A method for preparing isocyanate by photocatalysis using ZIF-8

Abstract

The present invention belongs to the technical field of isocyanate preparation, and specifically discloses a method for preparing isocyanate by photocatalysis using ZIF-8, which comprises the following steps: adding organic amine and chloroform into an organic solvent according to a mass ratio of 1:8-15 to obtain a mixed solution; adding ZIF-8 into the mixed solution and mixing evenly to obtain a mixed reaction system; irradiating ultraviolet light on the mixed reaction system, with the reaction temperature being 20-50°C, and in an oxygen-containing environment, the reaction time being 2-6 h, thus obtaining isocyanate. The use of ZIF-8 greatly improves the reaction efficiency. During the reaction process, harsh reaction conditions such as high temperature and high pressure are not required. The reaction conditions are mild, the yield is high, and there is no special requirement for the instrument.

Description

Technical Field

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

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

[0003] As an important chemical intermediate, isocyanates have extensive industrial applications, especially in the fields of polyurethanes, coatings, and adhesives. However, traditional methods for preparing isocyanates rely on the reaction of phosgene with amine compounds. Although they have relatively high reaction efficiency, phosgene, as a highly toxic substance, has great toxicity and corrosiveness. During its use, not only strict safety protection measures are required, but also there are significant environmental risks. Handling and transporting phosgene also bring additional costs and management burdens. Therefore, how to improve the reaction efficiency while reducing production risks and environmental pollution has become one of the research hotspots in the chemical industry today. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for preparing isocyanates by photocatalysis using ZIF-8. This method utilizes the ZIF-8 prepared to generate free radicals under ultraviolet light irradiation, promoting the oxidation reaction of chloroform compounds and organic amines to generate isocyanates.

[0005] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0006] A method for preparing isocyanates by photocatalysis using ZIF-8, comprising the following steps:

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

[0008] Adding ZIF-8 to the mixed solution and mixing evenly to obtain a mixed reaction system;

[0009] Irradiating the mixed reaction system with ultraviolet light, with the reaction temperature being 20 - 50 °C, in an oxygen-containing environment, and the reaction time being 2 - 6 hours to obtain isocyanates.

[0010] Chloroform is used as a reactant. The reaction mechanism of the organic amine and chloroform under the photocatalysis of ZIF-8 by ultraviolet light is that ZIF-8 generates free radicals under ultraviolet light irradiation, which are then transferred to chloroform to generate free radicals, and then react with the organic amine to generate the corresponding isocyanates. 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 feeding amount of ZIF-8 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 light power density of the ultraviolet light is 0.1 - 0.5 watt per square centimeter.

[0018] In some embodiments, the preparation method of ZIF-8 is as follows: A soluble zinc salt and 2-methylimidazole are mixed and dissolved in methanol at a molar ratio of 1:7 - 12, stirred evenly, aged at 20 - 30 °C for 20 - 30 h, after solid-liquid separation, the solid is washed and dried to obtain ZIF-8.

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

[0020] In some embodiments, it further includes the step of purifying the prepared isocyanate.

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

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

[0023] The use of ZIF-8 greatly improves the reaction efficiency. During the reaction process, harsh reaction conditions such as high temperature and high pressure are not required. The reaction conditions are mild, the yield is high, and there are no special requirements for the 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. Description of the Drawings

[0024] The accompanying drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation to the invention.

[0025] Figure 1 It is the SEM characterization diagram of ZIF-8 prepared in Example 1 of the present invention. Detailed Embodiments

[0026] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations 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 of ordinary skill in the technical field to which the present invention belongs.

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

[0028] Example 1

[0029] Preparation of ZIF-8:

[0030] Weigh 2.974 g of Zn(NO3)2·6H2O (zinc nitrate hexahydrate, molar mass 297.47 g / mol) and dissolve it in 50 mL of methanol. Stir well until completely dissolved to form a clear zinc salt solution.

[0031] At the same time, weigh 6.490 g of 2-methylimidazole (molar mass 82.11 g / mol) and dissolve it in 200 mL of methanol. Stir evenly to form a clear imidazole solution.

[0032] Mix the above zinc nitrate solution and 2-methylimidazole solution in a molar ratio of 1:10. Specifically, slowly pour 50 mL of the zinc nitrate solution into 200 mL of the imidazole solution while stirring to keep it evenly dispersed.

[0033] Under the condition of room temperature (about 25 °C), stir the mixed solution for 30 minutes to ensure uniform mixing. Let the mixed solution stand at room temperature for 24 hours to fully form the ZIF-8 precursor. Separate the precursor by centrifugation.

[0034] Centrifuge the aged mixture at 8000 rpm for 10 minutes and collect the precipitate. Wash the precipitate with 50 mL of methanol and repeat the washing 3 times to remove unreacted impurities and by-products.

[0035] Transfer the washed ZIF-8 precipitate to a vacuum drying oven and dry it under vacuum at 60 °C for 12 hours. Finally, high-purity ZIF-8 powder is obtained, with a mass of about 3.5 g. Perform SEM characterization on the obtained ZIF-8, and the results are as Figure 1 shown.

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

[0037] Mix 5 g of aniline with 50 mL of chloroform and add 50 mL of acetonitrile as a solvent. Add 0.5 g of ZIF-8 as a photocatalyst to the mixture and stir evenly. Under irradiation with 365 nm ultraviolet light (0.5 W / cm²), control the reaction temperature at 30 °C and react for 2 hours in an open state. After the reaction is completed, filter off the catalyst, distill off the solvent and unreacted substances, and distill the residue again to obtain 5.5 g of phenyl isocyanate, with a yield of 87%.

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

[0039] Example 2

[0040] Mix 5 g of aniline with 50 mL of chloroform and add 50 mL of acetonitrile as a solvent. Add 0.5 g of the ZIF-8 prepared in Example 1 as a photocatalyst to the mixture and stir evenly. Under irradiation with 365 nm ultraviolet light (0.1 W / cm²), control the reaction temperature at 30 °C and react for 6 hours in an open state. After the reaction is completed, filter off the catalyst, distill off the solvent and unreacted substances, and distill the residue again to obtain 5.7 g of phenyl isocyanate, with a yield of 90%.

[0041] The obtained product was identified by GCMS, and the peak of the product [M+H] + at 120.2 was found, indicating that the obtained product is the target product.

[0042] Example 3

[0043] Preparation of ZIF-8:

[0044] Weigh 2.974 g of Zn(NO3)2·6H2O (zinc nitrate hexahydrate, molar mass 297.47 g / mol) and dissolve it in 50 mL of methanol. Stir well until completely dissolved to form a clear 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] 50 mL of zinc nitrate solution was slowly poured into 200 mL of the imidazole solution while stirring to keep it evenly dispersed.

[0047] Under the condition of 30 °C, the mixed solution was stirred for 20 min to ensure uniform mixing. The mixed solution was left to stand and age 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. The precipitate was washed with 50 mL of methanol and the washing was repeated 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. Finally, high-purity ZIF-8 powder was obtained.

[0050] 5 g of aniline was mixed with 30 mL of chloroform, and 30 mL of acetonitrile was added as a solvent. 0.5 g of the ZIF-8 prepared in Example 3 was added to the mixture as a photocatalyst and stirred evenly. Under irradiation with 365 nm ultraviolet light (0.1 W / cm²), the reaction temperature was controlled at 30 °C, and the reaction was carried out for 6 hours in an open state. After the reaction, the catalyst was removed by filtration, the solvent and unreacted substances were removed by distillation, 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 peak of the product [M+H] + at 120.2 was found, indicating 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 the ZIF-8 prepared in Example 1 was added to the mixture as a photocatalyst and stirred evenly. Under irradiation with 365 nm ultraviolet light (0.1 W / cm²), the reaction temperature was controlled at 30 °C, and the reaction was carried out for 6 hours in an open state. After the reaction, the catalyst was removed by filtration, the solvent and unreacted substances were removed by distillation, 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 peak of the product [M+H] +The peak at 120.2 indicates that the obtained product is the target product.

[0055] Example 5

[0056] Mix 10 g of butylamine with 100 mL of chloroform, and add 100 mL of toluene as the solvent. Add 1 g of ZIF-8 prepared in Example 1. Under irradiation with 365 nm ultraviolet light (0.1 watt per square centimeter), control the reaction temperature at 30 °C. React for 2 hours under an open condition. After the reaction, filter to remove the catalyst, distill off the solvent and unreacted substances, and distill the residue again to obtain 11.5 g of butyl isocyanate with a yield of 85%.

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

[0058] Example 6

[0059] Mix 10 g of butylamine with 100 mL of chloroform, and add 100 mL of toluene as the solvent. Add 0.7 g of ZIF-8 prepared in Example 1. Under irradiation with 365 nm ultraviolet light (0.1 watt per square centimeter), control the reaction temperature at 30 °C. React for 2 hours under an open condition. After the reaction, filter to remove the catalyst, distill off the solvent and unreacted substances, and distill the residue 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 others are the same as in Example 2. The yield of phenyl isocyanate prepared 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 others are the same as in Example 2. The yield of phenyl isocyanate prepared is 84%.

[0064] Comparative Example 1

[0065] Mix 5 g of aniline with 50 mL of chloroform, and add 50 mL of acetonitrile as the solvent. Under irradiation with 365 nm ultraviolet light (0.1 watt per square centimeter), control the reaction temperature at 30 °C. React for 6 hours under an open condition. After the reaction, distill to obtain 1.3 g of phenyl isocyanate with a yield of 21%. The obtained product was identified by GCMS, and the peak of the product [M+H] + at 120.2 was found, indicating that the obtained product is the target product.

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

[0067] Comparative Example 2

[0068] Mix 5 g of aniline with 50 mL of chloroform, and add 50 mL of acetonitrile as the solvent. Add 0.05 g of the ZIF-8 prepared in Example 1 as the photocatalyst to the mixture and stir evenly. Under irradiation with 660 nm light (0.1 watt per square centimeter), the reaction temperature is controlled at 30 °C, and the reaction is carried out for 6 hours in an open state.

[0069] After the reaction is completed, filter to remove the catalyst, distill to remove the solvent and unreacted substances, and no product is obtained after redistilling the residue.

[0070] Comparative Example 3

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

[0072] Comparative Example 4

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

[0074] Comparative Example 5

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

[0076] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing isocyanate by photocatalysis using ZIF-8, characterized in that: It includes the following steps: Add organic amine and chloroform into an organic solvent according to a mass ratio of 1:8 - 15 to obtain a mixed solution; Add ZIF-8 into the mixed solution and mix evenly to obtain a mixed reaction system; Irradiate the mixed reaction system with ultraviolet light, the reaction temperature is 20 - 50 °C, in an oxygen-containing environment, and the reaction time is 2 - 6 h to obtain isocyanate; The organic amine is aniline, butylamine, propylamine or phenethylamine; The organic solvent is acetonitrile, toluene or tetrahydrofuran; The wavelength of the ultraviolet light is 300 - 400 nm; The light power density of the ultraviolet light is 0.1 - 0.5 watt per square centimeter.

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

2.

3. The method for preparing isocyanate by ZIF-8 photocatalysis according to claim 1, wherein: The feeding amount of ZIF-8 is 1% - 10% of the mass of the organic amine.

4. The method for preparing isocyanate by photocatalysis using ZIF-8 according to claim 3, characterized in that: The feeding amount of ZIF-8 is 5% - 10% of the mass of the organic amine.

5. The method for preparing isocyanate by photocatalysis using ZIF-8 according to claim 1, wherein: The preparation method of the ZIF-8 is: dissolve soluble zinc salt and 2-methylimidazole according to a molar ratio of 1:7 - 12 in methanol, stir evenly, age at 20 - 30 °C for 20 - 30 h, after solid-liquid separation, wash and dry the solid to obtain ZIF-8.

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

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