Method for synthesizing ionic liquids having a carbonate functional group and ionic liquids thus obtained

Abstract

The present invention relates to a method for synthesizing ionic liquids comprising a carbonate functional group characterized in that it comprises a step of reaction A without addition of lithium between a first reactant selected among an imidazolium, a pyrrolidinium or an ammonium and a second reactant being a methyl formate imidazolium. The first reactant is an imidazolium alcohol, a pyrrolidinium alcohol or an ammonium alcohol salt, the anion of which is NTf2. The second reactant is a chloromethyl formate imidazolium. The application of this method will be found in the field of green chemistry and more specifically in the production of ionic liquids which can be used in lithium batteries with a graphite electrode.

Claims

1. A method for synthesizing an ionic liquid comprising a carbonate functional group that is not coordinated with lithium, the method comprising reacting without adding lithium a first reactant selected from the group consisting of an imidazolium, a pyrrolidinium and an ammonium and a second reactant being a methyl formate imidazolium, wherein no reactant contains lithium.

2. The method according to claim 1, wherein the first reactant is an imidazolium, a pyrrolidinium or an ammonium alcohol.

3. The method according to claim 1, wherein the first reactant is an imidazolium alcohol, a pyrrolidinium alcohol or an ammonium alcohol salt, the anion of which is bis(trifluoromethanesulfonyl)imide (NTf2).

4. The method according to claim 1, wherein the reacting results in two products, with a main product being an ionic liquid comprising a carbonate functional group and a secondary product being a methyl imidazolium.

5. The method according to claim 4, further comprising recycling, by Hoffmann reaction, the secondary product methyl imidazolium into an imidazolium alcohol, forming the first reactant of the reacting.

6. The method according to claim 5, wherein methyl imidazolium reacts with 2-chloro-1-ethanol to form 1-ethanol-3-methyl imidazolium chloride.

7. The method according to claim 1, wherein the ionic liquid obtained is selected from the group consisting of 1-[2-(methoxycarbonyloxy)ethyl]-3-methylimidazolium, 1-[2-(ethoxycarbonyloxy)ethyl]-3-methylimidazolium, 1-[2-(propoxycarbonyloxy)ethyl]-3-methylimidazolium, 1-[2-(isopropoxycarbonyloxy)ethyl]-3-methylimidazolium, N-[2-(methoxycarbonyloxy)ethyl]-N-methylpyrrolidinium, N-[2-(ethoxycarbonyloxy)ethyl]-N-methylpyrrolidinium, N-[2-(propoxycarbonyloxy)ethyl]-N-methylpyrrolidinium, N-[2-(isopropoxycarbonyloxy)ethyl]-N-methylpyrrolidinium, N-trimethyl-N-2-[(methoxycarbonyloxy)ethyl]ammonium, N-trimethyl-N-2-[(ethoxycarbonyloxy)ethyl]ammonium, N-trimethyl-N-2-[(propoxycarbonyloxy)ethyl]ammonium, and N-trimethyl-N-2-[(isopropoxycarbonyloxy)ethyl]ammonium, wherein each ionic liquid is associated with a bis(trifluoromethanesulfonyl)imide anion.

8. The method according to claim 1, wherein reacting is executed at ambient temperature in an acetonitrile-based solution in argon atmosphere.

9. The method of claim 1, wherein the second reactant is a chloromethyl formate imidazolium.

10. The method according to claim 9, wherein the second reactant is obtained by a reaction between 1-methylimidazole and methylchloroformate.

11. The method according to claim 10, wherein the reaction is executed at 0 C. in an acetonitrile-based solution for 2 hours.

12. The method according to claim 10, wherein the second reactant obtained by a reaction between 1-methylimidazole and methylchloroformate is directly mixed with the first reactant.

13. The method according to claim 6, wherein the chlorine of 1-ethanol-3-methyl imidazolium chloride is substituted by NTf2 by reaction with lithium bis(trifluoromethanesulfonyl)imide (LiNTf2).

Description

(1) The appended drawings are provided as examples and are non-exhaustive depictions of the invention. They only show one embodiment of the invention and help it to be understood clearly.

(2) FIG. 1 illustrates an example of the step of reaction A of the synthesis method according to the invention.

(3) FIG. 2 illustrates the mechanism of the reaction A of the synthesis method according to the invention.

(4) FIG. 3 illustrates an exemplary step of recycling the secondary product resulting from the reaction A of the method according to the invention.

(5) FIG. 4 illustrates the mechanism of the reaction A of the synthesis of the second reactant of the method according to the invention.

(6) According to the invention, the method for synthesizing an ionic liquid comprises a reaction A between two reactants 1, 2.

(7) The first reactant is selected from imidazolium, pyrrolidinium or ammonium according to the type of ionic liquid desired to be synthesized. The first reactant 1 is advantageously an imidazolium, pyrrolidinium or ammonium alcohol. The first reactant is in the form of a salt the anion of which is bis(trifluoromethanesulfonyl)imide (also called NTf2 or TFSI), and the cation of which is imidazolium, pyrrolidinium or ammonium. The anion NTf2 makes the ionic liquid a hydrophobic characteristic, which makes synthesis and purification thereof easier.

(8) By way of non limiting example, the first reactant 1 is 1-ethanol-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, also called C1C2OHlm-NTf2. The first reactant is directly commercially available.

(9) The second reactant is methyl formate imidazolium. The second reactant is preferably chloromethyl formate imidazolium. For example, the second reactant 2 is 1-methyl-3-methylformateImidazolium chloride. The second reactant is advantageously obtained by a step of reaction between methyl-imidazole and methylchloroformate. The reaction advantageously takes place at 0 C. in acetonitrile. The reaction lasts for about 2 hours.

(10) Preferably, once the second reactant has been synthesized, the first reactant is directly mixed with the second reactant without separation thereof.

(11) This greatly facilitates the synthesizing method according to the invention.

(12) The step of reaction A between the first reactant and the second reactant enables the direct synthesis of the ionic liquid having at least one carbonate functional group. This step of reaction A is advantageously carried out in acetonitrile at room temperature, more specifically between 18 C. and 25 C. in argon atmosphere.

(13) For example, the ionic liquids which can be obtained using the method according to the invention are, as for the cation: 1-[2-(methoxycarbonyloxy)ethyl]-3-methylimidazolium 1[2-(ethoxycarbonyloxy)ethyl]-3-methylimidazolium 1[2-(propoxycarbonyloxy)ethyl]-3-methylimidazolium 1-[2-(isopropoxycarbonyloxy)ethyl]-3-methylimidazolium N-[2-(methoxycarbonyloxy)ethyl]-N-methylpyrrolidinium N-[2-(ethoxycarbonyloxy)ethyl]-N-methylpyrrolidinium N-[2-(propoxycarbonyloxy)ethyl]-N-methylpyrrolidinium N-[2-(isopropoxycarbonyloxy)ethyl]-N-methylpyrrolidinium N-trimethyl-N-2-[(methoxycarbonyloxy)ethyl]ammonium N-trimethyl-N-2-[(ethoxycarbonyloxy)ethyl]ammonium N-trimethyl-N-2-[(propoxycarbonyloxy)ethyl]ammonium N-trimethyl-N-2-[(isopropoxycarbonyloxy)ethyl]ammonium;

(14) The associated anion is bis(trifluoromethanesulfonyl)imide.

(15) The step of reaction A leads to two products, among which a main product which is the ionic liquid comprising at least one carbonate functional group and a secondary product.

(16) The ionic liquid obtained has a carbonate functional group. Advantageously, it is halide-free. As a matter of fact, chlorine in the second reactant is the anion of the secondary product. Besides, the step of reaction A involves no reactant containing lithium. The synthesis method according to the invention is executed without lithium. There is no coordination of lithium or halide with the carbonate functional group.

(17) The secondary product contains chloro-imidazolium from the second reactant. For example, the secondary product is methyl imidazolium chloride.

(18) The method of the invention also has the advantage of making it possible to recycle the secondary product into a reactant, specifically the first reactant. Recycling the secondary product of the step of reaction A is obtained by Hoffmann reaction. Such reaction cycle is described in patent application WO 01/77081. The step of recycling is preferably carried out between the secondary product and 2-chloro-1-ethanol. The product of this reaction includes a halide which is advantageously substituted by an anion selected for the first reactant. This anion is coordinated to the lithium. For example, chlorine is replaced by the NTf2 through an anion exchange with lithium-NTf2 (LiNTf2). The alcohol functional group carried by the first reactant and the halide salt too, the halide of which has been replaced by the NTf2, enables no chelation of the lithium cation. The product obtained is a first reactant for the reaction A of synthesis of the ionic liquid. The product obtained is 99.9% pure.

(19) The method according to the invention uses no lithium and advantageously enables the recycling of the secondary product. Thus it has many advantages and can be used in green chemistry.

EXAMPLE 1: SYNTHESIS OF THE SECOND REACTANT: 1-METHYL-3-METHYLFORMATEIMIDAZOLIUM CHLORIDE

(20) Methyl chloroformate (52 g, 550 mmol) is added dropwise to a solution of 1-methylimidazole (41 g, 500 mmol) in acetonitrile (200 mL) at 0 C. and the reaction lasts for 2 hours. 1-methyl-3-methylformateImidazolium chloride is obtained.

EXAMPLE 2: SYNTHESIS OF THE IONIC LIQUID COMPRISING A CARBONATE FUNCTIONAL GROUP: 1-[2-(METHOXYCARBONYLOXY)ETHYL]-3-METHYLIMIDAZOLIUMBIS(TRIFLUOROMETHANESULFONYL)IMIDE [EMCMLM]TFSI

(21) The first reactant 1-ethanol-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide, (50 g, 122 mmol) and the second reactant as obtained in Example 1: 1-methyl-3-methylformateImidazolium chloride (15.74 g, 111 mmol) are contacted at room temperature for one day. A slightly yellow product is obtained. The ionic liquid having a carbonate functional group is obtained with a yield of about 90%.

EXAMPLE 3: RECYCLING THE SECONDARY PRODUCT INTO THE FIRST REACTANT

(22) One exemplary recycling process is for example described in the International patent application published under number WO2005068404.