WO2000020115A1

WO2000020115A1 - Ionic salts

Info

Publication number: WO2000020115A1
Application number: PCT/GB1999/003279
Authority: WO
Inventors: Willi Keim; Peter Wasserscheid; Susanne Ziegert
Original assignee: Bp Chemicals Limited; Akzo Nobel Nv; Elementis Uk Limited
Priority date: 1998-10-06
Filing date: 1999-10-04
Publication date: 2000-04-13
Also published as: GB9821628D0; AU6111599A

Abstract

An ionic salt comprising at least one organo cation and at least one anion characterised in that the anion is of the formula [BX3Y]-, wherein X is a halogen and Y is selected from: (a) a halogen other than X, (b) an OR group wherein R is a C1-C30 hydrocarbyl group, (c) an -O(O)CL group in which L is hydrogen or a hydrocarbyl group and (d) an -O(O)CZ group where Z is a carboxylic, hydroxycarboxylic or a hydrocarbylene carboxylic group. The ionic salts may be used in combination with certain metal salts or complexes as catalysts for reactions such as hydroformylation, olefin polymerisation and hydrogenation.

Description

IONIC SALTS

This invention relates to novel ionic salts and particularly to their use as a solvent or as a catalyst in chemical reactions.

Ionic liquids are primarily a mixture of salts which are liquid at or below ambient temperatures. Such mixtures have conventionally included (alkyl) aluminium halides in combination with one or more imidazolium halides or pyridinium halides which in turn may be substituted in their respective heterocyclic rings by one or more hydrocarbyl groups. Such ionic liquids usually consist of a mixture in which the mole ratio of the (alkyl)aluminium halide to the imidazolium or pyridinium halide is usually > 1.0. It is also known from Wilkes, J S et al, J. Chem. Soc. (Chem. Commun.) 965 (1992) to produce dialkylimidazolium salts of anions such as nitrates, nitrites, tetrafluoroborate, methyl carbonate and sulphate and use thereof to catalyse chemical reactions. Furthermore, Fuller, J et al in J. Chem. Soc. (Chem. Commun.) 299-300 (1994) describe salts of dialkyl imidazolium cations in which the anions may be tetrafluoroborate or hexafluorophosphate. One of the problems with salts of this nature is that the anions are all symmetrical and consequently do not provide sufficient flexibility to enable the salts to be tailor-made for reactions and properties such as eg their solvating ability for reactants and catalysts, acidity, physical characteristics such as density or viscosity etc. For instance, the tetrafluoroborates and hexafluorophosphates are either highly viscous or are solids. It would be desirable to have the ability to adjust these properties according to the needs for specific reactions.

It has now been found that by using a specific type of boron containing anion, it is possible to produce ionic salts which have greater flexibility in their ability to be formulated for specific needs. Accordingly, the present invention is an ionic salt comprising at least one organo cation and at least one anion characterised in that the anion is of the formula [BX₃Y]^", wherein

X is a halogen and Y is selected from

(a) a halogen other than X,

(b) an OR group wherein R is a C1-C30 hydrocarbyl group,

(c) an -O(O)CL group in which L is hydrogen or a hydrocarbyl group and (d) an -O(O)CZ group where Z is a carboxylic, hydroxycarboxylic or a hydrocarbylene carboxylic group In (b) above R may be a substituted or unsubstituted, saturated or unsaturated hydrocarbyl group Preferably, the hydrocarbyl group, R, is an aliphatic, cycloaliphatic, aryl, alkaryl or aralkyl group In (c) above L may be a hydrocarbyl group The hydrocarbyl group may be substituted or unsubstituted, saturated or unsaturated

In particular, examples of [BX₃Y]^", include inter aha [BF₃C1]^", [BC1₃F]^", [BBr,Cl]\ [BBr F]\ [BI,F]^", [BF Br]^", [BCl₃Br]^" and [BF₃I]\ [BF₃OMe]^", [BF₃OEt]^", [BF^OPr]^", [BF^OBu]^" and the like wherein Me represents a methyl group, Et an ethyl group, Pr an n-propyl or an isopropyl group and Bu an n-butyl group or a secondary butyl group, and thus represent compounds in which X is OR and R is a hydrocarbyl group, [BF₃ O C(O) CH₃]^", [BF₃ O C(O) C₂H₅]^" and the like and thus represent compounds in which X is O(O)CL in which L is a hydrocarbyl group, and [BF, O C(O) C(O) OH]^", [BF₃ O C(O) CH₂ C(OH)(COOH) CH₂ C(O) OH]^" and the like and thus represent compounds in which X is O(O)CZ where Z is a carboxylic, hydroxycarboxylic or a hydrocarbylene carboxylic group

The desired anion may be derived by reacting a gas such as BX₃ with the appropriate mineral acid, alcohol or carboxylic acid

The organo-cations present in the salts of the present invention are suitably based on an element from Group V of the Periodic Table Specifically, the Group V element is suitably nitrogen, phosphorus, arsenic and antimony This organo-cation is then reacted with the anion as described above to obtain the ionic salts of the present invention

Thus, the appropriate organo cation may be derived from an amine, phosphine, arsine or stibene to form the ionic salt.

Examples of the Group V organo cations include wter alia: those which fall under the general formula [AR'R^ f or [R¹R²⁺A=CR³-R⁵-R³C=A⁺R²R¹] wherein A is selected from nitrogen, phosphorus, arsenic and antimony; R^]-R⁴ are independently selected from H or a hydrocarbyl group with the proviso that at least one of R'-R⁴ is a hydrocarbyl group; and R⁵ is an alkylene group (eg CH₂, CH₂CH₂ etc type group) or a phenylene group (eg C₆H₄ type group). Where R¹, R², R³ or R⁴ is a hydrocarbyl group it is preferably a C1-C30 hydrocarbyl group which may be substituted or unsubstituted, straight or branched chain, saturated or unsaturated. Preferably, the hydrocarbyl group is an alkyl, cycloalkyl, aryl, alkaryl or aralkyl group. Alternatively, the Group V organo- cations include those having a heterocyclic ring in which the heterocyclic ring has at least one of one heteroatom, A, selected from nitrogen, phosphorus, arsenic and antimony.

Specific examples of organo cations of Group V elements in which A is nitrogen include inter alia: the organo-nitrogen cations which may be heterocyclic ammonium cations or aliphatic, alicyclic or aromatic primary, secondary or tertiary ammonium cations. The ammonium cations may be substituted (e.g with a hydrocarbyl group) or unsubstituted. Where such ammonium cations are heterocyclic ammonium cations it is preferred that the heterocyclic ring is substituted with at least one hydrocarbyl group, for example, at least one alkyl group. Ammonium cations may be derived from amines selected from trialkyl amines, triaryl amines, alkyl diaryl amines, aryl dialkyl amines, hetrocyclic amines and any combinations thereof In particular, ammonium cations derived from aliphatic amines such as eg triethyl amines, trimethyl phenylamines and heterocyclic amines such as dialkyl imidazoles, pyrazoles and pyridines may be used with advantage. In the dialkyl imidazoles and the pyridines, the alkyl groups may be same or different eg l-methyl-3-ethylimidazole, l-methyl-3-butylimidazoles, l-ethyl-3- butylimidazolines, dimethylimidazole and diethylimidazoles, and the corresponding dialkyl derivatives of pyrazole and pyridine. In respect of the imidazoles and their salts, it should be noted that the 1- and 3- positions are interchangeable due to the symmetrical nature of the imidazole nucleus. Thus, where the cations are generated in the ionic salt by the combination of a non-cyclic hydrocarbyl substituted amine with an acid, such cations can be represented by the generic formula [NR'R²R³R⁴]⁺ or [R^!R²⁺N=CR³-R⁵- R³C=N⁺R²R^J] wherein R^]-R⁴ are independently selected from H or a hydrocarbyl group with the proviso that at least one of R^!-R⁴ is a hydrocarbyl group and R⁵ is an alkylene group (eg CH₂, CH₂CH₂ etc type group) or a phenylene group (eg CβFU type group). The hydrocarbyl group is preferably a C1-C30 hydrocarbyl group which may be substituted or unsubstituted, straight or branched chain, saturated or unsaturated. Preferably, the hydrocarbyl group is an alkyl, cycloalkyl, aryl, alkaryl or aralkyl group. In particular where the hydrocarbyl groups are substituted the substituent is suitably a hydroxyl group thereby resulting in the resultant primary, secondary or tertiary amino compound being an amino alcohol.

Similarly, the organo cations in which A is phosphorus that may be used in making the ionic salts of the present invention include inter alia cations of the formula [PR^]R²R³R⁴]^" or [R¹R²⁺P=CR -R⁵-R³C=P⁺R²R¹] wherein R'-R⁵ have the same meaning as described in the context of [NR^!R²R³R⁴]⁺ and [R¹R²⁺N=CR³-R⁵-R³C=N⁺R²R¹] above.

Corresponding organo cations in which A is arsenic or antimony will have correspondingly similar structures. Of these, organo cations which are based on nitrogen or phosphorus are particularly preferred.

The ionic salts can be prepared by reacting one or more of the organo cations with an appropriate amount of a source of [BX₃Y]^" anions. Alternatively, the ionic salt may be prepared by reacting a halide of the organo cations recited above with BX₃ in an appropriate amount. It would be apparent to those skilled in the art that the precise amount of the respective components that need to be reacted would depend upon the acidity of the anions used and the basicity of the organo cations. Similarly, due to the varied nature of the reactants, the temperature at which these organo cations and anions react would vary over a moderate range of temperature conditions such as eg from ambient to about 150°C. The duration of the reaction may vary over a moderately wide range of a few minutes to about a few days eg a week. The resultant ionic salts may then be purified to remove any unwanted ions or salts and any adventitious products such as water. The ionic salts of the present invention may be neutral or acidic and may be solids or liquids. Of particular advantage are salts which are liquids. These may be usable as ionic liquids either as such as catalysts or as a solvent or reaction medium for the reactants and catalysts used in such reactions. The ionic salts of organo nitrogen and organo phosphorus cations in particular are either liquids as such or are transformable into liquids by applying a small amount of heat, at or below 80°C. Such liquids can be said to fall generically under the term "ionic liquids" and the ionic liquids formed according to the present invention have numerous applications

More specifically, a typical example of the novel group of ionic salts of the present invention is N-ethyl-N'-methylimidazoliurn chloro-trifluoroborate (EMEVf BF₃C1^"), which can be prepared by adding to a cooled suspension of

N-ethyl-N'-methylimidazolium chloride in a solvent such as eg heptane, a solution of a molar excess of boron trifluoride in an alcohol such as eg methanol in an atmosphere inert under the reaction conditions with stirring After the addition is complete the cooling bath is removed, the mixture heated to moderately elevated temperature and the solvents and excess BF₃ removed therefrom to result in the desired product which can be characterised by NMR spectroscopy as shown in the Examples below A similar procedure is adopted for synthesising the corresponding N-butyl-N'-methylimidazolium chlorotrifluoroborate from N-butyl-N'-methylimidazolium chloride

A feature of the ionic salts of the present invention is that they can be used as a solvent in chemical reactions for reactants and products, or, may be used as a solvent for catalysts for chemical reactions In particular, they may be used as solvent for metal complexes which have catalytic activity for chemical reactions Such compounds are usually coordination compounds formed by the reaction of a transition metal with a ligand Examples of metal complexes that can be use in combination with the ionic salts or ionic liquids of the present invention include inter alia complexes of titanium, zirconium, nickel, rhodium, cobalt, palladium and platinum More specifically, such complexes include inter aha nickel acetylacetonate, nickel cyclooctadienyl acetylacetonate, rhodium acetylacetonate, rhodium carbonyl acetylacetonate, platinum diphenylphosphine dichloride, palladium tetraphenylphosphine, hydrido tetracarbonyl cobalt and the like In such a product the relative mole ratios of the metal complex or metal salt to the ionic salt or ionic liquid is suitably in the range from 0 0001 to 10 and is preferably in the range from 0 0001 to 1 Any water which may be adventitiously introduced into such a product from the metal complex used to prepare said product may either be left in or retained in the product - if such water is not likely to adversely affect any subsequent reaction in which the product is used - or, alternatively, it may be removed from the product eg by evaporation

Thus, according to a further embodiment, the present invention is a composition comprising (I) a metal salt or a metal complex capable of catalysing a chemical reaction and

(II) an ionic salt comprising at least one organo-cation and at least one anion characterised in that the anion is of the formula [BX₃Y]\ wherein X is halogen and

Y is selected from:

(a) a halogen other than X,

(b) an OR group wherein R is a C1-C30 hydrocarbyl group,

(c) an -O(O)CL group in which L is hydrogen or a hydrocarbyl group and

(d) an -O(O)CZ group where Z is a carboxylic, hydroxycarboxylic or a hydrocarbylene carboxylic group.

The metal salts or metal complexes (I) and the ionic salts (II) have already been described above and carry the same meaning as previously. The metal salt or metal complex capable of catalysing a chemical reaction is suitably present as a solution thereof in the ionic salt during the reaction. A further feature of the solutions of metal salts or metal complexes in ionisable compounds of the present invention is that they are stable under conditions in the range of -100°C to about 300°C and at pressures ranging from 1- 200 bar. As examples of chemical reactions catalysed by a metal salt or a metal complex catalyst dissolved in the ionic salts of the present invention include wter alia: hydroformylation, oligomerisation or polymerisation of olefins, telomerisation of olefins, hydrogenation and olefin metathesis.

As indicated above, the ionic salts when used in liquid form, if necessary after heating, are termed ionic liquids. The advantage of using the metal salts or complexes dissolved in such ionic liquids according to the present invention instead of the complexes alone is that the ionic liquids therein can facilitate the separation of the reactants and reaction products from the catalyst due to the high solvating effect of these ionic liquids for the catalyst. This feature also minimises the loss of the catalyst which is normally associated with separation process involving conventional distillation or flashing off processes.

The ability to vary the nature of the anion and the cation in the ionic salts of the present invention gives rise to a high degree of flexibility in the ability to adapt and choose a catalyst, solvent or reactant desirable for a given reaction The ionic salts can be used to control the acidity of the reaction mixture, the viscosity of the reaction mixture, the stability of the catalyst and to provide a reaction medium when the ionic salts are ionic liquids The present invention is further illustrated with reference to the following

Examples

1. Synthesis of N-ethvI-N'-methvIimidazo-ium chlorotrifluoroborate t.EMIMr.BF,Cin.

A 3-neck 500ml flask fitted with nitrogen purge, dropping funnel and distillation bridge was filled under N₂ with a suspension of N-ethyl-N'-methyl-imidazolium chloride (EMIM⁺ Cl^", 1 OOg, 0 683 mol) in dry heptane (200ml) The suspension was cooled with an ice bath Through the dropping funnel a solution of BF in methanol (approximately 50 weight % BF , 84 8 ml, 102 g, 0 75 mol) was added dropwise over 15 min After the addition was complete a biphasic reaction mixture was formed The cooling bath was then removed and the biphasic reaction mixture was heated to 50°C to complete reaction for one hour The reaction temperature was then increased to 120°C for 3 hours and methanol, the excess BF₃-methanol, and the heptane were removed by distillation at this temperature The mixture was then allowed to cool under N₂-atmosphere 143 5g (98% yield) of a slightly yellow ionic liquid was obtained The product was confirmed by NMR spectroscopy as follows NMR-data in CDC1₃

Η-NMR 1 02 ppm (t, 3H, -CH₃), 3 47 ppm (s, 3H, N-CH₃), 3 79 ppm (q, 2H, N-CH₂- ), 7 04, 7 10 (s, 2H, -C-H of imidazolium), 8 37 (s, 1H, N-CH-N of imidazolium) ¹³C-NMR 15 0 ppm (-CH₃), 35 9 ppm (N-CH₃), 44 9 ppm (N-CH₂-), 122 0, 123 6 ( -C- H of imidazolium), 135 9 (s, 1H, N-CH-N of imidazolium) ¹⁹F-NMR -151 2 ppm (d)

2. Synthesis of N-butyl-N'-methylimidazoIium chlorotrifluoroborate (■BMIM1⁺.BF C11 ):

A 3-neck 500ml flask fitted with nitrogen purge, dropping funnel and distillation bridge was filled under N₂ with a suspension of N-butyl-N'-methylimidazolium chloride (BMIM⁺ Cl^" , lOOg, 0 573 mol) in dry heptane (200ml) The suspension was cooled with an ice bath Through the dropping funnel a solution of BF₃ in methanol (71 2 ml, 85 6 g, approximately 50 weight % BF , 0 63 mol) was added dropwise over 15 min After the addition was complete a biphasic mixture was formed The cooling bath was removed and the biphasic reaction mixture was heated to 50°C to complete reaction for one hour The reaction temperature was then increased to 120°C for 3 hours and methanol, the excess BF₃-methanol and the heptane were removed by distillation at this temperature The mixture is then allowed to cool under N₂-athmosphere 138 9 g (98% yield) of a slightly yellow ionic liquid is obtained The product was confirmed by NMR spectroscopy as follows NMR-data in CDC1₃ 'H-NMR 0 82 ppm (t, 3H, -CH₃), 1 25 ppm (m, 2H, -CH₂-CH₃), 1 76 ppm (m, 2H, N- CH₂-CH₂-), 3 86 ppm (s, 3H, N-CH₃), 4 12 ppm (t, 2H, N-CH₂-), 7 39, (s, 2H, -C-H of imidazolium), 8 74 (s, 1H, N-CH-N of imidazolium)

¹³C-NMR 14 7 ppm (-CH,), 20 6 ppm (-CH₂-CH₃), 33 2 ppm (N-CH₂-CH₂-), 37 5 ppm (N-CBi), 60 0 ppm (N-CH₂-), 123 9, 125 2 ( -C-H of imidazolium), 137 5 (s, 1H, N- CH-N of imidazolium) "F-NMR -151 2 ppm (d)

Claims

Claims:

1. An ionic salt comprising at least one organo cation and at least one anion characterised in that the anion is of the formula [BX Y]^", wherein

X is a halogen and

Y is selected from: (a) a halogen other than X,

(b) an OR group wherein R is a C1-C30 hydrocarbyl group,

(c) an -O(O)CL group in which L is hydrogen or a hydrocarbyl group and

2. An ionic salt according to claim 1 wherein the organo-cation is based on an element of Group V of the Periodic Table

3. An ionic salt according to claim 2 wherein the Group V organo-cation is selected from i) the general formula [AR'R²R³R⁴]⁺ or [R¹R²⁺A=CR³-R⁵-R³C=A⁺R²R¹] wherein A is selected from nitrogen, phosphorus, arsenic and antimony; R'-R⁴ are independently selected from H or a hydrocarbyl group with the proviso that at least one of R'-R⁴ is a hydrocarbyl group and R is an alkylene group; and ii) organo-cations having a heterocyclic ring in which the heterocyclic ring has at least one of one heteroatom, A, selected from nitrogen, phosphorus, arsenic and antimony.

4. An ionic salt according to claim 2 or 3 wherein the organo-cation is based on nitrogen or phosphorus

5. An ionic salt according to any one of claims 1 to 4 wherein [BX₃Y]^" is selected from the group consisting of [BF₃C1]\ [BC1₃F]\ [BBr₃Cl]\ [BBr₃F]\ [BI₃F]\ [BF₃Br]^", [BCl₃Br]^" and [BF₃I]^"; [BF₃OMe]^', [BF₃OEt]^", [BF₃OPr]^", [BF₃OBu]^" wherein Me represents a methyl group, Et an ethyl group, Pr an n-propyl or an isopropyl group and Bu an n-butyl group or a secondary butyl group; [BF₃.O.C(O).CH₃]^", [BF₃.O.C(O).C₂H₅] , [BF₃.O.C(O).C(O).OH]\ [BF₃.O.C(O).CH₂.C(OH)(COOH).CH₂.C(O).OH]^"

6. An ionic salt according to any one of claims 1 to 4 wherein X is fluorine

7. An ionic salt according to any one of claims 1 to 6 wherein the ionic salt is an ionic liquid

8. A composition comprising:

(I) a metal salt or a metal complex capable of catalysing a chemical reaction and

(II) an ionic salt as defined in any one of claims 1 to 6

9. A composition according to claim 8 wherein the mole ratio of the metal salt or metal complex to the ionic salt is in the range 0.0001 to 10

10. A composition according to claim 8 or claim 9 wherein the ionic salt is an ionic liquid

1 1. Use of a composition according to any one of claims 8-10 as a catalyst for a chemical reaction wherein the chemical reaction is selected from the group consisting of hydroformylation, oligomerisation of olefins, polymerisation of olefins, telomerisation of olefins, hydrogenation and olefin metathesis.