KR20060054533A - Method for preparing unsymmetric linear carbonate - Google Patents

Abstract

Disclosed is a process for preparing asymmetric linear carbonates useful as solvents for lithium secondary batteries and the like from symmetric linear carbonates. The method for preparing an asymmetric linear carbonate may include: transesterifying a symmetric linear carbonate and a linear ester compound in the presence of a basic catalyst; And separating the asymmetric linear carbonate from the product of the transesterification reaction, wherein the linear ester compound is preferably an acetate compound.

Asymmetric linear carbonates, linear esters, acetates, dimethylcarbonates, diethylcarbonates, basic catalysts, nucleophilic or reducing metal salt catalysts, lithium methoxides.

Description

Method for preparing unsymmetric linear carbonate

The present invention relates to a method for producing an asymmetric linear carbonate, and more particularly, to a method for producing an asymmetric linear carbonate, which is useful as a solvent for a lithium secondary battery by transesterifying a symmetric linear carbonate and a linear ester compound.

Asymmetric linear carbonates, such as ethyl methyl carbonate (EMC), are commonly used as solvents (electrolytes) for lithium secondary batteries, and have better energy storage density, charge capacity, charge / discharge recovery, and stability than conventional solvents. Therefore, it is mainly used as a solvent for lithium secondary batteries especially.

As a method for preparing an asymmetric linear carbonate, there is a method using an ester reaction of an alkyl chloroformate and an alcohol in the presence of a basic catalyst, but the method has a very vigorous ester reaction, and phosgene and bisphenol-A There is a problem in that a highly toxic compound such as to be used as a starting material. In order to solve the above problem, Japanese Patent Laid-Open No. 6-166660 discloses a method of using a transesterification reaction of an alcohol having a symmetric linear carbonate and an alkyl group in the presence of a basic catalyst such as a metal carbonate. There is a problem in that the catalytic activity and the production yield are low, and the asymmetric linear carbonates, such as ethyl methyl carbonate, which is the final target compound, must be separated and purified from the reaction product containing three linear carbonates and two alcohols. U.S. Patent No. 5,962,720 also discloses an asymmetric linear by disproportionate transesterification of two different symmetric linear carbonates in the presence of a basic catalyst such as an alkoxide salt or an amide salt of a Group 1 or Group 2 metal which is a nucleophilic or reducing compound. A method of making carbonates is disclosed. The method has the advantage of high production yield without using alcohol, but the basic catalyst used must be separated by an alumina or silica gel column, and before the reaction is carried out in order to prevent a decrease in catalytic activity due to water or alcohol present in the raw material. There is a problem to remove the moisture of the raw material. In addition, Japanese Patent Laid-Open Nos. 2000-344715 and 2000-344718 disclose a method for producing an asymmetric linear carbonate even in the presence of water or alcohol using mixed oxides of Group 3B rare earth metals, but the reaction is 5 to 10. Under pressure of air pressure, there is a problem to be performed for a long time of 200 hours or more.

 It is therefore an object of the present invention to provide a process that can produce asymmetric linear carbonates in high yield in a short time since catalyst activity is not reduced.

Another object of the present invention is to provide a method for preparing a high-purity asymmetric linear carbonate because no by-products are generated and the linear ester compound and the catalyst can be easily separated.

In order to achieve the above object, the present invention comprises the steps of transesterifying a symmetric linear carbonate and a linear ester compound in the presence of a basic catalyst; And it provides a method for producing an asymmetric linear carbonate comprising the step of separating the asymmetric linear carbonate from the product of the transesterification reaction. Here, it is preferable to use an acetate compound as the ester compound, and as the basic catalyst, it is preferable to use lithium methoxide, lithium ethoxide, sodium methoxide, lithium amide, calcium hydride, a mixture thereof, and the like. .

Hereinafter, the present invention will be described in more detail.

In order to prepare the asymmetric linear carbonate according to the present invention, first, as shown in Scheme 1, the symmetric linear carbonate and the linear ester compound are transesterified in the presence of a basic catalyst.

In Scheme 1, R ₁ , R ₂ and R may each independently be a linear alkyl group, a branched alkyl group or a cyclic alkyl group, and R ₁ and R ₂ preferably have 1 to 10 carbon atoms. Linear alkyl groups, branched alkyl groups having 3 to 10 carbon atoms, or cyclic alkyl groups having 5 to 10 carbon atoms, and R is preferably a methyl group or an ethyl group.

As the symmetric linear carbonate, preferably linear alkyl carbonate, branched alkyl carbonate or cyclic alkyl carbonate may be used, more preferably linear alkyl carbonate having 1 to 10 carbon atoms, branched alkyl carbonate having 3 to 10 carbon atoms, Or a cyclic alkyl carbonate having 5 to 10 carbon atoms, and for example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, having a linear alkyl group having 1 to 4 carbon atoms, Di-n-butyl carbonate or di-t-butyl carbonate may be used. The linear ester compound is represented by the formula RCOOR ₂ (wherein R and R ₂ are each independently an organic bonding group such as a linear alkyl group, a branched alkyl group, or a cyclic alkyl group, R is preferably a methyl group or an ethyl group, and R ₂ is preferably Linear alkyl groups of 1 to 10 carbon atoms, branched alkyl groups of 3 to 10 carbon atoms, or cyclic alkyl groups of 5 to 10 carbon atoms. It is preferable to use an acetate compound as the linear ester compound, and non-limiting examples of the acetate compound include methyl acetate, methyl acetate, ethyl acetate, propyl acetate, and isopropyl acetate. acetate), n-butyl acetate, n-butyl acetate, t-butyl acetate, etc. can be illustrated. The amount of the symmetric linear carbonate and the linear ester compound is preferably in a molar ratio of 1:10 to 10: 1, more preferably 1: 9 to 9: 1, and 1: 1.5 to 1: 4, the maximum yield is obtained. Therefore, it is most preferable. If the molar ratio is out of the above range, there is a problem that the yield of the asymmetric linear carbonate as the final product is lowered.

As the basic catalyst used in the transesterification reaction, a nucleophilic or reducing metal salt catalyst may be used, and specifically, an alkoxide salt of a group 1 or group 2 metal, an amide salt of a group 1 or group 2 metal, a hydride of a metal ( hydrides, preferably hydrides of Group 1 or 2 metals, mixtures thereof, and the like, and more specifically lithium methoxide (LiOCH ₃ ), lithium ethoxide (LiOC ₂ H ₅ ), sodium methoxide (NaOCH ₃ ), lithium amide (LiNH ₂ ), calcium hydride (CaH ₂ ), or the like can be used. The amount of the catalyst used in the present invention is preferably 0.01 to 10% by weight, more preferably 0.1 to 5% by weight based on the entire symmetric linear carbonate and linear ester compound as a reactant. If the amount of the catalyst used is less than 0.01% by weight, the reaction rate is lowered. If the amount is more than 10% by weight, it is economically disadvantageous without any advantages.

The transesterification reaction can be carried out in conventional chemical reactors in a batch or continuous manner as is commonly used. It is preferable that the said reaction temperature is 50-250 degreeC, and especially when using a batch type chemical reactor, it is more preferable that the reactor internal temperature is 70-120 degreeC. If the reaction temperature is less than 50 ℃ the reaction rate is slow to decrease the productivity, if it exceeds 250 ℃ there is a problem that a large amount of by-products generated by decomposition of the reactant. The reaction pressure is not particularly limited but is preferably carried out at atmospheric pressure, the reaction time is not particularly limited, for example, in the range of 0.1 to 10 hours, more preferably 0.5 to 4 hours, Chromatography may be used until the composition of the reactants sampled at regular intervals does not change.

Next, a step of separating the asymmetric linear carbonate from the product of the transesterification reaction is carried out. Separation of the nonlinear carbonate as the target compound may be carried out using a conventional atmospheric pressure or reduced pressure distillation method. When the reaction product is distilled under atmospheric pressure or reduced pressure, distillation starts from the lower boiling compound to the higher boiling compound. For example, after transesterification of dimethyl carbonate and ethyl acetate, the reaction product is distilled to obtain methyl acetate (boiling point: 58 ° C). ), Ethyl acetate (boiling point: 77 ° C.), dimethyl carbonate (boiling point: 90 ° C.), ethyl methyl carbonate, diethyl carbonate (boiling point: 127 ° C.). The symmetric linear carbonate and linear ester compound separated in this separation process can be recovered and reused.

Hereinafter, the present invention will be described in more detail with reference to specific examples, but the scope of the present invention is not limited to the following examples.

Example 1

Into a 500 ml flask reactor equipped with a condenser, a magnetic stir bar was added, 1.3 mol (117 g) of dimethyl carbonate (DMC), 2.6 mol (229 g) of ethyl acetate (EA), and 0.35 g (0.1 wt%) of LiOCH _{3 as a} catalyst were added. The reaction was carried out by heating until the temperature of the reactor reached 78 ° C. while stirring. The steam generated during the reaction was sent to the condenser, condensed, and then refluxed back to the reactor, and the composition of the reactant sampled at regular intervals was measured using gas chromatography. After 3 hours from the time when the temperature of the reactor reached 78 ℃ was confirmed that the composition of the reactants no longer changed, the reaction was completed. After completion of the reaction, the reaction product was analyzed using gas chromatography to form new methyl acetate (MA) and ethyl methyl carbonate (EMC), and the molar ratio of methyl acetate (MA): ethyl acetate (EA) was 1: 1 and the molar ratio of dimethyl carbonate (DMC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) is 1: 2: 1, and the reaction yield of ethyl methyl carbonate (EMC) is 50 compared to dimethyl carbonate (DMC). It was%. Next, the reaction product was distilled under normal pressure while maintaining a reflux ratio of 5 or more in a 50-step theoretical stage distillation column to obtain ethylmethyl carbonate having a purity of 99% (distillation yield: 80%).

Example 2

The reaction was carried out in the same manner as in Example 1, except that 0.5% by weight of LiNH ₂ (1.73 g) was used instead of 0.1% by weight of LiOCH ₃ and the reaction time was 4 hours. After completion of the reaction, the reaction product was analyzed using gas chromatography. As a result, the molar ratio of methyl acetate: ethyl acetate in the reaction product was 1: 1, and the molar ratio of dimethyl carbonate: ethyl methyl carbonate: diethyl carbonate was 1: As 2: 1, the reaction yield of ethylmethyl carbonate was 50% compared to dimethyl carbonate. Next, the reaction product was subjected to atmospheric distillation while maintaining a reflux ratio of 5 or more in a theoretical stage 50 stage distillation column to obtain ethyl methyl carbonate having a purity of 99% (distillation yield: 78%).

Example 3

The reaction was carried out in the same manner as in Example 1, except that 1.3 mol (153 g) of diethyl carbonate (DEC) and 2.6 mol (192.4 g) of methyl acetate (MA) were used instead of 1.3 mol of dimethyl carbonate and 2.6 mol of ethyl acetate. Was performed. After completion of the reaction, the reaction product was analyzed using gas chromatography. As a result, the molar ratio of ethyl acetate: methyl acetate in the reaction product was 1: 1, and the molar ratio of diethyl carbonate: ethyl methyl carbonate: dimethyl carbonate was 1: As 2: 1, the reaction yield of ethylmethyl carbonate was 50% compared to diethyl carbonate. Next, the reaction product was distilled under atmospheric pressure while maintaining a reflux ratio of 5 or more in a 50-step theoretical stage distillation column to obtain ethyl methyl carbonate having a purity of 99% (distillation yield: 81%).

Comparative Example 1

The reaction was carried out in the same manner as in Example 1, except that 2.5 mol (115 g) of ethanol was used instead of 2.6 mol of ethyl acetate and the reaction time was 4 hours. After completion of the reaction, the reaction product was analyzed using gas chromatography. As a result, unreacted ethanol was 4.6% by weight and 9.4% by weight of methanol as a by-product. The ratio was 1: 1.6: 1, and the reaction yield of ethylmethyl carbonate was 44% compared to dimethyl carbonate.

Since the method for producing an asymmetric linear carbonate according to the present invention does not decrease the catalytic activity, there is an advantage in that the asymmetric linear carbonate can be produced in a high yield in a short time, and also no by-products are produced, and the linear ester compound and the catalyst are easy. Since it can be separated easily, there is an advantage that a high purity asymmetric linear carbonate can be obtained.

Claims (6)

Transesterifying the symmetric linear carbonate and the linear ester compound in the presence of a basic catalyst; And Separating the asymmetric linear carbonate from the product of the transesterification reaction. The method of claim 1, wherein the linear ester compound is an acetate compound. The method of claim 1, wherein the linear ester compound is selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate and t-butyl acetate. The method of claim 1, wherein the basic catalyst is a nucleophilic or reducing metal salt catalyst. The method of claim 1, wherein the basic catalyst is selected from the group consisting of lithium methoxide, lithium ethoxide, sodium methoxide, lithium amide, calcium hydride and mixtures thereof, the amount of the basic catalyst is the symmetric linear Method for producing an asymmetric linear carbonate that is 0.01 to 10% by weight relative to the total carbonate and linear ester compound. The method of claim 1, wherein the separating the asymmetric linear carbonate is performed by distilling the product of the transesterification reaction.