MOFs (Metal-Organic Frameworks) catalyst for oxidative coupling of aromatic amine as well as preparation method and application of MOFs catalyst

Abstract

The invention relates to an MOFs (Metal-Organic Frameworks) catalyst for oxidative coupling of aromatic amine as well as a preparation method and application of the MOFs catalyst. And the MOFs catalyst is an MOF-808 catalyst. The structure is simple and clear, and the catalyst has good catalytic activity and cycling stability; h2O2 can be effectively activated, and aromatic amine can be efficiently and selectively oxidized, so that the conversion rate of aromatic amine and the selectivity of products can be improved in a method for preparing azoic compounds by catalyzing aromatic amine oxidation.

Description

Technical Field

[0001] This invention relates to the field of azo compound synthesis technology, and more particularly to a MOF catalyst for the oxidative coupling of aromatic amines, its preparation method and application. Background Technology

[0002] Aromatic azobenzene compounds are a class of compounds containing O - -N + =N structure compounds, due to their unique physical, chemical, and bioelectronic isostatic properties, have wide applications in dyes, functional materials, energy materials, and pharmaceuticals. Traditionally, azobenzene compounds are mainly prepared from inexpensive aromatic amine raw materials through oxidative condensation reactions. However, traditional oxidants such as potassium permanganate, sodium perborate, and persulfate are not only expensive but also generate large amounts of harmful chemical waste. In recent years, with the development of green chemistry, hydrogen peroxide (H2O2) has attracted much attention due to its environmental friendliness. However, the activation of H2O2 usually requires the participation of a catalyst, and different catalysts have significant differences in selectivity and efficiency. Therefore, precise control of the catalyst structure is key to achieving efficient activation of H2O2 and selective oxidation of aniline.

[0003] Metal-organic frameworks (MOFs), as an emerging type of nanoporous material, are coordination polymers formed by the self-assembly of metal ions and organic ligands. They hold significant research value in fields such as gas adsorption, chemical catalysis, biomedicine, and electrochemistry. CN109928898A discloses a green method for preparing azo compounds using MOF-derived magnetic nanoparticles as a recyclable catalyst. This method uses Co@CN as a catalyst, aromatic hydrocarbon nitro compounds as raw materials, and hydrazine hydrate as a reducing agent to synthesize azobenzene compounds in an alcohol solution. While this synthesis method can reduce production costs and is environmentally friendly, the reaction is carried out at 50°C, the highest yield is 82%, and the post-processing is complex.

[0004] Therefore, designing and providing a MOF catalyst with good catalytic activity and excellent cycling stability for the oxidative coupling of aromatic amines is of great significance for the catalytic oxidation of aromatic amines to prepare high-yield azo compounds. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a MOF catalyst for the oxidative coupling of aromatic amines, its preparation method, and its application. The MOF catalyst for the oxidative coupling of aromatic amines is simple to prepare, exhibits good catalytic effect, and demonstrates excellent cycle stability. In catalyzing the oxidation of aromatic amines to prepare azo compounds, it can achieve efficient activation of H₂O₂ and selective oxidation of aniline, resulting in azo compound synthesis methods that offer advantages such as mild reaction conditions, high selectivity, high conversion rate, environmental friendliness, and simple operation.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a MOF catalyst for the oxidative coupling of aromatic amines, wherein the MOF catalyst is a MOF-808 catalyst.

[0008] The MOF catalyst for the oxidative coupling of aromatic amines provided by this invention is MOF-808 catalyst, which is simple to prepare, has good catalytic effect and excellent cycle stability. It can effectively achieve the purpose of activating H2O2 and selectively oxidizing aromatic amines. Therefore, when catalyzing the oxidation of aromatic amines to prepare azo compounds, it can obtain excellent comprehensive effects of high aromatic amine conversion rate and good product selectivity.

[0009] As a preferred technical solution in this invention, the MOF-808 catalyst is MOF-808(6OH).

[0010] Preferably, the MOF-808(6OH) has the structure shown in formula (I):

[0011] Zr6(μ3-O)4(μ3-OH)4(BTC) 1.97 (FA) 0.12 (OH) 5.97 (H2O) 5.97 Formula (I).

[0012] This invention uses MOF-808(6OH) as a MOF catalyst, which has a simple and well-defined structure and good catalytic activity and cycle stability. It can better activate H2O2 and efficiently and selectively oxidize aromatic amines, thereby further improving the conversion rate and product selectivity of aromatic amines in the method of catalytic oxidation of aromatic amines to prepare azo compounds.

[0013] In a second aspect, the present invention provides a method for preparing a MOF catalyst for the oxidative coupling of aromatic amines as described in the first aspect, the method comprising the following steps:

[0014] After reacting zirconium salt and organic ligand, the resulting product is treated with hydrochloric acid to obtain the MOF catalyst for the oxidative coupling of aromatic amines.

[0015] Preferably, the hydrochloric acid treatment includes dispersing the reaction product in hydrochloric acid and stirring at 80-100°C for 12-36 hours.

[0016] Among them, 80-100℃ can be, for example, 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃ or 100℃, and 12-36h can be, for example, 12h, 15h, 18h, 20h, 23h, 25h, 28h, 30h, 32h, 34h or 36h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the range.

[0017] Preferably, the mass concentration of the product obtained from the reaction in hydrochloric acid is 10 g / L.

[0018] Preferably, the hydrochloric acid includes a 0.5-1.5M hydrochloric acid solution, for example, it can be 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, 1.1M, 1.2M, 1.3M, 1.4M or 1.5M, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0019] The MOF catalyst obtained by hydrochloric acid treatment in this invention is MOF-808(6OH). When the hydrochloric acid used is a 0.5-1.5M hydrochloric acid solution, it can improve the production efficiency of the obtained MOF-808(6OH) and reduce the production cost. When the molar concentration of the hydrochloric acid solution is lower than 0.5M, the acidity is too low, resulting in poor removal of coordinated formate ions, requiring multiple hydrochloric acid treatments, which not only reduces the production efficiency but also increases the production cost. When the molar concentration of the hydrochloric acid solution is higher than 1.5M, the acidity is too high, which can cause some MOF-808 to dissolve, which is not conducive to the preparation of the MOF catalyst MOF-808(6OH).

[0020] It should be noted that "0.5-1.5M" in this invention refers to 0.5-1.5 mol / L.

[0021] Preferably, the hydrochloric acid treatment further includes separation, washing, and drying steps.

[0022] Preferably, the separation method includes centrifugal separation and / or filtration separation.

[0023] Preferably, the washing liquid includes deionized water.

[0024] Preferably, the number of washing cycles is 4-6 times, for example, 4, 5 or 6 times.

[0025] Preferably, the drying method is vacuum drying.

[0026] It should be noted that the drying temperature and time in this invention are not specifically limited and can be adjusted according to actual conditions. Exemplary values ​​include, but are not limited to, 70-90℃ and 6-20h. For example, 70-90℃ can be 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃, or 90℃, and 6-20h can be 6h, 8h, 10h, 12h, 14h, 16h, 18h, or 20h, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific values ​​included in the range.

[0027] As a preferred embodiment of the present invention, the zirconium salt includes zirconium oxychloride octahydrate and / or zirconium chloride.

[0028] Preferably, the organic ligand comprises pyromellitic acid.

[0029] Preferably, the molar ratio of the zirconium salt to the organic ligand is (1-3):1, wherein (1-3) can be, for example, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8 or 3, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0030] Preferably, the reaction is carried out in a solvent.

[0031] Preferably, the solvent includes N,N-dimethylformamide.

[0032] It should be noted that the present invention does not impose any special limitation on the molar concentration of the zirconium salt in the solvent. Conventional reaction concentrations in the art are applicable, including but not limited to 0.03-0.5 mol / L, such as 0.03 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, or 0.5 mol / L, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0033] Preferably, the reactants also include a regulator.

[0034] Preferably, the regulator comprises formic acid.

[0035] Preferably, the molar ratio of the regulator to the organic ligand is (800-1100):1, wherein (800-1100) can be, for example, 800, 820, 850, 880, 900, 920, 950, 1000, 1050 or 1100, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0036] Preferably, the reaction is carried out in a hydrothermal reactor.

[0037] Preferably, the reaction temperature is 90-110℃, for example, it can be 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃ or 110℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0038] Preferably, the reaction time is 15-25 hours, for example, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours or 25 hours, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0039] Preferably, the reaction further includes a post-processing step.

[0040] Preferably, the post-processing method includes cooling, separation, washing, and drying.

[0041] It should be noted that the cooling temperature is not specifically limited and can be adjusted according to actual needs, including but not limited to room temperature.

[0042] Preferably, the separation method in the post-processing includes centrifugation and / or filtration separation.

[0043] Preferably, the washing method in the post-treatment includes washing with N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) 2-4 times each, for example, 2 times, 3 times or 4 times, and the number of times DMF and THF are used for washing can be the same or different.

[0044] Preferably, the drying method in the post-processing includes drying using a vacuum oven.

[0045] It should be noted that the drying temperature and time in the post-processing of this invention are not specifically limited and can be adjusted according to the actual situation. Exemplary values ​​include, but are not limited to, 70-90℃ and 6-20h. For example, 70-90℃ can be 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃ or 90℃, and 6-20h can be 6h, 8h, 10h, 12h, 14h, 16h, 18h or 20h, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific values ​​included in the range.

[0046] As a preferred embodiment of the present invention, the hydrochloric acid treatment further includes a digestion test step.

[0047] Preferably, the digestion test includes first dispersing the crude product obtained after hydrochloric acid treatment in a digestion solution for digestion, and then performing nuclear magnetic resonance hydrogen spectrum testing on the supernatant after digestion.

[0048] Preferably, the digestion solution comprises a heavy aqueous solution of sodium hydroxide.

[0049] Preferably, the mass concentration of the crude product in the digestion solution is 6-10 g / L, for example, it can be 6 g / L, 6.5 g / L, 7 g / L, 7.5 g / L, 8 g / L, 8.5 g / L, 9 g / L, 9.5 g / L or 10 g / L, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0050] Preferably, the mass concentration of sodium hydroxide in the heavy aqueous solution of sodium hydroxide is 40-60 g / L, for example, it can be 40 g / L, 42 g / L, 44 g / L, 46 g / L, 48 g / L, 50 g / L, 52 g / L, 54 g / L, 56 g / L, 58 g / L or 60 g / L, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0051] Preferably, the digestion time is 18-30 hours, for example, it can be 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours or 30 hours, as well as specific values ​​between the above-mentioned values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0052] As a preferred embodiment of the present invention, if the proportion of formate ions in the proton nuclear magnetic resonance spectrum test is higher than 1% of the peak area of ​​pyromellitic tricarboxylate, the hydrochloric acid treatment step is repeated.

[0053] This invention employs a digestion test to detect the content of formate ions to determine whether hydrochloric acid treatment should continue. Through the ingenious combination of digestion test and hydrochloric acid treatment, the structure of the obtained MOFs can be precisely controlled, so that the obtained MOF catalyst is MOF-808(6OH), thereby enabling better efficient activation of H2O2 and selective oxidation of aromatic amines. This allows for the efficient preparation of different azo compounds by oxidizing and condensing aromatic amines at room temperature and lower temperatures.

[0054] Preferably, the preparation method of the MOF catalyst for the oxidative coupling of aromatic amines specifically includes the following steps:

[0055] (1) Mix zirconium salt and organic ligand with solvent in a molar ratio of (1-3):1, add regulator, and react at 90-110℃ for 15-25h; after the reaction is completed, cool, separate, wash and dry the reaction solution;

[0056] (2) Take the dried product obtained in step (1) and disperse it in hydrochloric acid. After stirring at 80-100℃ for 12-36h, the crude product is obtained after separation, washing and drying.

[0057] (3) Take the crude product obtained in step (2) and disperse it in the digestion solution. After digestion for 18-30 hours, perform nuclear magnetic resonance hydrogen spectrum test. If the proportion of formate ions is higher than 1% of the peak area of ​​pyromellitic tricarboxylate, repeat the hydrochloric acid treatment step in step (2) until the proportion of formate ions is not higher than 1% of the peak area of ​​pyromellitic tricarboxylate, and obtain the MOFs catalyst.

[0058] Thirdly, the present invention provides a method for preparing azo oxide compounds by catalytic oxidation of aromatic amines, the method comprising: oxidizing aromatic amines to obtain azo oxide compounds under the catalysis of the MOFs catalyst described in the first aspect.

[0059] Preferably, based on the mass percentage of aromatic amines as 100%, the mass percentage of the MOF catalyst is ≤32% and not 0, for example, it can be 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30% or 32%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0060] This invention applies MOF catalysts to the oxidative coupling reaction of aromatic amines, effectively achieving efficient activation of H2O2 and selective oxidation of aromatic amines. In the reaction catalyzing the oxidation of aromatic amines to prepare azo compounds, the addition amount of MOFs not exceeding 32% of the aromatic amine mass exhibits better catalytic activity. Excessive addition leads to an overly rapid oxidation reaction, resulting in the formation of over-oxidized products and reduced product selectivity. Conversely, insufficient addition results in excessively long reaction times, and prolonged continuous reactions can easily reduce catalyst activity, although this does not significantly affect the conversion rate of aromatic amines or the product selectivity. Furthermore, the optimal catalytic effect is achieved when the addition amount is 21.5% of the aromatic amine mass, resulting in the best overall effect in terms of both aromatic amine conversion and product selectivity.

[0061] Preferably, the aromatic amine includes substituted or unsubstituted aniline, heterocyclic aromatic amine and alkyl diphenylamine, wherein the substituent is selected from halogen, C1-C5 alkyl, C1-C3 alkoxy, nitro or amino.

[0062] In this invention, C1-C5 can be C1, C2, C3, C4 or C5, and C1-C3 can be C1, C2 or C3.

[0063] Preferably, the heterocyclic aromatic amine comprises 3-aminopyridine.

[0064] Preferably, the alkyl diphenylamine includes 2,2′-ethylenediphenylamine.

[0065] Preferably, the raw materials for the oxidation reaction also include H2O2.

[0066] Preferably, the molar ratio of H2O2 to aromatic amine is (2.1-2.5):1, wherein (2.1-2.5) can be, for example, 2.1, 2.2, 2.3, 2.4 or 2.5, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0067] Preferably, the oxidation reaction is carried out in an organic solvent.

[0068] Preferably, the organic solvent includes ethanol.

[0069] It should be noted that the molar concentration of the aromatic amine in the organic solvent is not particularly limited, and commonly used molar concentrations in the art are applicable, including but not limited to 0.1-0.5 mol / L, such as 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.15 mol / L, or 0.5 mol / L, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0070] Preferably, the temperature of the oxidation reaction is 0-60℃, for example, it can be 0℃, 10℃, 20℃, 30℃, 40℃, 50℃ or 60℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0071] In this invention, the use of specific MOF catalysts enables the oxidation reaction to proceed at room temperature or lower temperatures, resulting in milder reaction conditions, safer operation, lower energy consumption, and greater practicality. Furthermore, by applying these specific MOF catalysts to the catalytic oxidation of aromatic amines to prepare azo compounds, this invention achieves better product selectivity by lowering the temperature and reducing hydrogen peroxide content.

[0072] Preferably, the oxidation reaction time is 1.5-3 hours, for example, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours or 3 hours, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0073] Preferably, the oxidation reaction further includes a post-processing step.

[0074] Preferably, the post-processing step includes separation and purification.

[0075] Preferably, the separation method includes centrifugal separation and / or filtration separation.

[0076] Preferably, the purification method includes evaporation crystallization.

[0077] Compared with the prior art, the present invention has at least the following beneficial effects:

[0078] (1) The MOFs catalyst for the oxidative coupling of aromatic amines provided by the present invention is simple to prepare, has good catalytic effect and good cycle stability, and can effectively achieve the purpose of activating H2O2 and selectively oxidizing aromatic amines. In the method of catalyzing the oxidation of aromatic amines to prepare azo compounds, it can make the aromatic amine achieve a conversion rate of 90.0-99.6% and a product selectivity of 87.3-99.5%, and can still maintain a high conversion rate (95.4%) and high selectivity (90.8%) after 15 consecutive uses.

[0079] (2) The MOF catalyst for the oxidative coupling of aromatic amines provided by the present invention is further preferably MOF-808(6OH). Its preparation method is simple and easy to operate. By combining hydrochloric acid treatment and digestion test, the structure of the obtained MOF-808(6OH) can be precisely controlled, thereby having a better catalytic effect. This significantly improves the conversion rate and selectivity in the method of catalyzing the oxidation of aromatic amines to prepare azo compounds, enabling the aromatic amines to achieve a conversion rate of 98% and a product selectivity of 97%. Attached Figure Description

[0080] Figure 1 The 1H NMR spectrum is obtained from the digestion test procedure in Example 1. Detailed Implementation

[0081] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0082] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available.

[0083] Example 1

[0084] This embodiment provides a MOF catalyst for the oxidative coupling of aromatic amines, the preparation method of which includes the following steps:

[0085] (1) Zirconium oxychloride octahydrate (322 mg, 1 mmol) and trimesic acid (70 mg, 0.33 mmol) were mixed with N,N-dimethylformamide (10 mL), and formic acid (10 mL, 265 mmol) was added. The mixture was dissolved by sonication to obtain a clear and transparent colorless solution. The solution was transferred to a polytetrafluoroethylene liner in a hydrothermal reactor and reacted in an oven at 100 °C for 18 h. After the reaction was completed, the hydrothermal reactor was cooled, and the suspension was removed and centrifuged to separate the solid product from the mother liquor. The solid product was washed three times with 20 mL of DMF, and then washed three times with 20 mL of tetrahydrofuran. The washed solid was placed in a vacuum oven and dried under vacuum at 80 °C for 12 h, and then ground in a mortar.

[0086] (2) Take 50 mg of the ground product obtained in step (1) and disperse it in 5 mL of 1 M hydrochloric acid solution. Stir at 90 °C for 24 h. Centrifuge the hydrochloric acid-treated solid and wash it 5 times with 10 mL of deionized water. Dry the washed solid under vacuum at 80 °C for 12 h to obtain the crude product;

[0087] (3) Disperse 5 mg of the crude product obtained in step (2) in 0.6 mL of 30% sodium hydroxide heavy water solution, digest for 24 h, and then take out the supernatant for nuclear magnetic resonance hydrogen spectrum testing. Figure 1 The MOF catalyst for the oxidative coupling of aromatic amines was obtained.

[0088] like Figure 1 As shown, in the 1H NMR spectrum of the digestion test in this embodiment, the peak with a chemical shift of 8.25 is the peak of trimesic acid, and the peak with a chemical shift of 8.30 is the peak of formic acid. According to the peak area integral, the proportion of formate ions in the peak area of ​​trimesic acid is 1%, so the hydrochloric acid treatment step is not repeated, and the MOF catalyst for the oxidative coupling of aromatic amines is obtained.

[0089] Example 2

[0090] This embodiment provides a MOF catalyst for the oxidative coupling of aromatic amines, the preparation method of which includes the following steps:

[0091] (1) Zirconium chloride (233 mg, 1 mmol) and trimesic acid (70 mg, 0.33 mmol) were mixed with N,N-dimethylformamide (10 mL), and formic acid (10 mL, 265 mmol) was added. The mixture was dissolved by sonication to obtain a clear and transparent colorless solution. The solution was transferred to a polytetrafluoroethylene liner in a hydrothermal reactor and reacted in an oven at 90 °C for 25 h. After the reaction was completed, the hydrothermal reactor was cooled, and the suspension was removed and centrifuged to separate the solid product from the mother liquor. The solid product was washed three times with 20 mL of DMF, and then washed three times with 20 mL of tetrahydrofuran. The washed solid was placed in a vacuum oven and dried under vacuum at 80 °C for 12 h, and then ground in a mortar.

[0092] (2) Take 50 mg of the ground product obtained in step (1) and disperse it in 5 mL of 0.5 M hydrochloric acid solution. Stir at 80 °C for 36 h. Centrifuge the hydrochloric acid-treated solid and wash it 5 times with 10 mL of deionized water. Dry the washed solid under vacuum at 80 °C for 12 h to obtain the crude product;

[0093] (3) Disperse 5 mg of the crude product obtained in step (2) in 0.6 mL of sodium hydroxide heavy water solution, digest for 24 h, take out the supernatant, and perform nuclear magnetic resonance hydrogen spectrum test to obtain the MOFs catalyst for the oxidative coupling of aromatic amines.

[0094] In this embodiment, the proportion of formate ions in the peak area of ​​trimesoate was determined based on the proton NMR spectrum obtained from the digestion test (the determination method is the same as in Example 1). The hydrochloric acid treatment was performed twice, and the treatment time was 36 hours each time.

[0095] Example 3

[0096] This embodiment provides a MOF catalyst for the oxidative coupling of aromatic amines, the preparation method of which includes the following steps:

[0097] (1) Zirconium oxychloride octahydrate (107 mg, 0.33 mmol) and trimesic acid (70 mg, 0.33 mmol) were mixed with N,N-dimethylformamide (10 mL), and formic acid (12.5 mL, 330 mmol) was added. The mixture was sonicated to obtain a clear and transparent colorless solution. The solution was transferred to a polytetrafluoroethylene liner in a hydrothermal reactor and reacted in an oven at 110 °C for 15 h. After the reaction was completed, the hydrothermal reactor was cooled, and the suspension was removed. The solid product was separated from the mother liquor by centrifugation. The solid product was washed three times with 20 mL of DMF, and then washed three times with 20 mL of tetrahydrofuran. The washed solid was placed in a vacuum oven and dried under vacuum at 80 °C for 12 h, and then ground in a mortar.

[0098] (2) Take 50 mg of the ground product obtained in step (1) and disperse it in 5 mL of 1.5 M hydrochloric acid solution. Stir at 100 °C for 12 h. Centrifuge the hydrochloric acid-treated solid and wash it 5 times with 10 mL of deionized water. Dry the washed solid under vacuum at 80 °C for 12 h to obtain the crude product;

[0099] (3) Disperse 5 mg of the crude product obtained in step (2) in 0.6 mL of sodium hydroxide heavy water solution, digest for 24 h, take out the supernatant, and perform nuclear magnetic resonance hydrogen spectrum test to obtain the MOFs catalyst for the oxidative coupling of aromatic amines.

[0100] In this embodiment, the proportion of formate ions in the peak area of ​​trimesoate was determined based on the proton NMR spectrum obtained from the digestion test (the determination method is the same as in Example 1). The hydrochloric acid treatment was performed a total of 6 times, and the treatment time was 12 hours each time.

[0101] Example 4

[0102] This embodiment provides a MOF catalyst for the oxidative coupling of aromatic amines. The only difference between this embodiment and Example 1 is that the hydrochloric acid treatment step is not repeated when the proportion of formate ions measured in the digestion test step (3) is 10% of the peak area of ​​pyromellitic tricarboxylate. Other raw materials, addition amounts and preparation methods are the same as in Example 1.

[0103] Example 5

[0104] This embodiment provides a MOF catalyst MOF-808 material, which differs from Example 1 only in that steps (2) and (3) are omitted, while the other raw materials, addition amounts and preparation methods are the same as in Example 1.

[0105] Application Example 1

[0106] This application example provides a method for preparing azo oxides by catalytic oxidation of aromatic amines, which includes the following steps:

[0107] After thoroughly grinding the MOF catalyst (Example 1), 20 mg of it was mixed with 3 mL of ethanol, 93 mg of aniline (1 mmol), and 0.22 mL of 30% H2O2 solution (2.15 mmol). The mixture was stirred at 25 °C for 1.5 h. After the reaction was completed, the MOF catalyst was removed by centrifugation, yielding an ethanol solution of azobenzene oxide. The solution was then evaporated and crystallized to obtain azobenzene oxide crystalline product.

[0108] The NMR characterization data of the azobenzene crystal product are as follows:

[0109] 1 H NMR (400MHz, CDCl3): δ8.36-8.34 (d, J = 8.3Hz, 2H), 8.21-8.19 (d, J = 8.2Hz, 2H), 7.61-7.50 (m, 5H), 7.44-7.41 (t, J = 7.4Hz, 1H).

[0110] Application Example 2

[0111] This application example provides a method for preparing azo oxides by catalytic oxidation of aromatic amines, which includes the following steps:

[0112] After thoroughly grinding the MOF catalyst (Example 2), 20 mg of it was mixed with 3 mL of ethanol, 93 mg of aniline, and 0.20 mL (2 mmol) of 30% H2O2 solution. The mixture was stirred at 0 °C for 3 h. After the reaction was completed, the MOF catalyst was removed by centrifugation, yielding an ethanol solution of azobenzene oxide. The solution was then evaporated and crystallized to obtain azobenzene oxide crystalline product.

[0113] Application Example 3

[0114] This application example provides a method for preparing azo oxides by catalytic oxidation of aromatic amines, which includes the following steps:

[0115] After thoroughly grinding the MOF catalyst (Example 3), 20 mg of it was mixed with 3 mL of ethanol, 93 mg of aniline (1 mmol), and 0.25 mL of 30% H2O2 solution (2.5 mmol). The mixture was stirred at 60 °C for 1 h. After the reaction was completed, the MOF catalyst was removed by centrifugation, yielding an ethanol solution of azobenzene oxide. The solution was then evaporated and crystallized to obtain azobenzene oxide crystalline product.

[0116] Application Example 4

[0117] This application example provides a method for preparing azo oxides by catalytic oxidation of aromatic amines, which includes the following steps:

[0118] After thoroughly grinding the MOF catalyst (Example 1), 30 mg of it was mixed with 3 mL of ethanol, 94 mg (1 mmol) of 3-aminopyridine, and 0.22 mL (2.15 mmol) of 30% H2O2 solution. The mixture was stirred at 45 °C for 3 h. After the reaction was completed, the MOF catalyst was removed by centrifugation, yielding an ethanol solution of 1,2-bis(pyridin-3-yl)azo-1-oxide. The solution was then evaporated and crystallized to obtain crystalline product of 1,2-bis(pyridin-3-yl)azo-1-oxide.

[0119] The NMR characterization data of the 1,2-bis(pyridin-3-yl)azo-1-oxide crystal product are as follows:

[0120] 1 H NMR (400MHz, CDCl3): δ9.55(d,J=2.6Hz,1H),9.22(d,J=2.4Hz,1H),8.81(dd,J=4.8,1.5Hz,1H),8.75(d dd,J=8.4,2.4,1.6Hz,1H),8.64-8.54(m,2H),7.49(dd,J=8.4,4.8Hz,1H),7.43(dd,J=8.4,4.8Hz,1H).

[0121] Application Example 5

[0122] This application example provides a method for preparing azo compounds by catalytic oxidation of aromatic amines. The difference between this method and Application Example 1 is that the amount of MOF catalyst added is adjusted from 20 mg to 35 mg, while the other raw materials, amounts added, and preparation methods are the same as in Application Example 1.

[0123] Application Example 6

[0124] This application example provides a method for preparing azo compounds by catalytic oxidation of aromatic amines. The difference between this method and Application Example 1 is that the amount of MOF catalyst added is adjusted from 20 mg to 30 mg, while the other raw materials, amounts added, and preparation methods are the same as in Application Example 1.

[0125] Application Example 7

[0126] This application example provides a method for preparing azo oxides by catalytic oxidation of aromatic amines, which includes the following steps:

[0127] After thoroughly grinding the MOF catalyst (Example 1), 30 mg was mixed with 3 mL of ethanol, 106 mg (0.5 mmol) of 2,2′-ethylenediphenylamine, and 0.22 mL (2.15 mmol) of 30% H2O2 solution, and stirred at 45 °C for 3 h. After the reaction was completed, the MOF catalyst was removed by centrifugation to obtain an ethanol solution of 11,12-dihydrodibenzo[c,g][1,2]diazine-5-oxide. The solution was evaporated and crystallized to obtain crystalline product of 11,12-dihydrodibenzo[c,g][1,2]diazine-5-oxide.

[0128] The NMR characterization data of the 11,12-dihydrodibenzo[c,g][1,2]diazoazine-5-oxide crystal product are as follows:

[0129] 1 H NMR (400MHz, CDCl3): δ7.16-7.00 (m, 4H), 6.99-6.91 (m, 3H), 6.86 (d, J = 7.8Hz, 1H), 3.31 (ddd, J = 14.6, 10. 3,5.5Hz,1H),3.16(ddd,J=14.8,10.2,4.6Hz,1H),2.90(ddd,J=14.2,10.0,4.7Hz,1H),2.85-2.74(m,1H).

[0130] Application Example 8

[0131] This application example provides a method for preparing azo compounds by catalytic oxidation of aromatic amines. The difference between this method and Application Example 1 is that the MOF catalyst (Example 1) is replaced with an equal mass of MOF catalyst (Example 4), while the other raw materials, amounts added, and preparation methods are the same as in Application Example 1.

[0132] Application Example 9

[0133] This application example provides a method for preparing azo compounds by catalytic oxidation of aromatic amines. The difference between this method and Application Example 1 is that the MOF catalyst (Example 1) is replaced with an equal mass of MOF catalyst (Example 5), while the other raw materials, amounts added, and preparation methods are the same as in Application Example 1.

[0134] Comparative Application Example 1

[0135] This comparative application example provides a method for preparing azo compounds by catalytic oxidation of aromatic amines. The difference between this method and Application Example 1 is that no MOF catalyst is added, while the other raw materials, amounts added, and preparation methods are the same as in Application Example 1.

[0136] I. The conversion rate and selectivity analysis methods / calculation formulas for Application Examples 1-9 and Comparative Application Example 1 are as follows:

[0137] The concentrations of each substance in the solution after the reaction were quantified by gas chromatography. 1 mmol of undecane was added as an internal standard. The peak areas of each substance in the chromatogram were compared with those of the internal standard, and the concentrations of each substance were calculated by using a standard curve.

[0138] Conversion rate: [1 - (concentration of aromatic amine / initial concentration of aromatic amine)] × 100%;

[0139] Selectivity: [Product concentration × 2 / (Initial concentration of aromatic amine - Concentration of aromatic amine)] × 100%.

[0140] The test results are shown in Table 1.

[0141] Table 1

[0142] Conversion rate / % Selectivity / % Application Example 1 98.5 97.1 Application Example 2 90.6 99.5 Application Example 3 99.5 87.3 Application Example 4 90.0 93.9 Application Example 5 99.6 87.8 Application Example 6 98.7 92.6 Application Example 7 97.5 97.8 Application Example 8 97.8 95.2 Application Example 9 94.3 91.7 Comparative Application Example 1 0.0 0.0

[0143] The test results show that:

[0144] (1) As can be seen from Application Examples 1 to 9, when the MOFs catalyst provided by the present invention catalyzes the oxidation of aromatic amines to prepare azo compounds, it can effectively activate H2O2 and has a good catalytic effect, enabling aromatic amines to achieve a conversion rate of 90.0-99.6% and a product selectivity of 87.3-99.5%.

[0145] (2) As can be seen from Application Examples 1, 4 and 7, the MOFs catalyst provided by the present invention can play a good catalytic activity in the catalytic oxidation of different aromatic amines to prepare azo compounds, and has a wide range of applications.

[0146] (3) By comparing Application Example 5 and Application Example 6, it can be seen that the amount of MOF catalyst added in Application Example 5 is higher than 32% of the total mass of aromatic amine. Although the conversion rate of the measured product is slightly improved, its selectivity is significantly reduced. This shows that by controlling the amount of MOF catalyst added, the present invention can further improve the comprehensive technical effect of aromatic amine conversion rate and product selectivity.

[0147] (4) By comparing Application Example 1 with Application Examples 8 and 9, it can be seen that the MOF catalyst used in Application Example 8 was not fully treated with hydrochloric acid during the preparation process, and the resulting MOF catalyst was MOF-808(6OH) with a non-single and definite structure. Compared with Application Example 1, the conversion rate of aromatic amines and the product selectivity were both reduced. The MOF catalyst used in Application Example 9 was not treated with hydrochloric acid during the preparation process, that is, the MOF catalyst obtained was MOF-808 instead of MOF-808(6OH). Compared with Application Example 1, the conversion rate of aromatic amines and the product selectivity were both significantly reduced. This shows that the MOF catalyst of the present invention, by further optimizing it to MOF-808(6OH) (i.e., by cleverly combining digestion test and hydrochloric acid treatment during the preparation process), can significantly improve its catalytic activity in the oxidative coupling of aromatic amines, thereby obtaining excellent comprehensive technical effects of high conversion rate of aromatic amines and good product selectivity.

[0148] (5) By comparing application examples 1-9 with comparative application example 1, it can be seen that the MOFs catalyst provided by the present invention has excellent catalytic activity when applied to the catalytic oxidation of aromatic amines to prepare azo compounds, thereby obtaining excellent comprehensive technical effects of high conversion rate of aromatic amines and good product selectivity. Without the addition of the MOFs catalyst of the present invention, it is impossible to achieve efficient catalytic oxidation of aromatic amines to prepare azo compounds.

[0149] II. Experiments on the Application of MOF Catalysts

[0150] The MOF catalyst from Application Example 1 (Example 1) was recovered for reuse experiments. The reaction conditions and operations were the same as in Application Example 1. The experimental results are shown in Table 2.

[0151] Table 2

[0152] Conversion rate / % Selectivity / % Application Example 1 98.5 97.1 Apply 1 98.8 96.4 Apply 4 97.7 94.1 Apply 9 96.8 93.0 Apply 14 95.4 90.8

[0153] As can be seen from Table 2, the MOF catalyst provided by this invention has excellent cycling stability. It can still maintain high conversion (95.4%) and high selectivity (90.8%) after 15 consecutive uses in the reaction of catalyzing the oxidation of aromatic amines to prepare azo compounds in high yield.

[0154] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A MOFs catalyst for oxidative coupling of aromatic amines, characterized in that, The MOFs catalyst is a MOF-808 catalyst.

2. The MOFs catalyst according to claim 1, characterized in that, The MOF-808 catalyst is a MOF-808(6OH); Preferably, the MOF-808(6OH) has a structure shown in formula (I): Zr6(μ3-O)4(μ3-OH)4(BTC) 1.97 (FA) 0.12 (OH) 5.97 (H2O) 5.97 Formula (I).

3. A process for the preparation of MOFs catalysts for the oxidative coupling of aromatic amines according to claim 1 or 2, characterized in that, The preparation method comprises the following steps: After the reaction of the zirconium salt and the organic ligand, the obtained product is treated with hydrochloric acid to obtain the MOFs catalyst for aromatic amine oxidative coupling.

4. The production method according to claim 3, characterized by, The hydrochloric acid treatment comprises dispersing the obtained product in hydrochloric acid and stirring at 80-100℃ for 12-36h; Preferably, the mass concentration of the obtained product in the hydrochloric acid is 10g / L; Preferably, the hydrochloric acid comprises a 0.5-1.5M hydrochloric acid solution; Preferably, the hydrochloric acid treatment further comprises the steps of separation, washing and drying.

5. The production method according to claim 3 or 4, characterized by, The zirconium salt comprises zirconium oxychloride octahydrate and / or zirconium chloride; Preferably, the organic ligand comprises trimesic acid; Preferably, the molar ratio of the zirconium salt to the organic ligand is (1-3):1; Preferably, the reaction is carried out in a solvent; Preferably, the solvent comprises N,N-dimethylformamide; Preferably, the raw material of the reaction further comprises a regulator; Preferably, the regulator comprises formic acid; Preferably, the molar ratio of the regulator to the organic ligand is (800-1100):

1.

6. The method of any one of claims 3-5, wherein, The temperature of the reaction is 90-110℃; Preferably, the reaction time is 15-25h; Preferably, the reaction further comprises a post-treatment step after the reaction; Preferably, the post-treatment method comprises cooling, separation, washing and drying.

7. The method of any one of claims 3-6, wherein, The hydrochloric acid treatment further comprises a digestion test step; Preferably, the digestion test comprises dispersing the obtained crude product after the hydrochloric acid treatment in a digestion solution for digestion, and then testing the supernatant after digestion by nuclear magnetic resonance hydrogen spectrum; Preferably, the digestion solution comprises a heavy water solution of sodium hydroxide; Preferably, the mass concentration of the crude product in the digestion solution is 6-10g / L; Preferably, the digestion time is 18-30h; Preferably, if the proportion of formate ions is higher than 1% of the peak area of trimesate ions in the nuclear magnetic resonance hydrogen spectrum test, the hydrochloric acid treatment step is repeated.

8. The method of any one of claims 3-7, wherein, The preparation method specifically comprises the following steps: (1) mixing the zirconium salt and the organic ligand in a molar ratio of (1-3):1 with a solvent, adding a regulator, and reacting at 90-110℃ for 15-25h; after the reaction, the reaction solution is cooled, separated, washed and dried; (2) dispersing the dried product obtained in step (1) in hydrochloric acid, stirring at 80-100℃ for 12-36h, and then separating, washing and drying to obtain a crude product; (3) dispersing the crude product obtained in step (2) in a digestion solution, testing by nuclear magnetic resonance hydrogen spectrum after digestion for 18-30h; if the proportion of formate ions is higher than 1% of the peak area of trimesate ions, repeat the hydrochloric acid treatment step in step (2); until the proportion of formate ions is not higher than 1% of the peak area of trimesate ions, to obtain the MOFs catalyst.

9. A process for the catalytic oxidation of an aromatic amine to produce an oxoazo compound, characterized in that, The method comprises: obtaining an azo compound by oxidizing an aromatic amine under catalysis of the MOFs catalyst according to claim 1 or 2.

10. The method of claim 9, wherein, The mass percentage of the MOFs catalyst is ≤32% and not 0, based on 100% of the mass percentage of the aromatic amine; Preferably, the aromatic amine comprises substituted or unsubstituted aniline, heterocyclic aromatic amine and alkyl diphenylamine, wherein the substituted substituent is selected from halogen, C1-C5 alkyl, C1-C3 alkoxy, nitro or amino; Preferably, the heterocyclic aromatic amine comprises 3-aminopyridine; Preferably, the alkyl diphenylamine comprises 2,2'-ethylenediphenylamine; Preferably, the raw material of the oxidation reaction further comprises H2O2; Preferably, the molar ratio of H2O2 to aromatic amine is (2.1-2.5):1; Preferably, the temperature of the oxidation reaction is 0-60℃; Preferably, the time of the oxidation reaction is 1.5-3h.

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