Preparation method of novel polyacid catalyst and application of novel polyacid catalyst in green catalysis of aldehyde and indole reaction

Abstract

The invention belongs to the technical field of catalysts, and provides a novel polyacid catalyst of which the molecular formula is [(CH3) 2NH2] 9 [SbIII3 (A-alpha-PW9O34) 2]. 7H2O. The polyacid catalyst is prepared by mixing and dissolving sodium dihydrogen phosphate, dimethylamine hydrochloride and Na9 [SbW9O33]. 19.5 H2O according to a certain proportion in water and reacting under a water bath condition. Under the reaction conditions of normal temperature, normal pressure and no solvent, the application of the catalyst to synthesis of diaryl methane and derivatives thereof by green catalysis of aldehyde and indole reaction is studied.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to a method for preparing a novel polyacid catalyst and its application in the green catalytic reaction of aldehydes and indole. Background Technology

[0002] The synthesis of indole and its derivatives, more specifically bis(indole)methanes (BIMs), has been a hot research topic in organic chemistry due to the range of interesting biological and pharmacological properties these compounds possess. Naturally occurring in cruciferous vegetables, BIMs have been shown to be effective antifungal, antibacterial, anti-inflammatory, and even anticancer agents. Traditionally, the synthesis of BIMs has involved the acidic condensation of aldehydes with indole using various protic or Lewis acids. However, due to increased environmental awareness, the focus has shifted to the development of greener synthetic technologies.

[0003] Polyoxometalates (POMs) are a class of polynuclear metal-oxygen clusters composed of oxides of early transition metals, including vanadium (V), molybdenum (Mo), tungsten (W), niobium (Nb), and tantalum (Ta). Due to their excellent physical and chemical properties, POMs have been widely used in proton conductors, catalysis, and medicine. Their tunable acidity, thermal stability, and unique chemoselectivity and regioselectivity have led to their extensive application in acid-catalyzed reactions. Existing literature reports studies using POMs as solid acid catalysts to catalyze the reaction of aldehydes with indole to produce BIMs. In 2004, Zolfigol et al. used H3PMo… 12 O 40 Using ~xH₂O as a solid acid catalyst, the reaction was carried out in DMSO at 120 °C for 1 hour, achieving a 93% yield of the target product. In 2011, Tayebee et al. used H₆P₂W 18 O 62 • 24H2O (Dawson type) serves as a highly efficient, water-resistant, and environmentally friendly heteropolyacid catalyst, catalyzing the electrophilic substitution reaction of indole with various aldehydes and ketones under solvent-free conditions at 120 °C to generate the corresponding di(indole)methane derivatives with a yield of 78%. In 2023, Giagani Vassan et al. developed a light-assisted synthesis method for BIMs, achieving yields exceeding 90% in a short reaction time using water as a solvent. However, most existing reported methods for synthesizing diarylmethanes using polyacids require unsuitable solvents and high temperatures. Therefore, developing a mild and green method for the synthesis of diarylmethanes is essential. Based on this, this application was developed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a novel, mild, and green method for preparing polyacid catalysts and their application in the green catalytic reaction of aldehydes and indole to synthesize diarylmethane compounds.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A novel polyacid catalyst with the chemical formula [(CH3)2NH2]9[Sb III 3(A-α-PW9O 34 [2]·7H2O. This polyacid catalyst belongs to the triclinic crystal system, space group [missing information]. P-1 Cell parameters a = 11.9516(2) Å, b = 16.5658(4) Å, c = 22.0910(4) Å, V = 4088.16(14) Å3, Z =2, R 1 = 0.0469, wR 2 = 0.1089 .

[0006] The preparation method of the above-mentioned novel polyacid catalyst includes the following steps: Sodium dihydrogen phosphate, dimethylamine hydrochloride, and Na₂[SbW₁O] 33 19.5H2O is dissolved in distilled water and stirred at room temperature (approximately 10-30 min). The pH is adjusted to 2.0-2.5, and then heated at 85 ± 5 ℃ for 1.5-2 h. After the reaction is complete, the mixture is cooled and filtered. Colorless blocky crystals precipitate from the filtrate, which is the novel polyacid catalyst.

[0007] Among them, the polyacid precursor Na9[SbW9O] 33 ]·19.5H2O can be prepared according to the literature (M. Boesing, I. Loose, H. Pohlmann, et al. Chemistry - A European Journal, 1997,3(43):1232-1237).

[0008] Specifically, sodium dihydrogen phosphate, dimethylamine hydrochloride, and Na₂[SbW₁₉O₂] 33 The molar ratio of 19.5H2O is 7-8:58-59:2. More preferably, sodium dihydrogen phosphate, dimethylamine hydrochloride, and Na₂[SbW₂O]₂ are used. 33 The ratio of 19.5H2O to water is 0.12 g: 0.48 g: 0.56 g: 20 mL.

[0009] Furthermore, the pH value can be adjusted to maintain at 2.0-2.5 by adding 1-3 mol / L HCl.

[0010] This invention also provides the application of the above-mentioned novel polyacid catalyst in the green catalytic reaction of aldehydes and indole.

[0011] A second objective of this invention is to provide a method for preparing diarylmethane compounds, which involves reacting an aldehyde with an indole under solvent-free conditions using the aforementioned polyacid catalyst. The general formulas (a and b) of the reaction substrates aldehyde and indole are as follows: R1 includes the aliphatic aldehydes and aromatic aldehydes mentioned in Application Example 13, and R2 includes indoles with different substituents mentioned in Example 14.

[0012] Furthermore, the molar ratio of the polyacid catalyst to the aldehyde is 0.02-0.03:1.

[0013] Furthermore, the reaction temperature is 20-25 °C, and the reaction time is 20-30 min.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention is the first to synthesize a novel polyacid catalyst using a water bath method, with the molecular formula [(CH3)2NH2]9[Sb III 3(A-α-PW9O 34 The structure of the phosphotungsten carbide (α- ... Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 These are schematic diagrams of the ball-and-stick (left) and polyhedral (right) structures of the polyacid catalyst anion. This indicates that through three Sb... 3+ Ions are inserted into two triple-vacant [A-α-PW9O] 34 ] 9- The building blocks form sandwiched dimer anions; Figure 2 It is the hydrogen bond network of the polyacid catalyst along the a-axis direction; Figure 3 This is the infrared spectrum of the polyacid catalyst; Figure 4This is the X-ray powder diffraction pattern of the polyacid catalyst; Figure 5 The thermogravimetric analysis (TGA) curve of the polyacid catalyst is shown. Figure 6 The yields of diarylmethane produced from aldehydes and indole by the polyacid catalyst with different loadings; Figure 7 The yields of the polyacid catalyst catalyzing the formation of diarylmethane from aldehydes and indole at different reaction times are: Figure 8 The yield of the polyacid catalyst after four cycles under the conditions of Application Example 1 is shown. Figure 9 The infrared spectrum of the recovered sample after the polyacid catalyst was used as a catalyst for aldehydes and indole four times. Figure 10 The X-ray powder diffraction pattern of the sample after the polyacid catalyst was used as a catalyst for aldehydes and indole four times. Figure 11 This is a hypothetical mechanism for the synthesis of diarylmethane catalyzed by the polyacid catalyst. Specific implementation methods Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0016] It should be understood that the terminology used in this invention is for describing particular embodiments only and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0017] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of the invention. Various modifications and variations to the specific embodiments described in this specification are apparent to those skilled in the art without departing from the scope or spirit of the invention. Other embodiments derived from this specification will be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0018] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0019] Generally, antimony ions are often used as heteroanions in polyoxometalates, with only a few reported as sandwich units. A sandwich phosphotungstic acid salt [(CH3)2NH2]9[Sb] was successfully developed using a conventional aqueous solution synthesis method. III 3(A-α-PW9O 34 [2]·7H2O. Structural analysis shows that the polyacid catalyst is produced via antimony ions (Sb ions)... 3+ ) and triple-vacant phosphotungstate [PW9O 34 ] 9- The units are interconnected to form a sandwich structure. The polyacid catalyst possesses abundant hydrogen bonds and converts aldehydes and indoles to 3,3'-(phenylmethylene)bis(1... H The reaction of (-indole) exhibits catalytic activity. The catalytic yield of the polyacid catalyst reaches 91.0%, which is far superior to that of the classic triple-vacant Keggin-type {PW9}. In addition, the polyacid catalyst shows good activity and reliability in catalyzing similar reactions with different substrates.

[0020] Unless otherwise specified, "room temperature" in this invention refers to 20-25°C.

[0021] The technical solution of the present invention will be further illustrated by the following embodiments.

[0022] In the following embodiments: 1. Unless otherwise stated, all other reagents are of analytical grade and can be used directly without further purification.

[0023] 2. Powder X-ray diffraction (PXRD) analysis was performed on a Bruker D8 ADVANCE diffractometer using Cu Kα radiation at a scan rate of 5 ° / min.

[0024] 3. Thermogravimetric analysis (TGA) was performed on a NETZSCH STA 449 F5 instrument under flowing nitrogen conditions, with a temperature range of 30 to 1000 °C, a heating rate of 10 °C / min, and a nitrogen flow rate of 25 mL / min.

[0025] 4. Fourier transform infrared (FT-IR) spectra were acquired on a Bruker Vertex 70 spectrometer using the potassium bromide pellet method, with a acquisition range of 400 to 4000 cm⁻¹.

[0026] 6. Nuclear magnetic resonance (NMR) spectra were performed on a Bruker AVANCE NEO 500 spectrometer using deuterated chloroform and tetramethylsilane as an internal standard.

[0027] 7. Single-crystal X-ray diffraction (SCXRD) analysis was performed on a Bruker D8 VENTURE single-crystal diffractometer using graphite-monochromated Mo Kα radiation at 150 K. 8. Absorption correction was performed using the SADABS multi-scan absorption correction program.

[0028] 9. Using Olex2 software, the structure is analyzed using the direct method through the ShelXT structure parser, and then refined using the least squares method through the ShelXL refinement software package.

[0029] Example 1 A novel polyacid catalyst with the molecular formula [(CH3)2NH2]9[Sb III 3(A-α-PW9O 34 )2]·7H2O.

[0030] The preparation method of the above-mentioned novel polyacid catalyst includes the following steps: 1) Add sodium dihydrogen phosphate (0.12 g, 0.77 mmol), a polyacid precursor, and Na₂[SbW₁₉O₂]₂ to the solution. 33 19.5H2O (0.56 g, 0.20 mmol) and dimethylamine hydrochloride (0.48 g, 5.88 mmol) were dissolved in 20 mL of distilled water. After stirring for 15 min, the pH was adjusted to 2.5 with 1 mol / L HCl aqueous solution and stirred at room temperature for 20 min. 2) Place the solution obtained in step 1) into a 90°C water bath and heat with stirring for 2 hours. After the reaction is complete, remove the solution, cool it to room temperature, filter it, and allow the filtrate to stand and slowly evaporate for three weeks to precipitate colorless blocky crystals, which are the novel polyacid catalyst based on Na9[SbW9O] 33 The yield of the novel polyacid catalyst was 56.1% after the reaction of 19.5H2O.

[0031] The crystal structure of the polyacid catalyst prepared in Example 1 was determined and characterized using X-ray single-crystal diffraction technology. Its unit cell parameters are as follows: triclinic system, space group [missing information]. P -1 Cell parameters a = 11.9516(2)Å, b = 16.5658(4) Å, c = 22.0910(4) Å, V = 4088.16(14) Å3 , Z =2, R 1 = 0.0469 wR 2 = 0.1089. Under solvent-free conditions, without the need for an additional energy source, diarylmethane and its derivatives can be synthesized efficiently from aldehydes and indoles.

[0032] Figure 1 This is a schematic diagram of the ball-and-stick structure of the polyacid catalyst anion. The diagram shows the effect of three Sb atoms. 3+ Ions are inserted into two triple-vacant [A-α-PW9O] 34 ] 9- The target product is a sandwich-shaped dimer anion formed from building blocks.

[0033] Figure 2 This is the hydrogen bond network of the polyacid catalyst along the a-axis, as shown in the figure [(CH3)2NH2]. + The ions have a dual function: they can balance the negative charge of the polyanions and promote the formation of NH···O hydrogen bonds. Each [Sb III 3(A-α-PW9O 34 )2] 9− The unit passes through nine [(CH3)2NH2] + The ions bind to the anions of the six adjacent polyacid catalysts (Figure 2).

[0034] Figure 3 The infrared spectrum of the polyacid catalyst is shown in Figure 3. In the mid-wavenumber region, a distinct absorption peak is observed at 1586 cm⁻¹, attributed to the OH bending vibration of the lattice and coordinated water molecules, while the weak peak at 1465 cm⁻¹ corresponds to the CH bending vibration of the [(CH₃)₂NH₂]⁺ cation. In the low-wavenumber region (ν < 1000 cm⁻¹), five characteristic vibrational peaks are observed at 1071, 1036, 954, 886, and 739 cm⁻¹, with the peaks at 1071 and 1036 cm⁻¹ attributed to P. V -O vibration, while the peaks of 954, 886 and 739 correspond to the WO at the end, respectively. t WO shared by corners b WO shared with the side c vibration.

[0035] Figure 4 This is the X-ray powder diffraction pattern of the polyacid catalyst, from... Figure 4 It can be seen that the synthesized polyacid catalyst has high purity.

[0036] Figure 5 This is the thermogravimetric analysis (TGA) curve of the polyacid catalyst. From... Figure 5 It can be seen that the first stage of weight loss of the polyoxometalate catalyst corresponds to the loss of water of crystallization. A second weight loss occurred between 345-1000 °C, with a weight loss rate of 15.78%, which is attributed to the loss of nine [(CH3)2NH2]⁺ cations, accompanied by the collapse of the polyoxometalate skeleton.

[0037] Elemental analysis of the polyacid catalyst revealed: M = 5347.24 g·mol⁻¹ -1 Calculated values ​​(%): C, 4.00; N, 2.36; H, 1.61. Measured values: C, 3.86; N, 2.30; H, 1.77. Based on thermogravimetric and elemental analysis results, the structural formula of the polyacid catalyst was determined to be [(CH3)2NH2]9[Sb III 3(A-α-PW9O 34 )2]·7H2O.

[0038] Application Example 1 The polyacid catalyst was used to catalyze the synthesis of diarylmethane and its derivatives, with benzaldehyde and indole selected as model substrates. As shown in Table 1, benzaldehyde and indole reacted at room temperature for 20 minutes under solvent-free conditions to produce 3,3'-(phenylmethylene)bis(1 H -indole), the reaction equation is as follows ( Figure 11 (This is a hypothesized possible mechanism for the synthesis of diarylmethanes).

[0039] The specific steps are as follows: 0.1 mmol of benzaldehyde, 0.2 mmol of indole, and 13 mg (0.0025 mmol) of the aforementioned polyacid catalyst are reacted at room temperature for 20 minutes to generate 3,3'-(phenylmethylene)bis(1 H -Indole), with a yield of 91.0%.

[0040] Application Example 2-12 Similar to Application Example 1, the differences are shown in Table 1. Table 1 Optimization of reaction conditions Note: Yield b was obtained by proton NMR spectroscopy (NMR spectroscopy). 1 HNMR determination; "-" indicates no addition; "{PW9}" refers to Na9[PW9O] 34 ].

[0041] As shown in Table 1, excellent results were achieved in solvents such as methanol and dichloromethane when screening with various common organic and green solvents (with the polyacid catalyst loaded at 2.5 mol%). The control reaction without a catalyst yielded almost no product. Under optimized conditions, Na9PW9O... 34 No product was formed when 7H₂O was used as a catalyst. When Sb₂O₃ was used as a catalyst, the product yield was only 9%. When dimethylamine hydrochloride was used as a catalyst, the product yield was only 23%. This clearly demonstrates that the abundant hydrogen bonds formed between the dimethylamine cation and the polyacid anion are beneficial to the uniform distribution of protons, which can increase the efficiency of the catalytic reaction.

[0042] Application Example 13 The polyacid catalyst was tested using different substrates, and the experimental method was the same as in Application Example 1. The reaction substrates, reaction formulas, and product structures are shown below. The aldehyde compounds can be benzaldehyde, 4-fluorobenzaldehyde, 4-chlorobenzaldehyde, 3-chlorobenzaldehyde, 4-nitrobenzaldehyde, 4-methylbenzaldehyde, 3-methylbenzaldehyde, 3-methoxybenzaldehyde, 2-furanaldehyde, anthracene-9-carboxaldehyde, 2-naphthaldehyde, cyclohexylcarboxaldehyde, isovaleraldehyde, isobutyraldehyde, n-butyraldehyde, etc.

[0043] Application Example 14 The polyacid catalyst was tested using different substrates, and the experimental method was the same as in Application Example 1. The reaction substrates, reaction formulas, and product structures are shown below. The indole compounds can be 6-bromoindole, 2-methylindole, 6-methoxyindole, 2-phenylindole, N-methylindole, 1-phenylindole, etc.

[0044] As can be seen, except for the low yield of substrates with large steric hindrance, the yields of other products all exceeded 60%, indicating that the polyacid catalyst has good catalytic effect on various substrates. Furthermore, this invention proposes a reasonable reaction mechanism (Figure 11). Mechanistic studies show that the NH group of the polyacid catalyst and the carbonyl group of the aldehyde form a hydrogen-bonded active intermediate [I] through intermolecular hydrogen bonding. Subsequently, the indole undergoes electrophilic substitution at the C-3 position to generate intermediate [II]. Intermediate [II] undergoes hydrogen transfer and loses a water molecule to generate intermediate [III]. Finally, another indole molecule performs a nucleophilic attack on intermediate [III] to obtain the final diarylmethane product [IV].

[0045] Figure 6The yields of diarylmethane produced from aldehydes and indole catalyzed by the polyacid catalyst at different loadings were measured. The effect of the amount of polyacid catalyst added on the effect was investigated. Under the conditions of Application Example 1, when 2.5% of the catalyst was used and the reaction was continued for 20 minutes, diarylmethane was obtained in a yield of 91%. Increasing the amount of the polyacid catalyst added to 7.5% yielded a diarylmethane yield of 97%.

[0046] Figure 7 The yields of the polyacid catalyst catalyzing the formation of diarylmethane from aldehydes and indole at different reaction times are shown. To optimize the reaction time, the polyacid catalyst was subjected to reactions for 5, 10, 20, 40, and 60 minutes under the conditions of Application Example 1, with a loading of 2.5 mol% of the polyacid catalyst, yielding yields of 58%, 78%, 91%, 92%, and 93%, respectively.

[0047] Figure 8 This describes the yield of the polyacid catalyst after four cycles under the conditions of Application Example 1. The catalytic stability of the polyacid catalyst was tested by subjecting it to four cycles under the conditions of Application Example 1. Figure 8 It can be seen that the polyacid catalyst still has high catalytic stability after four cycles, and the yield of diarylmethane is 89% after four cycles.

[0048] Figure 9 The image shows the recovered FT-IR spectra of the samples after four repeated catalytic reactions using the polyacid catalyst as a catalyst for aldehydes and indole. The figures show that the polyacid catalyst exhibits similar FT-IR spectra before and after catalysis, indicating that the polyacid catalyst maintains structural stability after catalysis.

[0049] Figure 10 The image shows the X-ray powder diffraction pattern of the sample after the polyacid catalyst was used as a catalyst for aldehydes and indole four times. Figure 10 It can be seen that the PXRD patterns of the polyacid catalyst before and after catalysis have similar peak positions compared with the simulated XRD. The difference in peak intensity may be due to the different preferential orientation of the XRD peaks of the polyacid catalyst during the collection process.

Claims

1. A novel polyacid catalyst, characterized in that, The molecular formula of this polyacid catalyst is [(CH3)2NH2]9[Sb III 3(A-α-PW9O 34 [2]·7H2O; This novel polyacid catalyst belongs to the triclinic crystal system, space group [missing information]. P-1 Cell parameters a = 11.9516(2) Å, b = 16.5658(4) Å, c = 22.0910(4) Å, V = 4088.16(14) Å 3 , Z =2, R1 = 0.0469, wR 2 = 0.1089.

2. The method for preparing the novel polyacid catalyst according to claim 1, characterized in that, Includes the following steps: Sodium dihydrogen phosphate, dimethylamine hydrochloride, and Na₂[SbW₁O] 33 19.5H2O was dissolved in distilled water and stirred at room temperature. The pH was adjusted to 2.0-2.5, and then heated at 85 ± 5 ℃ for 1.5-2 h. After the reaction was completed, the mixture was cooled and filtered. Colorless blocky crystals precipitated from the filtrate, which is the novel polyacid catalyst.

3. The preparation method of the novel polyacid catalyst as described in claim 2, characterized in that, Sodium dihydrogen phosphate, dimethylamine hydrochloride and Na₂[SbW₁O₂] 33 The molar ratio of 19.5H2O is 7-8:58-59:

2.

4. The preparation method of the novel polyacid catalyst as described in claim 1, characterized in that, The pH value was adjusted to be maintained at 2.0-2.5 by adding 1-3 mol / L HCl dropwise.

5. The application of the novel polyacid catalyst of claim 1 in the green catalytic reaction of aldehydes and indole.

6. A method for preparing a diarylmethane compound, characterized in that, Under solvent-free conditions, the novel polyacid catalyst described in claim 1 is used as a catalyst to catalyze the reaction of aldehydes and indole to generate diarylmethane compounds.

7. The method for preparing the diarylmethane compound as described in claim 6, characterized in that, The molar ratio of the polyacid catalyst to the aldehyde is 0.02-0.03:

1.

8. The method for preparing the diarylmethane compound as described in claim 6, characterized in that, The reaction temperature is 20-25 °C, and the reaction time is 20-30 min.

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