A trivalent vanadium complex catalyst containing a bidentate ligand, its preparation method and use

Abstract

The present invention discloses a trivalent vanadium complex catalyst containing a bidentate ligand, its preparation method and use. The structural general formula of the trivalent vanadium complex catalyst containing a bidentate ligand is #imgabs0# or #imgabs1#, wherein R1, R2, and R3 are each one of a hydrogen atom, a methyl group, and an isopropyl group. The trivalent vanadium complex catalyst containing a bidentate ligand of the present invention is used for catalyzing the polymerization of ethylene and its polar monomers. By changing the ligand backbone structure, the steric hindrance effect and electronic effect of the catalyst are precisely regulated, the polymerization reaction process is controlled, and a functionalized polyolefin material with a high polar monomer insertion rate and high molecular weight is obtained.

Description

Technical Field

[0001] The present invention relates to the fields of organometallic catalysts for olefin polymerization and olefin coordination polymerization, and particularly to a trivalent vanadium complex catalyst containing a bidentate ligand, a preparation method thereof, and uses thereof. Background Art

[0002] Polyolefins are the polymers with the largest production volume industrially, accounting for more than half of the world's production of thermoplastics. Due to the simple and stable C-H backbone structure, polyethylene has excellent properties and is widely used in various fields of industrial production. However, due to many factors such as the non-polarity of the material itself and the low surface energy, the dyeability, adhesiveness, hydrophilicity, antistatic property of polyolefin materials, and the compatibility with other polar polymers or inorganic fillers are poor, which limits the further application of related materials. Therefore, functionalizing non-polar polyolefin materials, that is, introducing polar functional groups into their molecular chains to significantly improve the flexibility, adhesion, protective properties, surface properties, solvent resistance, miscibility with other polymers, and rheological properties of polymer materials, has become one of the important research directions for expanding the application fields of polyolefin materials.

[0003] As a kind of polyolefin catalyst that is cheap, highly active, and has a simple preparation process, early transition metal catalysts are widely used in industrial production. However, due to the highly electrophilic nature of early transition metals themselves, in the copolymerization reaction of olefin polar monomers, the metal center is easily poisoned by polar functional groups, resulting in a decrease in catalytic activity. Therefore, how to overcome this drawback has become an issue that global researchers are concerned about currently. Summary of the Invention

[0004] The purpose of the present invention is to provide a trivalent vanadium complex catalyst containing a bidentate ligand, a preparation method thereof, and uses thereof. The trivalent vanadium complex catalyst containing a bidentate ligand is used for catalyzing the (co)polymerization of ethylene and its polar monomers. By adjusting the ligand backbone, the steric hindrance and electronic effect of the catalyst are precisely controlled, the polymerization reaction process is controlled, and a functionalized polyolefin material with a high polar monomer insertion rate and high molecular weight is obtained.

[0005] In one aspect of the present invention, a trivalent vanadium complex catalyst containing a bidentate ligand is proposed. According to an embodiment of the present invention, its structural general formula is:

[0006]

[0007] Wherein, R1, R2, and R3 are each one of a hydrogen atom, a methyl group, and an isopropyl group.

[0008] In another aspect of the present invention, a preparation method of a trivalent vanadium complex catalyst containing a bidentate ligand is proposed. According to an embodiment of the present invention, the method includes the following steps:

[0009] (1) Synthesis of ligands: 2,6 - diisopropyl - N,N - dimethylaniline was reacted with 2 - pyridinecarboxaldehyde, furfural, and thiophene - 2 - carbaldehyde in methanol solution to obtain N,N - bidentate ligand C1, N,O - bidentate ligand C2, and N,S - bidentate ligand C3;

[0010] (2) Synthesis of trivalent vanadium complex catalyst: (THF)3VCl3 and C1, C2, C3 were respectively dissolved in dichloromethane and reacted. The solvent was removed under vacuum to obtain a solid powder, which was recrystallized with dichloromethane and n - hexane to obtain the trivalent vanadium complex catalyst containing bidentate ligands.

[0011] In addition, according to the preparation method of a trivalent vanadium complex catalyst containing bidentate ligands in the above - mentioned embodiments of the present invention, the following additional technical features may also be included:

[0012] In some embodiments of the present invention, in step (1), the molar ratio of 2 - thiophenecarboxaldehyde, furfural or 2 - pyridinecarboxaldehyde to 2,6 - diisopropyl - N,N - dimethylaniline is 1:1 - 1.2, the reaction time is 10 - 12 h, and the reaction temperature is room temperature;

[0013] In step (2), the molar ratio of (THF)3VCl3 to C1, C2, C3 is respectively 1:1 - 1.2, and the reaction time is 10 - 12 h.

[0014] In some embodiments of the present invention, in step (2), the preparation method of (THF)3VCl3 includes the following steps: under a nitrogen atmosphere, vanadium chloride was suspended in tetrahydrofuran and stirred until the precipitate became a dark purple transparent liquid. Toluene was removed, and the solvent was removed under reduced pressure to obtain a pink - purple solid. Subsequently, the solid was diluted with dichloromethane and recrystallized three times with n - hexane. The remaining solvent was dried by suction to finally obtain a pink - purple solid, which is the (THF)3VCl3.

[0015] In some embodiments of the present invention, in step (2), the molar ratio of VCl3 to tetrahydrofuran is 1:1 - 1.2, the stirring time is 46 - 48 h, and the stirring temperature is 70 - 75 °C.

[0016] The general formula for the synthesis of a trivalent vanadium complex catalyst containing bidentate ligands is as follows:

[0017]

[0018] Among them, R1, R2, and R3 are each one of a hydrogen atom, a methyl group, and an isopropyl group.

[0019] In another aspect of the present invention, the present invention provides a use of a trivalent vanadium complex catalyst containing a bidentate ligand. According to an embodiment of the present invention, the trivalent vanadium complex catalyst containing a bidentate ligand is applied to catalyze the homopolymerization of ethylene.

[0020] In another aspect of the present invention, the present invention provides a use of a trivalent vanadium complex catalyst containing a bidentate ligand. According to an embodiment of the present invention, the trivalent vanadium catalyst is applied to catalyze the copolymerization of ethylene and a polar monomer having an allyl structure to prepare a functionalized polyolefin material.

[0021] In some embodiments of the present invention, the specific application process includes the following steps: under the protection of anhydrous and anaerobic nitrogen, a cocatalyst, a polar monomer D, and a solvent E are added to a high-pressure reaction kettle. Finally, a trivalent vanadium complex catalyst containing a bidentate ligand is added, ethylene is introduced and stirred for reaction, methanol is added to terminate the reaction, and the obtained product is washed with methanol and then vacuum dried until the mass remains unchanged to obtain a polymerization product.

[0022] In some embodiments of the present invention, the polar monomer D is one of 6-chloro-1-hexene, methyl acrylate, ethyl acrylate, butyl acrylate, tert-butyl acrylate, methyl methacrylate, norbornene, allyl chloride, 10-undecen-1-ol, and methyl 10-undecenoate. The cocatalyst is diethylaluminum chloride, the solvent E is toluene, the molar ratio of the trivalent vanadium complex catalyst containing a bidentate ligand to the polar monomer D is 1:500 - 3000, the reaction temperature is 0 - 80 °C, and the stirring reaction time is 5 - 10 min.

[0023] The above catalytic polymerization general formula is as follows:

[0024]

[0025] Among them, R1, R2, and R3 are each one of a hydrogen atom, a methyl group, and an isopropyl group, FG is the group of the polar monomer D, and Cat is the trivalent vanadium complex catalyst containing a bidentate ligand of the present invention.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The trivalent vanadium complex catalyst containing a bidentate ligand of the present invention is used to catalyze the polymerization of ethylene and its polar monomers. By changing the ligand backbone structure, a ligand with a large aniline side group is synthesized to increase the steric effect, thereby protecting the metal center from being poisoned by polar functional groups, and the backbone structure can be changed to increase the steric effect and electronic effect, control the polymerization reaction process, and obtain a functionalized polyolefin material with a high polar monomer insertion rate and high molecular weight.

[0028] (2) For the first time, the present invention conducts the catalytic coordination polymerization reaction of trivalent vanadium complexes containing NN, SN, and ON bidentate ligands for ethylene-polar monomers, explores the influence of different ligand structures on the polymerization activity, makes up for the blank of preparing functionalized polyolefin materials by copolymerizing polar monomers with early transition metals, and further expands the application scope of related catalysts, with strong original innovation.

[0029] (3) The present invention realizes the copolymerization of ethylene and various polar monomers by synthesizing a trivalent vanadium metal catalytic system; realizes the copolymerization of ethylene-polar monomers with early transition metals. The trivalent vanadium catalytic system containing bidentate ligands further broadens the range of types of copolymerizable polar monomers, providing another idea for the catalyst design of preparing functionalized polyolefins. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is the proton nuclear magnetic resonance spectrum of the N,S bidentate ligand prepared in Example 1 of the present invention;

[0031] Figure 2 is the infrared spectrum of the trivalent vanadium complex catalyst containing bidentate ligands prepared in Example 1 of the present invention. Among them, the abscissa is the wave number (cm -1 ), the ordinate is the density (%), SN-1' refers to the trivalent vanadium complex catalyst containing N,N bidentate ligands, SN-1 refers to the N,N bidentate ligand, the upper curve is SN-1', and the lower curve is SN-1;

[0032] Figure 3 is the infrared spectrum of the trivalent vanadium complex catalyst containing bidentate ligands prepared in Example 2 of the present invention. Among them, the abscissa is the wave number (cm -1 ), the ordinate is the density (%), NN-1' refers to the trivalent vanadium complex catalyst containing N,N bidentate ligands, NN-1 refers to the N,N bidentate ligand, the upper curve is NN-1', and the lower curve is NN-1;

[0033] Figure 4 is the infrared spectrum of the trivalent vanadium complex catalyst containing bidentate ligands prepared in Example 3 of the present invention. Among them, the abscissa is the wave number (cm -1 ), the ordinate is the density (%), ON-1' refers to the trivalent vanadium complex catalyst containing N,N bidentate ligands, ON-1 refers to the N,N bidentate ligand, the upper curve is ON-1', and the lower curve is ON-1;

[0034] Figure 5 is the high-temperature proton nuclear magnetic resonance spectrum of the copolymer prepared in Example 5 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0036] Example 1

[0037] A method for preparing a trivalent vanadium complex catalyst containing a bidentate ligand includes the following steps:

[0038] (1) Preparation of (THF)3VCl3: Under a nitrogen atmosphere, vanadium chloride (0.50 g, 3.18 mmol) was suspended in 40 mL of tetrahydrofuran and stirred at 75 °C for 48 h. It changed from a precipitate to a dark purple transparent liquid. Most of the toluene was removed by an oil pump, and the solvent was removed under reduced pressure to obtain a pink-purple solid. Subsequently, the solid was diluted with dichloromethane and recrystallized three times with n-hexane. The remaining solvent was again removed by an oil pump, and finally 987.8 mg of pink-purple solid a was obtained, with a yield of 83.2%.

[0039] (THF)3VCl3 has the following structural formula:

[0040]

[0041] (2) Synthesis of N,S bidentate ligand: 2,6-diisopropyl dimethylaniline (0.54 g, 4.46 mmol) and an appropriate amount of thiophenecarboxaldehyde (0.50 g, 4.46 mmol) were reacted in a methanol solution at room temperature for 12 h to obtain the required S,N bidentate ligand C3. The reaction system was spotted on a plate, and it was found that the reactants completely reacted and there was only one product spot. The above was to ensure complete reaction. The solution in the single-necked flask was rotary evaporated to remove the solvent to obtain 1.130 g of a yellow viscous liquid, with a yield of 86.3%.

[0042] The structural formula of S,N bidentate ligand C3 is as follows:

[0043]

[0044] Figure 1 is the 1H NMR spectrum of the N,S bidentate ligand, indicating that the structure of the prepared catalyst is correct.

[0045] (3) Weigh the N,S bidentate ligand (72 mg, 0.27 mmol) in a glove box, weigh (THF)3VCl3 (100 mg, 0.27 mmol), dissolve the two in 10 mL of DCM (dichloromethane) and mix them in a 20 mL screw-cap bottle, and stir at room temperature for more than 12 h to ensure complete reaction. At the beginning of the reaction, it was observed that a red precipitate immediately appeared in the black solution. After the reaction was completed, the solvent was removed under vacuum to obtain a light red solid. Tetrahydrofuran was added dropwise until the product was just completely dissolved. The precipitate was recrystallized with 5 mL of dichloromethane and 10 mL of n-hexane, and the supernatant was removed. After repeating three times, the lower layer suspension was dried under reduced pressure to remove the solvent, and 110.8 mg of a light red solid (a trivalent vanadium complex catalyst containing a bidentate ligand) was obtained, with a yield of 77.6%.

[0046] The structural formula of the trivalent vanadium complex catalyst containing a bidentate ligand is as follows:

[0047]

[0048] Figure 2 It is the infrared spectrum of the trivalent vanadium complex catalyst containing a bidentate ligand, indicating that the structure of the prepared catalyst is correct.

[0049] Example 2

[0050] A preparation method of a trivalent vanadium complex catalyst containing a bidentate ligand, comprising the following steps:

[0051] (1) Synthesis of the N,N bidentate ligand: React 2,6-diisopropyl dimethylaniline (1.30 g, 4.46 mmol) with 2-pyridinecarboxaldehyde (0.39 g, 4.47 mmol) in a methanol solution at room temperature for 12 h to obtain the required N,N bidentate ligand. The reaction system was spotted on a TLC plate, and it was found that the reactants had completely reacted and there was only one product spot. To ensure complete reaction, the solution in the single-necked flask was rotary evaporated to remove the solvent to obtain 1.01 g of a yellow viscous liquid, with a yield of 89.5%.

[0052] (2) Weigh the N,N bidentate ligand (54 mg, 0.27 mmol) in a glove box, weigh the (THF)3VCl3 prepared in Example 1 (100 mg, 0.27 mmol), dissolve the two in 10 mL of DCM (dichloromethane) and mix them in a 20 mL screw-cap bottle, and stir at room temperature for more than 12 h to ensure complete reaction. At the beginning of the reaction, it was observed that a red precipitate immediately appeared in the black solution. After the reaction was completed, the solvent was removed under vacuum to obtain a light red solid. Tetrahydrofuran was added dropwise until the product was just completely dissolved. The precipitate was recrystallized with 5 mL of dichloromethane and 10 mL of n-hexane, and the supernatant was removed. After repeating three times, the lower layer suspension was dried under reduced pressure to remove the solvent, and 103.2 mg of a light red solid (a trivalent vanadium complex catalyst containing a bidentate ligand) was obtained, with a yield of 82.1%.

[0053] The structural formula of the trivalent vanadium complex catalyst containing a bidentate ligand is as follows:

[0054]

[0055] Example 3

[0056] A preparation method of a trivalent vanadium complex catalyst containing a bidentate ligand, comprising the following steps:

[0057] (1) Synthesis of the O,N bidentate ligand: React 2,6 - diisopropyl - N,N - dimethylaniline (1.08 g, 4.46 mmol) with an appropriate amount of furfural (0.35 g, 4.47 mmol) in a methanol solution at room temperature for 12 h to obtain the required N,N bidentate ligand. Spot - plate the reaction system after the reaction and find that the reactants have completely reacted and there is only one product spot. To ensure complete reaction, rotary - evaporate the solution in the single - neck flask to remove the solvent, obtaining 1.08 g of a yellow viscous liquid with a yield of 84.9%.

[0058] (2) Weigh the O,N bidentate ligand (63 mg, 0.27 mmol) in a glove box, weigh (THF)3VCl3 (100 mg, 0.27 mmol) prepared in Example 1, dissolve the two in 10 mL of DCM (dichloromethane) and mix them in a 20 - mL screw - cap flask, and stir at room temperature for more than 12 h to ensure complete reaction. At the beginning of the reaction, a red precipitate immediately appears in the black solution. After the reaction ends, remove the solvent under vacuum to obtain a light - red solid, and add tetrahydrofuran dropwise until the product is just completely dissolved. Recrystallize the precipitate with 5 mL of dichloromethane and 10 mL of n - hexane, remove the supernatant, repeat three times, and then remove the solvent from the lower - layer suspension under reduced pressure to obtain 97.1 mg of a light - red solid (trivalent vanadium complex catalyst containing a bidentate ligand) with a yield of 76.8%.

[0059] The structural formula of the trivalent vanadium complex catalyst containing a bidentate ligand is as follows:

[0060]

[0061] Example 4

[0062] Ethylene polymerization: In an anhydrous and anaerobic nitrogen glove box, take 1 μmol of the trivalent vanadium complex catalyst containing an N,N ligand prepared in Example 2 in a 10 - mL schleck flask and add 8 g of toluene; take 1500 μmol of the cocatalyst diethylaluminum chloride and add it to another schleck flask and add 6.5 g of toluene to ensure that the total reaction volume is 20 mL. Take the two flasks out of the glove box, connect them to a double - manifold to displace nitrogen and then set aside. Dry the polymerization reactor at 100 °C for 6 h and then evacuate it for 3 h. Place the reactor body in an ice - water bath until the temperature of the reactor body is kept constant at 0 °C for standby.

[0063] After the polymerization reaction device was purged with nitrogen three times, nitrogen was continuously introduced. 1500 μmol of the cocatalyst diethylaluminum chloride and the trivalent vanadium complex catalyst containing the bidentate ligand were respectively added to the reaction kettle, and the magnetic stirrer was started for stirring. The ethylene valve was quickly opened, ethylene gas was introduced, and after the nitrogen in the kettle was discharged through the valve above the reaction kettle, the polymerization started. During the reaction process, the temperature of the kettle body and the pressure of the ethylene gas were kept constant until the polymerization was completed.

[0064] After the reaction was completed, the reaction solution was poured into 100 mL of methanol and stirred continuously. Then, 15 mL of concentrated hydrochloric acid was slowly added and stirred for 12 h. The above mixed solution was filtered by suction to obtain a white solid polymer, and the polymer was placed in a vacuum drying oven and dried at 60 °C under vacuum for 6 h until the weight was constant.

[0065] The ethylene polymerization reaction formula is as follows:

[0066]

[0067] Example 5

[0068] Ethylene-6-chloro-1-hexene copolymerization: In an anhydrous and oxygen-free nitrogen glove box, 3 μmol of the trivalent vanadium complex catalyst containing the NN bidentate ligand was taken in a 10 mL schleck bottle and 4 g of toluene was added; 1500 μmol of the cocatalyst diethylaluminum chloride was taken in another schleck bottle and 6.5 g of toluene was added; 6-chloro-1-hexene (240 mg, 2 mmol) was taken in a 10 mL schleck bottle, and then 4 g of toluene was added to ensure that the total reaction volume was 20 mL. The three schleck bottles were taken out of the glove box, connected to a double-row tube, purged with nitrogen, and then reserved. The polymerization reaction kettle was dried at 100 °C for 6 h and then evacuated for 3 h.

[0069] After the polymerization reaction device was purged with nitrogen three times, nitrogen was continuously introduced. The cocatalyst diethylaluminum chloride and the trivalent vanadium complex catalyst containing the bidentate ligand were respectively added to the reaction kettle, and the magnetic stirrer was started for stirring. The ethylene valve was quickly opened, ethylene gas was introduced, and after the nitrogen in the kettle was discharged through the valve above the reaction kettle, the polymerization started. During the reaction process, the temperature of the kettle body and the pressure of the ethylene gas were kept constant until the polymerization terminated.

[0070] After the reaction was completed, the reaction solution was poured into 100 mL of methanol and stirred continuously. Then, 15 mL of concentrated hydrochloric acid was slowly added and stirred for 12 h. The above mixed solution was filtered by suction to obtain a white solid polymer, and the polymer was placed in a vacuum drying oven and dried at 40 °C under vacuum for 6 h until the weight was constant.

[0071] The polymerization reaction formula is as follows:

[0072]

[0073] Figure 5 It is the high-temperature nuclear magnetic resonance hydrogen spectrum of the polymer obtained by polymerization, indicating that 6-chloro-1-hexene can successfully copolymerize with ethylene.

[0074] The above content is only an example and illustration of the structure of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution. As long as they do not deviate from the structure of the present invention or exceed the scope defined by this claims, they should fall within the protection scope of the present invention.

Claims

1. A trivalent vanadium complex catalyst containing a bidentate ligand, characterized in that, The structural general formula is as follows: Among them, R1, R2, and R3 are each one of a hydrogen atom, a methyl group, and an isopropyl group.

2. A preparation method of a trivalent vanadium complex catalyst containing a bidentate ligand according to claim 1, characterized in that, It includes the following steps: (1) Synthesis of ligands: React 2,6 - diisopropyl - N - methylaniline with 2 - pyridinecarboxaldehyde, furfural, and thiophene - 2 - carboxaldehyde respectively in a methanol solution to obtain N,N - bidentate ligand C1, N,O - bidentate ligand C2, and N,S - bidentate ligand C3; (2) Synthesis of trivalent vanadium complex catalyst: Dissolve (THF)3VCl3 and C1, C2, C3 in dichloromethane respectively for reaction, remove the solvent under vacuum to obtain a solid powder, and recrystallize with dichloromethane and n - hexane to obtain the trivalent vanadium complex catalyst containing bidentate ligands.

3. The preparation method of a trivalent vanadium complex catalyst containing bidentate ligands according to claim 2, characterized in that: In the step (1), the molar ratio of 2 - formylthiophene, furfural or 2 - pyridinecarboxaldehyde to 2,6 - diisopropyl - N - methylaniline is 1:1 - 1.2, and the reaction time is 10 - 12 h; In the step (2), the molar ratio of (THF)3VCl3 to C1, C2, C3 is 1:1 - 1.2 respectively, and the reaction time is 10 - 12 h.

4. The preparation method of a trivalent vanadium complex catalyst containing a bidentate ligand according to claim 2, characterized in that: In the step (2), the preparation method of (THF)3VCl3 includes the following steps. Under a nitrogen atmosphere, suspend vanadium chloride in tetrahydrofuran, stir, change from precipitation to a dark purple transparent liquid, extract toluene, remove the solvent under reduced pressure to obtain a pink - purple solid, then dilute the solid with dichloromethane and perform three - time recrystallization with n - hexane, and drain the remaining solvent to finally obtain a pink - purple solid, which is the said (THF)3VCl3.

5. The preparation method of a trivalent vanadium complex catalyst containing a bidentate ligand according to claim 4, characterized in that: In the step (2), the molar ratio of VCl3 to tetrahydrofuran is 1:1 - 1.2, the stirring time is 46 - 48 h, and the stirring temperature is 70 - 75 °C.

6. Use of the trivalent vanadium complex catalyst containing a bidentate ligand according to claim 1, characterized in that: The trivalent vanadium complex catalyst containing bidentate ligands is applied to catalyze the homopolymerization of ethylene.

7. Use of a trivalent vanadium complex catalyst containing a bidentate ligand according to claim 1, characterized in that: The trivalent vanadium catalyst is applied to catalyze the copolymerization of ethylene and a polar monomer with an allyl structure to prepare a functionalized polyolefin material.

8. Use of a trivalent vanadium complex catalyst containing a bidentate ligand according to claim 7, characterized in that, The specific application process includes the following steps: Under the protection of anhydrous and oxygen - free nitrogen, add a cocatalyst, a polar monomer D, and a solvent E into a high - pressure reaction kettle, finally add the trivalent vanadium complex catalyst containing bidentate ligands, introduce ethylene and stir for reaction, add methanol to terminate the reaction, wash the obtained product with methanol, and dry it under vacuum until the mass remains unchanged to obtain a polymerization product.

9. Use of a trivalent vanadium complex catalyst containing a bidentate ligand according to claim 8, characterized in that: The polar monomer D is one of 6 - chloro - 1 - hexene, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, allyl chloride, 10 - undecen - 1 - ol, and methyl 10 - undecenoate. The cocatalyst is diethylaluminum chloride, the solvent E is toluene, the molar ratio of the trivalent vanadium complex catalyst containing bidentate ligands to the polar monomer D is 1:500 - 3000, the reaction temperature is 0 - 80 °C, and the stirring reaction time is 5 - 10 min.

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