Method for preparing isocyanate by adopting ZIF-8 photocatalysis

Abstract

The invention belongs to the technical field of isocyanate preparation, and particularly discloses a method for preparing isocyanate through ZIF-8 photocatalysis, which comprises the following steps: adding organic amine and chloroform into an organic solvent according to the mass ratio of 1: (8-15) to obtain a mixed solution; adding ZIF-8 into the mixed solution, and uniformly mixing to obtain a mixed reaction system; the mixed reaction system is irradiated with ultraviolet light, the reaction temperature ranges from 20 DEG C to 50 DEG C, the reaction time ranges from 2 h to 6 h in the oxygen-containing environment, and the isocyanate is obtained. By using the ZIF-8, the reaction efficiency is greatly improved, harsh reaction conditions such as high temperature and high pressure are not needed in the reaction process, the reaction conditions are mild, the yield is high, and special requirements on instruments are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of isocyanate preparation, and particularly relates to a method for preparing isocyanate by adopting ZIF-8 photocatalysis. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Isocyanate is an important chemical intermediate, especially in the fields of polyurethane, coatings and adhesives. However, the traditional method of preparing isocyanate relies on the reaction of phosgene and amine compounds. Although it has a high reaction efficiency, phosgene is a highly toxic substance with great toxicity and corrosiveness. It not only requires strict safety protection measures during use, but also has great environmental risks. The handling and transportation of phosgene also brings additional costs and management burdens. Therefore, how to improve reaction efficiency while reducing production risks and reducing environmental pollution has become one of the research hotspots in the chemical industry today. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing isocyanate by using ZIF-8 photocatalysis. The method utilizes the prepared ZIF-8 to generate free radicals under ultraviolet light irradiation to promote the oxidation reaction of chloroform compounds and organic amines to generate isocyanate.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A method for preparing isocyanate by using ZIF-8 photocatalysis comprises the following steps:

[0007] Adding organic amine and chloroform into an organic solvent at a mass ratio of 1:8-15 to obtain a mixed solution;

[0008] Add ZIF-8 to the mixed solution and mix well to obtain a mixed reaction system;

[0009] The mixed reaction system is irradiated with ultraviolet light at a reaction temperature of 20-50° C. in an oxygen-containing environment for a reaction time of 2-6 hours to obtain isocyanate.

[0010] Chloroform is used as a reactant. The reaction mechanism of organic amine and chloroform under the ultraviolet photocatalysis of ZIF-8 is that ZIF-8 generates free radicals under ultraviolet light, which are then transferred to chloroform to generate free radicals, and then react with organic amine to generate corresponding isocyanate. The organic solvent is used to fully dissolve and disperse the organic amine and chloroform.

[0011] In some embodiments, the organic amine is aniline, butylamine, propylamine or phenethylamine.

[0012] In some embodiments, the organic solvent is acetonitrile, toluene or tetrahydrofuran.

[0013] Preferably, the volume ratio of the organic solvent to chloroform is 0.8-1.2:0.8-1.2.

[0014] In some embodiments, the amount of ZIF-8 added is 1%-10% of the mass of the organic amine.

[0015] Preferably, the feeding amount of ZIF-8 is 5%-10% of the mass of the organic amine, such as 5%, 6%, 7%, 8%, 9% or 10%.

[0016] In some embodiments, the wavelength of the ultraviolet light is 300-400 nm.

[0017] Preferably, the optical power density of the ultraviolet light is 0.1-0.5 W / cm2.

[0018] In some embodiments, the preparation method of ZIF-8 is: mixing a soluble zinc salt and 2-methylimidazole in a molar ratio of 1:7-12 and dissolving them in methanol, stirring evenly, aging at 20-30°C for 20-30h, and after solid-liquid separation, washing and drying the solid to obtain ZIF-8.

[0019] The preparation method of ZIF-8 is relatively simple and convenient for large-scale preparation. The prepared ZIF-8 can photocatalyze the reaction of organic amines and chloroform under ultraviolet light to prepare isocyanates, which is beneficial to improving the reaction efficiency and yield of isocyanate preparation.

[0020] In some embodiments, the method further comprises the step of purifying the prepared isocyanate.

[0021] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0022] ZIF-8 has a large specific surface area (usually 1500m 2 / g or more), the pore size distribution is uniform, which can effectively adsorb reactants and promote the reaction. Under ultraviolet light, in an oxygen-containing environment (such as air), ZIF-8 can generate active free radicals through zinc ion excitation, which in turn triggers the reaction of chloroform compounds with organic amines to generate isocyanates.

[0023] The use of ZIF-8 greatly improves the efficiency of the reaction. The reaction process does not require harsh reaction conditions such as high temperature and high pressure. The reaction conditions are mild, the yield is high, and there is no special requirement for instruments. It not only avoids the toxicity problem of the traditional phosgene method, but also realizes the mild oxidation of organic amines to prepare isocyanates through photocatalytic free radical reactions. The photocatalytic effect of ZIF-8 significantly increases the free radical generation rate and optimizes the reaction conditions. It can meet the green and safety requirements in industrial-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 This is a SEM characterization image of ZIF-8 prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0027] The present invention will be further described below in conjunction with the embodiments.

[0028] Example 1

[0029] Preparation of ZIF-8:

[0030] Weigh 2.974 g of Zn(NO 3 ) 2 6H 2 O (zinc nitrate hexahydrate, molar mass of 297.47 g / mol) was dissolved in 50 mL of methanol and stirred until completely dissolved to form a transparent zinc salt solution.

[0031] Meanwhile, 6.490 g of 2-methylimidazole (molar mass: 82.11 g / mol) was weighed and dissolved in 200 mL of methanol and stirred evenly to form a transparent imidazole solution.

[0032] The zinc nitrate solution and the 2-methylimidazole solution were mixed at a molar ratio of 1:10. Specifically, 50 mL of the zinc nitrate solution was slowly poured into 200 mL of the imidazole solution, stirring while adding to maintain uniform dispersion.

[0033] The mixed solution was stirred for 30 minutes at room temperature (about 25° C.) to ensure uniform mixing. The mixed solution was allowed to stand at room temperature for 24 hours to fully form the ZIF-8 precursor. The precursor was separated by centrifugation.

[0034] The aged mixture was centrifuged at 8000 rpm for 10 minutes to collect the precipitate, which was washed with 50 mL of methanol for 3 times to remove unreacted impurities and by-products.

[0035] The washed ZIF-8 precipitate was transferred to a vacuum drying oven and vacuum dried at 60°C for 12 hours. Finally, a high-purity ZIF-8 powder with a mass of about 3.5 g was obtained. The obtained ZIF-8 was characterized by SEM. Figure 1 shown.

[0036] The preparation method of phenyl isocyanate is as follows:

[0037] 5g of aniline was mixed with 50mL of chloroform, and 50mL of acetonitrile was added as a solvent. 0.5g of ZIF-8 was added to the mixture as a photocatalyst and stirred evenly. Under 365nm ultraviolet light (0.5 watts / square centimeter), the reaction temperature was controlled at 30°C, and the reaction was carried out in an open state for 2 hours. After the reaction was completed, the catalyst was filtered off, the solvent and unreacted products were distilled off, and the residue was distilled again to obtain 5.5g of phenyl isocyanate with a yield of 87%.

[0038] The obtained product was identified by GCMS, and the product [M+H] + The peak at 120.4 indicated that the obtained product was the target product.

[0039] Example 2

[0040] 5 g of aniline was mixed with 50 mL of chloroform, and 50 mL of acetonitrile was added as a solvent. 0.5 g of ZIF-8 prepared in Example 1 was added to the mixture as a photocatalyst and stirred evenly. Under 365 nm ultraviolet light (0.1 watt / cm2), the reaction temperature was controlled at 30°C, and the reaction was carried out in an open state for 6 hours. After the reaction was completed, the catalyst was filtered off, the solvent and unreacted products were distilled off, and the residue was distilled again to obtain 5.7 g of phenyl isocyanate with a yield of 90%.

[0041] The obtained product was identified by GCMS, and the product [M+H] + The peak 120.2 indicated that the obtained product was the target product.

[0042] Example 3

[0043] Preparation of ZIF-8:

[0044] Weigh 2.974 g of Zn(NO 3 ) 2 6H 2 O (zinc nitrate hexahydrate, molar mass of 297.47 g / mol) was dissolved in 50 mL of methanol and stirred until completely dissolved to form a transparent zinc nitrate solution.

[0045] Meanwhile, 8.231 g of 2-methylimidazole was weighed and dissolved in 200 mL of methanol and stirred evenly to form a transparent imidazole solution.

[0046] Slowly pour 50 mL of zinc nitrate solution into 200 mL of imidazole solution, stirring while adding to maintain uniform dispersion.

[0047] The mixed solution was stirred at 30°C for 20 minutes to ensure uniform mixing. The mixed solution was allowed to stand at room temperature for 30 hours to fully form the ZIF-8 precursor. The precursor was separated by centrifugation.

[0048] The aged mixture was centrifuged at 8000 rpm for 10 minutes to collect the precipitate, which was washed with 50 mL of methanol for 3 times to remove unreacted impurities and by-products.

[0049] The washed ZIF-8 precipitate was transferred to a vacuum drying oven and vacuum dried at 60°C for 12 hours to finally obtain high-purity ZIF-8 powder.

[0050] 5 g of propylamine was mixed with 30 mL of chloroform, and 30 mL of acetonitrile was added as a solvent. 0.5 g of ZIF-8 prepared in Example 3 was added to the mixture as a photocatalyst and stirred evenly. Under 365 nm ultraviolet light (0.1 watt / cm2), the reaction temperature was controlled at 30°C, and the reaction was carried out in an open state for 6 hours. After the reaction was completed, the catalyst was filtered off, the solvent and unreacted products were distilled off, and the residue was distilled again to obtain 5.4 g of phenyl isocyanate with a yield of 85%.

[0051] The obtained product was identified by GCMS, and the product [M+H] + The peak 120.2 indicated that the obtained product was the target product.

[0052] Example 4

[0053] 5 g of aniline was mixed with 50 mL of chloroform, and 50 mL of acetonitrile was added as a solvent. 0.05 g of ZIF-8 prepared in Example 1 was added to the mixture as a photocatalyst and stirred evenly. Under 365 nm ultraviolet light irradiation (0.1 watt / square centimeter), the reaction temperature was controlled at 30°C, and the reaction was carried out in an open state for 6 hours. After the reaction was completed, the catalyst was filtered off, the solvent and unreacted products were distilled off, and the residue was distilled again to obtain 5.1 g of phenyl isocyanate with a yield of 80%.

[0054] The obtained product was identified by GCMS, and the product [M+H] + The peak 120.2 indicated that the obtained product was the target product.

[0055] Example 5

[0056] 10 g of butylamine was mixed with 100 mL of chloroform, and 100 mL of toluene was added as a solvent. 1 g of ZIF-8 prepared in Example 1 was added, and the reaction temperature was controlled at 30° C. under 365 nm ultraviolet light irradiation (0.1 W / cm2), and the reaction was carried out in an open state for 2 hours. After the reaction was completed, the catalyst was filtered out, and the solvent and unreacted products were distilled off. The residue was distilled again to obtain 11.5 g of butyl isocyanate, with a yield of 85%.

[0057] The obtained product was identified by GCMS, and the product [M+H] + The peak at 100.3 indicated that the obtained product was the target product.

[0058] Example 6

[0059] 10 g of butylamine was mixed with 100 mL of chloroform, and 100 mL of toluene was added as a solvent. 0.7 g of ZIF-8 prepared in Example 1 was added, and the reaction temperature was controlled at 30° C. under 365 nm ultraviolet light irradiation (0.1 W / cm2), and the reaction was carried out in an open state for 2 hours. After the reaction was completed, the catalyst was filtered out, and the solvent and unreacted products were distilled off. The residue was distilled again to obtain 11.5 g of butyl isocyanate, with a yield of 82%.

[0060] Example 7

[0061] The difference from Example 2 is that the wavelength of the ultraviolet light is replaced with 300 nm, and the rest is the same as Example 2. The yield of the prepared phenyl isocyanate is 86%.

[0062] Example 8

[0063] The difference from Example 2 is that the wavelength of the ultraviolet light is replaced with 400 nm, and the rest is the same as Example 2. The yield of the prepared phenyl isocyanate is 84%.

[0064] Comparative Example 1

[0065] 5g of aniline was mixed with 50mL of chloroform, and 50mL of acetonitrile was added as solvent. Under 365nm ultraviolet light (0.1 watt / cm2), the reaction temperature was controlled at 30°C, and the reaction was carried out in an open state for 6 hours. After the reaction, 1.3g of phenyl isocyanate was obtained by distillation, with a yield of 21%. The obtained product was identified by GCMS, and the product [M+H] was found. + The peak 120.2 indicated that the obtained product was the target product.

[0066] From the comparison between Example 2 and Comparative Example 1, it can be seen that the addition of ZIF-8 photocatalyst can effectively improve the yield of isocyanate.

[0067] Comparative Example 2

[0068] 5 g of aniline was mixed with 50 mL of chloroform, and 50 mL of acetonitrile was added as a solvent. 0.05 g of ZIF-8 prepared in Example 1 was added to the mixture as a photocatalyst and stirred evenly. Under 660 nm light irradiation (0.1 W / cm2), the reaction temperature was controlled at 30°C, and the reaction was carried out in an open state for 6 hours.

[0069] After the reaction was completed, the catalyst was filtered off, the solvent and unreacted products were distilled off, and the residue was distilled again without obtaining a product.

[0070] Comparative Example 3

[0071] The difference from Example 2 is that chloroform is replaced by acetonitrile, and the rest is the same as Example 2. The yield of the prepared phenyl isocyanate is 0%.

[0072] Comparative Example 4

[0073] The difference from Example 2 is that chloroform is replaced by tetrahydrofuran, and the rest is the same as Example 2. The yield of the prepared phenyl isocyanate is 0%.

[0074] Comparative Example 5

[0075] The difference from Example 2 is that chloroform is omitted, and the rest is the same as Example 2. The yield of the prepared phenyl isocyanate is 0%.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing isocyanate using ZIF-8 photocatalysis, characterized in that: The steps include: Adding organic amine and chloroform into an organic solvent at a mass ratio of 1:8-15 to obtain a mixed solution; Add ZIF-8 to the mixed solution and mix well to obtain a mixed reaction system; The mixed reaction system is irradiated with ultraviolet light at a reaction temperature of 20-50° C. in an oxygen-containing environment for a reaction time of 2-6 hours to obtain isocyanate.

2. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 1, characterized in that: The organic amine is aniline, butylamine, propylamine or phenethylamine.

3. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 1, characterized in that: The organic solvent is acetonitrile, toluene or tetrahydrofuran.

4. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 3, characterized in that: The volume ratio of the organic solvent to chloroform is 0.8-1.2:0.8-1.

2.

5. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 1, characterized in that: The feeding amount of ZIF-8 is 1%-10% of the mass of the organic amine.

6. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 5, characterized in that: The feeding amount of ZIF-8 is 5%-10% of the mass of the organic amine.

7. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 1, characterized in that: The wavelength of the ultraviolet light is 300-400nm.

8. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 7, characterized in that: The optical power density of the ultraviolet light is 0.1-0.5 W / cm2.

9. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 1, characterized in that: The preparation method of ZIF-8 is as follows: a soluble zinc salt and 2-methylimidazole are mixed in a molar ratio of 1:7-12 and dissolved in methanol, stirred evenly, aged at 20-30° C. for 20-30 h, and after solid-liquid separation, the solid is washed and dried to obtain ZIF-8.

10. The method for preparing isocyanate by using ZIF-8 photocatalysis according to claim 1, characterized in that: The method also includes the step of purifying the prepared isocyanate.

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