A method for preparing cyclic carbonate by catalyzing carbon dioxide with phosphine-based complex

Abstract

The present invention relates to a method for synthesizing cyclic carbonates by catalyzing carbon dioxide with a phosphine-based complex, the method uses a phosphine-based complex synthesized by a phosphine oxide compound and a transition metal salt as a catalyst, catalyzes the reaction of carbon dioxide and an epoxy compound, and synthesizes the corresponding cyclic carbonates under the conditions of 0.5%-5.0% of the molar amount of the epoxy compound, a reaction pressure of 1-4 MPa, a reaction temperature of 100 DEG C-150 DEG C, and a reaction time of 1-6 h. The catalyst used in the present invention is environmentally friendly, cheap and easy to obtain, simple to prepare, small in amount, and excellent in catalytic performance, and can achieve high selectivity and high yield synthesis of cyclic carbonates, and the catalyst is easy to separate, has good cycle stability, belongs to an environmentally friendly catalyst, and has great industrial application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of green catalysis and relates to a method for preparing cyclic carbonate by catalyzing carbon dioxide and epoxy compounds with a phosphine-based complex. Background Art

[0002] In recent years, with the acceleration of industrialization, energy issues have received more and more attention, and the carbon dioxide content in the atmosphere has increased sharply, which has seriously aggravated the greenhouse effect, seawater acidification and other problems. In order to reduce the carbon emissions caused by energy use, carbon dioxide (CO2) is used as a resource, which can not only reduce the content of atmospheric CO2 and reduce the greenhouse effect, but also obtain high value-added chemical products, which is of great significance for environmental protection and resource utilization. The synthesis of cyclic carbonates by cycloaddition of CO2 and epoxy compounds to achieve 100% atom economy is an effective way to achieve CO2 emission reduction and resource utilization. In addition, the synthesized cyclic carbonates are a class of polar organic solvents with stable properties and low toxicity, which can be used as electrolytes, fuel additives, etc., and can also be used as raw materials to participate in various cyclization, carbonylation and transesterification reactions for the preparation of a variety of important chemicals.

[0003] Since CO2 is structurally stable and difficult to activate, the key to achieving the chemical conversion of CO2 lies in the development of efficient catalysts. At present, the catalysts for the synthesis of cyclic carbonates from CO2 and epoxides mainly include homogeneous catalysts such as metal Salen and Salphen complexes, ionic liquids, quaternary ammonium salts, quaternary phosphonium salts, alkali metal salts, and organic bases. For example, Wang et al. (Contemporary Chemical Industry, 2020 (3): 4.) prepared a bifunctional Schiff base metal complex and used it to catalyze the reaction of CO2 and epoxides. The catalytic system composed of the prepared complex and tetrabutylammonium chloride had a target yield of 99% under optimal conditions, but there were problems such as separation difficulties and high energy consumption after the reaction was completed. Liu Dinghua et al. synthesized a biligand zinc complex catalyst and used it for the preparation of cyclic carbonates by cycloaddition of CO2 and epoxides (CN 104492488 A). They had high cyclic carbonate yields for different epoxides, but the pressure to obtain the ideal product yield was 4 MPa, and the reaction conditions were relatively harsh. There was also the problem of time-consuming and energy-consuming treatment of the system after the reaction. Heterogeneous catalysts have the advantages of being easy to separate from reactants and easy to operate in the reaction system, and are a research hotspot for multiple synthetic reactions. Currently, heterogeneous catalysts developed for the cycloaddition reaction of CO2 and epoxides include supported catalysts such as metal oxides, molecular sieves, functionalized polymers, and metal organic framework materials, which can solve the problem of catalyst recovery difficulties to a certain extent. However, the above-mentioned heterogeneous catalysts are usually low in activity in the reaction, the preparation process is cumbersome, the active components are easily lost, and the service life is short. For example, Zhang et al. (Chemical Communications, 2015, 51, 15708) used Friedel-Crafts alkylation to crosslink quaternary phosphonium salts into polymers and explored the application of such catalysts in the cycloaddition reaction of CO2 and epoxides. After adding ZnBr2, the catalyst activity was significantly improved, and it had good substrate applicability, but the catalytic activity needed to be further improved. Deng et al. (Nature Communications, 2013, 4, 1960) prepared porous organic polymers based on salen-metal units by sonogashira coupling for catalytic cycloaddition reaction of CO2 and epoxides. However, the catalytic system requires the addition of quaternary ammonium salts, which makes it difficult to separate the products. Ding et al. (CN 107537564A) prepared a heterogeneous catalyst containing a quaternary phosphonium salt-phosphorus ligand organic porous copolymer, and obtained a highly active catalyst by adjusting the copolymer monomer ratio and metal loading, but the catalytic active components are easily lost.

[0004] Based on the above reports, the development and use of highly active and environmentally friendly catalysts has become an inevitable development trend. The phosphine-based complex proposed in the present invention is a catalyst synthesized from transition metal salts and phosphine oxide compounds, which is simple to synthesize, cheap, low-toxic or non-toxic, has strong Lewis acidity, exhibits excellent catalytic effect when used to catalyze the cycloaddition reaction of CO2 and epoxy compounds, and is easy to recycle and reuse, and is expected to become an excellent substitute for traditional catalysts. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for synthesizing cyclic carbonate by chemically converting carbon dioxide under certain conditions using a phosphine-based complex catalyst, and the phosphine-based complex system is simple to synthesize, low in price, highly stable, reusable, and environmentally friendly, while avoiding the use of volatile organic solvents and co-catalysts, thereby realizing clean resource utilization of carbon dioxide. The reaction equation for preparing cyclic carbonate by cycloaddition of carbon dioxide and epoxy compounds is as follows:

[0006]

[0007] In order to solve the above technical problems, the present invention proposes a method for preparing cyclic carbonate by catalyzing the reaction of carbon dioxide and epoxy compounds under certain conditions using a phosphine-based complex, that is, using the phosphine-based complex as a catalyst, carbon dioxide and epoxy compounds as raw materials, and preparing the cyclic carbonate through a cycloaddition reaction, wherein the phosphine-based complex is prepared from a phosphine oxide compound and a transition metal salt.

[0008] The phosphine complex structural formula is as follows:

[0009]

[0010] In the formula, R1, R2, and R3 groups are all selected from any one of phenyl, benzyl, or C1-C8 alkyl; M is one of Zn, Cu, Mn, Fe, Al, Co, and Ni; and X is one of Cl, Br, and I.

[0011] Preferably, the R1, R2, R3 groups are phenyl, benzyl, C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl or C8 alkyl, preferably C4 alkyl-C8 alkyl or phenyl.

[0012] Preferably, the epoxy compound has the structural formula

[0013]

[0014] Any one of .

[0015] Preferably, the phosphine oxide compound is any one of tri-n-butylphosphine oxide (Bu3PO), tri-n-octylphosphine oxide (Oc3PO) and triphenylphosphine oxide (Ph3PO).

[0016] Preferably, the metal salt is any one of zinc salt, aluminum zinc salt and copper salt.

[0017] Specifically, the metal salt includes, but is not limited to, the following examples: zinc bromide, copper bromide, zinc chloride, copper chloride, aluminum chloride, aluminum bromide, nickel bromide, nickel chloride, manganese bromide, manganese chloride, iron bromide, iron chloride, cobalt chloride, and cobalt bromide.

[0018] Preferably, the molar ratio of the phosphine oxide compound to the transition metal salt is (0.1-5):1, for example, it can be 0.1:1, 0.5:1, 1:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1 or 5:1, preferably 2:1 or 3:1.

[0019] Preferably, the phosphine-based complex is prepared by reflux and stirring a transition metal salt and a phosphine oxide compound at 50-100° C. for 2-12 hours, preferably at 60° C. for 3 hours.

[0020] Preferably, the cycloaddition reaction temperature of carbon dioxide and epoxy compound is 100°C-150°C, for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C or 150°C, preferably 130°C or 140°C.

[0021] Preferably, the pressure of the carbon dioxide and epoxy compound cycloaddition reaction is 1-4 MPa, for example, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa or 4 MPa, preferably 3 MPa-4 MPa.

[0022] Preferably, the amount of catalyst used is 0.5%-5% of the molar amount of the epoxy compound, for example, it can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5 or 5.0, preferably 0.5%-1.0%.

[0023] As a further optimization of the present invention, the cycloaddition reaction time of carbon dioxide and epoxy compound is 1-6 h, for example, it can be 1 h, 2 h, 3 h, 4 h, 5 h or 6 h, preferably 3 h-5 h.

[0024] The beneficial effects of adopting the above technical solution are:

[0025] (1) The method for preparing cyclic carbonate esters by catalysis of phosphine-based complexes of the present invention has high catalytic activity compared with existing catalysts, and the dosage of the complex catalyst of the present invention is only 0.5%-1.0%, and the reaction takes only 3-5 hours; the yield of propylene carbonate synthesized by the catalyst in 3 hours can reach 92%.

[0026] (2) The phosphine-based complex catalyst can catalyze the cycloaddition reaction of epoxides with different substituents and carbon dioxide, showing good universality and recyclability. Compared with other complex catalysts reported for this system, the catalyst synthesis is cleaner and more efficient. In catalytic applications, based on the synergistic effect of nucleophilic groups and hydrogen bonds, epoxy compounds can be efficiently activated for ring opening, allowing the catalytic process to occur rapidly, showing good prospects for industrial application.

[0027] (3) The phosphine-based complex catalyst proposed in the present invention can activate and ring-open epoxy compounds through the synergistic effect of halogen nucleophilic groups and hydrogen bonds. The phosphine-based complex used in this method has simple and efficient synthesis, low price, easy acquisition, and environmental friendliness, while avoiding the use of toxic organic solvents. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the infrared spectrum of one of the phosphine-based complexes (Bu3PO-ZnBr2) of the present invention;

[0029] Figure 2 This is the H NMR spectrum of one of the phosphine-based complexes (Bu3PO-ZnBr2) of the present invention;

[0030] Figure 3 This is the thermogravimetric spectrum of one of the phosphine-based complexes (Bu3PO-ZnBr2) of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail in conjunction with specific implementation methods. The following examples are only used to illustrate the present invention and are not intended to limit the present invention.

[0032] Example 1 Preparation of phosphine complex

[0033] Tributylphosphine oxide and zinc bromide were added into a single-necked flask at a molar ratio of 2:1, respectively, and heated, stirred and refluxed at 60°C for 3 hours to prepare Bu3PO-ZnBr2.

[0034] Trioctylphosphine oxide and zinc bromide were added into a single-necked flask at a molar ratio of 2:1, heated, stirred and refluxed at 60°C for 3 hours to prepare Oc3PO-ZnBr2.

[0035] Triphenylphosphine oxide and zinc bromide were added into a single-necked flask at a molar ratio of 2:1, heated and stirred under reflux at 60°C for 3 hours to prepare Ph3PO-ZnBr2.

[0036] Attached Figure 1 To characterize the structure of Bu3PO-ZnBr2 by infrared; Figure 2 The structure of Bu3PO-ZnBr2 was characterized by NMR. Figure 3 The thermal stability of Bu3PO-ZnBr2 was characterized by thermogravimetric analysis.

[0037] Example 2

[0038] Take the catalyst Bu prepared in Example 1 PO-ZnBr and reactant propylene oxide and join in 50mL autoclave successively, wherein propylene oxide 4mL (i.e. 3.32g), catalyst 0.0946g, catalyst accounts for 0.25mol% of propylene oxide molar content, and carbonic acid gas is passed into reactor by gas replacement method to remove the air in the reactor, and the reaction temperature is 130 ℃, 3MPa CO pressure condition, and continuous reaction is 3h; After finishing, the reaction is cooled to room temperature, and the product is quantitatively analyzed by gas chromatography, and the propylene carbonate product yield is 92%, and the selectivity is 99%.

[0039] Example 3

[0040] The specific experimental process and detection method are the same as those in Example 2, except that the phosphine-based complex is changed to Ph3PO-ZnBr2 prepared in Example 1, the amount of catalyst is changed to 0.8 mol% of the molar content of propylene oxide, and the reaction time is changed to 6 h. The yield of propylene carbonate product is 82% and the selectivity is 95%.

[0041] Example 4

[0042] The specific experimental process and detection method are the same as those in Example 2, except that the phosphine-based complex is changed to Oc3PO-ZnBr2 prepared in Example 1, and the amount of catalyst is changed to 1 mol% of the molar content of propylene oxide. The yield of propylene carbonate product is 91% and the selectivity is 98%.

[0043] Example 5

[0044] The specific experimental process and detection method are the same as those in Example 2, except that the amount of the phosphine complex is changed to 1 mol% of the molar content of propylene oxide, and the reaction time is changed to 5 h. The yield of propylene carbonate product is 94% and the selectivity is 99%.

[0045] Example 6

[0046] The specific experimental process and detection method are the same as in Example 2, except that propylene oxide is replaced by other epoxy compounds with different substituents, and the cycloaddition reaction is carried out with dioxide respectively. The results are shown in Table 1.

[0047] Table 1 Results of cycloaddition reactions of different epoxides with carbon dioxide catalyzed by phosphine complexes

[0048]

[0049]

[0050] Examples 9-13

[0051] The specific implementation conditions and steps are the same as those in Example 2, except that the phosphine-based complex catalyst is replaced by the phosphine-based complex catalyst recovered in Example 2. Five cycle tests are carried out under the same conditions, and the results are shown in Table 2.

[0052] Table 2 Experimental results of catalyst recycling in Examples 9-13

[0053]

[0054] Comparative Example 1

[0055] The specific experimental process and detection method are the same as in Example 2, except that the phosphine-based complex catalyst is changed to tributylphosphine oxide, and the catalyst dosage is changed to 0.5 mol% of the molar content of propylene oxide. The yield of propylene carbonate product is 8% and the selectivity is 99%.

[0056] Comparative Example 2

[0057] The specific experimental process and detection method are the same as in Example 2, except that the phosphine-based complex catalyst is replaced by zinc bromide, and only a trace amount of propylene carbonate is produced.

[0058] Comparative Example 3

[0059] The specific experimental process and detection method are the same as those of Comparative Example 2, except that the amount of tributylphosphine oxide is changed to 1 mol% of the propylene oxide content, the yield of propylene carbonate product is 9%, and the selectivity is 99%.

[0060] From comparative examples 1-3, it can be seen that when the catalyst of the reaction system is only an oxide phosphine compound or a metal salt, no matter whether the catalyst content is increased or the reaction time is prolonged, or even the catalyst content and the reaction time are increased at the same time, the maximum yield of the catalytic cyclic carbonate synthesis can only reach 9%. The phosphine-based complex provided by the present invention can obtain a propylene carbonate product yield of 92% and a selectivity of 99% under relatively good conditions.

[0061] According to the above results, it is fully demonstrated that the phosphine-based complex catalyst of the present invention exhibits a good catalytic effect on the reaction system and has good catalyst recycling performance, which greatly reduces the cost of industrial application.

[0062] The present invention uses the above-mentioned embodiment to illustrate the method for preparing cyclic carbonate by catalyzing carbon dioxide with a phosphine-based complex of the present invention, but the present invention is not limited to the above-mentioned embodiment, that is, it does not mean that the present invention must rely on the above-mentioned embodiment to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing cyclic carbonate by catalyzing carbon dioxide and epoxy compounds using a phosphine-based complex, characterized in that: A phosphine-based complex synthesized from a phosphine oxide compound and a transition metal salt is used as a catalyst to catalyze the cycloaddition of an epoxy compound and carbon dioxide to synthesize a cyclic carbonate. The structural formula of the phosphine-based complex is as follows: In the formula, R1, R2, and R3 groups are all selected from any one of phenyl, benzyl, or C1-C8 alkyl; M is Zn; X is Br; The phosphine oxide compound is Any of the following: The transition metal salt is zinc bromide; The amount of the phosphine complex used is 0.5%-5.0% of the molar amount of the epoxy compound.

2. The method according to claim 1, characterized in that The reaction equation for preparing cyclic carbonate by cycloaddition of carbon dioxide and epoxy compounds is as follows: In the formula, the epoxy compound is selected from Any one of .

3. The method according to claim 1, characterized in that The molar ratio of the phosphine oxide compound to the transition metal salt is (0.1-5):

1.

4. The method according to claim 1, characterized in that: The phosphine-based complex is prepared by reflux and stirring a transition metal salt and a phosphine oxide compound at 50-100° C. for 2-12 hours.

5. The method according to claim 1, characterized in that The cycloaddition reaction temperature of the carbon dioxide and the epoxy compound is 100°C-150°C.

6. The method according to claim 1, characterized in that The pressure of the carbon dioxide and epoxy compound cycloaddition reaction is 1-4 MPa.

7. The method according to claim 1, characterized in that The cycloaddition reaction time of the carbon dioxide and the epoxy compound is 1-6 hours.

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