EP2203428A1

EP2203428A1 - Method for producing imidazolium salts

Info

Publication number: EP2203428A1
Application number: EP08803874A
Authority: EP
Inventors: Georg Degen; Christoph Stock
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2007-09-21
Filing date: 2008-09-09
Publication date: 2010-07-07
Also published as: WO2009040242A1

Abstract

A method for producing imidazolium salts of the formula (I), where R1 and R3, independently of one another, denote an organic residue having 1 to 20 carbon atoms, R2, R4, and R5, independently of one another, denote an H atom or an organic residue having up to 20 carbon atoms, and A denotes an anion except for a carbonate anion, characterized in that, in a first step of the method an imidazolium salt of the formula (Il) is produced by the reaction of imidazoles of the formula (III), where the residues R have the above meanings, with an alkyl carbonate of the formula (IV), where R3 has the above meaning, and in a second step of the method, the obtained imidazolium salts of the formula (Il) are reacted with acids or salts containing the anion A in order to form the imidazolium salt (I), the reaction being performed in both steps of the method in the presence of methanol, and the content of methanol in the first step of the method being at least 100 parts by weight of methanol and in the second step of the method being at least 50 parts by weight, relative to 100 parts by weight of the sum of the materials used of the formulas (III) + (IV) employed in the first step of the method in each case.

Description

Process for the preparation of imidazolium salts

description

The invention relates to a process for the preparation of imidazolium salts of the formula I.

wherein R ¹ and R ³ independently of one another represent an organic radical having 1 to 20 C atoms,

R ² , R ⁴ and R ⁵ independently of one another are an H atom or an organic radical having up to 20 C atoms and

A- stands for an anion other than a carbonate anion, which is characterized in that

in a first process step, an imidazolium salt of the formula II

by reaction of imidazoles of the formula

wherein the radicals R have the above meaning, with

an alkyl carbonate of formula IV

RO- 1 C = O wherein R ^{3 has} the above meaning, is prepared and

in a second process step, the resulting imidazolium salts of the formula II are reacted with acids or salts which contain the anion A- to form the imidazolium salt I,

wherein the reaction takes place in both process steps in the presence of methanol and the content of methanol in the first process step at least 100 parts by weight of methanol and in the second process step at least 50 parts by weight, based in each case to 100 parts by weight of the sum of the first Process step used starting materials of formula III + IV is.

Imidazolium salts having a melting point of less than 200 ^° C., in particular imidazolium salts which are liquid at room temperature, have many uses as ionic liquids. B. as a technical solvent or equipment, eg. B. for dissolving cellulose or as adsorbent in adsorption heat pumps.

What is desired, therefore, is a process which is as simple and cost-effective as possible for its production, whereby this process should be as selective as possible and by-products should be avoided as far as possible.

The preparation of imidazolium salts with alkyl carbonates as anion is described in EP-A-1398318. 1, 3 disubstituted imidazoles are reacted with carbonic acid diesters; the reaction can be carried out in the presence of an inert solvent. Methanol is named as a solvent and used in the examples. However, methanol is completely removed before further reaction.

Also, JP 2004-207451 discloses a corresponding implementation. It is called a variety of solvents, including methanol.

WO 2005/021484 describes a process for the preparation of imidazolium salts by anion exchange, starting, for. B. of imidazolium salts with alkyl carbonates as anion, the reaction of these salts with an acid.

DE-A 19 836 477 describes the preparation of an imidazolium carboxylate with the carboxylate group as substituent on the imidazole ring, corresponding to a compound of the above formula VI. The reaction of 1-methylimidazole with dimethyl carbonate leads to the substituted imidazole carboxylate in high yields. The reaction can be carried out in the presence or absence of solvent. In the previously described process for the preparation of imidazolium salts of the formula I, the high proportion of by-products is disadvantageous.

The object of the invention was therefore a process for the preparation of imidazolium salts of the formula I with as few by-products as possible, the process should be as simple and inexpensive as possible.

Accordingly, the method defined above was found.

To the process product

By the method according to the invention are imidazolium salts of the formula I.

R ² , R ⁴ and R ⁵ independently of one another are an H atom or an organic radical having up to 20 C atoms and A "is an anion.

R 1 and R 3 are preferably independently of one another an organic radical having 1 to 10 C atoms. The organic radical may also contain further heteroatoms, in particular oxygen atoms, nitrogen, sulfur or phosphorus atoms or functional groups, for example hydroxyl groups, ether groups, ester groups or carbonyl groups.

In particular, R 1 and R 3 are a hydrocarbon radical which, in addition to carbon and hydrogen, may at most also contain hydroxyl groups, ether groups, ester groups or carbonyl groups.

R 1 and R 3 are particularly preferably independently of one another a hydrocarbon radical having 1 to 20 C atoms, in particular having 1 to 10 C atoms, which does not contain any other heteroatoms, eg. As oxygen or nitrogen. The hydrocarbon radical may be aliphatic (which also includes unsaturated aliphatic groups) or aromatic, or may contain both aromatic and aliphatic groups. Preferably, R 1 and R 2 are an aliphatic hydrocarbon radical. Examples of hydrocarbon radicals which may be mentioned are the phenyl group, benzyl group, a phenyl group or benzyl group, alkyl groups and alkenyl groups substituted by one or more C1 to C4 alkyl groups, in particular the allyl group.

Most preferably, R 1 and R 3 are a C 1 to C 10 alkyl group. As the alkyl group, a C1 to C6 alkyl group is particularly preferred, in a particular embodiment, the alkyl group is a C1 to C4 alkyl group.

Most preferably, R 1 and R 3 are each independently a methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl or tert-butyl group, one wherein the methyl, ethyl, n-propyl and n-butyl group have special significance.

Preferably, R ^{1 is} a C ¹ to C 6, especially a C ¹ to C ⁴ alkyl group.

Preferably, R ^{3 is} a methyl group.

R ² is preferably an H atom.

R 4 and R 5 are preferably, independently of one another, a hydrogen atom or an organic radical having 1 to 10 C atoms. The organic radical may also contain further heteroatoms, in particular oxygen atoms, nitrogen, sulfur or phosphorus atoms or functional groups, for example hydroxyl groups, ether groups, ester groups or carbonyl groups.

In particular, R4 and R5 stand for a hydrocarbon radical, which may contain, in addition to carbon and hydrogen, at most hydroxyl groups, ether groups, ester groups or carbonyl groups.

R4 and R5 are particularly preferably independently of one another a hydrocarbon radical having 1 to 20 C atoms, in particular having 1 to 10 C atoms, no other heteroatoms, z. As oxygen or nitrogen. The hydrocarbon radical may be aliphatic (including unsaturated aliphatic groups) or aromatic, or may contain both aromatic and aliphatic groups. Preferably, R 1 and R 2 are an aliphatic hydrocarbon radical.

Examples of hydrocarbon radicals which may be mentioned are the phenyl group, benzyl group, a phenyl group or benzyl group, alkyl groups and alkenyl groups, in particular the allyl group, substituted by one or more C1 to C4 alkyl groups. Most preferably, R4 and R5 represent a hydrogen atom or a C1 to C10 alkyl group. As the alkyl group, a C1 to C6 alkyl group is particularly preferred, in a particular embodiment, the alkyl group is a C1 to C4 alkyl group.

Most preferably, R 1 and R 3 independently represent a hydrogen atom or a methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl or tert-butyl group, one wherein the methyl, Ethyl, n-propyl and n-butyl group have special significance.

In a particular embodiment, R4 and R5 are each H atoms.

The anion A "in formula I, apart from a carbonate anion, may be any anion.

The anion is preferably selected so that the imidazolium salt of formula 1 has a melting point (at 1 bar) of less than 200 ⁰ C, in particular 100 ⁰ C, particularly preferably less than 50 ° C and has C most preferably less than 30 ^0, which is an ionic liquid is. In particular, the imidazolium salt of the formula I is liquid at room temperature.

In particular, compounds having a carboxylate group (in short, carboxylates) are suitable. Preferred carboxylates are the anions of alkanecarboxylic acids, especially of C1 to C4 alkanecarboxylic acids, preferably the acetate anion.

Suitable anions may furthermore be selected from the following groups (listed polyvalent anions are the counter anions of a number corresponding to the valence imidazolium cations, R ^a and R ^b are independently an organic radical having preferably 1 to 20 C atoms, more preferably a hydrocarbon radical and very particularly preferably an aliphatic radical, in particular a C1 to C10 alkyl group):

The group of halides and halogen-containing compounds of the formulas:

• F, Cl, Br, I, BF ₄ ^" , PF ₆ ^" , AICI ₄ -, Al ₂ Cl ₇ ^" , Al ₃ CII ₀ -, AIBr ₄ -, FeCl ₄ -, BCI ₄ -, SbF ₆ ^", AsF _^6," ZnCl ₃ -, SnCl ₃ -, CuCl ₂ -, CF ₃ SO ₃ -, (CF ₃ SOs) ₂ N-, CF ₃ CO ₂ -, CCl ₃ CO ₂ -, CN ^", ^SCN" .

OCN-, NO ² ", NO ³ ", N (CN) -;

• the group of sulfates, sulfites and sulfonates of the general formulas: SO ₄ ^{2 "} , HSO ₄ -, SO ₃ ^2" , HSO ₃ -, R ³ OSO ₃ -, R ³ SO ₃ -;

• the group of phosphates of the general formulas: PO ₄ ^{3 "} , HPO ₄ ^2" , H ₂ PO ₄ -, R ³ PO ₄ ^{2 "} , HR ³ PO ₄ -, R ³ R ^b PO ₄ -;

The group of phosphonates and phosphinates of the general formula: R ³ H PO ₃ -, R ³ R ^b PO ₂ -, R ³ R ^b PO ₃ -; The group of phosphites of the general formulas: PO ₃ ^{3 "} , HPO ₃ ^2" , H ₂ PO ₃ -, R ³ PO ₃ ^{2 "} , R ³ HPO ₃ -, R ³ R ^b PO ₃ -;

The group of phosphonites and phosphinites of the general formula: R ³ R ^b PO ₂ -, R ³ HPO ₂ -, R ³ R ^b P0-, R ³ HPO-; The group of borates of the general formulas:

BO ₃ ^{3 "} , HBO ₃ ^2" , H ₂ BO ₃ -, R ³ R ^b BO ₃ -, R ³ HBO ₃ -, R ³ BO ₃ ^{2 "} , B (0R ³ ) (0R ^b ) (0R ^c ) (0R ^d ) -, B (HSO ₄ ) ^" , B (R ³ SO ₄ ) -;

• the group of boronates of the general formulas: R ³ BO ₂ ² -, R ³ R ^b B0-; The group of silicates and silicic acid esters of the general formulas:

SiO ₄ ^{4 "} , HSiO ₄ ³ -, H ₂ SiO ₄ ² -, H ₃ SiO ₄ -, R ³ SiO ₄ ^3" , R ³ R ^b Si0 ₄ ² -, R ³ R ^b R ^c Si0 ₄ -, HR ³ SiO ₄ ^{2 "} , H ₂ R ³ SiO ₄ ^" , HR ³ R ^b Si0 ₄ -;

The group of the alkyl or aryl silane salts of the general formulas: R ³ SiO ₃ ³ , R ³ R ^b SiO ₂ ² , R ³ R ^b R ^c SiO, R ³ R ^b R ^c SiO ₃ ^" , R ³ R ^b R 1 Si0 ₂ -, R ³ R ^b Si0 ₃ ² -; • the group of the carboximides, bis (sulfonyl) imides and sulfonyl imides of the general formulas:

Preferred anions are the above carboxylates, especially acetate, rhodanide (SCN), alkanesulfonates such as methanesulfonate, ethanesulfonate and bis (sulfonyl) imides, most preferably the above carboxylates, especially the acetate.

To the first process step

In the first process step, an imidazolium salt of the formula

by reaction of imidazoles of the formula

wherein the radicals R have the above meaning, with an alkyl carbonate of formula IV

R-O- 1 C = O

wherein R ^{3 has} the above meaning, prepared.

The alkyl carbonate is preferably dimethyl carbonate.

The molar ratio of the imidazole used to the alkyl carbonate can be chosen arbitrarily, for optimum yields and avoiding excessive excess of one of the two reactants are molar ratios of 1 mole of imidazole to 0.5 to 2 moles of alkyl carbonate, in particular from 1 mole of imidazole to 1, 2 bis 1, 6 moles of alkyl carbonate useful.

The reaction is preferably carried out at elevated pressures and temperatures.

The temperature is preferably 50 to 200 ⁰ C, particularly preferably 80 to 200 ⁰ C, most preferably 100 to 180 ° C.

The pressure may preferably be 2 to 50 bar, in particular 5 to 30 bar.

The reaction can be carried out in the presence or absence of a catalyst.

The reaction is carried out according to the invention in the presence of methanol. The methanol content is preferably at least 125 parts by weight, in particular at least 150 parts by weight, more preferably at least 200 parts by weight and very particularly preferably at least 250 parts by weight per 100 parts by weight of the sum of the starting materials of the formula III ( Imidazole) and IV (dialkyl carbonate). More than 800 parts by weight of methanol, in particular more than 500 parts by weight of methanol are generally not used.

If desired, further solvents can be used in the reaction. Water, water-miscible organic solvents or water-immiscible organic solvents may be used.

In particular, the reaction can be carried out in the presence or absence of water. The components III and IV can be used in equimolar amounts. Preferably, one of the components, more preferably the imidazole of formula III is used in deficit. The first process step is preferably considered terminated when a conversion of more than 90%, in particular more than 95%, particularly preferably more than 98%, very particularly preferably more than 99%, based on the components III and IV (with equimolar starting amounts) or to the components used in deficit.

For the second process step

Optionally, work-up may be carried out before the second process step. Solvent, including methanol, may be used, for example. partially removed.

Also in the second process step, the reaction according to the invention is carried out in the presence of methanol. The methanol content is preferably at least 75 parts by weight, in particular at least 100 parts by weight, particularly preferably at least 125 parts by weight and very particularly preferably at least 150 parts by weight, in a particular embodiment at least 200 or 250 parts by weight 100 parts by weight of the sum of the starting materials of the formula III (imidazole) and IV (dialkyl carbonate) in the first process step. More than 800 parts by weight of methanol, in particular more than 500 parts by weight of methanol are generally not used.

In particular, the methanol used in the first process step is not removed.

Preferably, in the second process step, the solution obtained after the first process step is used without prior work-up or without removal (distillation) of individual constituents thereof.

In the second process step, an acid or salt containing the anion A "is added to the solution The acidity of the acid or salt should be such that the carbonate anion in formula II (preferably methylcarbonate anion) is converted to the corresponding alcohol (methanol) and In the presence of water, the hydroxycarbonate anion first forms from the carbonate anion by hydrolysis, so that the decomposition results in water (instead of alcohol) and carbon dioxide.

The anion A of the acid or salt then replaces the carbonate anion. This implementation is z. As described in WO 2005/021484 (carbonate method).

Suitable acids for this purpose are hydrogen acids, suitable salts are those which contain hydrogen as a cation or in covalently bonded form. As acids and salts, particular mention may be made of carboxylic acids or their salts or hydrogen acids or salts of the abovementioned anions.

The reaction can be carried out at atmospheric pressure. An overpressure is not necessary but not a hindrance.

Elevated temperatures can be helpful; Preference is given to temperatures of 20 to 100 ^° C., in particular 30 to 70 ^° C.

The acid or the salt which contains the anion A "can be used in any desired amounts, depending on the desired conversion, Preferably, the acid or salt is used in excess or in stoichiometric amounts In particular, the desired or required amount can be obtained in advance be determined by titration.

By the process according to the invention, solutions of the imidazolium salt of the formula I are preferably obtained in which the total by weight of the by-products of the formula V

of formula VI

and the formula VII

in total less than 10 parts by weight per 100 parts by weight of the imidazolium salt of the formula I amount, wherein the radicals R ¹ to R ^{5 have} the above meaning. The total weight of the three by-products of the formula V, VI and VII is particularly preferably less than 8 parts by weight, in particular less than 5 parts by weight, very preferably less than 2 parts by weight, in particular less than 1 part by weight and in one particular embodiment less than 0.5 or even less than 0.1 part by weight per 100 parts by weight of the imidazolium salt of the formula I.

The solution obtained initially has the above methanol content indicated for the second process step. The methanol and other optional solvents may then be removed if desired.

Examples

Comparative Example 1 Synthesis of EMIM (ethylmethylimidazole) methyl carbonate with 30% by weight of methanol

36.04 g of 1-ethylimidazole, 54.05 g of dimethyl carbonate and 38.61 g of methanol are stirred in an autoclave for 36 h at 140 ⁰ C under 13 bar autogenous pressure. After cooling, the reaction mixture to 3.21 wt .-%, not further convertible 4/5 carboxylate, the formulas VI and VII, based on the sum of all imidazolium compounds.

Comparative Example 2

Synthesis of EMIM methyl carbonate with 40 wt% methanol

24.26 g of 1-ethylimidazole, 36.39 g of dimethyl carbonate and 40.43 g of methanol are stirred in an autoclave for 36 h at 140 ⁰ C under 15 bar autogenous pressure. After cooling, the reaction mixture to 1, 9 wt .-% not further convertible 4/5 carboxylate of the formula VI or VII, based on the sum of all imidazolium compounds.

example 1

Synthesis of EMIM methyl carbonate with 60 wt% methanol

27.42 g of 1-ethylimidazole, 41, 11 g of dimethyl carbonate and 102.8 g of methanol are stirred in an autoclave at 140 ° C for 48 h under 16 bar autogenous pressure. After cooling, the reaction mixture contains 0.322% by weight of 4/5-carboxylate of the formula VI or VII which is not further convertible, based on the sum of all imidazolium compounds. Comparative Example 3 (60% by weight of methanol and then distilling off the methanol)

10.94 g of 1-ethylimidazole, 16.01 g of dimethyl carbonate and 40.43 g of methanol are stirred in an autoclave for 36 h at 140 ⁰ C. This creates an autogenous pressure of 15 bar. After cooling, the solvent is removed on a rotary evaporator at 50 ⁰ C and 16 mbar. The permanent red-brown solution contains 2.3% by weight of 4/5-carboxylate of the formula VI or VII which is not further convertible, based on the sum of all imidazolium compounds.

Example 4

Synthesis of EMIM acetate

1828 g of 1-ethylimidazole, 2741 g of dimethyl carbonate and 6853.5 g of methanol are stirred in an autoclave for 48 h at 140 ⁰ C and an autogenous pressure of -17 - 19 bar. After cooling to room temperature, the reaction product is drained from the autoclave. 20 g of the discharge are titrated at 50 ^° C. with 1N HCl in order to determine the required amount of acetic acid which is required for the conversion into the acetate. 1120 g of acetic acid are then added to the reaction mixture at room temperature. The reaction mixture is heated to 50 ⁰ C and stirred at this temperature for 12 h. Subsequently, all Leitsieder be distilled off in vacuo. There remain 3174 g of EMIM acetate.

Example 5

Synthesis of EMIM methanesulfonate (methanol content 60% by weight)

1624.7 g of a reaction of EMIM methyl carbonate (28.7 wt .-%) are initially charged at room temperature. 241, 1g methylsulfonic acid are added via a dropping funnel. The reaction mixture is heated to 50 ⁰ C and stirred at this temperature for 12 h. It is cooled again to room temperature and then the solvent is distilled off in vacuo. There remain 514 g of EMIM methanesulfonate. (Content of 2-carboxylate (Formula V) 0.99 wt%, 4/5 carboxylate (Formula VI, VII) 0.82 wt%, 1-EI 0.05 wt%). Example 6

Synthesis of EMIM Rhodanide (methanol content 60% by weight)

326.9 g of a reaction of EMIM methyl carbonate (30.6 wt .-%) are introduced at room temperature. 40.9 g of ammonium thiocyanate are dissolved in 120 ml of methanol and added by means of a dropping funnel. The reaction mixture is first stirred for 3 hours at room temperature and then at 80 ^° C. for 12 hours. After cooling, the low boilers are distilled off in vacuo. There remain 91 g of EMIM Rhodanide

Example 7

Synthesis of EMIM hydrogen sulfate (methanol content 60% by weight)

213.5 g of a reaction product of EMIM methyl carbonate (30.8% by weight) are initially charged at room temperature. 34.72 g conc. Sulfuric acid are added via a dropping funnel. The reaction mixture is heated to 50 ⁰ C and stirred at this temperature for 12 h. It is cooled again to room temperature and then the solvent is distilled off in vacuo. There remain 73.5 g of EMIM hydrogen sulfate.

Example 8

Synthesis of EMIM chloride (methanol content 60% by weight)

213.5 g of a reaction product of EMIM methyl carbonate (30.8% by weight) are initially charged at room temperature. 29.5 ml of hydrochloric acid (37%) are added via a dropping funnel. The reaction mixture is heated to 50 ⁰ C and stirred at this temperature for 12 h. It is cooled again to room temperature and then the solvent is distilled off in vacuo. There remain 51.8 g of EMIM chloride.

Claims

claims

1. A process for the preparation of imidazolium salts of the formula I.

R ² , R ⁴ and R ⁵ independently represent an H atom or an organic

Rest with up to 20 carbon atoms and stand

A- stands for an anion other than a carbonate anion, characterized in that

in a first process step, an imidazolium salt of the formula II

by reaction of imidazoles of the formula

wherein the radicals R have the above meaning, with

an alkyl carbonate of formula IV

R-O- 1 C = O

wherein R ^{3 has} the above meaning, is prepared and in a second process step, the resulting imidazolium salts of the formula II are reacted with acids or salts which contain the anion A- to form the imidazolium salt I,

wherein the reaction takes place in both process steps in the presence of methanol and the content of methanol in the first process step at least 100 parts by weight of methanol and in the second process step at least 50 parts by weight, based in each case to 100 parts by weight of the sum of the first Process step used feedstocks of formula III + IV is.

2. The method according to claim 1, characterized in that R ^{3 is} a methyl group.

3. The method according to claim 1 or 2, characterized in that R ^{2 is} an H atom.

4. The method according to any one of claims 1 to 3, characterized in that R ² 'R ⁴ and R ^{5 are} H atoms.

5. The method according to any one of claims 1 to 4, characterized in that the reaction in the presence of more than 150 parts by weight of methanol, based on 100 parts by weight of the sum of the starting materials of formula III + IV, is performed.

6. The method according to any one of claims 1 to 5, characterized in that the reaction in the presence of more than 200 parts by weight of methanol, based on 100 parts by weight of the sum of the starting materials of formula III + IV, is performed.

7. The method according to any one of claims 1 to 6, characterized in that before carrying out the second process step no methanol is removed from the solution obtained in the first process step.

8. The method according to any one of claims 1 to 7, characterized in that the reaction is carried out in the presence of water.

9. The method according to any one of claims 1 to 8, characterized in that

Implementation is carried out in the absence of water.

10. The method according to any one of claims 1 to 9, characterized in that the solution obtained, based on 100 parts by weight of the imidazolium salt of the formula I, less than 10 parts by weight of by-products of the formula V

of formula VI

and the formula VII

contains, wherein the radicals R ¹ to R ^{5 have} the above meaning.

1 1. A solution containing an imidazolium salt of the formula I, at least 50 parts by weight of methanol and less than 10 parts by weight of by-products of the formula V, VI and the formula VII, in each case based on 100 parts by weight of the imidazolium salt Formula I.