A process for the preparation of 3-cyanobenzoic acid

Abstract

The application discloses a new method for preparing 3-cyanobenzoic acid. The method uses 3-cyanotoluene as a reactant, oxygen as an oxidant, water as a solvent, and a magnetic loaded azacrown ether salt ionic liquid as a catalyst, and 3-cyanobenzoic acid is prepared through a high-selectivity oxidation reaction without adding other organic solvents and additives. After the reaction is completed, the catalyst phase and the product phase can be separated conveniently through an external magnetic field, and the catalyst can be recycled and utilized. The application has the advantages of simple operation, high reaction efficiency, good stability of the catalyst, mild reaction conditions, high efficiency and high selectivity, no ecological environment risk, and is an environment-friendly new method for preparing 3-cyanobenzoic acid, and has a good market promotion prospect.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, specifically relating to a novel method for the selective oxidation of 3-cyanotoluene to prepare 3-cyanobenzoic acid by magnetically supported nitrogen crown ether salt ionic liquid. Background Technology

[0002] 3-Cyanobenzic acid is an important fine chemical intermediate, widely used in the production of compounds such as pharmaceuticals, pesticides, fluorescent whitening agents, high-end liquid crystal materials, and functional polymer materials. Currently, the main methods for producing 3-cyanobenzic acid are as follows (Ruan Huayi, Zhang Wangxi, Xu Baoming, et al. Green synthesis of methyl 3-cyanobenzate [J]. Petrochemical, 2013, 42(1): 60-64): (1) Isophthalonitrile hydrolysis method, using isophthalonitrile as raw material to selectively hydrolyze 3-cyanobenzic acid. This method has low selectivity, it is not easy to control the single hydrolysis of the two cyano groups, the side reaction has a large impact, the yield is low, and there is a lot of waste; (2) Halogenated benzonitrile carboxylation method, using halogenated benzonitrile as raw material to carry out carboxylation reaction. This method has too harsh reaction conditions, the reaction process is relatively complicated, the operation is inconvenient, and there are environmental pollution problems; (3) Halogenated benzoic acid cyanation method, using halogenated benzoic acid as raw material and metal cyanide (such as 3-Cyanobenic acid is prepared by cyanidation of Zn(CN)2 and NaCN. The metal cyanide in this method is highly toxic and the amount of catalyst used is large, which is not suitable for industrial production. (4) Diazotization of 3-carboxyaniline: 3-carboxyaniline is used as raw material. Diazotization reaction is carried out to generate a diazo intermediate, which is then reacted with cuprous cyanide double salt to produce 3-cyanobenic acid by Sandmeier reaction. This method requires the use of highly toxic metal cyanide and the intermediate diazo salt is easy to decompose and explode. The reaction conditions are relatively harsh and the wastewater treatment is very troublesome. (5) Oxidation of 3-cyanotoluene: 3-cyanobenic acid is prepared by oxidation reaction of raw material 3-cyanotoluene. This process has a simple synthesis route and low production cost. It is a promising method. However, the current process requires a large amount of chromium trioxide and strong acid, which can easily cause a large pollution problem. Other preparation methods include the oxidation of 3-chloromethylbenzonitrile: using 3-cyanotoluene as raw material, it first reacts with chlorine to produce 3-chloromethylbenzonitrile, and then oxidizes it with hydrogen peroxide to produce 3-cyanobenzoic acid (CN 103214396 B). This method has problems such as generating a lot of waste, the catalyst cannot be recycled, it is environmentally unfriendly, and the post-treatment is troublesome.

[0003] Oxygen is an inexpensive, safe, and environmentally friendly oxidant that does not harm the environment. Catalytic oxidation of 3-cyanotoluene to 3-cyanobenzoic acid using oxygen as an oxidant is a promising clean oxidation method. Patents CN1125043C and CN1524842A use a divalent cobalt salt as a catalyst and sodium bromide as a co-catalyst, with 3-cyanotoluene as a raw material, acetic acid, and the organic solvent chlorobenzene added, to obtain the target product through oxidation. However, these methods suffer from drawbacks such as low catalyst activity, low reaction selectivity, harsh operating conditions, complex reaction processes, inability to recover the catalyst, and the need for toxic organic solvents, posing serious environmental safety hazards. Therefore, the preparation of 3-cyanobenzoic acid is a challenging topic. Researching and developing novel catalytic reaction systems for the oxygen-selective oxidation of 3-cyanotoluene to 3-cyanobenzoic acid—which are simple to operate, efficient, highly selective, and environmentally friendly—is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a new method for preparing 3-cyanobenzoic acid by selective oxidation of 3-cyanotoluene with oxygen, which is simple to operate, efficient, green and environmentally friendly.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for the selective oxidation of 3-cyanotoluene to prepare 3-cyanobenzoic acid by magnetically supported azacrown ether salt ionic liquid catalyzing oxygen, that is, using 3-cyanotoluene as raw material, magnetically supported azacrown ether salt ionic liquid as heterogeneous catalyst, oxygen as oxidant, water as solvent, and without the addition of other organic solvents and additives, to achieve the selective oxidation of 3-cyanotoluene to prepare 3-cyanobenzoic acid.

[0006] The catalytic reaction principle of this invention is as follows:

[0007]

[0008] The catalyst is a magnetically supported nitrogen crown ether salt ionic liquid.

[0009] The chemical reaction process and structure for preparing the magnetically supported aza-crown ether salt ionic liquid used in this invention are as follows:

[0010]

[0011] In the general formula, the anion of the ionic liquid can be HPW. 12 O 40 H2PMo 11 VO 40 H7PMo6V6O 40The anion, and the transition metal M, can be any one of Mn, Cr, and Co. The preparation process of the general formula MFe₂O₄@SiO₂@GMILanion catalyst includes the following steps:

[0012] (1) Aza-18-crown-6 and 3-chloropropyltriethoxysilane in solvent 90-100 o C proceeds to the reaction, and in some reactions the reaction is completed after 20-30 hours. After the reaction is completed, the solvent is recovered and dried to obtain intermediate 1.

[0013] (2) Intermediate 1 reacts with chloropentane in a solvent at 90-100°C. o C proceeds to the reaction, and in some reactions the reaction is completed after 20-30 hours. After the reaction is completed, the solvent is recovered and dried to obtain intermediate 2.

[0014] (3) Intermediate 2, hydrochloric acid solution and potassium chloride are refluxed and stirred in the solvent. In some reactions, the reaction is completed after 20-30 hours. After the reaction, the solvent is recovered and dried to obtain intermediate 3.

[0015] (4) Intermediate 3 reacts with heteropolyacids in solvent at 50-60°C o In reaction C, the reaction is completed after 20-30 hours in some reactions. The product after the reaction is completed is washed with methanol and dried to obtain ionic liquid 4.

[0016] (5) Ionic liquid 4 continues to react with magnetic silica support in solvent at 100-110 °C o After reaction C (which takes 20-30 hours to complete in some reactions), the mixture is filtered and dried to obtain magnetically loaded azacrown ether salt ionic liquid 5.

[0017] The catalyst specifically includes MnFe2O4@SiO2@GMILHPW 12 O 40 MnFe2O4@SiO2@GMILH2PMo 11 VO 40 MnFe2O4@SiO2@GMILH7PMo6V6O 40 CrFe2O4@SiO2@GMILHPW 12 O 40 CrFe2O4@SiO2@GMILH2PMo 11 VO 40 CrFe2O4@SiO2@GMILH7PMo6V6O 40 CoFe2O4@SiO2@GMILHPW 12 O 40 CoFe2O4@SiO2@GMILH2PMo11 VO 40 Or CoFe2O4@SiO2@GMILH7PMo6V6O 40 .

[0018] The solvents used in steps (1), (2), (3), (4), and (5) include toluene, tetrahydrofuran, and methanol. During the reaction, all added solvents are in excess.

[0019] The molar ratio of aziro-18-crown-6 to 3-chloropropyltriethoxysilane in step (1) is 1:1-1.5, preferably 1:1.

[0020] In step (2), the molar ratio of intermediate 1 to chloropentane is 1:1-1.5, preferably 1:1.

[0021] The molar ratio of intermediate 2, hydrochloric acid and potassium chloride in step (3) is 1:1-1.5:1-1.5, preferably 1:1:1.

[0022] In step (4), the heteropoly acid is H3PW. 12 O 40 H4PMo 11 VO 40 or H9PMo6V6O 40 The molar ratio of intermediate 3 to heteropolyacid is 1:1-2, preferably 1:1-1.5.

[0023] In step (5), the magnetic silica support is MnFe2O4@SiO2, CrFe2O4@SiO2, or CoFe2O4@SiO2, and the mass ratio of ionic liquid 4 to magnetic silica support is 0.2-1:1, preferably 0.5-1:1.

[0024] Further preferred options are:

[0025] The molar ratio of aza-18-crown-6 to 3-chloropropyltriethoxysilane in step (1) is 1:1.

[0026] In step (2), the molar ratio of intermediate 1 to chloropentane is 1:1.

[0027] In step (3), the molar ratio of intermediate 2, hydrochloric acid, and potassium chloride is 1:1:1.

[0028] In step (4), the heteropoly acid is H3PW. 12 O 40 H4PMo 11 VO 40 or H9PMo6V6O 40The molar ratio of intermediate 3 to heteropolyacid is 1:1-1.5.

[0029] In step (5), the magnetic silica support is MnFe2O4@SiO2, CrFe2O4@SiO2, or CoFe2O4@SiO2, and the mass ratio of ionic liquid 4 to magnetic silica support is 0.5-1:1.

[0030] Thermal stability test results show that this type of magnetically supported azacrown ether salt ionic liquid has good stability at 200°C. o It can be used well below C.

[0031] The present invention is characterized by using 3-cyanotoluene as a reactant, oxygen as an oxidant, water as a solvent, and a magnetically supported nitrogen crown ether salt ionic liquid as a catalyst. The materials and catalyst are added and mixed in proportion and stirred to react.

[0032] The reaction temperature described in this invention is 30~90℃, preferably 50~80℃.

[0033] The reaction time described in this invention is 2 to 9 hours, preferably 3 to 7 hours.

[0034] The oxygen flow rate described in this invention is 2~20 mL / min, preferably 5~12 mL / min.

[0035] The catalyst used in this invention is 1-15% of the mass of 3-cyanotoluene, preferably 1-10%.

[0036] The magnetically supported nitrogen-based crown ether salt ionic liquid catalyst of this invention is MnFe2O4@SiO2@GMILHPW 12 O 40 MnFe2O4@SiO2@GMILH2PMo 11 VO 40 MnFe2O4@SiO2@GMILH7PMo6V6O 40 CrFe2O4@SiO2@GMILHPW 12 O 40 CrFe2O4@SiO2@GMILH2PMo 11 VO 40 CrFe2O4@SiO2@GMILH7PMo6V6O 40 CoFe2O4@SiO2@GMILHPW 12 O 40 CoFe2O4@SiO2@GMILH2PMo 11 VO 40 Or CoFe2O4@SiO2@GMILH7PMo6V6O40 One of them. Preferred is the magnetically supported nitrogen-based crown ether salt ionic liquid catalyst CrFe2O4@SiO2@GMILH7PMo6V6O. 40 Or CoFe2O4@SiO2@GMILH2PMo 11 VO 40 .

[0037] The present invention discloses a novel method for the selective oxidation of 3-cyanotoluene to 3-cyanobenzoic acid by a magnetically supported nitrogen crown ether salt ionic liquid catalyst. After the reaction, the magnetic heterogeneous catalyst is deposited at the bottom of the reactor. The catalyst phase and the product phase can be separated by an external magnetic field. The obtained product is analyzed by liquid chromatography. The recovered magnetic catalyst can be recycled without further treatment and fed into the next batch of catalytic reactions in proportion.

[0038] The key technology of the method for preparing 3-cyanobenzoic acid according to the present invention is the use of magnetically supported aza-crown ether salt ionic liquid to catalyze the highly selective oxidation of 3-cyanotoluene to obtain 3-cyanobenzoic acid. The functionalized magnetically supported ionic liquid catalytic reaction for the preparation of 3-cyanobenzoic acid in this invention has a unique reaction process. There is a synergistic effect between the ionic liquid's cations and anions and the active sites of the magnetic support. The metal active sites of the support activate 3-cyanotoluene, while the cations and anions of the ionic liquid absorb and activate oxygen, thereby greatly enhancing its catalytic activity and achieving a highly efficient and selective catalytic oxidation reaction.

[0039] Compared with existing oxidation technologies, the advantages of this invention are as follows: (1) The magnetically supported nitrogen crown ether salt ionic liquid catalyst has high catalytic activity and good stability. The product phase and catalyst phase are easily separated, and the catalyst can be well recovered and recycled. Under the condition of no other organic solvents and additives, a highly selective catalytic reaction occurs. (2) The oxidation process has good selectivity, high product yield, and mild reaction conditions. The product yield is higher than 60%, more preferably higher than 70%, more preferably higher than 80%, and more preferably higher than 90%. The purity of the obtained product is higher than 80%, more preferably higher than 85%, more preferably higher than 90%, more preferably higher than 95%, and more preferably higher than 98%. (3) The reaction process is simple to operate, does not require the addition of organic solvents and other additives, and the oxidation process is environmentally friendly. Attached Figure Description

[0040] Figure 1 The preferred catalyst in Example 1 is CrFe2O4@SiO2@GMILH7PMo6V6O. 40 and CoFe2O4@SiO2@GMILH2PMo 11 VO 40 SEM image.

[0041] Figure 2 This is the liquid chromatogram of the optimal product obtained in Example 9.

[0042] Figure 3 This is a diagram showing the catalyst recycling situation in Example 14.

[0043] Figure 4 This is a diagram showing the catalyst recycling situation in Example 15. Detailed Implementation

[0044] The following embodiments are merely descriptions of the best embodiments of the present invention and do not limit the scope of the present invention in any way. The essence of the present invention is further explained through the following examples.

[0045] Example 1

[0046] A method for preparing magnetically supported nitrogen-based crown ether salt ionic liquid catalysts includes the following steps:

[0047]

[0048] (1) Aza-18-crown-6 (0.2 mol) and 3-chloropropyltriethoxysilane (0.2 mol) were reacted in toluene (120 mL) at 95°C. o After reacting at C for 30 hours, the solvent was recovered and dried to obtain intermediate 1.

[0049] (2) Intermediate 1 (0.15 mol) and chloropentane (0.15 mol) were reacted in toluene (100 mL) at 95-100 ppm. o After reacting at C for 24 hours, the solvent was recovered and dried to obtain intermediate 2.

[0050] (3) Intermediate 2 (0.12 mol), 1 mol / L hydrochloric acid (0.12 mol) and potassium chloride (0.12 mol) were refluxed and stirred in tetrahydrofuran (70 mL) for 24 hours. The solvent was recovered and dried to obtain intermediate 3.

[0051] (4) Intermediate 3 (0.1 mol) was reacted with a heteropoly acid (selected from H3PW) in methanol (100 mL) solvent. 12 O 40 H4PMo 11 VO 40 or H9PMo6V6O 40 (0.12 mol) at 55-60 o After reacting at C for 30 hours, the mixture was washed with methanol and dried to obtain ionic liquid 4.

[0052] (5) Ionic liquid 4 (2 g) was further reacted with a magnetic silica support (4 g) selected from MnFe2O4@SiO2, CrFe2O4@SiO2, or CoFe2O4@SiO2) in toluene (50 mL) solvent at 105-110 °C. o After reacting at C for 30 hours, the mixture was filtered and dried to obtain magnetically loaded nitrogen crown ether salt ionic liquid 5.

[0053] The catalysts prepared with magnetically supported nitrogen-containing crown ether salt ionic liquids 5 are, in order: MnFe2O4@SiO2@GMILHPW 12 O 40 MnFe2O4@SiO2@GMILH2PMo 11 VO 40 MnFe2O4@SiO2@GMILH7PMo6V6O 40 CrFe2O4@SiO2@GMILHPW 12 O 40 CrFe2O4@SiO2@GMILH2PMo 11 VO 40 CrFe2O4@SiO2@GMILH7PMo6V6O 40 CoFe2O4@SiO2@GMILHPW 12 O 40 CoFe2O4@SiO2@GMILH2PMo 11 VO 40 and CoFe2O4@SiO2@GMILH7PMo6V6O 40 And conduct experiments in the following cases:

[0054] Example 2

[0055] 0.05 mol of 3-cyanotoluene was added to the reactor. (MnFe2O4@SiO2@GMILHPW) 12 O 40 (0.7 g), water (30 mL), oxygen was introduced at a flow rate of 18 mL / min, and the reaction was continued at 90 °C with stirring for 8 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized with ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 57%. HPLC analysis showed that the purity of the product was 87.4%.

[0056] Example 3

[0057] 0.05 mol of 3-cyanotoluene, MnFe2O4@SiO2@GMILH2PMo was added to the reactor. 11 VO40 (0.7 g), water (30 mL), oxygen was introduced at a flow rate of 15 mL / min, and the reaction was continued at 85 °C with stirring for 8 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized with ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 71%. HPLC analysis showed that the product purity was 86.9%.

[0058] Example 4

[0059] 0.05 mol of 3-cyanotoluene was added to the reactor. (MnFe2O4@SiO2@GMILH7PMo6V6O) 40 (0.6 g), water (30 mL), oxygen was introduced at a flow rate of 15 mL / min, and the reaction was continued at 85 °C with stirring for 8 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized from ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 73%. HPLC analysis showed that the product purity was 89.4%.

[0060] Example 5

[0061] 0.05 mol of 3-cyanotoluene was added to the reactor. (CrFe2O4@SiO2@GMILHPW) 12 O 40 (0.5 g), water (30 mL), oxygen was introduced at a flow rate of 15 mL / min, and the reaction was continued at 80 °C with stirring for 8 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized with ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 68%. HPLC analysis showed that the product purity was 90.2%.

[0062] Example 6

[0063] 0.05 mol of 3-cyanotoluene was added to the reactor, along with CrFe2O4@SiO2@GMILH2PMo. 11 VO 40 (0.4 g), water (30 mL), oxygen was introduced at a flow rate of 12 mL / min, and the reaction was continued at 75 °C with stirring for 6 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized from ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 86%. HPLC analysis showed that the product purity was 96.2%.

[0064] Example 7

[0065] 0.05 mol of 3-cyanotoluene was added to the reactor. (CrFe₂O₄@SiO₂@GMILH7PMo₆V₆O) 40 (0.4 g), water (30 mL), oxygen was introduced at a flow rate of 10 mL / min, and the reaction was continued at 70 °C with stirring for 6 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized with ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 93%. HPLC analysis showed that the purity of the product was 97.4%.

[0066] Example 8

[0067] 0.05 mol of 3-cyanotoluene was added to the reactor. (CoFe2O4@SiO2@GMILHPW) 12 O 40 (0.6 g), water (30 mL), oxygen was introduced at a flow rate of 15 mL / min, and the reaction was continued at 85 °C with stirring for 8 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized from ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 72%. HPLC analysis showed that the product purity was 91.5%.

[0068] Example 9

[0069] 0.05 mol of 3-cyanotoluene was added to the reactor, along with CoFe2O4@SiO2@GMILH2PMo. 11 VO 40 (0.4 g), water (30 mL), oxygen was introduced at a flow rate of 10 mL / min, and the reaction was continued at 70 °C with stirring for 5 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized with ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 96%. HPLC analysis showed that the purity of the product was 98.3%.

[0070] Example 10

[0071] 0.05 mol of 3-cyanotoluene was added to the reactor. (CoFe₂O₄@SiO₂@GMILH7PMo₆V₆O) 40 (0.5 g), water (30 mL), oxygen was introduced at a flow rate of 15 mL / min, and the reaction was continued at 75 °C with stirring for 7 hours. After the reaction was completed, the catalyst phase and crude product could be separated and recovered by an external magnetic field. The crude product was recrystallized with ethanol and dried to obtain the product 3-cyanobenzoic acid, with a yield of 91%. HPLC analysis showed that the purity of the product was 94.2%, the same as in Example 9.

[0072] Example 11

[0073] 0.05 mol of 3-cyanotoluene, 0.8 g of MnFe₂O₄@SiO₂, and 30 mL of water were added to a reactor. Oxygen was introduced at a flow rate of 20 mL / min, and the reaction was continued at 90 °C with stirring for 9 hours. After the reaction was completed, the catalyst phase and crude product were separated and recovered by an external magnetic field. The crude product was recrystallized from ethanol and dried to obtain 3-cyanobenzoic acid, with a yield of 37%. HPLC analysis showed that the product purity was 65.3%.

[0074] Example 12

[0075] 0.05 mol of 3-cyanotoluene, 0.8 g of CrFe₂O₄@SiO₂, and 30 mL of water were added to a reactor. Oxygen was introduced at a flow rate of 18 mL / min, and the reaction was continued at 90°C with stirring for 8 hours. After the reaction was completed, the catalyst phase and crude product were separated and recovered by an external magnetic field. The crude product was recrystallized from ethanol and dried to obtain 3-cyanobenzoic acid, with a yield of 46%. HPLC analysis showed that the product purity was 69.5%.

[0076] Example 13

[0077] 0.05 mol of 3-cyanotoluene, 0.8 g of CoFe₂O₄@SiO₂, and 30 mL of water were added to a reactor. Oxygen was introduced at a flow rate of 18 mL / min, and the reaction was continued at 90°C with stirring for 8 hours. After the reaction was completed, the catalyst phase and crude product were separated and recovered by an external magnetic field. The crude product was recrystallized from ethanol and dried to obtain 3-cyanobenzoic acid, with a yield of 42%. HPLC analysis showed that the product purity was 71.8%.

[0078] Example 14

[0079] The catalyst in Example 7 was recovered, and the catalytic reaction was carried out under the conditions in Example 7. The recovered catalyst was reused 5 times. The experimental results showed that the catalyst activity was not reduced, the yield of 3-cyanobenzoic acid was 87~92%, and the purity of the product was over 96%.

[0080] Example 15

[0081] The catalyst in Example 9 was recovered, and the catalytic reaction was carried out under the conditions in Example 9. The recovered catalyst was reused 5 times. The experimental results showed that the catalyst activity was not reduced, the yield of 3-cyanobenzoic acid was 90-96%, and the purity of the product was over 97%.

Claims

1. A method for preparing 3-cyanobenzoic acid, characterized in that, Using 3-cyanotoluene as a raw material, a magnetically supported azacrown ether salt ionic liquid as a heterogeneous catalyst, oxygen as an oxidant, and water as a solvent, a catalytic oxidation reaction was carried out. After the reaction was completed, the product phase and the catalyst phase were separated by an external magnetic field. The magnetically supported azacrown ether salt ionic liquid is a compound with the following structural formula: ； The metal M in the carrier MFe₂O₄@SiO₂ is selected from any one of Mn, Cr, or Co, and the anion is... Selected from HPW 12 O 40 2- H2PMo 11 VO 40 2- H7PMo6V6O 40 2- Any one of them.

2. The method for preparing 3-cyanobenzoic acid according to claim 1, characterized in that, The preparation method of the catalyst includes the following steps: (1) Aza-18-crown-6 and 3-chloropropyltriethoxysilane were reacted in a solvent at 90-100℃. After the reaction was completed, the solvent was recovered and dried to obtain intermediate 1. (2) Intermediate 1 reacts with chloropentane in a solvent at 90-100℃. After the reaction is complete, the solvent is recovered and dried to obtain intermediate 2. (3) Intermediate 2, hydrochloric acid solution and potassium chloride were refluxed and stirred in a solvent, and the solvent was recovered and dried to obtain intermediate 3; (4) Intermediate 3 reacts with heteropoly acid in solvent at 50-60℃. After the reaction is complete, the product is washed with methanol and dried to obtain ionic liquid 4. (5) Ionic liquid 4 was further reacted with magnetic silica support in solvent at 100-110℃, then filtered and dried to obtain magnetically loaded azacrown ether salt ionic liquid 5.

3. The method for preparing the catalyst according to claim 2, characterized in that, The solvents in steps (1), (2), (3), (4), and (5) include toluene, tetrahydrofuran, and methanol. During the reaction, all added solvents are in excess. The molar ratio of aziro-18-crown-6 to 3-chloropropyltriethoxysilane in step (1) is 1:1-1.

5.

4. The method for preparing the catalyst according to claim 2, characterized in that, In step (2), the molar ratio of intermediate 1 to chloropentane is 1:1-1.5; The molar ratio of intermediate 2, hydrochloric acid and potassium chloride mentioned in step (3) is 1:1-1.5:1-1.

5.

5. The method for preparing the catalyst according to claim 2, characterized in that, In step (4), the heteropoly acid is H3PW. 12 O 40 H4PMo 11 VO 40 or H9PMo6V6O 40 The molar ratio of intermediate 3 to heteropolyacid is 1:1-2; In step (5), the magnetic silica support is MnFe2O4@SiO2, CrFe2O4@SiO2, or CoFe2O4@SiO2, and the mass ratio of ionic liquid 4 to magnetic silica support is 0.2-1:

1.

6. The method for preparing 3-cyanobenzoic acid according to claim 1, characterized in that, The reaction temperature is 30~90℃.

7. The method for preparing 3-cyanobenzoic acid according to claim 1, characterized in that, The reaction time is 2 to 9 hours.

8. The method for preparing 3-cyanobenzoic acid according to claim 1, characterized in that, Oxygen is introduced during the reaction at a flow rate of 2-20 mL / min; the amount of catalyst used is 1-15% of the mass of 3-cyanotoluene.

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