Composition comprising a macrocyclic compound and an organic acid and its use in metal extraction

Abstract: A composition comprising a chelating compound which is a macrocyclic compound containing at least two coordinating centres in the ring, at least one of which is a neutral base moiety, and an organic acid containing at least one akyl or alkenyl group containing 8 or more carbon atoms. The macrocyclic compound contains at least 10 ring atoms and especially at least 12 ring atoms. The neutral base moitey is typically a nitrogen moiety. Preferably there are at least four coordinating centres at least two of which are neutral base moieties. The acid can be an alkyl or alkenyl substituted acid for example a long chain carboxylic acid. The composition can be used as an extractant system for the selective extraction of metals from an aqueous phase into an organic phase.

Description: The present invention relates to compositions which are capable of coordinating with metals and the use of such compositions for the treatment of solutions containing metal ions. The use of compounds having coordinating centres to form complexes with metals is well known. One application of this is in a solvent extraction process wherein a metal is extracted from one liquid phase into an immiscible liquid phase. Typically in a solvent extraction process an aqueous solution containing desired metal values is contacted with an immiscible phase, typically a hydrocarbon liquid such as a predominantly aliphatic hydrocarbon liquid, containing a compound which complexes with the metal and extracts it into the non-aqueous phase. The metal may then be recovered by a further extraction step in which the non-aqueous phase containing the metal is contacted with a different aqueous phase into which the metal is extracted and from which it can be recovered by suitable procedures such as electro-winning. A wide range of compounds has been proposed for use in solvent extraction processes, and most of these compounds contain one or more coordinating centres in the molecule. Macrocyclic compounds containing coordinating centres in the ring are capable of forming metal complexes and have advantage over the more conventional extractants in that the size and geometry of the ring may be chosen to be selective for specific metals. Thus, the interaction of 17- to 19- membered macrocycles containing oxygen and nitrogen donor atoms with nickel (II), cobalt (II) and copper (II) has been reported by Lindoy et al (J. Am. Chem. Soc. 1983, 105 , 4645-4651). The interaction of 14- to 17-membered oxygen and nitrogen containing macrocycles with cobalt (II), zinc (II) and cadmium (II) has also been reported by Lindoy et al (Inorg. Chem. 1980, 19 , 3360-3365). However, some potentially useful compounds of this type are liable to protonation and the protonated materials are water soluble to some extent and are liable to be removed from the non-aqueous phase when used in contact with solutions of low pH, such as 5 or lower. Organic compounds having large hydrocarbon, for example alkyl, substituents have little water solubility. However, the preparation of macrocyclic compounds of this type necessitates additional steps in the production of the product and may modify the properties of the final product and change its complexing behaviour. We have now found that the characteristics of certain macrocyclic compounds can be appreciably modified by a simple mixing process. According to the present invention there is provided a composition comprising (a) a chelating compound which is a macrocyclic compound containing at least two coordinating centres in the ring, at least one of which is a neutral base moiety, and (b) an organic acid containing at least one alkyl or alkenyl group containing 8 or more carbon atoms. The composition is preferably one in which the number of moles of component (b) is at least equal to the number of moles of component (a). Whilst a substantial molar excess of component (b) can be present in the composition, for example a molar ratio of (b) to (a) of 10:1 or more, in general no benefit is gained by the use of such excess quantities of component (b). It is generally preferred that the molar ratio of (b) to (a) does not exceed 5:1 and useful results have been obtained when the molar ratio of (b) to (a) is 2:1 up to 4:1. Conveniently, the number of moles of component (b) should be sufficient to equal the number of neutral base moieties which are present in component (a). Component (a) of the composition of the present invention is a macrocyclic compound and contains at least 10 ring atoms, and especially at least 12 ring atoms. In general the macrocyclic compound will contain not more than 30 ring atoms. A range of useful macrocyclic compounds contain 14 to 20 ring atoms. The macrocyclic compound contains at least two coordinating centres in the ring, but it is generally preferred to use a compound having at least four coordinating centres in the ring. Preferred macrocyclic compounds are those which contain at least two neutral base moieties in the ring. The, or each, neutral base moiety is preferably a nitrogen moiety which may be, for example, a tertiary amino (-NR-) or secondary amino grouping (-NH-). The group R in the tertiary amino grouping is a hydrocarbyl group which may optionally be substituted with at least one inert group such as an alkoxy group or halogen atom, which does not adversely affect the coordinating characteristics of the nitrogen moiety. Coordinating centres, which are other than the neutral base moiety, which may be present in the macrocyclic compound include oxygen and sulphur moieties and the like. Particularly preferred macrocyclic compounds which may be used as component (a) of the composition contain two or three nitrogen moieties and two or three further coordinating centres which are oxygen and/or sulphur moieties, for example two oxygen moieties. The macrocyclic compounds which can be used as component (a) may be represented by the general formula where R¹ and R², which may be the same or different, are divalent groups; X is a neutral base moiety; and Y is a coordinating centre. The groups R¹ and R² link X and Y and the linkage may include further coordinating centres. The coordinating centres X and Y, and any further coordinating centres present in R¹ and R², are preferably separated by at least one carbon atom and more generally by two or three carbon atoms. However, the coordinating centres may be separated by more than three carbon atoms, for example by four carbon atoms. In the macrocyclic compounds, the coordinating centres may be separated by the same number of carbon atoms or by different numbers of carbon atoms. Preferably, each of the groups R¹ and R² is, or includes, at least two atoms of an additional cyclic ring such as cyclohexane, cyclohexene, cyclohexadiene or benzene, and most preferably R¹ and R² contain the adjacent ring atoms only of the cyclic ring. The preferred macrocyclic compounds which include at least four coordinating centres may be represented by the general formula where R³ and R⁴, which may be the same or different, are divalent groups which do not include coordinating centres in the linking atoms, X¹ and X², which may be the same or different, are neutral base moieties Y¹, Y², Y³ and Y⁴, which may be the same or different, are coordinating centres; CH₂ represents a methylene group; a is a positive integer; b is zero or a positive integer; c is zero or one; d is a positive integer; e is zero or a positive integer; f is zero or one; x is a positive integer; and y is a positive integer where b and c are both zero or are both positive; and e and f are both zero or are both positive. The groups X¹ and X² are preferably the same and are -NH- groups or -NR- groups, where R is as hereinbefore defined. The group R can be an alkyl, aryl alkaryl or aralkyl group or can be an alkaryl or aralkyl group which is further substituted by an aryl or alkyl group respectively. The group R is conveniently a group which contains up to 30 carbon atoms, particularly up to 30 alkyl carbon atoms. The group R may be a benzyl group of an alkyl substituted benzyl group for example 4-alkylbenzyl group such as a 4-t-butylbenzyl group or a 4-dodecylbenzyl group. Y³ and/or Y⁴, if present, may be a neutral base moiety and is then preferably the same as X¹ and X². If Y³ and/or Y⁴, when present, is a coordinating centre other than a neutral base moiety, it is typically oxygen or sulphur and may be the same as, or different from, one or both of the groups Y¹ and Y². The groups Y¹ and Y² may be neutral base moieties but are preferably either oxygen or sulphur and especially both Y¹ and Y² are oxygen. The groups R³ and R⁴ are preferably both the same and are groups -PhCR⁵R⁶- where Ph is a 1,2-phenylene group, which may be optionally substituted; and R⁵ and R⁶, which may be the same or different, are hydrogen or a hydrocarbyl group, which may be optionally substituted. The optional substituents in the group Ph are inert groups such as an alkyl group, an alkoxy group or a halogen atom. Any substituent groups in the group Ph are preferably located in the 4-position relative to the group Y¹ or Y². If the substituent is an alkyl group or an alkoxy group, it is conveniently one containing up to 30 carbon atoms, for example up to 24 carbon atoms as in t-butyl, nonyl or dodecyl groups. The group -CR⁵R⁶- is typically linked to X¹ or X². It is preferred that at least one of the groups R⁵ or R⁶ is a hydrogen atom. Compounds in which both of the groups R⁵ and R⁶ are hydrogen, that is in which the groups R³ and R⁴ are -PhCH₂-, are generally more readily prepared and hence are generally preferred. If either or both of the groups R⁵ and R⁶ are optionally substituted hydrocarbyl groups they may be any of the groups which are disclosed herein as the group R. However it may be preferred that R⁵ and/or R⁶ is a lower alkyl group, that is one containing 1 to 4 carbon atoms such as a methyl group. If the value of both b and c is zero, the group (CH₂) b (Y³) c is absent. However, if both b and c have a positive value, one or more of the groups (CH₂) b (Y³) c is present, depending on the value of x. The value of x is typically one or two and generally is one. Similarly, if the value of both e and f is zero, the group (CH₂) e (Y⁴) f is absent. If both e and f are positive, one or more of the groups (CH₂) e (Y⁴) f is present depending on the value of y. The value of y is typically one or two and generally is one. The value of a and d, and b and e when these have a positive value, is typically from 1 up to 4 and especially is two or three. Compounds of formula (II) which can be used as component (a) in the composition of the present invention include, inter alia those set out in Table One hereafter, in all of which R³ and R⁴ are -PhCH₂- (that is R⁵ and R⁶ are both hydrogen) where Ph is an unsubstituted 1,2-phenylene group and the CH₂ is linked to X¹ or X², e and f are both zero and the value of x is one. Compound No. X¹ b Y³ c d X² Y² a Y¹ 1 NH zero - zero 3 NH O 2 O 2 NH 2 NH 1 2 NH O 2 O 3 NH 3 NH 1 3 NH O 2 O 4 NH 2 NH 1 2 NH O 1 O 5 NH 2 S 1 2 NH O 2 O 6 NH 2 NH 1 2 NH O 4 O 7 NH 2 NH 1 2 NH S 1 S 8 NH 2 S 1 2 NH S 1 S 9 NH 2 NH 1 2 NH S 2 S 10 NH 2 S 1 2 NH S 2 S 11 NH 2 NH 1 2 NH S 2 O 12 NH 2 S 1 2 NH S 2 O 13 NH 2 O 1 2 NH S 2 O 14 NH 2 NH 1 2 NH 0 3 0 Other macrocyclic compounds include derivatives of compounds in Table One, these derivatives being as follows:- Compound 15 is a modification of compound 1 in which R³ and R⁴ are -PhCH₂- in which Ph is a 1,2-phenylene group having a nonyl group in the 4- position relative to the oxygen atom which is Y¹ or Y². Compound 16 is a modification of compound 2 in which R³ and R⁴ are -PhCH₂- in which Ph is a 1,2-phenylene group having a t-butyl group in the 4- position relative to the oxygen atom which is Y¹ or Y². Compound 17 is similar to compound 16 with the exception that the t-butyl group is replaced by a nonyl group. Compound 18 is a modification of compound 2 in which X¹, Y³ and X² are all the same and are all -NR- groups where R is benzyl (-CH₂C₆H₅). Compound 19 is similar to compound 18 with the exception X¹, Y³ and X² are all the same and are all -NR- groups where R is 4-t-butylbenzyl (-CH₂C₆H₄ t C₄H₉). Compound 20 is similar to compound 18 with the exception X¹, Y³ and X² are all the same and are all -NR- groups where R is 4-dodecylbenzyl (-CH₂C₆H₄C₁₂H₂₅). Compound 21 is a modification of compound 2 in which Y³ is a -NR-group where R is 4-dodecylbenzyl. Compound 22 is a modification of compound 1 in which R³ and R⁴ are both -Ph CH(CH₃)-. Compound 23 is a modification of compound 2 in which R³ and R⁴ are both -Ph CH(CH₃)-. A wide range of macrocyclic compounds are known and can be selected to give a desired effect. Compounds of this type are described by Lindoy in "Heavy Metal Chemistry of Mixed Donor Macrocyclic Ligands: Strategies for Obtaining Metal Ion Recognition" in Progress in Macrocyclic Chemistry, edited by R.M.Izett and J.J.Christensen, Vol.3, pages 53 to 92. Compound of this type can be prepared in the manner outlined by Lindoy or in the references noted by Lindoy. Compounds including an alkyl substituted 1,2-phenylene group can be prepared using the corresponding alkyl-substituted hydroxybenzaldehyde. Compounds in which X¹, Y³ and X² are -NR- groups can be obtained by reacting the corresponding macrocyclic compound in which X¹, Y³ and X² are -NH- with the appropriate benzyl halide. The compound in which Y³ is -NR- can be prepared using a triamine containing the group -NR-. The compound in which R³ and R⁴ are both -Ph CH(CH₃)- is prepared using 2-hydroxyacetophenone and an increased reaction time. The organic acid is conveniently a carboxylic acid since these are generally more readily available. The acid may be a halogen substituted acid such as 2-bromohexadecanoic acid. The organic acid contains and alkyl or alkenyl group of at least 8 carbon atoms and preferably at least 10 carbon atoms. The alkyl or alkenyl group typically does not contain more than 24 carbon atoms. The alkyl or alkenyl group may be a straight or branched chain group. A mixture of acids can be used having alkyl or alkenyl groups with different numbers of carbon atoms or different isometric alkyl or alkenyl groups, or both. Acids which may be used as component (b) of the composition include nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid and octadecenoic acid. Acids other than carboxylic acids which may be used include di(2-ethylhexyl) phosphoric acid, dinonylnaphthalene sulphonic acid, dodecylbenzene sulphonic acid and an alkyl sulphonic acid mixture for example a mixture whereof the alkyl groups contain from 13 to 18 carbon atoms with about 95% by weight being alkyl groups containing 14 to 17 carbon atoms. The compositions of the present invention are soluble in water-immiscible liquid media such as paraffinic hydrocarbons, aromatic hydrocarbons and halohydrocarbons, although the solubility is dependent on the components of the composition and also the nature of the water - immiscible liquid medium. However, the compositions, or the macrocyclic component thereof, are less susceptible to extraction into an aqueous phase than the macrocyclic compound alone under otherwise the same conditions. The compositions of the present invention are prepared by mixing together the components thereof in the desired proportions. The mixing is conveniently effected in a solvent for the components, particularly a hydrocarbon or halohydrocarbon solvent. The components may be dissolved separately in a solvent and the two solutions then mixed together or one component may be added to a solution of the other component. Mixing may be effected at any suitable temperature and is conveniently effected at ambient temperature although higher temperatures, for example up to 100°C or more, or lower temperatures, for example 0°C or lower, may be used if desired or necessary, for example to increase the rate at which a component dissolves. The macrocyclic component of the composition is preferably one which is capable of forming a complex with a metal and the compositions of the present invention are capable of forming complexes with metals. Some of the macrocyclic compounds which may be used as a component (a) of the composition of the present invention are believed to be new materials. Thus, as a further aspect of the present invention, there are provided compounds of the general formula II wherein at least one of the groups R³ or R⁴ is a group -PhCR⁵R⁶ wherein Ph is a 1,2-phenylene group which is substituted with an alkyl group containing at least 4 carbon atoms and/or at least one of the groups R⁵ and R⁶ is a phenyl group, a benzyl group or an alkyl group. Preferred compounds are those in which Ph is a 1,2-phenylene group which is substituted with an alkyl group containing at least six carbon atoms, for example a nonyl or dodecyl group. The substituent group may be a mixture of different groups containing different numbers of carbon atoms or containing mixtures of isomers for example mixtures of nonyl isomers. Further preferred compounds are those in which one of R⁵ and R⁶ is a hydrogen atom and the other is a lower alkyl group, for example, a methyl group. As a further aspect, there are provided compounds of the general formula II in which at least one of X¹, Y³ and X² is a group -NR- where R is a benzyl group or an alkyl-substituted benzyl group, especially a 4-alkylbenzyl group such as 4-nonylbenzyl or 4-dodecylbenzyl. A further compound within the present invention is of general formula II in which R³ or R⁴ is a group -Ph CR⁵R⁶-, where Ph is a 1,2-phenylene group which is substituted with an alkyl group containing at least 4 carbon atoms and at least one of X¹, Y³ and X² is a group -NR- where R is as defined. Particular compounds of this type are those in which Ph is substituted with a nonyl or dodecyl group and at least one of X¹, Y³ and X² is a group -NR- where R is a benzyl group or a 4-alkylbenzyl group. The composition of the present invention may be used in systems in which the formation of a metal complex is desirable. Thus, the composition may be used in a solvent extraction process. Alternatively, the composition may be impregnated into a membrane to give a membrane which permits the passage of only certain metal species. The composition may be used in a solvent extraction process using known solvent extraction procedures. More specifically, as a further aspect of the present invention there is provided a solvent extraction process for extracting metal values from aqueous solutions of metal salts which comprises the steps of (1) contacting the aqueous solution containing metal salts with a solution of an extractant in a water-immiscible organic solvent, wherein the extractant is a composition comprising components (a) and (b) as hereinbefore described; (2) separating the aqueous solution from the solution of the extractant in the water-immiscible solvent into which metal has been extracted; and (3) contacting the resultant organic phase with an aqueous strip solution whereby the metal transfers into the aqueous strip solution. The compositions of the present invention form complexes with many metals and the particular metal which can be extracted is dependent on the composition of the aqueous phase, specifically what metals are present, and the particular macrocyclic compound which is present as component (a) of the composition. Thus, by the determination of metal ion distribution constants in single-metal extraction experiments, and by other procedures, we have found macrocyclic compounds which give compositions which are capable of extracting specific metals from aqueous solution. Thus, when the metal ion is cobalt(II), suitable macrocyclic compounds which can be used as component (a) of the composition include compounds 2, 4, 6, 7 and especially 11, as defined in Table One. When the metal ion is nickel(II), suitable macrocyclic compounds which can be used as component (a) of the composition include compounds 2, 6, 7, 9 and 11, as defined in Table One. When the metal ion is copper(II), suitable macrocyclic compounds include compounds 5, 10, 12, especially 2, 3, 7 and most especially 1, 6, 11 and 14 as defined in Table One, and also compounds 16 and 22 and very preferably compounds 15, 17 and 21 as hereinbefore defined. For both zinc(II) and cadmium(II), suitable macrocyclic compounds which can be used as component (a) of the composition include compounds 2, 3, 4, 7, 9 and 11, as defined in Table One. For silver(I), suitable macrocyclic compounds which can be used as component (a) of the composition include compounds 7 to 13, as defined in Table One and also compounds 18, 19 and 20 as hereinbefore defined. Selective extraction experiments have also been carried out with pairs of metal ions. It has been found that copper(II) is selectively extracted from a mixture of copper(II) and nickel(II) using a composition containing macrocyclic compounds 2, 7, 11 and especially 6, as defined in Table One. It has also been found that cadmium(II) is selectively extracted from a mixture of cadmium(II) and zinc(II) using a composition containing macrocyclic compounds 2 and 11, as defined in Table One. It has also been found that silver is selectively extracted from mixtures of silver and another metal using a composition containing macrocyclic compound 18 as hereinbefore defined and a similar effect may also be obtained using macrocyclic compounds 19 and 20. Using a composition containing macrocyclic compound 17 as hereinbefore defined, copper may be extracted at a lower pH than when using many other macrocyclic compounds and a similar effect may also be obtained using macrocyclic compound 15. It will be appreciated that the foregoing is merely illustrative of macrocyclic compounds which are effective to extract certain metals from an aqueous phase and is not limiting either in respect of the macrocyclic compounds which can be used or the metals which can be extracted. It will also be appreciated that the optimum extraction conditions will depend on the mixture being used, the metals present in the initial aqueous phase and the pH of the extraction stage (step 1) and the pH of the strip stage (step 3). The solvent extraction process which is a further aspect of the present invention may be incorporated into a wide variety of different methods for the overall recovery of metals from their ores or from other metal-bearing sources. Details of these methods will vary depending on the metal concerned and the nature and composition of the leach solution obtained by leaching the metal from its ore or other source. Whilst the solvent extraction process is not limited to any single overall method for the recovery of metals, it will be appreciated that the solvent extraction process may be only one step in an integrated process for the recovery of the metal from the ore. Such an integrated process may include the following steps: 1. Leaching of the ore with a suitable aqueous solution, and removing any undissolved solids; 2. Contacting the leach solution from step 1, which contains the desired metal in solution, with a solution in a water-immiscible solvent of the composition of components (a) and (b), whereby the metal is transferred into the organic phase; 3. Separating the organic phase containing the extracted metal from the aqueous phase; 4. Contacting the organic phase from step 3 with an aqueous strip solution whereby the metal transfers into the aqueous strip solution; 5. Separating the organic phase containing the stripped extractant from the aqueous strip solution containing a salt of the metal; and 6. Recovering the metal from the strip solution, for example by electrolysing the strip solution from step 5 to recover the metal. In a fully integrated process of this type it is highly desirable that the solutions be re-circulated between the various stages. Thus aqueous strip solution used in step 4 may be derived from the electrolysis step 6 which is denuded in the metal ion. Similarly the organic phase containing the stripped extractant which is separated in step 5 is preferably re-circulated to the extraction stage 2. The leaching in stage 1 may be effected using any suitable leaching agent which may be acidic or basic. In stage 2, the composition should be resistant to the species in the leach solution and be capable of extracting the desired metal from the leach solution. This will depend on the choice of both the macrocyclic compound and the organic acid. In stage 4, the aqueous strip solution may be water or an aqueous acid or alkaline solution. The strip solution should be effective to strip the desired metal values from the organic phase without extracting either of components (a) and (b) into the aqueous phase. With many of the macrocyclic compounds it is convenient to effect extraction and stripping with aqueous solutions having a pH which is in the range from about 1 up to 7, which is not more than, and in general is lower than, the pH of the leach solution. The composition of the present invention may be used as a solution in many of the water-immiscible organic solvents which have been proposed for use in a solvent extraction process. Such water-immiscible organic solvents include aliphatic, aromatic and alicyclic hydrocarbons and chlorinated hydrocarbons such as perchloroethylene, trichloroethane and trichloroethylene. Mixtures of solvents may be used. Especially preferred in conventional hydrometallurgical practice are mixed hydrocarbon solvents such as high boiling, high flash point, petroleum fractions (for example kerosene) with varying aromatic content. In general, hydrocarbon solvents having a high aromatic content, for example AROMASOL H which consists essentially of a mixture of trimethylbenzenes and is commercially available from Imperial Chemical Industries PLC (AROMASOL is a registered trade mark), provide a higher solubility for the extractant and the extracted metal whilst kerosene having a relatively low aromatic content, for example ESCAID 100 which is a petroleum distillate comprising 20% aromatics, 56.5% paraffins and 23.4% naphthenes commercially available from ESSO (ESCAID is a registered trade mark) may, in certain cases, improve the hydrometallurgical performance of the extractant. The concentrations of the macrocyclic compound and the organic acid in the water-immiscible organic solvent may be chosen to suit the particular leach solution to be treated. The concentration of the macrocyclic compound in the organic phase may be up to about 2 Molar, and especially up to 1 Molar in the organic solvent. The concentration of the organic acid is related to the concentration of the macrocyclic compound and typically is such as to provide at least one mole of the organic acid for each mole of the macrocyclic compound. The extraction stage and the strip stage of the solvent extraction process may conveniently take place at ambient temperature. However it may be possible to improve the net metal transfer from the leach solution to the strip solution if the extraction stage and strip stage are operated at different temperature, for example if the extraction stage is operated at ambient temperature whilst the strip stage is operated at elevated temperature such as about 50°C. The invention is illustrated by the following Examples in which all parts and percentages are by weight unless otherwise stated. Preparation of 6,7,8,9,10,11,17,18-octahydro-5H-dibenzo[e,n][1,4]dioxa[8,12]diazacyclopentadecine This is compound 1 as defined in Table One and was prepared by a multistage process of reacting 1,2-dibromoethane with salicylaldehyde; reacting the product with 1,3-diaminopropane and reducing this product with sodium borohydride, using procedures as noted by Lindoy in "Heavy Metal Chemistry of Mixed Donor Macrocyclic Ligands: Strategies for Obtaining Metal Ion Recognition", noted previously herein. Stage 1: Preparation of 1,4-bis(2-formylphenyl)-1,4-dioxabutane Salicylaldehyde (97.6g) was dissolved in 80cm³ of ethanol. An aqueous solution of sodium hydroxide (32g) of 1dm³ of water was added to give a yellow solution. 1,2-dibromoethane (73.6g) was then added followed by sufficient ethanol to give an homogeneous solution. The mixture was stirred under nitrogen and heated to reflux temperature and maintained at reflux temperature under nitrogen for 44 hours. The mixture was allowed to cool and a solid precipitated. The solid was filtered off and dried. The solid was mixed with hexane at a temperature of about 65°C, sufficient chloroform was added to dissolve the solid and the mixture was allowed to cool and a solid crystallised. The solid had a melting point of 128-130°C, corresponding closely to the reported melting point of 129°C for 1,4-bis(2-formylphenyl)-1,4-dioxabutane. Stage 2: Preparation of 3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane-1,11-diene A solution of 8.1g of the product of Stage 1 in methanol (150cm³) was stirred at ambient temperature and a solution of 1,3-diaminopropane (2.3g) in methanol (50cm³) was added dropwise. The solution was stirred, heated to reflux temperature, maintained at reflux temperature for 0.5 hours and distilled water (150cm³) added. The mixture was cooled to 0-5°C for 0.5 hours and a precipitate formed which was filtered off, washed with water and dried at 50°C. A yield of 9g of 3,4:9,10-dibenzo-1,12-diazo-5,8-dioxacyclopentadecane-1,11-diene was obtained. Stage 3: Preparation of 6,7,8,9,10,11,17,18-octahydro-5H-dibenzo[e,n][1,4]dioxa[8,12]diazacyclopentadecine A solution of 2g of the product of Stage 2 and 0.2g of disodium tetraborate (borax) in methanol (40cm³) was stirred and heated to reflux temperature. The mixture was maintained at reflux temperature and 0.6g of sodium borohydride was added portionwise to the refluxing mixture. After one hour at reflux temperature, the mixture was allowed to cool to ambient temperature, cold water was added and a precipitate which was formed was filtered off. The solid was recrystallised from a chloroform/hexane mixture as in Stage 1. The solid had a melting point of 144-146°C, corresponding closely to the reported melting point of 143°C for 6,7,8,9,10,11,17,18-octahydro-5H-dibenzo[e,n][1,4]dioxa[8,12]diazacyclopentadecine, compound 1 as defined in Table One. If desired, stages 2 and 3 can be effected without separating a solid product at the end of stage 2. More specifically, after refluxing with the amino compound for an appropriate time, disodium tetraborate is added and then the sodium borohydride is added portionwise to the refluxing mixture. It is generally more convenient to combine stages 2 and 3, particularly if the macrocyclic compound is one containing more than 17 atoms in the macrocyclic, that is compounds 3 , 6 and 14 in Table One, since with such compounds it has been found that the di-imine product of stage 2 is difficult to isolate as a solid but generally forms an oil. Compounds 2 to 14 as defined in Table One can be prepared using similar procedures or using procedures described by Lindoy in Progress in Macrocyclic Chemistry, edited by R M Izett and J J Christensen, Vol 3, pages 53 to 92. Compounds 15,16 and 17 can be prepared in a similar manner by replacing the salicylaldehyde of stage 1 with the corresponding 5-alkyl-2-hydroxybenzaldehyde in an equivalent molar amount. Compounds 18, 19 and 20 can be prepared from compound 2 by reaction with a benzyl bromide or a 4-alkylbenzylbromide. Exemplary preparations are set out hereafter as Stages 4A and 4B. Stage 4A: Preparation of 6,9,12-tri(4-t-butylbenzyl)-6,7,8,9,10,11, 12,13,19,20-decahydro-5H-dibenzo[e,p,][1,4]dioxa[8,11,14]triazacycloheptadecine 0.68g of compound 2 (6,7,8,9,10,11,12,13,19,20-decahydro-5H-dibenzo[e,p,][1,4]dioxa[8,11,14]triazacycloheptadecine) were stirred in 10cm³ of dimethylsulphoxide and 0.5g of potassium hydroxide were added. 1.4g of 4-t-butylbenzylbromide were added and the mixture was stirred and heated to reflux temperature and maintained at reflux temperature for two hours. A white solid precipitated, the mixture was cooled to ambient temperature and the solid was filtered off. The solid was then dissolved in chloroform and the chloroform solution was washed three times with water. The chloroform solution was then dried using anhydrous magnesium sulphate. The chloroform was then evaporated off using a rotary evaporator. 0.8g of a white solid product was obtained. Stage 4B: Preparation of 6,9,12-tribenzyl-6,7,8,9,10,11,12,13,19,20-decahydro-5H-dibenzo[e,p][1,4] dioxa [8,11,14]triazacycloheptadecine A solution of 1.41g of benzyl chloride in 100cm³ of acetonitrile was added to 2g of a finely powered sample of compound 2 and 4.2g of sodium bicarbonate. The mixture was refluxed overnight. 100cm³ of dilute hydrochloric acid were added and the aqueous layer was washed twice using 100cm³ of dichloromethane for each wash. An excess of sodium hydroxide was then added to the aqueous layer to raise the pH to pH 14. The solution was allowed to cool and the reaction products were extracted into dichloromethane which was washed three times with water. The organic phase was then evaporated to dryness. The product obtained was recrystallised from acetonitrile and the crystals obtained were dried over phosphorus pentoxide and then under vacuum (10mm) overnight. Compound 21 is prepared using a similar procedure to that described for compound 1 with the exception that the amino compound used in Stage 2 was 4-[4-dodecylbenzyl]diethylenetriamine (the preparation of which is described in Stage 5 hereafter), and Stages 2 and 3 were effected without separating the di-imine product of Stage 2. Stage 5: Preparation of 4-[4-dodecylbenzyl]diethylenetriamine. a) Preparation of di-phthalimido derivative 148.1g of phthalic anhydride and 51.6g of diethylene triamine were stirred together in 300cm³ of xylene and the mixture was stirred and heated to 180°C. The water produced was collected by means of a Dean and Stark leg. After maintaining the mixture at 180°C for three hours a total of 15cm³ of water had been collected. The reaction mixture was allowed to cool, and the solid which precipitated was filtered off. The filtered solid was ground up, washed with xylene and then hexane. The solid was recrystallised from a chloroform/hexane mixture. b) Preparation of 4-dodecylbenzyl derivative 29.9g of the phthalimido derivative obtained in (a) were stirred in 500cm³ of acetonitrile containing 41.4g of potassium carbonate. 33.9g of 4-dodecybenzyl bromide were added. The mixture was stirred, heated to reflux temperature, maintained at reflux for 18 hours and then filtered hot. The filtrate was evaporated using a rotary evaporator and the residue was dissolved in chloroform. The chloroform solution was treated with silica gel, filtered and then evaporated to remove the chloroform leaving a pale yellow oil. c) Preparation of 4-[4-dodecylbenzyl]diethylenetriamine . 52.17g was the 4-dodecylbenzyl derivative obtained in (b) were dissolved in 500cm³ of ethanol. Hydrazine hydrate (45g) was added dropwise. The mixture was stirred, heated to reflux temperature and maintained under gentle reflux for two hours. The mixture was cooled to ambient temperature and filtered. The filtrate was evaporated using a rotary evaporator. The residue was dissolved in chloroform. The chloroform solution was filtered and washed three times with water using 100cm³ of water for each wash. The chloroform solution was then dried using anhydrous magnesium sulphate and filtered. The filtrate was evaporated by rotary evaporation to give 32.78g of a golden yellow oil. Compound 22 and 23 were prepared using a similar procedure to that described with the exception that salicylaldehyde was replaced by 2-hydroxyacetophenone, in stage 1 reflux temperature was maintained for 48 hours and in stage 2, the reflux temperature was maintained for 48 hours. Stage 3 was effected by adding sodium borohydride to the product mixture from stage 2 (after 48 hours at reflux temperature) without separating product from stage 2. In the preparation of compound 23, diethylenetriamine was used in stage 2. Example 1 Copper(II) acetate (0.04g) was dissolved in 50cm³ of distilled water. 0.062g of compound 1 and 0.08g of dodecanoic acid were dissolved in 50cm³ of a mixture of SOLVESSO 150 (a high boiling, high flash point, aromatic hydrocarbon solvent containing trimethylbenzene, commercially available from Exxon Chemicals. SOLVESSO is a registered trade mark.) and n-decanol containing 10% v/v of n-decanol. The two solutions were stirred vigorously together for two hours and the phases were then allowed to separate and were subjected to analysis for copper. The following results were obtained: Original copper (II) acetate solution 250 ppm (w/v) copper Final copper (II) acetate solution 6 ppm (w/v) copper Organic phase 235 ppm (w/v) copper. For comparison the foregoing procedure was repeated omitting the dodecanoic acid from the organic phase. It was noted that the aqueous phase became more intensely coloured, signifying the formation of a copper complex in the aqueous phase. Dodecanoic acid was then added to the organic phase and the organic phase became coloured whilst the colour was discharged from the aqueous phase. Example 2 A solution of 0.156g of compound 1 and 1.0g of dodecanoic acid was formed in 500cm³ of the SOLVESSO 150/n-decanol mixture. A further solution of 0.1g of copper(II) acetate was formed in 500cm³ of distilled water. 50cm³ of each of the two solutions were stirred together rapidly at ambient temperature for 1.5 hours. Stirring was stopped and the phases were allowed to separate. A blue-green organic phase separated and this was run off. The optical density of the organic solution was measured using a spectrophotometer. The organic phase was then stirred for one hour at ambient temperature with 50cm³ of 0.01M aqueous sulphuric acid. When stirring was stopped, a colourless organic phase separated. The organic phase was run off and filtered through Whatman IPS filter paper. The foregoing procedure was carried out a total of four times, using the same organic phase throughout but using a fresh sample of the aqueous copper (II) acetate solution and of the sulphuric acid for each repeat cycle. A change of only 1% in the optical density of the organic phase was noted between the first and fourth cycle. Examples 3 to 8 A number of macrocyclic compounds were used in experiments to determine the metal ion distribution of cobalt(II). In each experiment, 5cm³ of an aqueous phase and 5cm³ of an organic phase were shaken together in a sealed, 20cm³ glass vial using a horizontal shaker operating at 150 oscillations per minute. Shaking was continued for one hour at a controlled temperature of 22 ± 2°C. The aqueous phase contained cobalt(II) nitrate at a concentration of 1 x 10⁻³ mol.dm³ in a buffer solution containing 1 x 10⁻² mol.dm⁻³ of a 2,6-lutedine-3-sulphonic acid/sodium hydroxide mixture. The relative proportions of the components of the buffer mixture were varied depending on the desired pH. The organic phase was a solution, in chloroform, of 1 x 10⁻³ mol.dm⁻³ of the macrocyclic compound and 4 x 10⁻³ mol.dm⁻³ of hexadecanoic acid. Control experiments were carried out in the absence of the macrocyclic compound. No detectable extraction was observed in the control experiments. The metal-ion distribution constants (D m ) were calculated by subtracting the amount of metal ion remaining in the aqueous phase at the end of the experiment from that remaining in the aqueous phase of the control experiments. D m is the ratio of the metal ion concentration in the organic phase at the end of the experiment compared to the sum of the initial metal ion concentration in both phases. The results obtained are set out in Table Two, in which the compound number corresponds to the compounds as defined in Table One. Example Macrocyclic Compound D m pH 4.7 pH 5.6 3 2 <0.05 0.32 4 3 <0.05 0.16 5 4 <0.05 0.33 6 6 0.09 0.33 7 7 <0.05 0.29 8 11 ND 0.44 ND means not determined. Examples 9 to 13 The procedure described for Examples 3 to 8 was repeated with the exceptions that nickel(II) nitrate was used rather than cobalt(II) nitrate, shaking was continued for 40 hours and the pH of the aqueous solution was 4.7. The results obtained are set out in Table Three. Example Macrocyclic Compound D m 9 2 0.24 10 6 0.39 11 7 0.43 12 9 0.36 13 11 0.41 Examples 14 to 21 The procedure described for Examples 9 to 13 was repeated with the exceptions that copper(II) nitrate was used rather than nickel(II) nitrate and shaking was continued for one hour. The results obtained are set out in Table Four. Example Macrocyclic Compound D m 14 2 0.57 15 3 0.64 16 5 0.32 17 6 0.87 18 7 0.52 19 10 0.31 20 11 0.90 21 12 0.42 Examples 22 to 27 The procedure described for Examples 3 to 8 was repeated with the exception that zinc(II) nitrate was used rather than cobalt(II) nitrate. The results obtained are set out in Table Five. Example Macrocyclic Compound D m pH 4.7 pH 5.6 22 2 0.11 0.37 23 3 0.13 0.42 24 4 ND 0.28 25 7 0.09 0.32 26 9 ND 0.34 27 11 <0.05 0.34 Examples 28 to 33 The procedure described for Examples 3 to 8 was repeated with the exception that cadmium(II) nitrate was used rather than cobalt(II) nitrate. The results obtained are set out in Table Six. Example Macrocyclic Compound D m pH 4.7 pH 5.6 28 2 0.07 0.52 29 3 <0.05 0.32 30 4 ND 0.32 31 7 <0.05 0.33 32 9 ND 0.56 33 11 0.15 0.52 Examples 34 to 40 The procedure described for Examples 3 to 8 was repeated with the exception that silver(I) nitrate was used rather than cobalt(II) nitrate. The results obtained are set out in Table Seven. Example Macrocyclic Compound D m pH 4.7 pH 5.6 34 7 0.56 0.87 35 8 0.76 0.82 36 9 ND 0.83 37 10 ND 0.92 38 11 0.46 0.81 39 12 ND 0.80 40 13 ND 0.84 Examples 41 to 45 The procedure described for Examples 3 to 8 was repeated with the exception that the aqueous phase contained 0.5 x 10⁻³ mol.dm⁻³ of copper(II) nitrate and 0.5 x 10⁻³ mol.dm⁻³ of nickel(II) nitrate and was buffered to pH 4.7. D m was determined for each of the metals. The results obtained are set out in Table Eight. Example Macrocyclic Compound D m Ni(II) Cu(II) 41 2 <0.05 0.59 42 5 <0.05 0.20 43 6 <0.05 0.83 44 7 <0.05 0.63 45 11 <0.05 0.65 Examples 46 to 48 The procedure described for Examples 41 to 45 was repeated with the exceptions that zinc (II) nitrate and cadmium (II) nitrate were used and the pH was 5.6. The results obtained are set out in Table Nine. Example Macrocyclic Compound D m Zn(II) Cd(II) 46 2 0.07 0.55 47 3 0.22 0.11 48 11 0.06 0.57 It will be noted that the particular metal which is selectively extracted is dependent on the macrocyclic compound. When the procedure of Examples 46 to 48 was repeated using a pH of 4.7, the value of D m for both metals was less than 0.1 in all experiments. Examples 49 to 52 Transport experiments were carried out in a water-jacketed U-tube. In the base of the U-tube was placed 3.6cm³ of a chloroform solution. In each arm of the tube was located, in contact with the chloroform solution, 3.5cm³ of an aqueous phase. The chloroform solution was provided with a magnetic stirrer and each aqueous phase was provided with vertically oscillating agitators. The chloroform phase contained a macrocyclic compound (1 x 10⁻³ mol.dm⁻³) and hexadecanoic acid (4 x 10⁻³ mol.dm⁻³). One aqueous phase contained 5 x 10⁻² mol.dm⁻³ nickel (II) nitrate and 5 x 10⁻² mol.dm⁻³ copper (II) nitrate and was buffered to pH 4.7 as in Examples 3 to 8. The other aqueous phase was buffered to pH 4.7 (as in Examples 3 to 8) and contained 0.1 mol.dm⁻³ of sodium nitrate. The transfer of the metal ions from one aqueous phase to the other was determined after 100 hours at a temperature of 25 ± 0.1°C. The organic/aqueous phase interface was 1.0cm². The rate of transfer was determined as mmol.h⁻¹ cm ⁻². The results obtained are given in Table Ten. Example Macrocyclic Compound Transfer rate Ni(II) Cu(II) 49 2 <7 x 10⁻⁷ 6.7 x 10⁻⁶ 50 5 <7 x 10⁻⁷ 3.3 x 10⁻⁵ 51 7 <7 x 10⁻⁷ 5.5 x 10⁻⁶ 52 11 <7 x 10⁻⁷ 5.6 x 10⁻⁶ In all cases the rate of transfer of nickel (II) was below the level of detection of the metal. Examples 53 to 57 The procedure described for Examples 49 to 52 was repeated with the exception that the buffered aqueous solution of sodium nitrate was replaced by a solution containing 0.05 mol.dm⁻³ of ethylenediamine tetra-acetic acid which had been adjusted to pH 7.0 by the addition of NaOH. The results obtained are given in Table Eleven. Example Macrocyclic Compound Transfer rate Ni(II) Cu(II) 53 2 <7 x 10⁻⁷ 8.9 x 10⁻⁵ 54 5 <7 x 10⁻⁷ 8.8 x 10⁻⁵ 55 6 <7 x 10⁻⁷ 1.5 x 10⁻⁴ 56 7 <7 x 10⁻⁷ 3.8 x 10⁻⁵ 57 11 <7 x 10⁻⁷ 1.6 x 10⁻⁴ Examples 58 to 60 The procedure described for Examples 53 to 57 was repeated with the exceptions that the aqueous solution containing nickel(II) and copper(II) was replaced by an aqueous solution containing zinc(II) nitrate and cadmium(II) nitrate and buffered either to pH 4.7 or pH 5.6. The results obtained are set out in Table Twelve. Ex Macrocyclic Compound Transfer rate pH 4.7 pH 5.6 Zn(II) Cd(II) Zn(II) Cd(II) 58 2 6.9 x 10⁻⁷ 2.6 x 10⁻⁵ 2.1 x 10⁻⁶ 6.6 x 10⁻⁵ 59 3 5.8 x 10⁻⁶ 4.3 x 10⁻⁷ 3.4 x 10⁻⁵ 4.0 x 10⁻⁶ 60 11 7.9 x 10⁻⁷ 5.7 x 10⁻⁵ 1.3 x 10⁻⁶ 7.9 x 10⁻⁵ Example 61 Copper(II) nitrate (0.12g) was dissolved in 50cm³ of distilled water. 0.169g of compound 2 and 0.256g of hexadecanoic acid were dissolved in 50cm³ of a mixture of SOLVESSO 150 and n-decanol (containing 10%v/v of n-decanol). The two solutions were stirred vigorously together for two hours and the phases were then allowed to separate. The aqueous phase was deep blue and the organic phase was essentially colourless. The procedure was repeated except that compound 2 and the hexadecanoic acid were dissolved in Escaid 100. A similar result was obtained. The procedure was repeated except that compound 2 and the hexadecanoic acid were dissolved in chloroform. The aqueous phase was pale blue and the organic phase was deep blue. Example 62 The various experiments described in Example 61 were repeated using an equivalent molecular proportion of compound 14 as the macrocyclic compound. The results obtained were similar to those obtained in Example 61. Example 63 The first experiment of Example 61 was repeated using an equivalent molecular proportion of compound 15 as the macrocyclic compound. The aqueous phase was essentially colourless and the organic phase was pale green. Using chloroform as the organic solvent, a similar result was obtained. Example 64 The experiments described in Example 61 were repeated using an equivalent molecular proportion of compound 16 as the macrocyclic compound. In all cases the organic phase was a deep red-blue in colour and the aqueous phase was essentially colourless. Example 65 The experiments described in Example 61 were repeated using an equivalent molecular proportion of compound 17 as the macrocyclic compound. The results obtained were similar to those obtained in Example 64. Example 66 The first experiment of Example 61 was repeated using an equivalent molecular proportion of compound 21 as the macrocyclic compound. The organic phase was a deep blue in colour and the aqueous phase was essentially colourless. Examples 67 to 73 The procedure of Examples 3 to 8 was repeated using an equivalent molecular proportion of compound 18 as the macrocyclic compound. The aqueous phase contained 1 x 10⁻³ mol dm⁻³ of a different metal nitrate in each experiment. The pH of the aqueous solution in all experiments was buffered to a pH of 5 using a mixture of 2 molar acetic acid and 2 molar sodium acetate as the buffer. The transfer time was 24 hours. The metal ion distribution constants was determined for each metal and the results are set out in Table Thirteen. Example Metal D m 67 Ag⁺ 0.130 68 Pb²⁺ 0.024 69 Zn²⁺ 0.007 70 Cd²⁺ 0.035 71 Ni²⁺ 0.000 72 Co²⁺ 0.028 73 Cu²⁺ 0.023 The amount of nickel ion extracted was below the limit of detection and hence is reported as giving no extraction. Examples 74 to 81 Transport experiments were carried out in a manner similar to that described for Examples 49 to 52. The experiments were carried out in a beaker of diameter 5.7cm having an open tube of internal diameter 2.5cm located vertically within the beaker. 50cm³ of a chloroform solution containing macrocyclic compound 18 (1 x 10⁻³ mol.dm⁻³) and hexadecanoic acid (4 x 10⁻³ mol.dm⁻³) were placed in the beaker, the lower end of the open tube being immersed in the chloroform solution with clearance between the lower end of the tube and the base of the beaker. Within the tube were placed 10cm³ of an aqueous source phase which contained 5 x 10⁻³ mol.dm⁻³ of a metal salt and which was buffered to pH 5 using an acetic acid/sodium acetate mixture as in Examples 67 to 73. Around the outside of the tube were placed 30cm³ of an aqueous receiving phase which was buffered to pH3 using a mixture of formic acid and sodium hydroxide. The chloroform solution was in contact with both of the aqueous phases but the only contact between the aqueous phases was through the chloroform solution. The chloroform solution was stirred by means of a magnetic stirring bar rotating at 120 r.p.m. The aqueous phases were not stirred. The concentration of the metal in the receiving aqueous phase was determined after 24 hours at 25°C. The results are set out in Table Fourteen. Example Metal Concentration in Receiving phase (mol.dm⁻³) 74 Ag⁺ 5.91 x 10 ⁻⁴ 75 Pb²⁺ 4.15 x 10 ⁻⁶ 76 Cu²⁺ 3.16 x 10 ⁻⁵ 77 Ni²⁺ 0.00 78 Co²⁺ 1.60 x 10 ⁻⁶ 79 Zn²⁺ 3.06 x 10 ⁻⁷ 80 Cd²⁺ 1.78 x 10 ⁻⁷ 81 Hg²⁺ 1.99 x 10 ⁻⁵ The amount of nickel ion in the receiving phase was below the limit of detection and hence is reported as giving no extraction. Example 82 to 91 The transport experiments of Examples 74 to 81 were repeated with the exception that in all cases the aqueous source phase contained two metals, one of which was silver. Each of the metals was present in the source phase at a concentration of 10⁻² mol.dm⁻³. The competitive transport rate was determined by determination of the concentration of each metal in the aqueous receiving phase at the end of each experiment. The results are set out in Table Fifteen. Example Second Metal Relative Concentration 82 Mn 2369 83 Mg 1930 84 Hg 0.717 85 Ca 505 86 Cu 72 87 Pb 468 88 Ni 927 89 Cd 15760 90 Zn 1576 91 Co 3864 Relative concentration is the concentration of silver in the aqueous receiving phase divided by the concentration of the second metal in the aqueous receiving phase. Examples 92 to 119 A series of experiments was carried out using either compound 2, compound 16 or compound 17 as the macrocyclic compound. The procedure used was as described for Example 1 with the exception that an equivalent molecular proportion of copper(II) nitrate was used and an equivalent molecular proportion of the appropriate macrocyclic compound was used. The organic solution and the aqueous solution were stirred together to form an emulsion and stirring was continued for a sufficient time to allow the pH of the emulsion to stabilise. The pH of the emulsion was measured using a pH meter, stirring was stopped and the two phases were allowed to separate. A sample of the organic phase was removed by pipette and filtered through Whatman 1PS phase separation paper to remove any entrained aqueous phase. The organic solution was transferred to a 10mm quartz cell. The absorbance of the solution was measured using a Perkin-Elmer Lambda 15 u.v./visible spectophotometer and the absorption peak height was recorded. The organic solution was returned to the vessel containing the organic and aqueous phases. The contents of the vessel were stirred and the pH of the emulsion was adjusted by the addition of dilute nitric acid or dilute aqueous sodium hydroxide solution as required. The procedure was repeated several times to determine the variation of the optical density (absorbance) of the organic phase with variation of pH of the emulsion. The variation of optical density of the organic phase with the pH of the emulsion is set out in Table Sixteen. Ex Macrocycle 2 Ex Macrocycle 16 Ex Macrocycle 17 pH OD pH OD pH OD 92 11.0 1.44 101 5.7 1.58 111 4.8 1.70 93 8.8 1.44 102 5.3 1.59 112 4.4 1.63 94 8.0 1.40 103 4.7 1.6 113 3.5 1.56 95 6.6 1.25 104 3.9 1.48 114 3.2 1.46 96 6.2 1.06 105 3.7 1.34 115 3.0 1.12 97 5.7 0.74 106 3.4 0.84 116 2.7 0.60 98 4.4 0.11 107 3.2 0.47 117 2.5 0.30 99 4.0 0.06 108 2.9 0.17 118 2.2 0.11 100 3.6 0.0 109 2.7 0.10 119 2.0 0.0 110 1.8 0.0 pH is the pH of the emulsion before the organic phase is separated. OD is the optical density (absorbance) of the organic phase, determined as described. Example 120 The procedure of Examples 92 to 119 was repeated using compound 16 as the macrocyclic compound. The optical density of the organic phase was determined and samples of the organic phase were analysed for copper content. Two curves were drawn, one of optical density of the organic phase against pH of the aqueous solution and the other of copper content of the organic phase against pH of the aqueous solution. A very close correlation between the two curves was noted. Examples 121 to 125 The procedure of Examples 111 to 119 was repeated using 0.296g of macrocyclic compound 17 and 0.335g of 2-bromohexadecanoic acid in 50cm³ of a mixture of SOLVESSO 150 and n-decanol (containing 10% v/v of n-decanol). The variation of optical density of the organic phase with the pH of the emulsion is set out in Table Seventeen. Example pH OD 121 3.39 1.36 122 2.82 0.99 123 2.44 0.39 124 2.27 0.15 125 2.04 0.0 Example 126 A solution of 2.96g of compound 17 and 2.56g of hexadecanoic acid was formed in 500cm³ of the SOLVESSO 150/n-decanol mixture. A further solution of 1.205g of copper(II) nitrate was formed in 500cm³ of distilled water. 50cm³ of each of the two solutions were stirred together rapidly at ambient temperature for 1.5 hours. Stirring was stopped and the phases were allowed to separate. A blue-green organic phase separated and this was run off. The optical density of the organic solution was measured using a spectrophotometer. The organic phase was then stirred for one hour at ambient temperature with 50cm³ of 0.01M aqueous sulphuric acid. When stirring was stopped, a colourless organic phase separated. The organic phase was run off and filtered through Whatman IPS filter paper. The foregoing procedure was carried out a total of three times, using the same organic phase throughout but using a fresh sample of the aqueous copper(II) nitrate solution and of the sulphuric acid for each repeat cycle. A change of only 1% in the optical density of the organic phase was noted between the first and third cycle.

Claims: A composition comprising (a) a chelating compound which is a macrocyclic compound containing at least two coordinating centres in the macrocyclic ring, at least one of which is a neutral base moiety; and (b) an organic acid containing at least one alkyl or alkenyl group containing 8 or more carbon atoms. A composition as claimed in claim 1 wherein the number of moles of component (b) is at least equal to the number of moles of component (a). A composition as claimed in either claim 1 or claim 2 wherein component (a) contains at least 12, and not more than 30, ring atoms in the macrocyclic ring. A composition as claimed in any one of claims 1 to 3 wherein component (a) contains at least four coordinating centres in the macrocyclic ring of which at least two are neutral base moieties. A composition as claimed in claim 4 wherein component (a) contains, in the macrocyclic ring, two or three nitrogen moieties and two or three further coordinating centres which are oxygen and/or sulphur moieties. A composition as claimed in any one of claims 1 to 5 wherein component (a) has the general formula II where R³ and R⁴, which may be the same or different, are divalent groups which do not include coordinating centres in the linking atoms; X¹ and X², which may be the same or different, are neutral base moieties; Y¹, Y², Y³ and Y⁴, which may be the same or different, are coordinating centres; CH₂ represents a methylene group; a is a positive integer; b is zero or a positive integer; c is zero or one; d is a positive integer; e is zero or a positive integer; f is zero or one; x is a positive integer; and y is a positive integer. where b and c are both zero or are both positive integers; and e and f are both zero or are both positive integers. A composition as claimed in claim 6 wherein, in component (a), X¹ and X² are both -NH- groups or are both -NR- groups, where R is a hydrocarbyl group which is optionally substituted with at least one alkoxy group or halogen atom. A composition as claimed in either claim 6 or claim 7 wherein in component (a), each of the groups R³ and R⁴ is a group -PhCR⁵R⁶- where Ph is a 1,2-phenylene group which may be substituted with an alkyl group, an alkoxy group or a halogen atom; and R⁵ and R⁶, which may be the same or different, are hydrogen or a hydrocarbyl group which may be substituted with at least one alkoxy group or halogen atom. A composition as claimed in claim 1 wherein component (a) is a compound of Formula II selected from the group consisting of compounds 1 to 23 wherein e and f are both zero; and x is 1; and wherein, in compounds 1-14, R³ and R⁴ are -PhCH₂- wherein Ph is an unsubstituted 1,2-phenylene group and the CH₂ is linked to X¹ or X²; and wherein X¹, b, Y³, c, d, X², Y², a and Y¹ are as follows: Compound No. X¹ b Y³ c d X² Y² a Y¹ 1 NH zero - zero 3 NH O 2 O 2 NH 2 NH 1 2 NH O 2 O 3 NH 3 NH 1 3 NH O 2 O 4 NH 2 NH 1 2 NH O 1 O 5 NH 2 S 1 2 NH O 2 O 6 NH 2 NH 1 2 NH O 4 O 7 NH 2 NH 1 2 NH S 1 S 8 NH 2 S 1 2 NH S 1 S 9 NH 2 NH 1 2 NH S 2 S 10 NH 2 S 1 2 NH S 2 S 11 NH 2 NH 1 2 NH S 2 O 12 NH 2 S 1 2 NH S 2 O 13 NH 2 O 1 2 NH S 2 O 14 NH 2 NH 1 2 NH 0 3 0 and wherein Compound 15 is a modification of compound 1 in which R³ and R⁴ are -PhCH₂- in which Ph is a 1,2-phenylene group having a nonyl group in the 4- position relative to the oxygen atom which is Y¹ or Y²; Compound 16 is a modification of compound 2 in which R³ and R⁴ are -PhCH₂- in which Ph is a 1,2-phenylene group having a t-butyl group in the 4- position relative to the oxygen atom which is Y¹ or Y²; Compound 17 is similar to compound 16 with the exception that the t-butyl group is replaced by a nonyl group; Compound 18 is a modification of compound 2 in which X¹, Y³ and X² are all the same and are all -NR- groups where R is benzyl (-CH₂C₆H₅); Compound 19 is similar to compound 18 with the exception X¹, Y³ and X² are all the same and are all -NR- groups where R is 4-t-butylbenzyl (-CH₂C₆H₄ t C₄H₉); Compound 20 is similar to compound 18 with the exception X¹, Y³ and X² are all the same and are all -NR- groups where R is 4-dodecylbenzyl (-CH₂C₆H₄C₁₂H₂₅); Compound 21 is a modification of compound 2 in which Y³ is a -NR-group where R is 4-dodecylbenzyl; Compound 22 is a modification of compound 1 in which R³ and R⁴ are both -Ph CH(CH₃)-, and Compound 23 is a modification of compound 2 in which R³ and R⁴ are both -Ph CH(CH₃)-. A composition as claimed in any one of claims 1 to 9 wherein component (b) is a carboxylic acid. A solvent extraction process for extracting metal values from aqueous solutions of metal salts which comprises the steps of (1) contacting the aqueous solution containing metal salts with a solution of an extractant in a water-immiscible organic solvent; (2) separating the aqueous solution from the solution of the extractant in the water-immiscible solvent into which metal has been extracted; and (3) contacting the resultant organic phase with an aqueous strip solution whereby the metal transfers into the aqueous strip solution wherein the aqueous solution of metal salts is contacted with a solution in a water-immiscible organic solvent of an extractant which is a composition as claimed in any one of claims 1 to 10. A process as claimed in claim 11 wherein the metal is copper(II) and the extractant contains one of compounds 15, 17 or 21 as defined in claim 9. A process as claimed in claim 11 wherein the metal is silver(I) and the extractant contains one of compounds 18, 19 or 20 as defined in claim 9. A compound of the general formula II where R³ and R⁴, which may be the same or different, are divalent groups of the formula -PhCR⁵R⁶-; X¹ and X 2, which may be the same or different, are -NH- or -NR-groups; Y¹, Y² and Y⁴ which may be the same or different, are coordinating centres; Y 3, is a coordinating centre and may be the same as, or different from, X¹ and/or X²; Ph, is a 1,2-phenylene group which may be substituted with an alkyl group, an alkoxy group or a halogen atom; R⁵ and R⁶, which may be the same or different, are hydrogen or a hydrocarbyl group which may be substituted with at least one alkoxy group or halogen atom; R is a hydrocarbyl group which is optionally substituted with at least one alkoxy group or halogen atom; a is a positive integer; b is zero or a positive integer; c is zero or one; d is a positive integer; e is zero or a positive integer; f is zero or one; x is a positive integer; and y is a positive integer; where b and c are both zero or are both positive integers; e and f are both zero or are both positive integers; and wherein Ph is 1,2-phenylene group which is substituted with an alkyl group containing at least 4 carbon atoms and/or at least one of the groups R⁵ and R⁶ is a phenyl group, a benzyl group or an alkyl group; and/or at least one of the groups X¹, Y³ and X² is a group -NR- in which the group R is a benzyl group or a 4-alkylbenzyl group. A compound as claimed in claim 14 wherein Ph is a 1,2-phenylene group substituted by an alkyl group containing at least six carbon atoms. A compound as claimed in claim 14 or claim 15 wherein one of the groups R⁵ and R⁶ is hydrogen and the other of groups R⁵ and R⁶ is a lower alkyl group containing one to four carbon atoms. A compound of formula II which is compound 15, 16, 17, 18, 19, 20, 21, 22 or 23 as defined in claim 9.

Inventors: BALDWIN DARREN SYLVESTER, LINDOY LEONARD FRANCIS, TASKER PETER ANTHONY, BALDWIN, DARREN SYLVESTER, LINDOY, LEONARD FRANCIS, TASKER, PETER ANTHONY
Applicants: ZENECA LTD, ZENECA LIMITED
Application year: 1989
Main classification: C07D273
IPC codes: C07D285, C07D291, B01D11, C01G5, C22B3, C01G3, C01B31, C07D273, C09K3