CN118165014B - Preparation method and application of ionic zinc catalyst - Google Patents

Abstract

The invention discloses a method for preparing an ionic zinc catalyst. The method comprises placing salicylaldehyde, tetraethylenepentamine, zinc bromide and methanol in a round-bottom flask for reaction. After the reaction is completed, the reaction is filtered and the filtrate is slowly volatilized to obtain crystals of the ionic zinc catalyst. The method of the invention has the advantages of fast reaction speed, simple reaction process, high purity of the obtained product and simple post-processing. In the carbon dioxide cycloaddition reaction, the conversion rate is as high as 99% and the selectivity is as high as 99%.

Description

Preparation method and use of ionic zinc catalyst

Technical Field

The invention belongs to the technical field of catalyst material preparation, and relates to the preparation technology of ionic zinc catalyst.

Technical Background

Carbon dioxide is a typical greenhouse gas. Excessive emissions of carbon dioxide in recent years are the main cause of global warming. Therefore, the capture and storage of carbon dioxide has become a focus of chemists. However, its capture and storage in underground rock formations may lead to further geological and environmental degradation. Therefore, a practical solution is to convert carbon dioxide into high-value-added organic compounds. Among the many examples of catalytic conversion of carbon dioxide, the cycloaddition of carbon dioxide to form cyclic carbonates is one of the most successful routes. Since cyclic carbonates have a wide range of applications, they can be used as electrolyte solvents for lithium-ion batteries, excellent organic solvents and dye additives, and can replace a variety of other toxic chemical reagents. A variety of catalytic systems have been reported, such as alkali metal salts, onium salts, metal complexes, ionic liquids, metal oxides, and some solid-supported catalysts. However, most catalytic systems have the disadvantages of using halogen-containing catalysts, requiring co-catalysts or solvents, which in turn cause environmental pollution problems (Jianwen Li, et al, J. CO ₂ Util. 69 (2023) 102384. Dr. Kazuto Takaishi, et al, Angew. Chem. Int. Ed. 58 (2019) 9984-9988.), therefore, from the perspective of environment and economy, it is of great significance to develop greener catalysts. In the past few decades, the design and evaluation of homogeneous catalysts and heterogeneous catalysts have made some progress. Considering practical applications, heterogeneous catalysts that are easy to recycle and reuse have received more favor. Metal complexes have attracted widespread attention as CO ₂ cycloaddition reaction catalysts due to their special advantages such as low cost, low toxicity, and the ability to adjust the structure according to specific requirements.

Based on the above literature and the development concept of green chemistry, it is very necessary to design an environmentally friendly ionic zinc efficient catalytic system for the cycloaddition of carbon dioxide to form cyclic carbonates.

Through searching, no published patent documents related to the present invention application have been found.

Summary of the invention

The purpose of the present invention is to solve the problems of halogen in the catalyst and large amount of catalyst in the catalytic conversion of carbon dioxide cycloaddition reaction. A one-pot method for preparing a single-component catalyst of an ionic zinc catalyst is provided, so as to play a synergistic catalytic role in the carbon dioxide cycloaddition reaction and achieve the goal of realizing carbon dioxide cycloaddition under the action of a relatively low amount of a single-component catalyst.

The design ideas of the present invention are as follows:

1. The zinc halide and organic ligand are synthesized in situ by a one-pot method to construct a zinc complex, which synergistically catalyzes the carbon dioxide cycloaddition at multiple active sites during the reaction process;

2. The ionic multi-site catalyst is synthesized by reacting zinc halide with salicylaldehyde and tetraethylenepentamine in the presence of methanol. The [ZnBr ₄ ] ^2- active site in the catalyst plays a role in the ring opening of the epoxide compound during the catalytic process, and the N active site in the ligand is used to absorb carbon dioxide.

3. Apply ionic multi-site single-component catalysts with clear structures to the cycloaddition reaction of carbon dioxide to achieve the goal of obtaining cyclic carbonates with high carbon dioxide conversion rate and high selectivity.

The crystal structure information of this type of catalyst was obtained by the following method:

The crystals of ionic multi-site single-component catalysts were synthesized by conventional solvothermal method. The specific experimental method is described as follows:

In a clean round-bottom flask, salicylaldehyde and tetraethylenepentamine are added in sequence and mixed with the solvent, and the mixture is refluxed and stirred at 60-100°C for 2-6 hours, and then zinc halide is added, and the mixture is stirred for another 2 hours, and then filtered while hot, and the filtrate is allowed to stand at room temperature for 2-4 weeks to evaporate slowly, thereby obtaining [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH, with a yield of about 30-50%.

The preferred solution is that the molar ratio of salicylaldehyde:tetraethylenepentamine:Zn(OAc) ₂ is 0.5-2.5:0.17-0.85:0.33-1.65, and the solvent used is methanol.

The product was characterized by single crystal X-ray diffraction and powder X-ray diffraction to obtain accurate information about the crystal structure. The specific results are as follows:

The molecular formula of the crystal is [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH, in which the cation part is a binuclear Zn2 unit located at the center of the positive ion structure framework. Due to the flexibility of the N5O3 ligand and the presence of multiple coordination sites, two different coordination modes are observed for the Zn atom. The anion is a [ZnBr ₄ ] ^2- unit, and the two are combined together by the electrostatic attraction between the anion and the cation. Through structural analysis, it is found that this type of catalyst contains two active centers, one is the [ZnBr ₄ ] ^2- active site, and the other is the binuclear Zn2 unit active site. Both contribute to the carbon dioxide cycloaddition reaction. [ZnBr ₄ ] ^2- can provide an environment for the ring opening of the epoxide compound, and the binuclear Zn2 unit provides a catalytic center for the carbon dioxide cycloaddition reaction, which is expected to play a synergistic catalytic role.

This invention is mainly to synthesize a carbon dioxide cycloaddition ionic zinc single-component catalyst, which has been applied to carbon dioxide cycloaddition reactions. This type of catalyst can achieve carbon dioxide cycloaddition reactions without solvent or catalyst, with a conversion rate of up to 99% and a selectivity of up to 100%. The preparation method of this type of catalyst has a simple reaction process.

The above-mentioned cyclic compounds are epichlorohydrin, epibromohydrin, epoxystyrene, etc. The conversion rate and selectivity are detected by gas chromatography.

The objective of the present invention is achieved through the following technical solutions:

Its molecular structure is:

The molecular formula is: [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

The single-component dual-active-center catalyst provided by the present invention has the following characteristics:

1. The preparation method is simple and the catalysts have clear molecular structures, which is conducive to studying the mechanism of catalytic reactions.

2. The catalyst has [ZnBr4] ^2- and binuclear Zn2 unit active sites, which can play a synergistic catalytic role in the carbon dioxide cycloaddition.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. Schematic diagram of the crystal structure of the compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH (for clarity of the structure, hydrogen atoms and water solvent molecules are removed);

Figure 2. RXRD characterization of compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH, where the upper line is the synthesized sample and the lower line is the simulated sample.

Table 2. List of the results of the cycloaddition of compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH to carbon dioxide.

DETAILED DESCRIPTION

Specific Example 1: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

In a clean round-bottom flask, salicylaldehyde (2.5 mmol) and tetraethylenepentamine (0.85 mmol) were added in sequence and mixed with MeOH (10 mL), and refluxed and stirred at 80°C for 4 h, then zinc bromide (1.65 mmol) was added, and stirred for another 2 h, and filtered while hot, and the resulting solution was allowed to stand at room temperature for 2 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 50%.

Specific Example 2: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

In a clean round-bottom flask, salicylaldehyde (2.5 mmol) and tetraethylenepentamine (0.68 mmol) were added in sequence and mixed with MeOH (10 mL), and refluxed and stirred at 80°C for 4 h, then zinc bromide (1.65 mmol) was added, and stirred for another 2 h, and filtered while hot, and the resulting solution was allowed to stand at room temperature for 3 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 37%.

Specific Example 3: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

In a clean round-bottom flask, salicylaldehyde (2 mmol) and tetraethylenepentamine (0.68 mmol) were added in sequence and mixed with MeOH (10 mL), and refluxed and stirred at 80°C for 4 h, then zinc bromide (1.65 mmol) was added, and stirred for another 2 h, and filtered while hot, and the resulting solution was allowed to stand at room temperature for 4 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 30%.

Specific Example 4: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

Salicylaldehyde (0.50 mmol) and tetraethylenepentamine (0.17 mmol) were added to a clean round-bottom flask in sequence, mixed with MeOH (10 mL), refluxed and stirred at 80°C for 4 h, then zinc bromide (0.11 mmol) was added, stirred for another 2 h, filtered while hot, and the resulting solution was allowed to stand at room temperature for 4 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 32%.

Specific Example 5: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

In a clean round-bottom flask, salicylaldehyde (2.5 mmol) and tetraethylenepentamine (0.68 mmol) were added in sequence and mixed with MeOH (10 mL), and refluxed and stirred at 80°C for 4 h, then zinc bromide (0.55 mmol) was added, and stirred for another 2 h, and filtered while hot, and the resulting solution was allowed to stand at room temperature for 4 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 38%.

Specific Example 6: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

In a clean round-bottom flask, salicylaldehyde (2 mmol) and tetraethylenepentamine (0.68 mmol) were added in sequence and mixed with MeOH (10 mL), and refluxed and stirred at 80°C for 4 h, then zinc bromide (1.65 mmol) was added, and stirred for another 2 h, and filtered while hot, and the resulting solution was allowed to stand at room temperature for 2 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 43%.

Specific Example 7: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

Salicylaldehyde (2.5 mmol) and tetraethylenepentamine (0.85 mmol) were added to a clean round-bottom flask in sequence, and the mixture was mixed with MeOH (10 mL). The mixture was refluxed and stirred at 100°C for 4 h, and then zinc bromide (1.65 mmol) was added, and the mixture was stirred for another 2 h. The mixture was filtered while hot, and the resulting solution was allowed to stand at room temperature for 2 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 39%.

Specific Example 8: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

In a clean round-bottom flask, salicylaldehyde (2.5 mmol) and tetraethylenepentamine (0.85 mmol) were added in sequence and mixed with MeOH (10 mL), and refluxed and stirred at 60°C for 4 h, then zinc bromide (1.65 mmol) was added, and stirred for another 2 h, and filtered while hot, and the resulting solution was allowed to stand at room temperature for 3 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 42%.

Specific Example 9: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

In a clean round-bottom flask, salicylaldehyde (2.5 mmol) and tetraethylenepentamine (0.85 mmol) were added in sequence and mixed with MeOH (10 mL), and refluxed and stirred at 80°C for 2 h, then zinc bromide (1.65 mmol) was added, and stirred for another 2 h, and filtered while hot, and the resulting solution was allowed to stand at room temperature for 2 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 45%.

Specific Example 10: Preparation of Compound [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

In a clean round-bottom flask, salicylaldehyde (2.5 mmol) and tetraethylenepentamine (0.85 mmol) were added in sequence and mixed with MeOH (10 mL), and refluxed and stirred at 80°C for 6 h, then zinc bromide (1.65 mmol) was added, and stirred for another 2 h, and filtered while hot, and the resulting solution was allowed to stand at room temperature for 2 weeks to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH. The yield was 50%.

As shown in Table 1, the crystallographic data of the compound [[Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH

Specific Example 11: Application of Ionic Zinc Catalyst Single Component Catalyst to Carbon Dioxide Cycloaddition Reaction

example:

5 mmol of epoxy compound was placed in a 20 mL reactor, and 0.05 mmol of catalyst was added. 2 MPa of carbon dioxide was introduced and heated and stirred while maintaining the temperature at 100 degrees Celsius. After 4 hours of reaction, the epoxy compound in the reaction solution was detected by gas chromatography. The specific data are shown in Table 2. Results of the cycloaddition reaction of compound [Zn2(L)]2[ZnBr4]·4CH3OH on epoxy compound:

Claims (2)

1. A method for preparing an ionic zinc catalyst, characterized in that: the steps are: adding salicylaldehyde and tetraethylenepentamine and a solvent to a clean round-bottom flask in sequence, mixing, reflux stirring at a certain temperature, then adding zinc halide, stirring for 2 hours, then filtering while hot, and standing the filtrate at room temperature for 2-4 weeks to slowly volatilize to obtain [Zn ₂ (L)] ₂ [ZnBr ₄ ]·4CH ₃ OH, wherein L is a ligand, and the structural formula is as follows: ; The molar ratio of salicylaldehyde: tetraethylenepentamine: Zn(OAc) ₂ is 0.5~2.5: 0.17~0.85:0.33~1.65, the solvent used is methanol, the reaction temperature is 60~100°C, and the reflux stirring time is 2~6h. 2. Use of the ionic zinc catalyst obtained by the preparation method as claimed in claim 1 in catalyzing carbon dioxide cycloaddition reaction.