A process for the preparation of poly-2,3-dimethylaniline

Abstract

This invention relates to the field of polyaniline derivative preparation technology, and more particularly to a method for preparing poly2,3-dimethylaniline. The invention provides a method for preparing poly2,3-dimethylaniline, comprising the following steps: mixing nitric acid solution and 2,3-dimethylaniline until completely dissolved, and adding Fe... 3+ The catalyst is subjected to a first heat treatment, hydrogen peroxide is added, and a second heat treatment is performed to obtain the poly(2,3-dimethylaniline); the molar ratio of nitric acid to 2,3-dimethylaniline in the nitric acid solution is (0.95~1.3):1. The poly(2,3-dimethylaniline) prepared by the above method has a high yield, reaching over 90%.

Description

Technical Field

[0001] This invention relates to the field of polyaniline derivative preparation technology, and more particularly to a method for preparing poly2,3-dimethylaniline. Background Technology

[0002] Polyaniline (PANI) is an effective additive in anti-corrosion coatings, and its low toxicity, non-polluting nature, and low price have made it highly popular. While PANI has achieved some commercial application, its rigid molecular chain and strong intermolecular forces result in poor solubility and processability, significantly limiting its commercial prospects. Research has found that PANI molecular chains with substituents on the benzene ring have lower rigidity, which is considered an effective way to improve PANI's solubility and processability. Poly(2,3-dimethylaniline) (P(2,3-DMA)), as one of the main derivatives of PANI, can reduce the rigidity of the PANI molecular chain and decrease in interchain forces due to the steric hindrance effect of the two methyl groups (-CH3) on the benzene ring, thus significantly improving PANI's solubility and showing promising application prospects in corrosion protection.

[0003] Poly(2,3-dimethylaniline), as a novel functional polymer material, has been subject to limited research both domestically and internationally regarding its synthesis process. One preparation method involves solution in-situ polymerization to synthesize doped poly(2,3-dimethylaniline), which exhibits superior solubility and corrosion resistance compared to polyaniline. However, this method utilizes ammonium persulfate (APS) as the primary oxidant, and the reduction product (ammonium sulfate) from this oxidant easily causes environmental pollution and increases product costs, inevitably leading to a loss of market competitiveness. Existing technologies also employ different acid doping methods for preparing poly(2,3-dimethylaniline). Phosphoric acid doping yields only around 75%, while camphor sulfonic acid, sulfuric acid, and hydrochloric acid doping yields do not exceed 70%. Although these methods significantly improve the solubility and corrosion resistance of poly(2,3-dimethylaniline), their low yields, the use of APS as the oxidant, high costs, environmental pollution, and the significant salt production from the ammonium persulfate oxidation system make treatment extremely difficult. Furthermore, existing technologies also utilize APS / Fe... 2+ A method for preparing poly-2,3-dimethylaniline using composite oxidants, involving the addition of a reducing agent Fe. 2+ When combined with APS, the activation energy of the redox reaction between the two is greatly reduced. Although the product has excellent crystallization properties, the yield is only 54.5%. In the existing technology, a single oxidant is used to synthesize poly2,3-dimethylaniline. Although the process is simple, the yield is low, with the highest yield being only 70.43%.

[0004] In summary, the yields of poly(2,3-dimethylaniline) prepared by existing technologies are all low, and it is relatively difficult to improve the yield. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing poly(2,3-dimethylaniline), wherein the poly(2,3-dimethylaniline) prepared by the method has a high yield, which can reach more than 90%.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing poly(2,3-dimethylaniline), comprising the following steps: Mix nitric acid solution and 2,3-dimethylaniline until completely dissolved, then add Fe. 3+ The catalyst is subjected to a first heat preservation, hydrogen peroxide is added, and a second heat preservation is performed to obtain the poly(2,3-dimethylaniline); The molar ratio of nitric acid to 2,3-dimethylaniline in the nitric acid solution is (0.95~1.3):1.

[0007] Preferably, the mass percentage concentration of the nitric acid solution is 3% to 4%; The mixing temperature is 40~50℃.

[0008] Preferably, the Fe 3+ The catalyst includes one or more of ferric chloride, ferric nitrate and ferric sulfate.

[0009] Preferably, the Fe 3+ The molar ratio of catalyst to 2,3-dimethylaniline is (0.02~0.03):1.

[0010] Preferably, the temperature of the first heat preservation is 40~50℃ and the time is 0.5~1h.

[0011] Preferably, the hydrogen peroxide has a mass percentage concentration of 25% to 30%.

[0012] Preferably, the molar ratio of H2O2 and 2,3-dimethylaniline in the hydrogen peroxide is (1.8~2.3):1.

[0013] Preferably, the hydrogen peroxide is added over a period of 1 to 3 hours.

[0014] Preferably, the second heat preservation temperature is 40~50℃ and the time is 2~4h.

[0015] Preferably, after the second insulation is completed, post-processing is also included; The post-processing includes sequential cooling crystallization, filtration, washing, and drying.

[0016] This invention provides a method for preparing poly(2,3-dimethylaniline), comprising the following steps: mixing nitric acid solution and 2,3-dimethylaniline until completely dissolved, and adding Fe... 3+ The catalyst is subjected to a first heat treatment, hydrogen peroxide is added, and a second heat treatment is performed to obtain the poly(2,3-dimethylaniline); the molar ratio of nitric acid to 2,3-dimethylaniline in the nitric acid solution is (0.95~1.3):1. The preparation method of this invention controls the molar ratio of nitric acid to 2,3-dimethylaniline within the above range, which can ensure the yield of poly(2,3-dimethylaniline). When the molar ratio is greater than 1.3, due to the high content of nitric acid in the reaction system and its large proportion in the solution space structure, the nitric acid nitrate salt does not dissolve in the solution, and the corresponding yield will gradually decrease. When the molar ratio is less than 0.95, nitric acid preferentially forms nitric acid nitrate salt with 2,3-dimethylaniline, and there is no acid-catalyzed oxidation activity of hydrogen peroxide in the reaction system, which also leads to a significant decrease in the reaction yield. Meanwhile, the applicant found that when using a ferrous catalyst, the ferrous catalyst catalyzes the rapid oxidation rate of hydrogen peroxide, leading to high oxidation of poly(2,3-dimethylaniline) with different degrees of polymerization, resulting in a decrease in the final yield. Using Fe... 3+ The catalyst serves two purposes: firstly, iron itself possesses oxidizing properties, capable of oxidizing 2,3-dimethylaniline to synthesize poly-2,3-dimethylaniline, thus increasing the yield; secondly, after its oxidizing effect, iron is reduced to ferrous iron, which acts as a catalyst for hydrogen peroxide, facilitating the oxidation of 2,3-dimethylaniline. Simultaneously, due to the oxidation of iron itself, the ferrous catalyst in the hydrogen peroxide solution becomes insufficient, reducing the high oxidation rate of poly-2,3-dimethylaniline by hydrogen peroxide, thereby reducing the hydrogen peroxide / Fe ratio. 3+ The combination of catalysts increased the reaction yield; then only in H2O2 / Fe 3+ The catalytic system still inevitably suffers from over-oxidation of 2,3-dimethylaniline. Therefore, this invention further uses nitric acid as the acid system and the steric hindrance effect generated by nitric acid and the dimethyl group of 2,3-dimethylaniline greatly reduces the over-oxidation, ultimately achieving a poly(2,3-dimethylaniline) yield of over 90%.

[0017] In summary, the iron catalyst prepared by the method described in this invention is Fe. 3+ Under acidic conditions, not only Fe 3+ It can exist stably while enhancing its oxidizing properties. In the reaction solution, iron catalysts oxidize 2,3-dimethylaniline to synthesize poly-2,3-dimethylaniline, while Fe... 3+ Converted to Fe 2+ Therefore, Fe 3+ It combines directly with hydrogen peroxide, utilizing Fe 3+ During the catalytic synthesis of poly(2,3-dimethylaniline), Fe was generated. 2+The catalytic oxidation of hydrogen peroxide was achieved by utilizing the steric hindrance effect of the dimethyl groups in nitric acid and 2,3-dimethylaniline. Experiments verified that this successfully avoided the hydrogen peroxide / Fe... 2+ Fenton degradation oxidation improved the synthesis yield.

[0018] Fe 2+ + H2O2→ Fe 3+ + OH - + •OH The beneficial effects of this invention are as follows: 1) Using H2O2 / Fe 3+ The synthesis of poly(2,3-dimethylaniline) using the HNO3 catalytic system can achieve a yield of over 90%, which is significantly higher than that of hydrogen peroxide / Fe2O3. 2+ The yield of the oxidation system and the ammonium persulfate oxidation system increased by 10-20%; 2) Due to the high yield, the corresponding impurity content in the mother liquor is low, which increases the feasibility of reusing the mother liquor. The small molecule polymers contained in the mother liquor can be further recovered. 3) The reaction mother liquor is relatively simple to treat, and the COD content is 50% lower than that of the ammonium persulfate oxidation system, which greatly reduces the difficulty of treatment. In addition, the ammonium persulfate oxidation system produces a lot of salt, which is very difficult to treat. This invention does not produce salt, which further reduces the difficulty of post-treatment. 4) This invention uses hydrogen peroxide as the oxidant, which is a green oxidant. The reaction produces •OH and OH-. - It is ultimately produced in the form of water, which further reduces the difficulty of post-processing. Detailed Implementation

[0019] This invention provides a method for preparing poly(2,3-dimethylaniline), comprising the following steps: Mix nitric acid solution and 2,3-dimethylaniline until completely dissolved, then add Fe. 3+ The catalyst is subjected to a first heat preservation, hydrogen peroxide is added, and a second heat preservation is performed to obtain the poly(2,3-dimethylaniline); The molar ratio of nitric acid to 2,3-dimethylaniline in the nitric acid solution is (0.95~1.3):1.

[0020] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0021] In this invention, the mass percentage concentration of the nitric acid solution is preferably 3% to 4%, more preferably 3%, 3.2%, 3.4%, 3.6%, 3.8%, or 4%. In an embodiment of this invention, the mass percentage concentration of the nitric acid solution may be 3.65% or 4%.

[0022] This invention typically uses hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, and dodecylbenzenesulfonic acid instead of nitric acid. It was found that phosphoric acid, acetic acid, and dodecylbenzenesulfonic acid are weak acids, making it difficult to promote the oxidation effect of hydrogen peroxide, resulting in a lower yield of poly(2,3-dimethylaniline). Furthermore, the presence of dimethyl groups in the benzene ring of 2,3-dimethylaniline leads to poor water solubility. When forming ammonium salts under acidic conditions, these salts are difficult to dissolve in solution, significantly reducing the contact area between the raw material and the oxidant. This reduces the number of oxidation reaction sites in 2,3-dimethylaniline, further decreasing the product yield. However, using nitric acid as the acid system allows the nitric acid aniline salt formed with 2,3-dimethylaniline to dissolve completely in solution. Simultaneously, the larger spatial structure of nitric acid in solution hinders the high-level oxidation of poly(2,3-dimethylaniline) with different degrees of polymerization by hydrogen peroxide. High-level oxidation would convert poly(2,3-dimethylaniline) into carbon dioxide and water. Therefore, the introduction of nitric acid enables the effective synthesis of poly(2,3-dimethylaniline).

[0023] In this invention, the molar ratio of nitric acid to 2,3-dimethylaniline in the nitric acid solution is (0.95~1.3):1, preferably 0.95:1, 1.0:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, or 1.3:1. In embodiments of this invention, the molar ratio of nitric acid to 2,3-dimethylaniline in the nitric acid solution can be 1.14:1, 0.95:1, or 1.30:1.

[0024] In this invention, the mixing temperature is preferably 35~50℃, more preferably 35℃, 36℃, 38℃, 40℃, 42℃, 44℃, 46℃, 48℃ or 50℃. In an embodiment of this invention, the mixing temperature can be 37℃.

[0025] In this invention, the Fe 3+ The catalyst preferably includes one or more of ferric chloride, ferric nitrate, and ferric sulfate, when the Fe 3+ When the catalyst is two or more of the specific choices mentioned above, the present invention does not impose any special limitation on the ratio of the specific substances; they can be mixed in any ratio. In the embodiments of the present invention, the Fe... 3+ The catalyst can be ferric nitrate, ferric chloride, or ferric nitrate and ferric chloride in a mass ratio of 3.72:1.

[0026] In this invention, the Fe 3+ The molar ratio of the catalyst to 2,3-dimethylaniline is preferably (0.02~0.03):1, more preferably 0.02:1, 0.022:1, 0.024:1, 0.026:1, 0.028:1 or 0.03:1. In embodiments of the present invention, the Fe... 3+The molar ratio of the catalyst to 2,3-dimethylaniline can be 0.027:1.

[0027] The present invention relates to the Fe 3+ There are no special restrictions on the process of adding the catalyst; any process well known to those skilled in the art can be used.

[0028] In this invention, the temperature of the first heat preservation is preferably 40~50℃, more preferably 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃ or 50℃; the heat preservation time is preferably 0.5~1h, more preferably 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1h. In an embodiment of this invention, the temperature of the first heat preservation can be 44℃, and the heat preservation time can be 0.5h.

[0029] In this invention, the mass percentage concentration of the hydrogen peroxide is preferably 25% to 30%, more preferably 25%, 26%, 27%, 28%, 29%, or 30%. In an embodiment of this invention, the mass percentage concentration of the hydrogen peroxide can be 27.5%.

[0030] In this invention, the molar ratio of H2O2 to 2,3-dimethylaniline in the hydrogen peroxide is preferably (1.8~2.3):1, more preferably 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1 or 2.3:1. In embodiments of this invention, the molar ratio of H2O2 to 2,3-dimethylaniline in the hydrogen peroxide can be 2.01:1 or 2.3:1.

[0031] In this invention, the hydrogen peroxide is preferably added over a period of 1 to 3 hours, more preferably over 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours. In an embodiment of this invention, the hydrogen peroxide is added over a period of 3 hours.

[0032] In this invention, the preferred temperature for the second heat preservation is 40-50°C, more preferably 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, or 50°C; the preferred time is 2-4 hours, more preferably 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. In an embodiment of this invention, the temperature for the second heat preservation can be 46°C, and the time can be 3 hours.

[0033] After the second heat preservation, the present invention preferably includes a post-treatment, which preferably includes sequential cooling and crystallization to 30°C, filtration, washing, and drying. The present invention does not impose any special limitations on the cooling and crystallization and filtration processes; any process well-known to those skilled in the art can be used. In the present invention, the washing is preferably performed using distilled water; the present invention does not impose any special limitations on the washing process; any process well-known to those skilled in the art can be used. In the present invention, the drying temperature is preferably 60~65°C, more preferably 60°C, 61°C, 62°C, 63°C, 64°C, or 65°C; the vacuum degree is preferably 10~20 kPa, more preferably 10 kPa, 12 kPa, 14 kPa, 16 kPa, 18 kPa, or 20 kPa; the time is preferably 6~12 h, more preferably 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, or 12 h. In an embodiment of the present invention, the drying temperature can be 60°C, the vacuum degree can be 12 kPa, and the time can be 8 h.

[0034] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0035] The yield in the following examples and comparative examples is calculated as follows: (W1-W2) / W2×100%, where W1 is the mass of poly(2,3-dimethylaniline) and W2 is the mass of 2,3-dimethylaniline. Example 1 In a reaction flask, 3029.54 g of a 3.65% nitric acid solution (1.75 mol HNO3) and 187 g of 1.53 mol 2,3-dimethylaniline (HNO3 to 2,3-dimethylaniline molar ratio 1.14:1) were added sequentially. The mixture was stirred and heated to 37°C until the solid was completely dissolved. Then, 10.16 g of 0.042 mol ferric nitrate was added, and the mixture was kept at 44°C for 30 min. Finally, 372.84 g of a 27.5% nitric acid solution was slowly added dropwise. Hydrogen peroxide (3.08 mol of H2O2, with a molar ratio of H2O2 to 2,3-dimethylaniline of 2.01:1) was added dropwise over 3 hours. The mixture was then kept at 46°C for 3 hours. After the reaction was complete, the mixture was cooled to 30°C to crystallize. The mixture was filtered, and the filter cake was washed with distilled water until neutral. The resulting filter cake was then dried in a vacuum oven at 60°C and 12 kPa for 8 hours to obtain poly(2,3-dimethylaniline) (171.07 g, black powder, yield 91.48%, COD: 16800 mg / L).

[0036] Example 2 Referring to Example 1, the difference is that the molar ratio of HNO3 to 2,3-dimethylaniline in the nitric acid solution is 0.95:1, wherein the mass of the nitric acid solution with a mass concentration of 3.65% is 2508.78 g, and the mass of 2,3-dimethylaniline is 187 g, to obtain poly-2,3-dimethylaniline (product yield 90.8%, COD: 18290 mg / L).

[0037] Example 3 Referring to Example 1, the difference is that ferric nitrate was replaced with ferric chloride, and the amount of ferric chloride used was 6.81 g, to obtain poly(2,3-dimethylaniline) (product yield 92.5%, COD: 15140 mg / L).

[0038] Example 4 Referring to Example 1, the difference is that ferric nitrate was replaced with ferric chloride and ferric nitrate, with ferric chloride used in an amount of 1.95g and ferric nitrate used in an amount of 7.26g, to obtain poly(2,3-dimethylaniline) (product yield 93.2%, COD: 13320mg / L).

[0039] Example 5 Referring to Example 1, the difference is that the 3.65% nitric acid solution was replaced with a 4% nitric acid solution, and the amount of the 4% nitric acid solution used was 2756.25g, to obtain poly(2,3-dimethylaniline) (product yield: 94.6%, COD: 10992mg / L).

[0040] Example 6 Referring to Example 1, the difference is that the molar ratio of H2O2 to 2,3-dimethylaniline in the hydrogen peroxide was replaced with a molar ratio of 2.3:1, instead of 2.01:1. The mass of hydrogen peroxide was 665.86 g, and the mass of 2,3-dimethylaniline was 187 g, resulting in poly(2,3-dimethylaniline) (product yield: 93.3%, COD: 12388 mg / L).

[0041] Comparative Example 1 Referring to Example 1, the difference is that 3029.54g of 3.65% nitric acid solution was replaced with 1601.63g of 4% hydrochloric acid solution, and the reaction time was kept at the temperature for 5 hours to obtain poly(2,3-dimethylaniline) (product yield 72.3%, COD: 39260mg / L).

[0042] Comparative Example 2 Referring to Example 1, the difference is that 10.16g of ferric nitrate was replaced with 7.56g of ferrous nitrate, and the reaction time was kept at the temperature for 7 hours to obtain poly(2,3-dimethylaniline) (product yield: 74.5%, COD: 36842mg / L).

[0043] Comparative Example 3 Referring to Example 1, the difference is that hydrogen peroxide was not added, and the reaction time was kept at a constant temperature for 12 hours to obtain poly(2,3-dimethylaniline) (product yield: 74.5%, COD: 36842 mg / L).

[0044] Comparative Example 4 Referring to Example 1, the difference is that 3029.54g of 3.65% nitric acid solution (1.75mol of HNO3), 10.16g of ferric nitrate (0.042mol), and 372.84g of 27.5% hydrogen peroxide were replaced with 698.30g of ammonium persulfate (APS) and 7496.62g of 4% H3PO4 solution. The reaction was kept at a constant temperature for 3 hours to obtain poly(2,3-dimethylaniline) (product yield 78.3%, COD: 34377mg / L).

[0045] As can be seen from the data of Examples 1-6 and Comparative Examples 1-4, the yield of poly(2,3-dimethylaniline) synthesized using the hydrogen peroxide system of the present invention can reach at least 90%, compared to Comparative Example 2 (hydrogen peroxide / Fe). 2+ The yield of the reaction mixture (oxidation system) and Comparative Example 4 (ammonium persulfate oxidation system) is increased by 10-20%. Due to the higher yield, the impurity content in the mother liquor is correspondingly lower, increasing the feasibility of mother liquor reuse. Small molecule polymers contained in the mother liquor can be further recovered. The mother liquor treatment is relatively simple, and the COD content is 50% lower than that of the ammonium persulfate oxidation system, greatly reducing the treatment difficulty. In addition, the ammonium persulfate oxidation system produces a lot of salt, which is very difficult to treat. The salt content of this invention is relatively low. This invention uses hydrogen peroxide as an oxidant, which is a green oxidant. The ·OH and OH produced in the reaction are... - It is ultimately produced in the form of water, which further reduces the difficulty of post-processing.

[0046] Comparative Example 5 Referring to Example 1, the difference is that 3029.54g of nitric acid solution with a mass concentration of 3.65% was replaced with 2774.36g of sulfuric acid with a mass concentration of 3.1%, and the reaction time was kept at the temperature for 5 hours to obtain poly(2,3-dimethylaniline) (product yield 54%, COD: 68582mg / L).

[0047] Comparative Example 6 Referring to Example 1, the difference is that 3029.54g of nitric acid solution with a mass concentration of 3.65% was replaced with 2635.10g of acetic acid with a mass concentration of 4%, and the reaction time was kept at a constant temperature for 5 hours to obtain poly(2,3-dimethylaniline) (product yield 9%).

[0048] Example 7 Referring to Example 1, the difference is that the molar ratio of HNO3 in the nitric acid solution to 2,3-dimethylaniline is 1.30:1, wherein the mass of the nitric acid solution with a mass concentration of 3.65% is 3433.07g, and the mass of 2,3-dimethylaniline is 187g, resulting in poly(2,3-dimethylaniline) (product yield 91%, COD: 17956mg / L).

[0049] Comparative Example 5 Referring to Example 1, the difference is that the molar ratio of HNO3 in the nitric acid solution to 2,3-dimethylaniline is 0.8:1, wherein the mass of the nitric acid solution with a mass concentration of 3.65% is 2112.66g, and the mass of 2,3-dimethylaniline is 187g, resulting in poly(2,3-dimethylaniline) (product yield 69.5%, COD: 42280mg / L).

[0050] Comparative Example 6 Referring to Example 1, the difference is that the molar ratio of HNO3 to 2,3-dimethylaniline in the nitric acid solution is 1.50:1, wherein the mass of the nitric acid solution with a mass concentration of 3.65% is 3961.23 g, and the mass of 2,3-dimethylaniline is 187 g, yielding poly(2,3-dimethylaniline) (product yield 79.7%, COD: 26238 mg / L).

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing poly-2,3-dimethylaniline, characterized in that, Includes the following steps: Mix nitric acid solution and 2,3-dimethylaniline until completely dissolved, then add Fe. 3+ The catalyst is subjected to a first heat preservation, hydrogen peroxide is added, and a second heat preservation is performed to obtain the poly(2,3-dimethylaniline); The molar ratio of nitric acid to 2,3-dimethylaniline in the nitric acid solution is (0.95~1.3):

1.

2. The preparation method according to claim 1, characterized in that, The mass percentage concentration of the nitric acid solution is 3%~4%; The mixing temperature is 40~50℃.

3. The preparation method according to claim 1, characterized in that, The Fe 3+ The catalyst includes one or more of ferric chloride, ferric nitrate and ferric sulfate.

4. The preparation method according to claim 1 or 3, characterized in that, The Fe 3+ The molar ratio of catalyst to 2,3-dimethylaniline is (0.02~0.03):

1.

5. The preparation method according to claim 4, characterized in that, The first insulation temperature is 40~50℃, and the time is 0.5~1h.

6. The preparation method according to claim 1, characterized in that, The hydrogen peroxide has a mass percentage concentration of 25% to 30%.

7. The preparation method according to claim 6, characterized in that, The molar ratio of H2O2 and 2,3-dimethylaniline in the hydrogen peroxide is (1.8~2.3):

1.

8. The preparation method according to claim 7, characterized in that, The hydrogen peroxide is added over a period of 1 to 3 hours.

9. The preparation method according to any one of claims 1, 5 to 8, characterized in that, The second insulation temperature is 40~50℃, and the time is 2~4h.

10. The preparation method according to claim 9, characterized in that, After the second insulation is completed, post-processing is also included; The post-processing includes sequential cooling crystallization, filtration, washing, and drying.