Process for treating iminium salt-based ionic liquids

Abstract

The present invention relates to a process for treating an ionic liquid, in which process an iminium salt, in particular in the form of an imidazolium salt, is reacted with an alcoholate to give an iminium-alcoholate adduct, then the salt formed from the cation of the alcoholate and the anion of the iminium salt is separated out, and then an iminium salt is reformed by addition of an acid. Owing to the much lower polarity in comparison with the iminium salt, the iminium-alcoholate adduct allows easy separation of polar impurities or clean exchange of the anion of the iminium salt when the added acid has a different anion from that originally present in the iminium salt.

Description

[0001] Process for the treatment of iminium salt-based ionic liquids

[0002] DESCRIPTION

[0003] The present invention relates to a process for treating an ionic liquid, in which an iminium salt, preferably in the form of an imidazolium salt, is reacted with an alkoxide to form an iminium alkoxide adduct. Subsequently, the salt formed from the alkoxide cation and the anion of the iminium salt is separated, and then an iminium salt is reformed by adding an acid. Due to its significantly lower polarity compared to the iminium salt, the iminium alkoxide adduct allows for easy removal of polar impurities or a clean exchange of the anion of the iminium salt (= anion metathesis) if the added acid has a different anion than that originally contained in the iminium salt.

[0004] State of the art

[0005] Iminium salt-based ionic liquids are used as solvents or reaction media in many processes (see, for example, "Ionic Liquids for Clean Technology," KR Seddon, J. Chem. Tech. Biotechnol. 1997, 68, 351-356; "Room Temperature Molten Salts," NN Ene, Roum. Chem. Q. Rev. 1993, 1, 333-351). In these applications, separation of the desired products results in ionic liquids that are contaminated by unreacted reactants, added auxiliaries, or reaction products.

[0006] Recycling contaminated ionic liquids is difficult due to their special properties. These compounds typically have boiling points or sublimation points significantly above 300 °C. Only ionic liquids containing special anions, such as N(SO2F)2, are reasonably stable at these temperatures, so they can often be distilled on a small scale. However, this also requires considerable energy. Against this background, there is a need for a generally applicable purification or recycling process that can also be carried out at lower temperatures (<200 °C).

[0007] A further problem with the use of ionic liquids is that iminium salt-based ionic liquids available on an industrial scale mostly contain chloride ions as an anionic component, with l-butyl-3-methylimidazolium chloride (1) produced on an industrial scale by BASF SE being an example.

[0008] However, many processes require iminium salt-based ionic liquids containing other, e.g., reactive, strongly nucleophilic anions such as iodide, thiocyanate, or cyanide. Such reactive ionic liquids can generally be prepared from chloride salts of iminium salt-based ionic liquids through reactions known as "anion metathesis."

[0009] A variety of anion exchange processes have been developed for guanidinium salt-based ionic liquids, which are briefly presented below: a) Double conversion

[0010] A solution of the salt AX, whose anions X' are to be exchanged, is mixed with the solution of another salt BY containing the desired anion Y'. In this process, the cation B + of the salt BY is chosen such that the salt BX is insoluble and precipitates. After separation of the salt BX, the resulting solution of the desired ionic liquid AY is evaporated, and AY is isolated as a residue. A large number of guanidinium salts with different anions have been prepared using this principle (see, for example, W. Kantlehner, J. Mezger, I. Tiritiris, R. Kreß, W. Frey, Z. Naturforsch. 2021, 76b, 133-162). Guanidinium salts with anions containing organofluorine-containing groups are sparingly soluble in water. When water-soluble guanidinium salts are mixed with aqueous solutions containing alkali metal salts with organofluorine-containing anions, such as CFaSChLi, CFaSChNa, C^SO5Na, or N(CF3SO2N)2Na, the guanidinium salts precipitate (see EP 1363345 A2 or DE 10325051A1). b) Decomposition of acid-labile anions

[0011] For salts with acid-sensitive anions, such as carbonates or bicarbonates, acid can be added to exchange the anion to form carbonic acid. Subsequent carbon dioxide elimination forms the ionic liquid with the anion of the added acid. c) Complexation of anions with Lewis acids

[0012] This reaction produces the corresponding guanidinium tetrafluoroborates from guanidinium fluorides and guanidinium chlorides with boron trifluoride etherate (cf., for example, W. Kantlehner, J. Mezger, I. Tiritiris, R. Kreß, W. Frey, Z Naturforsch. 2021, 76b, 133-162). d) Alkylation of the anions of ionic liquids

[0013] For salts with strongly nucleophilic anions, anion exchange can be achieved by alkylating the anion. For less nucleophilic anions, alkylation can still be achieved with very strong alkylating agents. For example, guanidinium chlorides are converted into guanidinium tetrafluoroborates with triethyloxonium tetrafluoroborate, releasing volatile ethyl chloride and diethyl ether (see, for example, W. Kantlehner, J. Mezger, I. Tiritiris, R. Kreß, W. Frey, Z Naturforsch. 2021, 76b, 133-162).

[0014] In addition, especially for the anion metathesis of ionic liquids based on imidazole salts, there are also possibilities of reaction with silver salts (with deposition of silver halides), reaction with HPFß to form hexafluorophosphate salts or reaction with acetate-loaded ion exchange resins to form acetate salts.

[0015] As this compilation shows, however, there is currently no generally applicable anion metathesis process for iminium salt-based ionic liquids that allows the introduction of any anion, regardless of the type of anion to be exchanged.

[0016] The difficulty with the described processes is also that for the reaction to take place, differences in the specific properties of the ionic liquid used as starting material and the ionic liquid obtained as product must be present, suitable reagents such as alkylating agents must be available, or complexable or decomposable anions must be present in the ionic liquid used as starting material.

[0017] There is therefore a need for a process that is as generally applicable as possible and by which ionic liquids with more easily accessible anions such as halide and especially chloride can be converted into corresponding ionic liquids with other anions in a simple and as cost-effective manner as possible.

[0018] The present invention addresses this need.

[0019] Finally, reference should be made to the publication by Bredereck H. et al., Chem. Ber. 1965, 98, pp. 1078ff., which describes the reaction of N,N,N',N'-tetramethylformamidinium methylsulfate with sodium methylate to form the aminal ester bis-dimethylaminomethoxymethane. Subsequently, analogous aminal esters were obtained by reaction with ethylates, i-propylates, and i-butylates in Angew. Chem Int. Ed. Engi. 1967, p. 311. Korshin et al. describe the reaction of 4-anilino-1,3-diphenylimidazolium chloride with sodium methoxide to form the corresponding aminal ester in Zh. Org. Khim. 1993, 29, pp. 577-87.

[0020] Description of the invention

[0021] In the investigations underlying the present invention, it was surprisingly discovered that not only guanidinium salt-based ionic liquids, but iminium salt-based ionic liquids in general, can be converted into iminium alcoholate adducts belonging to the orthoamide class of compounds through the addition of alcoholates. Due to their electrically neutral structure, these adducts can be purified from polar impurities and salts. Furthermore, such a treatment has the advantage that, at the orthoamide or adduct stage, an acid can be added that has a different anion than the ionic liquid from which the orthoamide or adduct was generated. This corresponds to an anion exchange (anion metathesis) in the overall reaction.

[0022] Accordingly, the present invention relates to a process for the treatment of an ionic liquid based on a substituted or unsubstituted iminium salt (Im+ X ), wherein the iminium salt is reacted in a first step i) with an alkoxide to form an electrically neutral iminium-alcoholate adduct, in a second step ii) the salt formed from the cation of the alkoxide and the anion X- of the iminium salt is separated and in a third step iii) the electrically neutral iminium-alcoholate adduct is reacted with an acid HY to form an iminium salt Im + Y _ where X and Y may be the same or different. This process is further described below via a reaction scheme, wherein the iminium salt is in the form of an imidazolium salt (Im + X _ , 1) is present, which represents a preferred iminium salt in the context of this invention. In the following reaction equation, compound 2 denotes a non-charged or electrically neutral imidazole-alcoholate adduct and compound 3 denotes the imidazolium salt Im + Y _ .

[0023] As mentioned, the iminium salt which is subjected to the treatment according to the invention is, in a preferred embodiment, present as an imidazolium salt. However, the iminium salt can also have a cation that is not based on an imidazole ring, such as an N,O-bisalylated pyrrolidone, R 1 -C(NR 2 2)2 + , R 1 -C(NR 2 )(SR2) + or a guanidinium cation (C(NR 2 2)3 + ), where R 2 may be the same or different in the structures shown, and denotes a hydrocarbon radical, preferably in the form of an alkyl radical, and wherein R 1denotes a hydrocarbon radical, preferably in the form of an alkyl radical. Further possible iminium salts that can be treated in the process described here include the following l,3-dialkyl-l,3,4-triazolium salts (4), 2,3,5-trialkyl-l,3-oxazolium salts (5), 2,3,5-trialkyl-l,3,4-oxazolium salts (6), 2,3,5-trialkyl-l,3-thiazolium salts (7), 2,3,4-trialkyl-l,3,4-thiadiazolium salts (7), 1,2-dialkylpyrimidinium salts (9), and 1,2,3-trialkyl-3,4,5,6-tetrahydropyrimidinium salts (10):

[0024] In a first embodiment, X and Y are identical (see the following figure using the example of an ionic liquid with an imidazolium cation), i.e., compound 1 is the same as compound 3a. Such a process is advantageously designed as a process for purifying the reacted ionic liquid 1, in which polar and, in particular, ionic impurities are separated from the iminium alkoxide adduct with the salt in step ii). Impurities to be separated include impurities such as those typically encountered in applications of ionic liquids, e.g., formate, acetate, butanoate, chloride, bromide, iodide, or tetrafluoroborate.

[0025] The possibility of separating impurities and purifying the product is illustrated by the properties of N,N,N',N',N",N"-hexamethylguanidinium chloride 1 and the tris(dimethylamino)ethoxymethane 2 derived from it:

[0026] The guanidinium salt 11 has a melting point of 296 °C (cf. W.

[0027] Kantlehner, E. Haug, WW Mergen, P. Speh, T. Maier, JJ Kapasakalidis, H.-J. Brauner, H. Hagen, Synthesis 1983, 13, 904-905) and is insoluble in diethyl ether, ethyl acetate, benzene, or cyclohexane. Upon addition of sodium ethylate, the orthoamide derivative 5 forms as an adduct from the guanidinium salt 11 as a colorless to pale yellow liquid with a boiling point of 73 °C / 10 Torr (see W.

[0028] Kantlehner, WW Mergen, Synthesis 1979, 11, 343-344), which is miscible with ether, ethyl acetate, benzene, cyclohexane in any ratio.

[0029] In a second embodiment, X and Y are different, ie compound 1 is, as far as the anion is concerned, different from compound 3. Such a process is described as a process for producing an ionic liquid in + Y' from an ionic liquid In + X _in which the anion Y- is different from the anion X" contained in the starting product. In this embodiment, it is preferred if X- is a halide, in particular in the form of chloride, or the anion of a CI or C2 carboxylic acid (ie formate or acetate). Very particular preference is given to X- being chloride.

[0030] If an alcoholic alkoxide solution is used as the "alcoholate source" in step i), it may be advantageous to remove excess alcohol following the reaction to avoid subsequent solvent mixtures with the alcohol, which may promote less complete removal of the impurities or salts. The alcohol can be separated from the mixture by any suitable method for removal, for example distillation or vacuum treatment. Alternatively, an alcohol can be used as a solvent for the ionic liquid (preferably in the form of methanol or ethanol), for example, to facilitate separation of the salt in step ii) via filtration.

[0031] The alkoxide added to the substituted or unsubstituted imidazolium salt in step i) of the process according to the invention is advantageously a C1-C4 alkoxide, with methanolate and ethanolate being particularly preferred. The cation of the alkoxide can particularly preferably be an alkali metal cation, more preferably in the form of sodium or potassium. Sodium is generally preferred for reasons of cost and availability.

[0032] The processes according to the first or second embodiment can expediently be further configured such that an aprotic non-polar solvent is added to the mixture in step ii) before the salt formed from the cation of the alkoxide and the anion X- of the iminium salt is separated. With regard to the nature of the aprotic non-polar solvent, the present invention is not subject to any relevant restrictions, i.e., aliphatic or aromatic hydrocarbons can be used as solvents, where "aliphatic" includes "cycloaliphatic" forms. Suitable aliphatic or aromatic hydrocarbon solvents are, for example, hexane, pentane, cyclohexane, cyclopentane, toluene, benzene, or xylene, or mixtures of the solvents mentioned. Other suitable solvents are ethers such as diethyl ether or methyl t-butyl ether, or esters such as ethyl acetate or ethyl propionate, and nitriles such as acetonitrile.Also suitable, but less favorable for toxicological reasons, are halogenated and especially chlorinated hydrocarbons such as dichloromethane or chloroform. However, the solvent is not limited to the specific examples mentioned; rather, it is of relevance that the iminium alkoxide adduct dissolves in the solvent, while polar impurities are not dissolved and remain as residues.

[0033] Furthermore, it is desirable, but not absolutely necessary, that the solvent has a lower boiling point than the iminium alkoxide adduct, since in this case the solvent can subsequently be removed from the mixture by distillation. "Distillation" here also includes cases of treatment under reduced pressure, in which the solvent is evaporated and subsequently recondensed by appropriate cooling.

[0034] Alternatively, it is possible, particularly when a carboxylic acid such as a fatty acid is used as the HY, to carry out the process in the presence of water as solvent, with a protic solvent such as alcohol (e.g., as a solvent for an alkoxide used) also being present. The water can form the majority of the solvent and, for example, account for more than 80 wt.%, preferably more than 90 wt.%, and even more preferably more than 93 wt.% of the total amount of solvent in the mixture.

[0035] The separation of the salt formed from the alkoxide cation and the iminium salt anion can be carried out in step ii) using any method suitable for the separation of solid or denser residues. In one example, the salt is separated by filtration, preferably at ambient temperature (20 to 28°C) or a lower temperature above the deposition temperature of the iminium alkoxide adduct. The "deposition temperature" refers to the temperature at which the iminium alkoxide adduct is no longer dissolved, e.g., as a result of crystallization or phase separation. In another embodiment, the separation is carried out by decanting the solution of the iminium alkoxide adduct in an aprotic, nonpolar solvent, optionally after centrifugation to concentrate undissolved components at the bottom of a reaction vessel.For steps i) and ii), the temperature also plays a certain role. It should be chosen so that, on the one hand, the iminium salt and the resulting iminium alcoholate adduct are in liquid form, while, on the other hand, the temperature should not be so high that the iminium alcoholate adduct undergoes significant decomposition. It is preferred that the temperature for steps i) and ii) be kept below 120°C, in particular below 100°C, and more preferably below 80°C.

[0036] As already mentioned, the anion of the iminium salt used in step i) is preferably a halide and particularly preferably chloride if the process according to the invention produces a product with a Y- different from X-. However, even in a process in which X- and Y' are the same, X- can be present as a halide or chloride. In this case, however, a significantly wider range of anions for X- is conceivable, as described below. In particular, the anion can also be a carboxylate, alkyl sulfate, alkyl- or arylsulfonate.

[0037] The acid added in step iii) in the processes according to both embodiments described above can be any acid that reacts with the imidazole alkoxide orthoamide to release alcohol (ROH), i.e., it must be a protic acid. Suitable acids of this type include, but are not limited to, hydrochloric acid, hydrobromic acid, hydroiodic acid, C1-C18 carboxylic acids, e.g., formic acid, acetic acid, or propionic acid, methanesulfonic acid, dialkylphosphonic acid, particularly in the form of dimethyl or diethylphosphonic acid, thiocyanuric acid, hydrogen cyanide, cyanic acid, nitric acid, nitrous acid, sulfuric acid, alkylsulfuric acid, alkyl- or arylsulfonic acid, HN(SO2CF3)2, trifluoroacetic acid, and trifluoromethanesulfonic acid.

[0038] Y- in the above-mentioned compound 3 can also be an adduct of a carboxylic acid and a deprotonated carboxylic acid (in the form R-CO-HOCOR), in which the proton of the carboxylic acid is stabilized by the carboxylate group of the deprotonated carboxylic acid.

[0039] The acid added in step iii) can be added at a suitable temperature, which can be adjusted depending on the reactivity of the iminium alkoxide adduct and its stability against undesired decomposition. In one embodiment, the acid is added at ambient temperature (20 to 28°C). In another embodiment, the acid is added at a reduced temperature, e.g., at -30°C to 15°C or -20°C to 0°C. To complete the reaction, the reaction mixture can subsequently be heated to a higher temperature, e.g., 45 to 100°C or 60 to 90°C.

[0040] If the iminium salt used in the process according to the invention is an imidazolium salt, it is preferred if the imidazolium cation contained in the salt is substituted at the nitrogen atoms (T- and 3'-positions) and is preferably unsubstituted at the 4'- and 5'-positions. The carbon atom at the 2'-position may be unsubstituted (ie, have an additional bonded hydrogen atom, R 2 = H) or substituted, for example, by an alkyl group which may contain one or more substituents selected from alkyl, in particular C1-C6-alkyl, alkoxy, in particular C1-C6-alkoxy, aryl, in particular phenyl. Alternatively, the carbon atom at the 2'-position may be substituted by an aryl radical (e.g. in the form of phenyl) or by NR2, where R may be an alkyl or aryl radical, and the two Rs may be the same or different. R is preferably a C1-C4 alkyl radical, and most preferably R = methyl.

[0041] In a particularly preferred embodiment, the imidazolium cation of the imidazolium salt is in the 1'- and 3'-position (corresponding to the radicals R 1 and R 3 in the reaction scheme above) or in the 1'-, 2'- and 3'-position (corresponding to the residues R 1 , R 2 and R 3 in the reaction scheme above) is substituted with (C1-C6)-alkyl groups, where a 2'-position may be substituted with aryl or alkylaryl in addition to alkyl, and the alkyl group may have an alkyloxy or aryloxy substituent. R 1 and R 3can be the same or different. In an even more preferred embodiment, the imidazolium cation of the imidazolium salt is selected from the group consisting of l-ethyl-3-methylimidazolium, 1,3-dimethylimidazolium, l-butyl-3-methylimidazolium cation, l-butyl-3-ethylimidazolium, 1,3-diethylimidazolium, l-ethyl-3-isopropylimidazolium, l-allyl-3-methylimidazolium, l-allyl-3-ethylimidazolium, l-allyl-3-isopropylimidazolium, and l-allyl-3-butylimidazolium cations.

[0042] The anion X- of the compound included in the process according to the invention

[0043] Imidazolium salt is preferably selected from halides, in particular chloride, bromide or iodide, the carboxylate of a Cl-C18 carboxylic acid, in particular a Cl-C12 carboxylic acid such as acetate, formate, propionate, butanoate or octanoate, a dialkyl phosphate, in particular in the form of dimethyl or diethyl phosphate, dialkyl phosphonate such as dimethyl or diethyl phosphonate, methylsulfonate, thiocyanate, cyanate, nitrate, nitrite, N(SO2CF3)2, N(SO2C4F9)2 and trifluoromethanesulfonate.

[0044] In step iii) of the described process, the alcohol is reformed from the added acid and the alkoxide bound in the iminium alkoxide adduct, which is usually undesirable for further use of the formed imidazolium salt as an ionic liquid. It is therefore preferred if the process according to the invention additionally comprises a step in which the alcohol is removed from the formed product. For suitable processes for this purpose, reference can be made to the above information on processes for removing excess alcohol, with distillation and / or vacuum treatment being particularly suitable.

[0045] If the iminium cation of the treated ionic liquid has an imidazolium cation having an alkyl substituent in the 2'-position with a hydrogen substituent bonded in the a-position of the C atom directly bonded to the 2-imidazole carbon atom (13), a 2-alkylidene imidazole 15 can be formed in equilibrium with the imidazole alcoholate adduct 14 by elimination of alcohol:

[0046]

[0047] 16

[0048] In Formula 13, the residues R 1 and R 3 , which may be the same or different, have the same meaning as described above and the radicals R 2 and R 4 can be the same or different, and have the same meaning as R 2 above including the possibility that R 2 and R 4= H. Such 2-alkylidene-imidazoles are known not to have high thermal stability, so that isolation of these products is usually only possible with significant losses in yield (see, for example, WO 2007 / 131498 A1). It is therefore preferred if imidazole-alcoholate adducts from which alcohol can be eliminated are treated under very mild thermal conditions, e.g., less than 120°C and in particular less than 100°C, in steps i) and ii). In this way, significant decomposition via the 2-alkylidene-imidazoles is avoided. For this purpose, it is further preferred if the processing is carried out under conditions in which the 2-alkylidene-imidazole formed makes up a proportion of 2 to 80% by weight, and more preferably 5 to 30% by weight, of the total amount of imidazole-alcoholate adduct and 2-alkylidene-imidazole.In particular, the process described here is not intended to isolate pure 2-alkylidene-imidazole, although this is unnecessary because both the imidazole-alcoholate adduct and the 2-alkylidene-imidazole are converted into the imidazolium salt by the addition of acid. In such a case, in order to subsequently correctly adjust the required amount of acid to be added and to avoid introducing excess acid into the system, it may be advantageous for the process to additionally include a step for determining the amount of acid to be added in step iii) that is required to completely convert the mixture of imidazole-alcoholate adduct of 2-alkylidene-imidazole into the imidazolium salt (i.e., a stoichiometric amount based on the molar amount of imidazole units in the mixture).Such a tuning is possible, for example, by determining the imidazole alcoholate adduct to 2-alkylidene-imidazole ratio by NMR or by titration.

[0049] In a further aspect, the present invention relates to an imidazolium salt (Im +Y ), which is obtainable by the process described above, and wherein Y- is selected from the group comprising bromide, iodide, a C3-C18 carboxylic acid, a dialkyl phosphonate, in particular in the form of dimethyl or diethyl phosphonate, a dialkyl phosphate, in particular in the form of dimethyl or diethyl phosphate, methylsulfonate, thiocyanate, cyanate, nitrate, nitrite, an alkyl sulfate, an alkyl or arylsulfonate, in particular in the form of the dimethyl or diethyl derivatives, N(SO2CF3)2 and trifluoromethanesulfonate. If Y- is a C3-C18 carboxylic acid (and in particular a C10 to C18 carboxylic acid), it is also possible that Y- is in the form of an adduct of deprotonated carboxylic acid and carboxylic acid, as stated above. Such an imidazolium salt is characterized by a high purity of the anion, which, for example,at least 90 mol% (based on the total amount of anions in the imidazolium salt), more preferably at least 95 mol%, even more preferably at least 98 mol% and even more preferably at least 99 mol% is formed from the specified anion (e.g. thiocyanate).

[0050] In individual cases, it is possible, in particular when water is used as solvent for the reaction of the ionic liquid with the alkoxide, and an anion Y- with a large non-polar fraction (such as a carboxylate, in particular of a fatty acid, with at least 4 C atoms, preferably at least 8 C atoms and more preferably 10 to 18 C atoms) is used, that the process is carried out in such a way that the separation of the salt formed from the cation of the alkoxide and the anion X- of the iminium salt according to step ii) after the addition of an acid HY with formation of an iminium salt Im + Y _according to step iii). In this case, the desired product salt of the ionic liquid can be obtained after precipitation and / or crystallization from the reaction mixture and separation of the dissolved salts formed from the alkoxide and the anion X-.

[0051] The described process allows for the simple regeneration of ionic liquids, separating polar impurities or salts that cannot be removed from the ionic liquids by extraction with non-polar solvents. Furthermore, the described process allows for the simple and cost-effective production of iminium salts with unusual and commercially unavailable anions, which would otherwise have to be produced using significantly more complex processes.

[0052] In the following, the present invention is illustrated in more detail using exemplary embodiments, which, however, are not to be regarded in any way as limiting or restricting the scope of protection of the application.

[0053] Examples: 17

[0054] 1.8 g of a 30% solution of sodium methylate (0.01 mol) in methanol are added dropwise to a stirring suspension of 1.76 g (0.01 mol) of l-butyl-3-methylimidazolium chloride (17) and 2.56 g (0.01 mol) of palmitic acid in 30 ml of water. A colorless precipitate forms. The mixture is heated to boiling with stirring, resulting in a nearly clear solution, which is filtered while hot. The waxy, colorless mass that separates from the filtrate upon cooling is filtered off with suction, washed twice with 20 ml of methanol each time, and dried. Yield: 2.11 g (64.7%, based on the palmitic acid used) of 18a with a melting point of 54 °C. Upon cooling, a small amount (approx. 0.15 g) of a colorless product precipitates from the methanol, which is filtered off with suction. Evaporation of the filtrate yields another 1.1 g (33.7%, based on the palmitic acid used) of slightly contaminated 18a with a melting point of 48 °C.

[0055] C40H78N2O4 (651.04) calc. C 73.79, H 12.08, N 4.30; found C 74.24, H 11.95, N 4.39

[0056] Example 2: Preparation of l-ethyl-3-methyl-imidazolium octanoate (18b)

[0057] Preparation of 18b using diethyl ether and methanol as solvent

[0058] To 2.92 g (0.02 mol) of EMIMCI (17) in 20 ml of methanol and 10 ml of diethyl ether, 3.60 g (0.2 mol) of sodium methylate solution (30% in methanol), which had previously been diluted with 10 ml of methanol, was added with stirring. The colorless precipitate formed was separated after 15 min. The filtrate was treated with stirring with 2.88 g (0.02 mol) of caprylic acid (octanoic acid) in 10 ml of ether. After standing for 2 h, the clear mixture was evaporated in vacuo, leaving a gelatinous, glassy mass, which was then freed from the solvents. The residue was boiled with 30 ml of acetonitrile with stirring for 15 min, during which the gelatinous mass was occasionally broken up. After cooling, the mixture was filtered off with suction. The filter residue was washed with 15 ml of ether. The filtrate (acetonitrile / ether) is filtered through a fluted filter and then evaporated in vacuo. Yield: 3.4 g (73%) of EMIMOCT (18b), a yellow oil with n 20 D = 1.4806 (commercial product from proionic >98%, n 2 = 1.4805).

[0059] 2.92 g (0.02 mol) of l-ethyl-3-methylimidazolium chloride (17) in a mixture of 10 ml of methanol and 10 ml of acetonitrile are added dropwise with stirring to 3.60 g (0.02 mol) of a 30% sodium methoxide solution, which was made up to 10 ml prior to addition. A colorless precipitate immediately forms. After the addition is complete, the mixture is stirred for a further 5 min and then filtered.

[0060] The filtrate is treated with 2.88 g (0.02 mol) of octanoic acid in 5 ml of acetonitrile while stirring, resulting in a voluminous, gelatinous precipitate forming upon heating. After approximately 20 minutes of stirring, the precipitate is filtered off with suction. The filtrate is evaporated in vacuo to yield a voluminous, gelatinous mass, which is then heated under reflux with 15 ml of acetonitrile while stirring for 15 minutes, occasionally breaking up the gelatinous, clumped mass. After cooling, the precipitate is filtered off with suction.

[0061] A small amount of gelatinous mass separates from the filtrate and is filtered off. After evaporation of the filtrate in vacuo, 2.64 g (52%) of l-ethyl-3-methylimidazolium octanoate (18b) remains as a pale yellow oil. 2 = 1.4801 (commercial product from proionic >98%, n 2 = 1.4805).

[0062] Production of 18b in methanol

[0063] 2.92 g (0.02 mol) of l-ethyl-3-methylimidazolium chloride (17) (EMIMCI) in 10 ml of methanol are treated with 3.60 g (0.02 mol) of sodium methoxide solution (30% in methanol), which has been made up to 10 ml with methanol, while stirring. A colorless precipitate (NaCI) immediately forms, which is filtered off after 15 min of stirring.

[0064] The filtrate is treated with 2.88 g (0.02 mol) of octanoic acid in 5 ml of methanol with stirring. The reaction mixture remains clear and is evaporated, towards the end in vacuo. The residue is heated under reflux with stirring using 15 ml of acetonitrile. Upon cooling, a colorless, waxy solid precipitates, which is filtered off with suction and washed with ether. After evaporating the filtrate – towards the end in vacuo – an oily substance remains alongside a glassy jelly. The mixture is heated with 10 ml of acetonitrile with stirring, forming a clear solution. Upon cooling, a small amount of glassy mass separates, which is filtered off with suction. Evaporating the filtrate in vacuo gives 2.28 g (45%) of l-ethyl 3-methylimidazolium octanoate 18b as a pale yellow oil, with n 20 D = 1.4803 (commercial product from proionic >98%, n 20 D = 1.4805).

Claims

Claims 1. A process for the treatment of an ionic liquid based on a substituted or unsubstituted iminium salt (Im + X ), preferably an imidazolium salt, characterized in that the iminium salt is reacted in a first step i) with an alkoxide to form an electrically neutral iminium-alcoholate adduct, in a second step ii) the salt formed from the cation of the alkoxide and the anion X- of the iminium salt is separated and in a third step iii) the electrically neutral iminium-alcoholate adduct is reacted with an acid HY to form an iminium salt Im + Y _ is implemented, where X and Y can be the same or different.

2. The process according to claim 1, characterized in that the process is designed as a process for purifying a reacted ionic liquid, in which in step ii) polar and in particular ionic impurities are separated together with the resulting salt which was formed during the formation of the iminium alcoholate adduct.

3. A process according to claim 1, characterized in that the process is used as a process for producing an ionic liquid in + Y _ from an ionic liquid (In + X ) in which the anion Y- is separated from the anion X- in the starting product Im + X _ is different.

4. The process according to at least one of claims 1 to 3, characterized in that an aprotic non-polar solvent, preferably in the form of an aliphatic or aromatic hydrocarbon, a halogenated hydrocarbon, an ether or an ester, is added to the mixture in step ii) before the salt formed from the cation of the alcoholate and the anion X- of the iminium salt is separated.

5. Process according to at least one of the preceding claims, characterized in that the separation of the salt is carried out by filtration, preferably at ambient temperature (23°C) or a lower temperature above the deposition temperature of the iminium alcoholate adduct.

6. Process according to at least one of the preceding claims, characterized in that the anion of the iminium salt used in step i) is a carboxylate, alkyl sulfate, alkyl or arylsulfonate, tetrafluoroborate, dialkylphosphonate or a halide, preferably in the form of chloride.

7. The process according to at least one of the preceding claims, characterized in that the acid used in step iii) is an acid selected from the group comprising hydrochloric acid, hydrobromic acid, hydroiodic acid, C1-C18 carboxylic acids, dialkylphosphonic acids, in particular in the form of dimethyl or diethylphosphonic acid, dialkylphosphonic acids such as dimethyl or diethylphosphoric acid, methanesulfonic acid, thiocyanic acid, hydrogen cyanide, cyanic acid, nitric acid, nitrous acid, sulfuric acid, alkylsulfuric acid, alkyl- or arylsulfonic acid, HN(SO2CF3)2, trifluoroacetic acid and trifluoromethanesulfonic acid.

8. Process according to at least one of the preceding claims, characterized in that the iminium cation of the iminium salt is an imidazolium cation which is substituted in the 1'- and 3'-position or in the 1'-, 2'- and 3'-position with (Cl-C6)-alkyl groups, where the 2'-position may be substituted not only by alkyl but also by aryl or alkylaryl, and the alkyl group may have an alkyloxy or aryloxy substituent.

9. The method according to claim 8, characterized in that the imidazolium cation is selected from the group consisting of l-ethyl-3-methylimidazolium, 1,3-dimethylimidazolium, l-butyl-3-methylimidazolium, l-butyl-3-ethylmethylimidazolium, 1,3-diethylimidazolium, l-ethyl-3-isopropylimidazolium, 1-allyl-3-methylimidazolium, l-allyl-3-ethylimidazolium, l-allyl-3-isopropylimidazolium, l-allyl-3-butylimidazolium cations.

10. Process according to at least one of the preceding claims, characterized in that in step i) a C1-C4 alkoxide, preferably a methanolate or ethanolate, is used, wherein the alkoxide is particularly preferably an alkali metal alkoxide and further preferably a sodium or potassium alkoxide.

11. The process according to at least one of the preceding claims, further comprising a measure for removing the alcohol formed from the acid and the iminium alcoholate adduct in step iii), wherein the removal is preferably designed as distillation and / or vacuum treatment.

12. The process according to at least one of the preceding claims, wherein the treatment with the alkoxide in step i) forms, in addition to an electrically neutral imidazole-alcoholate adduct, a 2-alkylidene-imidazole which preferably accounts for a proportion of 2 to 80% by weight and more preferably 5 to 30% by weight in the mixture of imidazole-alcoholate adduct and 2-alkylidene-imidazole.

13. The process according to claim 12, further comprising a step for determining the proportion of 2-alkylidene-imidazole in the total amount of imidazole-alcoholate adduct and 2-alkylidene-imidazole, and preferably additionally comprising a step for determining the stoichiometric amount of acid to be added in step iii) which is required to completely convert the imidazole-alcoholate adduct and 2-alkylidene-imidazole into imidazolium salt.

14. The process according to claim 1 to 3 and 6 to 13, wherein water is used as solvent for the reaction of the ionic liquid with the alkoxide, and an anion Y- with a large non-polar portion, in particular a carboxylate of a fatty acid with at least 4 carbon atoms, is used, and wherein the process is carried out such that the separation of the salt formed from the cation of the alkoxide and the anion X- of the iminium salt according to step ii) after the addition of an acid HY with formation of an iminium salt Im + Y _ in accordance with step iii).

15. Imidazolium salt (Im +Y ), obtainable by a process according to any one of claims 3 to 13, wherein Y- is selected from bromide, iodide, a C3-C18 carboxylic acid, an adduct of deprotonated C3-C18 carboxylic acid and corresponding C3-C18 carboxylic acid, a dialkyl phosphonate, in particular in the form of dimethyl or diethyl phosphonate, a dialkyl phosphate, in particular in the form of dimethyl or diethyl phosphate, methylsulfonate, thiocyanate, cyanate, nitrate, nitrite, Alkyl sulfate, alkyl or aryl sulfonate, particularly in the form of the dimethyl or diethyl derivatives, N(SO2CF3)2 and trifluoromethanesulfonate.

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