Method for catalytically synthesizing carbonic ester by using hydrogen bond donor functionalized UCST type polymeric ionic liquid

Abstract

The invention belongs to the technical field of green catalysis, and relates to a method for catalytically synthesizing cyclic carbonate by using hydrogen bond donor functionalized UCST type polymeric ionic liquid. According to the method, acrylamide is used as a hydrogen bond donor and is subjected to RAFT copolymerization with 1-vinyl-3-alkyl imidazole ionic liquid to synthesize a series of hydrogen bond donor functionalized UCST type polymeric ionic liquid, and the UCST type polymeric ionic liquid is used for efficiently catalyzing conversion of a low-concentration epoxy substrate (15-100 mol%) dispersed in cyclic carbonate to the cyclic carbonate. The optimized polymeric ionic liquid can show catalytic activity equivalent to that of monomer homogeneous catalysis under a milder condition, and the product yield reaches 92.6% under the conditions that the reaction temperature is 90-120 DEG C, the reaction pressure is 1-3 MPa and the reaction time is 1-6 h. The UCST type polymeric ionic liquid has the characteristics that compared with the traditional polymeric ionic liquid, the UCST type polymeric ionic liquid functionalized by the hydrogen bond donor is gradually dissolved in the reaction process, so that active sites in the polymeric ionic liquid are fully utilized, and the UCST type polymeric ionic liquid has the advantage of higher catalytic activity; compared with other UCST type polymeric ionic liquids, the hydrogen bond donor in the hydrogen bond donor functionalized UCST type polymeric ionic liquid can cooperate with anions of the ionic liquid to activate epoxy, so that the catalytic activity is further improved, and the UCST type polymeric ionic liquid can show catalytic activity equivalent to homogeneous catalysis of a monomer under a relatively mild condition.

Description

Technical Field

[0001] This invention relates to the field of green catalysis technology for CO2 fixation and conversion, and in particular to a method for synthesizing UCST-type polymeric ionic liquid catalysts with hydrogen bond donor functionalization, as well as a method for catalyzing the synthesis of cyclic carbonates from CO2 and epoxides. Background Technology

[0002] Since the Industrial Revolution, the extensive use of fossil fuels has driven rapid social development but also resulted in massive emissions of the greenhouse gas CO2. The continuously rising CO2 levels in the atmosphere seriously threaten ecological, energy, and environmental security. In recent years, CO2 control has attracted widespread attention from academia and industry. Using CO2 as a cheap, readily available, and safe C1 resource in chemical reactions can mitigate the greenhouse effect while bringing economic benefits. Among these methods, the synthesis of cyclic carbonates from CO2 and epoxides is a 100% atom-economic reaction, and the resulting cyclic carbonates have a wide range of applications, including battery electrolytes, coatings, and dyes.

[0003] Currently, catalysts for the synthesis of cyclic carbonates from CO2 and epoxides include metal halides, metal oxides, complexes, organic bases, and polymeric ionic liquids. Among them, polymeric ionic liquids are considered excellent catalysts for epoxide addition reactions due to their designable structure and high stability. However, for traditional polymeric ionic liquids, the active sites embedded within the polymer backbone are difficult to fully utilize, limiting their catalytic activity. For example, CN114276322A discloses a method for the photo-initiated preparation of cyclic carbonates using a polymeric ionic liquid material. However, after catalyzing the cycloaddition of propylene oxide and CO2 at 120°C for 2 hours, the polymeric ionic liquid catalyst only yielded a 53% product yield. Developing UCST-type polymeric ionic liquids is an effective way to solve the problem of insufficient utilization of active sites in polymeric ionic liquids. For example, CN119954765A discloses a method for the synthesis of cyclic carbonates using a UCST-type polymeric ionic liquid. In this method, the UCST-type polymeric ionic liquid can dissolve in cyclic carbonates at high temperatures, thus fully utilizing the active sites and efficiently catalyzing the conversion of low-concentration propylene oxide dispersed in the cyclic carbonate into the corresponding product. However, the UCST-type polymeric ionic liquid catalyst disclosed in CN119954765A has the problem of having a single type of active site and relatively high reaction conditions.

[0004] Based on the above situation, there is an urgent need in this field to develop a UCST-type polymeric ionic liquid catalyst with multiple active sites. Therefore, using acrylamide as a hydrogen bond donor, a series of hydrogen bond donor-functionalized UCST-type polymeric ionic liquids were prepared by RAFT copolymerization with halogenated 1-vinyl-3-alkylimidazolium. These liquids can gradually dissolve at high temperatures, and the hydrogen bond donors can synergistically activate epoxy with the ionic liquid anions, thus achieving the goal of highly efficient catalytic reactions. Summary of the Invention

[0005] This invention addresses the problem of insufficient utilization of internal active sites in traditional polymeric ionic liquid catalysts and the limited variety of active sites in existing UCST-type polymeric ionic liquids. It proposes a method for synthesizing cyclic carbonates using hydrogen-bond donor-functionalized UCST-type polymeric ionic liquids. The key feature is that the hydrogen-bond donor-functionalized UCST-type polymeric ionic liquid can gradually dissolve in the reaction system at high temperatures, and the hydrogen-bond donor can synergistically activate the epoxy with the ionic liquid anion. First, using acrylamide as a hydrogen-bond donor, a series of hydrogen-bond donor-functionalized UCST-type polymeric ionic liquids are synthesized via RAFT copolymerization with halogenated 1-vinyl-3-alkylimidazolium. Then, using these hydrogen-bond donor-functionalized UCST-type polymeric ionic liquids as catalysts, and with the product cyclic carbonate as a solvent, cyclic carbonates are synthesized using epoxy compounds with different substituents as substrates.

[0006] The first objective of this invention is to provide a UCST-type polymeric ionic liquid with hydrogen bond donor functionalization that has a highly efficient catalytic ability for the synthesis of carbonates from CO2 and epoxides.

[0007] The polymeric ionic liquid catalyst involved in this invention has the following structure:

[0008]

[0009] Preferably, m, n, p, and q are each independently selected from any natural number, and m ≥ 10, n ≥ 2;

[0010] Preferably, R1 is independently selected from hydrogen atoms or any group, such as -CN, -OCH3, -COOH, -CH3, -NH2, -OH, etc.;

[0011] Preferably, X - For Cl - ,Br - I - Any one of them.

[0012] The second objective of this invention is to provide a method for preparing a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid, characterized in that the preparation method includes the following steps:

[0013] (1) Add a certain molar ratio of acrylamide, halogenated 1-vinyl-3-alkylimidazolium, trithiocarbonate chain transfer reagent and azobisisobutyronitrile to a Schlenk flask, add a certain amount of solvent, and mix evenly at room temperature.

[0014] (2) After evacuating the above Schlenk bottle, an inert gas is introduced;

[0015] (3) Place the Schlenk flask filled with inert gas in an oil bath at a certain temperature, polymerize for a period of time, and then quench the reaction by passing air through it.

[0016] (4) Most of the solvent was removed by rotary evaporation, and the residue was washed with solvent. The obtained solid was then dried in a vacuum drying oven to obtain the catalyst product.

[0017] Preferably, the molar ratio of acrylamide to halogenated 1-vinyl-3-alkylimidazole is in the range of 0.03:1 to 2:1.

[0018] Preferably, the molar ratio of the polymerizing monomer, the trithiocarbonate chain transfer agent, and the azobisisobutyronitrile is in the range of 60:3:1 to 10:3:1;

[0019] Preferably, the solvent is any one of methanol, ethanol, acetonitrile, and ethyl acetate;

[0020] Preferably, the inert gas is either nitrogen or argon.

[0021] Preferably, the oil bath temperature range is 50–90°C, for example 60°C, 70°C, or 80°C;

[0022] Preferably, the polymerization time is 12 to 72 hours, for example, 24 hours, 36 hours, 48 ​​hours, or 60 hours.

[0023] A third objective of this invention is to provide a method for synthesizing cyclic carbonates using a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid catalyzed by hydrogen bonding, characterized in that the method for synthesizing cyclic carbonates comprises the following steps:

[0024] An epoxy compound dispersed in a cyclic carbonate and a certain amount of UCST-type polymeric ionic liquid functionalized with hydrogen bond donors are placed in a sealed reactor, and CO2 gas is introduced into the reactor at room temperature. The reaction is then maintained at a certain temperature for a period of time to convert the epoxy compound into a cyclic carbonate. After the reaction is completed, the temperature is lowered, and the UCST-type polymeric ionic liquid is recovered from the reaction system by temperature-controlled phase separation.

[0025] Preferably, the concentration of the epoxy compound dispersed in propylene carbonate is 15–100 mol%.

[0026] Preferably, the amount of catalyst used is 1 to 6 mol% of the amount of reactant epoxide, for example, 2 mol%, 3 mol%, 4 mol%, 5 mol%.

[0027] Preferably, the cycloaddition reaction is carried out at a temperature of 90–120°C; for example, 90°C, 110°C, or 120°C.

[0028] Preferably, the reaction pressure of the cycloaddition reaction is 1 to 3 MPa, for example 1 MPa, 2 MPa, or 3 MPa;

[0029] Preferably, the reaction time of the cycloaddition reaction is 1 to 6 hours; for example, 1 hour, 2 hours, 3 hours, 4 hours, or 6 hours.

[0030] Preferably, the epoxy compound includes any one of ethylene oxide, propylene oxide, epibutylene oxide, epichlorohydrin, styrene oxide, cyclohexane oxide, and cyclopentane oxide;

[0031] Preferably, the yield of the cyclic carbonate is 50% to 95%;

[0032] Preferably, the recovery rate of the UCST-type polymeric ionic liquid recovered by temperature-controlled phase separation after the reaction is 35% to 100%.

[0033] Compared with previous patents, the advantages of this invention are:

[0034] (1) This invention uses acrylamide and halogenated 1-vinyl-3-alkylimidazolium as monomers to synthesize a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid via RAFT polymerization. This polymeric ionic liquid has thermosensitive properties and can gradually dissolve during catalytic reactions, allowing for full utilization of active sites. Furthermore, the hydrogen bond donor can synergistically activate epoxides with the anions of the ionic liquid, thereby efficiently promoting the formation of cyclic carbonates.

[0035] (2) Compared with traditional polymeric ionic liquid catalysts, this type of hydrogen bond donor-functionalized UCST polymeric ionic liquid gradually dissolves during the reaction, allowing the active sites inside the polymeric ionic liquid to be fully utilized, resulting in higher catalytic activity. Compared with other UCST polymeric ionic liquids, this type of hydrogen bond donor-functionalized UCST polymeric ionic liquid has a variety of active sites. The hydrogen bond donors can synergistically activate the epoxy with the anions of the ionic liquid, further enhancing the catalytic activity. It can exhibit catalytic activity comparable to that of its monomer homogeneous catalysis under milder conditions. Detailed Implementation

[0036] To facilitate a better understanding of the present invention, specific embodiments are provided below for further explanation. However, the present invention is not limited to the technical scope of the embodiments; all embodiments described herein fall within the technical scope of the present invention without departing from the spirit and intent described above.

[0037] Example 1: Synthesis of UCST-type polymeric ionic liquid 1 functionalized with hydrogen bond donors:

[0038] Acrylamide, halogenated 1-vinyl-3-ethylimidazolium, 2-(dodecyltrithiocarbonyl)-2-methylpropionic acid, and azobisisobutyronitrile (AIBN) in a molar ratio of 9:51:3:1 were added to a Schlenk flask, along with a certain amount of methanol, and mixed thoroughly at room temperature. The Schlenk flask was then evacuated and purged with an inert gas. The inert gas-purged flask was placed in an oil bath at 70°C and reacted for a period of time, followed by air quenching. Most of the solvent was removed by rotary evaporation, and the residue was washed with solvent. The obtained solid was then dried in a vacuum drying oven for 24 hours to obtain the catalyst product. The synthesized hydrogen-bonded donor-functionalized UCST-type polymeric ionic liquid 1 has the following structure:

[0039]

[0040] Example 2: Synthesis of UCST-type polymeric ionic liquid 2 functionalized with hydrogen bond donors:

[0041] The preparation method is as described in Example 1, except that halogenated 1-vinyl-3-butylimidazole is substituted for halogenated 1-vinyl-3-ethylimidazole, and the molar ratio of acrylamide, halogenated 1-vinyl-3-butylimidazole, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, and azobisisobutyronitrile is adjusted to 18:42:3:1. The synthesized hydrogen bond donor-functionalized UCST-type polymeric ionic liquid 2 has the following structure:

[0042]

[0043] Example 3: Synthesis of UCST-type polymeric ionic liquid 3 functionalized with hydrogen bond donors:

[0044] The preparation method is as described in Example 2, by replacing the molar ratio of 18:42:3:1 with a molar ratio of 30:30:3:1.

[0045] Example 4: Synthesis of UCST-type polymeric ionic liquid 4 functionalized with hydrogen bond donors:

[0046] The preparation method is as described in Example 2, by replacing the molar ratio of 30:30:3:1 with a molar ratio of 36:24:3:1.

[0047] The present invention utilizes a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid as a catalyst to efficiently catalyze the cycloaddition of epoxides dispersed in cyclic carbonates with CO2. The following examples illustrate the method, but the present invention is not limited to the technical scope of the examples. All examples are within the technical scope of the present invention without departing from the spirit described above.

[0048] Example 5:

[0049] 20 mmol of propylene carbonate, 10 mmol of propylene oxide, and UCST-type polymeric ionic liquid 3, functionalized with a hydrogen bond donor containing 0.3 mmol of halide anions, were added to a 25 ml stainless steel high-pressure reactor equipped with magnetic induction. The reactor was then sealed. 2 MPa of CO2 was introduced into the reactor at room temperature, and the reaction was carried out at 120 °C for 2 h to obtain the product cyclic carbonate in a yield of 92.2%.

[0050] Example 6:

[0051] The only difference from Example 5 is that the catalyst is replaced with a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid 1, and the yield of propylene carbonate is 86.9%.

[0052] Example 7:

[0053] The only difference from Example 5 is that the catalyst is replaced with a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid 2, and the yield of propylene carbonate is 90.2%.

[0054] Example 8:

[0055] The only difference from Example 5 is that the catalyst is replaced with a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid 4, and the yield of propylene carbonate is 87.7%.

[0056] Example 9:

[0057] The only difference from Example 5 is that the temperature was changed to 100°C, and the yield of propylene carbonate was 60.7%.

[0058] Example 10:

[0059] The only difference from Example 9 is that the reaction time was changed to 4 hours, and the yield of propylene carbonate was 81.2%.

[0060] Example 11:

[0061] The only difference from Example 10 is that the catalyst was replaced with a UCST-type polymeric ionic liquid 3 functionalized with a hydrogen bond donor containing 0.04 mmol of halide anion, and the yield of propylene carbonate was 92.6%.

[0062] Example 12:

[0063] The only difference from Example 11 is that the catalyst is replaced with the corresponding molar amounts of halogenated 1-vinyl-3-butylimidazolium and acrylamide, and the yield of propylene carbonate is 90.7%.

[0064] Example 13:

[0065] The difference from Example 11 is that the epoxy compound is replaced with 100 mol% epoxide bromide, the catalyst is replaced with UCST type polymeric ionic liquid 3 functionalized with a hydrogen bond donor of 0.01 mmol halide anion, and the yield of the corresponding cyclic carbonate is 99.6%.

[0066] In summary, this invention provides a simple and feasible method for synthesizing UCST-type polymeric ionic liquids with hydrogen bond donor functionalization. These liquids gradually dissolve during the catalytic addition reaction of epoxy with CO2, allowing full utilization of the active sites within the polymeric ionic liquid. Furthermore, the hydrogen bonds can synergistically activate the epoxy with the ionic liquid anions, achieving highly efficient catalytic reaction.

[0067] Although the present invention has been described in detail above with general description and specific embodiments, modifications or improvements can be made by those skilled in the art based on the present invention, and all such modifications or improvements fall within the scope of the present invention. Therefore, any modifications or improvements made without departing from the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for synthesizing cyclic carbonates using UCST-type polymeric ionic liquids catalyzed by hydrogen bond donor functionalization, characterized in that, The hydrogen bond donor-functionalized UCST-type polymeric ionic liquid catalyst is formed by RAFT polymerization of acrylamide and halogenated 1-vinyl-3-alkylimidazolium monomers in different molar ratios, using trithiocarbonate chain transfer agents, and has the structure shown in Formula 1: Where m, n, p and q are each independently selected from any natural number, and m≥10, n≥2; R1 is independently selected from hydrogen atoms or any group, such as -CN, -OCH3, -COOH, -CH3, -NH2, -OH, etc. X - For Cl - ,Br - I - Any one of them.

2. The method for synthesizing cyclic carbonates catalyzed by a UCST-type polymeric ionic liquid with hydrogen bond donor functionalization according to claim 1, characterized in that, The trithiocarbonate chain transfer agent described herein has the structure shown in Formula 2: Where m is independently selected from any natural number, and m≥10; R is independently selected from hydrogen atoms or any group, such as -CN, -OCH3, -COOH, -CH3, -NH2, -OH, etc.

3. The method for synthesizing cyclic carbonates using a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid according to claim 1, characterized in that, The preparation method of the hydrogen bond donor-functionalized UCST-type polymeric ionic liquid catalyst includes the following steps: Acrylamide, halogenated 1-vinyl-3-alkylimidazolium, azobisisobutyronitrile and trithiocarbonate chain transfer reagents were dissolved in a solvent in a certain molar ratio, and then polymerized for a period of time under an inert gas atmosphere. After the reaction was completed, the solvent was removed by rotary evaporator, the residue was washed with solvent, and the obtained polymeric ionic liquid was dried to constant weight under vacuum conditions of 50-100℃ to remove a small amount of solvent.

4. The method for synthesizing cyclic carbonates using a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid according to claim 1, characterized in that, The hydrogen bond donor-functionalized UCST polymeric ionic liquid is soluble in cyclic carbonates at 80–150 °C and precipitates from the cyclic carbonates at temperatures below 100 °C.

5. The method for synthesizing cyclic carbonates using a hydrogen bond donor-functionalized UCST-type polymeric ionic liquid catalysis according to claim 1, characterized in that, The UCST polymeric ionic liquid is functionalized with hydrogen bond donors, wherein the hydrogen bond donors and ionic liquid anions synergistically activate the epoxy ring-opening process.

6. The method for synthesizing cyclic carbonates using hydrogen bond donor-functionalized UCST-type polymeric ionic liquids according to claim 1, characterized in that, The method for synthesizing cyclic carbonates includes the following steps: An epoxy compound dispersed in a cyclic carbonate and a certain amount of hydrogen bond donor-functionalized UCST-type polymeric ionic liquid were placed in a sealed reactor, and CO2 gas was introduced into the reactor at room temperature. The reaction was then maintained at a certain temperature for a period of time to convert the epoxy compound into a cyclic carbonate. After the reaction was completed, the temperature was lowered, and the hydrogen bond donor-functionalized UCST-type polymeric ionic liquid was recovered from the reaction system by temperature-controlled phase separation.

7. The synthesis step of the cyclic carbonate method according to claim 6, characterized in that, The concentration of the epoxy compound dispersed in the cyclic carbonate is 10–100 mol%; the amount of UCST-type polymeric ionic liquid functionalized with hydrogen bond donor is 0.5–7 mol% of the added epoxy compound; the pressure of the CO2 gas is 0.5–4 MPa; the reaction temperature is 50–130 °C; and the reaction time is 0.5–8 h.

8. The synthesis step of the cyclic carbonate according to claim 6, characterized in that, The epoxy compound is any one of ethylene oxide, propylene oxide, butane oxide, epichlorohydrin, bromopropane, styrene oxide, cyclohexane oxide, and cyclopentane oxide.

9. The synthesis step of the cyclic carbonate according to claim 6, characterized in that, The yield of the cyclic carbonate is 40-99%.

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