A method for preparing o-fluorobenzaldehyde by oxidizing o-fluorotoluene

Abstract

This invention discloses a modified manganese-oxygen octahedral molecular sieve, wherein cobalt is loaded onto the octahedral molecular sieve, and all cobalt ions are inserted into the crystal lattice of the octahedral molecular sieve; and / or the cobalt component exists in an amorphous form; the X-ray diffraction pattern of the modified manganese-oxygen octahedral molecular sieve does not show characteristic diffraction peaks of cobalt or cobalt oxides. A method for preparing the modified manganese-oxygen octahedral molecular sieve is also provided, as well as a method for using the modified manganese-oxygen octahedral molecular sieve as a catalyst to catalyze the oxidation of o-fluorotoluene to o-fluorobenzaldehyde. The catalyst has a high specific surface area, mixed valence states of manganese ions, and a rich pore environment, exhibiting excellent redox capabilities. The preparation method has advantages such as mild synthesis conditions and simple equipment. The method for oxidizing o-fluorotoluene to o-fluorobenzaldehyde provided by this invention has advantages such as excellent catalytic activity, simple catalyst separation, and high selectivity.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene. Background Technology

[0002] Oxidation of o-fluorotoluene to obtain o-fluorobenzaldehyde is a promising industrial production method for o-fluorobenzaldehyde. As an intermediate in organic synthesis, o-fluorobenzaldehyde is used in various fields such as pharmaceuticals, dyes, and pesticides. However, improving the conversion rate and selectivity of o-fluorobenzaldehyde remains a challenge. Currently, the main industrial method for producing o-fluorobenzaldehyde is chlorination hydrolysis, but this method suffers from drawbacks such as difficulty in controlling the oxidation depth and severe equipment corrosion, and also causes serious environmental problems. The oxidation of o-fluorotoluene to prepare o-fluorobenzaldehyde is a key organic synthesis reaction. Traditional oxidation methods use heavy metal oxides such as potassium dichromate, potassium permanganate, and chromium trioxide-pyridine, generating large amounts of heavy metal waste that severely pollute the environment. In recent years, with the emergence of the concept of green chemistry, green selective oxidation using air or oxygen as a clean oxygen source has received widespread attention and made some progress. However, because air-oxygen oxidation generally requires high temperatures, o-fluorobenzaldehyde is easily further oxidized to the corresponding acid, resulting in poor selectivity for aldehydes. Therefore, in the air-oxygen oxidation process of o-fluorotoluene, the main product is o-fluorobenzoic acid, while o-fluorobenzaldehyde appears as a very low-content byproduct. To address the shortcomings of existing o-fluorobenzaldehyde synthesis processes, the industry is currently exploring the design and development of efficient methods and catalysts for the oxygen oxidation of o-fluorobenzaldehyde to produce aromatic aldehydes with strong application prospects. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a cobalt-supported manganese-oxygen octahedral molecular sieve catalyst and its preparation method, and also provides a method for the oxidation of o-fluorotoluene to prepare o-fluorobenzaldehyde.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A modified manganese-oxygen octahedral molecular sieve, wherein cobalt is loaded on the manganese-oxygen octahedral molecular sieve, and the following conditions (1) and / or (2) are satisfied: (1) All cobalt ions are inserted into the crystal lattice of the manganese-oxygen octahedral molecular sieve; (2) The cobalt component exists in an amorphous form; Furthermore, the X-ray diffraction pattern of the modified manganese octahedral molecular sieve does not contain characteristic diffraction peaks of cobalt or cobalt oxide.

[0006] The modified manganese-oxygen octahedral molecular sieve has a cobalt / manganese molar ratio of 1-3:10.

[0007] The preparation method of the modified manganese-oxygen octahedral molecular sieve includes the following steps: Step 1: Prepare the reaction system The reaction system is an aqueous solution system. The reaction system includes a cobalt source, a manganese source, acetic acid, and water. The concentration of cobalt in the reaction system is 0.05-0.15 mol / L; The molar ratio of cobalt to total manganese in the reaction system is (1-3):10; The cobalt source is selected from one or more of cobalt chloride, cobalt nitrate hexahydrate, and cobalt acetate; The manganese source is provided by manganese acetate and potassium permanganate, with a molar ratio of manganese acetate to potassium permanganate of 3:(1-2); The amount of acetic acid used is 0.1-2% of the water volume; Step 2: Hydrothermal reaction The reaction system obtained in step S1 was subjected to a constant temperature and pressure reflux hydrothermal reaction. Step 3: Post-reaction processing After the hydrothermal reaction is completed, the mixture is allowed to cool naturally to room temperature, and then subjected to solid-liquid separation, washing, and drying to obtain the intermediate product. Step 4: Roasting The intermediate product was calcined in air at 450-650 °C and cooled to obtain the modified manganese-oxygen octahedral molecular sieve.

[0008] In the preparation method described above, in step 1, a) Dissolve manganese acetate in water, add acetic acid, heat and stir to obtain a precursor solution; b) Add the cobalt source aqueous solution to the precursor solution, heat and stir to mix evenly, and obtain the first mixed solution; c) Dissolve potassium permanganate in water and add it dropwise to the first mixed solution. Mix well to obtain the reaction system.

[0009] In the preparation method described above, in step 2, the temperature of the hydrothermal reaction is 75-90 ℃, and the time of the hydrothermal reaction is 4-24 h.

[0010] In the preparation method described above, in step 4, the heating rate is 3-10 °C / min, and the calcination time is 0.5-8 h.

[0011] A method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene, using acetic acid as solvent, a modified manganese-oxygen octahedral molecular sieve prepared according to claim 1 or 2, or any one of claims 3-6 as catalyst, and potassium bromide as initiator, to react o-fluorotoluene with oxygen to generate o-fluorobenzaldehyde.

[0012] The method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene includes the following steps: S1: Dissolve o-fluorotoluene in acetic acid; S2: Add catalyst and initiator to the solution obtained in step S1. The catalyst is a modified manganese-oxygen octahedral molecular sieve prepared according to claim 1 or 2, or any one of claims 3-6. The initiator is potassium bromide; S3: Introduce oxygen into the reaction solution obtained in step S2, and stir, heat, and reflux the reaction. S4: After the reaction is complete, cool to room temperature, filter to remove the catalyst and collect the liquid phase, and separate o-fluorobenzaldehyde from the liquid phase.

[0013] The method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene, In step S1, the mass-to-volume ratio of o-fluorotoluene to acetic acid is 5-20 g: 100 mL; In step S2, the catalyst is a modified manganese-oxygen octahedral molecular sieve with a cobalt / manganese molar ratio of 1-3:10. In step S2, the amount of catalyst added is 0.5-12.5% ​​of the mass of o-fluorotoluene; In step S2, the amount of initiator added is 0.4-10% of the mass of o-fluorotoluene; In step S3, the oxygen flow rate is 0.1-0.4 min according to the air velocity meter. -1 ; In step S3, the heating reaction temperature is 70-130 ℃.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The cobalt-supported manganese-oxygen octahedral molecular sieve catalyst provided by this invention has a high specific surface area, mixed valence states of manganese ions, and a rich pore environment, which enables the catalyst to have excellent redox capabilities, form active oxygen on the surface, and have good ion exchange properties, thereby solving the problem of selective adsorption and catalysis of molecules in the prior art.

[0015] The method for preparing cobalt-loaded manganese-oxygen octahedral molecular sieve catalysts provided by this invention has advantages such as mild synthesis conditions and simple equipment. The prepared catalyst has advantages such as high crystallinity, regular pore structure, and uniform cobalt loading.

[0016] The method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene provided by this invention has the advantages of being environmentally friendly, having mild reaction conditions, producing safe products, exhibiting excellent catalytic activity, simple catalyst separation, and high selectivity. Attached Figure Description

[0017] Figure 1 XRD patterns of OMS-2 and 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2 samples.

[0018] Figure 2 Nitrogen isothermal adsorption-desorption curves for OMS-2 and 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2 samples.

[0019] Figure 3 SEM images of OMS-2 and 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2 samples. Among them, OMS-2 (A,A1); 10Co-OMS-2 (B,B2); 20Co-OMS-2 (C,C2); 30Co-OMS-2 (D,D2).

[0020] Figure 4 The image shows the EDS elemental mapping analysis of the 20Co-OMS-2 sample. (A) Electron image of 20Co-OMS-2; (B) Layered image of Mn atoms; (C) Layered image of O atoms; (D) Layered image of Co atoms.

[0021] Figure 5 Infrared spectra of OMS-2 and 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2 samples.

[0022] Figure 6 Catalytic activity of OMS-2 with different cobalt loadings (different catalyst types): conversion of o-fluorotoluene (A), selectivity of o-fluorobenzaldehyde (B), and yield of o-fluorobenzaldehyde (C).

[0023] Figure 7 Catalytic activity for different amounts of 20Co-OMS-2 used: conversion of o-fluorotoluene (A), selectivity of o-fluorobenzaldehyde (B), and yield of o-fluorobenzaldehyde (C).

[0024] Figure 8 Catalytic activity of 20Co-OMS-2 under different initiator dosages: conversion of o-fluorotoluene (A), selectivity of o-fluorobenzaldehyde (B), and yield of o-fluorobenzaldehyde (C).

[0025] Figure 9 Catalytic activity of 20Co-OMS-2 under different oxygen flow rates: conversion of o-fluorotoluene (A), selectivity of o-fluorobenzaldehyde (B), and yield of o-fluorobenzaldehyde (C).

[0026] Figure 10Catalytic activity of 20Co-OMS-2 at different reaction temperatures: conversion of o-fluorotoluene (A), selectivity of o-fluorobenzaldehyde (B), and yield of o-fluorobenzaldehyde (C).

[0027] Figure 11 Catalytic activity of 20Co-OMS-2 under different reactant ratios: conversion of o-fluorotoluene (A), selectivity of o-fluorobenzaldehyde (B), and yield of o-fluorobenzaldehyde (C). Detailed Implementation

[0028] The technical solution of the present invention will be further illustrated below through embodiments.

[0029] The chemical reagents and equipment used in the examples are listed in Tables 1 and 2, respectively. All water used in the experiments was deionized water, and all chemical reagents used were purchased directly from the supplier without further purification.

[0030] Table 1 Chemical reagents used in the experiment

[0031] Table 2. Instruments and equipment used in the experiment

[0032] The oxidation reaction apparatus mainly includes a 250 mL three-necked flask; a 5-30 mL·min⁻¹ rotor flow meter; and a DF-101B type thermostatic magnetic stirrer, using dry O₂ as the oxygen source. The acetic acid concentration is 99.5 wt%.

[0033] Example 1: Preparation of catalysts OMS-2 and samples of 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2 1.1 The preparation method of manganese-oxygen octahedral molecular sieve catalyst is as follows: (1) Weigh 7.35 g (0.03 mol) manganese acetate tetrahydrate and dissolve it in 40 mL of deionized water. Transfer the solution to a 250 mL three-necked flask, add 1 mL of acetic acid, and place the flask in a 90 °C water bath at a speed of 400 r·min. -1 Keep for 1 hour; (2) Weigh 3.16 g (0.02 mol) of potassium permanganate and dissolve it in 40 mL of deionized water. Transfer the solution to a separatory funnel and add it dropwise to a three-necked flask. Rinse the flask with deionized water until the potassium permanganate is completely removed.

[0034] (3) Place the three-necked flask in a water bath at 90 °C and rotate at 400 r·min. -1 Maintain the reflux reaction for 24 hours.

[0035] (4) After the reaction is complete, the solid is filtered out by vacuum filtration after cooling to room temperature. The solid is then rinsed three times with 20 mL of deionized water. The filtered solid is then dried in an 80 °C oven for 10 h. (5) Transfer the dried solid into a crucible and place it in a muffle furnace. Heat the furnace in air at 5 °C·min. -1 The heating rate was increased from room temperature to 450 °C, calcined for 2 h, and then naturally cooled to room temperature. The obtained manganese-oxygen octahedral molecular sieve (denoted as OMS-2) was collected and stored.

[0036] 1.2 Preparation of Cobalt-Supported Manganese Oxygen Octahedral Molecular Sieves Catalysts 1.2.1 The preparation method of 10Co-OMS-2 includes the following steps: (1) Weigh 7.35 g (0.03 mol) manganese acetate tetrahydrate and dissolve it in 40 mL of deionized water. Transfer the solution to a 250 mL three-necked flask, add 1 mL of acetic acid, and place the flask in a 90 °C water bath at a speed of 400 r·min. -1 Maintain for 1 h; the concentration of the acetic acid is 99.5 wt%.

[0037] (2) Weigh 1.455 g (0.005 mol) cobalt nitrate hexahydrate as the cobalt source and dissolve it in 20 mL of deionized water, then transfer it to a three-necked flask; (3) Weigh 3.16 g (0.02 mol) of potassium permanganate and dissolve it in 40 mL of deionized water. Transfer the solution to a separatory funnel and add it dropwise to a three-necked flask. Rinse the flask with deionized water until the potassium permanganate is completely removed.

[0038] (4) Place the three-necked flask in a water bath at 90 °C and set the magnetic stirrer speed to 400 r·min. -1 The reaction was maintained under reflux for 24 hours at normal pressure.

[0039] (5) After the reaction is complete, allow the mixture to cool naturally to room temperature and then filter out the solid using vacuum filtration. Rinse the solid three times with 20 mL of deionized water and place the filtered solid in an 80 °C oven to dry for 10 h. (6) Transfer the dried solid into a crucible and place it in a muffle furnace. Heat the furnace in air at 5 °C·min. -1 The heating rate was increased from room temperature to 450 °C, calcined for 2 h, and then naturally cooled to room temperature. The obtained cobalt-loaded manganese oxygen octahedral molecular sieve (denoted as 10Co-OMS-2) was collected and stored.

[0040] 1.2.2 Following the preparation method of 10Co-OMS-2, the amount of cobalt nitrate hexahydrate was adjusted to 2.91 g (0.01 mol). The remaining steps and parameters were the same as those for 10Co-OMS-2, and cobalt-loaded manganese-oxygen octahedral molecular sieves (denoted as 20Co-OMS-2) were obtained.

[0041] 1.2.3 Following the preparation method of 10Co-OMS-2, the amount of cobalt nitrate hexahydrate was adjusted to 4.365 g (0.015 mol). The remaining steps and parameters were the same as those for 10Co-OMS-2, and cobalt-loaded manganese-oxygen octahedral molecular sieves (denoted as 30Co-OMS-2) were obtained.

[0042] The cobalt / manganese molar ratio in the 10Co-OMS-2 is 1:10, in the 20Co-OMS-2 it is 2:10, and in the 30Co-OMS-2 it is 3:10.

[0043] Example 2 Catalyst Crystal Phase Analysis The phase structure of the catalyst was determined using a graphite monochromator and Cu-K. a The X-ray source was operated at 80 kV and 30 mA, with a scan range (2θ) set to 5–90° and a scan rate of 10 °·min. -1 Record the XRD pattern. The XRD pattern results are as follows: Figure 1 As shown.

[0044] Depend on Figure 1 As can be seen, major diffraction peaks appeared at 2θ = 12.6°, 17.9°, 28.7°, 37.5°, 41.9°, 49.9°, and 60.1°, which are basically consistent with the standard diffraction peak pattern of crypto-KMnO4. It can be inferred that the synthesized OMS-2, 10Co-OMS-2, 20Co-OMS-2, and 30Co-OMS-2 are all crystal phases of crypto-KMnO4 (KMn8O4). 16 (#JCPDS29-1020). No Co diffraction peaks were found in 30Co-OMS-2, suggesting that the doped cobalt is either inserted into the OMS-2 lattice or exists in an amorphous state. Furthermore, the characteristic peaks of the OMS-2, 10Co-OMS-2, 20Co-OMS-2, and 30Co-OMS-2 did not shift relative to the characteristic peaks on the standard card, nor did they show any loss or increase in characteristic peaks. The main characteristic peaks were very sharp, indicating that the catalysts were all well-crystallized and free of impurities.

[0045] The grain size is calculated from (2-1).

[0046] (2-1) In the formula, d is the grain diameter (nm), θ is the diffraction angle, and K is a constant. When β is the half-width, K is 0.89; when β is the integral width, K is 1.0.

[0047] Calculations show that the grain sizes of OMS-2, 10Co-OMS-2, 20Co-OMS-2, and 30Co-OMS-2 are 127, 116, 120, and 107 Å, respectively.

[0048] Example 3: N2 Adsorption-Desorption Analysis The N2 adsorption-desorption isotherms were determined using a physical adsorption analyzer. The specific surface area of ​​the catalyst was calculated using the Brunauer-Emmett-Teller (BET) equation; the pore volume and average pore size were calculated using the Barrett-Joyner-Halenda (BJH) equation. Nitrogen adsorption-desorption experiments were performed on OMS-2 and 10Co-OMS-2, 20Co-OMS-2, and 30Co-OMS-2 samples. The adsorption-desorption isotherms were determined based on the measured values ​​(see...). Figure 2 Data processing was performed. The specific surface area of ​​the samples was calculated using the BET method, and the pore volume and average pore diameter were calculated using the BJH method. The structural property parameters are summarized in Table 3.

[0049] Depend on Figure 2 It can be observed that the nitrogen isotherm adsorption-desorption curves exhibit typical type IV isotherm characteristics, indicating the presence of mesoporous structures in the material. Furthermore, the curves rise significantly in the region of higher relative pressure (close to 1), possibly suggesting the presence of macroporous structures as well. The presence of both mesopores and macropores facilitates the diffusion of reactant molecules and the transport of reactive oxygen species.

[0050] As shown in Table 3, the specific surface area of ​​OMS-2 relative to unloaded cobalt is 54.16 m². 2 ·g -1 With an average pore size of 10.62 nm, the specific surface area of ​​10Co-OMS-2 increased to 71.86 m². 2 ·g -1 The average pore size increased to 12.90 nm, indicating that Co was successfully loaded into the OMS-2 lattice, enlarging the lattice diameter and thus increasing the specific surface area and average pore size. With increasing Co loading, the specific surface area and average pore size of the catalyst decreased slightly, remaining between 65.32 and 71.86 nm. 2 ·g -1 And 11.55-12.90 nm. Compared with unsupported OMS-2 powder, Co-OMS-2 catalyst has a larger specific surface area and a wider substrate attachment space, which is beneficial to improving the reaction efficiency of the oxidation of o-fluorotoluene to produce o-fluorobenzaldehyde.

[0051] Table 3. Structural properties of OMS-2 and 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2

[0052] Example 4 Scanning Electron Microscopy Analysis OMS-2 and 10Co-OMS-2, 20Co-OMS-2, and 30Co-OMS-2 samples were mounted on the sample stage and sputtered with gold using a Quorum SC7620 sputtering system at a current of 10 mA for 45 s. Analysis was performed using a ZEISS Sigma 360 scanning electron microscope. The accelerating voltage for SEM morphology observation was 3 kV. EDS energy dispersive spectroscopy and elemental mapping analysis were performed only on the 20C samples under the following conditions: accelerating voltage 20 kV, acquisition time 60 s, and working distance 8.5 mm. The SEM morphology results of the OMS-2 and 10Co-OMS-2, 20Co-OMS-2, and 30Co-OMS-2 samples are shown below. Figure 3 As shown. The EDS spectrum and mapping results of the 20Co-OMS-2 sample are as follows. Figure 4 As shown.

[0053] Depend on Figure 3 As can be seen from A, the OMS-2 is a nanorod-like structure with uniform diameter and length ranging from tens of nanometers to hundreds of nanometers, and the surface of the nanorod is smooth.

[0054] Depend on Figure 3 As can be seen from BD, with the increase of Co loading, the diameter of the nanorods becomes thicker and the surface becomes rougher, indicating that the catalyst obtained after loading Co still maintains the initial nanorod shape of OMS-2 molecular sieve; however, the surface of the sample becomes increasingly rough with the increase of Co loading; the diameter of the sample becomes increasingly larger with the increase of Co loading, indicating that Co is loaded into the OMS-2 lattice.

[0055] Micro-area composition analysis was performed on fragments of the 20Co-OMS-2 catalyst. Figure 4 The results are consistent with the above assumptions. Overall, the supported Co content is relatively low and dispersed, with no obvious large particles, which is consistent with the previous characterization results. Furthermore, based on the degree of dispersion of the Co element response signal within the catalyst, it indicates that the hydrothermal reaction can yield a well-dispersed supported heterogeneous OMS-2 catalyst.

[0056] Example 5: Fourier Transform Infrared Chromatography Analysis The Fourier transform infrared spectroscopy (FT-IR) analysis used in this embodiment was performed on a Bruker TENSOR II infrared spectrometer with an MCT detector. The samples were processed using the KBr pellet method. The test conditions were as follows: spectral range 8000-350 cm⁻¹. -1 Signal-to-noise ratio: 50000:1, scanning speed: 40 frames / second, resolution: 0.4 cm. -1 Under these conditions, infrared spectra of OMS-2 and 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2 samples were collected respectively.

[0057] Generally, the infrared absorption signals of metal oxides are distributed in the mid-infrared and far-infrared regions, mainly concentrated in the 1150-50 cm⁻¹ range. -1 .Depend on Figure 5 It can be seen that at 550-500 cm -1 650-600 cm -1 Two sharp peaks were observed within the range, which are the stretching vibration peaks of Co-O and Mn-O bonds in OMS-2 and 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2 samples.

[0058] As the cobalt-manganese ratio of the catalyst is adjusted, the peak intensity of the Co-O bond and the peak intensity of the Mn-O bond also change accordingly. Figure 5 In the catalysts 10Co-OMS-2, 20Co-OMS-2, and 30Co-OMS-2, the absorbance of the Mn-O and Co-O bonds, respectively, increased significantly compared to that of the OMS-2 catalyst. With increasing Co and Mn ratios, the peak shapes of the Co-O and Mn-O peaks became sharper, and their intensities also increased significantly.

[0059] Example 6: Method for preparing o-fluorobenzaldehyde by catalytic oxidation of o-fluorotoluene A method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene includes the following steps: 1) Dissolve o-fluorotoluene in a solvent and transfer it to a 250 mL three-necked flask and mix well; 2) Add the catalyst and initiator to the solution obtained in step 1); 3) Oxygen is introduced into the reaction liquid from the bottom of the reactor through a gas supply pipe, and the reaction is stirred, heated, and refluxed in a heat-insulating, heat-collecting, constant-temperature magnetic stirrer. 4) After the reaction in step 3) is completed, cool to room temperature, filter to remove the catalyst and collect the liquid phase, and separate o-fluorobenzaldehyde from the liquid phase.

[0060] The acetic acid concentration was 99.5 wt%. The oxygen concentration was 99.9 wt%. The initiator was potassium bromide. The separation was performed by vacuum distillation to obtain o-fluorobenzaldehyde.

[0061] Table 4. Conditions and parameters for each group of reactions in Examples 8-14

[0062] As shown in Table 6, the different solvents described in Example 8 are acetic acid, isopropanol, ethanol, dimethyl sulfoxide, nitrobenzene, dioxane, butyl acetate, dimethylformamide, acetonitrile, and benzyl benzoate.

[0063] like Figure 6 As shown, the different catalyst types described in Example 9 are OMS-2, 10Co-OMS-2, 20Co-OMS-2 and 30Co-OMS-2.

[0064] like Figure 7 As shown, the different catalyst dosages described in Example 10 are 0 mg, 25 mg (0.5% of the mass of o-fluorotoluene), 125 mg (2.5% of the mass of o-fluorotoluene), and 625 mg (12.5% ​​of the mass of o-fluorotoluene).

[0065] like Figure 8 As shown, the different amounts of potassium bromide used in Example 11 are 0 mg, 20 mg (0.4% of the mass of o-fluorotoluene), 100 mg (2% of the mass of o-fluorotoluene), and 500 mg (10% of the mass of o-fluorotoluene).

[0066] like Figure 9 As shown, the different oxygen flow rates described in Example 12 are 0 mL·min -1 5 mL·min -1 10 mL·min -1 20 mL·min -1 The solvent usage, calculated according to space velocity, is 0 min. -1 0.1 min -1 0.2min -1 0.4 min -1 In this invention, space velocity refers to the ratio of the volume of gas introduced per minute to the volume of the reaction system under standard conditions, and is used to measure the flow efficiency of gas in the reactor.

[0067] like Figure 10 As shown, the different reaction temperatures described in Example 13 are 80 °C, 90 °C, 100 °C, and 110 °C.

[0068] According to the reaction conditions and parameters set in Table 4, after each reaction in each embodiment started, the reaction solution was sampled every hour, cooled to room temperature, filtered to remove the catalyst, and the liquid phase was collected. The obtained liquid phase was a mixture of four liquid substances including o-fluorotoluene, acetic acid, KBr, and o-fluorobenzaldehyde. The conversion rate (X) of o-fluorotoluene was determined and calculated according to the method described in Example 7. 邻氟甲苯 ), selectivity of o-fluorobenzaldehyde (S 邻氟苯甲醛 ) and yield (Y 邻氟苯甲醛 The experimental results and analysis are shown in Examples 8-13.

[0069] Example 7 Conversion rate of o-fluorotoluene (X) 邻氟甲苯 ), selectivity of o-fluorobenzaldehyde (S 邻氟苯甲醛 ) and yield (Y 邻氟苯甲醛 Methods for the determination and calculation of ) Step 1: Establish the internal standard working curve o-Fluorotoluene (o-fluorobenzaldehyde) standard stock solution (0.3 g·mL) –1 ): Accurately weigh 15.000 g of o-fluorotoluene (o-fluorobenzaldehyde) standard into a 50 mL volumetric flask using an electronic balance, dilute to the mark with acetonitrile solution, shake well, and store in a sealed container at 0°C-4°C.

[0070] o-Fluorotoluene (o-fluorobenzaldehyde) series of standard working solutions: Accurately measure 7.5 mL, 5 mL, 2.5 mL, 1.25 mL, and 0.625 mL of o-fluorotoluene (o-fluorobenzaldehyde) standard stock solution and place them into five 10 mL volumetric flasks. Then, dilute each flask to the mark with acetonitrile solution to prepare solutions with concentrations of 0.24 g·mL⁻¹. –1 0.16 g·mL –1 0.08 g·mL –1 0.04 g·mL –1 and 0.02 g·mL –1 o-fluorotoluene (o-fluorobenzaldehyde) series of standard working solutions.

[0071] Internal standard solution (0.01 g·mL) –1 ): Accurately weigh 5.00 g of o-dichlorobenzene into a 500 mL volumetric flask, dilute to the mark with acetonitrile, shake well, and store in a sealed container at 0 °C-4 °C.

[0072] Establishment of standard curves: 0.4 mL of o-fluorotoluene (o-fluorobenzaldehyde) series standard working solutions were transferred into five 10 mL volumetric flasks, and 1 mL of internal standard solution was accurately transferred and diluted to the mark with acetonitrile. After shaking well, 0.2 μL of each solution was injected. The ratio of the area of ​​each series of o-fluorotoluene (o-fluorobenzaldehyde) standard to the area of ​​the internal standard was measured. The standard curves are shown in Table 5.

[0073] Gas chromatography conditions: A 30 m × 0.25 mm DB-WAX gas chromatographic column was used. Nitrogen gas was purged for 5 min before turning on the instrument, and the flow rate was set to 40 mL / min. –1 After turning on the instrument, set the vaporization chamber temperature to 260 °C, the flame ionization detector (FID) temperature to 260 °C, and the column temperature to 80 °C. Once the set temperatures are reached, purge with 400 mL / min. –1 air and 40 mL·min –1 Hydrogen gas was introduced for 1 minute, and the tail gas flow rate was set to 40 mL / min. –1 The split ratio was set to 30:1. The programmed temperature rise was from an initial temperature of 80 °C, at a rate of 10 °C / min. -1 Heat to 120 °C for 4 min and hold for 8 min. Once the baseline has leveled off, inject 0.2 μL of the sample to be tested.

[0074] Table 5 Standard curves for each substance

[0075] Step 2: Sample Measurement and Calculation Transfer 1.0 mL of the filtered liquid product from step 4) of Example 6 into a 10 mL volumetric flask, and add 1.0 mL of a 0.01 g·mL⁻¹ solution. -1 The internal standard, o-dichlorobenzene solution, was diluted to the mark with acetonitrile and analyzed by gas chromatography under the same conditions as in the first step.

[0076] Based on the gas chromatography analysis results, the conversion rate (X) of o-fluorotoluene was calculated using equations (2-2)–(2-6). 邻氟甲苯 ) and the selectivity of o-fluorobenzaldehyde (S 邻氟苯甲醛 ) and yield (Y 邻氟苯甲醛 ).

[0077] (2-2) The amount of o-fluorotoluene consumed by o-fluorobenzaldehyde ( mol) =Amount of o-fluorobenzaldehyde produced (mol)= (2-3) (2-4) (2-5) (2-6) Example 8: Effect of Solvent In organic reactions, the solvent is a hidden reactant. Through solvation, polarity, and hydrogen bonding, it determines the reaction rate, product distribution, and even whether a reaction occurs, without directly participating in the breaking and formation of chemical bonds.

[0078] The test results of this embodiment are shown in Table 6.

[0079] Table 6. Effects of different solvents on the oxidation of o-fluorotoluene

[0080] As shown in Table 1, no reaction occurs in butyl acetate, dimethylformamide, acetonitrile, and benzyl benzoate. Only o-fluorobenzoic acid is obtained in isopropanol, dimethyl sulfoxide, and nitrobenzene. The solvent participates in the reaction in dioxane and ethanol. Only when acetic acid is used as the solvent does the reaction of o-fluorotoluene produce o-fluorobenzaldehyde. Therefore, acetic acid is chosen as the reaction solvent.

[0081] Example 9: Effect of Cobalt Loading The active component is the part of the catalyst that provides active sites. Insufficient loading will lead to underutilization of the catalyst surface space, while excessive loading will cause blockage of the catalyst channels, reducing the exposure of active sites. Under steady state, the reaction rate is such that the amount of reactant component that diffuses to the outer surface of the catalyst per unit time is equal to the actual amount of reactant reacting within the catalyst particles.

[0082] The test results of this embodiment are as follows: Figure 6 As shown. From Figure 6 It can be seen that the selectivity of o-fluorobenzaldehyde remains basically stable or slightly decreases over time. This is because the addition of Co is key to the activation of the reaction substrate. As the active component is introduced, the activation effect of the catalyst on the reaction substrate increases from weak to strong. The increase in Co loading improves the reaction conversion rate within a certain range.

[0083] Meanwhile, the loading of Co affects the internal diffusion mass transfer process. As shown by the N2 adsorption-desorption results, with the increase of the active component loading, the accumulation of the active component in the catalyst increases the internal surface area of ​​the catalyst, increasing the internal diffusion resistance, slowing the diffusion of reactants and products, leading to a decrease in reaction conversion rate, and exacerbating the over-oxidation of o-fluorobenzaldehyde. Figure 6 It can be seen that, under the same conditions, when the loading is 10%, the yield of o-fluorobenzaldehyde is the highest, at 42.2%, after 3 hours. Based on the above analysis, the preferred loading is 20%.

[0084] Example 10 Effect of catalyst dosage In catalytic reactions, adding more catalyst provides more reaction sites, allowing the reaction to proceed faster. However, in selective oxidation, excessive catalyst can cause the reaction to proceed violently and stop at undesirable sites, typically manifesting as over-oxidation. In this reaction, excessive catalyst will cause o-fluorotoluene to over-oxidize to o-fluorobenzoic acid, reducing the selectivity and yield of o-fluorobenzaldehyde. Conversely, insufficient catalyst will slow down the reaction due to a lack of reaction sites, wasting time and causing the introduced oxygen to be lost without participating in the reaction, resulting in resource waste.

[0085] The test results of this embodiment are as follows: Figure 7 As shown. By Figure 7 It is evident that the catalyst plays a crucial role in the reaction. Without a catalyst, the reaction rate of o-fluorotoluene is very low, and there is no selectivity for o-fluorobenzaldehyde. Furthermore, the amount of catalyst significantly affects the conversion rate of cinnamaldehyde. However, with increasing catalyst dosage, the selectivity of o-fluorotoluene oxidation for o-fluorobenzaldehyde decreases. This is mainly attributed to the fact that increased catalyst dosage generates more active oxygen species in the system and provides more oxidative active sites. These excess active sites continue to oxidize o-fluorobenzaldehyde, leading to over-oxidation of the product and exacerbating other side reactions. Therefore, the conversion rate continuously increases with increasing catalyst dosage. When the catalyst dosage increased from 25 mg to 125 mg, the conversion rate of o-fluorotoluene increased from 32.30% to 76.69% after 4 h, and the yield increased from 20.76% to 44.22%. However, when the dosage increased to 625 mg, the conversion rate only increased by about 3%, while the highest yield of o-fluorobenzaldehyde decreased by nearly 19%. Taking into account the effects of catalyst dosage on reaction conversion and the yield of o-fluorobenzaldehyde, the preferred catalyst dosage is 125 mg.

[0086] Example 11 Effect of initiator dosage Using bromine as an initiator, bromine plays a role in electron transfer and inducing the generation of free radicals in this reaction. Therefore, the addition of bromine can reduce the induction period of the reaction and increase the oxidation reaction rate.

[0087] The test results of this embodiment are as follows: Figure 8 As shown. From Figure 8 It can be seen that when potassium bromide is not added to the reaction system, the reaction proceeds very slowly, and the selectivity and yield for o-fluorobenzaldehyde are almost zero. With the increase of sodium bromide dosage, both the conversion rate of o-fluorotoluene and the selectivity for o-fluorobenzaldehyde show an upward trend. This is because in the cobalt-manganese reaction system, Br... -The generation of Br· accelerates the conversion of oxygen into reactive substances, thus speeding up the reaction. However, with further increases in potassium bromide, when the bromide dosage exceeds a critical value, the selectivity and yield of o-fluorobenzaldehyde rapidly decline. This is because excess bromine readily reacts with metal ions to form metal polybrominates, leading to deep oxidation of o-fluorobenzaldehyde. Considering the combined effects of initiator dosage on the reaction conversion rate and the yield of o-fluorobenzaldehyde, the preferred initiator dosage is 100 mg.

[0088] Example 12 Effect of Oxygen Flow Rate Oxygen flow rate, as the oxidant in the reaction process, is a crucial factor affecting the effectiveness of this catalytic oxidation reaction. The flow rate of oxygen, as the oxidant in this reaction, influences the contact between oxygen and the reactants during the reaction.

[0089] The test results of this embodiment are as follows: Figure 9 As shown. From Figure 9 It can be seen that when the oxygen flow rate is 0 mL·min -1 At first, the conversion rate of o-fluorotoluene was very low, which was attributed to the reaction of o-fluorotoluene with residual oxygen in the reaction system. When the oxygen flow rate increased, the yield of o-fluorobenzaldehyde showed a trend of first increasing and then decreasing. The main reason for this phenomenon is that this reaction is a gas-liquid-solid catalytic oxidation reaction. When the oxygen flow rate is low, the contact between the solid and liquid phases and oxygen is limited, resulting in low conversion and yield. As the oxygen flow rate increases, the conversion rate of o-fluorotoluene and the yield of o-fluorobenzaldehyde also increase. When the oxygen flow rate continues to increase, the excess oxygen accelerates the oxidation process of o-fluorotoluene, but also leads to more over-oxidation of o-fluorobenzaldehyde, generating o-fluorobenzoic acid and other byproducts. Furthermore, with the continuous increase in oxygen flow rate, the excessive flow rate causes the formation of continuous large bubbles in the reaction system, providing a shortcut for oxygen escape. This results in oxygen leaving the reaction system without sufficient contact with the catalyst, wasting oxygen and causing a slight decrease in the conversion rate. Figure 9 It can be seen that when the yield of o-fluorobenzaldehyde is 10 mL·min, the yield of o-fluorobenzaldehyde is... -1 At that time, the oxygen flow rate is at its maximum, therefore the preferred oxygen flow rate is 10 mL / min. -1 .

[0090] Example 13 Effect of reaction temperature For the oxidation of organic matter, the reaction temperature has a significant impact on the reaction efficiency.

[0091] The test results of this embodiment are as follows: Figure 10 As shown. By Figure 10It can be seen that in this reaction system, the conversion rate of o-fluorotoluene increases with increasing reaction temperature, but the selectivity and yield of o-fluorobenzaldehyde initially increase and then decrease, and continue to decline with increasing time. Generally, for oxidation reactions of organic compounds, increasing reaction time inevitably leads to a continuous increase in conversion rate. The yield results of benzaldehyde at different temperatures, ranked in descending order, are: 90 °C > 80 °C > 70 °C > 60 °C. The highest yield is achieved at 90 °C, and the reaction yield reaches its peak of 44.22% after about 3 hours of reaction. Therefore, considering the combined effects of temperature on conversion rate and selectivity, the preferred reaction temperature is 90 °C.

[0092] Example 14 Effect of reactant ratio In chemical reactions, due to collision theory, as the concentration of reactants increases, the number of molecules per unit volume increases, the frequency of intermolecular collisions increases, and the probability of effective collisions also increases, thus accelerating the reaction rate. However, as the concentration increases, side reactions also increase, and selectivity decreases.

[0093] In this embodiment, in Experiment 1, M=1 g, V=50 mL; in Experiment 2, M=5 g, V=50 mL; and in Experiment 3, M=25 g, V=25 mL. The experimental results are as follows: Figure 11 As shown. By Figure 11 It can be seen that when the amount of acetic acid is fixed at 50 ml, increasing the amount of o-fluorotoluene from 1 g to 5 g increases the selectivity and yield of o-fluorobenzaldehyde in the reaction. This indicates that at a low concentration of o-fluorotoluene, the reaction oxidizes o-fluorotoluene to o-fluorobenzaldehyde and then continues the reaction to produce o-fluorobenzoic acid. However, when the amount of o-fluorotoluene is further increased to 25 g, the selectivity and yield of o-fluorobenzaldehyde in the reaction decrease significantly. Therefore, considering the combined effect of reactant ratio on conversion and selectivity, the mass-volume ratio of o-fluorotoluene to acetic acid is 5-20 g:100 mL; that is, 5-20 g of o-fluorotoluene is added to every 100 mL of acetic acid.

[0094] It should be noted that in Examples 8-14, the amount of o-fluorotoluene used was measured by mass to eliminate the influence of temperature on liquid volume and thus ensure experimental accuracy. However, in actual production, for ease of operation, volumetric measurement can be used, and temperature correction or density conversion can be used to meet the accuracy requirements of production proportions.

[0095] At 25 °C, the density of o-fluorotoluene is 1.001 g / mL, and the volume of 5 g of o-fluorotoluene is approximately equal to 5 ml. In actual production, the volume ratio of o-fluorotoluene to acetic acid can preferably be 5-20:100.

Claims

1. A modified manganese-oxygen octahedral molecular sieve, characterized in that, The manganese-oxygen octahedral molecular sieve is loaded with cobalt and satisfies the following conditions (1) and / or (2): (1) All cobalt ions are inserted into the crystal lattice of the manganese-oxygen octahedral molecular sieve; (2) The cobalt component exists in an amorphous form; Furthermore, the X-ray diffraction pattern of the modified manganese octahedral molecular sieve does not contain characteristic diffraction peaks of cobalt or cobalt oxide.

2. The modified manganese-oxygen octahedral molecular sieve as described in claim 1, characterized in that, The modified manganese-oxygen octahedral molecular sieve has a cobalt / manganese molar ratio of 1-3:

10.

3. The method for preparing the modified manganese-oxygen octahedral molecular sieve as described in claim 1, characterized in that, Includes the following steps: Step 1: Prepare the reaction system The reaction system is an aqueous solution system. The reaction system includes a cobalt source, a manganese source, acetic acid, and water. The concentration of cobalt in the reaction system is 0.05-0.15 mol / L; The molar ratio of cobalt to total manganese in the reaction system is (1-3):10; The cobalt source is selected from one or more of cobalt chloride, cobalt nitrate hexahydrate, and cobalt acetate; The manganese source is provided by manganese acetate and potassium permanganate, with a molar ratio of manganese acetate to potassium permanganate of 3:(1-2); The amount of acetic acid used is 0.1-2% of the water volume; Step 2: Hydrothermal reaction The reaction system obtained in step S1 was subjected to a constant temperature and pressure reflux hydrothermal reaction. Step 3: Post-reaction processing After the hydrothermal reaction is completed, the mixture is allowed to cool naturally to room temperature, and then subjected to solid-liquid separation, washing, and drying to obtain the intermediate product. Step 4: Roasting The intermediate product was calcined in air at 450-650 °C and cooled to obtain the modified manganese-oxygen octahedral molecular sieve.

4. The preparation method according to claim 3, characterized in that, In step 1, a) Dissolve manganese acetate in water, add acetic acid, heat and stir to obtain a precursor solution; b) Add the cobalt source aqueous solution to the precursor solution, heat and stir to mix evenly, and obtain the first mixed solution; c) Dissolve potassium permanganate in water and add it dropwise to the first mixed solution. Mix well to obtain the reaction system.

5. The preparation method according to claim 3, characterized in that, In step 2, the temperature of the hydrothermal reaction is 75-90 ℃, and the time of the hydrothermal reaction is 4-24 h.

6. The preparation method according to claim 3, characterized in that, In step 4, the heating rate is 3-10 °C / min, and the calcination time is 0.5-8 h.

7. A method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene, characterized in that, Using acetic acid as a solvent, the modified manganese-oxygen octahedral molecular sieve prepared according to claim 1 or 2, or any one of claims 3-6, is used as a catalyst, and potassium bromide is used as an initiator to react o-fluorotoluene with oxygen to generate o-fluorobenzaldehyde.

8. The method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene as described in claim 7, characterized in that, Includes the following steps: S1: Dissolve o-fluorotoluene in acetic acid; S2: Add catalyst and initiator to the solution obtained in step S1. The catalyst is a modified manganese-oxygen octahedral molecular sieve prepared according to claim 1 or 2, or any one of claims 3-6. The initiator is potassium bromide; S3: Introduce oxygen into the reaction solution obtained in step S2, and stir, heat, and reflux the reaction. S4: After the reaction is complete, cool to room temperature, filter to remove the catalyst and collect the liquid phase, and separate o-fluorobenzaldehyde from the liquid phase.

9. The method for preparing o-fluorobenzaldehyde by oxidation of o-fluorotoluene as described in claim 8, characterized in that, In step S1, the mass-to-volume ratio of o-fluorotoluene to acetic acid is 5-20 g: 100 mL; In step S2, the catalyst is a modified manganese-oxygen octahedral molecular sieve with a cobalt / manganese molar ratio of 1-3:

10. In step S2, the amount of catalyst added is 0.5-12.5% ​​of the mass of o-fluorotoluene; In step S2, the amount of initiator added is 0.4-10% of the mass of o-fluorotoluene; In step S3, the oxygen flow rate is 0.1-0.4 min according to the air velocity meter. -1 ; In step S3, the heating reaction temperature is 70-130 ℃.

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