Salen metal complex material containing imidazolyl ionic liquid and pyridine ring

Abstract

The invention discloses preparation and application of a Salen metal complex material containing imidazolyl ionic liquid and a pyridine ring (MVIM-Salen), and belongs to the technical field of synthesis of ionic liquid metal complex catalytic materials. According to the method, salicylaldehyde containing imidazolyl ionic liquid and 2, 3-diaminopyridine are subjected to an ammonia-aldehyde condensation reaction to construct a Salen structure, a VIM-Salen complex (MVIM-Salen) material containing metal active sites is prepared through metal coordination, and the MVIM-Salen material has ionic liquid, halogen anions and metal active sites and is used for synthesizing dimethyl carbonate (DMC) through concerted catalysis of CO2. The MVIM-Salen catalytic material has the advantages of multiple active sites, uniform distribution, better stability, simple synthesis process, low synthesis cost, green and environment-friendly synthesis process and the like. The prepared MVIM-Salen catalytic material is applied to synthesis of DMC from CO2, and shows excellent catalytic performance under relatively mild reaction conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of ionic liquid metal complex catalytic material synthesis, and specifically relates to the preparation of an imidazole-containing ionic liquid and a pyridine ring Salen metal complex material through an ammonia-aldehyde condensation reaction and a metal coordination reaction, and the application of the material in the catalytic conversion of carbon dioxide. Background Art

[0002] CO 2 It is a non-toxic, widely available, renewable resource with stable properties and is widely used in refrigeration, fire extinguishing, manufacturing carbonated beverages and producing chemical products. 2 As raw materials, it can synthesize chemical products such as carbamate, formamide, oxazolidinone, methanol, formic acid, polyurea, cyclic carbonate and dimethyl carbonate. Among them, dimethyl carbonate is an important "green" chemical intermediate. The main synthesis methods are phosgene method, CH 3 OH oxidative carbonylation and CO 2 Conversion method. Phosgene method has been basically eliminated due to problems such as highly toxic raw materials and serious equipment corrosion. 3 In addition to the OH oxidative carbonylation method, the ester exchange method, the methanol direct method and the urea alcoholysis method all use CO 2 As raw material, CO 2 The resource utilization of PO and EO is of great significance. The ester exchange method is mature, has a long industrialization time, high production safety, non-toxicity in the entire reaction process, high product yield, and can produce diols. It is the main production method of DMC at home and abroad. With the continuous expansion of PO and EO scale and the continuous reduction of prices, the market competitiveness of this process will become stronger and stronger.

[0003] CO 2 The catalytic mechanism of the cycloaddition reaction mainly includes three steps: ring opening of the epoxide, CO 2 The CO bond in the epoxide is easy to form a hydrogen bond, which is polarized by the hydrogen bond and then breaks. After the CO bond breaks, the ring-opening step of the epoxide is completed; 2 Generally activated by Lewis acid or Lewis base active sites, CO 2 After being activated, the spatial configuration of the molecule changes to a bent shape, and at the same time, the C=O bond begins to break and insert into the ring-opened epoxide to form an unclosed carbonate. Finally, under the action of electrostatics, the catalyst will be reduced and removed from the reaction system, causing the donor ion of the ring-opening of the epoxide to also detach, and then the molecule begins to close the ring to generate the product cyclic carbonate.

[0004] CH 3 The catalytic mechanism of OH transesterification reaction includes three steps: methoxyl molecules (CH 3 O- ), the cleavage of the cyclic carbonate CO bond, and the formation of the product molecule. First, CH 3 The OH molecule removes protons under the action of Lewis base active sites to form CH 3 O - The C=O in the cyclic carbonate is activated by hydrogen bonds, and secondly, CH 3 O - The molecule will attack the CO bond in the cyclic carbonate, breaking the CO bond to form an open-ring carbonate. The broken CO bond will form an oxygen anion (O - ), O - Continue and CH 3 OH molecules form hydrogen bonds. Similarly, the CH 3 O - The molecule continues to attack the unbroken CO bonds in the ring-opened carbonate, and finally, all hydrogen bonds are broken to form product molecules. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a material containing an imidazolyl ionic liquid and a pyridine ring Salen metal complex, and to apply the material to catalyze the reaction of propylene oxide with CO under relatively mild conditions. 2 Propylene carbonate was synthesized by the cycloaddition method, and dimethyl carbonate was synthesized by the propylene carbonate-methanol transesterification method.

[0006] In order to achieve the above-mentioned purpose of the invention, the present invention adopts the following technical solutions: An imidazolyl-containing ionic liquid and pyridine ring Salen metal complex material: a halogenated compound and an imidazolyl-containing compound are used to synthesize an imidazolyl-containing ionic liquid VIM, the ionic liquid is reacted with 2,3-diaminopyridine through an ammonia aldehyde condensation reaction to generate a Salen ligand VIM-Salen, and a metal ion is combined with the Salen ligand through a coordination reaction to finally generate a pyridine ring Salen metal complex MVIM-Salen. Specific synthesis steps: (1) Weigh an aldehyde-containing compound, hydrobromic acid and paraformaldehyde, mix them and stir them thoroughly at a suitable temperature. After the reaction is completed, wash and extract them to obtain a halogenated compound containing a halogen anion, 5-bromomethyl-3-tert-butyl-salicylaldehyde.

[0007] (2) Dissolving the halogenated compound 5-bromomethyl-3-tert-butyl-salicylaldehyde in an organic solvent to prepare a solution A; adding the imidazolyl-containing compound to the solution A, stirring the solution at a suitable temperature, and after the reaction is completed, filtering, washing, and drying the solution to obtain the imidazolyl-containing ionic liquid VIM.

[0008] (3) Dissolve the imidazolyl-containing ionic liquid in an organic solvent to prepare a solution B, add 2,3-diaminopyridine to the solution B, and add a dehydrating agent at the same time, stir thoroughly at a suitable temperature, and after the reaction is completed, filter, wash, and dry to obtain a biimidazole Salen ligand VIM-Salen.

[0009] (4) Add the bisimidazole Salen ligand into an organic solvent to prepare solution C, add the metal salt into solution C, stir thoroughly at a suitable temperature, and after the reaction is completed, filter and dry on an adsorbent pad to obtain a pyridine ring Salen metal complex MVIM-Salen.

[0010] The aldehyde-containing compound in step (1) is 3-tert-butyl-salicylaldehyde.

[0011] The suitable temperature in step (1) is 50-80°C and the stirring time is 15-24h.

[0012] In step (1), the molar ratio of the aldehyde-containing compound, hydrobromic acid and paraformaldehyde is 1.0:5.0-8.0:1.2-1.5.

[0013] In step (2), the organic solvent is acetonitrile.

[0014] The suitable temperature in step (2) is 20-30°C and the stirring time is 20-30h.

[0015] In step (2), the molar ratio of the imidazole compound to the halogenated compound is 1.0-1.5:1.0.

[0016] In step (3), the organic solvent is ethanol.

[0017] In step (3), the dehydrating agent is a molecular sieve.

[0018] In step (3), the suitable temperature is 20-30°C and the stirring time is 15-24h.

[0019] In step (3), the molar ratio of the imidazolyl ionic liquid to 2,3-diaminopyridine is 1.0:1.0-1.2.

[0020] In step (4), the metal salts are anhydrous manganese chloride and anhydrous sodium acetate.

[0021] The organic solvent in step (4) is dichloromethane.

[0022] In step (4), the suitable temperature is 20-30°C and the stirring time is 36-50h.

[0023] In step (4), the molar ratio of the Salen ligand to anhydrous manganese chloride is 1.0:1.0-1.05, and the molar ratio of the Salen ligand to anhydrous sodium acetate is 1.0:1.8-2.3.

[0024] The adsorbent in step (4) is diatomaceous earth.

[0025] The present invention uses the bifunctional pyridine ring Salen metal complex material as a catalyst in the cycloaddition reaction and the transesterification reaction. The specific operation is as follows: propylene oxide and the bifunctional Salen metal complex material are added to a high-pressure reactor, and an excess of 0.5-2.5 MPa of CO is charged into the reactor. 2 , stir the reaction at a temperature of 80-160°C for 1-5 hours to obtain propylene carbonate; add excess methanol to the product of the previous step, stir the reaction at a temperature of 80-160°C for 4-10 hours to finally obtain dimethyl carbonate.

[0026] The beneficial effect of the present invention is that the Lewis base sites of the ionic liquid and the Lewis acid sites of the metal center are simultaneously fixed in the complex material through covalent bonds and coordination bonds. The complex material prepared by this method solves the problem that conventional catalytic materials such as metal oxides have few surface active sites and a single active site effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Synthesis diagram for preparing Salen metal complex material MVIM-Salen; Figure 2 It is the liquid phase mass spectrum of 5-bromomethyl-3-tert-butyl-salicylaldehyde; Figure 3 It is a liquid phase high-resolution mass spectrometry spectrum of the imidazolyl-containing ionic liquid VIM; Figure 4 is the infrared spectrum of Salen ligand VIM-Salen; Figure 5 This is the infrared spectrum of the Salen metal complex material MVIM-Salen. DETAILED DESCRIPTION

[0028] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0029] Example 1 (1) Synthesis of halogenated compounds containing halogen anions Weigh 10 mmol 3-tert-butyl salicylaldehyde, 75 mmol hydrobromic acid and 15 mmol paraformaldehyde respectively, under nitrogen protection, stir magnetically at 70 ° C for 20 h, collect the yellow viscous liquid, wash with deionized water and extract to obtain the halogenated compound 5-bromomethyl-3-tert-butyl-salicylaldehyde containing halogen anions.

[0030] (2) Synthesis of VIM-containing imidazolyl ionic liquid 8 mmol of 5-bromomethyl-3-tert-butyl-salicylaldehyde was weighed and dissolved in 20 mL of acetonitrile to prepare solution A, 8.3 mmol of 1-vinylimidazole was weighed and added to solution A, and under nitrogen protection, magnetic stirring was carried out at room temperature for 24 hours. After the reaction was completed, the solvent was evaporated, and the yellow viscous liquid was collected, washed with ethyl acetate, and dried in a vacuum oven to obtain an imidazole-containing ionic liquid VIM.

[0031] (3) Synthesis of VIM-Salen biimidazole Salen ligand 7 mmol of imidazole-containing ionic liquid VIM was weighed and dissolved in 20 mL of ethanol to prepare solution B, 3.5 mmol of 2,3-diaminopyridine was weighed and added to solution B, and an appropriate amount of molecular sieves were added at the same time. The solution was magnetically stirred at room temperature for 20 hours, and a brown solution was collected. The molecular sieves were removed by filtration to obtain a clear and transparent orange solution. Finally, the solvent ethanol was removed by repeated azeotropic distillation to obtain the bisimidazole Salen ligand VIM-Salen.

[0032] (4) Synthesis of MVIM-Salen pyridine ring Salen metal complex materials 2.68 mmol of bisimidazole Salen ligand VIM-Salen was weighed and dissolved in 20 ml of dichloromethane to prepare solution C. 2.68 mmol of anhydrous manganese chloride and 5.36 mmol of anhydrous sodium acetate were weighed respectively and added to solution C. The mixture was magnetically stirred at room temperature for 48 h. The brown precipitate was collected, washed with dichloromethane and dried to obtain the pyridine ring Salen metal complex material MVIM-Salen.

[0033] Figure 1 Synthesis diagram of the Salen metal complex material MVIM-Salen prepared for this example.

[0034] Figure 2 This is the liquid phase mass spectrum of 5-bromomethyl-3-tert-butyl-salicylaldehyde. Because free bromide ions are easily lost in mass spectrometry testing, the theoretical mass-to-nuclear ratio (m / z) of 5-bromo-3-tert-butyl salicylaldehyde can be obtained as 191.11 according to the molecular weight calculation software. Figure 2 It can be seen that the peak of m / z 191.1014 exists in the actual sample, indicating that the brominated compound 5-bromomethyl-3-tert-butyl-salicylaldehyde is successfully synthesized.

[0035] Figure 3 This is a high-resolution mass spectrometry spectrum of the liquid phase containing imidazolyl ionic liquid VIM. Because free bromide ions are easily lost in mass spectrometry testing, the theoretical mass-to-nuclear ratio (m / z) of the 1-vinyl ionic liquid VIM can be obtained as 285.16 according to the molecular weight calculation software. Figure 3It can be seen that the peak of m / z 285.15966 exists in the actual sample, indicating that the 1-vinyl ionic liquid VIM is successfully synthesized.

[0036] Figure 4 This is the infrared spectrum of Salen ligand VIM-Salen. At 1390.447 cm -1 and 1363.448cm -1 The bending vibration peaks of the tert-butyl methyl and methylene groups are at 2863.82 cm -1 The characteristic peak of polyformaldehyde methylene is at 3068.241 cm -1 The CH stretching vibration peak of the imidazolium cation near 1648.866 cm -1 The double bond characteristic peak at 1157.099 cm -1 The imidazole ring stretching vibration peaks nearby are present, which proves that the ionic liquid is successfully grafted onto the Salen ligand. Due to the aldol condensation reaction, the characteristic peak of the aldehyde group disappears, and the peak at 3407.657 cm -1 、1552.441 cm -1 and 1612.225cm -1 New absorption peaks appeared nearby, corresponding to the stretching vibration absorption peak of Schiff base phenolic hydroxyl OH, the ring deformation vibration absorption peak of pyridine molecule plane, and the stretching vibration peak of C=N bond. Combined with the above analysis, it is proved that VIM-Salen was successfully synthesized.

[0037] Figure 5 This is the infrared spectrum of the Salen metal complex material MVIM-Salen. There is a 1157.099cm -1 The imidazole ring stretching vibration peak is at 1648.866 cm -1 The double bond characteristic peak is 3407.657 cm -1 、1552.441cm -1 and 1612.225cm -1 The absorption peaks correspond to the stretching vibration absorption peak of the Schiff base phenolic hydroxyl group OH, the ring deformation vibration absorption peak of the pyridine molecule plane, and the stretching vibration peak of the C=N bond. They correspond to the characteristic peaks in the VIM-Salen(py) spectrum, proving that the structure of Salen remains basically the same before and after the reaction. In addition, at 566.4872cm -1 and 417.5131cm -1 New vibration absorption peaks appeared at , which are Mn-O and Mn-N stretching vibration peaks, proving that the metal Mn ion was successfully coordinated to the Salen ligand. In summary, the ionic liquid functionalized Salen metal complex material containing pyridine ring MVIM-Salen was successfully synthesized.

[0038] Application Example 1 Weigh 5 g of propylene oxide and 0.3 g (6 wt.%) of Salen metal complex material into a high-pressure reactor and fill it with 2 MPa CO 2 , stirring reaction at 110℃ for 1.5h, taking out the reaction liquid for gas chromatography analysis. After sampling, methanol (alcohol ester ratio 15:1) was added, stirring reaction at normal pressure and 110℃ for 8h, taking out the reaction liquid for gas chromatography analysis. Through single factor experimental determination, PC yield and PO conversion rate reached more than 99.9%, and DMC yield reached 63.0%.

[0039] Compared with other similar catalytic materials (e.g. CN118084978A), this catalytic material uses a cheaper synthetic material during the synthesis process, which reduces the synthesis cost. Salen monomers contain vinyl double bonds, which can be subsequently polymerized into polymers by free radical polymerization to improve the stability of the catalyst. In terms of the structural composition of this catalyst, the ionic liquid active center is located at the 5th position of salicylaldehyde, and its active site is more likely to contact the reactant, thereby increasing the reaction rate. In the cycloaddition reaction, the PC yield can reach more than 95% in only 0.5 hours, and the yield can reach more than 99% in 1.5 hours. It also has good catalytic activity in the transesterification reaction, realizing a catalyst "one pot, two steps" catalytic CO 2 Converted into DMC, greatly reducing production costs.

[0040] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a material containing an imidazolyl ionic liquid and a pyridine ring Salen metal complex, characterized in that: The following steps are involved: (1) mixing an aldehyde-containing compound, polyformaldehyde and hydrobromic acid, stirring them sufficiently for reaction, and then washing and extracting them to obtain a halogenated compound containing a halogen anion; (2) dissolving the halogenated compound in an organic solvent to prepare solution A, adding the imidazolyl-containing compound, stirring the mixture to react, washing and rotary drying to obtain an imidazolyl-containing ionic liquid containing a halogen anion; (3) dissolving the imidazolyl-containing ionic liquid in an organic solvent to prepare solution B, adding 2,3-diaminopyridine and a dehydrating agent, stirring the reaction sufficiently, filtering and repeating azeotropy to obtain a bisimidazolyl-salen ligand; (4) Dissolve the bisimidazole-Salen ligand in an organic solvent to prepare solution C, add metal salt, stir the reaction thoroughly, and then filter by adsorption to obtain the MVIM-Salen complex.

2. The method according to claim 1, characterized in that: The aldehyde-containing compound in step (1) is 3-tert-butyl salicylaldehyde; and the halogenated compound in step (2) is 5-bromomethyl-3-tert-butyl-salicylaldehyde.

3. The method according to claim 1, characterized in that: In step (1), the reaction temperature is 60° C., the stirring time is 15-24 hours, and the molar ratio of the aldehyde-containing compound, hydrobromic acid and polyformaldehyde is 1.0:5.0-8.0:1.2-1.

5.

4. The method according to claim 1, characterized in that: In step (2), the organic solvent is acetonitrile, the reaction temperature is 20-30° C., the stirring time is 20-30 h, and the molar ratio of the imidazole-containing compound to the halogenated compound is 1.0-1.5:1.

0.

5. The method according to claim 1, characterized in that: In step (3), the organic solvent is ethanol, the reaction temperature is 20-30° C., the stirring time is 15-24 h, and the molar ratio of the imidazolyl ionic liquid to 2,3-diaminopyridine is 1.0:1.0-1.

2.

6. The method according to claim 1, characterized in that: In step (4), the metal salts are anhydrous manganese chloride and anhydrous sodium acetate, the organic solvent is dichloromethane, the reaction temperature is 20-30° C., the stirring time is 36-50 hours, and the molar ratio of the biimidazole Salen ligand, anhydrous manganese chloride and anhydrous sodium acetate is 1.0:1.0-1.05:1.8-2.

3.

7. An imidazolyl-containing ionic liquid and a pyridine ring-Salen metal complex material prepared by the method according to any one of claims 1 to 6.

8. An application of an imidazolyl-containing ionic liquid and a pyridine ring-Salen metal complex material prepared by the method according to any one of claims 1 to 6, characterized in that: The MVIM-Salen complex material is used as a catalyst in the cycloaddition reaction of carbon dioxide and propylene oxide to produce propylene carbonate, and in the reaction of propylene carbonate and methanol to synthesize dimethyl carbonate.

9. The use according to claim 8, characterized in that: The reaction conditions for generating propylene carbonate are: CO2 0.5-2.5MPa, reaction temperature 80-160°C, reaction time 0.5-4h; the reaction conditions for generating dimethyl carbonate are: reaction temperature 80-160°C, reaction time 4-10h.

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