Improved ionogel confined palladium on carbon catalyst, its preparation method and application

Abstract

This invention relates to the field of fine chemical catalysis technology, specifically to an improved ion-gel confined palladium-on-carbon catalyst, its preparation method, and its applications. The catalyst uses N,N-dimethylacetamide (DMAc) as a solvent and potassium acetate as a base, with the addition of a catalytic amount of antioxidant 168 [(tris(2,4-di-tert-butylphenyl) phosphite)], and the reaction is carried out under milder CO pressure (1.0-1.6 MPa) and temperature (90-110 °C). This improved catalyst, in synergy with the optimized process, unexpectedly enables the high conversion and selectivity of 4-bromobenzyl sulfone derivatives to 4-methylsulfonylbenzoic acid derivatives, while maintaining the catalyst's excellent recyclability and stability. This invention provides a highly efficient, green, and easily industrialized synthetic route for the target product.

Description

Technical Field

[0001] This invention relates to the field of fine chemical catalysis technology, specifically to an improved ion-gel confined palladium-carbon catalyst, its preparation method, and its application. Background Technology

[0002] Carbonylation is a core method for efficiently introducing carboxyl or ester groups into organic molecules, playing an irreplaceable role in the synthesis of pharmaceutical, pesticide, and material intermediates. Among these, palladium-catalyzed carbonylation of halogenated aromatic hydrocarbons has attracted significant attention due to its relatively mild conditions and high atom economy. Developing heterogeneous palladium catalysts that are highly active, highly selective, and recyclable is crucial for achieving the green and economical industrialization of this type of reaction.

[0003] Iongels, as functional materials composed of ionic liquids and three-dimensional networks, have shown great potential in catalysis, electrochemistry, and electronic devices due to their high thermal stability, designable ionic environment, and unique confinement effect. Confining active metals within an iongel network can effectively stabilize nanoscale metal particles, and by regulating the adsorption and diffusion behavior of reactants in the gel microenvironment, it may be possible to achieve fine-tuning of catalytic selectivity.

[0004] We previously developed an "ion-gel confined palladium-carbon catalyst." This catalyst was prepared by loading palladium nanoparticles onto activated carbon and further coating them with a coordination-crosslinked ion-gel shell composed of [BMIM]PF6 / FeCl3 / 2,2'-bipyridine. This catalyst exhibited excellent catalytic activity, selectivity, and recyclability in the carbonylation of dihalothiophenes (such as 2,5-dibromothiophene) to prepare thiophene-2,5-dicarboxylic acid, providing a highly efficient route for the synthesis of heterocyclic carboxylic acids.

[0005] However, when extending the aforementioned excellent catalyst system to substrates with different structures, we discovered its limitations. Particularly for substrates containing strong electron-withdrawing groups (-SO2CH3), such as 4-bromophenyl sulfone derivatives, directly applying the existing catalysts and reaction processes generally resulted in insufficient substrate conversion and low selectivity for the target carboxylic acid product. This may be because the strong electron-withdrawing groups affect the adsorption and activation modes of the substrate at the catalyst's active sites, and the existing ion-gel microenvironment has not been optimally adapted to this. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, the present invention aims to provide an improved ion-gel confined palladium-on-carbon catalyst, its preparation method, and its applications. The improved catalyst, in synergy with the optimized process, unexpectedly enables the high conversion and selectivity of 4-bromophenylsulfone derivatives to 4-methylsulfonylbenzoic acid derivatives, while maintaining the catalyst's excellent recyclability and stability. This invention provides a highly efficient, green, and easily industrialized synthetic route for the target product.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing an improved ion-gel confined palladium-on-carbon catalyst, characterized by comprising the following steps: Palladium salt is dissolved in an acidic solution, and then an alcohol-water mixed solvent is added to adjust the pH value, forming an impregnation solution.

[0008] After the activated carbon support is activated, it is dispersed in the impregnation solution, a reducing agent is added, and the mixture is heated and reduced under an inert atmosphere. After post-treatment, a supported palladium-carbon catalyst is obtained.

[0009] The obtained supported palladium-on-carbon catalyst was reacted with 3-(triethoxysilyl)propylimidazolium salt in an organic solvent. After removing the solvent, an intermediate was obtained.

[0010] The intermediate is contacted with a solution containing an ionic liquid, a metal salt, and a coordinating agent to form a coated gel layer, thereby obtaining an improved ion-gel confined palladium-carbon catalyst for the carbonylation reaction of 4-bromophenylsulfone derivatives.

[0011] The ionic liquid comprises 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; the metal salt comprises ferric chloride and copper trifluoromethanesulfonate; and the ligand is 2,2'-bipyridine, 1,10-phenanthroline or derivatives thereof.

[0012] In a preferred embodiment of the present invention, the amount of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 20%-80% of the total molar amount of the ionic liquid; the amount of copper trifluoromethanesulfonate accounts for 10%-50% of the total molar amount of the metal salt; and the molar ratio of ionic liquid, metal salt and ligand is 1: (0.05-0.4): (0.02-0.25).

[0013] In a preferred embodiment of the present invention, the amount of [BMIM]NTf2 accounts for 40%-60% of the total molar amount of the ionic liquid; and the amount of Cu(OTf)2 accounts for 20%-40% of the total molar amount of the metal salt.

[0014] In a preferred embodiment of the present invention, the acidic solution is a hydrochloric acid solution with a concentration of 3wt%-10wt%; the volume ratio of alcohol to water in the alcohol-water mixed solvent is 1-0.5:5; the pH is adjusted to a range of 4-7; the activation treatment includes at least one of pickling, oxidation treatment or high-temperature calcination; the reducing agent is formaldehyde, hydrazine hydrate or sodium borohydride; the heating reduction temperature is 40℃-80℃ and the time is 1h-6h; the organic solvent is toluene, xylene or benzene.

[0015] Another objective of this invention is to obtain an improved ion-gel confined palladium-carbon catalyst prepared by the aforementioned preparation method.

[0016] The application of the improved ion-gel confined palladium-carbon catalyst described in this invention in the carbonylation reaction of 4-bromophenylsulfone derivatives.

[0017] The present invention uses the improved ion-gel confined palladium-carbon catalyst described above to obtain a 4-methylsulfonylbenzoic acid derivative after carbonylation reaction of a 4-bromophenylsulfone derivative with carbon monoxide.

[0018] The general formula of the 4-bromophenyl sulfone derivative described in this invention is: 4-Br-(R) n -Ar-SO2CH3 where Ar is a benzene ring; n is 0, 1, 2 or 3; and R is independently selected from halogens, trifluoromethyl, C1-C4 alkyl, C1-C4 alkoxy or five-membered heterocycles.

[0019] The carbonylation reaction was carried out in a polar aprotic solvent, a weakly basic carboxylate, a modified ion-gel confined palladium-on-carbon catalyst, a catalytic amount of antioxidant 168, and a carbon monoxide atmosphere.

[0020] The polar aprotic solvent described in this invention is N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone.

[0021] The weakly basic carboxylate is potassium acetate, sodium acetate, or cesium acetate; the carbon monoxide pressure is 0.8 MPa-2.0 MPa, the reaction temperature is 80℃-120℃, and the reaction time is 8h-20h.

[0022] The amount of the improved ion-gel confined palladium-carbon catalyst is 0.1%-5% of the mass of the 4-bromophenyl sulfone derivative.

[0023] The 4-bromobenzyl sulfone derivatives are one or more of the following: 4-bromobenzyl sulfone, 4-bromo-2-fluorobenzyl sulfone, 4-bromo-3-chlorobenzyl sulfone, 4-bromo-3-chloro-2-methylbenzyl sulfone, 4-bromo-3-methyl-2(4,5-dihydroisoxazole)benzyl sulfone, 4-bromo-3-chloro-2-[(5-methyl-2-oxoylide-1,3,4-oxadiazol-3(2H)-yl)methyl]benzyl sulfone, 4-bromo-3-chloro-2-[(2,2,2-trifluoroethoxy)methyl]benzyl sulfone, 4-bromo-3-methyl-2-[(2-methoxyethoxy)methyl]benzyl sulfone, 2-bromo-5-trifluoromethylbenzyl sulfone, 4-bromo-2-trifluoromethylbenzyl sulfone, 4-bromo-3-methyl-2-trifluoromethylbenzyl sulfone, and 4-bromo-3-chloro-2(4,5-dihydroisoxazole)benzyl sulfone.

[0024] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention achieves unexpected synergistic catalytic effects by specifically adjusting the chemical composition of the ionogel shell (introducing [BMIM]NTf2 and Cu(OTf)2) and combining it with a specially optimized reaction process (using DMAc solvent, potassium acetate, antioxidant 168 and mild conditions), enabling high conversion and high selectivity of 4-bromophenyl sulfone derivatives that were originally difficult to convert efficiently.

[0025] 2. This invention successfully overcomes the problem of existing catalyst systems being "unsuitable" for new substrates, effectively expanding the application scope of catalysis technology to aromatic ring systems containing strongly electron-withdrawing methyl sulfone groups, and providing a brand-new dedicated solution for the green synthesis of such important intermediates.

[0026] 3. The improved catalyst of this invention achieves high performance while fully inheriting the excellent reusability, stability and easy separation and recovery characteristics of the previously developed catalyst. Moreover, the optimized process conditions are mild and the solvent is recyclable, which meets the requirements of green chemistry and industrial production. Attached Figure Description

[0027] Figure 1 This study compares the catalytic activity of different catalyst systems for the carbonylation reaction of 4-bromophenyl sulfone. Series 1 is a prior art catalyst (unmodified ion-gel confined palladium-carbon catalyst); Series 2 is an improved catalyst (but without the addition of antioxidant 168); and Series 3 is the improved catalyst of this invention plus optimized process (addition of antioxidant 168, DMAc solvent, and potassium acetate).

[0028] Figure 2 The effect of the molar fraction of [BMIM]NTf2 in the ionic liquid on the conversion of 4-bromophenyl sulfone is shown, where X-axis represents the percentage of [BMIM]NTf2 in the total molar amount of the ionic liquid (%); and Y-axis represents the conversion rate of 4-bromophenyl sulfone (%).

[0029] Figure 3 The effect of Cu(OTf)2 molar fraction in the metal salt on the conversion rate of 4-bromophenyl sulfone is shown, where X-axis represents the percentage of Cu(OTf)2 in the total molar amount of the metal salt (%); Y-axis represents the conversion rate of 4-bromophenyl sulfone (%).

[0030] Figure 4 This is a schematic diagram of the reaction process of the present invention. Detailed Implementation

[0031] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0033] Example C1 The preparation steps of an improved ion-gel confined palladium-on-carbon catalyst are as follows: (1) Dissolve PdCl2 in 5wt% hydrochloric acid solution, add mixed solvent at a volume ratio of water:methanol = 1:4, adjust pH to 4 to form impregnation solution, wherein the mass ratio of PdCl2, hydrochloric acid solution and methanol-water mixed solvent is 0.1:10:4.

[0034] (2) The coconut shell activated carbon carrier was washed twice with 8% HCl, oxidized with 30% H2O2 for 1 hour, and dried at 80℃ for 4 hours. The specific surface area of ​​the coconut shell activated carbon carrier was 400 m². 2 / g; then the activated carrier was added to 5 times the mass of the impregnation solution and ultrasonically treated for 30 min. Formaldehyde (4 times the molar amount of Pd) was added and reduced at 50℃ for 2 h under an inert atmosphere. The product was filtered, washed three times with deionized water, and dried under nitrogen at 80℃ for 2 h to obtain the carrier palladium on carbon (Pd / C).

[0035] (3) The palladium on carbon (Pd / C) support and 3-(triethoxysilyl)propylimidazolium salt were refluxed in toluene for 12 h at a molar ratio of 1:0.25, with the amount of toluene being 4 times the mass of the palladium on carbon support, to achieve covalent bonding; then the toluene was removed by vacuum distillation at 50-75℃ and -0.09-0.1 MPa to obtain the product of covalent bonding between palladium on carbon (Pd / C) support and 3-(triethoxysilyl)propylimidazolium salt.

[0036] Steps (1) to (3) are exactly the same as the previously developed preparation method for "ion-gel confined palladium-carbon catalyst". The core improvement lies in step (4) - the construction of the gel shell:

[0037] (4) The covalently bonded product obtained in step (3) was impregnated in an acetonitrile solution containing an ionic liquid, a metal salt, and 2,2'-bipyridine. The ionic liquid was a mixture of [BMIM]PF6 and [BMIM]NTf2 in a molar ratio of 1:1; the metal salt was a mixture of FeCl3 and Cu(OTf)2 in a molar ratio of 7:3. The molar ratio of [BMIM]PF6, the total amount of the metal salt, and 2,2'-bipyridine was maintained at 1:0.1:0.05. The reaction was carried out at 70°C for 6 hours to form a cross-linked gel shell, and finally dried under vacuum at 80°C for 4 hours to obtain the improved catalyst. The mass percentage of Pd in ​​the obtained catalyst was approximately 0.5%.

[0038] Comparative Example D1 (using only the original catalyst): Preparation of the basic catalyst D1# (1) Dissolve PdCl2 in 5wt% hydrochloric acid solution, add mixed solvent at a volume ratio of water:methanol = 1:4, adjust pH to 4 to form impregnation solution, wherein the mass ratio of PdCl2, hydrochloric acid solution and methanol-water mixed solvent is 0.1:10:4.

[0039] (2) The coconut shell activated carbon carrier was washed twice with 8% HCl, oxidized with 30% H2O2 for 1 hour, and dried at 80℃ for 4 hours. The specific surface area of ​​the coconut shell activated carbon carrier was 400 m². 2 / g; then the activated carrier was added to 5 times the mass of the impregnation solution and ultrasonically treated for 30 min. Formaldehyde (4 times the molar amount of Pd) was added and reduced at 50℃ for 2 h under an inert atmosphere. The product was filtered, washed three times with deionized water, and dried under nitrogen at 80℃ for 2 h to obtain the carrier palladium on carbon (Pd / C).

[0040] (3) The palladium on carbon (Pd / C) support and 3-(triethoxysilyl)propylimidazolium salt were refluxed in toluene for 12 h at a molar ratio of 1:0.25, with the amount of toluene being 4 times the mass of the palladium on carbon support, to achieve covalent bonding; then the toluene was removed by vacuum distillation at 50-75℃ and -0.09-0.1 MPa to obtain the product of covalent bonding between palladium on carbon (Pd / C) support and 3-(triethoxysilyl)propylimidazolium salt.

[0041] Steps (1)-(3) are exactly the same as in Example C1. Step (4) is carried out in accordance with the steps (4) of the previously developed "ion gel confined palladium carbon catalyst", that is, the gel shell is prepared using pure [BMIM]PF6 and pure FeCl3. The remaining steps are the same as in Example C1.

[0042] Comparative Example D2 (catalyst modified only, process unchanged): Improved catalyst C1# The preparation method is the same as in Example C1 of this invention.

[0043] Comparative Example D3 (process modified only, catalyst unchanged): Basic catalyst D1# The preparation method is the same as that of comparative example D1.

[0044] Application Example 1: Carbonylation of 4-bromophenyl sulfone (1) In a 250 mL high-pressure reactor, add 4-bromophenyl sulfone derivative (100 mmol), N,N-dimethylacetamide (DMAc, 80 mL), potassium acetate (120 mmol), antioxidant 168 (20% of the catalyst mass) and catalyst (2% of the substrate mass).

[0045] (2) After replacing the air in the reactor with N2 three times, carbon monoxide was introduced to the initial pressure of 1.2 MPa. The reaction system was heated to 100°C and reacted for 12 hours with stirring at 600 rpm.

[0046] (3) After the reaction is complete, cool to room temperature and release the residual gas. Filter to separate the catalyst. After removing most of the solvent from the filtrate by vacuum distillation, add dilute hydrochloric acid (2M) to acidify to pH≈2. Solid precipitates out. Filter, wash with water and dry to obtain crude product.

[0047] (4) The crude product was analyzed by high performance liquid chromatography (HPLC) to calculate the substrate conversion rate and the selectivity of the target carboxylic acid product. The separated catalyst was washed three times each with DMAc and ethanol, and dried under vacuum at 80°C for 2 hours to obtain the 4-methylsulfonylbenzoic acid derivative.

[0048] Example E1: Carbonylation of 4-bromophenyl sulfone Substrate: 4-bromophenyl sulfone Using catalyst C1# and the process of this invention: substrate conversion >99%, 4-methyl sulfone benzoic acid selectivity 98%, and separation yield 92%.

[0049] Catalyst reuse performance: After 5 consecutive reuses, the product yield remained stable between 90% and 92%.

[0050] Example E2: Carbonylation of 4-bromo-2-fluorobenzyl sulfone Substrate: 4-bromo-2-fluorobenzyl sulfone Using catalyst C1# and the process of this invention: substrate conversion rate 98%, 2-fluoro-4-methylsulfonylbenzoic acid selectivity 95%, and separation yield 90%.

[0051] Example E3: Carbonylation of 4-bromo-3-chloro-2-methylbenzyl sulfone Substrate: 4-bromo-3-chloro-2-methylbenzyl sulfone (for testing the steric hindrance effect of the ortho-methyl group) Using catalyst C1# and the process of this invention: substrate conversion rate 96%, 3-chloro-2-methyl-4-methylsulfonylbenzoic acid selectivity 94%, and separation yield 85%.

[0052] Example E4: Carbonylation of 4-bromo-3-chloro-2-[(2,2,2-trifluoroethoxy)methyl]benzenesulfone Substrate: 4-bromo-3-chloro-2-[(2,2,2-trifluoroethoxy)methyl]benzenesulfone (for testing complex steric and electronic effects) Using catalyst C1# and the process of this invention: substrate conversion rate 97%, corresponding carboxylic acid product selectivity 95%, and separation yield 88%.

[0053] Comparative process (using existing processes): Except for replacing the solvent system with "toluene-water (1:1, v / v)", replacing the base with "sodium carbonate", increasing the initial CO pressure to 1.8 MPa, and increasing the reaction temperature to 115 °C, the rest of the operation is the same as the "General Evaluation Method" mentioned above.

[0054] Comparative experimental group (taking 4-bromophenyl sulfone as an example) To clearly demonstrate the synergistic improvement effect of the present invention, comparative experiments were conducted on the same substrate (4-bromophenyl sulfone), and the results are shown in Table 1 below.

[0055] For different substrates, reaction evaluations were conducted using existing technologies and the catalysts and process conditions described in this invention, and the results are summarized in Table 1.

[0056] Table 1 shows the reaction evaluation using existing technologies and the catalysts and process conditions described in this invention. The above specific implementation methods fully demonstrate that: When the existing catalyst (D1#) and process were directly applied to treat the 4-bromophenyl sulfone derivative (Comp-1), the conversion and selectivity were not ideal, confirming the inapplicability of the original system to the new substrate.

[0057] While improving the catalyst (Comp-2) or optimizing the process (Comp-3) alone can lead to some improvement, neither can achieve efficient and highly selective conversion.

[0058] Only by using the specific improved catalyst (C1#) provided in this application, combined with the optimized process specifically designed for it (DMAc solvent, potassium acetate base, mild conditions), can a series of 4-bromophenyl sulfone derivatives with different structures achieve high conversion and high selectivity carbonylation reactions, perfectly solving the technical problems raised in the background art.

[0059] The improved catalyst of this application not only achieves high catalysis efficiency but also fully inherits the excellent reusability and stability of the previously developed catalysts.

[0060] The method described in this application can achieve efficient conversion of 4-bromophenylsulfone derivatives with various substitution types (halogen, alkyl, heterocyclic, fluorine / oxygen chain, strong electron-withdrawing group) and different substitution positions (ortho, meta), which fully demonstrates its excellent substrate versatility and strongly supports its commercial application prospects.

[0061] The effect of the [BMIM]NTf2 content on catalytic performance was tested to demonstrate the scientific validity of the range (20%-80%, preferably 40%-60%) in the claims. Using the same substrate (4-bromophenyl sulfone) as an example, the results are shown in Table 2 below.

[0062] Table 2 shows the effect of the [BMIM]NTf2 ratio on catalytic performance. The data forms a "volcano-shaped" curve, clearly showing that the performance of [BMIM]NTf2 is significantly better than the two ends when the proportion is 20%-80%, and reaches and maintains the optimal platform in the 40%-60% range.

[0063] Next, the optimized metal salt ratio data were analyzed. Taking the same substrate (4-bromophenyl sulfone) as an example, the effect of the Cu(OTf)2 ratio on the catalytic performance was tested to demonstrate the scientific validity of the range (10%-50%, preferably 20%-40%) in the claims. The results are shown in Table 3. Table 3 shows the optimized metal salt ratio data. Similar to the ionic liquid data, the introduction of Cu(OTf)₂ significantly improved catalytic performance in the range of 10%–50%, with an optimal range of 20%–40%. This demonstrates the synergistic effect of the mixed metal salts and provides solid evidence for its protection range.

[0064] Finally, using the same substrate (4-bromophenyl sulfone) as an example, the cyclic stability (recycled 10 times) and reactivity of the catalyst were evaluated based on the improved catalyst and optimized process of this patent. The substrate conversion, product selectivity, and Pd loss (Pd content in the filtrate detected by ICP-MS) were collected and summarized, and the results are shown in Table 4. Table 4 summarizes the catalyst's cyclic stability (repeated 10 times), reaction activity, substrate conversion, product selectivity, and Pd loss (Pd content in the filtrate determined by ICP-MS). The catalyst maintained high activity (separation yield >85%) after 10 consecutive uses, and the Pd loss was extremely low (Pd content in the filtrate after the 10th use was only 1.3 ppm), demonstrating that the ion gel shell has excellent confinement and stabilizing effects.

[0065] Figure 4 The flowchart of the reaction process shows that the present invention produces an unexpected synergistic catalytic effect by specifically adjusting the chemical composition of the ion gel shell (introducing [BMIM]NTf2 and Cu(OTf)2) and combining it with a specially optimized reaction process (using DMAc solvent, potassium acetate, antioxidant 168 and mild conditions), which enables the 4-bromophenyl sulfone derivative, which was originally difficult to convert efficiently, to achieve high conversion rate and high selectivity.

[0066] This invention successfully overcomes the problem of existing catalyst systems being "unsuitable" for new substrates, effectively expanding the application scope of catalysis technology to aromatic ring systems containing strongly electron-withdrawing methyl sulfone groups, and providing a novel and dedicated solution for the green synthesis of such important intermediates.

[0067] The improved catalyst of this invention achieves high performance while fully inheriting the excellent reusability, stability and easy separation and recovery characteristics of the previously developed catalyst. Furthermore, the optimized process conditions are mild and the solvent is recyclable, meeting the requirements of green chemistry and industrial production.

[0068] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0069] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an improved ion-gel confined palladium-carbon catalyst, characterized in that, Includes the following steps: Palladium salt is dissolved in an acidic solution, and then an alcohol-water mixed solvent is added to adjust the pH value to form an impregnation solution. The activated carbon support was activated and then dispersed in the impregnation solution. A reducing agent was added, and the mixture was heated and reduced under an inert atmosphere. After post-treatment, a supported palladium-carbon catalyst was obtained. The obtained supported palladium-on-carbon catalyst was reacted with 3-(triethoxysilyl)propylimidazolium salt in an organic solvent. After removing the solvent, an intermediate was obtained. The intermediate is contacted with a solution containing an ionic liquid, a metal salt and a ligand to react and form a coated gel layer, thereby obtaining an improved ion-gel confined palladium-carbon catalyst for the carbonylation reaction of 4-bromophenylsulfone derivatives. The ionic liquid comprises 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; the metal salt comprises ferric chloride and copper trifluoromethanesulfonate; and the ligand is 2,2'-bipyridine, 1,10-phenanthroline or derivatives thereof.

2. The method for preparing the improved ion-gel confined palladium-carbon catalyst according to claim 1, characterized in that, The amount of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt accounts for 20%-80% of the total molar amount of the ionic liquid; the amount of copper trifluoromethanesulfonate accounts for 10%-50% of the total molar amount of the metal salt; the molar ratio of ionic liquid, metal salt and ligand is 1:(0.05-0.4):(0.02-0.25).

3. The method for preparing the improved ion-gel confined palladium-carbon catalyst according to claim 1, characterized in that, The amount of [BMIM]NTf2 accounts for 40%-60% of the total molar amount of the ionic liquid; the amount of Cu(OTf)2 accounts for 20%-40% of the total molar amount of the metal salt.

4. The method for preparing the improved ion-gel confined palladium-carbon catalyst according to claim 1, characterized in that, The acidic solution is a hydrochloric acid solution with a concentration of 3wt%-10wt%; the volume ratio of alcohol to water in the alcohol-water mixed solvent is 1-0.5:5; the pH is adjusted to a range of 4-7; the activation treatment includes at least one of acid washing, oxidation treatment or high-temperature calcination; the reducing agent is formaldehyde, hydrazine hydrate or sodium borohydride; the heating reduction temperature is 40℃-80℃ and the time is 1h-6h; the organic solvent is toluene, xylene or benzene.

5. An improved ion-gel confined palladium-carbon catalyst prepared by the method described in any one of claims 1-4.

6. The application of the improved ion-gel confined palladium-on-carbon catalyst according to claim 5 in the carbonylation reaction of 4-bromophenylsulfone derivatives.

7. The application of the improved ion-gel confined palladium-on-carbon catalyst according to claim 6 in the carbonylation reaction of 4-bromophenylsulfone derivatives, characterized in that, Using the improved ion-gel confined palladium-carbon catalyst, a carbonylation reaction was carried out between a 4-bromophenyl sulfone derivative and carbon monoxide to obtain a 4-methyl sulfone benzoic acid derivative.

8. The application of the improved ion-gel confined palladium-on-carbon catalyst according to claim 7 in the carbonylation reaction of 4-bromophenylsulfone derivatives, characterized in that, The general formula of the 4-bromophenyl sulfone derivative is: 4-Br-(R) n -Ar-SO2CH3 where Ar is a benzene ring; n is 0, 1, 2 or 3; R are each independently selected from halogens, trifluoromethyl, C1-C4 alkyl, C1-C4 alkoxy or five-membered heterocycles; The carbonylation reaction was carried out in a polar aprotic solvent, a weakly basic carboxylate, a modified ion-gel confined palladium-on-carbon catalyst, a catalytic amount of antioxidant 168, and a carbon monoxide atmosphere.

9. The application of the improved ion-gel confined palladium-on-carbon catalyst according to claim 7 in the carbonylation reaction of 4-bromophenylsulfone derivatives, characterized in that, The polar aprotic solvent is N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; The weakly basic carboxylate is potassium acetate, sodium acetate, or cesium acetate; the carbon monoxide pressure is 0.8 MPa-2.0 MPa, the reaction temperature is 80℃-120℃, and the reaction time is 8h-20h. The amount of the improved ion-gel confined palladium-carbon catalyst is 0.1%-5% of the mass of the 4-bromophenyl sulfone derivative.

10. The application of the improved ion-gel confined palladium-on-carbon catalyst according to claim 7 in the carbonylation reaction of 4-bromophenyl sulfone derivatives, characterized in that, The 4-bromobenzyl sulfone derivatives are one or more of the following: 4-bromobenzyl sulfone, 4-bromo-2-fluorobenzyl sulfone, 4-bromo-3-chlorobenzyl sulfone, 4-bromo-3-chloro-2-methylbenzyl sulfone, 4-bromo-3-methyl-2(4,5-dihydroisoxazole)benzyl sulfone, 4-bromo-3-chloro-2-[(5-methyl-2-oxoylide-1,3,4-oxadiazol-3(2H)-yl)methyl]benzyl sulfone, 4-bromo-3-chloro-2-[(2,2,2-trifluoroethoxy)methyl]benzyl sulfone, 4-bromo-3-methyl-2-[(2-methoxyethoxy)methyl]benzyl sulfone, 2-bromo-5-trifluoromethylbenzyl sulfone, 4-bromo-2-trifluoromethylbenzyl sulfone, 4-bromo-3-methyl-2-trifluoromethylbenzyl sulfone, and 4-bromo-3-chloro-2(4,5-dihydroisoxazole)benzyl sulfone.

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