Monatomic copper catalyst, preparation method and application

Abstract

The invention discloses a monatomic copper catalyst, a preparation method and application of the monatomic copper catalyst in synthesis of 4, 4-diphenyl ether dianhydride. Adding sulfur-doped carbon nitride into a Cu salt solution, and dipping and adsorbing; and filtering, drying and calcining in an inert atmosphere to obtain the monatomic Cu-SNC catalyst. The preparation method comprises the following steps: reacting 3, 4-dimethylphenol and 3, 4-dimethylchlorobenzene in an organic solvent A under shielding gas under the catalysis of a monatomic copper catalyst and alkali to obtain 3, 3 ', 4, 4'-tetramethyl diphenyl ether as shown in a formula I; the compound 3, 3 ', 4, 4'-tetramethyl diphenyl ether shown in the formula I is oxidized into tetracid in a fixed bed reactor at the high temperature, then the tetracid is dehydrated into anhydride in a drying oven at the high temperature, and the 4, 4 '-diphenyl ether dianhydride shown in the formula II is obtained.The preparation method is novel, short in reaction step, good in selectivity, low in overall preparation cost and high in yield.

Description

Technical Field

[0001] The present invention relates to the technical field of compound synthesis, and in particular to a single-atom copper catalyst, a preparation method and application thereof in the synthesis of 4,4-biphenyl ether dianhydride. Background Art

[0002] 4,4-Biphenyl ether dianhydride (ODPA) is an aromatic polyimide monomer material. Since ODPA contains ether flexible groups, the polyimide synthesized with ODPA as a monomer can increase the flexibility of the entire molecular chain, and is also beneficial to reduce the intermolecular forces, lower the glass transition temperature, improve its processing performance, and expand the application field of polyimide.

[0003] At present, the main preparation methods of ODPA are: 1) 3,4-dimethyl ether phenol and 4-bromo-o-xylene are condensed to tetramethyl diphenyl ether, and then oxidized to monoether acid with potassium permanganate in pyridine medium. This method has difficulty in obtaining raw materials, low synthesis efficiency, and low practical application value. 2) US4933469, US5177002, and CN1121514A patents are for phthalic anhydride to be methylated and then nitrated to prepare 4-nitro-N-methylphthalimide, and then in the presence of a catalyst, bimolecular condensation etherification, and then hydrolysis, acidification, and dehydration to obtain ODPA. This method has a long process route, complex operation, low yield, high amount of three wastes, high cost, and is not easy to promote and apply. 3) 4-chlorophthalic anhydride reacts with sodium hydroxide to obtain 4-chlorophthalic acid sodium salt, which is then condensed with 4-chlorophthalic anhydride in a trichlorobenzene medium containing an organic phosphide to obtain ODPA. Although this method is simple, the selectivity of the reaction process is low, and many by-products are generated, resulting in low product yields and difficulties in subsequent purification. 4) Patent CN 116621797 A uses dimethylphenylboric acid as a raw material to carry out a coupling reaction with a dimethylphenol raw material to obtain an intermediate, and then an oxidation reaction is carried out. Due to the complex synthesis of boric acid raw materials, industrialization is also difficult. Therefore, it is of great significance to develop a new preparation method for ODPA and the catalyst used. Summary of the invention

[0004] In view of the shortcomings of the existing preparation methods of ODPA, the present invention proposes a single-atom copper catalyst, a preparation method and application in the preparation of ODPA.

[0005] The present invention provides a method for preparing a single-atom copper catalyst, comprising the following steps:

[0006] Step 1: Using sulfur-doped carbon nitride as a carrier and copper salt as a raw material, adding the carbon nitride into a Cu salt solution for impregnation and adsorption;

[0007] Step 2: Filter, dry and calcine the product of step 1 under an inert atmosphere to obtain a single-atom Cu-SNC catalyst.

[0008] Preferably, the sulfur source in the sulfur-doped carbon nitride is one or more of thiocysteine, thioacetamide, and thiourea.

[0009] Preferably, the Cu salt is one or more of copper chloride, copper acetate and copper nitrate.

[0010] Preferably, the concentration of the Cu salt is 1-10 wt %, and the solvent of the Cu salt is one or more of methanol, ethanol, water, and DMF.

[0011] The present invention also relates to a method for preparing 4,4'-biphenyl ether dianhydride shown in formula II, the method comprising the following steps:

[0012] S1: Under protective gas, 3,4-dimethylphenol and 3,4-dimethylchlorobenzene react in an organic solvent A under the catalysis of a single-atom copper catalyst prepared by any method of claims 1 to 6 and a base to obtain 3,3',4,4'-tetramethyl diphenyl ether shown in formula I;

[0013] S2: The compound of formula I, 3,3',4,4'-tetramethyl diphenyl ether, is oxidized to tetraacid in a fixed bed reactor at high temperature, and then dehydrated to anhydride in an oven at high temperature to obtain 4,4'-biphenyl ether dianhydride shown in formula II; the synthesis route is as follows:

[0014]

[0015] The catalyst in the fixed bed reactor in step S2 is selected from one of vanadium oxide, molybdenum oxide and copper oxide.

[0016] In the step S1, the organic solvent A is ethanol, and in the step S2, the temperature in the fixed bed reactor is 300-500°C.

[0017] The present invention uses 3,4-dimethylphenol as the main raw material, and constructs the main carbon skeleton of diphenyl ether through a novel single-atom copper catalytic coupling. The reaction steps are simple, and the coupling method uses a single-atom catalyst, which has higher reaction selectivity and high reaction yield; and then the oxidation is carried out by a fixed bed reaction, which is green and pollution-free, has a high yield, and belongs to a green synthesis process. Therefore, the preparation method of the present invention is novel, has short reaction steps, good selectivity, low overall preparation cost, and high yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the XRD pattern of the Cu-SNC catalyst prepared in Example 1;

[0019] Figure 2 This is the TEM characterization image of sulfur-substituted pyrolytic carbon nitride;

[0020] Figure 3TEM characterization image of Cu-SNC prepared in Example 1;

[0021] Figure 4 This is the spherical aberration electron microscopy image of the cobalt single atom catalyst of Cu-SNC prepared in Example 1. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but are not used to limit the present invention.

[0023] Unless otherwise specified, the raw materials used in the present invention are commercially available or prepared by conventional methods.

[0024] Example 1

[0025] Thiourea was added to the prepared carbonized nitrogen and pyrolyzed at 600°C, the ratio of the two was 1:1, the pyrolysis time was 2 hours, and the heating rate was 5°C / min. The sulfur-doped carbon nitride prepared above was added to a 5% copper chloride aqueous solution, fully impregnated and adsorbed, then filtered and dried, and then calcined and pyrolyzed in an inert atmosphere for 2 hours, the pyrolysis temperature was 900°C, and the single-atom Cu-SNC catalyst L1 was obtained.

[0026] Example 2

[0027] Thiocysteine ​​was added to the prepared carbonized nitrogen and pyrolyzed at 700°C, the ratio of the two was 1:2, the pyrolysis time was 3 hours, and the heating rate was 10°C / min. The prepared sulfur-doped carbon nitride was added to a 3% copper nitrate methanol solution for full impregnation and adsorption; then filtered and dried, and then calcined and pyrolyzed under an inert atmosphere for 3 hours, the pyrolysis temperature was 1000°C, and the single-atom Cu-SNC catalyst L2 was obtained.

[0028] Example 3

[0029] Thioacetamide was added to the prepared carbonized nitrogen and pyrolyzed at 800°C, the ratio of the two was 2:1, the pyrolysis time was 4 hours, and the heating rate was 50°C / min. The prepared sulfur-doped carbon nitride was added to 8% copper nitrate methanol solution for full impregnation and adsorption; then filtered and dried, and then calcined and pyrolyzed under an inert atmosphere for 4 hours, the pyrolysis temperature was 1100°C, and the single-atom Cu-SNC catalyst L3 was obtained.

[0030] Example 4

[0031] Under nitrogen protection, 122 grams of 3,4-dimethylphenol and 140.6 grams of 3,4-dimethylchlorobenzene (the molar ratio of the two is 1:1) are reacted in ethanol under the catalysis of single-atom copper catalyst L1 (1.22 grams) and sodium carbonate (122g) to obtain 3,3',4,4'-tetramethyl diphenyl ether shown in formula I; the above-mentioned I compound 3,3',4,4'-tetramethyl diphenyl ether is oxidized to tetraacid in a fixed bed reactor at high temperature, the reaction temperature is 300°C, the catalyst is vanadium oxide, and then dehydrated to anhydride in an oven at high temperature to obtain 4,4'-biphenyl ether dianhydride shown in formula II, with a yield of 249.9 grams and a total yield of 85%.

[0032] Example 5

[0033] Under nitrogen protection, 122 grams of 3,4-dimethylphenol and 281 grams of 3,4-dimethylchlorobenzene (the molar ratio of the two is 1:2) are reacted in ethanol under the catalysis of single-atom copper catalyst L2 (2.44 grams) and sodium carbonate (244 grams) to obtain 3,3',4,4'-tetramethyl diphenyl ether shown in formula I; the above-mentioned I compound 3,3',4,4'-tetramethyl diphenyl ether is oxidized to tetraacid in a fixed bed reactor at high temperature, the reaction temperature is 400°C, the catalyst is copper oxide, and then dehydrated to anhydride in an oven at high temperature to obtain 4,4'-biphenyl ether dianhydride shown in formula II, with a yield of 258.7 grams and a total yield of 88%.

[0034] Example 6

[0035] Under nitrogen protection, 122 grams of 3,4-dimethylphenol and 140.6 grams of 3,4-dimethylchlorobenzene (the molar ratio of the two is 1:1) are reacted in ethanol under the catalysis of single-atom copper catalyst L3 (1.22 grams) and sodium carbonate (122 grams) to obtain 3,3',4,4'-tetramethyl diphenyl ether shown in formula I; the above-mentioned I compound 3,3',4,4'-tetramethyl diphenyl ether is oxidized to tetraacid in a fixed bed reactor at high temperature, the reaction temperature is 500°C, the catalyst is molybdenum oxide, and then dehydrated to anhydride at high temperature in an oven to obtain 4,4'-biphenyl ether dianhydride shown in formula II, with a yield of 247 grams and a total yield of 84%.

[0036] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a single-atom copper catalyst, characterized in that: The following steps are involved: Step 1: Using sulfur-doped carbon nitride as a carrier and copper salt as a raw material, adding the carbon nitride into a Cu salt solution for impregnation and adsorption; Step 2: Filter, dry, calcine and pyrolyze the product of step 1 under an inert atmosphere to obtain a single-atom Cu-SNC catalyst.

2. The method for preparing a single-atom copper catalyst according to claim 1, characterized in that: The sulfur source in the sulfur-doped carbon nitride is one or more of thiocysteine, thioacetamide and thiourea.

3. The method for preparing a single-atom copper catalyst according to claim 1, characterized in that: The Cu salt is one or more of copper chloride, copper acetate and copper nitrate.

4. The method for preparing a single-atom copper catalyst according to claim 1, characterized in that: The concentration of the Cu salt is 1-10 wt %, and the solvent of the Cu salt is one or more of methanol, ethanol, water, and DMF.

5. A method for preparing 4,4'-biphenyl ether dianhydride shown in formula II, the method comprising the following steps: S1: Under protective gas, 3,4-dimethylphenol and 3,4-dimethylchlorobenzene react in an organic solvent A under the catalysis of a single-atom copper catalyst prepared by any method of claims 1 to 4 and a base to obtain 3,3',4,4'-tetramethyl diphenyl ether as shown in formula I; S2: The compound of formula I, 3,3',4,4'-tetramethyl diphenyl ether, is oxidized to tetraacid in a fixed bed reactor at high temperature, and then dehydrated to anhydride in an oven at high temperature to obtain 4,4'-biphenyl ether dianhydride shown in formula II; the synthesis route is as follows:

6. The method according to claim 5, characterized in that The catalyst in the fixed bed reactor in step S2 is selected from one of vanadium oxide, molybdenum oxide and copper oxide.

7. The method according to claim 5, characterized in that In the step S1, the organic solvent A is ethanol, and in the step S2, the temperature in the fixed bed reactor is 300-500°C.

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