Method for preparing asymmetric linear carbonates

Abstract

The present description relates to methods for preparing asymmetric linear carbonates.

Description

Technical Field

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0119070 filed in the Korean Intellectual Property Office on September 7, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present description relates to methods for preparing asymmetric linear carbonates. Background Art

[0003] Asymmetric linear carbonates are commonly used as electrolytes for lithium secondary batteries. Compared with existing electrolytes, asymmetric linear carbonates have excellent energy storage density, charge capacity, charge / discharge recovery, stability, etc. Therefore, asymmetric linear carbonates are commonly used as electrolytes, especially electrolytes for lithium secondary batteries.

[0004] As a method for preparing asymmetric linear carbonates, there is a method using an ester reaction of an alkyl chloroformate and an alcohol in the presence of a basic catalyst, but this method has the problem that the ester reaction is very violent and requires the use of highly toxic compounds such as phosgene and bisphenol A as starting materials. To remedy this problem, there is a method using a symmetrical linear carbonate and an alcohol having an alkyl group in the presence of a basic catalyst such as a metal carbonate for transesterification, but this method has the following problems: low catalytic activity and production yield, and the need to separate and purify the asymmetric linear carbonate such as ethyl methyl carbonate as the final target compound from a total of five reaction products including three types of linear carbonates and two types of alcohols. As another method, a method for preparing asymmetric linear carbonates using a mixed oxide of a Group 3 rare earth metal in the presence of moisture or alcohol is disclosed, but there is a problem that this method requires a long period of time of 200 hours or more. Summary of the Invention

[0005] Technical issues

[0006] This specification is directed to providing methods for preparing asymmetric linear carbonates.

[0007] Technical Solution

[0008] According to an exemplary embodiment of the present specification, there is provided a method for preparing an asymmetric linear carbonate, the method including subjecting a first symmetric linear carbonate and a second symmetric linear carbonate to transesterification under a catalyst represented by the following Chemical Formula 1.

[0009] [Chemical Formula 1]

[0010]

[0011] In Chemical Formula 1,

[0012] R1 to R3 are the same as or different from each other, and are each independently hydrogen; or a linear or branched alkyl group having 1 to 4 carbon atoms.

[0013] Beneficial effects

[0014] With the method for preparing an asymmetric linear carbonate according to an exemplary embodiment of the present specification, the process is simple and purification is easily performed, so that the asymmetric linear carbonate can be economically prepared. DETAILED DESCRIPTION

[0015] Hereinafter, this specification will be described in more detail.

[0016] According to an exemplary embodiment of the present specification, there is provided a method for preparing an asymmetric linear carbonate, the method including subjecting a first symmetric linear carbonate and a second symmetric linear carbonate to transesterification under a catalyst represented by the following Chemical Formula 1.

[0017] [Chemical Formula 1]

[0018]

[0019] In Chemical Formula 1,

[0020] R1 to R3 are the same as or different from each other, and are each independently hydrogen; or a linear or branched alkyl group having 1 to 4 carbon atoms.

[0021] In an exemplary embodiment of the present specification, a portion in which no substituent is indicated in Chemical Formula 1 may mean substituted with hydrogen.

[0022] According to an exemplary embodiment of the present specification, the catalyst of Chemical Formula 1 is an ionic liquid catalyst.

[0023] According to an exemplary embodiment of the present specification, the catalyst of Chemical Formula 1 is an amidine-based ionic liquid catalyst.

[0024] According to an exemplary embodiment of the present specification, the method for preparing an asymmetric linear carbonate does not include a solvent (solvent-free).

[0025] According to the preparation method in the related art, since two types of linear carbonates and an alcohol-based solvent are used, the preparation process is complicated, and at least five types of mixtures containing the final target compound are obtained using the alcohol-based solvent, making the purification process for obtaining the final target asymmetric linear carbonate very complicated.

[0026] According to an exemplary embodiment of the present specification, since the method for preparing an asymmetric linear carbonate is carried out when the first symmetric linear carbonate, the second symmetric linear carbonate, and the catalyst of Chemical Formula 1 participating in the transesterification reaction are all liquid substances and are uniformly mixed without using a solvent such as an alcohol-based solvent, a separate solvent is not required, making the process simple, and after the reaction is completed, only the first symmetric linear carbonate, the second symmetric linear carbonate, and the final target asymmetric linear carbonate are produced as a mixture of three types, so the product is easy to separate and purify, the process cost is low, and the obtained first symmetric linear carbonate and the second symmetric linear carbonate can be reused in the process of preparing an asymmetric linear carbonate, so the method for preparing an asymmetric linear carbonate is very economical compared to the method in the related art.

[0027] According to an exemplary embodiment of the specification, three types of mixtures may be separated and purified by fractional distillation using a difference in boiling points.

[0028] According to an exemplary embodiment of the present specification, the first symmetrical linear carbonate is dimethyl carbonate (DMC).

[0029] According to an exemplary embodiment of the present specification, the second symmetrical linear carbonate is diethyl carbonate (DEC).

[0030] According to an exemplary embodiment of the present specification, the temperature of the transesterification reaction is 80°C to 120°C, preferably 90°C to 100°C, and more preferably 95°C to 100°C.

[0031] When the reaction is carried out at the reaction temperature, the transesterification rate of the first symmetrical linear carbonate and the second symmetrical linear carbonate is optimized, and the yield of the asymmetrical linear carbonate is excellent.

[0032] According to an exemplary embodiment of the present specification, the transesterification reaction is a closed system reaction. A closed system reaction is a physical system that exchanges only energy but not substances with the outside, and the transesterification reaction is performed using only the first symmetrical linear carbonate, the second symmetrical linear carbonate, and the catalyst represented by Chemical Formula 1 without the inflow of external substances.

[0033] In the present specification, the alkyl group is linear or branched, and the number of carbon atoms of the alkyl group is 1 to 4. Specific examples of the alkyl group may include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, and the like.

[0034] According to an exemplary embodiment of the present specification, R1 is hydrogen, and R2 and R3 are the same as or different from each other, and are each independently hydrogen; methyl; or isopropyl.

[0035] According to an exemplary embodiment of the present specification, the catalyst represented by Chemical Formula 1 is any one selected from the following compounds.

[0036]

[0037] According to an exemplary embodiment of the present specification, the asymmetric linear carbonate prepared by the method for preparing an asymmetric linear carbonate is ethyl methyl carbonate (EMC).

[0038] According to an exemplary embodiment of the present specification, the asymmetric linear carbonate is ethyl methyl carbonate (EMC).

[0039] According to an exemplary embodiment of the present specification, an asymmetric linear carbonate may be used as an electrolyte for a lithium secondary battery.

[0040] Embodiments of the invention

[0041] Hereinafter, the present specification will be described in detail with reference to the embodiments for specifically describing the present specification. However, the embodiments according to the present specification can be modified in various forms, and the scope of the present specification is not to be construed as being limited to the embodiments described in detail below.

[0042] The embodiments of the present specification are provided to more clearly describe the present specification to those having ordinary skill in the art.

[0043] Synthesis Example 1. Preparation of Compound 1

[0044] 0.6 g of imidazole and 1.5 g of 1,8-diazabicyclo(5.4.0)undec-7-ene were placed in a 20 ml vial, and the resulting mixture was stirred at room temperature for 5 hours. When the reaction was completed, Compound 1 was obtained as a pale yellow liquid.

[0045]

[0046] Synthesis Example 2. Preparation of Compound 2

[0047] Compound 2 was obtained by synthesis in the same manner as in Synthesis Example 1, except that 0.8 g of 2-methyl-1H-imidazole was used instead of imidazole.

[0048]

[0049] Synthesis Example 3. Preparation of Compound 3

[0050] Compound 3 was obtained by synthesis in the same manner as in Synthesis Example 1, except that 0.8 g of 4-methyl-1H-imidazole was used instead of imidazole.

[0051]

[0052] Synthesis Example 4. Preparation of Compound 4

[0053] Compound 4 was obtained by synthesis in the same manner as in Synthesis Example 1, except that 1.1 g of 2-isopropyl-1H-imidazole was used instead of imidazole.

[0054]

[0055] Synthesis Example 5. Preparation of Compound 5

[0056] Compound 5 was obtained by synthesis in the same manner as in Synthesis Example 1, except that 1.1 g of 4-isopropyl-1H-imidazole was used instead of imidazole.

[0057]

[0058] Experimental Example. Preparation of ethyl methyl carbonate

[0059] Example 1

[0060] 10g dimethyl carbonate (DMC), 13.1g diethyl carbonate (DEC) (DMC:DEC=1:1, mol ratio) and 1 wt % of compound 1 (DMC standard 1 wt %) as catalyst are put into 100mL pressure reactor.The temperature is raised to 90 ℃ to 100 ℃, and the reaction is carried out under stirring for 4 hours.When the reaction is complete, gas chromatography (GC) analysis is carried out by sampling.

[0061] The reaction was carried out in a closed system and no additional pressure was applied.

[0062] The reaction proceeds as shown in the following Reaction Scheme 1 and does not produce products other than three types of substances.

[0063] [Reaction Scheme 1]

[0064]

[0065] Example 2

[0066] The reaction was carried out in the same manner as in Example 1, except that Compound 2 was used instead of Compound 1 as a catalyst.

[0067] Example 3

[0068] The reaction was carried out in the same manner as in Example 1, except that Compound 3 was used instead of Compound 1 as a catalyst.

[0069] Example 4

[0070] The reaction was carried out in the same manner as in Example 1, except that Compound 4 was used instead of Compound 1 as a catalyst.

[0071] Example 5

[0072] The reaction was carried out in the same manner as in Example 1, except that Compound 5 was used instead of Compound 1 as a catalyst.

[0073] Comparative Example 1

[0074] Dimethyl carbonate (DMC) (10 g), ethanol (EtOH) (5.1 g) (DMC:EtOH=1:1, molar ratio) and 1 wt % (DMC standard 1 wt %) of sodium ethoxide as a catalyst were placed in a 100 mL pressure reactor. The temperature was raised to 90° C. to 100° C., and the reaction was carried out under stirring for 4 hours. When the reaction was complete, GC analysis was performed by sampling.

[0075] The results of GC analysis of the materials prepared by the preparation methods of Examples 1 to 5 and Comparative Example 1 are shown in Table 1 below.

[0076] [Table 1]

[0077]

[0078] -DMC: dimethyl carbonate -DEC: diethyl carbonate

[0079] -EMC: Ethyl Methyl Carbonate

[0080] -MeOH: methanol

[0081] -EtOH: ethanol

[0082] In Table 1, in Comparative Example 1 using an alcohol-based solvent, which is a method in the related art, 5 types of mixtures containing EMC, which is a final target, were generated, making it difficult to separate and purify EMC.

[0083] In contrast, the preparation method according to an exemplary embodiment of the present specification is carried out when the first symmetrical linear carbonate, the second symmetrical linear carbonate, and the catalyst of Chemical Formula 1 involved in the transesterification reaction are all liquid substances and are uniformly mixed without using a solvent such as an alcohol-based solvent. Therefore, no separate solvent is required, making the process simple. In addition, after the reaction is completed, only DMC, DEC, and the final target EMC are produced as a mixture of three types. EMC is easy to separate and purify, the process cost is low, and DMC and DEC can be reused in the process of preparing an asymmetric linear carbonate. Therefore, it can be seen that the preparation method according to an exemplary embodiment of the present specification is very economical compared to the methods in the related art.

Claims

1. A method for preparing an asymmetric linear carbonate, comprising: The first symmetrical linear carbonate and the second symmetrical linear carbonate are subjected to transesterification in the presence of a catalyst represented by the following Chemical Formula 1: [Chemical Formula 1] Wherein, in Chemical Formula 1, R1 is hydrogen, and R2 and R3 are different from each other and are each independently hydrogen; or a linear or branched alkyl group having 1 to 4 carbon atoms, and At least one of R1 to R3 is a linear or branched alkyl group having 1 to 4 carbon atoms.

2. The method for preparing an asymmetric linear carbonate according to claim 1, wherein the method does not include a solvent. 3 . The method for preparing an asymmetric linear carbonate according to claim 1 , wherein the first symmetric linear carbonate is dimethyl carbonate (DMC). 4 . The method for preparing an asymmetric linear carbonate according to claim 1 , wherein the second symmetric linear carbonate is diethyl carbonate DEC. 5 . The method for preparing an asymmetric linear carbonate according to claim 1 , wherein the temperature of the transesterification reaction is 80° C. to 120° C.

6. The method for preparing an asymmetric linear carbonate according to claim 1, wherein R1 is hydrogen, and R2 and R3 are different from each other and are each independently hydrogen; methyl; or isopropyl.

7. The method for preparing an asymmetric linear carbonate according to claim 1, wherein the catalyst represented by Chemical Formula 1 is any one selected from the following compounds:

8. The method for preparing an asymmetric linear carbonate according to claim 1, wherein the asymmetric linear carbonate is ethyl methyl carbonate (EMC).

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