A method for the hydrogenation of nitro compounds catalyzed by a porous polymeric metal catalyst

Abstract

The present application relates to catalyst preparation technology, and aims to provide a method for catalyzing hydrogenation of nitro compounds by using a porous polymer-based metal catalyst. The method comprises: adding a nitro compound and the catalyst into a reactor, mixing uniformly, filling hydrogen for hydrogenation reaction, and obtaining an amine compound after the reaction; the catalyst is composed of a metal element as an active center and a porous polymer as a carrier, and the porous polymer is prepared by a solvothermal method from a polymer monomer. The catalyst used in the present application has very excellent hydrogenation activity, and can realize solvent-free hydrogenation of the nitro compound to the amine compound at normal temperature and pressure, which is conducive to realizing large-scale production and has low safety hazards. The present application provides a more efficient method for preparing the amine compound, the reaction temperature is low, no additional reaction aids need to be added in the synthesis process, no toxic and harmful by-products are generated after the reaction, and the whole synthesis process is green and environmentally friendly.

Description

Technical Field

[0001] This invention relates to catalyst preparation technology, specifically to a method for hydrogenating nitro compounds using a porous polymer-based metal catalyst. Background Technology

[0002] Amine compounds are widely used as important intermediates and raw materials in pharmaceuticals, dyes, polyurethanes, explosives, and agrochemicals. Aniline was first isolated in the 1820s. By the 1850s, aniline was widely used in the dye industry, making a significant contribution to the development of my country's dye industry. In the 20th century, the industrial production of aromatic amines via the hydrogenation of aromatic nitro compounds was achieved. The hydrogenation reaction of nitro compounds to prepare amine compounds has become a research hotspot in recent years.

[0003] Currently, traditional commercial production typically uses iron, zinc, tin, or metal sulfides as reducing agents to prepare aromatic amines. However, this method violates the basic principles of green chemistry and sustainable development, and also suffers from serious problems such as difficulty in product separation, reactor corrosion, and the generation of waste acid / alkali byproducts. Using hydrogen as a reducing agent and employing a recyclable heterogeneous transition metal catalyst for the catalytic hydrogenation of nitro compounds is a highly efficient and environmentally friendly method for preparing amine compounds. However, it usually requires the addition of additives (alkalis and metal salts) to the liquid-phase reaction system to assist the reaction, which can cause secondary pollution.

[0004] Therefore, it is of great significance to prepare highly active heterogeneous catalysts to catalytically hydrogenate nitro compounds to amine compounds under mild conditions without additives. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for hydrogenation of nitro compounds catalyzed by a porous polymer-based metal catalyst.

[0006] To solve the technical problem, the solution of the present invention is:

[0007] A method for hydrogenating nitro compounds using a porous polymer-based metal catalyst is provided, comprising the following steps:

[0008] A nitro compound and a catalyst are added to a reactor, with the catalyst having a mass fraction of 0.1–10% in the mixture. After thorough mixing, hydrogen gas is introduced to a pressure of 0.1–3 MPa, and a hydrogenation reaction is carried out at 15–180 °C. The reaction ends after 0.5–48 hours, yielding an amine compound.

[0009] The catalyst is composed of a metal element as the active center and a porous polymer as the support, with the metal loading being 0.01–5% (m / m). The porous polymer is prepared from polymer monomers by a solvothermal method and is one of polyvinylpyrrolidone (PVP), polyamide (PA), polyethyleneimine (PEI), or polydivinylbenzene (PDVB), or a composite material of two or more of polyvinylpyrrolidone (PVP), polyamide (PA), polyethyleneimine (PEI), or polydivinylbenzene (PDVB).

[0010] As a preferred embodiment of the present invention, the nitro compound is any one or more of the following: nitrobenzene, p-chloronitrobenzene, p-ethylenenitrobenzene, p-cyanonitrobenzene, p-methylnitrobenzene, 1,4-dinitrobenzene, p-aminonitrobenzene, and 1-nitrobutane.

[0011] In a preferred embodiment of the present invention, the metal element in the catalyst is any one or more of Pd, Pt, Rh, Ru, Ir, Au, Fe, Co, and Ni.

[0012] As a preferred embodiment of the present invention, the catalyst is prepared by the following method:

[0013] The porous polymer is uniformly dispersed in an organic solvent containing a metal element and stirred vigorously for more than 8 hours. After adding a reducing agent and stirring evenly, a reduction reaction is carried out at -20 to 50°C. After the reaction is completed, the solid product is filtered, washed, and dried to obtain the catalyst. The amount of porous polymer and metal element is controlled so that the metal loading in the final catalyst product is 0.01 to 5% (m / m). The reducing agent is NaBH4 or KBH4, and the molar ratio of metal element to reducing agent is 0.2 to 20.

[0014] As a preferred embodiment of the present invention, the catalyst is prepared by the following method:

[0015] The porous polymer was uniformly dispersed in an organic solvent containing metal elements and stirred vigorously for more than 8 hours. The mixture was filtered, washed and dried to obtain a solid product. The solid product was reduced with hydrogen at 50-450℃ to obtain a catalyst. The amounts of porous polymer and metal elements were controlled so that the metal loading in the final catalyst product was 0.01-5% (m / m).

[0016] As a preferred embodiment of the present invention, the method for preparing the porous polymer includes: dissolving the polymer monomer in an appropriate amount of organic solvent, then adding an initiator, and carrying out a hydrothermal reaction at 60-200°C for 12 hours; washing and drying the reaction product to obtain the porous polymer.

[0017] As a preferred embodiment of the present invention, the organic solvent is any one or more of ethanol (EtOH), methanol (MeOH), dimethylformamide (DMF), ethyl acetate (EA), or tetrahydrofuran (THF), and the mass of the solvent is 0 to 100 times the mass of the monomer.

[0018] As a preferred embodiment of the present invention, the initiator is tert-butyl hydroperoxide (TBHP), dicyclohexyl peroxide (DCPD), potassium persulfate (K2S2O8), or cyclohexanone peroxide (C). 12 H 22 O5) Any one of azobisisobutyronitrile (AIBN) or azobisisoheptanenitrile (ABVN), with the initiator mass being 0.01 to 1 wt% of the total mass of the reaction system.

[0019] Description of the invention principle:

[0020] The catalyst used in this invention is a metal catalyst supported on a porous polymer; wherein the porous polymer is prepared from polymer monomers by a solvothermal method, and there are various supporting schemes for the supported metal component.

[0021] Compared with traditional oxide supports, the porous polymer prepared by this invention has an excellent specific surface area (>600 m²). 2 The polymer ( / g) structure allows for better dispersion of the metal component, exposing more active sites and activating the substrate and hydrogen more efficiently, while avoiding the addition of metal salts. Due to the electronic modification of the metal by the interaction between the metal and the polymer support, the hydrogenation reaction products can be rapidly desorbed at the active sites, preventing further polymerization of amine compounds and eliminating the need for alkali-based polymerization inhibitors. Simultaneously, the porous polymer network structure stabilizes the metal nanoparticles, preventing metal loss and resulting in high cycle stability of the catalyst.

[0022] The entire reaction process of this invention can be achieved at a relatively low temperature and hydrogen pressure, avoiding the use of reaction aids. No toxic or harmful byproducts are generated during the reaction, making it green and environmentally friendly.

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] 1. The catalyst used in this invention has excellent hydrogenation activity and can realize solventless hydrogenation of nitro compounds to amine compounds at room temperature and pressure, which is conducive to large-scale production and has low safety risks.

[0025] 2. This invention provides a more efficient method for preparing amine compounds, with a low reaction temperature, no need to add additional reaction aids during the synthesis process, and no toxic or harmful byproducts generated after the reaction. The entire synthesis process is green and environmentally friendly. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to specific embodiments. All reactions in the following embodiments are carried out in a pressure vessel. These embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0027] Part 1: Preparation of Porous Polymers and Catalysts

[0028] The catalysts used in the various embodiments of the present invention are composed of a metal element as the active center and a porous polymer as the support, with the metal loading being 0.01-5% (m / m). The catalyst preparation process mainly includes two steps: preparing the porous polymer and supporting the metal element by a solvothermal method.

[0029] 1. Preparation of porous polymers by solvothermal method

[0030] In this invention, the porous polymer is prepared from polymer monomers by a solvothermal method and is one of polyvinylpyrrolidone (PVP), polyamide (PA), polyethyleneimine (PEI) or polydivinylbenzene (PDVB), or a composite material of two or more of polyvinylpyrrolidone (PVP), polyamide (PA), polyethyleneimine (PEI) or polydivinylbenzene (PDVB).

[0031] The preparation method of porous polymer includes: dissolving polymer monomers in an appropriate amount of organic solvent, then adding an initiator, and carrying out a hydrothermal reaction at 60-200℃ for 12 hours; washing and drying the reaction product to obtain the porous polymer.

[0032] The organic solvent is any one or more of ethanol (EtOH), methanol (MeOH), dimethylformamide (DMF), ethyl acetate (EA), or tetrahydrofuran (THF); the initiator is tert-butyl hydroperoxide (TBHP), dicyclohexyl peroxide (DCPD), potassium persulfate (K2S2O8), or cyclohexanone peroxide (C). 12 H 22 O5) Any one of azobisisobutyronitrile (AIBN) or azobisisoheptanenitrile (ABVN). The mass of the organic solvent is 0 to 100 times the mass of the monomer, and the mass of the initiator is 0.01 to 1 wt% of the total mass of the reaction system.

[0033] Examples 1-30

[0034] The porous polymer was prepared according to the above preparation steps, and the relevant data for each embodiment are shown in Table 1:

[0035] Table 1

[0036]

[0037]

[0038]

[0039] 2. Loading of metallic elements

[0040] In this invention, the catalyst preparation includes two steps: supporting a metal element in a porous polymer and reducing the metal element. Because the reduction schemes used differ, two options are available for the catalyst preparation process.

[0041] Method 1: The porous polymer is uniformly dispersed in an organic solvent containing a metal element and vigorously stirred (stirring speed above 2000 rpm) for more than 8 hours; after adding the reducing agent and stirring evenly, the reduction reaction is carried out at -20 to 50°C; after the reaction is completed, the solid product is filtered, washed and dried to obtain the catalyst; the amount of porous polymer and metal element is controlled so that the metal loading in the final catalyst product is 0.01-5% (m / m); the reducing agent is NaBH4 or KBH4, and the molar ratio of metal element to reducing agent is 0.2-20.

[0042] Method 2: The porous polymer is uniformly dispersed in an organic solvent containing metal elements and stirred vigorously (stirring speed above 2000 rpm) for more than 8 hours; the mixture is filtered, washed and dried to obtain a solid product; the solid product is reduced with hydrogen at 50-450℃ to obtain a catalyst; the amount of porous polymer and metal elements is controlled so that the metal loading in the final catalyst product is 0.01-5% (m / m).

[0043] Examples 31-66

[0044] The catalyst loading process was carried out according to the above preparation steps. The porous polymers used in each example were from Examples 1-4 to 1-8. Among them, in Examples 1-31 to 1-50 and 1-59 to 1-66, the catalyst was prepared using Method 1. In Examples 1-51 to 1-58, the catalyst was prepared using Method 2.

[0045] The relevant data for each embodiment are shown in Table 2:

[0046] Table 2

[0047]

[0048]

[0049]

[0050] Part Two: Catalytic Hydrogenation for the Preparation of Amine Compounds

[0051] In the following examples, the porous polymer-based metal catalyst prepared by the aforementioned operations is used to further catalyze the hydrogenation of nitro compounds to prepare amine compounds.

[0052] The preparation process of amine compounds includes: adding nitro compounds and catalysts to a reactor, wherein the mass fraction of the catalyst in the mixture is 0.1-10%; after mixing evenly, hydrogen gas is introduced to a pressure of 0.1-3 MPa, and a hydrogenation reaction is carried out at 15-180°C; the reaction ends after 0.5-48 hours, and amine compounds are obtained.

[0053] In Examples 2-1 to 2-23, amine compounds were prepared according to the above preparation steps, specifically including:

[0054] Weigh 10g of nitrobenzene, add 100mg of catalyst, and mix well; introduce 0.5MPa hydrogen gas, react at 15℃ for 12 hours to obtain the product aniline, and calculate the conversion rate of nitrobenzene and the selectivity of the corresponding aniline.

[0055] The relevant data for each embodiment are shown in Table 3.

[0056] Table 3

[0057]

[0058]

[0059] In Examples 2-24 to 2-34, the amine compounds were prepared according to the above preparation steps, specifically including:

[0060] Weigh 10g of nitrobenzene, add the catalyst from Examples 1-31, and mix well; introduce hydrogen gas to a certain pressure, react at a certain temperature for a period of time to obtain the product aniline; calculate the conversion rate of nitrobenzene and the selectivity of the corresponding aniline.

[0061] The relevant data for each embodiment are shown in Table 4.

[0062] Table 4

[0063]

[0064] Example 2-35

[0065] 10g of nitrobenzene was weighed and 100mg of catalyst (from Examples 1-31) was added, and the mixture was stirred until homogeneous. Hydrogen gas was introduced at 0.5MPa, and the reaction was carried out at 180℃ for 12 hours to obtain the product aniline. The conversion rate of nitrobenzene was calculated to be >99%, corresponding to a selectivity of >99.0% for aniline.

[0066] Examples 2-36

[0067] 10g of p-chloronitrobenzene was weighed and 100mg of catalyst (from Examples 1-31) was added, and the mixture was stirred until homogeneous. Hydrogen gas was introduced at 0.5MPa, and the reaction was carried out at 100°C for 12 hours to obtain the product p-chloroaniline. The conversion rate of p-chloronitrobenzene was calculated to be >99%, and the selectivity for p-chloroaniline was >99.0%.

[0068] Example 2-37

[0069] 10g of p-ethylenenitrobenzene was weighed and 100mg of catalyst (from Examples 1-31) was added, and the mixture was stirred until homogeneous. Hydrogen gas was introduced at 0.5MPa, and the reaction was carried out at 100°C for 12 hours to obtain the product p-ethyleneaniline. The conversion rate of p-ethylenenitrobenzene was calculated to be >99%, and the selectivity for p-ethyleneaniline was >99.0%.

[0070] Example 2-38

[0071] 10g of p-cyanonitrobenzene was weighed and 100mg of catalyst (from Examples 1-31) was added, and the mixture was stirred until homogeneous. Hydrogen gas was introduced at 0.5MPa, and the reaction was carried out at 100°C for 12 hours to obtain the product p-cyanoaniline. The conversion rate of p-cyanonitrobenzene was calculated to be >99%, and the selectivity for p-cyanoaniline was >99.0%.

[0072] Example 2-39

[0073] 10g of p-methylnitrobenzene was weighed and 100mg of catalyst (from Examples 1-31) was added, and the mixture was stirred evenly. Hydrogen gas was introduced at 0.5MPa, and the reaction was carried out at 100°C for 12 hours to obtain the product p-methylaniline. The conversion rate of p-methylnitrobenzene was calculated to be >99%, and the selectivity for p-methylaniline was >99.0%.

[0074] Example 2-40

[0075] 10g of 1,4-dinitrobenzene was weighed and 100mg of catalyst (from Examples 1-31) was added, and the mixture was stirred until homogeneous. Hydrogen gas was introduced at 0.5MPa, and the reaction was carried out at 100°C for 12 hours to obtain the product p-phenylenediamine. The conversion rate of 1,4-dinitrobenzene was calculated to be >99%, and the selectivity for p-phenylenediamine was >99.0%.

[0076] Example 2-41

[0077] 10g of p-aminonitrobenzene was weighed and 100mg of catalyst (from Examples 1-31) was added, and the mixture was stirred evenly. Hydrogen gas was introduced at 0.5MPa, and the reaction was carried out at 100°C for 12 hours to obtain the product p-phenylenediamine. The conversion rate of p-aminonitrobenzene was calculated to be >99%, and the selectivity for p-phenylenediamine was >99.0%.

[0078] Example 2-42

[0079] 10 g of 1-nitrobutane was weighed and 100 mg of catalyst (from Examples 1-31) was added. The mixture was thoroughly mixed. Hydrogen gas was introduced at 0.5 MPa, and the reaction was carried out at 100 °C for 12 hours to obtain the product butylamine. Calculations showed that the conversion rate of 1-nitrobutane was >99%, corresponding to a selectivity of >99.0% for butylamine.

[0080] As can be seen from the data of the above embodiments, the catalyst of the present invention exhibits excellent activity and selectivity in the solventless hydrogenation reaction of various nitro compounds.

[0081] Compared with existing technologies (such as Chem. Commun. 2012, 48, 3124–3126, ACS Catal. 2020, 10, 10350-10363 and ACS Catal. 2019, 9, 8404-8412), the catalyst of this invention is the most active noble metal-based catalyst in the solventless hydrogenation reaction of nitro compounds, and its activity is superior to that of many reported noble metal-based catalysts under solvent conditions.

[0082] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A method for hydrogenating nitro compounds using a porous polymer-based metal catalyst, characterized in that, Includes the following steps: Nitro compounds and catalysts are added to a reactor, with the catalyst mass fraction in the mixture being 0.1–10%. After thorough mixing, hydrogen gas is introduced to a pressure of 0.1–3 MPa, and a hydrogenation reaction is carried out at 15–180 °C. The reaction ends after 12–48 hours, yielding amine compounds. The catalyst is composed of a metal element as the active center and a porous polymer as the support, with the metal loading being 0.01–5% m / m; the metal element is any one or more of Pd, Pt, Rh, Ru, Ir, and Au; the porous polymer is prepared from polymer monomers via a solvothermal method, and the polymer monomers are vinylpyrrolidone and ethyleneimine, or vinylpyrrolidone and divinylbenzene, or vinylpyrrolidone, caprolactam, and ethyleneimine; The catalyst was prepared by the following method: The porous polymer is uniformly dispersed in an organic solvent containing a metal element and stirred vigorously for more than 8 hours. After adding a reducing agent and stirring evenly, a reduction reaction is carried out at -20~50℃. After the reaction is completed, the solid product is filtered, washed, and dried to obtain the catalyst. The amount of porous polymer and metal element is controlled so that the metal loading in the final catalyst product is 0.01~5% m / m. The reducing agent is NaBH4 or KBH4, and the molar ratio of metal element to reducing agent is 0.2~20. Alternatively, the catalyst can be prepared by the following method: The porous polymer was uniformly dispersed in an organic solvent containing metal elements and stirred vigorously for more than 8 hours. The mixture was filtered, washed and dried to obtain a solid product. The solid product was reduced with hydrogen at 50~450°C to obtain a catalyst. The amount of porous polymer and metal elements was controlled so that the metal loading in the final catalyst product was 0.01~5% m / m. The method for preparing the porous polymer includes: dissolving the polymer monomer in an appropriate amount of organic solvent, then adding an initiator, and carrying out a hydrothermal reaction at 60~200 °C for 12 h; The reaction product is washed and dried to obtain a porous polymer.

2. The method according to claim 1, characterized in that, The nitro compounds are any one or more of the following: nitrobenzene, p-chloronitrobenzene, p-ethylenenitrobenzene, p-cyanonitrobenzene, p-methylnitrobenzene, 1,4-dinitrobenzene, p-aminonitrobenzene, and 1-nitrobutane.

3. The method according to claim 1, characterized in that, The organic solvent is any one or more of ethanol, methanol, dimethylformamide, ethyl acetate or tetrahydrofuran, and the mass of the solvent is 0 to 100 times the mass of the monomer.

4. The method according to claim 1, characterized in that, The initiator is any one of tert-butyl hydroperoxide, dicyclohexyl peroxide, potassium persulfate, cyclohexanone peroxide, azobisisobutyronitrile, or azobisisoheptanenitrile, and the mass of the initiator is 0.01 to 1 wt% of the total mass of the reaction system.

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