WO2007110637A1

WO2007110637A1 - Method for extracting target alkaloid using an ionic liquid as extracting solvent

Info

Publication number: WO2007110637A1
Application number: PCT/GB2007/001121
Authority: WO
Inventors: Adam Walker
Original assignee: Bioniqs Limited
Priority date: 2006-03-28
Filing date: 2007-03-28
Publication date: 2007-10-04
Also published as: EP2001877A1; GB0606147D0

Abstract

Method for extracting a target alkaloid from a mixture of species, typically from plant matter, using an ionic liquid as an extracting solvent. The ionic liquid may in particular be an alkanolyl-, alkoxyalkyl- or aminoalkyl-substituted ammonium salt.

Description

METHOD FOR EXTRACTING TARGET ALKALOID USING AN IONIC LIQUID AS EXTRACTING SOLVENT

Field of the invention

This invention relates to a method for extracting a target substance from a mixture.

Background to the invention

It is often desired to extract target substances from their natural environment — common examples include essential oils such as those of use as perfumes or flavourings, naturally occurring alkaloids and other materials of pharmaceutical and/or nutritional value. Such substances often need to be extracted from plant material.

Alkaloids can be defined as naturally occurring organic compounds containing one or more basic nitrogen atoms. Over 10,000 different alkaloids have been isolated, the vast majority from plant sources. Most are pharmacologically active and many are of enormous medical and commercial importance. Well-known examples include morphine, codeine, thebaine, caffeine, cocaine, codeine, papaverine, quinine, vincamine, colchicine, reserpine, nicotine, strychnine and atropine.

Extraction techniques for alkaloids utilise their basic, alkali-like chemical behaviour. Whilst often poorly soluble in water in the free state, unlike most other natural products, alkaloids react with acids to form crystalline, water-soluble salts. Conventional extraction techniques therefore tend to use an initial extraction of the dried plant material using a water-immiscible organic solvent such as chloroform, often at high temperature; this extracts a large proportion of the organic components including free alkaloids, terpenes, oils, resins, etc. The alkaloids are then recovered by washing the chloroform extract with aqueous acid - this converts the alkaloids to salts and causes them to partition into the water phase, leaving non-basic natural products behind. The water and acid are then removed to recover the alkaloid salts; these may be purified using conventional chromatography and recrystallisation. Such techniques tend to be inefficient, as a proportion of the alkaloid is lost during each of the multiple extraction steps. In addition, the entire alkaloid component of the plant is extracted rather than just a given target molecule. Such techniques moreover tend to use hazardous, environmentally unfriendly solvents such as chloroform and hydrochloric acid.

A suitable solvent for use in an extraction process will depend on the nature of the target substance to be extracted and the conditions under which the extraction takes place. It must be capable of dissolving the target substance efficiently whilst not acting as a solvent for other, undesired species present (plant material from which the target is to be extracted, for example, and/or impurities). Ideally the solvent is also easy to separate from the target substance following extraction, and preferably also of low toxicity. Since often large volumes of solvent are needed to achieve reasonable yields in extraction processes, preferred solvents will also be relatively inexpensive and readily available, and ideally also recyclable or at least biodegradable so as to minimise the environmental impact of the processes.

In the past ionic liquids have been used in aqueous solvent systems for the extraction of alkaloids. For example, Li et al in J Chromatography B, 826 (2005): 58-62 and Chinese Chemical Letters, 16 (8): 1074-1076, 2005 described the extraction of the opium alkaloids codeine, papaverine and morphine from biological samples, using ionic liquids in two phase solvent systems. The ionic liquid used was BMIm (1-butyl- 3-methylimidazolium) chloride, and an additional salt such as K₂HPO₄ was used to ensure the correct extraction environment, in particular the correct pH.

It has now been found that ionic liquids, in particular certain classes of ionic liquids, can be of use in extracting alkaloids, for example from plant materials.

Statements of the invention

According to a first aspect of the present invention there is provided a method for extracting a target alkaloid from a mixture of species, which method comprises using an ionic liquid as an extracting solvent. A second aspect of the invention provides the use of an ionic liquid as a solvent to extract a target alkaloid from a mixture of species.

Ionic liquids are compounds which are composed primarily of ions yet are in liquid form, typically having a melting point below ambient temperature. They can be formed by combining suitable acid and base ions, either or both of which are relatively large, charge-delocalised, desymmetrised ions. These types of ion contribute to a reduction in the degree of order of the resulting salt, thus lowering its melting point.

An ionic liquid may comprise anions and cations, or alternatively (though less commonly) it may comprise zwitterions carrying both a positive and a negative charge on the same molecule.

Ionic liquids can possess a number of remarkable properties, including negligible vapour pressure, high solubilising power and a broad liquid temperature range. Such properties can render them useful alternatives to the solvents conventionally used in alkaloid extractions.

In the method of the invention, the target alkaloid may be any alkaloid, typically one of plant or fungal origin. It may be a synthetic or semi-synthetic alkaloid, but will more typically be naturally occurring. It may be selected from heterocyclic alkaloids (including pyrrolidine, indole, beta-carboline, gamma-carboline, evodiamine, piperidine, pyridine, tropane, xanthine, histamine, imidazole, guanidine, isoquinoline, morphine, protopine, quinoline, quinine, quinazoline, pyrazine, pyrrolizidine and pterine alkaloids); alkaloids with exocyclic N-atoms (including benzylamine, colchicines, muscarine and phenethylamine alkaloids); putrescine, spermidine and spermine alkaloids; peptide alkaloids; terpene and steroid alkaloids (including taxol) and dimeric bis-alkaloids. Other suitable target alkaloids are those listed above. In an embodiment of the invention, the target alkaloid is selected from caffeine, morphine and cocaine.

The mixture of species from which the target alkaloid is extracted may include any other species, at least one of which is to be separated from the target. The mixture may for example include the alkaloid and other undesired species such as impurities, unreacted starting materials or unwanted by-products from a previous process in which the target was involved or by which the target was formed. It may in particular include material from which the target alkaloid is to be extracted, for example plant or fungal material. Thus typically the target alkaloid will be extracted from its natural environment, in particular from plant material.

The mixture may contain alkaloids other than the target alkaloid, and/or other - typically organic - components of a material from which the target alkaloid is to be extracted. Thus for example, the invention may be used to extract a single target alkaloid from a mixture which includes one or more other, non-target, alkaloids, and/or to extract one or more target alkaloids from a mixture which includes one or more non- alkaloid species.

Any suitable technique may be used to extract the target alkaloid into the ionic liquid. At its simplest, the extraction will involve contacting the mixture of species with the ionic liquid for a period of time, and under conditions, suitable to allow the target alkaloid to dissolve in the ionic liquid. This contact may be under an elevated temperature and/or pressure, and/or may involve agitation of the mixture in the ionic liquid, and/or may involve pre-preparation of the mixture to facilitate extraction (for instance, comminution of plant material).

Following extraction of the target alkaloid into the ionic liquid, the mixture may then be filtered to remove undissolved species.

The target alkaloid may be recovered from the ionic liquid in any suitable manner. For example, the ionic liquid may be chemically modified, preferably in situ, to alter its ability to dissolve the target and hence cause target precipitation - suitable chemical modifications include changing the cation and/or the anion of the ionic liquid, for example by means of an ion exchange column; other suitable modifications are described in WO-2006/038013, in particular at pages 8-11. The pKa of the ionic liquid may be altered to render the target insoluble. Alternatively a cosolvent may be added to the system to cause "salting out" of the target. According to a third aspect of the present invention, there is provided a composition comprising a target alkaloid and an ionic liquid, this composition typically being the product of an extraction process according to the first or second aspect of the invention.

An "ionic liquid" is a compound composed substantially, although not necessarily exclusively, of ions, including a stable stoichiometric hydrate or other solvate of such an ionic material. Typically it will comprise both anions and cations. It may instead or in addition comprise zwitterions which carry both a positive and a negative charge.

An ionic liquid for use in the invention may contain cations which are all the same or which are different. It may contain anions which are all the same or which are different.

The ionic liquid used in the present invention should be in liquid form at the relevant operating temperature, by which is meant the temperature at which the target alkaloid is extracted into the ionic liquid. Preferably the ionic liquid is capable of existing in liquid form below 60 ⁰C, more preferably below 50 ⁰C, yet more preferably below 40 ⁰C, still more preferably below 30 ⁰C and most preferably at room temperature, which for the present purposes may be defined as from 18 to 25 ⁰C, typically about 20 ⁰C. This allows the target alkaloid to be extracted, if appropriate, at relatively low temperatures, thus reducing the risk of its degradation and also reducing the cost and complexity of, and hazards associated with, the extraction process.

An ionic liquid may in cases have a freezing point below 20 ⁰C, or even below 15 ⁰C or 10 ⁰C or 5 ⁰C. Preferably the freezing point of the ionic liquid is at least 5 ⁰C, more preferably at least 10⁰C and most preferably at least 15 °C below the temperature at which it is used to extract the target alkaloid.

The boiling point of the ionic liquid is preferably at least 200 °C. It may be above 500 °C.

According to the present invention, a target alkaloid can be extracted into a pure, single-phase ionic liquid, without the need for additional cosolvents and in particular in the absence of water. An ionic liquid used in the invention will generally contain 5 % or 1 % or less of water, by mass, preferably 1000 ppm or less and more preferably 100 ppm or less. (The above figures apply to the ionic liquid at the start of the extraction process; the liquid may subsequently absorb a certain amount of water as it extracts the target alkaloid, in particular if the extraction is carried out on fresh - as opposed to pre-dried — plant material.) It will suitably contain 1 % v/v or less, preferably 0.5 or 0.1 % v/v or less, of non-ionic liquid cosol vents such as organic solvents (for example alcohols, ethers, ketones and the like) - again these figures apply to the ionic liquid at the start of the extraction process.

The present invention can also typically be carried out in the absence of additional salts - in particular pH adjusting agents and buffers.

Preferably an ionic liquid used in the invention has a viscosity of less than 500 centipoise, or less than 400 or 300 or 200 or even 100 centipoise, at 25 ⁰C.

According to the present invention, the ionic liquid should be chosen to be a solvent for the target alkaloid under the relevant extraction conditions. Ideally it should be a solvent only for the target alkaloid, with undesired species in the mixture being substantially insoluble in the ionic liquid under the relevant conditions. It is possible to tailor ionic liquids, by appropriate choice of and/or manipulation of their cationic and anionic components, so as to be highly selective in the solutes which they are able to dissolve. This in turn can allow a high degree of extraction selectivity, and thence of overall yield and efficiency, when carrying out the present invention.

Suitable ionic liquids for use in the invention are for instance disclosed in WO- 2004/063383 and WO-2005/097731.

Preferably the ionic liquid comprises a nitrogen-based cation, more preferably based on a nucleus selected from ammonium cations (suitably primary, secondary or tertiary ammonium cations), pyrazolium cations, imidazolium cations, triazolium cations, pyridinium cations, pyridazinium cations, pyrimidinium cations, pyrazinium cations, pyrrolidinium cations and triazinium cations. Alternatively the ionic liquid may comprise a phosphorous-based cation such as a phosphonium ion. Such cations may be substituted at any carbon, nitrogen or phosphorous atom by any (cyclo)alkyl, (cyclo)alkenyl, (cyclo)alkynyl, alkoxy, alkenedioxy, aryl, arylalkyl, aryloxy, amino, aminoalkyl, thio, thioalkyl, hydroxyl, hydroxyalkyl, oxoalkyl, carboxyl, carboxyalkyl, haloalkyl or halogen including all salts, ethers, esters, pentavalent nitrogen or phosphorous derivatives or stereoisomers thereof. Suitable such substituents include those having one or more hydroxyl or alkoxyl groups, for example alkanolyl or alkoxyalkyl substituents.

Particularly preferred ionic liquids are those based on an optionally substituted nucleus selected from ammonium, imidazolium, pyridinium and pyrrolidinium cations. Ideally such ionic liquids contain cations which include a protonated nitrogen.

In cases however it may be preferred for the ionic liquid not to be an imidazolium salt.

The ionic liquid may in particular comprise a primary, secondary or tertiary ammonium cation, which is preferably N-substituted with at least one alkanol or alkoxyalkyl (preferably methoxyalkyl) group such as an ethanol, propanol, alkoxyethyl or alkoxypropyl, preferably an ethanol or alkoxyethyl, group. Such cations may additionally be N-substituted by one or two alkyl groups such as C₁ to C₆ alkyl groups, preferably C₁ to C₄ alkyl groups, in particular methyl, ethyl or propyl, preferably methyl or ethyl.

Thus, preferred ionic liquids for use in the invention may contain cations selected from alkanolammonium, alkyl alkanolammonium, dialkyl alkanolammonium, dialkanolammonium, alkyl dialkanolammonium, trialkanolammonium, alkoxyalkylammonium, alkyl alkoxyalkylammonium, dialkyl alkoxyalkylammonium, di(alkoxyalkyl) ammonium and alkyl di(alkoxyalkyl) ammonium cations.

Other ionic liquids for use in the invention contain cations selected from alkyl ammonium cations, dialkyl ammonium cations and trialkyl ammonium cations, in particular trialkyl ammonium cations.

Other ionic liquids for use in the invention contain ammonium cations substituted with one or more aminoalkyl groups, for example C₁ to C₆ or C₁ to C₄ aminoalkyl groups. The aminoalkyl group is preferably an alkyl group substituted with a primary -NH₂ group, suitably a terminal -NH₂ group.

In this context, an alkyl or alkoxyl group is preferably a C₁ to C₆ or C₁ to C₄, more preferably a C₁ to C₃ and most preferably a C₁ or C₂ alkyl or alkoxyl group. An alkanolyl group is preferably a C₂ to C₄, more preferably a C₂ or C₃ alkanolyl group.

Thus, a preferred ionic liquid for use in the present invention is one containing aliphatic ammonium cations, for instance cations of the general formula (I):

N⁺R¹R²R³R⁴ (I),

or more preferably of the formula (II):

N⁺HR¹R²R³ (II),

wherein R¹, R², R³ and R⁴ are each independently selected from hydrogen and hydrocarbyl, with the proviso that in each case at least one of R¹, R², R³ and R⁴, and preferably at least two, are not hydrogen.

The cation (I) or (II) may be a primary ammonium ion, in which only one of R , R , R and R⁴ is hydrocarbyl rather than hydrogen. It may be a secondary ammonium ion, in which only two of R¹, R², R³ and R⁴ are hydrocarbyl. It may be a tertiary ammonium ion, in which three of R¹, R², R³ and R⁴ are hydrocarbyl. It may be a quaternary ammonium ion, in which in formula (I), all four of R¹ to R⁴ are hydrocarbyl. Preferably, it is a secondary or a tertiary ammonium ion.

A hydrocarbyl group may be substituted with one or more substituents selected from nitrogen-containing functional groups (including nitrile, nitro or amino or another basic nitrogen-containing functional group), thiol, alkylthio, sulphonyl, thiocyanate, isothiocyanate, azido, hydrazino, halogen, alkyl, alkyl interrupted by one or more ether or thioether linkages, alkoxyl, alkenyl, hydroxyl, carbonyl (including aldehyde or ketone), carboxyl, boronate, silyl and substituted amino (eg, mono- or di-alkylamino or alkyamido). Preferably a hydrocarbyl group is a C₁ to C₈ or C₁ to C₆ hydrocarbyl group, more preferably a C₁ to C₄ hydrocarbyl group. It may for example be selected from alkyl, alkoxyalkyl, alkanolyl and other hydroxyl-substituted alkyl groups, and amino-substituted alkyl.

Preferred substituents for use in this context are selected from the group consisting of alkenyl, hydroxyl, alkoxyl, amino, thio, carbonyl and carboxyl groups. More preferably, substituents are selected from hydroxyl, alkoxyl and amino groups, most preferably from hydroxyl and alkoxyl groups.

In some cases, however, it may be preferred for a hydrocarbyl group to be unsubstituted, for example unsubstituted alkyl.

In one embodiment of the invention,

R¹ is a group -R⁵-O-R⁶;

R² and R³ (and in the case of cation (I) R⁴) are each independently either hydrogen or hydrocarbyl;

R⁵ is a divalent hydrocarbyl radical; and

R⁶ is hydrogen or hydrocarbyl.

Preferably R⁴ is -(CH₂)_n-, where n is an integer from 2 to 8, preferably from 2 to 6, more preferably from 2 to 4, such as 2 or 3.

In some cases it may be preferred for R⁶ to be an unsubstituted alkyl group such as CH₃ or (CBb)_nCH₃, with n being an integer for example from 1 to 4, preferably either 1 or 2 and most preferably 1. In other cases it may be preferred for R⁶ to be (CH₂)_nOH, with n being an integer suitably from 2 to 4, preferably either 2 or 3 and most preferably 2.

In other embodiments of the invention, either or both of R² and R³ may also be a group -R⁵-O-R⁶. hi particular, in a cation of formula (II), R² may be a group -R⁵-O-R⁶ (which may be the same as or different to, suitably the same as, R¹) and R³ may be hydrogen or alkyl, in particular hydrogen. Thus, a cation offormula (II) may be a di(alkoxyalkyl) ammonium ion, such as a di(methoxyalkyl) or a di(alkoxyethyl) ammonium ion.

In another embodiment, the ionic liquid contains a cation of the formula (III):

N⁺HR⁷R⁸R⁹ (III)

wherein R⁷ is an alkanolyl group;

R⁸ is a hydrocarbyl group; and

R⁹ is either hydrogen or hydrocarbyl.

R⁷ may contain more than one -OH group; in other words, it may comprise a diol or polyol. It may be straight or branched chain. It preferably contains from 1 to 12 carbon atoms, more preferably from 1 to 10, yet more preferably from 1 to 8, most preferably from 1 to 6 or from 1 to 4. Suitably R⁷ may be methanolyl, ethanolyl or propanolyl. Most suitably an alkanoyl group may be ethanolyl or propanolyl, in particular 3-hydroxypropyl. Preferably it contains a terminal -OH group.

R⁸ is preferably an alkyl or cycloalkyl group, suitably as defined above for R².

R⁸ may be an alkanolyl group, in particular as defined above for R⁷. In particular R⁷ and R⁸ may both be alkanolyl; R⁷ and R⁸ may then be different alkanolyl groups or, more preferably, the same. In one embodiment of the invention, R and R are both alkanolyl (preferably the same) and R⁹ is alkyl or cycloalkyl, suitably as defined above for R². hi another embodiment, R⁷ and R⁸ are both alkanolyl (preferably the same) and R⁹ is hydrogen.

In an embodiment of the invention, R⁹ is hydrogen. Thus, the cation (III) may for instance be an alkyl alkanolammonium ion or a dialkanolammonium ion. In another embodiment, both R⁸ and R⁹ are alkyl groups (suitably the same).

Particularly preferred ionic liquids for use in the invention include, as the cation (III), either a dialkyl alkanolammonium ion, a di(alkoxyalkyl) ammonium ion or an N-alkyl- bis(alkoxyalkyl) ammonium ion. The dialkyl alkanolammonium ion may be in particular a dimethyl alkanolammonium ion and/or a dialkyl ethanolammonium ion, more particularly a dimethyl ethanolammonium ion. The di(alkoxyalkyl) ammonium ion may be in particular a di(methoxyalkyl) and/or a di(alkoxyethyl) ammonium ion, more particularly a bis(2-methoxyethyl) ammonium ion. The N-alkyl-bis(alkoxyalkyl) ammonium ion may be an N-methyl-bis(alkoxyalkyl) ammonium ion or an N-alkyl- bis(methoxyalkyl) ammonium ion or an N-alkyl-bis(alkoxyethyl) ammonium ion, for example an N-methyl-bis(2-methoxyethyl) ammonium ion.

Thus in some cases it may be preferred for R⁵ to be an unsubstituted alkyl group such as CH₃ or (CH₂)_nCH₃, with n being an integer for example from 1 to 4, preferably either 1 or 2 and most preferably 1. In other cases it may be preferred for R⁵ to be (CH₂)_I1OH, with n being an integer suitably from 2 to 4, preferably either 2 or 3 and most preferably 2. This latter case, where R¹ is a (hydroxyalkoxy)alkyl group, may be particularly preferred when R² and R³ are both alkyl groups, in particular selected from methyl and ethyl groups, most particularly methyl groups; thus, the cation (I) may be a N,N-dialkyl-N-[(hydroxyalkoxy)alkyl] ammonium ion such as a N,N-dimethyl-N- [(hydroxyalkoxy)alkyl] ammonium ion, in particular a N,N-dimethyl-N-[(2- hydroxyethoxy)ethyl] ammonium ion.

An alkanolyl-substituted ionic liquid, for example a dialkyl alkanolammonium salt, may be of use for extracting polar alkaloids such as morphine. An alkoxyalkyl- sύbstituted ionic liquid, for example a di(alkoxyalkyl)ammonium salt or an N-alkyl- bis(alkoxyalkyl)ammonium salt, may be of use for extracting more lipophilic alkaloids such as caffeine

In general in the above descriptions, an alkyl group may be a C₁ to C₆ alkyl group, in particular C₁ to C₄ alkyl or Ci to C₃ alkyl, for example methyl or ethyl. An alkoxy group may be a C₁ to C₆ alkoxy group, in particular C₁ to C₄ or C₁ to C₃ alkoxy, for example methoxy or ethoxy. An alkanolyl group may be a C₁ to C₆ alkanolyl group, in particular C₁ to C₄ or C₂ to C₄ alkanolyl, for example ethanolyl or 2-hydroxypropyl.

Ammonium-based ionic liquids are of particular interest for the extraction of alkaloids because they are formed by the reaction of an amine with an acid in a similar way to that involved in the extraction of alkaloids, as discussed above. This means that, when an alkaloid is dissolved in a primary, secondary or tertiary ammonium-based ionic liquid, it can become an integral part of the ionic structure of the liquid. The extent of this solvent interaction, and hence the degree of solubility of the alkaloid in the ionic liquid, will be determined by the differences in pKa between the ionic liquid cation and the protonated alkaloid; in other words, the ionic liquid will convert the alkaloid to a salt whilst extracting it, which can then facilitate the selective recovery of the alkaloid from the ionic liquid. This can have huge potential advantages in terms of extraction selectivity and overall efficiency, with the correct matching of ionic liquid pKa to alkaloid pKa offering the possibility to extract one or more target alkaloids preferentially, even in the presence of many similar but non-target compounds.

The preferred ionic liquids referred to above are also often relatively inexpensive, biodegradable and of low toxicity, again beneficial in the context of the present invention.

In the present context, "hydrocarbyl" may be defined as any group containing carbon and hydrogen, which may also contain one or more heteroatoms such as oxygen, nitrogen, sulphur, phosphorous or halogen. The term embraces saturated, partially saturated and unsaturated groups, whether aromatic or aliphatic, whether straight chain, branched chain, cyclic or any combination thereof. Hydrocarbyl thus includes, but is not limited to, optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, aralkyl, alkaryl, heterocyclyl, heteroaryl, alkoxyl and moieties containing a combination of two or more such groups.

In the present context, a hydrocarbyl group preferably does not contain heteroatoms. It is preferably aliphatic. It preferably contains from 1 to 12 or from 1 to 8 or from 1 to 6 carbon atoms. Most preferably it is an alkyl group.

As used herein, "alkyl" includes both straight and branched chain alkyl radicals, of any chain length but typically of from 1 to 12 carbon atoms, more suitably from 1 to 10 or from 1 to 8 carbon atoms, preferably from 1 to 6 carbon atoms. Suitable examples of alkyl groups include methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl and tert-butyl. The term "cycloalkyl" encompasses aliphatic saturated hydrocarbyl ring-containing moieties such as for example cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl.

The term "alkenyl" includes both straight and branched chain alkenyl radicals, which contain one or more carbon-carbon double bonds. Again they may be of any chain length, typically from 2 to 12 carbon atoms, more suitably from 2 to 10 or from 2 to 8 carbon atoms, yet more preferably from 2 to 6 carbon atoms. Examples include ethylene, n-propyl-1-ene, n-propyl-2-ene and isopropylene.

"Cycloalkenyl" encompasses ring-containing groups where the ring structure incorporates one or more carbon-carbon double bonds.

The term "alkynyl" includes both straight and branched chain alkynyl radicals, which contain one or more carbon-carbon triple bonds. They may be of any chain length, typically from 2 to 12 carbon atoms, more suitably from 2 to 10 or from 2 to 8 carbon atoms, yet more preferably from 2 to 6 carbon atoms. "Cycloalkynyl" encompasses ring-containing groups where the ring structure incorporates one or more carbon- carbon triple bonds.

The term "aryl" includes aromatic (and thus at least partially unsaturated) hydrocarbyl groups, which will typically incorporate one or more cyclic structures. Such groups may contain for example from 3 to 12 carbon atoms, preferably from 3 to 10 or from 4 to 8 carbon atoms. They may be fused to one or more saturated or unsaturated rings. A typical example is phenyl. It is to be noted that the term "hydrocarbyl" also embraces radicals which combine both alkyl and aryl moieties, in particular aralkyl and alkaryl groups such as for instance benzyl.

The term "heterocyclyl" includes a ring system containing one or more heteroatoms selected for example from N, O and S. It may be saturated, unsaturated or partially unsaturated. The ring containing the heteroatom may be fused to one or more other rings, which in turn may be saturated, unsaturated or partially unsaturated and may themselves contain heteroatom(s). Typically a heterocyclyl radical will be a 3 to 10- membered ring system, preferably a 5 to 10-membered system, more preferably a 5- or 6-membered system. It may be or incorporate aromatic moieties. The term "alkoxy" includes both straight chain and branched alkyl radicals, for example of 1 to 12 carbon atoms, preferably of 1 to 8 or 1 to 6 carbon atoms, which contain one or more oxygen atoms or hydroxyl, typically in the form of a hydrocarbyl group linked to an oxygen atom. Examples include methoxy and ethoxy groups, as well as alcohols (which may be mono-, di- or polyols) such as in particular (CH₂)_nOH where n is an integer from for example 1 to 8, preferably from 1 to 6 or from 1 to 4.

The term "alkanolyl" includes both straight and branched chain radicals substituted with one or more, suitably one, hydroxyl group. Again an alkanolyl group may contain for example from 1 to 12 or from 1 to 10 carbon atoms, suitably from 1 to 8, more suitably from 1 to 6. The hydroxyl group is suitably terminal.

The term "halogen" means either F, Cl, Br or I, typically either F, Cl or Br, more typically either F or Cl.

An ionic liquid for use in the present invention preferably comprises an anion, for example a counterion X^m~ where m is an integer such as in particular 1, 2 or 3, preferably 1 or 2, most typically 1. This may be any suitable anion; the only theoretical constraint upon the choice of anion is its ionic weight in order to keep the freezing point of the ionic liquid below the desired temperature.

Examples of suitable anions include halides, halogenated inorganic or organic anions, nitrates, sulphates, phosphates, carbonates, sulphonates and carboxylates. The sulphonates and carboxylates may be alkylsulphonates and alkylcarboxylates, in which the alkyl group is a moiety, for example having 1 to 20 carbon atoms, selected from alkyl and alkyl substituted at any position with alkenyl, alkoxy, alkeneoxy, aryl, arylalkyl, aryloxy, amino, aminoalkyl, thio, thioalkyl, hydroxyl, hydroxyalkyl, carbonyl, oxoalkyl, carboxyl, carboxyalkyl or halogen, including all salts, ethers, esters, pentavalent nitrogen or phosphorous derivatives or stereoisomers thereof.

For example, the anion may be selected from bis(trifluoromethylsulphonyl)imide, carbonate, hydrogen carbonate, sulphate, hydrogen sulphate, sulphite, hydrogen sulphite, silicate, phosphate, hydrogen phosphate, dihydrogen phosphate, hydrogen phosphite, dihydrogen phosphite, metaphosphate, methanesulphonate, ethanesulphonate, benzenesulphonate, trifluoromethanesulphonate, ethylenediaminetetraacetate, fluoride, chloride, bromide, iodide, hexafluorophosphate, tetrafluoroborate, trifluoroacetate, pentafluoropropanoate, heptafluorobutanoate, oxalate, formate, acetate, propanoate, butanoate, pentanoate, hexanoate, heptanoate, octanoate, nonanoate, decanoate, benzoate, benezenedicarboxylate, benzenetricarboxylate, benzenetetracarboxylate, chlorobenzoate, fluorobenzoate, pentachlorobenzoate, pentafluorobenzoate salicylate, glycolate lactate, pantothenate, tartrate, hydrogen tartrate, mandelate, acrylate, methacrylate, crotonate, malate, pyruvate, oxaloacetate, succinate, citrate, fumarate, phenylacetate, gluconate, glyoxylate, mercaptoacetate, oxamate, sulphamate, methylphosphonate, ethylphosphonate, phenylphosphonate, phenylphosphinate, thiocyanate, isothiocyanate, cyanate, isocyanate, tbiosulphate, nitrate, nitrite, thiophosphate or dicyanamide.

In an embodiment of the invention, the anion is a halide - in particular a chloride - or a carboxylate - in particular a C₁ to C₁₀ or C₁ to C₈ carboxylate, such as for example an acetate, propionate, hexanoate, octanoate or lactate ion. In another embodiment of the invention, the anion is a carboxylate.

In an ionic liquid used according to the invention, the cation and anion should together be chosen to ensure that the material is liquid at the requisite temperature. Freezing point can be affected by factors such as the size of the ions, their degree of delocalisation of charge and their degree of symmetry, as described above and in the prior art literature relating to ionic liquids. The use of larger, and/or more charge- delocalised ions can for instance help to reduce the ionic liquid's freezing point.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Preferred features of each aspect of the invention may be as described in connection with any of the other aspects.

Other features of the present invention will become apparent from the following non- limiting examples. Generally speaking the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings). Thus features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Moreover unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

Example 1 - extraction of a target alkaloid

A target alkaloid may be extracted from plant material (for example leaves, flowers, seeds, seed heads or bark) by placing the plant material in a vessel with a suitable quantity of the chosen ionic liquid. The ionic liquid is ideally chosen to be capable of selectively dissolving the target alkaloid. The mixture of ionic liquid and plant material is stirred for an appropriate period of time and then filtered to remove the plant material.

The alkaloid may be recovered from the ionic liquid for instance by in situ chemical modification of the ionic liquid to alter its ability to dissolve the alkaloid, by addition of a benign cosolvent to precipitate the alkaloid as an insoluble salt or in other ways such as are described above. Alkaloids which might be extracted in this manner include caffeine (for example from tea leaves or coffee beans), morphine (from poppy straw), quinine (from Cinchona bark) and vincamine (from Madagascar periwinkle).

Morphine for example has a solubility in the ionic liquid BMLm PF₆ (l-butyl-3- methylimidazolium hexafluorophosphate) of 78 g/L, compared to a solubility in chloroform of only 3.3 g/L and in water of only 0.15 g/L. The greater ability of the ionic liquid to dissolve the alkaloid makes it potentially a much more useful extraction solvent than those used in conventional processes, and the possibility of tailoring the anions and/or cations of an ionic liquid to fine-tune its solvation powers can increase the selectivity, and hence the efficiency, of the extraction process.

Example 2 - extraction of caffeine

The extraction of caffeine from both green tea leaves and ground coffee beans was performed using the ionic liquid bis(2-methoxyethyl)ammonium chloride. In both cases, 3.O g of plant material was macerated with 20 ml of the ionic liquid in a Falcon tube for a period of 4 hours, after which the solvent was isolated from the biomass by Buchner filtration followed by microfiltration through 0.45 μm syringe filters. The extracts were diluted into a mobile phase of 20:79.9:0.1 methanol:water:orthophosphoric acid and analysed by HPLC on a Gemini 5 μm Cl 8 HOA column, running isocratically at a flow rate of 1 ml/min, according to the method of Wang et al. (Food Chemistry, 2000 (68), 115-121).

Analysis determined the following concentrations of caffeine in the extracts, equivalent to the indicated weight % of the plant material:

Table 1

These data demonstrate the successful extraction of caffeine into the ionic liquid bis(2- methoxyethyl)ammonium chloride. Other similar ionic liquids, for example ethanolammonium salts such as ethanolammonium formate or N-alkyl- bis(alkoxyalkyl)ammonium salts such as N-methyl-bis(2-methoxyethyl)ammonium chloride, could be used in the same manner.

Example 3 - extraction of opiates from dried poppy heads

This extraction was performed using the ionic liquid dimethylethanolammonium acetate. The dried poppy heads (1.5 g) were broken open and then placed in 10 ml of ionic liquid on a tilt table for 72 hours. A 1 ml sample of the solution was collected and centrifuged to remove debris. 50 μl of the resultant liquid was added to 200 μl of 10 niM KH₂PO₄ pH 3.5 buffer and filtered through a 0.22 μm syringe filter. 50 μl of this diluted sample was then analysed by HPLC on a Techsphere™ ODS 80 A 5 μm column, running isocratically (80 % 10 mM KH₂PO₄ pH 3.5, 20 % MeCN) at a flow rate of 1 ml/min, according to the method of Long etal. (Appl. Environ. Microbiol, 1995 (61), 3645-3649).

The analysis confirmed the presence of 53 % morphine (retention time 5.2 minutes), 23 % codeine (retention time 6.8 minutes) and 3 % thebaine (retention time 30.6 minutes) in the extracts. This confirms the successful extraction of the three alkaloids into the ionic liquid.

Claims

1. A method for extracting a target alkaloid from a mixture of species, which method comprises using an ionic liquid as an extracting solvent.

2. A method according to claim 1, wherein the target alkaloid is of plant or fungal origin.

3. A method according to claim 1 or claim 2, wherein the target alkaloid is selected from morphine, codeine, thebaine, caffeine, cocaine, quinine, vincamine, colchicine, reserpine, nicotine, strychnine, taxol, galanthamine, vincristine, vinblastine, ibogaine, mescaline, stachydrine, pleiocarpine, tuboxenine, vomicine, corynantheidine, alstophylline, cytosine, sparteine, cinchonamine, physostigmine, lysergic acid, theobromine, theophylline, cathinone, piperine, coniine, capsaicine, anabasine, hyoscine, salsoline, papaverine, hydrastine, emetine, cryptaustoline, corydine, nuciferine, protopine, sinomenine, montanine, erythroidine, galipine, camptothecin, candidine, lasiocarpine, elaeocarpine, lupinine, lythrine, betanine, cyclopeptine, leucopterin, ephedrine, allocolchicine, merucathine, muscarine, atisine, aconitine, taxusin, alginine, verticine, pleiomutine, voacanghie, villalstonine, brucine, emetine, tubulosine, tubocurarine, calycanthine, cancentrine, N- methylconiine, gamma-coniceine, tropacocaine, mesembrine, lophocerine, salsolidine, salsolinol, villamine, pleiocarpamine, villoine, macroline, macrolinol, dehydrobeninine, berberine, gentianine, talbotine, verballocine, aphelandrine, calebassine, bebeerine, olivacine, polyneuridine, cryogenine, vincadifformine, quebrachamine, eburnamonine, porantherine, maytansine, isocyclocelabenzine, pseudoephedrine, aporphine, apomorphine, apovincamine, bisnortoxiferine, secologanin, ajmalicine, conopharyngine, iboluteine, diaboline, dimethyltryptamine, gramine, 5 -hydroxy dimethyltryptamine, 5- methoxydimethyltryptamine, neopine, quinidine, cinchonine, kopsirachine, hygrine, pilocarpine, rutaecarpine, orientaline, oripavine, reticuline, norreticuline, salutaridinol, neopinone, coclaurine, norcoclaurine, julioprosopine, senecionine, batrachotoxin, epibatidine, pteropodine, lycopodine, aphelandrine, mitragynine, harmine, harmaline, vinorelbine, solanine, arecoline, muscimol, ibotenic acid and atropine.

4. A method according to claim 3, wherein the target alkaloid is selected from morphine, caffeine, quinine, taxol, galanthamine and vincamine.

5. A method according to any one of the preceding claims, wherein the mixture of species from which the target alkaloid is extracted includes plant or fungal material.

6. A method according to claim 5, wherein the mixture of species includes plant material.

7. A method according to any one of the preceding claims, wherein the mixture of species includes one or more alkaloids other than the target alkaloid.

8. A method according to any one of the preceding claims, wherein the extraction involves contacting the mixture of species with the ionic liquid for a period of time, and under conditions, suitable to allow the target alkaloid to dissolve in the ionic liquid.

9. A method according to any one of the preceding claims, wherein the target alkaloid is recovered from the ionic liquid by chemically modifying the ionic liquid so as to alter its ability to dissolve the target alkaloid and hence cause its precipitation.

10. A method according to claim 9, wherein the chemical modification of the ionic liquid is carried out in situ.

11. A method according to claim 9 or claim 10, wherein the chemical modification of the ionic liquid involves exchanging the cation and/or the anion of the ionic liquid.

12. A method according to any one of the preceding claims, wherein the target alkaloid is recovered from the ionic liquid by altering the pKa of the ionic liquid to render the target alkaloid insoluble.

13. A method according to any one of the preceding claims, wherein the target alkaloid is recovered from the ionic liquid by adding a cosolvent so as to cause

"salting out" of the target alkaloid.

14. A method according to any one of the preceding claims, wherein the ionic liquid is capable of existing in liquid form below 40 ⁰C.

15. A method according to claim 14, wherein the ionic liquid is capable of existing in liquid form at room temperature.

16. A method according to any one of the preceding claims, wherein the ionic liquid contains 1 % or less of water, by mass.

17. A method according to any one of the preceding claims, wherein the ionic liquid contains 0.1 % v/v or less of non-ionic liquid cosolvents.

18. A method according to any one of the preceding claims, which is carried out in the absence of additional pH-adjusting agents.

19. A method according to any one of the preceding claims, wherein the ionic liquid has a viscosity of less than 100 centipoise at 25 ⁰C.

20. A method according to any one of the preceding claims, wherein the ionic liquid contains a nitrogen-based cation.

21. A method according to claim 20, wherein the ionic liquid contains a cation selected from ammonium, imidazolium, pyridiniurn and pyrrolidinium cations.

22. A method according to claim 20 or claim 21 , wherein the ionic liquid contains a cation which includes a protonated nitrogen.

23. A method according to any one of claims 20 to 22, wherein the ionic liquid contains a primary, secondary or tertiary ammonium cation.

24. A method according to claim 23, wherein the ionic liquid contains a secondary or tertiary ammonium cation.

25. A method according to any one of claims 20 to 24, wherein the cation is N- substituted with at least one alkanolyl, alkoxyalkyl or aminoalkyl group.

26. A method according to claim 25, wherein the cation is N-substituted with at least one alkanolyl or alkoxyalkyl group

27. A method according to claim 26, wherein the ionic liquid contains cations selected from alkanolammonium, alkyl alkanolammonium, dialkyl alkanolammonium, dialkanolammonium, alkyl dialkanolammonium, trialkanolammonium, alkoxyalkylammonium, alkyl alkoxyalkylammonium, dialkyl alkoxyalkylammonium, di(alkoxyalkyl) ammonium, alkyl di(alkoxyalkyl) ammonium and dialkyl (hydroxyalkoxyalkyl) ammonium cations.

28. A method according to claim 27, wherein the ionic liquid contains di(alkoxyalkyl) ammonium cations, N-alkyl-bis(alkoxyalkyl) ammonium cations or dialkyl alkanolammonium cations.

29. A method for extracting a target alkaloid from a mixture of species, which method is substantially as herein described.

30. Use of an ionic liquid as a solvent to extract a target alkaloid from a mixture of species.

31. A composition comprising a target alkaloid and an ionic liquid.

32. A composition according to claim 31 , which is the product of a method according to any one of claims 1 to 29.