A method for preparing a cyclic carbonate

Abstract

The present invention discloses a method for preparing cyclic carbonates, which uses one or more of the natural biological source carnitines shown in formulas (I) to (IV) as catalysts to catalyze the cycloaddition reaction of epoxides with carbon dioxide to obtain cyclic carbonates. Compared with the existing catalytic systems, the present invention has obvious advantages such as being green, mild, efficient, metal-free, halogen-free, and solvent-free.

Description

Technical Field

[0001] The present invention belongs to the technical field of green catalytic synthesis, and specifically relates to a method for preparing cyclic carbonates. Background Art

[0002] Carbon dioxide, as a greenhouse gas causing climate change, has attracted great attention. Due to the combustion of carbonaceous fuels and human activities, 35 billion tons of carbon dioxide are produced annually. The carbon atoms in CO2 exist in their most oxidized state, which endows CO2 with inherent thermodynamic stability and kinetic inertness. Therefore, it is very difficult to convert CO2 into useful products and chemicals under normal conditions. Generally, the conversion of CO2 requires a large amount of energy input, which leads to high costs and greenhouse gas emissions.

[0003] The catalytic systems for cycloaddition reactions are divided into metal catalysis and organocatalysis. Among them, metal catalysis has high activity, but there is metal residue, which is seriously harmful to the human body and nature; relatively speaking, organocatalysis belongs to the green chemistry process, conforms to the green and sustainable development strategy, and is also a research hotspot in recent years.

[0004] Most organocatalysts require high temperature (>100 °C) and pressure (>10 atm). Therefore, developing a green, efficient, and inexpensive catalyst for cycloaddition reactions is an important research direction. Summary of the Invention

[0005] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments.

[0006] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method that can efficiently catalyze the reaction of epoxides and CO2 to synthesize cyclic carbonates and their derivatives. The catalyst used in this method is natural carnitine, and cyclic carbonates can be obtained through a one-step reaction, without the need for harsh reaction conditions such as high temperature, high pressure, anhydrous and anaerobic conditions, without solvents, and without metal residues. Even when the catalyst loading is low (catalyst: raw material ≤ 1 mol%), a yield of 97% or more can still be obtained in a short time. The catalyst used in this method is green, economical, has good chemical stability and higher catalytic efficiency, and the obtained cyclic carbonates have great application potential in the fields of food packaging, biomedicine, and microelectronics.

[0007] In order to achieve the above purpose, the present invention specifically adopts the following technical solutions:

[0008] The present invention selects four natural carnitines, which can effectively catalyze the cycloaddition of epoxides and carbon dioxide to obtain cyclic carbonates. The carnitines are shown as formulas I-IV:

[0009]

[0010]

[0011] The epoxide selected from the structure of formula V:

[0012]

[0013] wherein R 1 and R 2 are selected from hydrogen, branched or straight-chain alkyl having 1 to 4 carbon atoms, allyl, phenyl, halogen or alkyl-substituted phenyl, chlorine or bromine-substituted alkyl or R 3 -O-CH2-, said R 3 is selected from phenyl, phenyl substituted by alkyl having 1 to 4 carbon atoms, allyl or branched or straight-chain alkyl having 1 to 4 carbon atoms.

[0014] Preferably, the epoxide of formula V is selected from 3-chloro-1,2-epoxypropane, 3-bromo-1,2-epoxypropane, 1,2-epoxy-3-butene, 1,2-epoxy-5-hexene, 1,2-epoxyhexane, 1,2-epoxy-3-methoxypropane, 4-chlorostyrene epoxide, 2-(methoxymethyl)oxirane, 2-(tert-butoxymethyl)oxirane, 1-allyloxy-2,3-epoxypropane, 2-phenyloxirane, 1,2-epoxy-3-phenoxypropane or 2-[(2-methylphenoxy)methyl]oxirane, 1,2-epoxycyclohexane, 2-((benzyloxy)methyl)oxirane, 2,2-bis(glycidyloxyphenyl)propane polymer or bisphenol A epoxy resin (E-O3 type);

[0015] The structure of the epoxide is shown in the following table:

[0016]

[0017] Preferably, the reaction temperature of the preparation method is 80 to 120 °C, the initial pressure of carbon dioxide is 0.1 to 1 MPa, and the amount of the catalyst is 0.5 mol% to 5 mol%;

[0018] Particularly preferably, the reaction temperature of the preparation method is 100 °C and 120 °C, the initial pressure of carbon dioxide is 0.1 MPa, the pressure is increased to 1 MPa for the reaction, and the amount of the catalyst is 0.5 mol% to 1 mol%.

[0019] Preferably, the specific steps of the preparation method include:

[0020] (1) Adding natural-source carnitine and epoxide into a reaction tube, stirring at room temperature for 5 to 10 min, and then replacing the air in the reaction vessel with carbon dioxide for more than 3 times;

[0021] (2) Charge the reaction vessel with CO2 to an initial pressure of 0.1 MPa, heat it up to 100 °C or 120 °C, and increase the pressure to 1 MPa for reaction;

[0022] (3) React for 1 - 12 h, cool down, and obtain the cyclic carbonate by column chromatography of the reaction solution.

[0023] The mechanism of the inventive method of the present invention is as follows: The carboxylate anion of carnitine attacks the methylene group, opening the ring structure, and the quaternary ammonium salt cation activates carbon dioxide to carry out a cycloaddition reaction to obtain a five - membered cyclic carbonate.

[0024] Advantages of the present invention:

[0025] (1) The catalyst used in the present invention is of natural origin, green and environmentally friendly.

[0026] (2) The present invention provides a method for preparing cyclic carbonates from carbon dioxide and epoxides by a "one - pot method" under relatively mild conditions.

[0027] (3) The catalyst used in the present invention is metal - free, and the resulting product has no metal residue, having great application prospects in the fields of biomedicine, etc.; the catalytic system used in the present invention is halogen - free and has no corrosion to general aluminum metal containers, which is conducive to further industrial application research.

[0028] (4) The reaction process does not require the use of solvents, avoiding the toxicity of organic solvents; the catalyst loading used in the present invention is relatively low, and good yields can be obtained in a relatively short time.

[0029] In summary, compared with the existing catalytic systems, the present invention has obvious advantages such as being green, mild, efficient, metal - free, halogen - free, and solvent - free. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. Among them:

[0031] Figure 1 It is the 1H NMR spectrum of the cyclic carbonate obtained in Example 1;

[0032] Figure 2 It is the 1H NMR spectrum of the cyclic carbonate obtained in Example 11;

[0033] Figure 3 It is the 1H NMR spectrum of the cyclic carbonate obtained in Example 14;

[0034] Figure 41H NMR spectrum of the cyclic carbonate obtained in Example 15;

[0035] Figure 5 1H NMR spectrum of the cyclic carbonate obtained in Example 16;

[0036] Figure 6 1H NMR spectrum of the cyclic carbonate obtained in Example 17;

[0037] Figure 7 1H NMR spectrum of the cyclic carbonate obtained in Example 18;

[0038] Figure 8 1H NMR spectrum of the cyclic carbonate obtained in Example 19;

[0039] Figure 9 1H NMR spectrum of the cyclic carbonate obtained in Example 20. Detailed implementation manners

[0040] To make the above objects, features and advantages of the present invention more obvious and understandable, the following specific embodiments are used to describe the detailed implementation manners of the present invention in detail.

[0041] The 1H NMR spectra involved in the examples were measured using a Bruker Ascend TM-400 NMR spectrometer from Bruker Corporation, and the deuterated reagent used was deuterated chloroform (CDCl3).

[0042] The structures of the catalysts used in the following examples are as follows:

[0043]

[0044] The structures of the epoxides used in the following examples are as follows:

[0045]

[0046] Example 1:

[0047] Add acetyl carnitine (I) (0.1 mmol) and epoxide 9 (10 mmol) to a Schlenk reaction tube in sequence, and stir for 5 min. Replace the gas in the tube through a double-tube. Tie a balloon filled with CO2 to the rubber stopper at the tube mouth to provide the CO2 required for the reaction, and place it in an oil bath at 120 °C for 6 h. After the reaction is completed, cool it, separate it by column chromatography (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis was carried out by 1H NMR, and the conversion rate was 59% (±2.3%), and the selectivity was 99%. The 1H NMR spectrum of the product is as shown in the appendix Figure 1 as shown 11H NMR (400 MHz, Chloroform-d) δ 7.37 - 7.25 (m, 3H), 7.25 (dd, J = 7.4, 2.4 Hz, 2H), 5.57 (t, J = 8.0 Hz, 1H), 4.69 (t, J = 8.4 Hz, 1H), 4.22 (t, J = 8.2 Hz, 1H).

[0048] Example 2:

[0049] Add acetylcarnitine (I) (0.1 mmol) and epoxide 9 (10 mmol) into a stainless-steel pressure reaction tube in sequence, and stir for 5 min. Replace the air in the tube with CO2 three times by charging. Charge 1 MPa CO2 into the reaction tube, place it in an oil bath at 120 °C, and react for 4 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether: ethyl acetate = 5:1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by 1H NMR, and the conversion rate is 44% (±1.9%), and the selectivity is 99%.

[0050] Example 3:

[0051] Add acetylcarnitine (I) (0.1 mmol) and epoxide 9 (10 mmol) into a stainless-steel pressure reaction tube in sequence, and stir for 5 min. Replace the air in the tube with CO2 three times by charging. Charge 1 MPa CO2 into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by 1H NMR, and the conversion rate is 97% (±1.0%), and the selectivity is 99%.

[0052] Example 4:

[0053] Add acetylcarnitine (I) (0.05 mmol) and epoxide 9 (10 mmol) into a stainless-steel pressure reaction tube in sequence, and stir for 5 min. Replace the air in the tube with CO2 three times by charging. Charge 1 MPa CO2 into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by 1H NMR, and the conversion rate is 24% (±3.3%), and the selectivity is 99%.

[0054] Example 5:

[0055] Add acetylcarnitine (I) (0.1mmol) and epoxide 9 (10mmol) to a stainless steel pressure reaction tube in sequence and stir for 5min. Replace the air in the tube by filling CO2 three times. Fill the reaction vessel with 1MPa CO2 and put it into an oil pan at 120℃ for 12h. After the reaction is completed, cool it, separate it with a chromatographic column (petroleum ether: ethyl acetate = 5:1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis by nuclear magnetic hydrogen spectrum shows a conversion rate of 99% (±0.4%) and a selectivity of 99%.

[0056] Embodiment 6:

[0057] Add acetylcarnitine (1) (0.1mmol) and epoxide 9 (10mmol) to a stainless steel pressure reaction tube in sequence and stir for 5 minutes. Replace the air in the tube by filling CO2 three times. Fill the reaction vessel with 1MPa CO2 and put it into an oil pan at 100°C for 6 hours. After the reaction is completed, cool it, separate it with a chromatographic column (petroleum ether: ethyl acetate = 5:1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis by nuclear magnetic hydrogen spectrum shows a conversion rate of 12% (±2.3%) and a selectivity of 99%.

[0058] Embodiment 7:

[0059] Add acetylcarnitine (I) (0.1mmol) and epoxide 9 (10mmol) to a stainless steel pressure reaction tube in sequence and stir for 5min. Replace the air in the tube by filling CO2 three times. Fill the reaction vessel with 1MPa CO2 and put it into an oil pan at 80℃ for 6h. After the reaction is completed, cool it, separate it with a chromatographic column (petroleum ether: ethyl acetate = 5:1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis by nuclear magnetic hydrogen spectrum shows a conversion rate of 3% (±0.8%) and a selectivity of 99%.

[0060] Embodiment 8:

[0061] Add L-carnitine (II) (0.1mmol) and epoxide 9 (10mmol) to a stainless steel pressure reaction tube in sequence and stir for 5min. Replace the air in the tube by filling CO2 three times. Fill the reaction vessel with 1MPa CO2 and put it into an oil pan at 120℃ for 6h. After the reaction is completed, cool it, separate it with a chromatographic column (petroleum ether: ethyl acetate = 5:1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis by nuclear magnetic hydrogen spectrum shows a conversion rate of 10% (±1.2%) and a selectivity of 99%.

[0062] Embodiment 9:

[0063] Add γ-butyl betaine (III) (0.1mmol) and epoxide 9 (10mmol) to a stainless steel pressure reaction tube in sequence and stir for 5 minutes. Replace the air in the tube by filling CO2 three times. Fill the reaction vessel with 1MPa CO2 and put it into an oil pan at 120°C for 6 hours. After the reaction is completed, cool it, separate it with a chromatographic column (petroleum ether: ethyl acetate = 5:1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis by nuclear magnetic hydrogen spectrum shows a conversion rate of 26% (±1.6%) and a selectivity of 99%.

[0064] Embodiment 10:

[0065] Add β-homobetaine (IV) (0.1mmol) and epoxide 9 (10mmol) to a stainless steel pressure reaction tube and stir for 5 minutes. Replace the air in the tube by filling CO2 three times. Fill the reaction vessel with 1MPa CO2 and put it into an oil pan at 120℃ for 6 hours. After the reaction is completed, cool it, separate it with a chromatographic column (petroleum ether: ethyl acetate = 5:1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis by nuclear magnetic hydrogen spectrum shows a conversion rate of 66% (±2.0%) and a selectivity of 99%.

[0066] Embodiment 11:

[0067] Add acetylcarnitine (I) (0.1mmol) and epoxide 1 (10mmol) to a stainless steel pressure reaction tube in sequence and stir for 5 minutes. Replace the air in the tube by filling CO2 three times. Fill the reaction vessel with 1MPa CO2 and put it into an oil pan at 120°C for 6 hours. After the reaction is completed, cool it, separate it with a chromatographic column (petroleum ether: ethyl acetate = 5:1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis by nuclear magnetic hydrogen spectrum obtained a conversion rate of 99% (±0.4%) and a selectivity of 99%. The hydrogen spectrum of the product is shown in the attached figure. Figure 2 As shown, 1 H NMR (400MHz, Chloroform-d) δ4.99 (ddt, J=8.3, 5.7, 3.9Hz, 1H), 4.55 (t, J=8.7Hz, 1H), 4.33 (dd, J=8.9, 5.7Hz, 1H), 3.80 (dd, J=12.5, 4.3Hz, 1H), 3.69 (dd, J=12.5, 3.7Hz, 1H).

[0068] Embodiment 12:

[0069] Add acetylcarnitine (I) (0.1 mmol) and epoxide 2 (10 mmol) successively into a stainless-steel pressure reaction tube and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa of CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Perform qualitative and quantitative analysis by nuclear magnetic resonance hydrogen spectrum, and obtain a conversion rate of 99% (±0.4%) and a selectivity of 99%.

[0070] Example 13:

[0071] Add acetylcarnitine (I) (0.1 mmol) and epoxide 3 (10 mmol) successively into a stainless-steel pressure reaction tube and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa of CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Perform qualitative and quantitative analysis by nuclear magnetic resonance hydrogen spectrum, and obtain a conversion rate of 97% (±2.3%) and a selectivity of 99%.

[0072] Example 14:

[0073] Add acetylcarnitine (I) (0.1 mmol) and epoxide 4 (10 mmol) successively into a stainless-steel pressure reaction tube and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa of CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Perform qualitative and quantitative analysis by nuclear magnetic resonance hydrogen spectrum, and obtain a conversion rate of 88% (±1.9%) and a selectivity of 99%. The hydrogen spectrum of the product is as follows Figure 3 shown 1 H NMR (400 MHz, Chloroform-d) δ 5.78 (ddt, J = 16.9, 10.1, 6.6 Hz, 1H), 5.10 - 5.01 (m, 2H), 4.72 (qd, J = 7.7, 5.1 Hz, 1H), 4.52 (t, J = 8.1 Hz, 1H), 4.09 - 4.05 (m, 1H), 2.25 - 2.11 (m, 2H), 1.98 - 1.86 (m, 1H), 1.80 - 1.71 (m, 1H).

[0074] Example 15:

[0075] Add acetylcarnitine (I) (0.1 mmol) and epoxide 5 (10 mmol) into a stainless-steel pressure reaction tube in sequence, and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by a chromatographic column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by ¹H NMR, and the conversion rate is 64% (±1.7%), and the selectivity is 99%. The ¹H NMR spectrum of the product is as shown in the appendix Figure 4 as follows, 1 ¹H NMR (400 MHz, Chloroform-d) δ 4.70 (qd, J = 7.4, 5.3 Hz, 1H), 4.52 (t, J = 8.1 Hz, 1H), 4.17 - 4.01 (m, 1H), 1.74 (dddd, J = 44.8, 14.1, 8.6, 4.8 Hz, 2H), 1.41 - 1.26 (m, 5H), 0.93 - 0.85 (m, 3H).

[0076] Example 16:

[0077] Add acetylcarnitine (I) (0.1 mmol) and epoxide 6 (10 mmol) into a stainless-steel pressure reaction tube in sequence, and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by a chromatographic column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by ¹H NMR, and the conversion rate is 96% (±2.1%), and the selectivity is 99%. The ¹H NMR spectrum of the product is as shown in the appendix Figure 5 as follows, 1 ¹H NMR (400 MHz, Chloroform-d) δ 4.79 (ddt, J = 8.3, 6.1, 3.7 Hz, 1H), 4.47 (t, J = 8.4 Hz, 1H), 4.35 - 4.28 (m, 1H), 3.67 - 3.48 (m, 2H), 3.39 (s, 3H).

[0078] Example 17:

[0079] Add acetylcarnitine (I) (0.1 mmol) and epoxide 7 (10 mmol) successively into a stainless-steel pressure reaction tube, and stir for 5 min. Replace the air in the tube with CO2 three times by charging. Charge 1 MPa CO2 into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by 1H NMR, and the conversion rate is 94% (±1.4%), and the selectivity is 99%. The 1H NMR spectrum of the product is as shown in Figure 6 shown below, 1 H NMR (400 MHz, Chloroform-d) δ 4.80 - 4.74 (m, 1H), 4.47 (t, J = 8.2 Hz, 1H), 4.42 - 4.37 (m, 1H), 3.61 (dd, J = 10.3, 4.7 Hz, 1H), 3.53 (dd, J = 10.3, 3.6 Hz, 1H), 1.19 (s, 9H).

[0080] Example 18:

[0081] Add acetylcarnitine (I) (0.1 mmol) and epoxide 8 (10 mmol) successively into a stainless-steel pressure reaction tube, and stir for 5 min. Replace the air in the tube with CO2 three times by charging. Charge 1 MPa CO2 into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by 1H NMR, and the conversion rate is 99% (±0.4%), and the selectivity is 99%. The 1H NMR spectrum of the product is as shown in Figure 7 shown below, 1 H NMR (400 MHz, Chloroform-d) δ 5.96 - 5.70 (m, 1H), 5.32 - 5.09 (m, 2H), 4.79 (ddt, J = 9.2, 6.6, 3.6 Hz, 1H), 4.54 - 4.29 (m, 2H), 4.09 - 3.92 (m, 2H), 3.69 - 3.50 (m, 2H).

[0082] Example 19:

[0083] Add acetylcarnitine (1) (0.1 mmol) and epoxide 10 (10 mmol) into a stainless-steel pressure reaction tube in sequence, and stir for 5 min. Replace the air in the tube with CO2 three times by charging. Charge 1 MPa of CO2 into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by a chromatographic column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by 1H NMR, and the conversion rate is 99% (±0.4%), and the selectivity is 99%. The 1H NMR spectrum of the product is as shown in the appendix Figure 8 as follows 1 H NMR (400 MHz, Chloroform-d) δ 7.26 - 7.17 (m, 2H), 6.95 (tt, J = 7.5, 1.1 Hz, 1H), 6.85 - 6.76 (m, 1H), 4.96 (dddd, J = 8.1, 5.9, 4.4, 3.6 Hz, 1H), 4.58 - 4.45 (m, 1H), 4.23 - 4.06 (m, 1H).

[0084] Example 20:

[0085] Add acetylcarnitine (I) (0.1 mmol) and epoxide 11 (10 mmol) into a stainless-steel pressure reaction tube in sequence, and stir for 5 min. Replace the air in the tube with CO2 three times by charging. Charge 1 MPa of CO2 into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by a chromatographic column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by 1H NMR, and the conversion rate is 99% (±0.1%), and the selectivity is 99%. The 1H NMR spectrum of the product is as shown in the appendix Figure 9 as follows 1 H NMR (400 MHz, Chloroform-d) δ 7.16 (td, J = 4.5, 2.3 Hz, 2H), 6.93 (td, J = 7.4, 1.0 Hz, 1H), 6.82 - 6.73 (m, 1H), 5.05 (ddt, J = 8.6, 5.5, 3.3 Hz, 1H), 4.65 - 4.54 (m, 2H), 4.26 (dd, J = 10.6, 3.6 Hz, 1H), 4.13 (dd, J = 10.6, 3.1 Hz, 1H).

[0086] Example 21:

[0087] Add acetylcarnitine (I) (0.1 mmol) and epoxide 13 (10 mmol) successively into a stainless-steel pressure reaction tube and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa of CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by ¹H NMR, and the conversion rate is 93% (±1.5%), and the selectivity is 99%.

[0088] Example 22:

[0089] Add acetylcarnitine (I) (0.1 mmol) and epoxide 14 (10 mmol) successively into a stainless-steel pressure reaction tube and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa of CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 6 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by ¹H NMR, and the conversion rate is 70% (±1.3%), and the selectivity is 99%.

[0090] Example 23:

[0091] Add guanine (0.1 mmol), MTBD (0.1 mmol), and epoxide 9 (10 mmol) successively into a stainless-steel pressure reaction tube and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa of CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 24 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by ¹H NMR, and the conversion rate is 61% (±1.7%), and the selectivity is 99%.

[0092] Example 24:

[0093] Add γ-butyric acid (0.1 mmol), MTBD (0.1 mmol), and epoxide 9 (10 mmol) successively into a stainless-steel pressure reaction tube and stir for 5 min. Replace the air in the tube with CO₂ three times by charging. Charge 1 MPa of CO₂ into the reaction vessel, place it in an oil bath at 120 °C, and react for 24 h. After the reaction is completed, cool it, separate by chromatography column (petroleum ether∶ethyl acetate = 5∶1), and then dry the product to obtain a brown oily liquid. Qualitative and quantitative analysis is carried out by ¹H NMR, and the conversion rate is 43% (±3.0%), and the selectivity is 99%.

[0094] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a cyclic carbonate, characterized in that: One or more of the natural biological source carnitines shown in formulas (I)-(IV) are used as catalysts to catalyze the cycloaddition reaction of epoxides with carbon dioxide to obtain cyclic carbonates; The epoxides described are selected from the compounds shown in 1-14 below:

2. The method for preparing a cyclic carbonate according to claim 1, wherein: Including adding the carnitine and epoxide into a reaction vessel, stirring evenly at room temperature, charging CO2 and pressurizing, heating up, carrying out the reaction, cooling, and purifying to obtain cyclic carbonates.

3. The method for preparing a cyclic carbonate according to claim 1 or 2, characterized in that: The addition amount of the carnitine is 0.5 mol% to 5 mol% of the epoxide.

4. The method for preparing the cyclic carbonate according to claim 2, wherein: The pressure of CO2 is 0 to 1.5 MPa.

5. The method for preparing a cyclic carbonate according to claim 2, wherein: For the heating up, the temperature is 100 °C to 120 °C; for the carrying out of the reaction, the reaction time is 1 to 24 h.

6. The method for preparing a cyclic carbonate according to claim 2, characterized in that: The pressure of CO2 is 0.1 to 1 MPa; the addition amount of the carnitine is 0.5 mol% to 1 mol% of the epoxide.

7. The cyclic carbonate obtained by the method for preparing a cyclic carbonate according to claim 1, characterized in that: The cyclic carbonate is shown by the following formula:

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