Method for preparing DSD acid oxidation intermediate by using composite catalyst

Abstract

The invention relates to the technical field of fine chemical engineering, in particular to a method for preparing a DSD acid oxidation intermediate by using a composite catalyst. The preparation method comprises the following steps: dissolving NTS in deionized water, adding a composite catalyst, introducing air, dropwise adding a sodium hydroxide solution, heating and preserving heat, introducing oxygen, heating, determining an end point by TLC, filtering, cooling, dropwise adding concentrated sulfuric acid for neutralization, filtering, washing and drying to obtain a product. Wherein the composite catalyst is prepared by doping copper nitrate and manganous nitrate, performing primary sintering with tetraethoxysilane, and modifying with a silane coupling agent. According to the method, the catalytic activity and stability are improved through the defect-type spinel structure and the hydrophobic microstructure of the catalyst, side reactions are inhibited, the product yield is high, the purity is high, and the process is simple, convenient and efficient.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, and in particular to a method for preparing DSD acid oxidation intermediates using a composite catalyst. Background Technology

[0002] DSD acid (4,4'-diaminostilbene-2,2'-disulfonic acid) is a key intermediate in the synthesis of fine chemical products such as fluorescent whitening agents and dyes. The preparation process of its oxidation intermediate directly affects the quality of subsequent products. Currently, manganese-based catalysts are commonly used in industry to catalyze the oxidation of p-nitrotoluene-2,2'-sulfonic acid (NTS) to prepare DSD acid oxidation intermediates. However, traditional catalysts have significant drawbacks: on the one hand, pure manganese catalysts readily react with water molecules to form hydroxyl compounds in high-humidity reaction environments, leading to rapid deactivation of the catalyst due to surface hydroxylation and competitive adsorption at active sites, resulting in poor cycle stability. On the other hand, the byproduct formation pathways during the reaction are complex, such as parallel side reactions of NTS oxidation to aldehyde compounds and tandem side reactions of deep DNS oxidation, resulting in low product purity and insufficient yield. Furthermore, existing catalysts have limited ability to regulate the oxidation potential of the reaction system, cannot effectively promote the CC coupling reaction, and have small specific surface areas and easy aggregation of active sites, further limiting reaction efficiency. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a method for preparing DSD acid oxidation intermediates using a composite catalyst.

[0004] To achieve the above objectives, the present invention provides a method for preparing DSD acid oxidation intermediates using a composite catalyst, comprising the following steps:

[0005] (1) Add NTS to deionized water and stir until dissolved. Then add composite catalyst and stir while purging air to maintain normal pressure. Add sodium hydroxide solution dropwise, controlling the system alkali concentration to be 0.6-0.8 mol / L and the dropwise addition time to be 1-2 h. During the dropwise addition, raise the temperature to 43-47℃ and keep it at that temperature for 30-50 min to obtain reaction solution a.

[0006] (2) Stop the air supply, introduce oxygen, maintain the reaction pressure at 0.15-0.25 MPa, heat the reaction solution a to 55-60℃, and confirm the reaction endpoint by TLC at intervals. The TLC developing solvent is n-butanol: acetic acid: water = 4:1:5. Use Ehrlich reagent for color development. When the reaction endpoint is reached, filter, separate the composite catalyst, cool to room temperature, and then add concentrated sulfuric acid dropwise to neutralize until the solution color turns yellow instantly, accompanied by a large amount of yellow precipitate. Add concentrated sulfuric acid dropwise again until the solution pH = 2-3, filter, wash the product with deionized water until neutral, and dry to obtain the DSD acid oxidation intermediate;

[0007] The preparation method of the composite catalyst is as follows:

[0008] S1. Add copper nitrate and manganese nitrate to an ethanol / water mixture and stir until dissolved. Then add triblock copolymer P123 and stir for 10-20 min. Add tetraethyl orthosilicate and adjust the pH of the solution to 2-3 with dilute hydrochloric acid. Heat to 40-60℃ and stir for 18-24 h. Then transfer to an autoclave, heat to 100-110℃ and react for 18-24 h. Cool to room temperature, filter, wash, and dry. The product is heated to 500-600℃ in a muffle furnace at a heating rate of 3-7℃ and held for 4-6 h to obtain a silicon-based copper-manganese doped catalyst. The mesoporous silica prepared by triblock polymer P123 confines the copper-manganese oxide in the pores through physical confinement, preventing particle sintering and agglomeration during high-temperature calcination and maintaining the high specific surface area of ​​the catalyst.

[0009] S2. 3-Aminopropyltriethoxysilane was added to ethanol, heated to 50-60℃, and stirred for 20-40 min. Then, a silicon-based copper-manganese doped catalyst was added, heated to 60-80℃, and stirred for 6-12 h. The abundant silanol groups on the surface of silica reacted with the silane coupling agent, introducing a hydrophobic structure of silane and an amino active site. The reaction solution was filtered, the solid was collected, and then washed with toluene, ethanol, and acetone, respectively. After drying, the composite catalyst was obtained. The product was characterized by FTIR infrared spectroscopy and SEM.

[0010] Preferably, in (1), the NTS, deionized water and composite catalyst are in a weight ratio of 1:8-12:0.02-0.04.

[0011] Preferably, the air flow rate in step (1) is 2.2-3.2 L / min.

[0012] Preferably, the concentration of the sodium hydroxide solution (1) is 4 mol / L.

[0013] Preferably, the reaction endpoint in (2) refers to the point where the NTS fluorescent spots of the raw material are no longer visible on the TLC plate of the reaction solution.

[0014] Preferably, the concentration of concentrated sulfuric acid in (2) is 98%.

[0015] Preferably, the molar ratio of copper nitrate, manganese nitrate and tetraethyl orthosilicate in S1 is 7:3:20-30.

[0016] Preferably, the copper-manganese doped oxide prepared by copper nitrate and manganese nitrate in S1 at a molar ratio of 7:3 is subjected to high-temperature calcination to form a defect-type spinel structure, with the molecular formula Cu. 0.7Mn 0.3 O 1.05-1.10 Here it is abbreviated as Cu 0.7 Mn 0.3 O x After copper nitrate and manganese nitrate are sintered at high temperature to form copper oxide and manganese oxide, the following reaction continues: 0.7CuO + 0.3MnO2 → Cu 0.7 Mn 0.3 O x +(0.15-0.5X)O2↑, excess CuO breaks the standard spinel (AB2O4) stoichiometric ratio, Cu 2+ Squeezing into the octahedral position (Mn) 3+ This forced some Mn to maintain a high price (Mn 4+ This creates oxygen vacancies, while Cu 2+ Partially reduced to Cu + To balance the charge, the oxygen activation ability of the manganese catalyst is enhanced, and the abundant Cu + Cations and oxygen vacancies greatly promote the O2→O2 - →O - The transformation.

[0017] Preferably, in S1, the ethanol / water mixed solution, triblock copolymer P123, and tetraethyl orthosilicate are in a weight ratio of 20-30:0.03-0.07:1.

[0018] Preferably, the ethanol / water mixed solution in S1 refers to a mixture of ethanol and water in a weight ratio of 1:4.

[0019] Preferably, the concentration of dilute hydrochloric acid in S1 is 1 mol / L.

[0020] Preferably, in S2, the weight ratio of 3-aminopropyltriethoxysilane, silicon-based copper-manganese doped catalyst, and ethanol is 0.1-0.2:1:8-12.

[0021] Preferably, existing manganese-based catalysts are prone to deactivation under high humidity conditions due to competitive adsorption of water molecules and surface hydroxylation. In pure manganese catalysts, Mn 3+ Mn readily reacts with water to form hydroxyl compounds in high humidity environments. Copper doping can stabilize Mn through charge compensation effects. 3+ This reduces its tendency to react with water. At the same time, after grafting with silane coupling agent, the catalyst surface changes from a hydrophilic structure to a hydrophobic structure, forming a hydrophobic microstructure during the reaction process, which further protects the catalyst, prevents deactivation, and extends the catalyst's service life.

[0022] Preferably, according to literature reports, in the reaction of NTS to DNS, the generation of byproducts mainly occurs through two pathways:

[0023]

[0024] Cu in the composite catalyst of this invention 2+ By lowering the oxidation potential of the reaction system, the pathway of NTS oxidation to aldehyde compounds is blocked, thus suppressing parallel side reactions at the source; simultaneously, the Mn in the composite catalyst... 3+ The composite catalyst provides the necessary oxidative environment for CC coupling, accelerates the conversion of NTS to DNS, and reduces the chance of side reactions caused by feedstock retention. The amino group in the composite catalyst forms hydrogen bonds with the oxygen atoms in the sulfonic acid group of NTS, attracting NTS molecules to the catalytic active site, increasing the effective collision probability of the CC coupling reaction, reducing side reactions caused by disordered adsorption of NTS, and accelerating the reaction time due to the increased effective collisions. The amino group in the composite catalyst has a pKa of ≈ 9.5, exhibiting weak basicity, which can reduce the amount of sodium hydroxide used, keeping the system in a "low-side-reaction zone," thereby avoiding deep oxidation of DNS and inhibiting the occurrence of tandem side reactions. Finally, the high specific surface area and mesoporous structure of the catalyst allow DNS to quickly detach from the catalytic active site after generation, reducing the probability of it participating in side reactions as a substrate and avoiding the "red pot" phenomenon.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention constructs a defect-type spinel structure Cu 0.7 Mn 0.3 O x The catalytic effect is improved by utilizing the atomic-level synergistic effect of copper and manganese: on the one hand, excess Cu 2+ Squeezing into the octahedral position forces Mn 3+ Price increase to Mn 4+ Oxygen vacancies are formed and accompanied by Cu 2+ →Cu + Reduction lowers the dissociation energy barrier of O2, promoting the O2→O2 - →O - The transformation provides highly reactive oxygen species for CC coupling; on the other hand, bimetallic directional catalysis: Mn 4+ / Mn 3+ Redox pairs are the main reactions of the C-C coupling, Cu + / Cu 2+ It enables precise regulation of oxygen free radical generation pathways, preventing excessive oxidation caused by highly oxidizing hydroxyl radicals.

[0027] 2. This invention achieves multiple inhibitions of side reactions through the synergistic effect of multifunctional groups:

[0028] Parallel side reaction blocking: Cu 2+ Lowering the oxidation potential of the system blocks the formation pathway of aldehyde-based byproducts;

[0029] Suppression of tandem side reactions: The amino functional groups form a weakly alkaline microenvironment, reducing the amount of NaOH used and avoiding deep oxidation and hydrolysis of DNS under strong alkaline conditions. At the same time, the highly efficient catalytic ability accelerates the reaction time, reduces the generation of condensation products, and avoids the "red pot" phenomenon and the formation of excessive oxidation products.

[0030] 3. This invention stabilizes Mn through charge compensation effect by doping copper ions into a composite catalyst. 3+ This reduces the tendency of the catalyst to react with water to form hydroxyl compounds. At the same time, the silane coupling agent grafting changes the catalyst surface from hydrophilic to hydrophobic, forming a hydrophobic microstructure that physically blocks water molecules from contacting the active center. The mesoporous silica support provides mechanical stability and prevents the dissolution of active components. The three work together to delay catalyst deactivation, extend service life, and ensure the continuous and efficient progress of the reaction. Attached Figure Description

[0031] Figure 1 The SEM image of the composite catalyst prepared in Example 2 of this invention;

[0032] Figure 2 The FTIR infrared spectrum of the composite catalyst prepared in Example 2 of this invention;

[0033] Figure 3 This is a schematic diagram of the TLC at different reaction stages during the preparation of the DSD acid oxidation intermediate according to the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0035] Preparation Example 1: A specific preparation method for a composite catalyst, including the following steps:

[0036] S1. Add 8.86g of copper nitrate and 5.37g of manganese nitrate to 833.32g of ethanol / water mixed solution (ethanol and water are mixed in a weight ratio of 1:4), stir until dissolved, then add 1.25g of triblock copolymer P123, stir for 10min, then add 41.67g of tetraethyl orthosilicate, adjust the pH of the solution to 2 with 1mol / L dilute hydrochloric acid, heat to 40℃, stir for 18h, then transfer to an autoclave, heat to 100℃, react for 18h, cool to room temperature, filter, wash, dry, and the obtained product is heated to 500℃ in a muffle furnace at a heating rate of 3℃ and held for 4h to obtain a silicon-based copper-manganese doped catalyst;

[0037] S2. Add 1g of 3-aminopropyltriethoxysilane to 80g of ethanol, heat to 50℃, stir for 20min, then add 10g of silicon-based copper-manganese doped catalyst, heat to 60℃, stir for 6h, filter the reaction solution, collect the solid, wash with toluene, ethanol and acetone respectively, and dry to obtain the composite catalyst.

[0038] Preparation Example 2: A specific preparation method for a composite catalyst, including the following steps:

[0039] S1. Add 8.86g of copper nitrate and 5.37g of manganese nitrate to 1302.06g of ethanol / water mixed solution (ethanol and water are mixed in a weight ratio of 1:4), stir until dissolved, then add 2.6g of triblock copolymer P123, stir for 15min, then add 52.08g of tetraethyl orthosilicate, adjust the pH of the solution to 2.5 with 1mol / L dilute hydrochloric acid, heat to 50℃, stir for 21h, then transfer to an autoclave, heat to 105℃, react for 21h, cool to room temperature, filter, wash, dry, and the obtained product is heated to 550℃ in a muffle furnace at a heating rate of 5℃ and held for 5h to obtain a silicon-based copper-manganese doped catalyst;

[0040] S2. Add 1.5g of 3-aminopropyltriethoxysilane to 100g of ethanol, heat to 55℃, stir for 30min, then add 10g of silicon-based copper-manganese doped catalyst, heat to 70℃, stir for 9h, filter the reaction solution, collect the solid, wash with toluene, ethanol and acetone respectively, and dry to obtain the composite catalyst.

[0041] Preparation Example 3: A specific preparation method for a composite catalyst, including the following steps:

[0042] S1. Add 8.86g of copper nitrate and 5.37g of manganese nitrate to 1874.97g of ethanol / water mixed solution (ethanol and water are mixed in a weight ratio of 1:4), stir until dissolved, then add 4.37g of triblock copolymer P123, stir for 20min, then add 62.50g of tetraethyl orthosilicate, adjust the pH of the solution to 3 with 1mol / L dilute hydrochloric acid, heat to 60℃, stir for 24h, then transfer to an autoclave, heat to 110℃, react for 24h, cool to room temperature, filter, wash, dry, and the obtained product is heated to 600℃ in a muffle furnace at a heating rate of 7℃ and held for 6h to obtain a silicon-based copper-manganese doped catalyst;

[0043] S2. Add 2g of 3-aminopropyltriethoxysilane to 120g of ethanol, heat to 60℃, stir for 40min, then add 10g of silicon-based copper-manganese doped catalyst, heat to 80℃, stir for 12h, filter the reaction solution, collect the solid, wash with toluene, ethanol and acetone respectively, and dry to obtain the composite catalyst.

[0044] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 2 is that copper nitrate is not added.

[0045] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 2 is that no manganese nitrate is added.

[0046] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 2 is that the molar ratio of copper nitrate, manganese nitrate and tetraethyl orthosilicate is adjusted to 1:1:5.

[0047] Comparative Preparation Example 4: The difference between Comparative Preparation Example 4 and Preparation Example 2 is that the molar ratio of copper nitrate, manganese nitrate and tetraethyl orthosilicate is adjusted to 9:1:25.

[0048] Comparative Preparation Example 5: The difference between Comparative Preparation Example 5 and Preparation Example 2 is that the composite catalyst consists only of copper-manganese doped metal oxides. The specific preparation method is as follows: The specific preparation method of the composite catalyst includes the following steps:

[0049] 8.86 g of copper nitrate and 5.37 g of manganese nitrate were added to 100 g of deionized water and stirred until dissolved. 4 mol / L sodium hydroxide solution was added dropwise to adjust the pH of the reaction solution to 11. The solution was then transferred to an autoclave, heated to 105 °C, and reacted for 21 h. After cooling to room temperature, the solution was filtered, washed, and dried. The resulting product was heated to 550 °C in a muffle furnace at a heating rate of 5 °C and held for 5 h to obtain a composite catalyst.

[0050] Comparative Preparation Example 6: The difference between Comparative Preparation Example 6 and Preparation Example 2 is that copper-manganese doped metal oxides are prepared first, and then combined with tetraethyl orthosilicate to prepare a core-shell composite catalyst. The specific preparation method is as follows: The specific preparation method of the composite catalyst includes the following steps:

[0051] S1. Add 8.86g of copper nitrate and 5.37g of manganese nitrate to 100g of deionized water, stir until dissolved, add 4mol / L sodium hydroxide solution dropwise, adjust the pH of the reaction solution to 11, then transfer to an autoclave, heat to 105℃, react for 21h, cool to room temperature, filter, wash, dry, and the obtained product is heated to 550℃ in a muffle furnace at a heating rate of 5℃ and held for 5h to obtain copper manganese doped metal oxide;

[0052] S2. 5g of copper-manganese doped metal oxide was dispersed in 833.5g of ethanol / water mixed solution (ethanol and water were mixed in a weight ratio of 1:4), 1.67g of triblock copolymer P123 and 33.34g of tetraethyl orthosilicate were added, the pH was adjusted to 2.5 with 1mol / L dilute hydrochloric acid, the temperature was raised to 60℃, and the reaction was carried out for 21h. After filtration, washing and drying, the product was heated to 500℃ in a muffle furnace at a heating rate of 3℃ and held for 4h to obtain a core-shell structured silicon-based copper-manganese doped catalyst.

[0053] S3. Add 1.5g of 3-aminopropyltriethoxysilane to 100g of ethanol, heat to 55℃, stir for 30min, then add 10g of core-shell silicon-based copper-manganese doped catalyst, heat to 70℃, stir for 9h, filter the reaction solution, collect the solid, wash with toluene, ethanol and acetone respectively, and dry to obtain the composite catalyst.

[0054] Comparative Preparation Example 7: The difference between Comparative Preparation Example 7 and Preparation Example 2 is that a composite catalyst was prepared using copper oxide and manganese oxide with tetraethyl orthosilicate, instead of copper-manganese doped metal oxides. The specific preparation method is as follows: The specific preparation method of the composite catalyst includes the following steps:

[0055] S1. Manganese oxide and copper oxide were uniformly mixed in a molar ratio of 3:7 to prepare 5g of mixed powder. Then, 523.64g of ethanol / water mixed solution (ethanol and water were mixed in a weight ratio of 1:4) was added and stirred until dissolved. Then, 1.05g of triblock copolymer P123 was added and stirred for 15min. Then, 20.95g of tetraethyl orthosilicate was added. The pH of the solution was adjusted to 2.5 with 1mol / L dilute hydrochloric acid. The temperature was raised to 50℃ and stirred for 21h. Then, the mixture was transferred to an autoclave, heated to 105℃ and reacted for 21h. After cooling to room temperature, the mixture was filtered, washed, and dried. The product was heated to 550℃ in a muffle furnace at a heating rate of 5℃ and held for 5h to obtain a silicon-based copper manganese oxide catalyst.

[0056] S2. Add 1.5g of 3-aminopropyltriethoxysilane to 100g of ethanol, heat to 55℃, stir for 30min, then add 10g of silicon-based copper manganese oxide catalyst, heat to 70℃, stir for 9h, filter the reaction solution, collect the solid, wash with toluene, ethanol and acetone respectively, and dry to obtain the composite catalyst.

[0057] Comparative preparation example 8: 3-aminopropyltriethoxysilane was replaced with N-propyltriethoxysilane.

[0058] Comparative preparation example 9: Step S2 is omitted. The silicon-based copper-manganese doped catalyst prepared in S1 is a composite catalyst.

[0059] Example 1: A method for preparing DSD acid oxidation intermediates using a composite catalyst, specifically including the following steps:

[0060] (1) Add 100g NTS to 800g deionized water and stir until dissolved. Then add 2g of the composite catalyst prepared according to the preparation method of Preparation Example 1. While stirring, air is introduced to maintain normal pressure and the air flow rate is 2.2L / min. A sodium hydroxide solution with a concentration of 4mol / L is added dropwise, and the alkali concentration of the system is controlled to be 0.6mol / L. The dropwise addition time is 1h. During the dropwise addition, the temperature is raised to 43℃ and kept at the temperature for 30min to obtain reaction solution a.

[0061] (2) Stop the air supply, introduce oxygen, maintain the reaction pressure at 0.15 MPa, heat the reaction solution a to 65°C, and confirm the reaction endpoint time by TLC at regular intervals. The reaction endpoint is reached after 2.9 h. Filter, separate the composite catalyst, cool to room temperature, and then add 98% concentrated sulfuric acid dropwise to neutralize until the solution color turns yellow instantly, accompanied by a large amount of yellow precipitate. Add 98% concentrated sulfuric acid dropwise again until the solution pH = 2. Filter, wash the product with deionized water until neutral, and dry to obtain the DSD acid oxidation intermediate.

[0062] Example 2: A method for preparing DSD acid oxidation intermediates using a composite catalyst, specifically including the following steps:

[0063] (1) Add 100g NTS to 1000g deionized water and stir until dissolved. Then add 3g of the composite catalyst prepared according to the preparation method in Example 2. While stirring, air is introduced to maintain normal pressure and the air flow rate is 2.7L / min. A sodium hydroxide solution with a concentration of 4mol / L is added dropwise, and the alkali concentration of the system is controlled to be 0.75mol / L. The dropwise addition time is 1.5h. During the dropwise addition, the temperature is raised to 45℃ and kept at the temperature for 40min to obtain reaction solution a.

[0064] (2) Stop the air supply, introduce oxygen, maintain the reaction pressure at 0.20 MPa, heat the reaction solution a to 70°C, and confirm the reaction endpoint time by TLC at regular intervals. The reaction endpoint is reached after 2.7 h. Filter, separate the composite catalyst, cool to room temperature, and then add 98% concentrated sulfuric acid dropwise to neutralize until the solution color turns yellow instantly, accompanied by a large amount of yellow precipitate. Add 98% concentrated sulfuric acid dropwise again until the solution pH = 2.5. Filter, wash the product with deionized water until neutral, and dry to obtain the DSD acid oxidation intermediate.

[0065] Example 3: A method for preparing DSD acid oxidation intermediates using a composite catalyst, specifically including the following steps:

[0066] (1) Add 100g NTS to 1200g deionized water and stir until dissolved. Then add 3g of the composite catalyst prepared according to the preparation method of Preparation Example 3. While stirring, air is introduced to maintain normal pressure and the air flow rate is 3.2L / min. A sodium hydroxide solution with a concentration of 4mol / L is added dropwise, and the alkali concentration of the system is controlled to be 0.8mol / L. The dropwise addition time is 2h. During the dropwise addition, the temperature is raised to 47℃ and kept at the temperature for 50min to obtain reaction solution a.

[0067] (2) Stop the air supply, introduce oxygen, maintain the reaction pressure at 0.25 MPa, heat the reaction solution a to 75°C, and confirm the reaction endpoint time by TLC at regular intervals. The reaction endpoint is reached after 2.8 hours. Filter, separate the composite catalyst, cool to room temperature, and then add 98% concentrated sulfuric acid dropwise to neutralize until the solution color turns yellow instantly, accompanied by a large amount of yellow precipitate. Add 98% concentrated sulfuric acid dropwise again until the solution pH=3. Filter, wash the product with deionized water until neutral, and dry to obtain the DSD acid oxidation intermediate.

[0068] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Preparation Example 1, and the reaction reached the endpoint in 4.5 hours.

[0069] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Preparation Example 2, and the reaction reached its endpoint in 4 hours. Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Preparation Example 3, and the reaction reached its endpoint in 3.8 hours. Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Preparation Example 4, and the reaction reached its endpoint in 3.7 hours. Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Preparation Example 5, and the reaction reached its endpoint in 5 hours.

[0070] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Preparation Example 6, and the reaction reached its endpoint in 4.4 hours. Comparative Example 7: The difference between Comparative Example 7 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Preparation Example 7, and the reaction reached its endpoint in 4.2 hours. Comparative Example 8: The difference between Comparative Example 8 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Preparation Example 8, and the reaction reached its endpoint in 3.4 hours.

[0071] Comparative Example 9: The difference between Comparative Example 9 and Example 2 is that the composite catalyst was replaced with the composite catalyst prepared in Comparative Example 9, and the reaction reached the endpoint in 3.8 hours.

[0072] Comparative Example 10: The difference between Comparative Example 10 and Example 2 is that the reaction time is reduced to 2 hours.

[0073] Comparative Example 11: The difference between Comparative Example 11 and Example 2 is that the reaction time is extended to 4 hours.

[0074] Performance testing:

[0075] 1. The time to reach the reaction endpoint in Examples 1-3 and Comparative Examples 1-9 was statistically analyzed, and the results are shown in Table 1.

[0076] 2. High performance liquid chromatography was used to analyze the reaction solution before the product was precipitated by acid addition after the reaction was completed, and to determine the content of product and by-product. The results of Examples 1-3 and Comparative Examples 1-11 are shown in Table 1.

[0077] 3. High performance liquid chromatography was used to analyze the DSD acid oxidation intermediate obtained after precipitation and washing to determine the purity of the DSD acid oxidation intermediate. The obtained DSD acid oxidation intermediate was weighed and the yield was calculated. The experimental results are shown in Table 1.

[0078] Table 1 Performance Tests

[0079]

[0080] Wherein, NTS is: DND is: Aldehyde groups are: Peroxides are: The condensate is:

[0081]

[0082] 4. Catalyst Cyclic Stability Test: The catalysts prepared in Preparation Examples 1-3 and Comparative Examples 1-9 were subjected to cyclic stability tests according to the method for preparing DSD acid oxidation intermediates using composite catalysts in Example 2. After each reaction, the catalyst was centrifuged, filtered, washed, and dried before proceeding to the next round of testing. A total of five rounds of testing were conducted. The decay rate of DNS content in the reaction solution at the reaction endpoint was calculated as (first reaction content - fifth reaction content) / first reaction content × 100%, and the time to reach the reaction endpoint was calculated as h. The experimental results are shown in Table 2.

[0083] Table 2 Catalyst Cyclic Stability

[0084] DNS content decay rate / % Reaction endpoint time / h Example 1 7.2 3.0 Example 2 7.5 2.8 Example 3 8.0 2.9 Comparative Example 1 18.5 6.3 Comparative Example 2 15.3 7.3 Comparative Example 3 13.1 5.4 Comparative Example 4 10.5 6.1 Comparative Example 5 25.7 6.8 Comparative Example 6 18.2 5.6 Comparative Example 7 22.8 6.1 Comparative Example 8 9.5 3.7 Comparative Example 9 20.1 5.8

[0085] Performance Analysis:

[0086] As can be seen from the experimental data in Tables 1 and 2, Examples 1-3 exhibit significant advantages over the comparative examples in terms of reaction endpoint time, yield, product purity, and by-product control, with Example 2 showing the most outstanding overall performance. Its reaction endpoint time was 2.7 h, the product content in the reaction solution reached 96.54%, the product purity reached 98.14%, and the contents of various by-products were all at low levels. In the catalyst cycle stability test, the DNS content in the reaction solution decreased by 7.5%, and the reaction endpoint time did not change significantly, demonstrating excellent stability.

[0087] The superior performance of Example 2 can be analyzed from the following aspects:

[0088] From the perspective of catalytic mechanism, the composite catalyst used in Example 2 was prepared by doping copper nitrate and manganese nitrate in a molar ratio of 7:3, and then calcining at high temperature to form a defect-type spinel structure (Cu). 0.7 Mn 0.3 O x In this structure, the excess CuO disrupts the stoichiometry of standard spinel, causing Cu... 2+ Squeezing into the octahedral position, forcing some Mn 3+ Maintain high prices (Mn) 4+ This creates oxygen vacancies, and at the same time, Cu 2+ Partially reduced to Cu + To balance the charge, this process greatly enhances the activation ability of manganese catalysts for oxygen, promoting O2 oxidation. 2 →O2 - →O - The conversion provides sufficient active oxygen species for the reaction, accelerating the reaction rate. In addition, the mesoporous silica support prepared by the triblock copolymer P123 confines the copper manganese oxide within the pores through physical confinement, effectively preventing the sintering and agglomeration of particles during high-temperature calcination, maintaining the high specific surface area of ​​the catalyst, providing more active sites for the reaction, and further improving the catalytic efficiency.

[0089] From the perspective of side reaction suppression mechanism, during the reaction process, Cu in the composite catalyst... 2+ It can lower the oxidation potential of the reaction system, thereby blocking the pathway of NTS oxidation to aldehyde compounds, and fundamentally inhibiting the occurrence of parallel side reactions. Meanwhile, Mn... 3+The catalyst provides the necessary oxidative environment for CC coupling, accelerating the conversion of NTS to DNS, reducing the residence time of the raw materials, and thus reducing the chance of side reactions caused by the residence of the raw materials. In addition, the amino group in the catalyst forms hydrogen bonds with the oxygen atoms in the sulfonic acid group of NTS, attracting NTS molecules to the catalytic active center in a directional manner, which greatly increases the effective collision probability of the CC coupling reaction. This directional adsorption reduces the side reactions caused by the disordered adsorption of NTS, and the reaction time is accelerated due to the increased effective collisions. At the same time, the amino group has a pKa of ≈9.5, exhibiting weak basicity. This characteristic can reduce the amount of sodium hydroxide used, keeping the system in a "low-side-reaction zone", thereby avoiding deep oxidation of DNS and inhibiting the occurrence of tandem side reactions.

[0090] From the perspective of functional group interaction, 3-aminopropyltriethoxysilane was introduced through the S2 step in the preparation of the composite catalyst. This introduction of functional group brings about amino and silane structures. Among them, the amino group forms hydrogen bonds with the sulfonic acid group of NTS, which enables the directional adsorption of NTS, improves the selectivity of the reaction, and allows NTS to reach the active site more accurately to participate in the reaction, reducing ineffective collisions and side reactions. In addition, the slightly alkaline environment provided by the amino group can reduce the use of sodium hydroxide, reduce the alkalinity of the reaction solution, and thus inhibit the occurrence of tandem side reactions. On the other hand, the introduction of the silane structure changes the catalyst surface from hydrophilic to hydrophobic. This hydrophobic structure forms a hydrophobic microstructure during the reaction, which can effectively reduce the competitive adsorption of water molecules and the active site of the catalyst, reduce the degree of hydroxylation on the catalyst surface, thereby preventing catalyst deactivation and extending its service life.

[0091] From the perspective of hydrophobic structure, under high humidity conditions, the Mn in pure manganese catalyst... 3+ It readily reacts with water molecules to form hydroxyl compounds, leading to catalyst deactivation due to surface hydroxylation and competitive adsorption at active sites. In contrast, the composite catalyst used in Example 2 contains Cu... 2+ Doping of Mn can stabilize Mn through charge compensation effect 3+ Its core mechanism is as follows: when Cu 2+ After incorporation of a manganese-based catalyst, Cu in the defective spinel structure formed by high-temperature calcination 2+ The insertion of octahedral lattice sites forces some Mn to maintain a high valence state (Mn 4+ To balance the crystal structure, at this time, Cu 2+ Partially reduced to Cu + Through Cu 2+ →Cu + The charge conversion compensated for Mn 3+ →Mn 4+ The charge lost during the process forms Cu. + -Mn4+ Charge balance pairs, this charge compensation mechanism reduces Mn 3+ The content of Mn was reduced, thereby decreasing the Mn content. 3+ The probability of reacting with water molecules to form hydroxyl compounds fundamentally suppresses the tendency of catalyst to deactivate due to manganese ion hydrolysis. At the same time, the hydrophobic structure formed by silane coupling agent grafting and the charge compensation effect of copper ions work synergistically. The hydrophobic microstructure reduces the contact between water molecules and the catalyst surface through physical barrier, while the charge compensation of copper ions stabilizes the valence state of the active center from a chemical level. The combined effect of the two enables the catalyst to maintain structural stability in a high-humidity reaction environment, thereby improving the yield and purity of the product.

[0092] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing DSD acid oxidation intermediates using a composite catalyst, characterized in that, Includes the following steps: (1) Add NTS to deionized water and stir until dissolved. Then add composite catalyst and stir while purging air to maintain normal pressure. Add sodium hydroxide solution dropwise, controlling the system alkali concentration to be 0.6-0.8 mol / L and the dropwise addition time to be 1-2 h. During the dropwise addition, raise the temperature to 43-47℃ and keep it at that temperature for 30-50 min to obtain reaction solution a. (2) Stop the air supply, introduce oxygen, maintain the reaction pressure at 0.15-0.25 MPa, heat the reaction solution a to 65-75℃, confirm the reaction endpoint time by TLC at regular intervals, filter and separate the composite catalyst after reaching the reaction endpoint, cool to room temperature, then add concentrated sulfuric acid dropwise to neutralize until the solution color turns yellow instantly, accompanied by a large amount of yellow precipitate, add concentrated sulfuric acid dropwise again until the solution pH = 2-3, filter, wash the product with deionized water until neutral, and dry to obtain DSD acid oxidation intermediate; The preparation method of the composite catalyst is as follows: S1. Add copper nitrate and manganese nitrate to an ethanol / water mixture and stir until dissolved. Then add triblock copolymer P123 and stir for 10-20 min. Add tetraethyl orthosilicate and adjust the pH of the solution to 2-3 with dilute hydrochloric acid. Heat to 40-60℃ and stir for 18-24 h. Then transfer to an autoclave, heat to 100-110℃ and react for 18-24 h. Cool to room temperature, filter, wash, and dry. The product is heated to 500-600℃ in a muffle furnace at a heating rate of 3-7℃ and held for 4-6 h to obtain a silicon-based copper-manganese doped catalyst. S2. Add 3-aminopropyltriethoxysilane to ethanol, heat to 50-60℃, stir for 20-40 min, then add silicon-based copper-manganese doped catalyst, heat to 60-80℃, stir for 6-12 h, filter the reaction solution, collect the solid, wash with toluene, ethanol and acetone respectively, and dry to obtain the composite catalyst.

2. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, In (1), the NTS, deionized water and composite catalyst are in a weight ratio of 1:8-12:0.02-0.

04.

3. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, The air flow rate in (1) is 2.2-3.2 L / min.

4. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, The concentration of the sodium hydroxide solution (1) is 4 mol / L.

5. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, The reaction endpoint in (2) refers to the point where the NTS fluorescent spots of the raw material are no longer visible on the TLC plate of the reaction solution.

6. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, The concentration of concentrated sulfuric acid in (2) is 98%.

7. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, The molar ratio of copper nitrate, manganese nitrate, and tetraethyl orthosilicate in S1 is 7:3:20-30.

8. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, In S1, the ethanol / water mixture, triblock copolymer P123, and tetraethyl orthosilicate are mixed in a weight ratio of 20-30:0.03-0.07:

1. The ethanol / water mixture refers to the mixture of ethanol and water in a weight ratio of 1:

4.

9. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, The concentration of dilute hydrochloric acid in S1 is 1 mol / L.

10. The method for preparing DSD acid oxidation intermediates using a composite catalyst according to claim 1, characterized in that, In S2, the weight ratio of 3-aminopropyltriethoxysilane, silicon-based copper-manganese doped catalyst, and ethanol is 0.1-0.2:1:8-12.

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