Preparation method and application of melanin-like polydopamine nanoparticles

Abstract

The invention relates to the field of catalyst preparation, and in particular to a preparation method and application of melanin-like polydopamine nanoparticles. The method comprises the following steps: (1) adding a polypropylene glycol and ethylene oxide addition polymer (polyether), 3,3',5,5'-tetramethylbenzidine, trishydroxymethylaminomethane and dopamine hydrochloride to a mixed solvent of water and ethanol; (2) continuously stirring for a period of time; (3) centrifuging the step (2), and washing the obtained precipitate with deionized water and ethanol for several times; (4) drying the product at 80°C to obtain polydopamine nanoparticles. The preparation method of the polydopamine nanoparticles is simple, efficient and low in cost. The polydopamine nanoparticles can be used to catalyze the oxidative coupling of benzylamine to synthesize a catalyst for a Schiff base (N-benzylbutylamine), wherein the catalytic conversion rate of benzylamine is 99%, the target product is greater than 95%, the catalytic activity is still stable at 80°C, and the target product is stable and is not decomposed and converted into benzaldehyde.

Description

Technical Field

[0001] The invention relates to the field of catalyst preparation, and in particular to a preparation method and application of melanin-like polydopamine nanoparticles. Background Art

[0002] N-Benzylbutylamine is an important intermediate raw material in the fields of biology, agriculture, and pharmaceuticals. It can be widely used in organic synthesis fields such as reduction reactions, addition reactions, cyclization reactions, and azidation reactions. Therefore, the preparation of N-benzylbutylamine is one of the most dynamic research fields in organic synthetic chemistry. The traditional preparation method involves the condensation reaction between primary amines and ketones or aldehydes, involving catalysts such as Brønsted acids, Lewis acids, Lewis bases, and metals, which generates a large amount of inorganic salt chemical waste and causes water and soil pollution. Using air or oxygen as the only green oxidant, oxidative coupling of benzylamine is one of the most practical and green strategies to prepare N-benzylbutylamine. The biggest challenge faced by the preparation of this reaction process is how to control the reaction pathway to avoid the production of undesirable products such as nitrile or aldehyde.

[0003] In response to this problem, a variety of catalysts have been designed in recent years. The main catalytic systems are metal systems and non-metal systems. So far, a series of transition metal-based systems have been reported to be able to efficiently and selectively oxidize amines to imines. However, due to toxicity and separation issues, metal-catalyzed system processes are not suitable for pharmaceutical or biotechnology applications. Non-metal systems, such as mesoporous carbon ( Acs Catalysis , 2015, 5, 2788), graphite oxide ( Journal of the Iranian Chemical Society , 2022, 19, 2041; Green Chemistry , 2012, 14, 930), carbon nanotubes ( Carbon , 2020, 170, 338), Phthalocyanine ( Chemical Communications , 2020, 56, 3637), etc., and no metal ions will remain in the reaction system. However, traditional thermal catalytic systems usually have high reaction temperatures (over 80°C), which will inevitably lead to more energy consumption if operated in large quantities.

[0004] Therefore, it is of great practical significance to develop a simple, efficient, and cost-effective process to directly obtain N-benzylbutylamine via metal-free catalysis from benzylamine. Summary of the invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a method for preparing melanin-like polydopamine nanoparticles.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing melanin-like polydopamine nanoparticles, comprising the following steps:

[0007] (1) Adding polypropylene glycol and ethylene oxide addition polymer (polyether) F127, 3,3',5,5'-tetramethylbenzidine, tris(hydroxymethyl)aminomethane and dopamine hydrochloride into a mixed solvent of water and ethanol;

[0008] (2) Keep stirring for a while;

[0009] (3) centrifuging the reaction mixture obtained in step (2), and washing the resulting precipitate with deionized water and ethanol several times;

[0010] (4) The product is dried at 80°C to obtain melanin-like polydopamine nanoparticles.

[0011] Furthermore, in step (1), the mass ratio of the polypropylene glycol and ethylene oxide addition polymer (polyether), 3,3',5,5'-tetramethylbenzidine, trishydroxymethylaminomethane and dopamine hydrochloride is 20:20:1:6.

[0012] Furthermore, in step (1), the volume ratio of water to ethanol is 1:1, and the mass volume ratio of dopamine hydrochloride to water is 12 mg:5 mL.

[0013] Furthermore, the stirring time in step (2) is 24 hours.

[0014] Furthermore, the centrifugal speed in step (3) is 10000 rpm.

[0015] The present invention also provides the use of the melanin-like polydopamine nanoparticles obtained by the preparation method as a catalyst in catalyzing the coupling of benzylamine to synthesize Schiff base N-benzylbutylamine.

[0016] Furthermore, the application method comprises the following steps: benzylamine and acetonitrile are used as reaction raw materials, and melanin-like polydopamine nanoparticles are added as catalysts, and 1 atm. 2 Keep for 1 min and react at room temperature for 24 h.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The preparation method of the melanin-like polydopamine nanoparticles of the present invention is simple, efficient and low in cost; the prepared polydopamine nanoparticles can be used to catalyze the oxidative coupling of benzylamine to synthesize a catalyst for a Schiff base (N-benzylbutylamine), and the catalytic conversion rate of benzylamine is 99%, the target product (N-benzylbutylamine) is greater than 95%, and the target product is stable and is not decomposed and converted into benzaldehyde; the polydopamine nanoparticles of the present invention still maintain stable catalytic activity at 80°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a TEM image of polydopamine nanoparticles prepared by the preparation method of the present invention.

[0020] Figure 2 This is a comparison chart of the catalytic performance of the polydopamine nanoparticles of the present invention in Comparative Example 1.

[0021] Figure 3 Example 2 is a comparison chart of the catalytic performance of polydopamine nanoparticles at different reaction temperatures. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with specific embodiments. Example 1

[0023] Preparation of melanin-like polydopamine nanoparticles:

[0024] (1) Add 200 mg of polypropylene glycol and ethylene oxide (polyether), 200 mg of TMB (3,3',5,5'-tetramethylbenzidine), 10 mg of TRIS (trishydroxymethylaminomethane) and 60 mg of dopamine hydrochloride into a mixture of 25 ml of water and 25 ml of ethanol;

[0025] (2) Keep the reaction mixture in a stirring state for 24 hours;

[0026] (3) The reaction mixture obtained in step (2) was centrifuged at 10,000 rpm, and the precipitate was washed several times with deionized water and ethanol;

[0027] (4) The product is dried at 80°C to obtain polydopamine nanoparticles for later use.

[0028] The prepared polydopamine nanoparticles are Figure 1 As shown, the average particle size is 330nm, and the variation range is 130~430nm.

[0029] The polydopamine nanoparticles prepared above are used as catalysts to catalyze the coupling of benzylamine to synthesize Schiff base N-benzylbutylamine. The catalytic performance test includes the following steps:

[0030] (1) 4 mmol benzylamine and 2 ml acetonitrile were used as reaction raw materials, and the polydopamine nanoparticles prepared in Example were added as catalyst;

[0031] (2) Introduce 1 atm.O 2 Keep for 1 minute;

[0032] (3) React at room temperature for 24 hours;

[0033] (4) The conversion rate of benzylamine was 99%, and the target product was >95%. Figure 2 Shown

[0034] Comparative Example 1

[0035] G C 3 N 4 As a catalyst, the catalytic performance test method and steps are the same as in Example 1, and the same catalytic experimental conditions are used. Figure 2 As shown, under the same experimental conditions, gC 3 N 4 The conversion efficiency was only 1%. Example 2

[0036] The polydopamine nanoparticles prepared in Example 1 were subjected to catalytic reactions at different reaction temperatures. The catalytic reaction steps and parameters were the same as in Example 1, except that the reaction temperatures were set to 25°C, 40°C, 60°C, and 80°C, respectively. The catalytic reaction results were shown in FIG. Figure 3 As shown, at different reaction temperatures, the activities are compared, and the target product is stable and will not decompose with increasing temperature, indicating that the catalytic performance of the polydopamine nanoparticles prepared by the present invention is stable.

Claims

1. Use of melanin-like polydopamine nanoparticles as catalysts in catalyzing the coupling of benzylamine to synthesize Schiff base N-benzylbutylamine, It is characterized in that The preparation method of melanin-like polydopamine nanoparticles comprises the following steps: (1) adding a polypropylene glycol and ethylene oxide addition polymer, 3,3',5,5'-tetramethylbenzidine, tris(hydroxymethyl)aminomethane and dopamine hydrochloride into a mixed solvent of water and ethanol; (2) Keep stirring for a while; (3) centrifuging the reaction mixture obtained in step (2), and washing the resulting precipitate with deionized water and ethanol several times; (4) The product is dried at 80°C to obtain melanin-like polydopamine nanoparticles.

2. The use according to claim 1, It is characterized in that In step (1), the mass ratio of the polypropylene glycol and ethylene oxide addition polymer, 3,3',5,5'-tetramethylbenzidine, tris(hydroxymethyl)aminomethane and dopamine hydrochloride is 20:20:1:

6.

3. The use according to claim 1, It is characterized in that In step (1), the volume ratio of water to ethanol is 1:1, and the mass volume ratio of dopamine hydrochloride to water is 12 mg:5 mL.

4. The use according to claim 1, It is characterized in that The stirring time in step (2) is 24 h.

5. The use according to claim 1, It is characterized in that The centrifugal speed in step (3) is 10000 rpm.

6. The use according to claim 1, It is characterized in that The application method comprises the following steps: benzylamine and acetonitrile are used as reaction raw materials, and melanin-like polydopamine nanoparticles are added as catalysts, and 1 atm. 2 Keep for 1 min and react at room temperature for 24 h.

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