Synthesis of pyridine bases based on covalently structured framework catalysts

Abstract

This invention discloses a method for synthesizing pyridine bases based on a covalently structured catalyst, relating to the fields of organic synthesis and heterogeneous catalysis. In this invention, two monomers are dissolved in a solvent at a fixed molar ratio. The resulting COF-LZU1 powder is mixed with a metal precursor and then added back into the solvent. After vacuum drying, a Fe coordination intermediate, Fe-int / COF-LZU1, is obtained. Fe-int / COF-LZU1 is placed in a tube furnace to obtain a Fe-SA / COF-LZU1 catalyst. Formaldehyde, acetaldehyde, and ammonia are added to a reactor, along with the Fe-SA / COF-LZU1 catalyst, to obtain the pyridine base. This invention, through the unique structural design of COFs materials, provides the Fe-SA / COF-LZU1 catalyst with excellent cycle stability. The reaction process does not require high temperatures or highly corrosive reagents, reducing energy consumption and achieving efficient synthesis of pyridine bases under mild reaction conditions.

Description

Technical Field

[0001] This invention relates to the fields of organic synthesis and heterogeneous catalysis, and particularly to a method for synthesizing pyridine bases based on covalently organized catalysts. Background Technology

[0002] Pyridine bases are an important branch of nitrogen-containing heterocyclic compounds, with their molecular skeleton consisting of a five-membered carbon ring and a nitrogen atom forming a six-membered aromatic system. Based on the number and position of substituents on the ring, these compounds can be systematically divided into four main categories: unsubstituted parent pyridine, monomethyl-substituted methylpyridine, dimethyl-substituted dimethylpyridine, and trimethyl-substituted variants. These derivatives, with their unique electronic structure and acid-base tunability, occupy a central position in modern chemical engineering—not only as key building blocks in the synthesis of antibiotics, vitamins, and other drug molecules, but also playing an irreplaceable catalytic and structural regulation role in the development of novel pesticides, the modification of polymer materials, and the preparation of fine chemicals.

[0003] The synthesis of pyridine bases is typically carried out under high temperature and pressure or in the presence of a catalyst, and the catalysts used are mostly heavy metal catalysts with harsh reaction conditions. Publication number CN119100973A discloses a method for increasing the yield of the byproduct 3-methylpyridine in the synthesis of pyridine bases, and a method for synthesizing pyridine bases; however, the reaction temperature needs to reach 400-450°C after using a catalyst. o C. Furthermore, the catalyst regeneration temperature is too high, resulting in high energy consumption, which is not conducive to large-scale industrial production. Announcement No. CN111468177B discloses a molecular sieve catalyst for the preparation of pyridine bases, its preparation method, and its application. This method uses a molecular sieve catalyst with nano-bismuth trioxide attached to the surface of a titanium-silicon molecular sieve to catalyze the synthesis of pyridine bases. However, the catalyst in this method is prepared using the rare metal bismuth, which is too costly and requires high-power mercury lamp irradiation, making the catalyst preparation conditions extremely demanding. Summary of the Invention

[0004] The purpose of this invention is to provide a method for synthesizing pyridine bases based on covalently organized framework catalysts. Through the unique structural design of COF materials and the synergistic effect of multifunctional active sites, this technology achieves efficient synthesis of pyridine bases under mild reaction conditions. The Fe-SA / COF-LZU1 catalyst has excellent cycle stability, and the reaction process does not require high temperature or highly corrosive reagents, significantly reducing energy consumption and environmental burden, while greatly improving product selectivity, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The method for synthesizing pyridine bases based on covalently structured catalysts includes the following steps:

[0007] Step 1: Dissolve the two monomers in a solvent at a fixed molar ratio, then add the catalyst, and sonicate until both monomers are completely dissolved. Transfer the reaction solution to a pressure-resistant glass tube, seal it, and place it in an oven for heating. After the reaction is complete, centrifuge to collect the solid product, use a detergent to remove unreacted monomers and solvent, and place the washed solid in a vacuum oven to dry to obtain COF-LZU1 powder.

[0008] Step 2: After mixing COF-LZU1 powder with the metal precursor, a solvent was added and ultrasonically treated to form a uniform suspension. The mixture was then heated under reflux. After the reaction solution cooled to room temperature, it was centrifuged and the supernatant was discarded. The solid was washed with detergent to remove uncoordinated Fe species. After vacuum drying, Fe coordination intermediate Fe-int / COF-LZU1 was obtained. Fe-int / COF-LZU1 was placed in a tube furnace and the temperature was gradually increased while a mixed gas was introduced. After reacting at a constant temperature, the mixture was naturally cooled to room temperature to obtain Fe-SA / COF-LZU1 catalyst.

[0009] Step 3: Use Fe-SA / COF-LZU1 catalyst to catalyze the synthesis of pyridine base from formaldehyde, acetaldehyde and ammonia. Add formaldehyde, acetaldehyde and ammonia to the reactor, and add 0.5wt%-2wt% of Fe-SA / COF-LZU1 catalyst. The reaction is carried out at a pressure of 40bar-120bar and a temperature range of 80℃-100℃ for 6 hours to obtain pyridine base.

[0010] Further, the dual monomers are one of TAP (1,3,5-triaminobenzene) and DMTP (2,5-dimethoxyterephthalaldehyde), TAP and TA (terephthalic acid), PPD (p-phenylenediamine) and TA, PPD and DMTP, TAPT (tris(4-aminophenyl)amine) and BPDA (3,3',4,4'-biphenyltetracarboxylic dianhydride), TAPT and DMTP, and the molar ratio of the two monomers is 1:0.8-2.

[0011] Further, the solvent in step one is any one of the following: mesitylene and 1,4-dioxane, DMAC (NN dimethylacetamide) and mesitylene, THF (tetrahydrofuran) and methanol, with the volume ratio of the two solvents in each group being 1:1-2.

[0012] Furthermore, the catalyst in step one is one of glacial acetic acid, PTSA (p-toluenesulfonic acid), and TFA (trifluoroacetic acid), with a molar ratio of 10%-30%.

[0013] Furthermore, the frequency of the ultrasonic treatment in steps one and two is 20kHz-60kHz, and the ultrasonic time is 20min-60min.

[0014] Furthermore, the heating temperature in step one is 100℃-140℃, the reaction time is 48h-98h, and the detergent is ethanol and DMF (NN dimethylformamide).

[0015] Furthermore, the metal precursor in step two is Fe(acac)3, FeCl3, Fe(NO3)3, FeBr3, FeCl2, FeS, or Fe2S3, and the amount used is 0.5wt%-2wt%.

[0016] Furthermore, in step two, the solvent is ethanol or methanol, the heating temperature is 80℃-100℃, the reflux time is 24h-72h, and the detergent is methanol or ethanol.

[0017] Furthermore, the heating rate is gradually increased from 2℃ / min to 4℃ / min, the final temperature is 300℃ to 400℃, the reaction time is 1h to 3h, the mixed gas is H2 / Ar or H2 / N2 with a volume ratio of 20:80 to 5:95, and the gas flow rate is 30L / min to 50L / min.

[0018] Furthermore, the molar ratio of formaldehyde, acetaldehyde, and ammonia in step three is 1.0-1.4:1:2.

[0019] Reaction Mechanism: The covalent organic frameworks (COFs) of this invention are highly ordered, porous, and crystalline organic materials formed by organic molecules linked by strong covalent bonds. Compared with traditional catalysts, COFs have a highly designable structure; the organic units and connection methods can be precisely controlled through molecular design, facilitating the introduction of specific catalytic active sites. Their ordered pore structure promotes the diffusion and mass transfer of reactants and products. They possess excellent stability, exhibiting strong stability in high temperatures, acids, bases, or solvents, making them suitable for harsh reaction conditions. COFs can also integrate multiple catalytic active sites to achieve multi-step tandem reactions or synergistic catalysis. As heterogeneous catalysts, they can be recovered through simple filtration or centrifugation, exhibiting high structural stability and allowing for multiple recycling without significant deactivation.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The catalyst of this invention is the first to use a COFs (Copper-Oxide-Flame) single-atom catalyst based on dynamic bonding regulation to synthesize pyridine bases. Through the unique structural design of the COFs material, combined with the synergistic effect of multifunctional active sites, the catalyst exhibits high catalytic activity, excellent selectivity, and mild reaction conditions. The catalyst demonstrates excellent cycling stability in the efficient synthesis of pyridine bases under mild reaction conditions. In the first use of this catalyst to catalyze the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia, the yield of pyridine was 67%, and the yield of 3-methylpyridine was 24%. In the regenerated version of this catalyst, the yield of pyridine in the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was 66%, and the yield of 3-methylpyridine was 25%, significantly improving product selectivity.

[0022] 2. This invention utilizes the high specific surface area and tunable pore structure of COFs materials to load metal single atoms, achieving synergistic catalysis of aldehyde-amine condensation and cyclization. The catalyst has extremely high atomic utilization rate, can be recycled, significantly reduces raw material costs, reduces raw material waste, avoids the use of strong acids / bases, and the reaction process does not require high temperature or highly corrosive reagents, significantly reducing energy consumption and environmental burden. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: Using 1,3,5-triaminobenzene (TAP) and 2,5-dimethoxytetraphenyldialdehyde (DMTP) as bimonomers in a molar ratio of 1:1.5, they were dissolved in a 1:1 volume ratio of mesitylene / 1,4-dioxane mixed solvent. 0.5 mL of glacial acetic acid was added as a catalyst. After ultrasonic treatment at 40 kHz for 30 minutes, the mixture was sealed in a pressure-resistant glass tube and reacted at 120 °C for 72 hours. After centrifugation, the mixture was washed sequentially with DMF and ethanol, and then vacuum dried at 80 °C to obtain highly crystalline two-dimensional porous COFs (COF-LZU1 powder). 100 mg of COF-LZU1 powder and 0.1 mmol of metal precursor Fe(acac)3 were ultrasonically dispersed in ethanol at a frequency of 40 kHz for 30 minutes, then refluxed at 80 °C for 24 hours. After centrifugation, washing with ethanol and drying at 60 °C, the mixture was placed in a tube furnace and heated to 350 °C at a rate of 3 °C / min. It was then annealed for 2 hours in an atmosphere of H2 / Ar mixed gas with a volume ratio of 5:95 and a flow rate of 40 L / min to obtain the Fe single-atom supported catalyst Fe-SA / COF-LZU1.

[0025] The synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was catalyzed using a Fe-SA / COF-LZU1 catalyst. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor in a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar for 90 minutes. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 67%, and the yield of 3-methylpyridine was 24%.

[0026] After the reaction, the Fe-SA / COF-LZU1 catalyst was recovered by centrifugation, washed three times each with ethanol and deionized water to remove organic matter and salt residues, and dried under vacuum at 60°C for 6 hours. Then, it was placed in a tube furnace and annealed at 3°C / min to 350°C under a mixed H2 / Ar gas atmosphere at a flow rate of 40 L / min (volume ratio 5:95) for 2 hours to achieve dynamic bond repair and reduction of metal active sites. The regenerated Fe-SA / COF-LZU1 catalyst was used to catalyze the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor at a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar and 90 °C. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 66%, and the yield of 3-methylpyridine was 25%.

[0027] When the molar ratio of monomer 1,3,5-triaminobenzene (TAP) to monomer 2,5-dimethoxyterephthalaldehyde (DMTP) was 1:1.5 and the catalyst content was 1.0 wt%, other batches were carried out by changing the metal precursor. The pyridine yield and 3-methylpyridine yield results are shown in Table 1.

[0028]

[0029] Example 2: Using 1,3,5-triaminobenzene (TAP) and 2,5-dimethoxytetraphenyldialdehyde (DMTP) as bimonomers in a molar ratio of 1:1.5, they were dissolved in a 1:1 volume ratio of mesitylene / 1,4-dioxane mixed solvent. 0.5 mL of glacial acetic acid was added as a catalyst. After ultrasonic treatment at 40 kHz for 30 minutes, the mixture was sealed in a pressure-resistant glass tube and reacted at 120 °C for 72 hours. After centrifugation, the mixture was washed sequentially with DMF and ethanol, and then vacuum dried at 80 °C to obtain highly crystalline two-dimensional porous COFs (COF-LZU1 powder). 100 mg of COF-LZU1 powder and 0.1 mmol of metal precursor Fe(acac)3 were ultrasonically dispersed in ethanol at a frequency of 40 kHz for 30 minutes, then refluxed at 80 °C for 24 hours. After centrifugation, washing with ethanol and drying at 60 °C, the mixture was placed in a tube furnace and heated to 350 °C at a rate of 3 °C / min. It was then annealed for 2 hours in an atmosphere of H2 / Ar mixed gas with a volume ratio of 5:95 and a flow rate of 40 L / min to obtain the Fe single-atom supported catalyst Fe-SA / COF-LZU1.

[0030] The synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was catalyzed using a Fe-SA / COF-LZU1 catalyst. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor in a molar ratio of 1.2:1:2, along with 0.5 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar for 90 minutes. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 51%, and the yield of 3-methylpyridine was 20%.

[0031] After the reaction, the Fe-SA / COF-LZU1 catalyst was recovered by centrifugation, washed three times each with ethanol and deionized water to remove organic matter and salt residues, and then vacuum dried at 60°C for 6 hours. It was then placed in a tube furnace and annealed at 3°C / min to 350°C under a H2 / Ar mixed gas atmosphere at a volume ratio of 5:95 and a flow rate of 40 L / min to achieve dynamic bond repair and reduction of metal active sites for 2 hours. The regenerated Fe-SA / COF-LZU1 catalyst was used to catalyze the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor at a molar ratio of 1.2:1:2, along with 0.5 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar pressure and 90 °C. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 52%, and the yield of 3-methylpyridine was 19%.

[0032] When the metal precursor is Fe(acac)3 and the molar ratio of monomer 1,3,5-triaminobenzene (TAP) to monomer 2,5-dimethoxyterephthalaldehyde (DMTP) is 1:1.5, other batches were carried out by changing the catalyst content. The pyridine yield and 3-methylpyridine yield results are shown in Table 2.

[0033]

[0034] Example 3: Using 1,3,5-triaminobenzene (TAP) and 2,5-dimethoxytetraphenyldialdehyde (DMTP) as bimonomers in a molar ratio of 1:0.8, they were dissolved in a 1:1 volume ratio of mesitylene / 1,4-dioxane mixed solvent. 0.5 mL of glacial acetic acid was added as a catalyst. After ultrasonic treatment at 40 kHz for 30 minutes, the mixture was sealed in a pressure-resistant glass tube and reacted at 120 °C for 72 hours. After centrifugation, the mixture was washed sequentially with DMF and ethanol, and then vacuum dried at 80 °C to obtain highly crystalline two-dimensional porous COFs (COF-LZU1 powder). 100 mg of COF-LZU1 powder and 0.1 mmol of metal precursor Fe(acac)3 were ultrasonically dispersed in ethanol at a frequency of 40 kHz for 30 minutes, then refluxed at 80 °C for 24 hours. After centrifugation, washing with ethanol and drying at 60 °C, the mixture was placed in a tube furnace and heated to 350 °C at a rate of 3 °C / min. It was then annealed for 2 hours in an atmosphere of H2 / Ar mixed gas with a volume ratio of 5:95 and a flow rate of 40 L / min to obtain the Fe single-atom supported catalyst Fe-SA / COF-LZU1.

[0035] The synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was catalyzed using a Fe-SA / COF-LZU1 catalyst. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor in a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar for 90 minutes. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 49%, and the yield of 3-methylpyridine was 21%.

[0036] After the reaction, the Fe-SA / COF-LZU1 catalyst was recovered by centrifugation, washed three times each with ethanol and deionized water to remove organic matter and salt residues, and dried under vacuum at 60°C for 6 hours. Then, it was placed in a tube furnace and annealed at 3°C / min to 350°C under a H2 / Ar mixed gas atmosphere at a flow rate of 40 L / min (volume ratio 5:95) for 2 hours to achieve dynamic bond repair and reduction of metal active sites. The regenerated Fe-SA / COF-LZU1 catalyst was used to catalyze the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor at a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar and 90 °C. o The reaction was carried out within the temperature range of C for 6 hours, with a pyridine yield of 48% and a 3-methylpyridine yield of 22%.

[0037] When the metal precursor is Fe(acac)3, the catalyst content is 1.0 wt%, and the two monomers are 1,3,5-triaminobenzene (TAP) and 2,5-dimethoxyterephthalaldehyde (DMTP), other batches were carried out by changing the monomer molar ratio. The pyridine yield and 3-methylpyridine yield results are shown in Table 3.

[0038]

[0039] Example 4: Using 1,3,5-triaminobenzene (TAP) and terephthalic acid (TA) as bimonomers in a molar ratio of 1:1.5, they were dissolved in a 1:1 volume ratio of mesitylene / 1,4-dioxane mixed solvent. 0.5 mL of glacial acetic acid was added as a catalyst. After ultrasonic treatment at 40 kHz for 30 minutes, the mixture was sealed in a pressure-resistant glass tube and reacted at 120 °C for 72 hours. After centrifugation, the mixture was washed sequentially with DMF and ethanol, and then vacuum dried at 80 °C to obtain highly crystalline two-dimensional porous COFs (COF-LZU1 powder). 100 mg of COF-LZU1 powder and 0.1 mmol of metal precursor Fe(acac)3 were ultrasonically dispersed in ethanol at a frequency of 40 kHz for 30 minutes, then refluxed at 80 °C for 24 hours. After centrifugation, washing with ethanol and drying at 60 °C, the mixture was placed in a tube furnace and heated to 350 °C at a rate of 3 °C / min. It was then annealed for 2 hours in an atmosphere of H2 / Ar mixed gas with a volume ratio of 5:95 and a flow rate of 40 L / min to obtain the Fe single-atom supported catalyst Fe-SA / COF-LZU1.

[0040] The synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was catalyzed using a Fe-SA / COF-LZU1 catalyst. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor in a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar for 90 minutes. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 51%, and the yield of 3-methylpyridine was 22%.

[0041] After the reaction, the Fe-SA / COF-LZU1 catalyst was recovered by centrifugation, washed three times each with ethanol and deionized water to remove organic matter and salt residues, and dried under vacuum at 60°C for 6 hours. Then, it was placed in a tube furnace and annealed at 3°C / min to 350°C under a H2 / Ar mixed gas atmosphere at a flow rate of 40 L / min (volume ratio 5:95) for 2 hours to achieve dynamic bond repair and reduction of metal active sites. The regenerated Fe-SA / COF-LZU1 catalyst was used to catalyze the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor at a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar and 90 °C. o The reaction was carried out within the temperature range of C for 6 hours, with a pyridine yield of 52% and a 3-methylpyridine yield of 21%.

[0042] When the metal precursor is Fe(acac)3, the catalyst content is 1.0 wt%, the molar ratio of the two monomers is 1:1.5, and other batches are carried out by changing the two monomers, the pyridine yield and 3-methylpyridine yield results are shown in Table 4.

[0043]

[0044] Example 5: Using 1,3,5-triaminobenzene (TAP) and 2,5-dimethoxytetraphenyldialdehyde (DMTP) as bimonomers in a molar ratio of 1:1.5, they were dissolved in a 1:1 volume ratio of mesitylene / 1,4-dioxane mixed solvent. 0.5 mL of glacial acetic acid was added as a catalyst. After ultrasonic treatment at 40 kHz for 30 minutes, the mixture was sealed in a pressure-resistant glass tube and reacted at 120 °C for 72 hours. After centrifugation, the mixture was washed sequentially with DMF and ethanol, and then vacuum dried at 80 °C to obtain highly crystalline two-dimensional porous COFs (COF-LZU1 powder). 100 mg of COF-LZU1 powder and 0.1 mmol of metal precursor Fe(acac)3 were ultrasonically dispersed in ethanol at a frequency of 40 kHz for 30 minutes, then refluxed at 80 °C for 24 hours. After centrifugation, washing with ethanol and drying at 60 °C, the mixture was placed in a tube furnace and heated to 350 °C at a rate of 3 °C / min. It was then annealed for 2 hours in an atmosphere of H2 / Ar mixed gas with a volume ratio of 5:95 and a flow rate of 40 L / min to obtain the Fe single-atom supported catalyst Fe-SA / COF-LZU1.

[0045] The synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was catalyzed using a Fe-SA / COF-LZU1 catalyst. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor in a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar for 90 minutes. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 67%, and the yield of 3-methylpyridine was 24%.

[0046] After the reaction, the Fe-SA / COF-LZU1 catalyst was recovered by centrifugation, washed three times each with ethanol and deionized water to remove organic matter and salt residues, and dried under vacuum at 60°C for 6 hours. Then, it was placed in a tube furnace and annealed at 3°C / min to 350°C under a H2 / Ar mixed gas atmosphere at a flow rate of 40 L / min (volume ratio 5:95) for 2 hours to achieve dynamic bond repair and reduction of metal active sites. The regenerated Fe-SA / COF-LZU1 catalyst was used to catalyze the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor at a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar and 90 °C. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 66%, and the yield of 3-methylpyridine was 25%.

[0047] Comparative Example 1: 1,3,5-triaminobenzene (TAP) and 2,5-dimethoxytetraphenyldialdehyde (DMTP) were used as bimonomers in a molar ratio of 1:1.5 and dissolved in a 1:1 volume ratio of mesitylene / 1,4-dioxane mixed solvent. 0.5 mL of glacial acetic acid was added as a catalyst. After ultrasonic treatment at 40 kHz for 30 minutes, the mixture was sealed in a pressure-resistant glass tube and reacted at 120 °C for 72 hours. After centrifugation, the mixture was washed with DMF and ethanol in sequence and dried under vacuum at 80 °C to obtain highly crystalline two-dimensional COF-LZU1.

[0048] The synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was catalyzed using a COF-LZU1 catalyst. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor in a molar ratio of 1.2:1:2, along with 1.0 wt% of the COF-LZU1 catalyst. The reaction was carried out at 60 bar for 90 minutes. o The reaction was carried out in the temperature range of C for 6 hours, with a pyridine yield of 7% and a 3-methylpyridine yield of 4%.

[0049] Comparative Example 2: 1,3,5-triaminobenzene (TAP) and 2,5-dimethoxytetraphenyldialdehyde (DMTP) were used as bimonomers in a molar ratio of 1:1.5 and dissolved in a 1:1 volume ratio of mesitylene / 1,4-dioxane mixed solvent. 0.5 mL of glacial acetic acid was added as a catalyst. After ultrasonic treatment at 40 kHz for 30 minutes, the mixture was sealed in a pressure-resistant glass tube and reacted at 120 °C for 72 hours. After centrifugation, the mixture was washed with DMF and ethanol in sequence and dried under vacuum at 80 °C to obtain highly crystalline two-dimensional porous COFs (COF-LZU1 powder). 100 mg of COF-LZU1 powder and 0.1 mmol of metal precursor Al(Cl)3 were ultrasonically dispersed in ethanol at a frequency of 40 kHz for 30 minutes, then refluxed at 80 °C for 24 hours. After centrifugation, washing with ethanol and drying at 60 °C, the mixture was placed in a tube furnace and heated to 350 °C at a rate of 3 °C / min. It was then annealed for 2 hours in an atmosphere of H2 / Ar mixed gas with a volume ratio of 5:95 and a flow rate of 40 L / min to obtain the Al single-atom supported catalyst Al-SA / COF-LZU1.

[0050] The synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was catalyzed using an Al-SA / COF-LZU1 catalyst. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor in a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar for 90 minutes. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 48%, and the yield of 3-methylpyridine was 24%.

[0051] After the reaction, the Al-SA / COF-LZU1 catalyst was recovered by centrifugation, washed three times each with ethanol and deionized water to remove organic matter and salt residues, and then vacuum dried at 60°C for 6 hours. It was then placed in a tube furnace and annealed at 3°C / min to 350°C under a H2 / Ar mixed gas atmosphere at a volume ratio of 5:95 and a flow rate of 40 L / min to achieve dynamic bond repair and reduction of metal active sites for 2 hours. The regenerated Al-SA / COF-LZU1 catalyst was used to catalyze the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor at a molar ratio of 1.2:1:2, along with 1.0 wt% of the Al-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar and 90 °C. o The reaction was carried out within the temperature range of C for 6 hours, with a pyridine yield of 47% and a 3-methylpyridine yield of 24%. Other batches were carried out by changing the metal precursor, and the pyridine and 3-methylpyridine yields are shown in Table 5.

[0052]

[0053] Comparative Example 3: Using (3-aminopropyl)triethoxysilane (APTES) and vinyltriethoxysilane (VTES) as bismonomers in a molar ratio of 1:1.5, they were dissolved in a 1:1 volume ratio of mesitylene / 1,4-dioxane mixed solvent. 0.5 mL of glacial acetic acid was added as a catalyst. After ultrasonic treatment at 40 kHz for 30 minutes, the mixture was sealed in a pressure-resistant glass tube and reacted at 120 °C for 72 hours. After centrifugation, the mixture was washed with DMF and ethanol in sequence and dried under vacuum at 80 °C to obtain highly crystalline two-dimensional porous COFs (COF-LZU1 powder). 100 mg of COF-LZU1 powder and 0.1 mmol of metal precursor Fe(acac)3 were ultrasonically dispersed in ethanol at a frequency of 40 kHz for 30 minutes, then refluxed at 80 °C for 24 hours. After centrifugation, washing with ethanol and drying at 60 °C, the mixture was placed in a tube furnace and heated to 350 °C at a rate of 3 °C / min. It was then annealed for 2 hours in an atmosphere of H2 / Ar mixed gas with a volume ratio of 5:95 and a flow rate of 40 L / min to obtain the Fe single-atom supported catalyst Fe-SA / COF-LZU1.

[0054] The synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia was catalyzed using a Fe-SA / COF-LZU1 catalyst. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor in a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar for 90 minutes. o The reaction was carried out within the temperature range of C, and the reaction time was 6 hours. The yield of pyridine was 47%, and the yield of 3-methylpyridine was 19%.

[0055] After the reaction, the Fe-SA / COF-LZU1 catalyst was recovered by centrifugation, washed three times each with ethanol and deionized water to remove organic matter and salt residues, and dried under vacuum at 60°C for 6 hours. Then, it was placed in a tube furnace and annealed at 3°C / min to 350°C under a H2 / Ar mixed gas atmosphere at a flow rate of 40 L / min (volume ratio 5:95) for 2 hours to achieve dynamic bond repair and reduction of metal active sites. The regenerated Fe-SA / COF-LZU1 catalyst was used to catalyze the synthesis of pyridine bases from formaldehyde, acetaldehyde, and ammonia. Formaldehyde (30% aqueous solution), acetaldehyde, and ammonia were added to the reactor at a molar ratio of 1.2:1:2, along with 1.0 wt% of the Fe-SA / COF-LZU1 catalyst. The reaction was carried out at 60 bar and 90 °C. o The reaction was carried out within the temperature range of C for 6 hours, with a pyridine yield of 45% and a 3-methylpyridine yield of 21%. Other batches were carried out by changing the types of dimonomers, and the pyridine and 3-methylpyridine yields are shown in Table 6.

[0056]

[0057] Tables 1-6 show that different metal precursors, metal precursor contents, monomers, and monomer molar ratios affect the characteristics and distribution of metal sites in the Fe-SA / COF-LZU1 catalyst, their interaction with the support, the catalyst's pore structure and specific surface area, as well as the reactivity and impurity content of the precursor. These factors collectively determine the catalyst's performance, leading to varying yields in the catalytic synthesis of pyridine bases. The Fe-SA / COF-LZU1 catalyst prepared with Fe(acac)3 as the metal precursor, a metal precursor content of 1.0 wt%, two monomers of 1,3,5-triaminobenzene (TAP) and 2,5-dimethoxyterephthalaldehyde (DMTP), and a monomer molar ratio of 1:1.5 exhibits the best catalytic performance, with a pyridine yield of 67% and a 3-methylpyridine yield of 24%. After recovering the Fe-SA / COF-LZU1 catalyst and continuing to catalyze the reaction, the pyridine yield reached 66%, and the 3-methylpyridine yield reached 25%.

[0058] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for synthesizing pyridine bases based on covalently organized framework catalysts, characterized in that, Includes the following steps: Step 1: Dissolve the two monomers in a solvent at a fixed molar ratio, then add the catalyst, and sonicate until both monomers are completely dissolved. Transfer the reaction solution to a pressure-resistant glass tube, seal it, and place it in an oven for heating. After the reaction is complete, centrifuge to collect the solid product, use a detergent to remove unreacted monomers and solvent, and place the washed solid in a vacuum oven to dry to obtain COF-LZU1 powder. Step 2: After mixing COF-LZU1 powder with the metal precursor, a solvent was added and ultrasonically treated to form a uniform suspension. The mixture was then heated under reflux. After the reaction solution cooled to room temperature, it was centrifuged and the supernatant was discarded. The solid was washed with detergent to remove uncoordinated Fe species. After vacuum drying, Fe coordination intermediate Fe-int / COF-LZU1 was obtained. Fe-int / COF-LZU1 was placed in a tube furnace and the temperature was gradually increased while a mixed gas was introduced. After reacting at a constant temperature, the mixture was naturally cooled to room temperature to obtain Fe-SA / COF-LZU1 catalyst. Step 3: Use Fe-SA / COF-LZU1 catalyst to catalyze the synthesis of pyridine base from formaldehyde, acetaldehyde and ammonia. Add formaldehyde, acetaldehyde and ammonia to the reactor, and add 0.5wt%-2wt% of Fe-SA / COF-LZU1 catalyst. The reaction is carried out at a pressure of 40bar-120bar and a temperature range of 80℃-100℃ for 6 hours to obtain pyridine base. The dual monomers are one of TAP and DMTP, TAP and TA, PPD and TA, PPD and DMTP, TAPT and BPDA, and TAPT and DMTP, with a molar ratio of 1:0.8-2 between the two monomers. The metal precursors in step two are Fe(acac)3, FeCl3, Fe(NO3)3, FeBr3, FeCl2, FeS, and Fe2S3, and the amount used is 0.5wt%-2wt%.

2. The method for synthesizing pyridine bases based on a covalently organized framework catalyst as described in claim 1, characterized in that, The solvent in step one is any one of the following: mesitylene and 1,4-dioxane, DMAC and mesitylene, THF and methanol, with the volume ratio of the two solvents in each group being 1:1-2.

3. The method for synthesizing pyridine bases based on a covalently organized framework catalyst as described in claim 1, characterized in that, The catalyst in step one is one of glacial acetic acid, PTSA, and TFA, with a molar ratio of 10%-30%.

4. The method for synthesizing pyridine bases based on a covalently organized framework catalyst as described in claim 1, characterized in that, The ultrasonic treatment in steps one and two has a frequency of 20kHz-60kHz and an ultrasonic treatment time of 20min-60min.

5. The method for synthesizing pyridine bases based on a covalently organized framework catalyst as described in claim 1, characterized in that, The heating temperature in step one is 100℃-140℃, the reaction time is 48h-98h, and the detergent is ethanol and DMF.

6. The method for synthesizing pyridine bases based on a covalently organized framework catalyst as described in claim 1, characterized in that, The solvent in step two is ethanol or methanol, the heating temperature is 80℃-100℃, the reflux time is 24h-72h, and the detergent is methanol or ethanol.

7. The method for synthesizing pyridine bases based on a covalently organized framework catalyst as described in claim 1, characterized in that, The heating rate gradually increases from 2℃ / min to 4℃ / min, the final temperature is 300℃ to 400℃, the reaction time is 1h to 3h, the mixed gas is H2 / Ar or H2 / N2, the volume ratio is 20:80 to 5:95, and the gas flow rate is 30L / min to 50L / min.

8. The method for synthesizing pyridine bases based on a covalently organized framework catalyst as described in claim 1, characterized in that, The molar ratio of formaldehyde, acetaldehyde, and ammonia in step three is 1.0-1.4:1:2.

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