Dopo-based phosphorus-nitrogen-sulfur synergistic flame-retardant compound, preparation method and application thereof

Abstract

The present application relates to the technical fields of preparation and application of multi-element synergistic flame retardant, and particularly relates to a DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compound, a preparation method and application thereof.The preparation method of the DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compound comprises the following steps: (1) reacting 2-amino-1, 3, 4-thiadiazole with p-methylsulfonyl benzaldehyde to synthesize a Schiff base intermediate, and (2) adding DOPO to perform a phosphine hydrogen addition reaction to synthesize the DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compound.The DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compound is synthesized by using a one-pot method, and the reaction method is simple and efficient.In addition, the DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compound has a multi-element (P, S, N) synergistic flame-retardant effect, can significantly improve the flame retardancy of epoxy resin, and can also maintain high transparency and stable mechanical properties of the epoxy resin, and can be applied to optical electronic products.

Description

Technical Field

[0001] This invention belongs to the field of preparation and application technology of multi-element synergistic flame retardants, specifically relating to the preparation and application method of DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compounds. Background Technology

[0002] Epoxy resin is a thermosetting resin with excellent properties, including superior solvent resistance, corrosion resistance, high temperature resistance, electrical insulation, and high transparency. It has wide applications in industries such as electronics, electrical engineering, coatings, construction, optics, and insulation. However, epoxy resin is flammable, producing large amounts of smoke and toxic gases during combustion, which greatly limits its application in high-end fields. Therefore, developing highly efficient flame-retardant epoxy resins is of great significance for expanding the applications of epoxy resin.

[0003] Currently, halogenated flame retardants are the most commercially viable, but further research has revealed that the gases produced by their combustion are harmful to human health and pollute the environment. Phosphorus-containing flame retardants are the most widely researched type. In addition, nitrogen, sulfur, silicon, and boron atoms are added to achieve synergistic flame retardancy with phosphorus. Among these, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is an important intermediate for organic phosphorus-containing flame retardants. This intermediate exhibits high stability, and its phosphorus-hydrogen bonds can react with double bonds, carbonyl groups, epoxy groups, amino groups, and other functional groups, demonstrating high reactivity.

[0004] However, many flame retardants today improve flame retardancy but often sacrifice the light transmittance of epoxy resin. Chinese patent CN108864193A discloses a phosphorus-phenanthrene compound, its preparation method, and its uses. It first uses a benzaldehyde derivative with a 5-dimethyl-1,3,2-dioxocyclohexane-2-oxide group at the para position to undergo dehydration condensation with p-phenylenediamine or a similar compound with a diamine structure to obtain a Schiff base intermediate. Then, it undergoes an addition reaction with DOPO to prepare a phosphorus-phenanthrene flame retardant compound. Although this method has a reactive group (-NH) with epoxy groups, its large structure and large steric hindrance make it difficult to react with epoxy groups. This results in some flame retardant remaining free in the resin solution, leading to poor light transmittance and opaque resin after curing. As a result, it is difficult to balance flame retardancy with transparency and mechanical properties.

[0005] The disclosure of this background information is only for understanding the overall background of this invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] One of the objectives of this invention is to provide a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound that can solve the problem of achieving both transparency, mechanical properties and flame retardant properties in epoxy resins.

[0007] The above objectives are achieved through the following technical solutions:

[0008] A DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound is disclosed. This compound is synthesized by reacting 2-amino-1,3,4-thiadiazole with p-methylsulfonylbenzaldehyde to form a Schiff base intermediate (MBAT), which is then added to DOPO to obtain the DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound (MBATP). Because the Schiff base intermediate MBAT has low structural rigidity, it can reduce its impact on the mechanical properties of epoxy resins. Simultaneously, the synthesized MBATP has a small molecular weight, simple structure, low rigidity, and high compatibility with epoxy resins, resulting in minimal impact on the transparency of flame-retardant epoxy resins. This addresses the challenge of balancing the mechanical properties and transparency of flame-retardant epoxy resins.

[0009] The chemical structural formula of the DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound is as follows:

[0010]

[0011] The preparation method of the above-mentioned DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound adopts a simplified one-pot synthesis process. The reaction conditions for both steps remain unchanged, making it easy to control and facilitating industrialization. The specific steps are as follows:

[0012] S1: 2-Amino-1,3,4-thiadiazole and solvent were added to a four-necked round-bottom flask equipped with a condenser and a thermometer. The mixture was heated and stirred until completely dissolved. Then, p-methylsulfone benzaldehyde was added to the flask to carry out a condensation reaction and synthesize the Schiff base intermediate MBAT.

[0013] The preparation process of Schiff base intermediate MBAT is as follows:

[0014]

[0015] S2: DOPO is directly added to the solution of the Schiff base intermediate MBAT mentioned in step S1 to carry out a phosphorus hydroaddition reaction. After the reaction is completed, the temperature is lowered to room temperature and then post-processed to obtain a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound.

[0016] The preparation process of DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound (MBATP) is as follows:

[0017]

[0018] Preferably, the molar ratio of 2-amino-1,3,4-thiadiazole to p-methylsulfonylbenzaldehyde (DOPO) is 1:1 to 1.5:1 to 1.3. A slight excess of the latter two ensures complete conversion of the 2-amino-1,3,4-thiadiazole and Schiff base intermediates, guaranteeing the forward reaction and improving the conversion rate of the raw materials.

[0019] Preferably, the molar ratio of 2-amino-1,3,4-thiadiazole to p-methylsulfonylbenzaldehyde (DOPO) is 1:1:1.

[0020] Preferably, the ratio of the amount of 2-amino-1,3,4-thiadiazole to the volume of the solvent is 1 mol: 6000-8000 mL, ensuring that 2-amino-1,3,4-thiadiazole can be fully dissolved at the reaction temperature, avoiding waste of raw materials and increased difficulty in post-processing.

[0021] Preferably, the condensation reaction conditions are: stirring at 40–80°C for 6–12 hours. Below 40°C, 2-amino-1,3,4-thiadiazole cannot completely dissolve, and the reaction rate will decrease; above 80°C, the solvent will boil, thus affecting the reaction.

[0022] Preferably, the phosphorus hydroaddition reaction conditions are: 40–80°C for 8–24 hours. Precise control of the reaction temperature and time can effectively ensure the forward reaction proceeds, avoiding side reactions and reducing product yield.

[0023] Preferably, the solvent in step S1 is selected from one or more of anhydrous ethanol, methanol, dioxane, dichloromethane, chloroform, tetrahydrofuran, benzene, toluene, and acetonitrile. The reactants have high solubility in the above solvents, will not react with the reactants and intermediates, and are chemically and physically stable.

[0024] Preferably, the post-processing method in step S2 is as follows: the crude product is obtained by vacuum filtration or rotary evaporation, and unreacted aldehydes, Schiff base intermediates and DOPO are removed by repeated washing with anhydrous ethanol, and then dried under vacuum at 80-100°C for 12-24 hours.

[0025] The flame-retardant epoxy resin prepared from the above-mentioned DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compound has good compatibility with the epoxy groups in the epoxy resin, which can react with the -NH- group in the DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compound. This ensures high transparency and solves the problem of balancing the transparency, mechanical properties and flame-retardant properties of epoxy resin.

[0026] Preferably, the concentration of DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compounds in the flame-retardant epoxy resin is 1-7%.

[0027] Preferably, the concentration of DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compounds in the flame-retardant epoxy resin is 2-4%.

[0028] The preparation method of the flame-retardant epoxy resin includes the following steps:

[0029] V1: Weigh a certain amount of epoxy resin and heat it to 160℃. Add DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound and stir until a transparent and homogeneous solution is obtained. Keep it at this temperature for a period of time. The -NH- in the flame retardant can react with the epoxy groups in the epoxy resin. Good compatibility ensures high transparency.

[0030] V2: After cooling the solution described in V1 to 80-100°C, add the curing agent and stir at a reduced speed until completely dissolved. Lowering the temperature of the epoxy resin and adding the curing agent is to prevent the epoxy resin from curing too quickly and to increase the molding preparation time.

[0031] V3: Quickly pour the solution from step V2 into a preheated mold at 100°C, and cure it under certain conditions in an oven to obtain flame-retardant epoxy resin.

[0032] Preferably, the curing agent comprises 4,4-diaminodiphenylmethane (DDM).

[0033] Preferably, the curing conditions are: curing at 100℃ for 2-3 hours and curing at 150℃ for 3-4 hours. Curing at 100℃ for 2-3 hours ensures that the epoxy resin and the curing agent can react fully, avoiding problems such as bubbles or defects caused by too fast curing. Curing at 150℃ for 3-4 hours ensures that the epoxy resin is fully cured.

[0034] The present invention has the following beneficial effects:

[0035] This invention synthesizes a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound using 2-amino-1,3,4-thiadiazole, p-methylsulfonylbenzaldehyde, and DOPO. This compound can be effectively applied in epoxy resins. The synthesized Schiff base intermediate, MBAT, has a low molecular weight and low rigidity, ensuring the mechanical properties of the epoxy resin. Simultaneously, the DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound has a simple structure, low steric hindrance, and high compatibility with epoxy resins. It can uniformly disperse MBATP in epoxy resins, exhibiting stable flame retardant properties and minimal impact on the transparency of the flame-retardant epoxy resin. This flame-retardant epoxy resin holds promise for applications in optical and microelectronic materials.

[0036] The DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound provided by this invention utilizes the synergistic flame retardancy of three elements (phosphorus, nitrogen, and sulfur). With an addition of 4 wt% flame retardant, it can achieve a V-0 rating (UL-94). This not only reduces the amount added, significantly minimizing the impact on epoxy resin performance, but also achieves high flame retardant efficiency. Compared with traditional halogen flame retardants, it is more environmentally friendly and safer. Furthermore, the synthesis process is simple, the purification method is easy to operate, the reaction is easy to control, there are few side reactions, and the reaction waste liquid is easy to recycle. Attached Figure Description

[0037] Figure 1The infrared spectrum of the DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound in Example 1 of this invention;

[0038] Figure 2 The 1H-NMR NMR spectrum of the DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound in Example 1 of this invention;

[0039] Figure 3 The DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound in Example 1 of this invention 31 p-NMR spectrum;

[0040] Figure 4 The graph shows the transmittance test results of 1EP / MBATP-2, 1EP / MBATP-4 and epoxy resin prepared in Example 1 of this invention.

[0041] Figure 5 SEM images of residual carbon from 1EP / MBATP-2(b), 1EP / MBATP-4(c), and epoxy resin(a) prepared in Example 1 of this invention. Detailed Implementation

[0042] To clearly and completely describe the technical solution of this invention, the reaction process will be specifically described below with reference to the accompanying drawings in the embodiments of this invention. Furthermore, the embodiments described herein are only a part of this invention, not all of it; other embodiments not described herein are within the protection scope of this invention. In addition, the pharmaceuticals and reagents used in the embodiments are all available from commercially available sources.

[0043] Example 1

[0044] A method for preparing a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound is as follows:

[0045] Weigh 0.02 mol of 2-amino-1,3,4-thiadiazole and 150 mL of anhydrous ethanol into a 250 mL four-necked round-bottom flask equipped with a condenser and thermometer. Heat to 80 °C and stir until the solid is completely dissolved. Then add 0.02 mol of p-methylsulfonylbenzaldehyde to the flask and react for 12 h. Add 0.02 mol of DOPO and continue the reaction for another 12 h. Stop the reaction and allow it to cool naturally to room temperature. After filtration, wash the product three times with a total of 150 mL of anhydrous ethanol. Dry the product under vacuum at 80 °C for 24 h to obtain the DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound, denoted as MBATP, with a yield of 76.5%.

[0046] A method for applying a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound specifically includes the following steps:

[0047] Epoxy resin (EP, Hefei Jiangfeng Chemical Co., Ltd., epoxy value 44%) was heated to 160℃, MBATP was added, and the mixture was stirred until a clear and homogeneous solution was obtained. The solution was kept at this temperature for 10 minutes, and then slowly cooled to 90℃. Curing agent 4,4'-diaminodiphenylmethane (DDM) was added and stirred at a decreasing speed until completely dissolved. The solution was then quickly poured into a mold that had been preheated to 100℃ and cured in an oven at 100℃ for 2 hours and then at 150℃ for 3 hours to obtain flame-retardant epoxy resin.

[0048] In this embodiment, the concentrations of MBATP in the flame-retardant epoxy resin are 2 wt% and 4 wt%, and the concentration of 4,4'-diaminodiphenylmethane (DDM) is 19.58 wt%, which are denoted as 1EP / MBATP-2 and 1EP / MBATP-4, respectively.

[0049] The flame retardant compound prepared in Example 1 was characterized as follows:

[0050] Figure 1 The results of mid-infrared spectral characterization (KBr pellet method) are as follows: -NH- (3434cm) -1 ); C = N (1634cm) -1 ); P = O(1230cm) -1 ); P-0-Ar(1205cm) -1 974cm -1 ); PC (753cm) -1 ).

[0051] Figure 2 The results of the 1H NMR analysis (DMSO-d6, 500MHz) were as follows: δ (ppm): 7.00–8.32 (Ar-H); 5.35–5.45 (NH); 6.53–6.73 (C*-H).

[0052] Figure 3 Phosphorus NMR spectroscopy analysis (31PNMR (DMSO-d6, 400MHz), ppm): 27.01, 28.19 (PC).

[0053] The flame retardant performance test results of the flame retardant epoxy resin in Example 1 are shown in Table 1 below.

[0054] Table 1. Flame retardant performance test results of the flame retardant epoxy resin synthesized in Example 1 of the present invention.

[0055]

[0056] a. The limiting oxygen index test standard is ASTM D2863, and the sample size is 130×6.5×3mm.

[0057] b. The standard for vertical burning test is ASTM D3801, and the sample size is 130×13×3mm.

[0058] As shown in Table 1, the LOI value of pure epoxy resin is only 25%, which does not meet the UL-94 flame retardant rating requirements. With the addition of MBATP, the flame retardant rating and LOI value of the flame retardant EP gradually increase. When 2wt% MBATP is added, the LOI value of the flame retardant EP reaches 31.5%, and the flame retardant rating reaches V-1. When 4wt% MBATP is added, the LOI value of the flame retardant EP reaches 33.5%, and the flame retardant rating reaches V-0. This shows that the addition of MBATP greatly improves the flame retardant performance of epoxy resin.

[0059] The mechanical property test results of the flame-retardant epoxy resin in Example 1 are shown in Table 2 below.

[0060] Table 2. Mechanical property test results of the flame-retardant epoxy resin synthesized in Example 1 of this invention.

[0061]

[0062] The mechanical property testing standards are as follows: Tensile testing is conducted on a tensile testing machine according to GB / T1040-2006 standard. Three-point bending testing is conducted on a three-point bending machine according to GB / T9341-2008 standard. The average value of five test samples is taken for all tests.

[0063] Table 2 shows that the mechanical properties of flame-retardant EP are not significantly different from those of pure EP, with tensile strength, tensile modulus, and flexural modulus even slightly improved. This indicates that the incorporation of MBATP does not affect the mechanical properties of epoxy resin.

[0064] Figure 4 The transmittance test results for 1EP / MBATP-2, 1EP / MBATP-4, and epoxy resin (EP) are shown. The transmittance was measured at room temperature in the UV-Vis transmission spectrum of EP and MBATP samples (3 mm thick) within the range of 300–800 nm. Figure 4 As can be seen, the addition of MBATP has little effect on the light transmittance of epoxy resin.

[0065] Example 2

[0066] A method for preparing a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound is as follows: The difference from Example 1 is that "2-amino-1,3,4-thiadiazole (0.02 mol) and 150 mL anhydrous ethanol" is replaced with "2-amino-1,3,4-thiadiazole (0.02 mol) and 150 mL dioxane", and the rest is the same as in Example 1; the product 2MBATP is obtained with a yield of 75.3%.

[0067] A method for applying a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound specifically includes the following steps: Same as Example 1

[0068] In this embodiment, the flame-retardant epoxy resins are designated as 2EP / MBATP-2 and 2EP / MBATP-4, respectively.

[0069] The flame retardant performance test results of the flame retardant epoxy resin in Example 2 are shown in Table 3 below.

[0070] Table 3. Flame retardant performance test results of the flame retardant epoxy resin synthesized in Example 2 of this invention.

[0071]

[0072] The mechanical property test results of the flame-retardant epoxy resin in Example 2 are shown in Table 4 below.

[0073] Table 4 Mechanical properties of the flame-retardant epoxy resin synthesized in Example 2 of this invention

[0074]

[0075] Example 3

[0076] A method for preparing a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound is as follows: The difference from Example 1 is that the temperature is changed from 80°C to 60°C and anhydrous ethanol is replaced with anhydrous chloroform, otherwise the same as in Example 1; the product 3MBATP is obtained with a yield of 75.3%.

[0077] The application method of a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound specifically includes the following steps: same as in Example 1.

[0078] In this embodiment, the flame-retardant epoxy resins are designated as 3EP / MBATP-2 and 3EP / MBATP-4, respectively.

[0079] The flame retardant performance test results of the flame-retardant epoxy resin in Example 3 are shown in Table 5 below:

[0080] Table 5. Flame retardant performance test parameters of the flame retardant epoxy resin synthesized in Example 3 of the present invention.

[0081]

[0082] Table 6 Mechanical properties of the flame-retardant epoxy resin synthesized in Example 3 of the present invention

[0083]

[0084] Example 4

[0085] A method for preparing a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound is as follows: The difference from Example 3 is that anhydrous chloroform is replaced with anhydrous benzene; otherwise, the method is the same as in Example 3. The product 4MBATP is obtained with a yield of 75.3%. The specific application method of the DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound includes the following steps: same as in Example 3.

[0086] In this embodiment, the flame-retardant epoxy resins are designated as 4EP / MBATP-2 and 4EP / MBATP-4, respectively.

[0087] The flame retardant performance test results of the flame retardant epoxy resin in Example 4 are shown in Table 7 below.

[0088] Table 7. Flame retardant performance test results of the flame retardant epoxy resin synthesized in Example 4 of the present invention.

[0089]

[0090] The mechanical property test results of the flame-retardant epoxy resin in Example 4 are shown in Table 8 below.

[0091] Table 8 Mechanical properties of the flame-retardant epoxy resin synthesized in Example 1 of the present invention

[0092]

[0093] Example 5

[0094] A method for preparing a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound is as follows: the difference from Example 1 is that anhydrous ethanol is replaced with anhydrous toluene, otherwise the same as in Example 3, yielding product 5MBATP; yield 75.3%.

[0095] The application method of a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound specifically includes the following steps: same as in Example 1.

[0096] In this embodiment, the flame-retardant epoxy resins are designated as 5EP / MBATP-2 and 5EP / MBATP-4, respectively.

[0097] The flame retardant performance test results of the flame retardant epoxy resin in Example 5 are shown in Table 9 below.

[0098] Table 9. Flame retardant performance test results of the flame retardant epoxy resin synthesized in Example 5 of the present invention.

[0099]

[0100] The mechanical property test results of the flame-retardant epoxy resin in Example 5 are shown in Table 10 below.

[0101] Table 10 Mechanical properties of the flame-retardant epoxy resin synthesized in Example 1 of the present invention

[0102]

[0103] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the examples should be considered illustrative rather than restrictive from any point of view, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as relating to the claims.

[0104] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A flame-retardant epoxy resin, characterized in that, The concentration of DOPO-based phosphorus-nitrogen-sulfur synergistic flame-retardant compounds in the flame-retardant epoxy resin is 2-4 wt%. The DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound has the following structure: .

2. The flame-retardant epoxy resin according to claim 1, characterized in that, The specific steps for preparing the DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound are as follows: S1: 2-Amino-1,3,4-thiadiazole and solvent were added to a four-necked round-bottom flask equipped with a condenser and a thermometer. The mixture was heated and stirred until completely dissolved. Then, p-methylsulfone benzaldehyde was added to the flask to carry out a condensation reaction and synthesize the Schiff base intermediate MBAT. S2: DOPO is directly added to the solution of the Schiff base intermediate MBAT mentioned in step S1 to carry out a phosphorus hydroaddition reaction. After the reaction is completed, the temperature is lowered to room temperature and then post-processed to obtain a DOPO-based phosphorus-nitrogen-sulfur synergistic flame retardant compound.

3. The flame-retardant epoxy resin according to claim 2, characterized in that, The molar ratio of 2-amino-1,3,4-thiadiazole, p-methylsulfonylbenzaldehyde, and DOPO is 1:1~1.5:1~1.

3.

4. The flame-retardant epoxy resin according to claim 2, characterized in that, The ratio of the amount of 2-amino-1,3,4-thiadiazole to the volume of the solvent is 1 mol: 6000~8000 mL.

5. The flame-retardant epoxy resin according to claim 2, characterized in that, The condensation reaction conditions are: stirring at 40~80℃ for 6~12h.

6. The flame-retardant epoxy resin according to claim 2, characterized in that, The conditions for the phosphorus hydroaddition reaction are: reaction at 40~80℃ for 8~24h.

7. The flame-retardant epoxy resin according to claim 2, characterized in that, The solvents include one or more of anhydrous ethanol, methanol, dioxane, dichloromethane, chloroform, tetrahydrofuran, benzene, toluene, and acetonitrile.

8. The flame-retardant epoxy resin according to claim 2, characterized in that, The post-processing method is as follows: sequentially passing through vacuum filtration or rotary evaporation, washing, and drying.

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