A TEMPO immobilized catalyst, its preparation method and application

Abstract

The application discloses a TEMPO immobilized catalyst, a preparation method thereof and application of the TEMPO immobilized catalyst in benzoin oxidation reaction. In view of the problems that TEMPO is difficult to be recycled, TEMPO is prone to be lost in the existing immobilization mode, and the structure of a catalytic base material is unstable, etc., a TEMPO immobilized catalyst is prepared by reacting a dialdehyde trisphenyl (monomer I) with TEMPO with a monomer II with a labile methylene through a condensation reaction, a reaction center (TEMPO) of which is covalently immobilized on a catalyst framework, and the TEMPO immobilized catalyst has the characteristics of small deactivation rate, good stability, high activity, and simple filtration recycling and reuse.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a TEMPO immobilized catalyst and a preparation method and application thereof. Background Art

[0002] TEMPO (2,2,6,6-tetramethylpiperidinyl oxide or 2,2,6,6-tetramethylpiperidinyl-1-oxyl) is an important oxidation catalyst. Due to its excellent performance in catalytic reactions, it has become a major research hotspot in the field of catalysis. However, as a highly efficient catalyst, TEMPO is difficult to recover, resulting in high catalytic costs and significant pollution. Some have attempted to adsorb TEMPO onto catalytic substrates to immobilize and recover the TEMPO catalyst. However, not only does the structure of the catalytic substrate affect the catalytic reaction, but physically adsorbed TEMPO can easily fall off, resulting in TEMPO loss. Others have attempted to chemically bond TEMPO to the catalytic substrate, but these substrates are structurally unstable, significantly impacting catalytic performance.

[0003] Organic frameworks (COFs) offer significant advantages in catalysis. Their highly ordered structures and uniform, tunable pore sizes facilitate substrate transport and enable selective catalysis. Their large surface area provides abundant catalytically active sites. Covalently linked, they offer excellent chemical and thermal stability. Furthermore, their structures are easily functionalized and can be customized to suit diverse catalytic reactions, demonstrating excellent catalytic performance in heterogeneous catalysis.

[0004] Benzil is an important organic chemical raw material and can be used in the synthesis of various pharmaceuticals and photosensitizers, pesticides, printing inks for food packaging, and corrosion inhibitors for mild steel. It is primarily used as a photoinitiator for ultraviolet-induced resins and coatings. Within the effective wavelength range, its initiation efficiency, cure speed, film thickness, resistance to impurity interference, and compatibility with pigments are superior to those of benzoin ethers and benzophenones. Industrially synthesized benzil is often oxidized using concentrated nitric acid, which generates large amounts of environmentally unfriendly waste acid and nitrogen and oxygen gases. To better meet the requirements of green chemistry, the present invention provides a green and environmentally friendly oxidation method. Summary of the Invention

[0005] To address the above-mentioned issues, the present invention provides a TEMPO-supported catalyst, a preparation method thereof, and its use in benzoin oxidation reactions. The present invention reacts a TEMPO-containing dialdehyde terphenyl (monomer I) with a monomer II containing an active methylene group. The methylene group in monomer II is influenced by a strong electron-withdrawing group (cyano), causing the two hydrogen atoms on the methylene group to readily leave the catalyst, resulting in strong acidity. Therefore, under certain conditions, the catalyst can undergo a condensation reaction with the aldehyde group in monomer I, removing a molecule of water to form a carbon-carbon double bond, resulting in the structure shown below.

[0006]

[0007] Catalyst I obtained by reacting monomer I of formula (IV) with monomer II of formula (V-1)

[0008]

[0009] Catalyst II obtained by reacting monomer I of formula (IV) with monomer II of formula (V-II)

[0010] The TEMPO-supported catalyst obtained by the present invention has its reaction center (TEMPO) immobilized on the catalyst framework via a covalent bond. Compared with solutions where TEMPO is physically adsorbed on a support, the catalyst has a lower TEMPO deactivation rate, better stability, and higher activity. Furthermore, the catalyst can be recycled and reused after simple filtration after the reaction is completed. The present invention also discloses a method for using the catalyst to oxidize benzoin to benzil.

[0011] The technical solution adopted in the present invention is:

[0012] A TEMPO supported catalyst as shown in structure I and a preparation method thereof, wherein the catalyst is prepared by reacting a monomer A as shown in structure II and a monomer B as shown in structure III in a certain ratio in the presence of a catalyst for a certain time, followed by filtration and THF washing;

[0013]

[0014] The monomer A shown in structure II is preferably a dialdehyde terphenyl TEMPO amide shown in formula (IV); the monomer B shown in structure III is preferably two active methylene compounds shown in formula (V-1) and formula (V-2);

[0015]

[0016] The preparation method of the TEMPO immobilized catalyst comprises adding monomer A and monomer B in a certain proportion to an organic solvent, reacting at a temperature of 100 to 130° C. for 24 to 72 hours in the presence of a catalyst, wherein the organic solvent is o-dichlorobenzene or a mixed solvent of o-dichlorobenzene and n-butanol in a mass ratio of 1:0 to 3, and the catalyst is solid KOH or an aqueous solution of 1,8-diazabicyclo[5.4.0]undec-7-ene.

[0017] The preparation method of the TEMPO immobilized catalyst comprises the following steps: the catalyst is solid KOH or an aqueous solution of 1,8-diazabicyclo[5.4.0]undec-7-ene; the amount of solid KOH added is such that the molar ratio of monomer A to KOH is 1:3-5; the amount of the aqueous solution of 1,8-diazabicyclo[5.4.0]undec-7-ene added is such that the mass ratio of monomer A to the aqueous solution of 1,8-diazabicyclo[5.4.0]undec-7-ene is 1:4-7; and the concentration of the aqueous solution of 1,8-diazabicyclo[5.4.0]undec-7-ene is 4-7 mol / L.

[0018] In the preparation method of the TEMPO immobilized catalyst, the molar ratio of monomer A to monomer B is 1:0.67-1.

[0019] In the preparation method of the TEMPO immobilized catalyst, the reaction temperature is 100° C. to 130° C., preferably 110° C. to 120° C.; and the reaction time is 24 h to 72 h, preferably 36 h to 48 h.

[0020] The TEMPO supported catalyst is used in the oxidation of benzoin to prepare benzil. The raw material benzoin is dissolved in glacial acetic acid, sodium nitrite, 1,3-dibromo-5,5-dimethylhydantoin (hereinafter referred to as DBDMH) and the TEMPO supported catalyst are added, the temperature is raised in an oxygen environment, the catalyst is filtered out after a certain reaction time, the solvent glacial acetic acid is evaporated, and the product is washed with water to obtain the product.

[0021] The use of the TEMPO supported catalyst in the oxidation of benzoin to prepare benzil is characterized in that the molar ratio of sodium nitrite to benzoin is 0.2-0.4:1, the molar ratio of DBDMH to benzoin is 0.05-0.1:1, the reaction temperature is 40-90°C, preferably 50-70°C, and the reaction time is 1-2h.

[0022] The application of benzoin oxidation to prepare benzil, its reaction formula is as follows:

[0023]

[0024] The beneficial effects of the present invention are: providing a preparation method of a recyclable TEMPO immobilized catalyst and a green method in the benzoin oxidation reaction.

[0025] The present invention addresses the problems of TEMPO being difficult to recover, easy TEMPO loss, or unstable catalytic substrate structure in existing immobilization methods. A dialdehyde terphenyl (monomer I) containing TEMPO reacts with a monomer II containing an active methylene group to produce a TEMPO-supported catalyst through a condensation reaction. The reaction center (TEMPO) is immobilized on the catalyst framework via a covalent bond. The catalyst has the advantages of low TEMPO deactivation rate, good stability, high activity, and can be easily filtered, recovered, and reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a physical picture of the catalyst I obtained in the present invention;

[0027] Figure 2 This is a physical picture of the catalyst II obtained in the present invention;

[0028] Figure 3 is a scanning electron microscope (SEM) image of the catalyst I obtained in the present invention;

[0029] Figure 4 This is a scanning electron microscope (SEM) image of the catalyst II obtained in the present invention;

[0030] Figure 5 TEM image of the catalyst I obtained in the present invention;

[0031] Figure 6 This is a transmission electron microscope (TEM) image of catalyst II obtained in the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0033] Example 1

[0034] Monomer A (65.24 mg, 0.135 mmol), monomer B of formula (V-1) (38.1 mg, 0.09 mmol), KOH (30.3 mg, 0.54 mmol), 1.7 mL of o-dichlorobenzene and 3.3 mL of n-butanol were added to a reactor, stirred and heated to 100°C. After keeping the reaction warm for 72 hours, the mixture was filtered and the filter cake was washed with DMF and THF to obtain 95.3 mg of catalyst I with a yield of 92.2%.

[0035] The obtained catalyst I was a light yellow powder ( Figure 1 Scanning electron microscopy (SEM) analysis showed that the catalyst was in the form of round cake particles ( Figure 3), and the inter-particle has reticular voids, which is beneficial for the mass transfer of reactants on the surface of the catalyst. Transmission electron microscopy (TEM) analysis shows that the catalyst has a regular reticular structure Figure 5 ), indicating that the catalyst has good crystal form retention, which is beneficial for improving the selectivity of the reaction and reducing the generation of by-products.

[0036] Example 2

[0037] Monomer A (65.24 mg, 0.135 mmol), monomer B of formula (V-1) (38.1 mg, 0.09 mmol) and KOH (30.3 mg, 0.54 mmol), o-dichlorobenzene 1.7 mL and n-butanol 3.3 mL were added into the reactor, stirred and heated to 130°C, after 72 h of reaction, filtered, and the filter cake was washed with DMF, THF to obtain 95.8 mg of catalyst I, with a yield of 92.7%.

[0038] Example 3

[0039] Monomer A (65.24 mg, 0.135 mmol), monomer B of formula (V-1) (38.1 mg, 0.09 mmol) and KOH (30.3 mg, 0.54 mmol), o-dichlorobenzene 1.7 mL and n-butanol 3.3 mL were added into the reactor, stirred and heated to 130°C, after 72 h of reaction, filtered, and the filter cake was washed with DMF, THF to obtain 95.8 mg of catalyst I, with a yield of 92.7%.

[0040] Example 4

[0041] Monomer A (65.24 mg, 0.135 mmol), monomer B of formula (V-1) (38.1 mg, 0.09 mmol) and KOH (30.3 mg, 0.54 mmol), o-dichlorobenzene 1.7 mL and n-butanol 3.3 mL were added into the reactor, stirred and heated to 130°C, after 72 h of reaction, filtered, and the filter cake was washed with DMF, THF to obtain 95.8 mg of catalyst I, with a yield of 92.7%.

[0042] Example 5

[0043] Monomer A (65.24 mg, 0.135 mmol), monomer B of formula (V-1) (38.1 mg, 0.09 mmol) and KOH (30.3 mg, 0.54 mmol), o-dichlorobenzene 1.7 mL and n-butanol 3.3 mL were added into the reactor, stirred and heated to 130°C, after 72 h of reaction, filtered, and the filter cake was washed with DMF, THF to obtain 95.8 mg of catalyst I, with a yield of 92.7%.

[0044] The obtained catalyst II is a light yellow powder Figure 2Scanning electron microscopy (SEM) analysis showed that the catalyst was in the form of round cake particles ( Figure 4 ), there are network gaps between particles, which is conducive to the mass transfer of reactants on the catalyst surface. Transmission electron microscopy (TEM) analysis shows that the catalyst surface structure is uniform and the pores are regular ( Figure 6 ), indicating that the catalyst has good crystal form retention, which is beneficial to improving the selectivity of the reaction and reducing the formation of by-products.

[0045] Example 6

[0046] Monomer A (87.0 mg, 0.18 mmol), monomer B-2 of formula (V-2) (14.8 mg, 0.12 mmol) and KOH (40.4 mg, 0.72 mmol), 1.25 mL of o-dichlorobenzene and 3.75 mL of n-butanol were added to a reactor, stirred and heated to 100°C. After reacting for 72 hours, the mixture was filtered and the filter cake was washed with DMF and THF to obtain 82.6 mg of catalyst II with a yield of 81.1%.

[0047] Example 7

[0048] Monomer A (87.0 mg, 0.18 mmol), monomer B-2 of formula (V-2) (14.8 mg, 0.12 mmol) and KOH (40.4 mg, 0.72 mmol), 1.7 mL of o-dichlorobenzene and 3.3 mL of n-butanol were added to a reactor, stirred and heated to 130°C. After reacting for 72 hours, the mixture was filtered and the filter cake was washed with DMF and THF to obtain 89.8 mg of catalyst II with a yield of 88.2%.

[0049] Example 8

[0050] Monomer A (87.0 mg, 0.18 mmol), monomer B-2 of formula (V-2) (14.8 mg, 0.12 mmol), KOH (40.4 mg, 0.72 mmol) and 5 mL of o-dichlorobenzene were added to a reactor, stirred and heated to 130°C. After reacting for 24 hours, the mixture was filtered and the filter cake was washed with DMF and THF to obtain 80.6 mg of catalyst II with a yield of 79.2%.

[0051] Example 9

[0052] The raw material benzoin (42.4 mg, 0.2 mmol) was dissolved in 1 g of glacial acetic acid, and NaNO2 (4.1 mg, 0.06 mmol), DBDMH (4.3 mg, 0.015 mmol) and 4.2 mg of catalyst I were added. The above raw materials were placed in a three-necked flask, replaced with oxygen three times, sealed with a balloon, stirred and heated to 60°C, and reacted for 1.5 h. After the reaction was completed, the catalyst was filtered to remove the catalyst, and the filtrate was distilled under reduced pressure to remove the solvent. The filter cake was washed with water and then dried to obtain 40.7 mg of solid benzil product. The purity of the product was 98.3% as analyzed by liquid chromatography, and the molar yield was 95.3%.

[0053] Example 10

[0054] The raw material benzoin (42.4 mg, 0.2 mmol) was dissolved in 0.85 g of glacial acetic acid, and NaNO2 (2.8 mg, 0.04 mmol), DBDMH (5.7 mg, 0.02 mmol) and 12.7 mg of catalyst I were added. The above raw materials were placed in a three-necked flask, replaced with oxygen three times, sealed with a balloon, stirred and heated to 40°C, and reacted for 2 h. After the reaction was completed, the catalyst was filtered to remove the catalyst, and the filtrate was distilled under reduced pressure to remove the solvent. The filter cake was washed with water and then dried to obtain 40.2 mg of solid benzil product. The purity of the product was 98.8% as determined by liquid chromatography, and the molar yield was 94.6%.

[0055] Example 11

[0056] The raw material benzoin (42.4 mg, 0.2 mmol) was dissolved in 12.7 g of glacial acetic acid, and NaNO2 (5.5 mg, 0.08 mmol), DBDMH (2.9 mg, 0.01 mmol) and 8.5 mg of catalyst I were added. The above raw materials were placed in a three-necked flask, replaced with oxygen three times, sealed with a balloon, stirred and heated to 90°C, and reacted for 1 hour. After the reaction was completed, the catalyst was filtered to remove the catalyst, and the filtrate was distilled under reduced pressure to remove the solvent. The filter cake was washed with water and then dried to obtain 41.1 mg of solid benzil product. The purity of the product was 98.1% as determined by liquid chromatography, and the molar yield was 96.0%.

[0057] Example 12

[0058] The catalyst I-1 in Example 9 was replaced with an equal amount of catalyst II, and other conditions remained unchanged to obtain 39.3 mg of solid benzil product. The purity of the product was 98.6% as determined by liquid chromatography, and the molar yield was 92.2%.

[0059] Examples 13-17

[0060] The catalyst obtained by filtering after the reaction in Example 9 was dried to obtain recovered catalyst I. The recovered catalyst I was recycled and utilized in Examples 13-16.

[0061] The catalyst 1 in Example 9 was replaced with the recovered catalyst 1, and other conditions remained unchanged and recycled 5 times. The results are shown in the table below. As can be seen from the data in the table, after the catalyst 1 was recycled 5 times, the product purity and purity of the catalyst 1 were slightly different from those of Example 9, indicating that the recycling activity of the catalyst 1 is relatively high.

[0062]

Claims

1. A TEMPO supported catalyst, characterized in that: Its structure is shown in Formula I or Formula II:

2. The method for preparing the TEMPO supported catalyst according to claim 1, wherein The following steps are involved: Monomer A and monomer B react in the presence of a catalyst, and after the reaction, the TEMPO supported catalyst is obtained by filtering and washing; The monomer A is a dialdehyde terphenyl TEMPO amide as shown in formula (IV); the monomer B is two active methylene compounds as shown in formula (V-1) or formula (V-2); 3. The method for preparing the TEMPO supported catalyst according to claim 2, wherein: The reaction temperature is 100-130° C., and the reaction time is 24-72 hours.

4. The method for preparing the TEMPO supported catalyst according to claim 3, wherein: The reaction temperature is 110° C. to 120° C., and the reaction time is 36 h to 48 h.

5. The method for preparing the TEMPO supported catalyst according to claim 2, wherein: The organic solvent for the reaction is o-dichlorobenzene or a mixed solvent of o-dichlorobenzene and n-butanol, and the mass ratio thereof is 1:0.01-3.

6. The method for preparing the TEMPO supported catalyst according to claim 2, wherein: The catalyst is solid KOH or 1,8-diazabicyclo[5.4.0]undec-7-ene aqueous solution.

7. The method for preparing the TEMPO supported catalyst according to claim 2, wherein: The molar ratio of monomer A to monomer B is 1:0.67-1.

8. Use of the TEMPO supported catalyst as claimed in claim 1 in the preparation of benzil by oxidation of benzoin.

9. The use according to claim 8, characterized in that Specifically include: The raw material benzoin is dissolved in glacial acetic acid, sodium nitrite, 1,3-dibromo-5,5-dimethylhydantoin and TEMPO immobilized catalyst are added, the temperature is raised in an oxygen environment, the catalyst is filtered out after the reaction, the solvent glacial acetic acid is evaporated, and the product is washed with water to obtain benzil.

10. The use according to claim 9, characterized in that The molar ratio of sodium nitrite to benzoin is 0.2-0.4:1; The molar ratio of 1,3-dibromo-5,5-dimethylhydantoin to benzoin is 0.05-0.1:1; the reaction temperature is 40-90° C.; and the reaction time is 1-2 hours.

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