Preparation method of 4-dimethylaminopyridine and catalyst of 4-dimethylaminopyridine

Abstract

The invention provides a preparation method of 4-dimethylaminopyridine and a catalyst of 4-dimethylaminopyridine, and belongs to the technical field of organic chemistry. Comprising the following steps: (1) adding a catalyst into pyridine, heating, adding chlorine water, carrying out heat preservation reaction, adjusting the pH value of the solution by hydrochloric acid, separating an organic phase, carrying out reduced pressure distillation, and collecting distillate at 140-150 DEG C to obtain 4-chloropyridine; and (2) reacting 4-chloropyridine with dimethylacetamide, adding alkali liquor into the product to adjust the pH value of the solution, extracting with diethyl ether, concentrating, recrystallizing with ethyl acetate, filtering, washing and drying to obtain the 4-dimethylaminopyridine. The preparation method disclosed by the invention is simple, mild in condition, controllable and safe, the prepared 4-dimethylaminopyridine is relatively high in purity, the yield is also obviously improved, and the preparation method has a wide application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of organic chemistry, and in particular to a preparation method of 4-dimethylaminopyridine and a catalyst thereof. Background Art

[0002] Dimethylaminopyridine (DMAP) is a highly efficient catalyst widely used in chemical synthesis. It is a white crystalline powder with a molecular formula of C7H 10 N2. The molecular structure is as follows: .

[0003] Dimethylaminopyridine has a high catalytic ability in various types of reactions such as acylation, alkylation, and etherification in organic synthesis, drug synthesis, pesticides, dyes, and fragrances. The resonance of the electron-donating dimethylamino group in its structure and the parent ring (pyridine ring) can strongly activate the nitrogen atom on the ring for nucleophilic substitution, and significantly catalyze the acylation (phosphorylation, sulfonylation, carbonylation) of highly sterically hindered and low-reactive alcohols and amines. Its activity is about 10 times that of pyridine. 4-6 times. It has an extremely obvious effect on improving the yield. The catalyst has the characteristics of small dosage, mild reaction conditions, wide range of solvent selection, greatly shortened reaction time, and high reaction yield.

[0004] There are many reported DMAP synthesis methods, including 4-pyridone method, 4-chloropyridine method, 4-hydroxypyridine, 4-pyridinesulfonic acid method, 4-trimethylsilyloxypyridine method, etc. However, the industrial DMAP synthesis method mainly uses pyridine and SOCl2 as raw materials, reacts to obtain the intermediate product N-(4-pyridyl) chlorinated pyridine hydrochloride (i.e., bipyridinium salt), and then refluxes with DMF to prepare DMAP. The raw materials of this method are cheap and easy to obtain, the operation is relatively simple, and the process flow is relatively short, but the conversion rate of the raw material pyridine is low, generally below 40%. At the same time, the amount of dichlorothionyl is large, the discharge of three wastes is large and difficult to handle, and the pollution to the environment is very serious. It is reported that DMAP is prepared using 4-cyanopyridine as raw material, under the activation of 2-vinylpyridine, and dimethylamine aqueous solution as aminating reagent. The reaction conditions are relatively milder, and the reaction yield is greatly improved. However, the 2-vinylpyridine used in this method is expensive, and the recycling effect is not ideal, which hinders industrial application. Summary of the invention

[0005] The invention aims to provide a preparation method of 4-dimethylaminopyridine and a catalyst thereof. The preparation method is simple, the conditions are mild, and the preparation is controllable and safe. The prepared 4-dimethylaminopyridine has high purity and significantly improved yield, and has broad application prospects.

[0006] The technical solution of the present invention is achieved in this way: The present invention provides a method for preparing 4-dimethylaminopyridine, comprising the following steps: (1) Add a catalyst to pyridine, add chlorine water at a high temperature, keep the temperature to react, adjust the pH value of the solution with hydrochloric acid, separate the organic phase, perform vacuum distillation, collect the distillate at 140-150°C, and obtain 4-chloropyridine; (2) 4-chloropyridine is reacted with dimethylacetamide, and the product is added with alkaline solution to adjust the pH value of the solution, extracted with ether, concentrated, recrystallized with ethyl acetate, filtered, washed, and dried to obtain 4-dimethylaminopyridine.

[0007] As a further improvement of the present invention, the molar ratio of pyridine to Cl2 is 2:1-1.1; the reaction temperature is 85-95°C, and the reaction time is 10-12h.

[0008] As a further improvement of the present invention, the molar ratio of 4-chloropyridine to dimethylacetamide is 1-1.1:1, the reaction temperature is 220-230°C, the reaction time is 7-10h, the alkali solution is 30-40wt% NaOH or KOH, and the pH value of the adjustment solution is 11-12.

[0009] As a further improvement of the present invention, the catalyst is magnetic particles loaded with sulfur, and the preparation method is as follows: S1. Preparation of magnetic metal organic framework: Mix iron salt and cobalt salt and dissolve them in water, add disodium terephthalate, add them into a polytetrafluoroethylene-lined autoclave, heat and stir to react, filter, and calcine to obtain a magnetic metal organic framework; S2. Modification: adding the magnetic metal organic framework into water, adding tannic acid and a catalyst, heating and stirring to react, separating by magnet, washing, and drying to obtain a modified magnetic metal organic framework; S3. Loading: Add the modified magnetic metal organic framework into water, introduce sulfur dioxide gas, stir to react, then introduce hydrogen sulfide gas, stir to react, separate with a magnet, wash, and dry to obtain a catalyst.

[0010] As a further improvement of the present invention, in step S1, the iron salt is ferric chloride or ferric nitrate, and the cobalt salt is cobalt acetate.

[0011] As a further improvement of the present invention, the molar ratio of the iron salt, the cobalt salt and the disodium terephthalate in step S1 is 2:1:4-5, the temperature of the heating and stirring reaction is 105-115°C, the time is 44-52h, and the calcination temperature is 400-500°C, and the time is 1-2h.

[0012] As a further improvement of the present invention, the mass ratio of the magnetic metal organic framework, tannic acid and catalyst in step S2 is 12-15:3-5:0.5-1, the catalyst is a Tris-HCl solution with a pH of 8.5-9.5, the temperature of the heating and stirring reaction is 40-50°C, and the time is 2-4h.

[0013] As a further improvement of the present invention, in step S3, the ventilation volume of the sulfur dioxide gas is 3-5 mL / min, and the ventilation time is 20-30 min. The ventilation volume of the hydrogen sulfide gas is 5-10 mL / min, and the ventilation time is 30-40 min.

[0014] The present invention further protects a catalyst, the preparation method of which comprises the following steps: S1. Preparation of magnetic metal organic framework: 2 molar equivalents of iron salt and 1 molar equivalent of cobalt acetate are mixed and dissolved in water, 4-5 molar equivalents of disodium terephthalate are added, and added into a polytetrafluoroethylene-lined autoclave, heated to 105-115°C, stirred and reacted for 44-52h, filtered, and calcined at 400-500°C for 1-2h to obtain a magnetic metal organic framework; S2. Modification: adding 12-15 parts by weight of a magnetic metal organic framework to water, adding 3-5 parts by weight of tannic acid and 0.5-1 parts by weight of a catalyst, heating to 40-50°C, stirring for reaction for 2-4h, separating with a magnet, washing, and drying to obtain a modified magnetic metal organic framework; The catalyst is a Tris-HCl solution with a pH of 8.5-9.5; S3. Loading: Add the modified magnetic metal organic framework into water, introduce sulfur dioxide gas at a flow rate of 3-5 mL / min for 20-30 min, and stir to react for 10-20 min. Then introduce hydrogen sulfide gas at a flow rate of 5-10 mL / min for 30-40 min, and stir to react for 10-20 min. Separate with a magnet, wash, and dry to obtain the catalyst.

[0015] The present invention has the following beneficial effects: The present invention adopts a novel method to prepare 4-chloropyridine. After pyridine is catalyzed by a catalyst, it reacts with chlorine water (after preheating and vaporization) to obtain 4-chloropyridine. Compared with directly introducing chlorine gas, the reaction is more gentle and controllable. In addition, the reaction of chlorine gas and pyridine will also generate hydrogen chloride, which reacts with pyridine to form a salt. Therefore, after adding water, the salt directly enters the water, which is convenient for separation from the generated 4-chloropyridine, thereby promoting the right shift of chemical equilibrium and improving the reaction yield.

[0016] In addition, under the action of the sulfur-loaded catalyst, the reaction yield is improved, the reaction activation energy is increased, and the reaction temperature is slightly reduced, thereby improving the safety of the reaction.

[0017] The present invention uses a magnetic metal organic framework as a carrier, and has the advantages of porosity, large specific surface area, regular structure, controllability, easy functionalization, etc. At the same time, the magnetism is easy to separate, and after the surface is modified with tannic acid, it is convenient for the fixation of sulfur and the in-situ generation of sulfur, thereby increasing the sulfur loading amount and greatly improving the reaction catalytic activity.

[0018] The invention adopts the reaction of 4-chloropyridine and dimethylacetamide to prepare 4-dimethylaminopyridine, and the pH value is adjusted by alkali to facilitate the separation and purification of the product. After extraction and recrystallization, the obtained product has high purity and the yield is also improved to a certain extent.

[0019] The preparation method of the invention is simple, has mild conditions, is controllable and safe, the prepared 4-dimethylaminopyridine has high purity, the yield is also significantly improved, and has broad application prospects. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Preparation Example 1 Preparation of Catalyst The steps include: S1. Preparation of magnetic metal organic framework: 0.2 mol of ferric nitrate and 0.1 mol of cobalt acetate were mixed and dissolved in 200 mL of water, 0.4 mol of disodium terephthalate was added, and the mixture was added into a polytetrafluoroethylene-lined autoclave, heated to 105°C, stirred and reacted for 44 hours, filtered, and calcined at 400°C for 1 hour to obtain a magnetic metal organic framework; S2. Modification: 12 g of magnetic metal organic framework was added to 500 mL of water, 3 g of tannic acid and 0.5 g of catalyst were added, heated to 40 ° C, stirred for 2 h, separated by magnet, washed and dried to obtain a modified magnetic metal organic framework; The catalyst is a Tris-HCl solution with a pH of 8.5; S3. Loading: Add 10 g of modified magnetic metal organic framework into 500 mL of water, introduce sulfur dioxide gas at a flow rate of 3 mL / min for 20 min, and stir to react for 10 min. Then introduce hydrogen sulfide gas at a flow rate of 5 mL / min for 30 min, and stir to react for 10 min. Separate with a magnet, wash, and dry to obtain the catalyst.

[0022] Preparation Example 2 Preparation of Catalyst The steps include: S1. Preparation of magnetic metal organic framework: 0.2 mol ferric chloride and 0.1 mol cobalt acetate were mixed and dissolved in 200 mL water, 0.5 mol disodium terephthalate was added, and the mixture was added into a polytetrafluoroethylene-lined autoclave, heated to 115°C, stirred and reacted for 52 hours, filtered, and calcined at 500°C for 2 hours to obtain a magnetic metal organic framework; S2. Modification: 15 g of magnetic metal organic framework was added to 500 mL of water, 5 g of tannic acid and 1 g of catalyst were added, heated to 50 ° C, stirred for 4 h, separated by magnet, washed and dried to obtain a modified magnetic metal organic framework; The catalyst is a Tris-HCl solution with a pH of 9.5; S3. Loading: Add 10 g of modified magnetic metal organic framework into 500 mL of water, introduce sulfur dioxide gas at a flow rate of 5 mL / min for 30 min, and stir to react for 20 min. Then introduce hydrogen sulfide gas at a flow rate of 10 mL / min for 40 min, and stir to react for 20 min. Separate with a magnet, wash, and dry to obtain the catalyst.

[0023] Preparation Example 3 Preparation of Catalyst The steps include: S1. Preparation of magnetic metal organic framework: 0.2 mol of ferric nitrate and 0.1 mol of cobalt acetate were mixed and dissolved in 200 mL of water, 0.45 mol of disodium terephthalate was added, and the mixture was added into a polytetrafluoroethylene-lined autoclave, heated to 110°C, stirred and reacted for 47 hours, filtered, and calcined at 450°C for 1.5 hours to obtain a magnetic metal organic framework; S2. Modification: 13 g of magnetic metal organic framework was added to 500 mL of water, 4 g of tannic acid and 0.8 g of catalyst were added, heated to 45 ° C, stirred for 3 h, separated by magnet, washed, and dried to obtain a modified magnetic metal organic framework; The catalyst is a Tris-HCl solution with a pH of 9; S3. Loading: Add 10 g of modified magnetic metal organic framework into 500 mL of water, introduce sulfur dioxide gas at a flow rate of 4 mL / min for 25 min, and stir to react for 15 min. Then introduce hydrogen sulfide gas at a flow rate of 7 mL / min for 35 min, and stir to react for 15 min. Separate with a magnet, wash, and dry to obtain the catalyst.

[0024] Comparative Preparation Example 1 Compared with Preparation Example 3, the difference is that step S2 is not performed.

[0025] The details are as follows: S1. Preparation of magnetic metal organic framework: 0.2 mol of ferric nitrate and 0.1 mol of cobalt acetate were mixed and dissolved in 200 mL of water, 0.45 mol of disodium terephthalate was added, and the mixture was added into a polytetrafluoroethylene-lined autoclave, heated to 110°C, stirred and reacted for 47 hours, filtered, and calcined at 450°C for 1.5 hours to obtain a magnetic metal organic framework; S2. Loading: Add 10 g of magnetic metal organic framework into 500 mL of water, introduce sulfur dioxide gas at a flow rate of 4 mL / min for 25 min, and stir to react for 15 min. Then introduce hydrogen sulfide gas at a flow rate of 7 mL / min for 35 min, and stir to react for 15 min. Separate with a magnet, wash, and dry to obtain the catalyst.

[0026] Comparative Preparation Example 2 Compared with Preparation Example 3, the difference is that cobalt ferrite is used to replace the magnetic metal organic framework prepared in step S1.

[0027] The details are as follows: S1. Modification: 13 g of cobalt ferrite was added to 500 mL of water, 4 g of tannic acid and 0.8 g of catalyst were added, heated to 45 ° C, stirred for 3 h, separated by magnet, washed and dried to obtain modified cobalt ferrite; The catalyst is a Tris-HCl solution with a pH of 9; S2. Loading: Add 10 g of modified cobalt ferrite into 500 mL of water, introduce sulfur dioxide gas at a flow rate of 4 mL / min for 25 min, and stir to react for 15 min. Then introduce hydrogen sulfide gas at a flow rate of 7 mL / min for 35 min, and stir to react for 15 min. Separate with a magnet, wash, and dry to obtain the catalyst.

[0028] Test Example 1 N2 low temperature physical adsorption-desorption test: The specific surface area of ​​the catalysts prepared in Preparation Examples 1-3 or Comparative Preparation Examples 1-2 was tested using a fully automatic physical / chemical adsorption analyzer. The results are shown in Table 1.

[0029] Table 1 Group <![CDATA[Specific surface area (m 2 / g)]]> Preparation Example 1 192.5 Preparation Example 2 191.9 Preparation Example 3 194.2 Comparative Preparation Example 1 180.5 Comparative Preparation Example 2 65.2 It can be seen from the above table that the catalysts prepared in Preparation Examples 1-3 of the present invention have a relatively high specific surface area.

[0030] Example 1 This embodiment provides a method for preparing 4-dimethylaminopyridine, comprising the following steps: (1) Add the catalyst prepared in Preparation Example 1 to pyridine (the amount added is 0.5 wt% of pyridine), heat to 85°C, add chlorine water, the molar ratio of pyridine to Cl2 is 2:1, keep the temperature for 10 hours, adjust the pH value of the solution to 6.0 with hydrochloric acid, separate the organic phase, perform vacuum distillation, collect the distillate at 140°C, and prepare 4-chloropyridine; separate the catalyst with a magnet, wash, dry, and recover the catalyst; The chlorine water is vaporized into gas by the vaporization reactor, and then heated to 80°C by the buffer tank, flow meter and heater, and continuously enters the reactor to carry out chlorination reaction; (2) Mix 4-chloropyridine and dimethylacetamide in a molar ratio of 1:1, heat to 220°C, stir and react for 7 hours, add 30 wt% NaOH solution to the product to adjust the pH value of the solution to 11, extract with ether, concentrate, recrystallize with ethyl acetate, filter, wash and dry to obtain 4-dimethylaminopyridine with a melting point of 111-113°C.

[0031] Example 2 This embodiment provides a method for preparing 4-dimethylaminopyridine, comprising the following steps: (1) Add the catalyst prepared in Preparation Example 2 to pyridine (the amount added is 1 wt% of pyridine), heat to 95°C, add chlorine water, the molar ratio of pyridine to Cl2 is 2:1.1, keep the temperature for 12 hours, adjust the pH value of the solution to 6.2 with hydrochloric acid, separate the organic phase, perform vacuum distillation, collect the distillate at 150°C, and prepare 4-chloropyridine; separate the catalyst with a magnet, wash, dry, and recover the catalyst; The chlorine water is vaporized into gas by the vaporization reactor, and then heated to 90° C. by the buffer tank, flow meter, and heater, and continuously enters the reactor to perform chlorination reaction; (2) 4-chloropyridine and dimethylacetamide were mixed in a molar ratio of 1.1:1, heated to 230°C, stirred for reaction for 10 hours, 40 wt% KOH solution was added to the product to adjust the pH value of the solution to 12, extracted with ether, concentrated, recrystallized with ethyl acetate, filtered, washed, and dried to obtain 4-dimethylaminopyridine with a melting point of 111-113°C.

[0032] Example 3 This embodiment provides a method for preparing 4-dimethylaminopyridine, comprising the following steps: (1) Add the catalyst prepared in Preparation Example 3 to pyridine (the amount added is 0.8 wt% of pyridine), raise the temperature to 90°C, add chlorine water, the molar ratio of pyridine to Cl2 is 2:1.05, keep the temperature for 11 hours, adjust the pH value of the solution to 6.1 with hydrochloric acid, separate the organic phase, perform vacuum distillation, collect the distillate at 145°C, and prepare 4-chloropyridine; separate the catalyst with a magnet, wash, dry, and recover the catalyst; The chlorine water is vaporized into gas by the vaporization reactor, and then heated to 85°C by the buffer tank, flow meter and heater, and continuously enters the reactor to carry out chlorination reaction; (2) 4-chloropyridine and dimethylacetamide were mixed in a molar ratio of 1.05:1, heated to 225°C, stirred for reaction for 8 hours, 35 wt% NaOH solution was added to the product to adjust the pH value of the solution to 11.5, extracted with ether, concentrated, recrystallized with ethyl acetate, filtered, washed, and dried to obtain 4-dimethylaminopyridine with a melting point of 111-113°C.

[0033] Comparative Example 1-2 Compared with Example 3, the difference is that the catalyst is prepared by Comparative Preparation Example 1-2.

[0034] Comparative Example 3 Compared with Example 3, the difference is that the catalyst is replaced by sulfur (separated by filtration).

[0035] Test Example 2 The methods in Examples 1-3 of the present invention and Comparative Examples 1-3 were evaluated, and the results are shown in Table 2.

[0036] Table 2 Group Purity of 4-dimethylaminopyridine (%) Yield of 4-dimethylaminopyridine (%) Example 1 96.7 82.5 Example 2 96.2 82.0 Example 3 97.5 83.7 Comparative Example 1 95.1 77.3 Comparative Example 2 94.5 72.1 Comparative Example 3 94.2 67.5 It can be seen from the above table that the 4-dimethylaminopyridine prepared by the method in Examples 1-3 of the present invention has a high total yield and high purity.

[0037] Test Example 3 After the catalyst in Example 1-3 or Comparative Example 1-3 was separated, the catalytic reaction was repeated 5 times, and the result of the fifth reaction was evaluated. The results are shown in Table 3.

[0038] Table 3 Group Purity of 4-dimethylaminopyridine (%) Yield of 4-dimethylaminopyridine (%) Example 1 94.4 79.2 Example 2 94.9 80.4 Example 3 95.5 81.1 Comparative Example 1 90.7 71.2 Comparative Example 2 88.6 58.9 Comparative Example 3 86.1 32.7 It can be seen from the above table that the catalysts in Examples 1-3 of the present invention have good repeated catalytic activity.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing 4-dimethylaminopyridine, It is characterized in that The following steps are involved: (1) Add a catalyst to pyridine, add chlorine water at a high temperature, keep the temperature to react, adjust the pH value of the solution with hydrochloric acid, separate the organic phase, perform vacuum distillation, collect the distillate at 140-150°C, and obtain 4-chloropyridine; (2) reacting 4-chloropyridine with dimethylacetamide, adding alkali solution to the product to adjust the pH value of the solution, extracting with ether, concentrating, recrystallizing with ethyl acetate, filtering, washing, and drying to obtain 4-dimethylaminopyridine; The catalyst is a magnetic particle loaded with sulfur, and the preparation method is as follows: S1. Preparation of magnetic metal organic framework: Mix iron salt and cobalt salt and dissolve them in water, add disodium terephthalate, add them into a polytetrafluoroethylene-lined autoclave, heat and stir to react, filter, and calcine to obtain a magnetic metal organic framework; S2. Modification: adding the magnetic metal organic framework into water, adding tannic acid and a catalyst, heating and stirring to react, separating by magnet, washing, and drying to obtain a modified magnetic metal organic framework; S3. Loading: Add the modified magnetic metal organic framework into water, introduce sulfur dioxide gas, stir to react, then introduce hydrogen sulfide gas, stir to react, separate with a magnet, wash, and dry to obtain a catalyst.

2. The preparation method according to claim 1, It is characterized in that The pyridine, Cl 2 The molar ratio is 2:1-1.1; the reaction temperature is 85-95°C, and the reaction time is 10-12h.

3. The preparation method according to claim 1, It is characterized in that The chlorine water is vaporized into gas by the vaporization reactor, and then heated to 80-90° C. by the buffer tank, flow meter and heater, and continuously enters the reactor for chlorination reaction. The pH value of the solution adjusted by the hydrochloric acid is 6.0-6.

2.

4. The preparation method according to claim 1, It is characterized in that The molar ratio of 4-chloropyridine to dimethylacetamide is 1-1.1:1, the reaction temperature is 220-230° C., the reaction time is 7-10 h, the alkali solution is 30-40 wt % NaOH or KOH, and the pH value of the adjusted solution is 11-12.

5. The preparation method according to claim 1, It is characterized in that In step S1, the iron salt is ferric chloride or ferric nitrate, and the cobalt salt is cobalt acetate.

6. The preparation method according to claim 1, It is characterized in that In step S1, the molar ratio of the iron salt, the cobalt salt and the disodium terephthalate is 2:1:4-5, the temperature of the heating and stirring reaction is 105-115°C, the time is 44-52h, and the temperature of the calcination is 400-500°C, the time is 1-2h.

7. The preparation method according to claim 1, It is characterized in that In step S2, the mass ratio of the magnetic metal organic framework, tannic acid and catalyst is 12-15:3-5:0.5-1, the catalyst is a Tris-HCl solution with a pH of 8.5-9.5, the temperature of the heating and stirring reaction is 40-50° C., and the time is 2-4 hours.

8. The preparation method according to claim 1, It is characterized in that In step S3, the ventilation volume of the sulfur dioxide gas is 3-5 mL / min, and the ventilation time is 20-30 min. The ventilation volume of the hydrogen sulfide gas is 5-10 mL / min, and the ventilation time is 30-40 min.

9. A catalyst, It is characterized in that The preparation method comprises the following steps: S1. Preparation of magnetic metal organic framework: 2 molar equivalents of iron salt and 1 molar equivalent of cobalt acetate are mixed and dissolved in water, 4-5 molar equivalents of disodium terephthalate are added, and added into a polytetrafluoroethylene-lined autoclave, heated to 105-115°C, stirred and reacted for 44-52h, filtered, and calcined at 400-500°C for 1-2h to obtain a magnetic metal organic framework; S2. Modification: adding 12-15 parts by weight of a magnetic metal organic framework to water, adding 3-5 parts by weight of tannic acid and 0.5-1 parts by weight of a catalyst, heating to 40-50°C, stirring for reaction for 2-4h, separating with a magnet, washing, and drying to obtain a modified magnetic metal organic framework; The catalyst is a Tris-HCl solution with a pH of 8.5-9.5; S3. Loading: Add the modified magnetic metal organic framework into water, introduce sulfur dioxide gas at a flow rate of 3-5 mL / min for 20-30 min, and stir to react for 10-20 min. Then introduce hydrogen sulfide gas at a flow rate of 5-10 mL / min for 30-40 min, and stir to react for 10-20 min. Separate with a magnet, wash, and dry to obtain the catalyst.