochloric acid, sulfuric acid, nitric acid, hydrobromic acid, phosphoric acid, formic acid, and acetic acid, and the concentration of the acid is 0.1 to 5 mol / L; the pickling temperature is 40 to 80 °C, and the pickling time is 2 to 12 h. The alcohol used for alcohol washing is one or more of methanol, ethanol, n-propanol, isopropanol, and n-butanol; the alcohol washing temperature is 60 to 140 °C, and the alcohol washing time is 12 to 48 h.

7. The iron-based dipolar hypercrosslinked polymer prepared by the preparation method according to any one of claims 1-6 is applied to the oxidation reaction of α-hydroxyacetophenone to produce 2,2-dialkoxyacetophenone, characterized in that, The reaction is carried out with α-hydroxyacetophenone as the raw material, an iron-based dipolar hypercrosslinked polymer as the auxiliary agent, in two or more green mixed solvents and in the presence of an acid catalyst, without the participation of other oxidants; the reaction temperature is 60 to 120 °C, and the reaction time is 6 to 12 h. Among them, the two or more green mixed solvents at least include a first green solvent and a second green solvent. Among them, the first green mixed solvent is one of methanol, ethanol, isopropanol, and n-butanol, and the second green solvent is one of ethyl acetate, butyl acetate, dimethyl carbonate, diethyl carbonate, anisole, cyclopentyl methyl ether, and 2-methyltetrahydrofuran. The volume ratio of the first green solvent to the second green solvent is 1:1 to 3:

1.

8. The application according to claim 7, wherein The acid catalyst is an acid catalyst, preferably one or more of hydrochloric acid, hydrobromic acid, sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, formic acid, acetic acid, and benzoic acid.

9. The application according to claim 7, wherein The mass ratio of the iron-based dipolar hypercrosslinked polymer to the α-hydroxyacetophenone is 1:10 to 1:100, and the molar ratio of the acid catalyst to the α-hydroxyacetophenone is 1:1 to 1:

10.

10. The application according to claim 7, wherein The iron-based dipolar hypercrosslinked polymer in the reaction system can be recovered by filtration and reused as an auxiliary agent for the oxidation reaction of α-hydroxyacetophenone to produce 2,2-dialkoxyacetophenone.

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