A molybdenum trioxide-based catalyst, its preparation method, and a synthetic method for the catalytic preparation of C=N bond-containing organic nitrogen-containing compounds using the catalyst.

Abstract

This invention belongs to the field of catalyst technology, specifically relating to a molybdenum trioxide-based catalyst, its preparation method, and a method for synthesizing C=N-containing organic nitrogen-containing compounds using the same catalyst. The molybdenum trioxide-based catalyst is obtained by high-temperature pyrolysis of a Mo precursor under an inert atmosphere, with molybdenum trioxide as the active site and nitrogen-doped carbon material as the support. This catalyst can be used to catalyze the hydrogen transfer reduction of alcohols coupled with nitro compounds to synthesize C=N-containing organic nitrogen-containing compounds under conditions without added alkali. The catalyst preparation method of this invention is simple, exhibits good catalytic activity in the synthesis reaction of C=N-containing organic nitrogen-containing compounds by hydrogen transfer reduction of alcohols coupled with nitro compounds, and the catalyst can be cycled more than 10 times, showing good stability and excellent prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a molybdenum trioxide-based catalyst, its preparation method, and a synthetic method for preparing organic nitrogen-containing compounds containing C=N bonds using the same catalyst. Background Technology

[0002] Organic nitrogen-containing compounds with C=N bonds, such as imines and N-heterocyclic compounds, are important components of various fine chemicals, polymer materials, and pharmaceuticals. Traditionally, they are synthesized by condensation of aldehydes or ketones with corresponding amines in the presence of an acid catalyst. However, this process is difficult to handle due to the waste acid, requires the use of active aldehydes or ketones, has a limited substrate range, and is prone to aldehyde-amine polymerization reactions, resulting in low yields of organic nitrogen-containing compounds with C=N bonds. Therefore, researchers are increasingly focusing on developing new methods for synthesizing organic nitrogen-containing compounds with C=N bonds. Among these methods, the direct coupling of alcohols and amines is one of the most important for synthesizing C=N organic nitrogen-containing compounds. On the one hand, alcohols are readily available (obtainable from fossil resources or renewable biomass), inexpensive, and produce only hydrogen (in an inert atmosphere) or water (in an oxygen atmosphere) as byproducts during the reaction. On the other hand, this method can synthesize asymmetric imines with high atom utilization, exhibiting atom economy. However, in most cases, this process requires strong base additives such as KOH and t-BuOK to improve catalytic performance (Small, 2023, 2207941; Green Chem., 2012, 14, 2384-2387.), which contradicts the views of green chemistry and sustainable chemistry. Moreover, for industrial production, both the production process and the separation and purification process are very difficult.

[0003] To overcome the aforementioned difficulties, researchers have adopted a hydrogen-borrowing strategy to directly synthesize C=N bonded organic nitrogen-containing compounds from nitro compounds and alcohols through reductive coupling. This tandem reaction process requires no external reducing agent or purification intermediates, making it an effective approach for sustainable chemistry and attracting widespread interest from chemical scientists. The process involves dehydrogenating an alcohol to a carbonyl compound, then reducing the nitro compound in situ to a primary amine, and finally condensing the primary amine with the carbonyl compound formed by the dehydrogenation of the alcohol to generate a C=N bonded organic nitrogen-containing compound. However, currently, the C=N bond in this process is easily reduced to a CN bond, and the method is limited to reactive aromatic alcohols (Appl. Catal. B-Environ., 2022, 300, 120288; Phys. Chem. Chem. Phys., 2015, 17, 15012-15018.). Clearly, the synthesis of organic nitrogen-containing compounds from biomass-derived, inexpensive, and readily available fatty alcohols has extremely high research value. However, biomass alcohols are inert (e.g., ethanol is often used as an organic solvent), making their activation challenging, especially when using heterogeneous non-precious metal catalysts. Therefore, designing a simple, inexpensive, and readily available heterogeneous non-precious metal catalyst to achieve the selective reductive synthesis of C=N bonded organic nitrogen-containing compounds from nitro compounds with a wide range of fatty and aromatic alcohols under alkali-free conditions is both highly challenging and has significant industrial application value. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a molybdenum trioxide-based catalyst and a method for catalytically synthesizing organic nitrogen-containing compounds containing C=N bonds using the same catalyst. The molybdenum trioxide-based catalyst (denoted as Mo / NC-T, where "T" represents the pyrolysis temperature, the same below, and will not be described again) uses MoO3 as the active site and nitrogen-doped carbon material as the support. The catalytic synthesis of organic nitrogen-containing compounds containing C=N bonds is achieved by using the molybdenum trioxide-based catalyst to catalyze the hydrogen transfer reduction of alcohol compounds coupled with nitro compounds to synthesize organic nitrogen-containing compounds containing C=N bonds.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a molybdenum trioxide-based catalyst, wherein the catalyst uses MoO3 as the active site and nitrogen-doped carbon material as the support, and the mass percentage content of Mo element in the molybdenum trioxide-based catalyst is 8.6-16.4 wt.%; the catalyst is prepared by the following method: using a white powder of urea-ammonium molybdate-chitosan-acetic acid complex as a Mo precursor, and pyrolyzing it in a tube furnace under N2 atmosphere at 450-600℃ to prepare the catalyst (the obtained catalyst is denoted as Mo / NC-450~600, the same below).

[0007] The XRD pattern of the catalyst (as shown in the instruction manual)Figure 1 The results show that characteristic peaks of MoO3 appear at 2θ = 23.0 ± 0.2° (011), 25.0 ± 0.2° (200), 26.5 ± 0.2° (111), 34.6 ± 0.2° (211), 35.2 ± 0.2° (102), 42.2 ± 0.2° (220) and 53.4 ± 0.2° (400), indicating that Mo exists in the form of MoO3. Two broad and weak peaks appearing at 2θ = 28.0 ± 0.2° and 43.3 ± 0.2° are attributed to the (002) and (100) crystal planes of the hexagonal graphite structure; the broadness and weakness of these peaks indicate the formation of nitrogen-doped carbon material, thus indicating the acquisition of a nitrogen-doped carbon material supported on MoO3 catalyst.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned molybdenum trioxide-based catalyst, comprising the following steps:

[0009] Step (1): Mix urea and (NH4)6Mo7O 24 • 4H₂O (ammonium molybdate tetrahydrate) was dissolved in distilled water, and then chitosan was added to the solution with stirring. After the chitosan was completely dispersed, acetic acid was quickly added and stirred to obtain a uniform, translucent paste. The resulting translucent paste was dried at 60-100°C to obtain a white powder of urea-ammonium molybdate-chitosan-acetic acid complex, which served as a Mo precursor.

[0010] Step (2): The Mo precursor obtained in step (1) is placed in a tube furnace and heated from room temperature to a target temperature of 450–600°C at a heating rate of 1–3°C / min under a nitrogen (N2) atmosphere. The temperature is then maintained at the target temperature for 1–3 hours. Heating is then stopped, and the mixture is allowed to cool naturally to room temperature to obtain a black powder. This black powder is the catalyst, labeled Mo / NC-450–600.

[0011] Further, in step (1), the urea and (NH4)6Mo7O are added. 24 The ratio of 4H2O (ammonium molybdate tetrahydrate), distilled water, chitosan and acetic acid is 48-300g:1-4g:40-160mL:4-16g:4-16mL, preferably 96g:2g:80mL:8g:8mL.

[0012] Furthermore, the chitosan is a chitosan with a degree of deacetylation ≥95% and a viscosity of 100-200 mPa·s.

[0013] Further, in step (1), the acetic acid is acetic acid with a mass percentage >99.5%, and the stirring time for rapidly adding acetic acid and stirring is 20-60 min, preferably 30 min.

[0014] Further, in step (1), the drying process is drying in air, the drying temperature is preferably 80°C, and the drying time is 6-24 hours, preferably 12 hours.

[0015] Furthermore, in step (2), the heating rate in the tubular furnace is preferably 2℃ / min; the target temperature is preferably 500℃; and the holding time is preferably 2h.

[0016] A simplified flowchart of the above-mentioned method for preparing molybdenum trioxide-based catalysts is shown in the appendix to the specification. Figure 2 As shown.

[0017] Thirdly, this invention provides a method for synthesizing C=N-containing organic nitrogen-containing compounds by using the above-mentioned molybdenum trioxide-based catalyst to catalyze the hydrogen transfer reduction of alcohol compounds coupled with nitro compounds. Because the types of alcohol compounds and nitro compounds used as raw material components differ, the synthesis methods for C=N-containing organic nitrogen-containing compounds are correspondingly divided into three types, and the steps of each synthesis method are as follows:

[0018] Synthesis Method 1: When the alcohol compound is a fatty alcohol, the Mo / NC-T catalyst, alcohol compound and nitro compound are added to the reaction vessel in a ratio of 5-100 mg: 10-40 mL: 1-10 mmol. After sealing the reaction vessel, the air inside the reaction vessel is replaced with N2. Then, at 170-220℃, hydrogen transfer reduction coupling occurs to obtain an organic nitrogen-containing compound containing C=N bonds.

[0019] Synthesis Method 2: When the alcohol compound is an aromatic alcohol and / or furan alcohol, the Mo / NC-T catalyst, solvent, nitro compound and alcohol compound are added to the reaction vessel in a ratio of 5-100 mg: 10-40 mL: 1-10 mmol: 3-50 mmol. After sealing the reaction vessel, the air inside the reaction vessel is replaced with N2. Then, at 170-220 °C, the organic nitrogen-containing compound containing C=N bonds is obtained by hydrogen transfer reduction coupling.

[0020] Synthesis Method 3: When the alcohol compound is a vicinal diol, the Mo / NC-T catalyst, solvent, nitro compound and alcohol compound are added to the reaction vessel in a ratio of 5-100 mg: 10-40 mL: 1-10 mmol: 10-100 mmol. After sealing the reaction vessel, the air inside the reaction vessel is replaced with N2. Then, at 170-220 °C, the organic nitrogen-containing compound containing C=N bonds is obtained by hydrogen transfer reduction coupling.

[0021] Further, when the alcohol compound is a fatty alcohol, preferably, the Mo / NC-T catalyst, ethanol and nitrobenzene are added to the reaction vessel in a ratio of 20 mg: 10 mL: 1 mmol, the vessel is sealed, the air inside is replaced with N2, and the reaction is carried out at 200°C for 4-10 h to obtain an organic nitrogen-containing compound containing C=N bonds; more preferably, the reaction time is 10 h.

[0022] Further, when the alcohol compound is an aromatic alcohol, furanol, or vicinal diol, preferably, the Mo / NC-T catalyst, solvent, nitro compound, and alcohol compound are added to the reaction vessel in a ratio of 20 mg: 10 mL: 1 mmol: x mmol (x = 5 when the alcohol compound is an aromatic alcohol or furanol; x = 10 when the alcohol compound is a vicinal diol) and sealed. After sealing, the air inside the reaction vessel is replaced with N2, and the reaction is carried out at 200°C for 1-100 h. The organic nitrogen-containing compound containing C=N bonds is obtained by hydrogen transfer reduction coupling. More preferably, the reaction time is 8-48 h.

[0023] Furthermore, in the method for synthesizing organic nitrogen-containing compounds containing C=N bonds of the present invention, the Mo / NC-T catalyst is preferably Mo / NC-500.

[0024] Furthermore, in the method for synthesizing organic nitrogen-containing compounds containing C=N bonds of the present invention, when the alcohol compound is a fatty alcohol, the fatty alcohol acts as both a solvent and a reducing agent; when the alcohol compound is an aromatic alcohol, furan alcohol, and / or vicinal diol, the aromatic alcohol, furan alcohol, and vicinal diol act only as reducing agents.

[0025] Furthermore, when the alcohol compound is an aromatic alcohol, furan alcohol, and / or vicinal diol, the solvent is at least one of hexane, toluene, tetrahydrofuran, acetonitrile, and water, preferably acetonitrile.

[0026] Furthermore, the molecular structural formula of the nitro compound is any one of the following:

[0027]

[0028]

[0029] Furthermore, the molecular structural formula of the alcohol compound is any one of the following:

[0030]

[0031] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0032] 1. Compared with existing metal-based catalysts that use hydrogen (H2), sodium borohydride (NaBH4), and hydrazine hydrate (N2H4·H2O) as reducing agents, the method for synthesizing C=N bond-containing organic nitrogen-containing compounds catalyzed by the Mo / NC-T catalyst in this invention uses inexpensive, readily available, and widely sourced alcohol compounds as reducing agents and / or solvents. The process is simple, easy to operate, and the reaction conditions are mild, resulting in better selectivity for C=N bond-containing organic nitrogen-containing compounds in the product.

[0033] 2. Compared with the prior art, the method for synthesizing organic nitrogen-containing compounds containing C=N bonds in this invention realizes the synthesis of organic nitrogen-containing compounds containing C=N bonds by hydrogen transfer reduction coupling of alcohol compounds under heterogeneous catalyst conditions without external alkali (reaction temperature and time: 170-220℃, 1-100h).

[0034] 3. In the synthesis method of organic nitrogen-containing compounds containing C=N bonds of the present invention, the nitrogen-doped carbon material supported on MoO3 catalyst can be recycled more than 10 times. Even after repeated use, it still maintains high conversion rate and high selectivity. The catalyst has good stability and good prospects for industrial application. Attached Figure Description

[0035] Figure 1 XRD patterns for Mo / NC-T and NC-500.

[0036] Figure 2 This is a simplified flowchart of the preparation method of the catalyst Mo / NC-T of the present invention.

[0037] Figure 3 TEM images and elemental distribution maps of Mo / NC-500: (a) TEM image of Mo / NC-500 catalyst, (b) HR-TEM image, (c) high-angle annular dark-field imaging-scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive spectroscopy (EDS) elemental map. Detailed Implementation

[0038] The technical solution of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings, but the following embodiments are not intended to limit the scope of protection claimed by the present invention.

[0039] In the following examples, alcohols, nitro compounds, and various organic solvents were purchased from Sinopharm Shanghai Chemical Reagent Co., Ltd. or Shanghai Aladdin Biochemical Technology Co., Ltd. Ammonium molybdate tetrahydrate ((NH4)6Mo7O 24• 4H2O) and acetic acid (mass percentage content >99.5%) were purchased from Sinopharm Shanghai Chemical Reagent Co., Ltd., and urea and chitosan (degree of deacetylation ≥95%, viscosity 100-200 mPa·s) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., AR, >99.7%.

[0040] Example 1

[0041] A method for preparing a molybdenum trioxide-based catalyst (Mo / NC-500) includes the following steps:

[0042] Step (1): Mix 96g of urea and 2g of (NH4)6Mo7O 24 • 4H₂O was dissolved in 80 mL of distilled water, and then 8 g of chitosan was added to the solution with stirring. After the chitosan was completely dispersed, 8 mL of acetic acid was quickly added and stirred for 30 min to obtain a uniform, translucent paste. The resulting translucent paste was dried in air at 80 °C for 12 h to obtain a white powder of urea-ammonium molybdate-chitosan-acetic acid complex, which served as a Mo precursor.

[0043] Step (2): The Mo precursor obtained in step (1) is placed in a tube furnace and heated from room temperature to a target temperature of 500°C at a heating rate of 2°C / min in a nitrogen (N2) atmosphere. It is then held at 500°C for 2 hours (pyrolysis process), followed by stopping the heating and allowing it to cool naturally to room temperature to obtain a black powder. The resulting black powder is the catalyst, labeled Mo / NC-500.

[0044] The catalyst prepared in this embodiment was tested by ICP-OES, and the content of Mo was found to be 10.3 wt.%. XRD and TEM characterization were performed, and the characterization results are shown in the attached figures. Figure 1 and 3 The XRD pattern of the catalyst is shown in the attached specification. Figure 1 The TEM image shows characteristic peaks of MoO3 at 2θ = 23.0 ± 0.2° (011), 25.0 ± 0.2° (200), 26.5 ± 0.2° (111), 34.6 ± 0.2° (211), 35.2 ± 0.2° (102), 42.2 ± 0.2° (220) and 53.4 ± 0.2° (400), indicating that Mo exists in the form of MoO3. Two broad and weak peaks at 2θ = 28.0 ± 0.2° and 43.3 ± 0.2° belong to the (002) and (100) crystal planes of the hexagonal graphite structure; these broad and weak peaks indicate the formation of a nitrogen-doped carbon material structure, thus indicating that a nitrogen-doped carbon material-supported MoO3 catalyst was finally prepared. The TEM image of the catalyst (as shown in the attached specification) Figure 3The results show that lattice fringes with a lattice spacing of d = 0.356 nm were measured in the high-resolution TEM (HR-TEM) image of the Mo / NC-500. Figure 3 b), corresponding to the (200) crystal plane of MoO3, is consistent with the XRD results. High-angle annular dark-field-scanning transmission electron microscopy (HAADF-STEM) images show that MoO3 is uniformly dispersed on the surface of the nitrogen-doped carbon layer. Figure 3 c). Energy dispersive spectroscopy (EDS) further revealed the uniform distribution of N, O, and Mo elements on the carbon support in the Mo / NC-500 catalyst. Figure 3 c).

[0045] Examples 2 and 3

[0046] A method for preparing molybdenum trioxide-based catalysts (Mo / NC-450 and Mo / NC-600) comprises the following steps:

[0047] Except for adjusting the target temperature in step (2) of Example 1 to 450℃ and 600℃ respectively, the rest is the same as in Example 1, and the catalysts obtained are labeled as Mo / NC-450 and Mo / NC-600 respectively.

[0048] The XRD characterization results of catalysts Mo / NC-450 and Mo / NC-600 are attached. Figure 1 As shown; ICP-OES testing revealed that the Mo content was 8.6 wt.% and 16.4 wt.%, respectively.

[0049] Example 4

[0050] As a comparative example of the catalysts used in Examples 1-3, except that (NH4)6Mo7O was not added... 24 Except for 4H2O, the remaining steps and operations are the same as in Example 1, and the resulting catalyst is labeled NC-500.

[0051] The XRD characterization results of catalyst NC-500 are attached. Figure 1 As shown.

[0052] Examples 5-11

[0053] Examples 5-8

[0054] The molybdenum trioxide-based catalysts prepared in Examples 1-3 and catalyst NC-500 prepared in Example 4 catalyze the hydrogen transfer reduction coupling of ethanol with nitrobenzene to synthesize C=N-containing organic nitrogen-containing compounds. The steps are as follows:

[0055] 20 mg of catalyst Mo / NC-450 / 500 / 600 or NC-500, 10 mL of ethanol, and 1 mmol of nitrobenzene were added to a reaction vessel. After sealing, the air inside the reaction vessel was replaced with N2, and then the reaction was carried out at 200 °C for 5-36 h to obtain the hydrogen transfer reduction coupling product. The specific products obtained are shown in Table 1, where product 2 is the target product and product 1 is the nitrobenzene reduction intermediate (the same applies below, and will not be described in detail).

[0056] The catalyst Mo / NC-T exhibited catalytic activity throughout the target temperature range, with both conversion and target product selectivity initially increasing and then decreasing with increasing target temperature (as shown in Examples 5-7 of Table 1). Catalyst Mo / NC-500 showed the highest nitrobenzene conversion at 81.2%, and a selectivity of 84.4% for the target product N-phenylethyleneimine (as shown in Example 6 of Table 1). This synthesis reaction did not occur under the catalysis of the nitrogen-doped carbon catalyst NC-500 (as shown in Example 8 of Table 1). These results indicate that the active site for the ethanol hydrogen transfer reduction coupling of nitrobenzene is a Mo-containing compound. (From Appendix...) Figure 1 It can be seen that the main crystalline phase of the Mo-containing compound in the catalyst is MoO3. Therefore, the catalyst prepared is a MoO3 catalyst supported by nitrogen-doped carbon material.

[0057] Examples 9-11

[0058] The reaction time was varied to optimize the Mo / NC-T catalyst and obtain selectivity data for product 2 (N-phenylethyleneimine) after complete conversion of nitrobenzene. Catalysts Mo / NC-450, 500, and 600 were used, and the reaction times were different from those in Example 5.

[0059] The resulting products are shown in Examples 9-11 of Table 1. In these examples, the Mo / NC-500 catalyst achieved near-complete conversion of nitrobenzene and a 97.2% selectivity for N-phenylethyleneimine after a reaction time of 10 hours. This catalyst outperformed the Mo / NC-450 and Mo / NC-600 catalysts in both reaction time and target product selectivity. Therefore, the Mo / NC-500 catalysts from Examples 6 and 10 were selected for practicality testing.

[0060] Table 1. Effect of different catalysts on the products of the catalytic hydrogen transfer reduction of ethanol to nitrobenzene.

[0061]

[0062]

[0063]

[0064] The reaction time for Examples 5-8 was 5 hours; in Example 9, a represents a reaction time of 36 hours; in Example 10, b represents a reaction time of 10 hours; and in Example 11, c represents a reaction time of 36 hours.

[0065] Examples 12-15

[0066] The synthesis of C=N-containing organic nitrogen-containing compounds from ethanol via hydrogen transfer reduction coupling with nitrobenzene catalyzed by catalyst Mo / NC-500 at different reaction temperatures follows these steps:

[0067] 20 mg of Mo / NC-500 catalyst, 10 mL of ethanol, and 1 mmol of nitrobenzene were added to a reaction vessel. After sealing, the air inside the reaction vessel was replaced with N2, and the reaction was carried out at different temperatures for 5 h. The reaction time and the amount of catalyst remained constant, and only the reaction temperature was changed to obtain hydrogen transfer reduction coupling products. The specific products obtained are shown in Table 2.

[0068] As shown in Table 2, the reaction temperature has a significant impact on this reaction. With increasing reaction temperature, the conversion rate of nitrobenzene gradually increases, and the initial increase gradually slows down. After raising the temperature to 210℃, the selectivity of the N-phenylethyleneimine product did not significantly improve, and a small amount of other byproducts besides products 1 and 2 were detected. Therefore, the reaction temperature of 200℃ in Example 6 was selected for practicality testing.

[0069] Table 2. Effect of different reaction temperatures on the products of the ethanol hydrogen transfer reduction coupling nitrobenzene reaction catalyzed by Mo / NC-500 catalyst.

[0070]

[0071]

[0072] Examples 16-26

[0073] To optimize the reaction conditions of aromatic alcohols (synthesis method 2) in the synthesis of C=N-containing organic nitrogen-containing compounds by catalytic hydrogen transfer reduction coupling of nitrobenzene with alcohols, under different solvents, the catalyst Mo / NC-500 was used to catalyze the hydrogen transfer reduction coupling of benzyl alcohol to nitrobenzene to synthesize C=N-containing organic nitrogen-containing compounds. The steps are as follows:

[0074] 20 mg of Mo / NC-500 catalyst, 10 mL of solvent, 1 mmol of nitrobenzene, and 5 mmol of benzyl alcohol were added to a reaction vessel. After sealing, the air inside the reaction vessel was replaced with N2, and then the reaction was carried out at 200 °C for 8–18 h to obtain the hydrogen transfer reduction coupling product. The specific products obtained are shown in Table 3.

[0075] Table 3. Effect of different solvents on the products of the hydrogen transfer reduction coupling of benzyl alcohol with nitrobenzene

[0076]

[0077]

[0078] The reaction time for Examples 16-20 was 8 hours; in Example 21, a represents a reaction temperature of 180°C; in Example 22, b represents a reaction time of 11 hours; in Example 23, c represents a reaction time of 24 hours; in Example 24, d represents a reaction time of 12 hours; in Example 25, e represents a reaction time of 20 hours; and in Example 26, f represents 3 mmol of benzyl alcohol and a reaction time of 18 hours.

[0079] As shown in Table 3, Examples 16-20, the optimal solvent for the catalytic preparation of the imine product is acetonitrile. In Example 22, extending the reaction time to 11 hours, with the amount of nitrobenzene added remaining constant, the selectivity of product 2 (benzylaniline, hereinafter the same, will not be repeated) was >99.0%. Furthermore, the catalyst also exhibited certain catalytic activity in other solvents. By extending the reaction time to 12-24 hours, product 2 with a selectivity >97.2% could also be obtained in tetrahydrofuran, toluene, and hexane solvents. Since acetonitrile solvent is cheaper than hexane, tetrahydrofuran, and toluene, and is also more environmentally friendly, the acetonitrile solvents used in Examples 19 and 22 were selected for practicality testing.

[0080] Example 26 investigated the effect of the amount of reducing agent on the reaction product. 3 mmol of benzyl alcohol was used as the reducing agent, and the reaction time was 18 h (under equal reducing agent ratios, 3 mmol of benzyl alcohol is required to reduce 1 mmol of nitrobenzene to 1 mmol of aniline). The rest of the reaction was the same as in Example 19. The selectivity of product 2 is shown in Table 3 of Example 26. With 3 mmol of benzyl alcohol, after 18 h of reaction, the selectivity of product 2 was 95.9%, meaning that 4.1% of product 1 was not further converted to product 2.

[0081] Examples 27-75

[0082] The synthetic method for preparing C=N bond-containing organic nitrogen-containing compounds by hydrogen transfer reduction coupling of alcohols with catalyst Mo / NC-500 in Examples 10 and 22 is as follows:

[0083] Synthesis Method 1: When the alcohol compound is a fatty alcohol, the catalyst Mo / NC-T, the alcohol compound and the nitro compound are added to the reaction vessel in a ratio of 20mg:10mL:1mmol. After sealing the reaction vessel, the air inside the reaction vessel is replaced with N2. Then, the reaction is carried out at 200℃ for a certain time to obtain an organic nitrogen-containing compound containing C=N bonds.

[0084] Synthesis Method 2: When the alcohol is an aromatic alcohol or a furan alcohol, the catalyst Mo / NC-T, solvent, nitro compound and alcohol are added to the reactor in a ratio of 20 mg: 10 mL: 1 mmol: 5 mmol. After sealing the reactor, the air inside the reactor is replaced with N2. Then, the reaction is carried out at 200 °C for a certain time to obtain an organic nitrogen-containing compound containing C=N bonds.

[0085] Synthesis Method 3: When the alcohol compound is a vicinal diol, the catalyst Mo / NC-T, solvent, nitro compound and alcohol compound are added to the reaction vessel in a ratio of 20 mg: 10 mL: 1 mmol: 10 mmol. After sealing the reaction vessel, the air inside the reaction vessel is replaced with N2. Then, the reaction is carried out at 200 °C for a certain time to obtain an organic nitrogen-containing compound containing C=N bonds.

[0086] The specific selection of nitro compounds and alcohols, reaction times, and target products are shown in Table 4. When the substrate is a nitro compound and an alcohol, the target product is an imine compound (as shown in Examples 10, 22, and 27-56 in Table 4). When the substrate is o-nitroaniline and an alcohol, the target product is a benzimidazole compound (as shown in Examples 57-65 in Table 4); when the substrate is o-nitrophenol / o-nitrothiophenol and an alcohol, the target product is a benzoxazole and benzothiazole compound (as shown in Examples 66-70 in Table 4); when the substrate is o-nitroaniline and an o-diol, the target product is a quinoxaline compound (as shown in Examples 71-75 in Table 4). Throughout the entire substrate selection range, the target product selectivity is >91.3%, demonstrating the wide availability of starting materials for the synthetic reactions of this invention.

[0087] Table 4. Effects of different types of nitro compounds and alcohols on the target product of hydrogen transfer reduction coupling reaction.

[0088]

[0089]

[0090]

[0091]

[0092] In Examples 10, 27-30, 56-59, 64-66, and 69, the fatty alcohol was used as both a reducing agent and a solvent. In Examples 22, 31-55, 60-63, 67, 68, and 70, 'a' indicates that the solvent was acetonitrile and the amount of the reducing alcohol compound was 5 mmol. In Examples 71-75, 'b' indicates that the solvent was acetonitrile and the amount of the reducing alcohol compound was 10 mmol.

[0093] Examples 76-85

[0094] The most important advantage of heterogeneous catalysts is their recyclability. Since Example 6 shows the distribution of intermediate product (product 1) and target product (product 2), to better study the catalytic stability of the Mo / NC-500 catalyst, the stability of the catalyst was studied based on the hydrogen transfer reduction coupling of alcohols with nitro compounds to synthesize C=N-containing organic nitrogen-containing compounds using the Mo / NC-500 catalyst in Example 6. The steps were as follows:

[0095] 20 mg of catalyst Mo / NC-500, 10 mL of ethanol, and 1 mmol of nitrobenzene were added to a reactor. After sealing, the air inside the reactor was replaced with N2, and the reaction was carried out at 200 °C for 5 h to obtain the hydrogen transfer reduction coupling product. After the reaction, the catalyst Mo / NC-500 was collected by centrifugation and washed with water and ethanol 3-5 times each. This method was used to recover the catalyst after each repetition. After recovery, the catalyst was weighed, and the recovery rate was >95% each time. The recovered catalyst was directly used for the next synthesis reaction. The above steps were repeated (since there is less than 5% loss of the recovered catalyst after each use, the amount of other reactants used was reduced proportionally according to the weight of the recovered catalyst relative to the initial 20 mg). The conversion rate and selectivity of each use are shown in Table 5 below. Offline analysis was performed by gas chromatography. The selectivity of aniline and imine was determined. The test results showed that the catalytic activity of catalyst Mo / NC-500 did not decrease significantly after 10 cycles, indicating that the catalyst was stable.

[0096] Table 5. Cyclic experiments for the synthesis of C=N-containing organic nitrogen compounds from catalytic hydrogen transfer reduction coupling of ethanol and nitrobenzene.

[0097]

[0098]

Claims

1. A method for synthesizing C=N bond-containing organic nitrogen-containing compounds by catalytic hydrogen transfer reduction coupling of alcohol compounds with nitro compounds under conditions without added alkali, wherein the raw materials in the method include nitro compounds and alcohol compounds, characterized in that, The alcohols are fatty alcohols, aromatic alcohols, furans, or vicinal diols; the catalyst used in the synthesis method is a molybdenum trioxide-based catalyst, wherein the catalyst uses MoO3 as the active site and nitrogen-doped carbon material as the support, characterized in that the Mo content is 8.6-16.4 wt.%; The molybdenum trioxide-based catalyst is prepared by the following method: urea, ammonium molybdate tetrahydrate, chitosan and acetic acid are dissolved sequentially in distilled water, and after stirring and mixing, a uniform semi-transparent paste is obtained. The obtained semi-transparent paste is dried at 60-100℃ to obtain a white powder of urea-ammonium molybdate-chitosan-acetic acid complex. The white powder is used as a Mo precursor and pyrolyzed in a tube furnace at 450-600℃ under N2 atmosphere to prepare the catalyst.

2. The synthesis method according to claim 1, characterized in that, The preparation method of the molybdenum trioxide-based catalyst includes the following steps: Step (1): Dissolve urea and ammonium molybdate tetrahydrate in distilled water, and then add chitosan to the above solution with stirring; after the chitosan is completely dispersed, quickly add acetic acid and stir to obtain a uniform semi-transparent paste; dry the obtained semi-transparent paste at 60-100 °C to obtain a white powder of urea-ammonium molybdate-chitosan-acetic acid complex, which serves as a Mo precursor; Step (2): Place the Mo precursor obtained in step (1) above in a tube furnace and heat it from room temperature to a target temperature of 450-600 ℃ at a heating rate of 1-3 ℃ / min under a nitrogen atmosphere. Then maintain the target temperature for 1-3 h, stop heating, and allow it to cool naturally to room temperature to obtain a black powder. The black powder is the molybdenum trioxide-based catalyst.

3. The synthesis method according to claim 1 or 2, characterized in that, The ratio of urea, ammonium molybdate tetrahydrate, distilled water, chitosan, and acetic acid is 48-300 g: 1-4 g: 40-160 mL: 4-16 g: 4-16 mL.

4. The synthesis method according to claim 3, characterized in that, The ratio of urea, ammonium molybdate tetrahydrate, distilled water, chitosan, and acetic acid is 96 g: 2 g: 80 mL: 8 g: 8 mL.

5. The synthesis method according to claim 2, characterized in that, In step (1), the drying process is air drying; the drying temperature is 80℃ and the drying time is 6-24 h.

6. The synthesis method according to claim 5, characterized in that, The drying time is 12 hours.

7. The synthesis method according to claim 2, characterized in that, In step (2), the heating rate in the tubular furnace is 2℃ / min, the target temperature is 500℃, and the holding time is 2 h.

8. The synthesis method according to claim 1, characterized in that, Includes the following steps: When the alcohol compound is a fatty alcohol, the catalyst, fatty alcohol and nitro compound are added to the reaction vessel in a ratio of 5-100 mg: 10-40 mL: 1-10 mmol. After sealing the reaction vessel, the air inside the reaction vessel is replaced with N2. Then, the reaction is carried out at 170-220℃ to obtain the organic nitrogen-containing compound containing C=N bonds. When the alcohol compound is an aromatic alcohol or furan alcohol, the catalyst, solvent, nitro compound, aromatic alcohol or furan alcohol are added to the reaction vessel in a ratio of 5-100 mg: 10-40 mL: 1-10 mmol: 3-50 mmol. After sealing the reaction vessel, the air inside the reaction vessel is replaced with N2, and then the reaction is carried out at 170-220℃ to obtain the organic nitrogen-containing compound containing C=N bonds. When the alcohol compound is a vicinal diol, the catalyst, solvent, nitro compound and vicinal diol are added to the reaction vessel in a ratio of 5-100 mg: 10-40 mL: 1-10 mmol: 10-100 mmol. After sealing the reaction vessel, the air inside the reaction vessel is replaced with N2, and then the reaction is carried out at 170-220°C to obtain the organic nitrogen-containing compound containing C=N bonds.

9. The synthesis method according to claim 1, characterized in that, When the alcohol compound is a fatty alcohol, the fatty alcohol acts as both a solvent and a reducing agent; When the alcohol compound is an aromatic alcohol, furan alcohol, or vicinal diol, the aromatic alcohol, furan alcohol, or vicinal diol is used only as a reducing agent. The raw materials also include a solvent, which is at least one of hexane, toluene, tetrahydrofuran, acetonitrile, and water.

10. The synthesis method according to claim 9, characterized in that, When the alcohol compound is an aromatic alcohol, furan alcohol, or vicinal diol, the raw material also includes a solvent, wherein the solvent is acetonitrile.

11. The synthesis method according to any one of claims 8-10, characterized in that: The nitro compound has one of the following structural formulas:

12. The synthesis method according to any one of claims 8-10, characterized in that: The alcohol compounds have one of the following structural formulas:

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