Method for preparing N-aryl pyrrole compound

Abstract

The invention relates to a method for preparing an N-aryl pyrrole compound, and the method comprises the following steps: in the presence of hydrogen, an aromatic nitro compound and a 1, 4-dicarbonyl compound are contacted with a catalyst for a tandem cyclization reaction, and the catalyst comprises a carbon-coated nickel nano composite material; the carbon-coated nickel nano composite material comprises a nickel nano particle inner core and a graphitized carbon layer shell wrapping the surface of the nickel nano particle inner core, the lattice structure of the nickel nanoparticles comprises a face-centered cubic lattice structure and / or a close-packed hexagonal lattice structure; in an XPS spectrogram of the carbon-coated nickel nano composite material, a characteristic peak appears at 852.5 + / -0.4 eV; the pressure of the hydrogen atmosphere is 0.2 to 2.0 MPa. According to the method disclosed by the invention, the series cyclization reaction of the aromatic nitro compound and the 1, 4-dicarbonyl compound can be carried out in a green, efficient and mild manner, the N-aryl pyrrole compound is prepared, and the raw material conversion rate and the target selectivity are relatively high.

Description

Technical Field

[0001] This disclosure relates to the field of organic synthesis technology, and more specifically, to a method for preparing N-arylpyrrole compounds. Background Technology

[0002] N-arylpyrrole compounds, as a class of pyrrole derivatives, are the core units of many natural products and play an important role in antibacterial and antitumor effects.

[0003] Currently, N-arylpyrroles can be prepared via Hantzsch, Clauson-Kaas, Knorr, or Paal-Knorr condensation reactions. Among these, the Paal-Knorr method, which involves the condensation reaction of 1,4-dicarbonyl compounds with aniline compounds to produce N-arylpyrroles, offers advantages such as atom economy, high yield, readily available starting materials, and the formation of harmless byproducts (water). Aniline compounds can be industrially prepared by the catalytic hydrogenation of nitrobenzene compounds. Due to the ease and availability of nitrobenzene compounds, developing methods for the direct synthesis of N-arylpyrroles from nitrobenzene compounds is of significant importance.

[0004] The literature (Angew. Chem. Int. Ed. 2020, 59, 18679-18685) reports the preparation of a series of N-arylpyrrole compounds via a tandem reaction of 2,5-dimethoxytetrahydrofuran (or 2,5-hexanedione) with nitroaromatics using SiO2-supported nitrogen-doped graphene-coated cobalt / cobalt oxide core-shell particles (Co / NGr-C@SiO2-L) as a catalyst. Because this reaction typically requires 24 h at 120 °C and 4 MPa hydrogen pressure, and the yield of the target product is less than 90%, industrial implementation is challenging.

[0005] Patent CN 116574043 A discloses a method for preparing 2,5-dimethyl-N-arylpyrrole by catalyzing the tandem reaction of 2,5-hexanedione and nitroaromatics using nickel metal and manganese oxide supported on a support as catalysts. However, the method is hazardous because it uses nickel nitrate, a potentially explosive chemical, as the nickel source during catalyst preparation and requires the reduction of metallic nickel with hydrogen at high temperatures. Furthermore, the product yield decreases when this catalyst is used in solvent-free reactions, indicating certain limitations. Summary of the Invention

[0006] To overcome the problems of cumbersome catalyst preparation steps, high risk, harsh reaction conditions, and low product yield in the synthesis of N-arylpyrrole compounds by catalytic tandem cyclization reaction in existing technologies, this disclosure provides a synthetic method for preparing N-arylpyrrole compounds by tandem cyclization reaction. The method disclosed in this disclosure has the advantages of high safety, high catalytic activity, scalability, mild reaction conditions, and high selectivity for target products.

[0007] To achieve the above objectives, this disclosure provides a method for preparing N-arylpyrrole compounds, the method comprising: contacting an aromatic nitro compound and a 1,4-dicarbonyl compound with a catalyst in the presence of hydrogen to carry out a tandem cyclization reaction, wherein the catalyst comprises a carbon-coated nickel nanocomposite material; The carbon-coated nickel nanocomposite material includes a nickel nanoparticle core and a graphitized carbon layer shell covering the surface of the nickel nanoparticle core. The lattice structure of the nickel nanoparticles includes a face-centered cubic lattice structure and / or a close-packed hexagonal lattice structure. In the XPS spectrum of the carbon-coated nickel nanocomposite material, a characteristic peak appears at 852.5 ± 0.4 eV; The pressure of the hydrogen atmosphere is 0.2~2.0 MPa.

[0008] Optionally, the aromatic nitro compound includes nitrobenzene and / or chloronitrobenzene; The 1,4-dicarbonyl compound includes 2,5-hexanedione.

[0009] Optionally, the weight ratio of the catalyst, the aromatic nitro compound, and the 1,4-dicarbonyl compound is 1:(2~100):(2~100), preferably 1:(3~50):(3~50).

[0010] Optionally, the temperature of the tandem cyclization reaction is 90~155℃.

[0011] Optionally, the tandem cyclization reaction is carried out in the presence of a first solvent, which includes one or more of an alcohol having 1 to 5 carbon atoms, an ether having 1 to 5 carbon atoms, an alkane having 1 to 5 carbon atoms, and water.

[0012] Optionally, the average particle size of the carbon-coated nickel nanocomposite material is 3~100 nm.

[0013] Optionally, relative to the total weight of the carbon-coated nickel nanocomposite material, the content of Ni is 20-85% by weight, the content of C is 14-79% by weight, the content of O is 0.3-6% by weight, the content of N is 0-6% by weight, and the content of H is 0.1-2.5% by weight.

[0014] Optionally, the carbon-coated nickel nanocomposite material has two distribution peaks with mesopore sizes of 2-5 nm and 8-12 nm; Optionally, in the carbon-coated nickel nanocomposite material, the proportion of mesopore volume to total pore volume is greater than 50%; Optionally, the pickling loss rate of the carbon-coated nickel nanocomposite material is ≤40%.

[0015] Optionally, the method for preparing the carbon-coated nickel nanocomposite material includes the following steps: S1. Mix the nickel source, organic polyacid, and second solvent to obtain a mixed solution, and then remove the second solvent from the mixed solution to obtain a composite material precursor; S2. The composite material precursor is heat-treated under a processing atmosphere; The processing atmosphere includes an inert atmosphere and / or a reducing atmosphere.

[0016] Optionally, the nickel source includes one or more of nickel hydroxide, organic salts of nickel, nickel carbonate, and basic nickel carbonate; The organic polyacids include one or more of ethylenediaminetetraacetic acid, iminodiacetic acid, diethylenetriaminepentaacetic acid, 1,3-propanediaminetetraacetic acid, citric acid, maleic acid, pyromellitic acid, terephthalic acid, and malic acid. The second solvent includes water and / or ethanol; Optionally, the molar ratio of the nickel source (based on nickel element) to the organic polyacid (based on carboxyl group) is 1:(2~10).

[0017] Optionally, in step S2, the heat treatment conditions include: a heating rate of 1~20℃ / min, preferably 2~10℃ / min; a holding time of 1~360min, preferably 10~180min; and a holding temperature of 400~800℃, preferably 450~700℃. The inert atmosphere includes one or more of nitrogen, argon, neon, and helium; The reducing atmosphere includes hydrogen.

[0018] Optionally, the method for preparing the carbon-coated nickel nanocomposite material further includes: contacting the solid obtained by heat treatment with an acidic solution; The acidic solution includes one or more of hydrochloric acid solution, sulfuric acid solution and hydrofluoric acid solution, with a concentration of 0.1~3 mol / L.

[0019] Through the above technical solution, this disclosure uses carbon-coated nickel nanocomposite material with specific composition and structure as catalyst to catalyze the tandem cyclization reaction of aromatic nitro compounds and 1,4-dicarbonyl compounds in the presence of hydrogen and under limited hydrogen atmosphere pressure to prepare N-arylpyrrole compounds. It has the advantages of mild conditions, high raw material conversion rate and high selectivity of target product.

[0020] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is the X-ray diffraction pattern of the carbon-coated nickel nanocomposite material A1 prepared in Preparation Example 1 of this disclosure; Figure 2 This is a transmission electron microscope image of the carbon-coated nickel nanocomposite material A1 prepared in Preparation Example 1 of this disclosure; Figure 3 This is the Ni 2p X-ray photoelectron spectrum of the carbon-coated nickel nanocomposite material A1 prepared in Example 1 of this disclosure. Detailed Implementation

[0022] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0023] This disclosure provides a method for preparing N-arylpyrrole compounds, the method comprising: contacting an aromatic nitro compound and a 1,4-dicarbonyl compound with a catalyst in the presence of hydrogen to carry out a tandem cyclization reaction, wherein the catalyst comprises a carbon-coated nickel nanocomposite material; The carbon-coated nickel nanocomposite material includes a nickel nanoparticle core and a graphitized carbon layer shell covering the surface of the nickel nanoparticle core. The lattice structure of the nickel nanoparticles includes a face-centered cubic lattice structure and / or a close-packed hexagonal lattice structure. In the XPS spectrum of the carbon-coated nickel nanocomposite material, a characteristic peak appears at 852.5 ± 0.4 eV; The pressure of the hydrogen atmosphere is 0.2~2.0 MPa.

[0024] This disclosure utilizes a carbon-coated nickel nanocomposite material with a specific composition and structure as a catalyst. Under the presence of hydrogen and a limited hydrogen atmosphere pressure, this catalyst can efficiently catalyze the tandem cyclization reaction of aromatic nitro compounds and 1,4-dicarbonyl compounds to prepare N-arylpyrrole compounds without the introduction of other active components. It offers advantages such as mild conditions, high feed conversion rate, and high selectivity for the target product. Furthermore, because the catalyst material contains a core-shell structure with a carbon coating layer and a nickel metal core, the nickel nanoparticles in the core are highly stable, non-flammable, and have low hazard, making them suitable for storage and transportation, thus ensuring the safety of the composite material in use.

[0025] According to one embodiment of this disclosure, the tandem cyclization reaction is carried out in a reactor, and there are no special restrictions on the order in which the materials are added; those skilled in the art can select the appropriate order based on actual needs. For example, after H2 is introduced into the reactor, the catalyst, aromatic nitro compound, and 1,4-dicarbonyl compound can be simultaneously added to the reactor to carry out the tandem cyclization reaction.

[0026] According to one embodiment of this disclosure, the aromatic nitro compound includes nitrobenzene and / or chloronitrobenzene; the 1,4-dicarbonyl compound includes 2,5-hexanedione.

[0027] According to one embodiment of this disclosure, the weight ratio of the catalyst, the aromatic nitro compound, and the 1,4-dicarbonyl compound is 1:(2~100):(2~100), preferably 1:(3~50):(3~50). By controlling the weight ratio of the catalyst, the aromatic nitro compound, and the 1,4-dicarbonyl compound within the above range, better reaction efficiency and higher selectivity for the target product can be obtained.

[0028] According to one embodiment of this disclosure, the conditions for the tandem cyclization reaction include a temperature of 90-155°C, preferably 100-150°C. Under these conditions, a high feedstock conversion rate and target product selectivity can be obtained during the tandem cyclization reaction.

[0029] According to one embodiment of this disclosure, the pressure of the hydrogen atmosphere is 0.2~1.5 MPa. Under the above conditions, a tandem cyclization reaction can be carried out to obtain a high feed conversion rate and target product selectivity.

[0030] According to one embodiment of this disclosure, the tandem cyclization reaction may be carried out without a solvent or in the presence of a solvent. Preferably, to ensure sufficient contact of the raw materials, promote the tandem cyclization reaction, and improve the conversion rate of the raw materials and the selectivity of the target product, the tandem cyclization reaction is carried out in the presence of a first solvent, which includes one or more of an alcohol having 1 to 5 carbon atoms, an ether having 1 to 5 carbon atoms, an alkane having 1 to 5 carbon atoms, and water, for example, isopropanol.

[0031] According to this disclosure, the tandem cyclization reaction can be carried out, for example, in a reaction vessel. This disclosure does not impose any special limitations on the order in which the materials are added; those skilled in the art can select the appropriate order based on actual needs. For example, the catalyst, the 1,4-dicarbonyl compound, and the aromatic nitro compound can be added together to the reaction vessel for the reaction.

[0032] According to one embodiment of this disclosure, the tandem cyclization reaction can be carried out under stirred or unstirred conditions.

[0033] According to one embodiment of this disclosure, the carbon coating layer is a graphitized carbon layer. "Graphitized carbon layer" refers to a carbon structure in which a layered structure can be clearly observed under a high-resolution transmission electron microscope, rather than an amorphous structure.

[0034] According to one embodiment of this disclosure, the carbon coating layer is doped with oxygen and / or nitrogen.

[0035] According to one embodiment of this disclosure, the average particle size of the carbon-coated nickel nanocomposite material is 3~100nm, preferably 4~50nm, and more preferably 4~30nm.

[0036] According to one embodiment of this disclosure, the carbon-coated nickel nanocomposite material has two distribution peaks with mesopore sizes of 2~5nm and 8~12nm. The "distribution peak" refers to the mesopore distribution peak on the pore distribution curve obtained by calculating the desorption curve according to the Barrett-Joyner-Halenda (BJH) method. The carbon-coated nickel nanocomposite material with the above characteristics is beneficial to improving mass transfer efficiency.

[0037] In this disclosure, "mesopore" refers to a pore with a diameter in the range of 2 to 50 nm.

[0038] According to one embodiment of the present disclosure, in the carbon-coated nickel nanocomposite material, the proportion of mesopore volume to total pore volume is greater than 50%, preferably greater than 80%.

[0039] According to one embodiment of this disclosure, the pickling loss rate of the carbon-coated nickel nanocomposite material is ≤40%, preferably ≤30%, and more preferably ≤10%. "Pickling loss rate" refers to the proportion of nickel lost after pickling of the carbon-coated nickel nanocomposite material, reflecting the tightness of the carbon coating layer's coverage of the nickel nanoparticles. If the carbon coating layer does not tightly cover the nickel nanoparticles, the nickel in the core will be dissolved and lost by the acid after pickling. A higher pickling loss rate indicates a lower tightness of the carbon coating layer's coverage of the nickel nanoparticles; conversely, a lower pickling loss rate indicates a higher tightness of the carbon coating layer's coverage of the nickel nanoparticles. The "pickling loss rate" is measured and calculated as follows: Add 1 g of sample to 20 mL of sulfuric acid aqueous solution (1 mol / L), treat the sample at 90 °C for 8 h, then wash with deionized water until neutral, dry, weigh, and analyze, and calculate the acid washing loss rate according to the following formula.

[0040] Pickling loss rate = [1 - (mass fraction of nickel in the composite material after pickling × mass of the composite material after pickling) ÷ (mass fraction of nickel in the composite material to be pickled × mass of the composite material to be pickled)] × 100%.

[0041] According to one embodiment of this disclosure, relative to the total weight of the carbon-coated nickel nanocomposite material, the content of Ni is 20-85% by weight, the content of C is 14-79% by weight, the content of O is 0.3-6% by weight, the content of N is 0-6% by weight, and the content of H is 0.1-2.5% by weight. The analysis of the four elements (C, H, O, and N) of this invention is performed on an Elementar Micro Cube elemental analyzer. The specific operating method and conditions are as follows: 1-2 mg of sample is weighed in a tin cup, placed in an autosampler, and introduced into the combustion tube through a ball valve for combustion at a temperature of 1000°C (helium purging is used to remove atmospheric interference during sample introduction). The combusted gas is then reduced with copper to form nitrogen, carbon dioxide, and water. The mixed gas is separated by three desorption columns and sequentially detected by a TCD detector. Oxygen analysis utilizes high-temperature decomposition; under the action of a carbon catalyst, oxygen in the sample is converted into CO, which is then detected by a TCD detector. The nickel content is the normalized result after deducting the carbon, hydrogen, oxygen, and nitrogen content of the material.

[0042] According to a preferred embodiment of this disclosure, the XPS spectrum of the carbon-coated nickel nanocomposite material does not contain characteristic peaks for +2-valent nickel and +3-valent nickel.

[0043] According to one embodiment of this disclosure, a method for preparing the carbon-coated nickel nanocomposite material includes the following steps: S1. Mix the nickel source, organic polyacid, and second solvent to obtain a mixed solution, and then remove the second solvent from the mixed solution to obtain a composite material precursor; S2. The composite material precursor is heat-treated under a processing atmosphere; The processing atmosphere includes an inert atmosphere and / or a reducing atmosphere.

[0044] According to one embodiment of this disclosure, the composite material precursor refers to a transition metal compound obtained by dissolving a nickel source and a polycarboxylic acid in a second solvent to form a homogeneous solution, followed by direct evaporation to remove the solvent. The aforementioned solvent evaporation temperature and process can employ any feasible existing technology, such as drying in an oven at 80°C to 120°C, or spray drying, or freeze drying.

[0045] According to one embodiment of this disclosure, the type of nickel source used is conventional in the art, preferably including one or more of nickel hydroxide, organic acid salts and inorganic acid salts, more preferably including one or more of nickel hydroxide, organic acid salts of nickel, nickel carbonate and basic nickel carbonate, more preferably including basic nickel carbonate and / or nickel hydroxide. When the nickel source includes two or more types, this disclosure does not impose specific limitations on their proportions.

[0046] According to one embodiment of this disclosure, the type of organic polyacid used is conventional in the art, soluble in a second solvent, and capable of forming a complex with a nickel source. The number of carboxyl groups in the organic polyacid can be, for example, 2 to 4. The organic polyacid preferably includes one or more of ethylenediaminetetraacetic acid, iminodiacetic acid, diethylenetriaminepentaacetic acid, 1,3-propanediaminetetraacetic acid, citric acid, maleic acid, trimesic acid, terephthalic acid, and malic acid. When the organic polyacid includes two or more, this disclosure does not impose specific limitations on their proportions.

[0047] According to one embodiment of this disclosure, the second solvent is of a type conventional in the art, which can form a homogeneous solution with the nickel source and the organic polybasic acid, including one or more of water and saturated monohydric alcohols having 1 to 3 carbon atoms, preferably including one or more of water and / or ethanol; this disclosure does not impose specific limitations on the amount of the second solvent, as long as it can form a homogeneous solution with the nickel source and the organic polybasic acid.

[0048] According to one embodiment of this disclosure, the molar ratio of the nickel source (calculated as nickel element) to the organic polyacid (calculated as carboxyl group) is 1:(2~10), preferably 1:(2~6), and more preferably 1:(2~4).

[0049] According to one embodiment of this disclosure, the mixing conditions in step S1 are not specifically limited. For example, they may include: a time of 0.5 to 3 hours, a temperature of 50 to 110°C, and mixing can be carried out under stirring conditions. The stirring rate is not specifically limited, as long as a homogeneous solution can be formed.

[0050] To improve the catalytic activity of the composite material, according to one embodiment of this disclosure, in step S2, the heat treatment conditions include: a heating rate of 1~20℃ / min, preferably 2~10℃ / min; a holding time of 1~360min, preferably 10~180min; and a holding temperature of 400~800℃, preferably 450~700℃.

[0051] According to one embodiment of this disclosure, the type of inert atmosphere is conventional in the art, such as one or more of nitrogen, argon, neon and helium. When the inert atmosphere includes two or more types, this disclosure does not impose specific restrictions on their proportions, and the flow rate of the inert atmosphere is set according to actual usage requirements.

[0052] According to one embodiment of this disclosure, the reducing atmosphere includes hydrogen, and the flow rate of the reducing atmosphere is set according to actual usage requirements.

[0053] According to one embodiment of this disclosure, the method for preparing the carbon-coated nickel nanocomposite material further includes: contacting the solid obtained by heat treatment with an acidic solution at a temperature of 30~100℃, preferably 60~100℃, for a time of more than 1 hour, preferably 1~20 hours; the acidic solution preferably includes a non-oxidizing acid solution, preferably including one or more of hydrochloric acid solution, sulfuric acid solution and hydrofluoric acid solution, more preferably including hydrochloric acid solution / or sulfuric acid solution, with a concentration of 0.1~3 mol / L. The above treatment can remove the incompletely coated Ni core.

[0054] The present invention will be described in detail below through embodiments, but is not limited to the following embodiments.

[0055] The average particle size of the carbon-coated nickel composite was measured using TEM images. The average particle size of the nickel core particles was calculated from the XRD pattern using the Scherrer formula: D = kγ / (Bcosθ). Here, k is the Scherrer constant (k = 0.89), B is the full width at half maximum (FWHM), θ is the diffraction angle in radians, and γ is the X-ray wavelength (0.154054 nm).

[0056] The pore structure properties of the material were detected using the BET test method. Specifically, a Quantachrome AS-6B analyzer was used for the determination, and the pore distribution curve was calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0057] The elemental composition of the material surface was determined using X-ray photoelectron spectroscopy (XPS). The XPS used was a VG Scientific ESCALab220i-XL model equipped with Avantage V5.926 software. The XPS analysis conditions were as follows: monochromatic AlKα X-ray excitation source, power 330 W, and a base vacuum of 3 × 10⁻⁶. -9 mbar.

[0058] The surface morphology of the material was characterized by transmission electron microscopy (TEM). The TEM used was a JEM-2100 (Nippon Electron Ltd.), and the TEM testing conditions were: accelerating voltage of 200 kV.

[0059] Analysis of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) was performed on an Elementar Micro Cube elemental analyzer. The specific operating procedures and conditions were as follows: 1-2 mg of sample was weighed into a tin cup, placed in the autosampler tray, and introduced into the combustion tube through a ball valve. The combustion temperature was 1000℃ (helium purging was used to remove atmospheric interference during sample introduction). The combusted gas was then reduced with copper to form nitrogen, carbon dioxide, and water. The mixed gas was separated by three desorption columns and sequentially detected by a TCD detector. Oxygen analysis utilized high-temperature decomposition; under the action of a carbon catalyst, oxygen in the sample was converted to CO, which was then detected by a TCD detector.

[0060] The nickel content is the normalized result after deducting the carbon, hydrogen, oxygen, and nitrogen content of the material.

[0061] After the reaction is complete, the products are subjected to chromatographic analysis, and the reactant conversion rate and the selectivity of the target product are calculated using the following formulas: Conversion rate (%) = (Weight of reactants already reacted / Weight of reactants added) × 100%; Selectivity (%) = Weight of target product / Weight of reaction product × 100%.

[0062] Preparation Example 1 The carbon-coated nickel nanocomposite material A1 was prepared using the following steps: S1. Weigh 21.01g of citric acid monohydrate and 14.55g of basic nickel carbonate (the molar ratio of basic nickel carbonate based on nickel element to citric acid monohydrate based on carboxyl group is 1:3) and add them to 150mL of deionized water. Stir at 100℃ to obtain a homogeneous solution, and continue to heat to dryness. Grind the obtained solid to obtain the precursor.

[0063] S2. The obtained precursor was placed in a ceramic boat, and then the ceramic boat was placed in the constant temperature zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was increased to 600℃ at a rate of 10℃ / min. After holding the temperature for 120 min, the heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain carbon-coated nickel nanocomposite material A1.

[0064] Figure 1 This is the X-ray diffraction pattern of carbon-coated nickel nanocomposite A1 prepared in Example 1. Figure 1 The diffraction peaks show primarily of face-centered cubic nickel (fcc-Ni) and hexagonal close-packed nickel (hcp-Ni), indicating that its crystal structure includes both face-centered cubic and hexagonal close-packed lattice structures, while also exhibiting diffraction peaks characteristic of carbon materials. Using the Scherrer equation, the average particle size of the nickel core nanoparticles is calculated to be 11.7 nm.

[0065] Figure 2The image shows a TEM image of the carbon-coated nickel nanocomposite A1 prepared in Example 1. It can be seen from the image that the outer layer of the nickel nanoparticles is wrapped with several layers of graphitized carbon. The average particle size of the carbon-coated nickel nanoparticles is 13.5 nm, and the average particle size of the nickel core is about 12.5 nm, which is consistent with the calculation results based on the XRD spectrum.

[0066] Figure 3 The image shows the Ni 2p X-ray photoelectron spectrum of the carbon-coated nickel nanocomposite material prepared in Example 1, with a peak at 852.6 eV, which is attributed to NiO2p. 3 / 2 This means it contains elemental nickel. Elemental analysis showed that the nanomaterial contained 22.49% by weight of carbon, 0.55% by weight of hydrogen, and 1.46% by weight of oxygen. After normalization, the Ni content was 75.50% by weight.

[0067] Preparation Example 2 The carbon-coated nickel nanocomposite A2 was prepared using the following steps: S1. Weigh 10 mmol of nickel hydroxide and 10 mmol of citric acid and add them to 150 mL of deionized water (the molar ratio of nickel hydroxide based on nickel element to citric acid based on carboxyl group is 1:3). Stir at 80 °C to obtain a homogeneous solution, and continue to heat to dryness. Grind the solid to obtain the precursor.

[0068] S2. Place the precursor obtained in step S1 into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas at a flow rate of 150 mL / min, and heat it to 575℃ at a rate of 2.5℃ / min. After holding the temperature for 2 hours, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the composite material.

[0069] S3. Add the composite material obtained in step S2 to 50 mL of 1 mol / L H2SO4 solution, stir and reflux at 90 °C for 4 h, filter the solution, wash with deionized water until neutral, and then dry the powder in an oven at 100 °C for 2 h to obtain carbon-coated nickel nanocomposite material A2.

[0070] According to XRD tests, the nickel nanoparticles in composite material A2 have an fcc-Ni lattice structure, indicating that their lattice structure includes a face-centered cubic lattice structure.

[0071] In the Ni 2p X-ray photoelectron spectrum, a peak appears at 852.7 eV, which is attributed to Ni02p. 3 / 2 That is, it contains nickel in its elemental state.

[0072] The N2 adsorption-desorption isotherm and pore size distribution diagram show that the pore size distribution of composite material A2 has two distribution peaks at diameters of 3.3 nm and 6.3 nm.

[0073] Elemental analysis revealed that the nanomaterial contained 28.60 wt% C, 0.40 wt% H, and 1.94 wt% O, with a normalized Ni content of 69.06 wt%. The pickling loss rate was 16%.

[0074] Preparation Example 3 The carbon-coated nickel nanocomposite material A3 was prepared using the following steps: S1 Weigh 4.38 g (15 mmol) of ethylenediaminetetraacetic acid and 1.85 g (20 mmol) of nickel hydroxide (the molar ratio of nickel hydroxide based on nickel element to ethylenediaminetetraacetic acid based on carboxyl group is 1:3) and add them to 150 mL of deionized water. Stir at 75 °C to obtain a homogeneous solution, and continue to heat to dryness. Grind the solid to obtain the precursor.

[0075] S2. Place the precursor obtained in step S1 into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas at a flow rate of 80 mL / min, and heat it to 600℃ at a rate of 3℃ / min. After holding the temperature for 3 hours, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the composite material.

[0076] S3. The composite material obtained in step S2 is added to 60 mL of 0.5 mol / L H2SO4 solution, stirred and refluxed at 80 °C for 6 h, the solution is filtered, washed with deionized water until neutral, and the powder is placed in an oven at 100 °C for 2 h to obtain carbon-coated nickel nanocomposite material A3.

[0077] According to XRD tests, the lattice structure of nickel nanoparticles in composite material A3 is hcp-Ni and fcc-Ni, indicating that its lattice structure includes face-centered cubic lattice structure and close-packed hexagonal lattice structure.

[0078] The TEM images show that the nickel nanoparticles are coated with several layers of graphitized carbon, and the average particle size of the carbon-coated nickel nanocomposite is 12.6 nm.

[0079] In the Ni 2p X-ray photoelectron spectrum, a peak appears at 852.3 eV, which is attributed to Ni02p. 3 / 2 That is, it contains nickel in its elemental state.

[0080] The N2 adsorption-desorption isotherm and pore size distribution diagram show that the pore size distribution of composite material A3 exhibits two peaks at diameters of 3.7 nm and 10.0 nm. Mesopore volume accounts for 99.7% of the total pore volume.

[0081] Elemental analysis revealed that the nanomaterial contained 37.42 wt% carbon, 0.54 wt% hydrogen, 1.45 wt% nitrogen, and 1.86 wt% oxygen. The normalized nitrogen content was 58.73 wt%. The acid pickling loss rate was 12%.

[0082] The following examples illustrate a method for synthesizing N-arylpyrrole compounds via catalytic tandem cyclization reaction.

[0083] Example 1 80 mg of carbon-coated nickel nanocomposite material A1 obtained in Preparation Example 1, 246 mg of nitrobenzene, 3 mL of 2,5-hexanedione (density 0.973 g / mL), and 20 mL of isopropanol were added to a reaction vessel. After purging the reaction vessel with H2 four times, H2 was purged again to bring the pressure inside the reaction vessel to 0.5 MPa. The temperature was raised to the predetermined reaction temperature of 120 °C and the reaction was continued for 4 h. Heating was then stopped, the temperature was lowered to room temperature, the pressure was released, the reaction vessel was opened, and the product was taken out for chromatographic and mass spectrometric analysis. The results are listed in Table 1. The weight ratio of carbon-coated nickel nanocomposite A1, nitrobenzene and 2,5-hexanedione is 1:3.08:36.49.

[0084] Example 2 The method of Example 1 was followed, except that 246 mg of nitrobenzene was replaced with 315 mg of 4-nitrochlorobenzene. After reacting for 4 h, heating was stopped, the mixture was cooled to room temperature, the pressure was released, the reaction vessel was opened, and the product was taken out for chromatographic and mass spectrometric analysis. The results are listed in Table 1. The carbon-coated nickel nanocomposite material has a weight ratio of 1:3.94:36.49 for A1, 4-nitrochlorobenzene and 2,5-hexanedione.

[0085] Example 3 300 mg of carbon-coated nickel nanocomposite material A1 obtained in Preparation Example 1, 1.576 g of 4-nitrochlorobenzene, and 15 mL of 2,5-hexanedione were purged with H2 four times to replace the pressure inside the reactor. Then, H2 was purged again to bring the pressure inside the reactor to 0.4 MPa. The temperature was raised to the predetermined reaction temperature of 120 °C. During the reaction, when the reaction pressure dropped to 0.3 MPa, hydrogen gas was added back to bring the pressure back to 0.4 MPa. The reaction was continued for 5 h and then heating was stopped. After cooling to room temperature, the pressure was released, the reactor was opened, and the product was taken out for chromatographic and mass spectrometric analysis. The results are listed in Table 1. The carbon-coated nickel nanocomposite material has a weight ratio of 1:5.25:48.65 for A1, 4-nitrochlorobenzene and 2,5-hexanedione.

[0086] Example 4 The method of Example 1 was followed, except that 80 mg of the carbon-coated nickel nanocomposite material obtained in Example 1 was replaced with the carbon-coated nickel nanocomposite material obtained in Example 2. After reacting for 4 h, heating was stopped, the mixture was cooled to room temperature, the pressure was released, the reaction vessel was opened, and the product was taken out for chromatographic and mass spectrometric analysis. The parameters are listed in Table 1. The weight ratio of carbon-coated nickel nanocomposite A2, nitrobenzene and 2,5-hexanedione is 1:3.08:36.49.

[0087] Example 5 80 mg of carbon-coated nickel nanocomposite material A2 obtained in Preparation Example 2, 315 mg of 4-nitrochlorobenzene, 3 mL of 2,5-hexanedione, and 20 mL of isopropanol were added to a reaction vessel. After purging the reaction vessel with H2 four times, H2 was purged again to bring the pressure inside the reaction vessel to 0.5 MPa. The temperature was raised to the predetermined reaction temperature of 120°C and the reaction was continued for 4 h. After heating was stopped, the pressure was released after cooling to room temperature, the reaction vessel was opened, and the product was taken out for chromatographic and mass spectrometric analysis. The results are listed in Table 1. The carbon-coated nickel nanocomposite material A2, 4-nitrochlorobenzene and 2,5-hexanedione have a weight ratio of 1:3.94:36.49.

[0088] Example 6 The method of Example 1 was followed, except that 80 mg of the carbon-coated nickel nanocomposite material obtained in Example 1 was replaced with the carbon-coated nickel nanocomposite material obtained in Example 3. After reacting for 4 h, heating was stopped, the mixture was cooled to room temperature, the pressure was released, the reaction vessel was opened, and the product was taken out for chromatographic and mass spectrometric analysis. The results are listed in Table 1. The weight ratio of carbon-coated nickel nanocomposite A3, nitrobenzene and 2,5-hexanedione is 1:3.08:36.49.

[0089] Example 7 The method of Example 1 was used, except that the pressure of the hydrogen atmosphere was 1.9 MPa, and the results are listed in Table 1.

[0090] Comparative Example 1 The method was followed as in Example 1, except that the pressure of hydrogen gas introduced into the reactor was 2.5 MPa. After reacting at 120°C for 4 hours, heating was stopped, the mixture was cooled to room temperature, the pressure was released, the reactor was opened, and the product was taken out for chromatographic and mass spectrometric analysis. The results are listed in Table 1, and the selectivity of aniline was 55.4%.

[0091] Table 1

[0092] Based on the above data, it can be seen that using the carbon-coated nickel nanocomposite material disclosed herein as a catalyst, the tandem cyclization reaction of aromatic nitro compounds and 1,4-dicarbonyl compounds can be efficiently carried out in the presence of hydrogen to prepare N-arylpyrrole compounds. The reaction conditions are relatively mild, the feed conversion rate is high (above 99.9%), and the target selectivity is high. Furthermore, according to the comparison between Example 3 and Comparative Example 1, it can be seen that the method of this application can efficiently catalyze the tandem cyclization reaction of aromatic nitro compounds and 1,4-dicarbonyl compounds to generate N-arylpyrrole compounds without the use of solvents. According to the comparison between Examples 1 and 8, when the pressure of the hydrogen atmosphere is in the preferred range of 0.2~1.5 MPa, higher target selectivity can be obtained.

[0093] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0094] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0095] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing N-arylpyrrole compounds, the method comprising: In the presence of hydrogen, aromatic nitro compounds and 1,4-dicarbonyl compounds are contacted with a catalyst to carry out a tandem cyclization reaction, characterized in that the catalyst comprises a carbon-coated nickel nanocomposite material. The carbon-coated nickel nanocomposite material includes a nickel nanoparticle core and a graphitized carbon layer shell covering the surface of the nickel nanoparticle core. The lattice structure of the nickel nanoparticles includes a face-centered cubic lattice structure and / or a close-packed hexagonal lattice structure. In the XPS spectrum of the carbon-coated nickel nanocomposite material, a characteristic peak appears at 852.5 ± 0.4 eV; The pressure of the hydrogen atmosphere is 0.2~2.0 MPa.

2. The method according to claim 1, wherein, The aromatic nitro compounds include nitrobenzene and / or chloronitrobenzene; The 1,4-dicarbonyl compound includes 2,5-hexanedione.

3. The method according to claim 1, wherein, The weight ratio of the catalyst, the aromatic nitro compound, and the 1,4-dicarbonyl compound is 1:(2~100):(2~100), preferably 1:(3~50):(3~50).

4. The method according to claim 1, wherein, The temperature of the tandem cyclization reaction is 90~155℃.

5. The method according to claim 1, wherein, The tandem cyclization reaction is carried out in the presence of a first solvent, which includes one or more of the following: alcohols with 1 to 5 carbon atoms, ethers with 1 to 5 carbon atoms, alkanes with 1 to 5 carbon atoms, and water.

6. The method according to claim 1, wherein, The average particle size of the carbon-coated nickel nanocomposite material is 3~100 nm.

7. The method according to claim 1, wherein, Relative to the total weight of the carbon-coated nickel nanocomposite material, the content of Ni element is 20-85% by weight, the content of C element is 14-79% by weight, the content of O element is 0.3-6% by weight, the content of N element is 0-6% by weight, and the content of H element is 0.1-2.5% by weight.

8. The method according to claim 1, wherein, The carbon-coated nickel nanocomposite material has two distribution peaks with mesopore sizes of 2~5nm and 8~12nm; Optionally, in the carbon-coated nickel nanocomposite material, the proportion of mesopore volume to total pore volume is greater than 50%; Optionally, the pickling loss rate of the carbon-coated nickel nanocomposite material is ≤40%.

9. The method according to claim 1, wherein, The method for preparing the carbon-coated nickel nanocomposite material includes the following steps: S1. Mix the nickel source, organic polyacid, and second solvent to obtain a mixed solution, and then remove the second solvent from the mixed solution to obtain a composite material precursor; S2. The composite material precursor is heat-treated under a processing atmosphere; The processing atmosphere includes an inert atmosphere and / or a reducing atmosphere.

10. The method according to claim 9, wherein, The nickel source includes one or more of nickel hydroxide, organic salts of nickel, nickel carbonate, and basic nickel carbonate; The organic polyacids include one or more of ethylenediaminetetraacetic acid, iminodiacetic acid, diethylenetriaminepentaacetic acid, 1,3-propanediaminetetraacetic acid, citric acid, maleic acid, pyromellitic acid, terephthalic acid, and malic acid. The second solvent includes water and / or ethanol; Optionally, the molar ratio of the nickel source (based on nickel element) to the organic polyacid (based on carboxyl group) is 1:(2~10).

11. The method according to claim 9, wherein, In step S2, the heat treatment conditions include: a heating rate of 1~20℃ / min, preferably 2~10℃ / min; a holding time of 1~360min, preferably 10~180min; and a holding temperature of 400~800℃, preferably 450~700℃. The inert atmosphere includes one or more of nitrogen, argon, neon, and helium; The reducing atmosphere includes hydrogen.

12. The method according to claim 9, wherein, The method for preparing the carbon-coated nickel nanocomposite material further includes: contacting the solid obtained by heat treatment with an acidic solution; The acidic solution includes one or more of hydrochloric acid solution, sulfuric acid solution and hydrofluoric acid solution, with a concentration of 0.1~3 mol / L.

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