IONIC LIQUIDS AND USES THEREOF

This invention relates to ionic liquids and certain uses thereof. Particularly, it relates to the use of ionic liquids as surfactants (emulsiflers), and to the use of ionic liquid surfactants (emulsifiers) for forming stable emulsions and microemulsions. Room-temperature ionic liquids have been shown to be of great value in a wide variety of solvent applications owing to the ability to tailor their physical properties to the particular solvent application. This is achieved by varying the molecular structure of the components of the ionic liquid. Accordingly, ionic liquids have become known as "Designer Solvents" and have been subject to a great deal of interest in the chemical, pharmaceutical, petrochemical and chemical engineering industries.

An ionic liquid is an ionic material (typically an ion-pair) that is in a liquid state at a temperature of below 150°C, particularly, at a temperature of below 100 ⁰ C. Owing to ionic liquids being comprised entirely of dissociated ions, they show vastly reduced vapour pressures when compared with traditional organic solvents thereby minimizing the risk of atmospheric contamination. As ionic liquids are essentially non- volatile, they have a further advantage when compared with traditional organic solvents in that they have no odour thereby reducing health concerns. Yet a further advantage of ionic liquids when compared with traditional organic solvents is that they can be composed of ions of low toxicity. The flexibility of ionic liquids as solvents allows them to be tailored to have the desired solubility for the intended solute. Thus, ionic liquids have found utility as solvents for a wide variety of materials including heavy oils, coal residues, inorganic crystalline materials and silicon compounds. Ionic liquid solvents can also be tailored

to have the desired miscibility with an intended cosolvent. Thus, a wide variety of ionic liquids solvents are available which show the whole range of miscibility with water or organic cosolvents. Ionic liquids are also available that form stable emulsions with water or organic solvents where the ionic liquid forms either the continuous or discontinuous phase of the emulsion.

The present invention relates to the synthesis of certain selected surface active ionic liquids that are capable of reducing the interfacial surface tension between two or more phases selected from the group consisting of solid, liquid, gaseous, ionic and supercritical phases. The enhanced miscibility of the phases and/or the lowering of surface tension forces resulting from the employment of the ionic liquid surfactants of the present invention can be used to aid the formation of emulsions, microemulsions or foams.

In its broadest aspect, the present invention relates to a surfactant characterized in that the surfactant is a salt of general formula C ⁺ A ^" that is in a liquid state at a temperature below 150°C and at least one of the cation, C ⁺ , and the anion, A ^" , has a hydrophobic tail group attached to an ionic head group.

Preferably, both the cation, C ⁺ , and the anion, A ^" , of the surfactant (hereinafter "ionic liquid surfactant") have at least one hydrophobic tail group so that both the cation and anion have surface active properties. Thus, in a preferred embodiment of the present invention the surfactant is in a liquid state at a temperature below 150°C and is characterized in that the surfactant is an ionic liquid salt of general formula C ⁺ A ^" and the cation, C , comprises at least one hydrophobic tail group attached to a cationic head group and the anion, A ^" , comprises at least one hydrophobic tail group attached to an anionic head group. Where the cation, C ⁺ , has at least one hydrophobic tail group, it is preferred that the cation, C ⁺ , has 1 to 4 hydrophobic tail groups attached to the cationic head group. Where the anion, A ^" , has at least one hydrophobic tail group, it is preferred that the anion, A ^" , has 1 or 2 hydrophobic tail groups attached to the anionic head group.

Preferably, the hydrophobic tail groups are hydrocarbyl tail groups. Suitably, the hydrocarbyl tail group(s) of the cation, C ⁺ , and/or anion, A ^" , may be a halogenated hydrocarbyl group such as a fluorinated hydrocarbyl group. It is also possible for the hydrocarbyl tail group to bear substituents provided that the substituents do not adversely affect the desired surface active properties of the cation and/or anion.

Acceptable ^' substituents include alkoxy and hydroxyl groups. Generally, the hydrocarbyl tail group is an alkyl group, alkenyl group or alkynyl group having at least 8 carbon atoms. Preferably, the alkyl group, alkenyl group or alkynyl group has from 8 to 30 carbon atoms, more preferably 12 to 24 carbon atoms, most preferably 16 to 20 . carbon atoms. The alkyl, alkenyl or alkynyl group may be a straight chain or branched chain group. The hydrocarbyl tail group may also be an alkaryl substituent having at least 8, preferably, at least 10 carbon atoms, more preferably, at least 12 carbon atoms, for example, 12 to 24 carbon atoms. The hydrocarbyl tail group may also be a poly(oxyethylene) group, -(CH ₂ CH ₂ O) _x R (where R is H or methyl and x is an integer of from 4 to 15, preferably 5 to 10.

Suitably, the cation, C ⁺ is selected from the group consisting of:

(a) quaternary ammonium or phosphonium ions of general formula:

[R ¹ R ² R ³ R ⁴ M] ⁺ wherein M is N or P; R and R are independently selected from methyl or ethyl groups;

R is a C ₈ to C ₃₀ alkyl group, preferably a C ₁₂ to C ₂₈ alkyl group, for example, a C ₁₄ to

C ₂₄ alkyl group and

R ⁴ is selected from the group consisting of methyl, ethyl and a Cg to C ₃₀ alkyl group,

(preferably a C ₁₂ to C ₂₈ alkyl group, for example, a C ₁₄ to C ₂₄ alkyl group). Particularly, preferred quaternary ammonium or phosphonium cations of this class include hexadecyltrimethylphosphonium, hexadecyltriethylphosphonium, octadecyltrimethylphosphonium, octadecyltriethylphosphonium, dihexadecyldimethylphosphonium, dioctadecyldimethylphosphonium hexadecyltrimethylammonium, hexadecyltriethylammonium, octadecyltrimethylammonium, octadecyltriethylammonium, dihexadecyldimethylammonium, and dioctadecyldimethylammonium.

(b) quaternary ammonium or phosphonium ions of general formula:

[R ¹ R ² R ³ R ⁴ M] ⁺ wherein M is N or P; R ¹ and R ² are independently selected from methyl or ethyl groups;

R ³ is -(CH ₂ ) _π C ₆ H ₄ R' wherein n is an integer of from 0 to 5, preferably, 0 to 3; and R' is selected from the group consisting of H, Cl, Br, I, NO ₂ , C ₁ to C ₃₀ alkyl groups

(preferably C ₁ to C ₂₀ alkyl groups), -SO ₂ R", -SOR" and -C(O)R" (wherein R" is a Ci to C ₃₀ alkyl group, preferably a C ₁ to C ₂₀ alkyl group) with the proviso that the R ³ group has at least 8 carbon atoms; and

R ⁴ is a C ₈ to C ₃₀ alkyl group (preferably a C ₁₂ to C ₂₈ alkyl group, for example, a C ₁₄ to C ₂₄ alkyl group) or is an R ³ group.

(c) triethanolamine ester quaternary ammonium or phosphonium ions of general formula:

[(R ² CO ₂ CH ₂ CH ₂ ) ₂ M(R ¹ )CH ₂ CH ₂ OH] ⁺ wherein M is N or P; R ¹ is methyl or ethyl; and

R ² is a C ₅ to C ₃ o alkyl group, preferably a C ₁₀ to C ₂₈ alkyl group, more preferably a C ₁₄ to C ₂₄ alkyl group;

(d) quaternised polyoxyethylenated (POE) long-chain amines:

[R ¹ R ² NKCH ₂ CH ₂ O) _x H) ₂ I ⁺ wherein R ¹ and R ² are independently selected from methyl and ethyl; and x is an integer of from 4 to 15, preferably, 5 to 10;

(e) quaternary ammonium ions of general formula:

[R ¹ R ² R ³ NOR ⁴ J ⁺ wherein R ¹ and R ² are independently selected from methyl and ethyl; R ³ is a C ₈ to C ₃₀ alkyl group, preferably a C ₁₂ to C ₂₈ alkyl group, most preferably, a C ₁₄ to C ₂₄ alkyl group; and

R ⁴ is H or a C ₁ to C ₄ alkyl, preferably, H, methyl or ethyl.

Quaternary ammonium ions of this type may be prepared by protonating or alkylating the corresponding amine oxide, R ¹ R ² R ³ N ⁺ O ^' . (f) quaternary ammonium ions of general formula: [(CH ₃ ) ₃ N(CH ₂ CH ₂ O) _X R ¹ ] ⁺ wherein x is an integer of from 1 to 5, preferably 2 to 3 and R ¹ is a C ₁ to C ₃₀ alkyl group with the proviso that the -(CH ₂ CH ₂ O) _x R ¹ substituent has at least 8 carbon atoms.

Quaternary ammonium salts of this class are derived from choline, [(CH ₃ ) ₃ N(CH ₂ CH ₂ OH)] ⁺ .

(g) quaternary ammonium ions of general formula: [R ¹ R ² NCH ₂ CH ₂ NR ³ R ⁴ R ⁵ J ⁺ wherein R ¹ , R ² , R ³ and R ⁴ are independently selected from methyl and ethyl; and

R ⁵ is a hydrocarbyl group selected from (i) C ₈ to C ₃₀ alkyl groups or (ii) -(CH ₂ ) _n C ₆ H ₄ R' wherein n is an integer of from 0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO ₂ , C ₁ to C ₃₀ alkyl groups (preferably C ₁ to C ₂₀ alkyl groups), -SO ₂ R", -SOR" and -C(O)R" (wherein R" is a C ₁ to C ₃₀ alkyl group, preferably a C ₁ to C ₂₀ alkyl group) with the proviso that R ⁵ has at least 8 carbon atoms.

Quaternary ammonium ions of this class may, for example, be prepared from tetramethylethylenediamine or tetraethylethylenediamine by reaction with R ⁵ X where X is a good leaving group, for example, a halide.

The cation may also comprise an aromatic or non-aromatic heterocyclic ring structure having at least one hydrophobic tail group, preferably a hydrocarbyl tail group as a substituent on the heterocyclic ring. It is envisaged that the heterocyclic ring may have from 1 to 3 hydrocarbyl substituents. Suitably, the heterocyclic ring structure of the cation is selected from imidazolium, imidazolinium, pyridinium, pyrazolium, thiazolium, isothiazolinium, azathiozolium, oxothiazolium, oxazinium, oxazolium, oxaborolium, dithiozolium, trizdium, selenozolium, oxaphopholium, pyrollium, borolium, furanium,< thiophenium, phospholium, pentazolium, indolium, indolinium, oxazolium, isooxazolium, isotriazolium, tetrazolium, benzofuranium, diborzofuranium, benzothiophenium, dibenzothiophenium, thiadiazolium, pyrimidinium, pyrazinium, pyridazinium, piperazinium, piperidinium, morpholenium, pyranium, annolinium, phthalzinium, quinazolinium, quinaxalinium, quinolinium, isoquinolinium, thazinium, oxazinium, and azaannulenium. Preferably, the heterocyclic ring structure has at least one N heteroatom, and optionally an O heteroatom.

Preferred heterocyclic cations include: (a) non-aromatic heterocycles such as:

wherein M is N or P;

R ¹ is C ₈ to C ₃₀ alkyl group; and

R ² is selected from methyl, ethyl or a C ₈ to C ₃₀ alkyl group. Where R ¹ and R ² are both C ₈ to C ₃₀ alkyl groups, it is preferred that R ¹ and R ² are of different length, for example, R ¹ may be a C ₈ to C ₁₂ alkyl group and R ² a C ₁₆ to C ₃₀ alkyl group, (b) Imidazolium ions of the general formula:

wherein R ¹ is a C ₈ to C ₃₀ alkyl group, preferably a C ₁₂ to C ₂₈ alkyl group, for example, a C ₁₆ to C ₂₄ alkyl group;

R ² is selected from H, methyl and ethyl, preferably H; R ³ is selected from methyl, ethyl and C ₈ to C ₃₀ alkyl groups, preferably, methyl or ethyl; and

R ⁴ and R ⁵ are H or a halide (for example, Cl or Br). (c) pyridinium ions of the general formula:

wherein R ¹ is hydrophobic substituent selected from (i) C ₈ to C ₃₀ alkyl groups

(preferably, C ₁₂ to C ₂₀ alkyl groups) and (ii) -(CHb) _n CeH ₄ R' wherein n is an integer of from 0 to 5, R' is selected from the group consisting of H, Cl ₅ Br, I, NO ₂ , C ₁ to C ₃₀ alkyl groups (preferably C ₁ to C ₂₀ alkyl groups), -SO ₂ R", -SOR" and -C(O)R" (wherein R"

is a C ₁ to C ₃₀ alkyl group, preferably a C ₁ to C ₂₀ alkyl group) with the proviso that - (CH ₂ ) _J1 C ₆ H ₄ R' contains at least 8 carbon atoms; and

R ² and R ³ are independently selected from H and dimethylamino, or are R ¹ groups. Particularly preferred pyridinium ions of this class include dodecylpyridinium, 1,4- didodecylpyridinium, hexadecylpyridinium, 1,4-dihexadecylpyridinium, octadecylpyrinidium, 1 ,4-octadecylpyridinium, 4-(dimethylamino)dodecylpyridinium, 2-(dimethylamino)dodecylpyridinium, 4-(dimethylamino)hexadecylpyridinium and 2- (dimethylamino)hexadecylpyridmium. Where the pyridinium ion has a dimethylamino substituent in the 2- or 4- position, the pyridinium ion may be prepared from 4- dimethylaminopyridine or 2-dimethylaminopyridine respectively, (d) an oxazole of general formulae:

wherein R ¹ is a hydrocarbyl substituent selected from (i) C ₈ to C ₃₀ alkyl groups (preferably C ₁₂ to C ₂₈ alkyl groups) and (ii) -(CH ₂ ) _n C ₆ H ₄ R' wherein n is an integer from

0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO ₂ , C ₆ to C ₃₀ alkyl groups (preferably C ₁ to C ₂₀ alkyl groups), -SO ₂ R", -SOR" and -C(O)R" (wherein R" is a C ₁ to C ₃₀ alkyl group, preferably a C ₁ to C ₂₀ alkyl group) with the proviso that -

(CH ₂ ) _n C ₆ H ₄ R' contains at least 8 carbon atoms; and R and R ³ are independently selected from H, methyl or ethyl.

(e) derivatives of l,5-diazabicyclonon-5-ene (DBN) and l,9-diazabicycloundec-7-ene

(DBU) of general formulae:

wherein R is a hydrocarbyl substituent selected from (i) Cg to C ₃₀ alkyl groups and (ii) - (CH ₂ ) _n C ₆ H ₄ R' wherein n is an integer from 0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO ₂ , C ₁ to C ₃₀ alkyl groups (preferably C ₁ to C ₂₀ alkyl groups), -SO ₂ R' ' , -SOR' ' and -C(O)R' ' (wherein R" is a C ₁ to C ₃₀ alkyl group, preferably a Ci to C ₂₀ alkyl group) with the proviso that -(CH ₂ ) _H C ₆ H ₄ R' contains at least 8 carbon atoms.

Preferably, the anion, A ^" , is selected from the group consisting of: (a) dialkyl phosphase anions of the general formula: [R ¹ R ² P(O)O]- wherein R ¹ and R ² are independently selected from C ₈ to C ₃₀ , preferably C ₁₂ to C ₁₈ , alkyl groups. The alkyl groups may be branched or unbranched. Particularly preferred alkyl groups include dodecyl, hexadecyl, octadecyl, and 2,4,4-trimethylpentyl. A commercially available example of a dialkyl phosphase anion of general formula (II) is Cyanex-272™ (2,4,4-trimethylpentyl phosphase) :

(b) phosphates of general formula: [(R ¹ O)(R ² O)P(O)O]- wherein R ¹ and R ² are independently selected from C ₈ to C ₃₀ alkyl groups, preferably, C ₁₂ to C ₁₈ alkyl groups. The alkyl groups may be branched or unbranched.

(c) phosphoric acid esters of general formulae:

[R(OCH ₂ CH ₂ ) _x OP(O)(O) ₂ f [(R(OCH ₂ CHa) _x O) ₂ P(O)O]-

wherein x is an integer of from 4 to 15 and R is an alkyl group, preferably, methyl or ethyl.

(d) alkyl sulfate anions of general formula:

ROSO ₃ ^' wherein R is a straight chain or branched chain alkyl group having at least 8 carbon atoms, preferably, a C ₈ to C ₃₀ alkyl group, more preferably a C ₁₂ to C ₂₄ alkyl group, for example, a Ci ₆ to C ₂₀ alkyl group. Examples of alkyl sulfate anions include dodecyl sulfate, hexadecyl sulfate and octadecyl sulfate.

(e) sulfated polyoxyethylene (POE) straight chain alcohols of general formula: R(OCH ₂ CH ₂ ) _X SO ₄ - wherein R is a C ₈ to C ₃₀ alkyl group and x is an integer in the range 1 to 10, preferably, 2 to 5.

(f) alkyl sulfonate anions of general formula:

RSO ₃ - wherein R is a straight chain or branched chain alkyl group having at least 8 carbon atoms, preferably, a C ₈ to C ₃₀ alkyl group, more preferably a C ₁₂ to C ₂₄ alkyl group, for example, a C ₁₆ to C ₂ o alkyl group. Examples of alkyl sulfonate anions include dodecanesulfonate and hexadecanesulfonate.

(g) alkylbenzylsulfonates of general formula: RC ₆ H ₄ SO ₃ ^" where R is a C ₂ to C ₃₀ alkyl group, preferably, a Cg to Ci ₅ alkyl group. The alkyl group may be in the 2-, 3-, or 4- position on the phenyl ring, preferably, the 4-position. The alkyl group may be branched or unbranched. Preferably, the alkyl group is - CH(CH ₃ )(CH ₂ ) _n CH ₃ where n is an integer in the range 9 to 12. Preferred alkylbenzyl sulfonates include dodecylbenzenesulfonate, hexadecylbenzenesulfonate and octadecylbenzenesulfonate. (h) N-acyl-n-alkyltaurates of general formula:

RC(O)N(R')CH ₂ CH ₂ SO ₃ ^" wherein R is a straight chain or branched chain C ₄ to C ₃₀ alkyl group, and R' is methyl or ethyl.

(i) isethionates of general formula

RCOOCH ₂ CH ₂ SO ₃ - wherein R is a straight chain or branched chain C ₅ to C ₃₀ alkyl group.

G) sulfonic acid esters of general formula:

ROSO ₃ ^' wherein R is a straight chain or branched chain C ₈ to C ₃₀ alkyl group, (k) sulfosuccinate esters of general formula: R ¹ OOCCH ₂ CH(SO ₃ OCOOR ² wherein R ¹ and R ² are straight chain or branched chain C ₅ to C ₃₀ alkyl groups. (1) arylalkanesulfonates of general formula:

R(CH ₂ ) _m CH(C ₆ H ₄ R ¹ )(CH ₂ ) _n SO ₃ - wherein m and n are integers in the range 1 to 10; R is H or a C ₁ to C ₃₀ alkyl group; and

R ¹ is selected from the group consisting of H ₅ Cl, Br, I, NO ₂ , C ₁ to C30 alkyl groups (preferably a C ₁ to C ₂₀ alkyl group), -SO ₂ R', -SOR' and -C(O)R' (wherein R' is a C ₁ to C ₃₀ alkyl group, preferably a Ci to C ₂₀ alkyl group. Such sulfonates are prepared by sulfonating an olefin and then treating the intermediate product with an aromatic compound.

(m) alkyldiphenylether(di)sulfonates of general formula:

RC ₆ H ₃ (SO ₃ OOC ₆ H ₄ SO ₃ ^" wherein R is a C ₁ to C ₃₀ alkyl group. Such alkyldiphenylether(di)sulfonates are prepared by alkylating diphenyl ether and then sulfonating the reaction product. (n) carboxylate anions of general formula:

RC(O)O ^" wherein R is a straight chain or branched chain C ₇ to C ₃₀ alkyl or alkenyl group. For example, the carboxylate may be CH ₃ (CHa) ₁₀ CO ₂ ^" (laurate), CH ₃ (CH ₂ ) ₁₂ CO2 ^" (myristate), CH ₃ (CH ₂ ) _I i ₆ CO ₂ ^" (stearate), CH ₃ (CH ₂ ) ₁₈ CO ₂ ^" (arachidate), CH ₃ (CH ₂ ) ₅ CH=CH(CH ₂ ) ₇ CO ₂ ^" (palmitoleate), CH ₃ (CH2) ₇ CH=CH(CH2)7CO ₂ ^" (oleate), CH ₃ (CH2) ₄ CH=CHCH ₂ CH=CH(CH ₂ ) ₇ CO ₂ ^" (linoleate), CH ₃ CH ₂ CH=CHCH ₂ CH=CHCH ₂ CH=CH(CH ₂ ) ₇ CO ₂ ^" (linolenate), CH ₃ (CH ₂ ) ₄ (CH=CHCH ₂ ) ₄ (CH ₂ ) ₂ Cθ ₂ ^" (arachidonate). (o) borate anions of general formula: [(RCH ₂ CH ₂ ) _S R ¹ B] ^" wherein R is H or methyl and R ¹ is a straight chain or branched chain C ₈ to C ₃₀ alkyl group. Borate anions of this class may be prepared by reacting CH ₂ =CHR (R is H or methyl) with BH ₃ -Y (where Y forms a complex with BH ₃ , for example, BH ₃ .Y is a

borane tetrahydrofuran complex) followed by reaction of the intermediate compound

(RCH ₂ CH ₂ ) ₃ B with R ¹ ClTNa.

(p) borate anions of general formula:

γλ

O O R ¹ " R ²

wherein R ¹ and R ² are straight chain or branched chain C ₈ to C ₃₀ alkyl groups.

The ionic liquid surfactant may also be a protonated ionic liquid formed by the following reaction:

Aπion-H + [Anion] ^"

wherein the cation and/or the anion has at least one hydrophobic tail group, for example, a C ₈ to C ₃₀ alkyl substituent.

Many of the salts described above are novel, and the invention provides per se all novel salts described herein. Specific groups of novel salts include, but are not limited to, the following. A salt of the general formula Ia:

C ⁺ A ^" (Ia) the salt of general formula Ia existing in a liquid state at a temperature below 150°C; in which A ^" is an anion; and in which the cation, C ⁺ , comprises an imidazolium ion of the general formula:

wherein R ¹ is a C ₁₆ to C ₃₀ alkyl group; R ² is selected from H, methyl and ethyl; R ³ is selected from methyl, ethyl and C ₈ to C ₃₀ alkyl groups; and R ⁴ and R ⁵ are H, or halogen.

A salt of the general formula Ib:

C ⁺ A ^" (Ib) the salt of general formula Ib existing in a liquid state at a temperature below 150°C; in which A ^" is an anion; and in which the cation, C ⁺ , comprises a pyridinium ion of the general formula:

wherein R ¹ is a C ₈ to C ₃₀ alkyl group; and

R ² and R ³ are independently selected from (i) H; (ii) dimethylamino; (iii) C ₈ to C ₃₀ alkyl groups; and (iv) -(CH ₂ ) _H C ₆ H ₄ R' wherein n is an integer of from 0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO ₂ , C ₁ to C ₃₀ alkyl groups, -SO ₂ R", -SOR" and -C(O)R" (wherein R" is a C ₁ to C ₃₀ alkyl group) with the proviso that -(CH ₂ ) _H C ₆ H ₄ R' contains at least 8 carbon atoms. A salt of the general formula Ic:

C ⁺ A ^" (Ic)

the salt of general formula Ic existing in a liquid state at a temperature below 150°C; in which A ^" is an anion; and in which the cation, C ⁺ , is selected from one of the quaternary ammonium or phosphonium groups (a) to (g) defined above. A salt of the general formula Id:

C ⁺ A ^" (Id)

the salt of general formula Id existing in a liquid state at a temperature below 150°C; in which A ^' is an anion; and in which the cation, C ⁺ , is selected from one of the heterocyclic groups (a), (d) and (e) defined above A salt of the general formula Ie:

C ⁺ A ^' (Ie)

the salt of general formula Ie existing in a liquid state at a temperature below 150°C; in which A ^" is an anion of the general formula:

[R ¹ R ² P(O)O] ^" wherein R ¹ and R ² are independently selected from C ₈ to C ₃₀ alkyl groups; and in which the cation, C ⁺ , is an imidazolium ion of the general formula:

wherein R ¹ is an alkyl group having up to 15 carbon atoms; R ² is selected from H ₅ methyl and ethyl; R ³ is selected from methyl, ethyl and C ₈ to C ₃₀ alkyl groups; and R ⁴ and R ⁵ are H or halogen.

The ionic liquid surfactants (emulsifiers) of the present. invention may be classified using the hydrophilic-lipophilic balance (HLB) system that employs a scale of 0 to 20 based on the affinity of the surfactants for oil or water. Surfactants with low HLB values are more lipophilic while surfactants with higher HLB values are more hydrophilic. The HLB values of the ionic liquid surfactants may be determined empirically by comparison with conventional surfactants of predetermined HLB value.

In general, ionic liquid surfactants will have the following properties or functions based on their HLB values:

1-3 antifoaming properties 3-8 water in oil emulsification

7-9 wetting properties

9-18 oil in water emulsification

15-20 solubilizing properties.

In particular, surfactants with HLB values of 3 to 8 are more oil soluble and will form water in oil emulsions while surfactants having an HLB value of greater than 9, preferably, 9 to 18, are more water soluble and will form oil in water emulsions.

In one of its aspects, the present invention provides a water in oil or oil in water emulsion which comprises (i) an oil phase, (ii) an aqueous phase and (iii) an ionic liquid surfactant wherein the ionic liquid surfactant is a salt of general formula I: C ⁺ A ^' (I) the salt of general formula I existing in a liquid state at a temperature below 150°C; at least one of the cation, C ⁺ , and anion, A ^' , comprising a hydrophobic tail group attached to an ionic head group; and A ^" represents an anion containing phosphorus, or an alkyl sulfate anion of general formula: ROSO ₃ ^" wherein R is an alkyl group having at least 8 carbon atoms.

Preferred salts for use in this aspect of the invention are given above. Particularly preferred salts are those in which the anion A ^' is selected from the groups (a), (b) and (c), especially (a), given above. In a further aspect, the present invention provides a water in oil or oil in water emulsion which comprises (i) an oil phase, (ii) an aqueous phase and (iii) a novel ionic liquid surfactant as defined above.

An emulsion of the invention may be a microemulsion. An advantage of the microemulsion of the present invention is that it has a low interfacial tension of less than 1 mNm ^'1 .

As discussed above, depending upon the HLB value of the ionic liquid surfactant, the microemulsion may be an oil in water microemulsion where the oil is dispersed in a continuous aqueous phase or a water in oil microemulsion where the water is dispersed in a continuous oil phase. Preferably, the microemulsion in a water in oil microemulsion. The water in oil microemulsion of the present invention may be used for deploying water soluble or water dispersible oil field or gas field production chemicals as described in International Patent Application No. WO 0100747 or in enhanced oil recovery.

Microemulsions in general are known, see, for example "Microemulsions", Editor I D Robb, Plenum Press, New York, 1982 which is herein incorporated by reference. Microemulsions differ from conventional emulsions in that they form spontaneously upon mixing of the oil phase, aqueous phase and the surfactant. They also differ from ordinary emulsions in having droplets of very small size or in having microdomains having at least one dimension of length, breadth or thickness of very small size. Thus, microemulsions appear clear to the naked eye or even the optical microscope, compared to the larger droplets (greater than 100 nm diameter) of conventional cloudy emulsions.

Suitably, the aqueous phase of the water in oil microemulsion is distributed in a continuous oil phase in the form of droplets having a diameter in the range 1 to 100 nm or in the form of microdomains having at least one dimension of length, breadth or thickness in the range 1 to 100 nm. Where the aqueous phase of the water in oil microemulsion is distributed in the oil phase in the form of droplets, the droplets preferably have an average diameter in the range of 10 to 500 nm, more preferably 50 to 250 nm. The droplet size distribution is generally such that at least 90% of the diameters are within 20% or especially 10% of the average diameter. The microemulsions are transparent to the eye and are apparently isotropic.

Where the aqueous phase of the water in oil microemulsion is distributed in the oil phase in the form of microdomains, the microdomains preferably have at least one

dimension of length, breadth or thickness in the range 10 to 500 ran, more preferably 50 to 250 nni.

The oil phase is essentially any liquid which is immiscible with the aqueous phase. For example the oil phase may be selected from the group consisting of liquid alkanes (preferably C ₅ -C ₂₀ alkanes, more preferably C ₈ to C ₁₅ alkanes, most preferably C ₉ -C ₁₂ alkanes, for example, n-hexane, n-nonane, n-decane, and n-undecane), alkenes, liquid alkyl halides (for example, carbon tetrachloride or dichloromethane) and liquid aromatic hydrocarbons (for example, benzene, toluene and xylene). The oil phase may also be a paraffin oil, a natural oil (for example, a vegetable or animal oil), diesel, kerosene, gas oil, crude oil, lubricant base oil, liquid carbon dioxide, liquid chlorofluorocarbons such as CCIiF ₂ , CHCl ₂ F and CH ₃ CClF ₂ (known as freons), tetrahydrofuran, dimethyl formamide and dimethyl sulfoxide.

The aqueous phase may additionally comprise a water miscible solvent such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, butyl monoglycol ether, butyl diglycol ether, butyl triglycol ether, ethylene glycol mono butyl ether and ethylene glycol. Without wishing to be bound by any theory, it is believed that the presence of a water miscible solvent in the aqueous phase stabilizes the microemulsion so that less ionic liquid surfactant is required to form a stable microemulsion. The amount of water miscible solvent which may be present in the aqueous phase is in the range 0.5 to 50 % by weight, preferably 5 to 30 % by weight based on the total weight of water and water miscible solvent. However, an advantage of the ionic liquid surfactant of the present invention is that the microemulsion is stable even in the absence of a water miscible solvent.

Generally, a salt such as sodium chloride or magnesium sulfate is added to the aqueous phase of a conventional microemulsion in order to enhance the stability of the microemulsion. Thus, the aqueous phase of a conventional microemulsion is generally saturated with the salt. However, a further advantage of the microemulsion of the present invention is that there is no requirement to add a salt to stabilize the emulsion. However, if deemed desirable, a salt may be included in the aqueous phase of the emulsion.

The volume fraction of the aqueous phase in the microemulsion is generally in the range from 1-50%, preferably 10 to 40%, more preferably 23 to 30%.

The ionic liquid surfactant is suitably present in the microemulsion in an amount ranging from 0.1 to 5 mole %, preferably 0.25 to 2 mole %, for example 0.5 to 1 mole %.

Where the water in oil microemulsion of the present invention is used to deploy a water-soluble or water-dispersible production chemical, the aqueous phase of the microemulsion may comprise fresh, tap, river, sea, produced or formation water. The aqueous phase may have a total salinity of 0-250 g/1, for example 5-50 g/1. The aqueous phase may have a pH of 0.5-9. Where the aqueous phase comprises a sea-water solution of a highly acidic production chemical such as, for example, a scale inhibitor, the aqueous phase usually has a highly acidic pH of 0.1 - 1. In such cases it may be necessary to neutralise the acidity of the aqueous phase by using ammonium hydroxide or an alkali metal hydroxide, especially sodium hydroxide, potassium hydroxide or lithium hydroxide, in order to bring the pH of the formulation to within a preferred range of from 2-6. Preferably, the aqueous phase is neutralized prior to being mixed with the organic phase and surfactant to form the microemulsion.

Preferably, both the cation and the anion of the ionic liquid surfactant that is used to form the microemulsion have at least one hydrocarbyl tail group. Suitably, the cation of the ionic liquid surfactant has at least one hydrophobic tail group having a chain length of at least 16 carbon atoms, preferably 18 to 30 carbon atoms while the anion of the ionic liquid surfactant has at least one hydrophobic tail group having a chain length of 8 to 12 carbon atoms, preferably 8 to 10 carbon atoms. Alternatively, the anion of the ionic liquid may have at least one hydrophobic tail group having a chain length of at least 16 carbon atoms, preferably 18 to 30 carbon atoms while the cation has at least one hydrocarbyl tail group having a chain length of 8 to 12 carbon atoms, more preferably, 8 to 10 carbon atoms. Without wishing to be bound by any theory it is believed that where the cation and anion have hydrophobic tail groups that are of different length that this increases the stability of the microemulsion by enhancing the packing of the surfactant in the interfacial film. Mixtures of ionic liquid surfactants may be employed to prepare the microemulsion, for example, 2 or 3 ionic liquid surfactants.

It is important that the microemulsion is thermally stable. It is possible to devise microemulsions which are stable over a wide temperature range e.g. from ambient to 300 ⁰ C or from 90 to about 150°C. However, it is not essential that the microemulsion is

stable across the whole of the range of from ambient to 150°C. For example, the microemulsion may be stable between ambient and 70°C or between 40 and 80°C. The microemulsion of the present invention forms spontaneously on gentle mixing of the aqueous phase, the oil phase and the ionic liquid surfactant in any order; conveniently, the aqueous phase is mixed last into a mixture of the oil phase and the ionic liquid surfactant. If the material made is initially cloudy, then a microemulsion has not been produced, and minor adjustments to the relative proportions of the ingredients or a change in the nature of the ionic liquid surfactant or the temperature may be needed. The microemulsion can be characterized by x-ray diffraction to show the presence of the droplets or domains.

It is also envisaged that the ionic liquid surfactants may be used to form conventional emulsions, in which, for example, the internal phase of the emulsion is distributed in a continuous external phase in the form of droplets having a diameter in the range 0.01 to about 100 microns. Conventional emulsions differ from microemulsions in that it is necessary to input energy to form the emulsion. In principle, a microemulsion and a conventional emulsion may coexist.

The conventional emulsion may be an oil in water emulsion where an internal oil phase in dispersed in the form of droplets in a continuous external aqueous phase or a water in oil emulsion where an internal aqueous phase is dispersed in the form of droplets in a continuous external oil phase. As discussed above, the type of conventional emulsion is dependent upon the nature of the ionic liquid surfactant (emulsifier).

Preferably, the ionic liquid surfactant that is employed to generate the emulsion is comprised of a cation, C ⁺ , having at least one hydrophobic tail group attached to a cationic head group and an anion, A ^" , having at least one hydrophobic tail group attached to an anionic head group.

Mixtures of ionic liquid surfactants may be employed to prepare the conventional emulsion of the present invention, for example, 2 or 3 ionic liquid surfactants.

Where the ionic liquid surfactant has an HLB value of 3 to 8 and the surfactant is oil soluble, a water in oil emulsion may be formed by dissolving minor amounts of the oil soluble ionic liquid surfactant in the oil that is to form the continuous oil phase of

the emulsion. The concentration of oil-soluble ionic liquid surfactant in the resulting solution may be in the range of from 0.1 to 5 mole %, preferably 0.25 to 2 mole %, most preferably 0.5 to 1 mole %. The emulsion is preferably formed by pouring the aqueous phase into the solution of the oil-soluble ionic liquid surfactant in the oil phase while intensive blending is applied (thereby imparting energy to form the emulsion). The blending operation for the emulsion should be designed to minimize the size of the internal phase water droplets since this may increase the stability of the emulsion. The mixture should be vigorously stirred or sheared for about 5 to 20 minutes, the rate of shear being highly dependent on the size and type of mixing device employed. Stirring rate and times should be designed to form small aqueous droplets, preferably having average diameters of from about 0.3 to about 100 microns and preferably from about 1 to about 10 microns.

Preferably, the internal phase of the emulsion should amount to from 10 to 70 percent, more preferably from 30 to 60 percent of the total volume of the emulsion. Density control of the water in oil emulsion may be used to enhance its stability.

This may be accomplished by addition of weighting agents to the internal aqueous phase of the emulsion. For example, minor amounts of soluble salts such as sodium or potassium chloride may be added to the internal aqueous phase. Suitably, the aqueous phase may comprise from 0.5 to 20 percent by weight of soluble salts. Where the ionic liquid surfactant has an HLB value of greater than 9, preferably.

9 to 18, and is water soluble, an oil in water emulsion may be formed by dissolving minor amounts of the water soluble ionic liquid surfactant in the aqueous phase. The concentration of water-soluble ionic liquid surfactant in the resulting solution may be in the range of from 0.1 to 5 mole%, preferably 0.25. to 2 mole%. The emulsion is preferably formed by pouring the oil phase into the solution of the water-soluble ionic liquid surfactant in the aqueous phase while intensive blending is applied, as described above for the preparation of a water in oil emulsion. The blending operation for the emulsion should be designed to minimize the size of the internal phase oil droplets since this may increase the stability of the emulsion. Stirring rate and times should be designed to form small oil droplets having average diameters of from about 0.3 to about 100 microns and preferably from about 1 to about 10 microns.

Preferably, the internal oil of the emulsion should amount to from 1 to 80 percent, more preferably from 5 to 50 percent of the total volume of the emulsion.

Suitably, the water in oil emulsion may be used to deploy a water-soluble or water-dispersible production chemical, as described above for a water in oil microemulsion. The conventional emulsion may also act as the base fluid of a wellbore fluid, for example, a drilling fluid or completion fluid. An advantage of the conventional emulsion is that the use of the ionic liquid surfactant renders the emulsion more stable under high temperature and/or high pressure conditions than emulsions formed using conventional emulsifiers. The emulsions are also more tolerant of metal ions and are less likely to form scums.

The ionic liquid surfactants of the present invention have many other applications including their use:

1) to prepare foam compositions, for example, for mobility control in gas and/or gas condensate reservoirs where the foam is used to block a high permeability zone and to divert a gas into a low permeability zone. Examples of suitable foaming agents include l-octadecyl-3-methylimidazolium bis(2,4,4- trimethylpentyl)phosphate and 1-octadecylpyridinium bis(2,4,4- trimethylpentyl)phosphate .

2) as cleaning agents or degreasers (where the ionic liquid surfactant acts as an emulsifier or a wetting agent).

3) in personal hygiene products (where the ionic liquid surfactant acts as an emulsifier or a wetting agent).

4) as hydrophobic solvents, particularly, terpene free hydrophobic solvents

5) as a component of drilling fluids, for example, the ionic liquid surfactant may act as a heat transfer agent (to transfer heat from the drill bit), as a lubricant for the drill bit, as a weighting agent or as a fluid loss control agent. 6) as additives during oil production, for example, the surfactant may act as a gas hydrate inhibitor, corrosion inhibitor or drag reducer.

7) as additives during water flooding operations (enhanced oil recovery from oil wells)

8) as lubricants or lubricant additives 9) as hydraulic fluids or hydraulic fluid additives

10) for dispersion of oil spillages

11) as liquid media for chemical reactions (for example, micellar catalysis).

12) as phase transfer agents.

13) designer microemulsion compositions.

14) mechanical fluids such as milling or cutting fluids.

15) drug delivery agents.

The invention therefore further provides the use of a salt as defined above in the above applications. In one such embodiment, the invention provides a composition in the form of a foam, which comprises, as a foaming agent, a salt as defined above, especially a composition suitable for use in a gas and/or gas condensate reservoir.

The present invention is illustrated by the following Examples. Example 1 Preparation of l-octadecyl-3-methylimidazolium bis(2A4-1ximethyrpentyl)phosphonate rCismimirfisoCgbPCM

Bis(2,4,4-trimethylpentyl)phosphonic acid (Cyanex-272), (2.90 g, 10 mmol) and 1- octadecyl-3-methylimidazolium (3.54 g, 10 mmol) chloride were separately dissolved in 20 cm ³ of deionized water. The two solutions were mixed and sodium hydroxide (0.40 g, 10 mmol) was added. The resulting mixture was heated to a temperature of 80 °C and was then cooled to give two phases. The upper "hydrophobic" ionic liquid phase was separated and dried under vacuum to give a viscous oil: [C ₁₈ mim][(isoCs) ₂ PO ₂ ]; mp determined by differential scanning calorimetry (DSC) = -26°C, 9.0 Jg ^'1 . Example 2 Preparation of [Cismim] F(JSo-CsHn) ₂ PO?! / water / hexane microemulsion

Water (40 g), hexane (50 g) and [C ₁₈ mim][(iso-C ₈ ) ₂ PO ₂ ] (5 g) were mixed in a conical flask. Three phases spontaneously formed on mixing: a lower aqueous phase, a middle microemulsion phase and an upper hexane phase. The estimated volumes of these phases are as follows: Upper 20ml (hexane)

Middle 50ml (water in oil microemulsion)

Lower 35ml (water).

The compositions of the three phases were determined by NMR analysis (solvent = methanol-d ⁴ ). Composition (values in mol% rounded to the nearest 1%): Upper 100% Hexane

Middle 60% water, 39% hexane, 1% [C ₁₈ mim][(/-octyl) ₂ P0 ₂ ]

Bottom 99% water, 1 % hexane, 17 ppm [C ₁₈ mim] [(/-octyl) ₂ PO ₂ ]

Composition (weight %): Upper 100% Hexane

Middle 22% water, 69% hexane, 9% [Cigmim] [(/-octyl) ₂ PO ₂ ]

Lower 96% water, 4% hexane, 0.05 % [Cigmim] [(f-octyl) ₂ PO ₂ ] Example 3

Preparation of l-dodecyl-3-methylirnidazolium bis(2,4,4-trimethylpentyl)phosphonate rCijmimir(iso-Cj> Hn) ₂ PO ₂ I

An aqueous solution of potassium bis(2,4,4-trimethylpentyl)phosphinate (0.4 M) was derived from KOH and bis(2,4,4-trimethylpentyl)phosphonic acid (Cyanex 272™). 1- dodecyl-3-methylimidazolium chloride (3.54 g, 10 mmol) was separately dissolved in 20 cm ³ of deionised water and the resulting solution was mixed with 25 cm ³ of the aqueous solution of potassium bis(2,4,4-trimethylpentyl)phosphonate. The resulting mixture was stirred for 2 hours, then the ionic liquid product was extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give a viscous oil: [C ₁₂ mim][(iso-C ₈ Hn) ₂ PO ₂ ]; mp (glass transition) (DSC) = -47.3 ⁰ Q M Jg ^"1 . Example 4

Preparation of l-decyl-3-methylimidazolium bisC2,4,4-trimethylpentyl)ρhosphonate rCmmimirfiso-Cs Hn) ₂ PO ₂ ] Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272), (25. ml of 0.4 M solution in water, 10 mmol) and a solution of l-decyl-3- methylimidazolium (2.58 g, 10 mmol) chloride in 20 cm ³ of deionised water were mixed together. The resulting mixture was stirred for 2 hours, then the product was extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give a viscous oil: [C ₁₀ mim][(iso-C ₈ H ₁₇ ) ₂ PO ₂ ] mp (glass transition) (DSC) = -46.1 ⁰ C, 1.3 Jg ^'1 . Example 5

Preparation of a FCHJmJm][CiSo-CsHnI ₂ PO ₂ ] / water / hexane microemulsion Water (10 ml), hexane (10 ml) and [C ₁ OmIm][OsO-C ₈ Hn) ₂ PO ₂ ] (0.5 g) were mixed together in a 25 ml measuring cylinder. Three phases were observed to separate on standing and were visualised by the addition of rhodamine B dye {pa. 1 microgram). The phases were a lower aqueous phase, a middle microemulsion phase and an upper hexane phase.

Example 6

Preparation of l-heptyl-3-methylimidazolium bisf2A4-trimethylpentyl)phosphonate rc ₇ miml rfiso-CaHifbPOil

Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272), (16.36 ml of 0.4 M solution in water) and a solution of 1 -heptyl-3-methylimidazolium chloride (1.42 g, 6.56 mmol) in 20 cm ³ of deionised water were mixed together. The resulting mixture was stirred for 2 hours, then the product was extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give a viscous oil: [C ₇ mim][(iso-C ₈ ) ₂ PO ₂ ]. Example 7

Preparation of l-butyl-3-methylimidazolium bis(2A4-trimethylpentyl)phosphonate rC ₄ mimir(iso-CsHif) _z PO _z 1

Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272),

(11.88 ml of 0.4 M solution in water) and a solution of l-butyl-3-methylimidazolium (0.83 g, 4.75 mmol) chloride in 20 cm ³ of deionised water were mixed together. The resulting mixture was stirred for 2 hours, then the product was extracted with ethyl acetate. The ethyl acetate.was removed on a rotary evaporator and the product dried under vacuum to give a waxy solid: [C ₄ inim][(iso-C ₈ H ₁₇ ) ₂ PO ₂ ].

Example 8 Preparation of l-octadecyl-3-methylimidazolium dodecylsulfate

Sodium octadecylsulfate (1.20 g, 4.20 mmol) and l-octadecyl-3-methylimidazolium chloride (1.55 g, 4.20 mmol) were separately dissolved in 20 cm ³ of deionised water.

The two solutions were mixed together and stirred for 2 hours before being cooled to a temperature of 0 ⁰ C. A white precipitate was formed on cooling and was separated by filtration and dried under vacuum to give [C _1S mIm][C ₁₂ H ₂₅ SO ₄ ]; nip (DSC) = 81.3 °C

(solid to liquid crystal), 83 Jg ^"1 , and 148.0 ⁰ C, 2.8 Jg ^"1 .

Example 9

Preparation of l-dodecyl-3-methylimidazolium dodecylsulfate [Cnmim] [Ci ₂ H ₂₁ SO ₄ ]

Sodium dodecylsulfate (1.05 g, 3.65 mmol) and l-dodecyl-3-methylimidazolium (1.05 g, 3.65 mmol) chloride were separately dissolved in 20 cm ³ of deionised water and the solutions were then mixed together. The resulting mixture was stirred for 2 hours

before being extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give [C ₁₂ mim] [C ₁₂ H ₂₅ SO ₄ ]; mp (DSC) = 239 °C (decomposes slowly), 15.7 Jg ^'1 . Example 10 Preparation of l-heptyl-3-methylimidazolium dodecylsulfate [CTmJmIrCi ₂ H ₂ SSO ₄ ]

Sodium dodecylsulfate (1.85 g, 6.40 mmol) and l-heptyl-3-methylimidazolium (1.39 g, 6.40 mmol) chloride were separately dissolved in 20 cm ³ of deionised water and the solutions were then mixed together. The resulting mixture was stirred for 2 hours before being extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give [C ₇ mim] [C ₁₂ H ₂₅ SO ₄ ] as a waxy solid.

Example 11 Preparation of l-butyl-3-methylimidazolium dodecylsulfate

Sodium dodecylsulfate (1.70 g, 5.90 mmol) and l-butyl-3-methylimidazolium chloride (1.03 g, 5.90 mmol) were separately dissolved in 20 cm ³ of deionised water and the solutions were then mixed together. The resulting mixture was stirred for 2 hours before being extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give [C ₄ mim] [C ₁₂ H ₂₅ SO ₄ ] as a waxy solid.

Example 12

Preparation of 1-octadecylpyridinium bis(2A4-trimethyrpentyr)phosphonate rCisPvirfiso-CR HIf) ₂ PO ₂ ] Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272), (25 ml of 0.4 M solution in water, 10 mmol) and a solution of 1-octadecylpyridinium bromide (2.58 g, 10 mmol) in 20 cm ³ of deionised water were mixed together. The resulting mixture was stirred for 2 hours, then the product was extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give a paste: [Cispy] [(1So-CsHn) ₂ PO ₂ ]. Example 13 Preparation of ionic liquid - water — hexane microemulsions

Water (10 cm ), hexane (10 cm ) and ionic liquid (0.5 g) were mixed together in a 25 ml measuring cylinder. Three phases were observed and visualised by the addition of rhodamine B dye (ca. 1 microgram), with a lower aqueous phase, a middle microemulsion phase and an upper hexane phase. It was found that the volume of the middle microemulsion phase was dependent upon the structure of the ionic liquid surfactant.

Volume of middle microemulsion phase (rounded to the nearest 0.5 ml) [C ₁₈ mim] [(Z-OCt) ₂ PO ₂ ] (0.5 g) 5.5 ml

[Ci8py][0-oct) ₂ PO ₂ ] (0.5 g) 3.5 ml

[Cionώn] Ki-OCt) ₂ PO ₂ ] (0.5 g) 3.5 ml

Example 14 1 -ethyl-3-methylimidazolium bisf2 A4-trimethylpentyl)phosphonate | ^" C ₂ mim] [(iso-Cs Hn) ₂ PO ₂ I

Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272), (25.0 g of 0.4 M solution in water) and a solution of l-ethyl-3-methylimidazolium bromide (2.38 g, 12.5 mmol) in 20 cm ³ of deionised water were mixed together to form a hazy solution. Toluene (20 ml) was added and the solution was placed on a rotary evaporator to remove the toluene / water. This was repeated twice. More toluene was added (20 ml) to give 3 phases and the middle (microemulsion) and upper phases were separated and washed with distilled water (20 ml). The toluene and water were removed from the combined upper and middle phases and the resulting product was dried under vacuum to give a viscous oil: [C ₂ mim][(iso-C ₈ ) ₂ PO ₂ ]. Thus, [C ₂ mim][(iso- C ₈ H ₁₇ ) ₂ PO ₂ ] forms a microemulsion when mixed with toluene/water but is soluble in water in the presence of hexane.