A copper-based catalyst for catalyzing the oxidation of sulfide to produce sulfoxide, and its preparation method and application

Abstract

The present invention provides a copper-based catalyst for catalyzing the oxidation of sulfide to form sulfoxide, as well as a preparation method and application thereof, belonging to the technical field of transition metal coordination polymers. In this solution, salicylic acid is used as a ligand to synthesize the copper-based catalyst, which catalyzes the oxidation of sulfide to form sulfoxide. The catalytic efficiency is enhanced by regulating the internal structure of the molecule, which is beneficial to the synthesis and development of copper-based complexes on the one hand, and to the catalytic oxidation of sulfide on the other hand. After five cycles, the catalytic conversion rate of the catalyst can still reach more than 90%, without the occurrence of catalyst poisoning and the like. Moreover, the catalyst can catalytically convert different sulfide substrates into sulfoxide compounds with high conversion rate and selectivity.

Description

Technical Field

[0001] The invention belongs to the technical field of transition metal coordination polymers, and particularly relates to a copper-based catalyst for catalyzing the oxidation of sulfide to generate sulfoxide, and a preparation method and application thereof. Background Art

[0002] Sulfide oxidation catalysis has garnered significant attention in recent years, as sulfoxide, one of the sulfide oxidation products, is an important intermediate in the synthesis of many industrial products. While research on the selective oxidation of sulfides to sulfoxides rather than sulfones or other byproducts has been extensive, factors such as low oxygen atom utilization and high catalyst costs have hindered the industrialization of this reaction. While copper-based compounds have been shown to exhibit excellent catalytic activity, currently commonly used copper-based catalysts suffer from instability, low recyclability, and high cost. The use of small molecule ligands to coordinate copper-based catalysts enhances their catalytic performance by manipulating their internal molecular structure, which is beneficial for both the synthesis and development of copper-based complexes and the catalytic application of sulfide oxidation. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a copper-based catalyst for catalyzing the oxidation of sulfide to produce sulfoxide, as well as a preparation method and application thereof. Compound 1 Cu3(C2H5OH)2(C7H4O3)6(H2O)2 has good catalytic activity, will not cause catalyst poisoning after multiple catalytic reactions, and has good catalytic stability, and can maintain its structure unchanged during the catalytic process.

[0004] To achieve the above purpose, this scheme provides a copper-based catalyst for catalyzing the oxidation of sulfide to produce sulfoxide, the chemical formula of which is as follows: Cu3(C2H5OH)2(C7H4O3)6(H2O)2, and its structural formula is as follows:

[0005] ;

[0006] Cu3(C2H5OH)2(C7H4O3)6(H2O)2.

[0007] Based on a general inventive concept, the present invention also provides a method for preparing a copper-based catalyst for catalyzing the oxidation of sulfides to produce sulfoxides, comprising the following steps:

[0008] S1. Preparation of Cu3(C2H5OH)2(C7H4O3)6(H2O)2: Add an ethanol solution containing copper chloride dropwise into an ethanol solution containing a salicylic acid ligand, stir the mixed solution, filter it after the reaction is complete, evaporate and crystallize at 15-30°C, and let it stand to obtain dark blue block crystals, namely Cu3(C2H5OH)2(C7H4O3)6(H2O)2;

[0009] Preferably, in step S1, the concentration of copper chloride is 5 mmol, and the concentration of salicylic acid ligand is 5 mmol.

[0010] Preferably, the stirring temperature in step S1 is 15-30° C. and the stirring time is 6 hours.

[0011] Based on a general inventive concept, the present invention also provides an application of a copper-based catalyst for catalyzing the oxidation of sulfide to produce sulfoxide in catalyzing the oxidation conversion of sulfide to produce sulfoxide.

[0012] Preferably, the reaction conditions are: sulfide as the reaction substrate, H2O2 as the oxidant, ethanol as the solvent, the reaction temperature is 50°C, and the reaction time is 40 minutes under the condition of a copper-based catalyst.

[0013] Preferably, the molar ratio of the copper-based catalyst to the sulfide is 1:700-1000.

[0014] Catalytic mechanism of the copper-based catalyst in this scheme:

[0015] The three-dimensional structure of the compound Cu3(C2H5OH)2(C7H4O3)6(H2O)2 is composed of distinct one-dimensional chains. These chains are not linear but rather arranged in a zigzag pattern. Each set of three Cu ions and their corresponding coordinating atoms forms an asymmetric unit. The three Cu ions are centered around the Cu2 ion, with Cu1 and Cu3 arranged centrosymmetrically. Cu1 and Cu3 share the same coordination environment. One Cu1 ion is coordinated to four deprotonated salicylic acids: one provides two O atoms from its carboxyl group, one provides an O atom from its phenolic hydroxyl group, and the remaining two each provide an O atom from its carboxyl group. In addition to these five O atoms, Cu1 is also coordinated to a water molecule, forming a hexacoordinated distorted octahedral configuration. The water molecule is derived from the coordinated water in the copper acetate starting material. The Cu2 ion forms a hexacoordinated distorted octahedral configuration with two salicylic acids and two ethanol groups. Each salicylic acid provides an O in the phenolic hydroxyl group and an O in the carboxyl group as a coordinating molecule.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The catalytic system achieved efficient oxidation conversion of anisole (99%) and generated the target product sulfoxide with high selectivity (95%).

[0018] (2) The catalyst can convert different catalytic substrates into sulfoxide compounds with high conversion rate and selectivity, and has good catalytic activity for the reaction of catalytic oxidation of sulfides to produce sulfoxides.

[0019] (3) After five cycles, the catalytic conversion rate of the catalyst can still reach more than 90%. The catalyst has good catalytic activity and will not be poisoned after multiple catalytic reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 is the structural formula of the catalyst in Experimental Example 1, (A) is a schematic diagram of the overall structure, (B) is a schematic diagram of the one-dimensional chain structure, (C) is a schematic diagram of the unit structure composed of three Cu, (D) is the coordination environment of Cu1 in the structure, and (E) is the coordination environment of Cu2 in the structure;

[0022] Figure 2 The infrared characterization of compound 1 in Experimental Example 2, (A) is the infrared spectrum of the catalyst structure; (B) is the powder X-ray diffraction pattern of the catalyst;

[0023] Figure 3 The reusability of the catalyst in Experimental Example 5 is shown in Figure 5. (A) shows the catalytic conversion rate of the catalyst after five catalytic reactions; (B) shows a comparison of the powder XRD patterns of the catalyst before and after catalysis; and (C) shows the relationship between the catalytic yield and reaction time of the catalyst under different conditions.

[0024] Figure 4 The catalytic performance of the catalyst in Experimental Example 6 on different substrates. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0026] The following examples are provided to illustrate the present invention but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0027] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.

[0028] Example 1 Preparation of copper-based catalyst Cu3(C2H5OH)2(C7H4O3)6(H2O)2.

[0029] S1. Preparation of Cu₃(C₂H₅OH)₂(CₐH₄O₃)₆(H₂O)₂ (Compound 1). Add a 30 mL ethanol solution containing 5 mmol of copper chloride dropwise to a 20 mL ethanol solution containing a salicylic acid ligand (5 mmol). Stir the mixed solution at 30°C for 6 hours. After the reaction is complete, filter the solution and evaporate and crystallize at 15-30°C. After several days, dark blue blocky crystals, Compound 1, are obtained in an approximately 63% yield.

[0030] Experimental Example 1 Single crystal X-ray diffraction analysis of the copper-based catalyst Cu3(C2H5OH)2(C7H4O3)6(H2O)2 was investigated.

[0031] The single crystal X-ray diffraction analysis (SCXRD) of compound 1 is shown in Table 1 and Figure 1 The crystal test data and structure refinement related information of compound 1 are shown in Table 1. Figure 1 shown. Figure 1 A is the three-dimensional structure of compound 1. As can be seen from the figure, the three-dimensional structure of compound 1 is composed of different one-dimensional chains. Figure 1 B is the one-dimensional chain structure of compound 1. As can be seen from the figure, the one-dimensional chain is not linear, but arranged in a zigzag pattern. Every three Cu ions and their corresponding coordination atoms form an asymmetric unit, such as Figure 1 C. The three Cu ions are arranged with Cu2 ion as the symmetry center, and Cu1 and Cu3 are arranged in a centrosymmetric manner. The coordination environment of Cu1 and Cu3 is the same. For example, Figure 1 As shown in D. A Cu1 ion is coordinated with four deprotonated salicylic acids, one of which provides two O atoms in the carboxyl group as coordination atoms, one provides an O atom in the phenolic hydroxyl group, and the remaining two salicylic acids each provide an O atom in the carboxyl group as coordination atoms. In addition to coordinating with the five O atoms mentioned above, Cu1 also coordinates with a water molecule, thus forming a six-coordinated distorted octahedral configuration. The water molecule comes from the coordinated water in the copper acetate raw material. The Cu2 ion forms a six-coordinated distorted octahedral configuration with two salicylic acids and two ethanols. Each salicylic acid provides an O atom in the phenolic hydroxyl group and an O atom in the carboxyl group as coordination molecules.

[0032] Table 1 Crystal data and structure refinement parameters of compound 1

[0033]

[0034] Experimental Example 2 The infrared characterization of the structure of the copper-based catalyst Cu3(C2H5OH)2(C7H4O3)6(H2O)2 was investigated.

[0035] The infrared characterization of compound 1 is as follows Figure 2 As shown in the figure, it can be seen that the -1 The peaks at 1000~1700 cm can be attributed to the absorption peaks of the coordination bonds between Cu and different O atoms. -1 The peak at 3000 cm can be attributed to the absorption peaks of CC bond, CO bond, CP bond, etc. in different ligands. -1 The above peaks can be attributed to the absorption peaks of crystalline water in the CO2 structure in the air and water in the air during the test. Infrared characterization further shows that the structure of compound 1 is consistent with the SCXRD test.

[0036] Experimental Example 3 Powder X-ray diffraction (PXRD) analysis of the copper-based catalyst Cu3(C2H5OH)2(C7H4O3)6(H2O)2 was investigated.

[0037] In order to further characterize the structure of compound 1, the obtained SCXRD data were used to perform theoretical calculations on the PXRD of compound 1 and obtained a simulated spectrum. At the same time, the obtained crystal sample was ground and then subjected to powder X-ray diffraction (PXRD) testing. The results are as follows: Figure 2 As shown, it can be seen that the experimental results of compound 1 are consistent with the theoretical simulation results, which confirms that the obtained compound 1 sample has high purity.

[0038] Experimental Example 4 investigates the catalytic performance of the copper-based catalyst Cu3(C2H5OH)2(C7H4O3)6(H2O)2.

[0039] The catalyst Cu3(C2H5OH)2(C7H4O3)6(H2O)2 (Compound 1) was used to catalyze the oxidation of sulfide to form sulfoxide. The specific reaction conditions are shown in Table 2 below:

[0040] The reaction uses anisole as substrate and reacts at 10-70°C in the presence of a catalyst and solvent. The solvent is 5 mL, the amount of anisole is 0.7 mmol, the oxidant is 100 μL, the catalyst is 1 μmol, and the reaction time is 40 min.

[0041] ;

[0042] Table 2 Catalytic reaction conditions of compound 1 catalyst

[0043]

[0044] b Conversion rate was calculated by H-NMR spectrum, conversion rate = 1-remaining sulfide / total amount of substrate × 100%; c Selectivity was calculated by H-NMR spectrum, selectivity = sulfoxide / (sulfoxide + sulfone) × 100%.

[0045] As shown in Table 2 for reactions 1-4, with the same catalyst, solvent, and reaction temperature, thioanisole was virtually unoxidized when either tert-butyl hydroperoxide (TBHP) or oxygen was used as the oxidant. However, when H₂O₂ was used as the oxidant, the catalytic system achieved highly efficient oxidation conversion of thioanisole (99%) and produced the target sulfoxide with high selectivity (95%). This indicates that the oxidant significantly influences the reaction. Compared to H₂O₂, tert-butyl hydroperoxide has a larger molecular size, making it difficult to effectively bind to the catalyst 1 due to steric hindrance, thus hindering the catalytic process. Furthermore, the oxidizing ability of O₂ is weaker than that of H₂O₂, resulting in a low substrate conversion rate.

[0046] The reaction temperature has a significant effect on the performance of the catalytic system. As shown in reactions 5-7, when the temperature is raised to 70°C, after 40 minutes of reaction, the conversion rate of anisole is 99% and the sulfoxide selectivity is 88%. When the temperature is lowered to 10-35°C, the conversion rate of anisole decreases to 10-20%, which may be due to excessive oxidation under high temperature conditions. When the reaction temperature is lowered, the conversion rate of sulfide decreases significantly.

[0047] To further optimize catalytic conditions, the study also examined the effects of different solvents on the catalytic reaction. For example, in reactions 8-11, substrate conversion and product selectivity in acetonitrile and methanol were similar to those in ethanol. However, conversion was significantly lower in tetrahydrofuran and toluene. This suggests that protic solvents promote the catalytic reaction. Due to environmental concerns, ethanol was ultimately chosen as the reaction solvent for the catalytic system. Based on these studies, the optimal reaction conditions were determined to be: H₂O₂ as the oxidant, ethanol as the solvent, a reaction temperature of 50°C, and a reaction time of 40 minutes. These conditions achieved a good balance between conversion and selectivity, providing an important reference for industrial applications.

[0048] Experimental Example 5 The reusability of the copper-based catalyst Cu3(C2H5OH)2(C7H4O3)6(H2O)2 was investigated.

[0049] In order to evaluate the reusability of the catalyst, five rounds of catalytic reaction experiments were carried out on compound 1 under the optimal conditions. The results are as follows: Figure 3 As shown in A. It can be seen that when the cycle is repeated five times, the catalytic conversion rate of compound 1 can still reach more than 90%, indicating that compound 1 has good catalytic activity and will not cause catalyst poisoning after multiple catalytic reactions. By comparing the PXRD patterns of compound 1 before and after the reaction ( Figure 3 B), it can be seen that the structure of compound 1 did not change before and after the reaction, indicating that compound 1 has good catalytic stability and can maintain its structure unchanged during the catalytic process. In addition, in order to verify that the catalytic process is a heterogeneous catalytic process, a filtration experiment was performed on the reaction. When the reaction was reacted at 50°C for 20 minutes, the reaction solution was hot filtered, and then the filtrate was continued to react at 50°C for 20 minutes. During this period, a small amount of reaction solution was extracted every 5 minutes to test its conversion rate. The test results are as follows Figure 3 As shown in Figure C, the yield of compound 1 was 56.3% at 20 minutes, and the yield remained unchanged after hot filtration and subsequent reaction. This hot filtration experiment confirms the temporal trend of catalytic yield and the heterogeneous catalytic properties of compound 1. This facilitates subsequent catalyst recovery, reduces catalyst costs, and reduces the amount of impurities in the reaction system, facilitating product purification.

[0050] Experimental Example 6 The catalytic activity of the copper-based catalyst Cu3(C2H5OH)2(C7H4O3)6(H2O)2 on different substrates was investigated.

[0051] In order to further explore the catalytic activity of compound 1 for different substrates, five different thioethers were selected as substrates for testing. Figure 4 As shown, it can be seen that for different catalytic substrates, compound 1 can catalytically convert them into sulfoxide compounds with high conversion rate and selectivity, which shows that compound 1 has good catalytic activity for the reaction of catalytic oxidation of sulfides to form sulfoxides.

[0052] The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A copper-based catalyst for catalyzing the oxidation of sulfide to form sulfoxide, characterized in that: The chemical formula is as follows: Cu3(C2H5OH)2(C7H4O3)6(H2O)2, and its structural formula is as follows: ； Cu3(C2H5OH)2(C7H4O3)6(H2O)2; The Cu in the middle position in the structural formula is also coordinated with two ethanol molecules to form a six-coordinated deformed octahedral configuration, which is not shown in the structural formula.

2. A method for preparing a copper-based catalyst for catalyzing the oxidation of sulfides to form sulfoxides as claimed in claim 1, characterized in that: The following steps are involved: S1. Preparation of Cu3(C2H5OH)2(C7H4O3)6(H2O)2: Add an ethanol solution containing copper chloride dropwise into an ethanol solution containing a salicylic acid ligand, stir the mixed solution, filter it after the reaction is completed, evaporate and crystallize at 15-30°C, and let it stand to obtain dark blue block crystals, namely Cu3(C2H5OH)2(C7H4O3)6(H2O)2.

3. The preparation method according to claim 2, characterized in that The stirring temperature in step S1 is 15-30° C. and the stirring time is 6 hours.

4. Use of the copper-based catalyst for catalyzing the oxidation of sulfide to form sulfoxide as claimed in claim 1 or the copper-based catalyst prepared by the preparation method according to any one of claims 2 to 3 in catalyzing the oxidation of sulfide to form sulfoxide.

5. The use according to claim 4, characterized in that The reaction conditions are as follows: sulfide as reaction substrate, H2O2 as oxidant, ethanol as solvent, reaction temperature of 50°C, and reaction time of 40 minutes under the condition of copper-based catalyst.

6. The use according to claim 5, characterized in that The molar ratio of the copper-based catalyst to the sulfide is 1:700-1000.

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