The Process of Separating a Selected Ion From a Plurality of Other Ions in a Multiple Ion Solution by Contacting the Solution With a Macrocyclic Ligand Bonded to Silica Which Selectively Complexes With the Desired Ion

The present invention comprises a composition of matter and a process of using it. The composition of matter comprises silica, e.g. sand or silica gel, having a covalent bond to certain macrocyclic compounds through a hydrocarbon chain with or without an ether oxygen linkage. These certain macrocyclic compounds have at least four -- A CH.sub.2 -- CH.sub.2 -- groups in which A is selected from O, O-- CH.sub.2, S, S-- CH.sub.2, M-- R, and N-- (R)-- CH.sub.2 in which R is selected from H, lower alkyl, and benzyl and the hydrocarbon chain has an end group ##STR2## covalently bonded to silica in which X is selected from lower alkyl, phenyl, benzyl, halogen, -- O-- CH.sub.3, -- O-- C.sub.2 H.sub.5, and -- O-- Silca.

Representative families of compounds contemplated by the present invention are illustrated by the following structural formulae I to V.

According to the present invention a composition of matter comprises silica covalently bonded to a macrocyclic compound and having the formula I, II, III, IV or V below: ##STR3##

The process comprises selectively and quantitatively removing and concentrating a selected ion or group of ions present at low concentrations from a plurality of other ions in a multiple ion solution in which the other ions may be present at much higher concentrations by bringing the multiple ion solution into contact with a compound of the invention. The preferred embodiment disclosed herein involves carrying out the process by bringing a large volume of the multiple ion solution into contact with a compound of the invention as an addition compound to sand or silica gel in a separation column through which the mixture is first flowed to complex the desired ion or ions with said compound followed by the flow through the column of a small volume of a receiving liquid to break the complex by chemical or thermal means, dissolve the desired ions and carry them out of the column. Other equivalent apparatus may be used instead of a calcium, e.g., a slurry which is filtered, washed with a receiving liquid to break the complex and recover the desired ion. The desired metal ions are then recovered from the receiving phase by well known procedures.

More particularly, the process comprises forming a chemical covalent bond between silica, preferably sand or silica gel, and at least one of the compounds, placing the resulting bonded silica in a contacting device such as a tall column, causing a large volume of the mixture of ions to flow through the column where the desired ions complex with the bonded silica which separates them from the rest of the mixture which flows out of the column, then flowing a small volume of the receiving liquid through the column to break the complex and dissolve and carry out of the column the desired ion(s). The desired metal ions are then recovered from the receiving phase by well known procedures.

The fact is known that macrocyclic polyethers and other macrocyclic ligands present as solutes in a solvent such as water are characterized by their ability to selectively form strong bonds with particular ions or groups or ions present as solutes in the same solvent according to size, donor atom-related related and other well known selectivity rules as noted in articles by R. M. Izatt, J. S. Bradshaw, S. A. Nielsen, J. D. Lamb, J. J. Christensen, and D. Sen, THERMODYNAMIC AND KINETIC DATA FOR CATION.MACROCYCLE INTERACTION. Chem. Rev., 1985, Vol. 85, 271-339 and by L. F. Lindoy, in PROGRESS IN MACROCYGLIC CHEMISTRY, edited by R. M. Izatt and J. J. Christensen, JOHN WILEY & SONS, pages 53-92 (1987). However, researchers have not previously been able to incorporate macrocycles into separation systems where the behavior of the macrocycle in the separation system in comparison to that of the macrocycle as a solute is unchanged and/or the macrocycle will remain in the separation system. Articles such as those entitle ION-CHROMATOGRAPHIC SEPARATION OF SILICA GRAFTED WITH BENZO-18CROWN-6-ETHER by M. Lauthard and Ph. Germain, J. Liquid Chromatogr., 1985, Vol. 8, 2403-2415, and ION-CHROMATOGRAPHY ON POLY (CROWN ETHER-MODIFIED) SILICA POSSESSING HIGH AFFINITY FOR SODIUM by M. Nakajima, K. Kumura, E. Hayata and T. Shono, J. Liquid Chromatogr., 1984. Vol. 7, 2115-2125, have disclosed the bonding of crown ethers to silica gels but they and most other reported macrocycle bonded silicas contain a benzene group or other electron withdrawing groups as part of a macrocycle side chain which reduces the ability of the macrocycle to bond with ions in comparison to the situation where the macrocycle and ions are present as solutes in solution. The only other reported examples of bonding of macrocycles to sand or silica gel have involved bonding via a side chain connected to one of the electron rich macrocycle donor atoms, i.e., nitrogen. One such reference is entitled AN OXYGEN.NITROGEN DONOR MACROCYCLE IMMOBILIZED ON SILICA GEL. A REAGENT SHOWING HIGH SELECTIVITY FOR Cu(II) IN THE PRESENCE OF Co(II). Ni(II) OR Zn(II), by V. Dudler, L. F. Lindoy. D. Sallin, C. W. Schlaepfer. Aust. J. Chem., 1987, Vol. 40, p. 1557. However, such bonding changes the geometry of the compound and greatly reduces the ability of the macrocycle to interact with ions. Prior researchers in this field confined their research to analytical chromatographic applications and disclosed no concept of industrial separation applications where strong macrocycle.ion bonding is required to quantitatively recover the desired ion(s) from solution and high selectivity is required to obtain a product free from contaminants. The strength of macrocycle-ion bonding is particularly important when ions present in solution at low concentrations need to be recovered. The greater the value of the equilibrium constant for ion.macrocycle interaction, the lower the initial concentration of the ion in solution can be and still be efficiently and quantitatively complexed. Hence, the ability to attach these macrocycles to sand or silica gel without reducing the ability of the macrocycle to complex ions is of the utmost importance in the industrial use of macrocycles. The process of the present invention successfully accomplished this feat.

The compounds of the present invention comprise certain macrocyclic ligands covalently bonded to silica, e.g., sand or silica gel. The compounds are identified above. The process of the present invention uses the compounds, which are characterized by high selectivity for and removal of desired metal ions or groups of metal ions present at low concentrations from the source phase containing a mixture of metal ions with the ions one does not desire to remove present in much greater concentrations in the solution, in a separation device such as a column through which the solution is flowed. The process of selectively removing and concentrating the desired ion(s) is characterized by the ability to quantitatively complex from a large volume of solution the desired ion(s) when they are present at low concentrations. The said ions are recovered from the separation column by flowing through it a small volume of a receiving phase which contains a solubilized reagent which need not be selective, but which will strip the ions from the macrocyclic ligand quantitatively. The recovery of the desired metal ions from the receiving phase is easily accomplished by well known procedures.

The invention will be described and illustrated by reference to the drawings in which:

FIG. 1 represents schematically a suitable column for holding the silicamacrocyclic ligand (crown) materials through which a solution of metal ions can be flowed to complex selectively with a desired ion or group of ions in accordance with the invention.

FIG. 2-6 represent the group of families of neutral macrocyclic ligands covalently bonded to silica comprising the compounds of the invention., and

FIG. 7 represents a graph of the predicted (o points) and actual (curve) remaining amount of Sr.sup.2+ in a solution initially containing 1 M MgCl.sub.2 and 0.001 M SrCl.sub.2 after flowing the solution through an 18-crown-6 bonded silica gel column vs. the amount of volume of the solution which has been passed through the column. The analytical detection limit is listed for those experimental points where no Sr.sup.2+ could be detected.

Macrocycles which do not contain electron withdrawing groups and which are capable of being bonded to silica must be synthesized. Then the macrocycle must be covalently bonded to the sand or silica gel.

One method of preparing the compounds of FIG. 2 for example, is to react the allyloxy forms of the crowns with chlorodimethylsilane (or dichloromethylsilane) followed by heating the resulting chlorosilane (or dichlorosilane) with silica as follows: ##STR4##

The synthesis of the allyloxy forms of the crowns, which is not part of the present invention, is described in an article entitled FACILE SYNTHESIS OF HYDROXYMETHYLCROWN ETHERS by I. Ikeda, H. E. Mura and M. Okahara, Synthesis pages 73 and 74 (1984), which is incorporated herein by reference.

A method for preparing the macrocyclic compounds of FIG. 3 is to react the cryptand compound having a --CH.sub.2 --O--CH.sub.2 CH.dbd.CH.sub.2 side chain with chlorodimethylsilane (or dichloromethylsilane) in the presence of a platinum catalyst to convert the side chain to --CH.sub.2 --O--(CH.sub.2).sub.3 --Si(CH.sub.3)ClX (where X .dbd. (Cl or CH.sub.3) and heating this compound with silica as follows: ##STR5##

The synthesis of the --CH.sub.2--O--CH.sub.2 CH.dbd.CH.sub.2 substituted 2.2.2 cryptand (.dbd.n .dbd.1) which is not part of the present invention, is described in an article entitled SYNTHESIS OF HYDROXYMETHYL.FUNCTIONALIZED DIAZACROWNS AND CRYPTANDS by David A. Babb, Bronislaw P. Czech and Richard A. Bartsch, J. Heterocyclic Chem., Vol. 23, pages 609, 613 (1986), which is incorporated herein by reference.

A method of preparing the macrocyclic compounds of FIG. 4, for example, is to react 4-allyloxypyridino-18-crown-6 with chlorodimethylsilane (or dichloromethylsilane) and heating the resulting chlorosilane and silica as follows: ##STR6##

The synthesis of 4-allyloxypyridino--18-crown-6 (where n.dbd.1), which is not part of the present invention, is described in an article entitled PROTONIONIZABLE CROWN ETHERS. 3. SYNTHESIS AND STRUCTURAL STUDIES OF MACROCYCLIC POLYETHER LIGANDS CONTAINING A 4-PYRIDINE SUBCYCLIC UNIT, by Jerald S. Bradshaw, Yohji Nakatsuji, Peter Huszthy, Bruce E. Wilson, N. Kent Dalley and Reed M. Izatt, J. Heterocyclic Chem. Vol. 23, pages 353-360 (1986), which is incorporated herein by reference.

It should be emphasized that any macrocycle which can by synthesized with a --CH.sub.2 --CH.sub.2 CH.dbd.CH.sub.2 side chain or the like attached to one of the regular carbon atoms of the macrocycle could then be covalently bonded to sand or silica gel. The interaction properties of this bonded macrocycle will not differ from those of the unsubstituted macrocycle present as a solute in solution when such a macrocycle does not contain electron withdrawing substituent groups and the bonding to sand or silica gel does not occur via one of the macrocycle donor atoms. This will now be described in more detail in the following description of the metal ion recovery and concentration process.

The metal ion recovery and concentration process of the invention relates to the selective recovery of desired metal ions from mixtures thereof with other metal ions using the compounds of the invention as defined above. Effective methods of recovery and/or separation of metal ions, particularly silver, lead, cadmium, and other heavy metals, from one another in culinary water supplies, waste solutions deposits and industrial solutions and silver recovery from waste solutions, e.g., from emulsions on photographic and X-ray film, represent a real need in modern technology. These ions are typically present at flow concentrations in solutions containing other ions at much greater concentrations. Hence, there is a real need for a process to selectively recover and concentrate these hazardous and/or desirable ions. The present invention accomplishes this separation effectively and efficiently by the use of compounds selected from the families represented by FIGS. 2-5.

The process first involved selecting a macrocycle.bonded silica where the particular macrocycle will selectively complex the ion(s) of interest. There is a large data base for measurements of macrocycle.ion interactions where the macrocycle is unsubstituted and present as a solute in a solvent. Much of this data base is presented in an article by R. M. Izatt, J. S. Bradshaw, S. A. Nielsen, J. D. Lamb, J. J. Christensen. and D. Sen, THERMODYNAMIC AND KINETIC DATA FOR CATION.MACROCYCLE INTERAGTION, Chem. Rev. Vol. 85, 271-339 (1985). Previously, this data base has only provided general qualitative predictions about the behavior of macrocycles incorporated into separation processes. However, in the process of the invention the equilibrium constants for ionmacrocycle interaction for macrocycles present as solutes in solution vs. that for macrocycles bonded to silica show little or no variation. Data comparing the interaction of several ions with both types of the macrocycle 18-crown.6 are given as an example of this point in Table 1. It is emphasized that similar interaction with metal ions of the bonded macrocycle and macrocycle in solution is only obtained when electron withdrawing groups are not attached to the macrocycle and when the macrocycle is not attached to the silica via one of the donor atoms of the macrocycle.

The data base for macrocycle.cation interaction can be used in choosing a macrocycle for recovering a particular cation. The selective removal and

recover of Pb.sup.2+ and Ba.sup.2+ from aqueous solutions using 18-crown6 bonded to silica gel are examples of a suitable choice of macrocycle for a specific need. The data base measurements indicate that Pb.sup.2+ and Ba.sup.2+ are selectively complexed by 18-crown-6 by at least an order of magnitude over all other cations. The selectivity over cations often present in large excess (i.e., Na.sup.30 , K.sup.30 , Mg.sup.2+, Ca.sup.2+) is much greater. The equilibrium constant values in Table 1 confirms the suitability of the choice of 18-crown6 as an appropriate macrocycle for the task. The 18-crown-6 bonded silica gel has been tested for its ability to remove Pb.sup.2+ from H.sub.2 O. These data are presented in Table 2. The dimensions.

and capacity of the small column used are given as footnotes to the table. The data in Table 2 show that great reductions in aqueous Pb.sup.2+ concentrations can be achieved using the 18-crown-6 bonded silica gel column even when another cation is present in solution at much greater concentrations. Silica gel can interact with ions to some degree in and of itself. However, tests using a plain silica gel column under conditions identical to those performed with the macrocycle bonded silica gel showed that the aqueous stream Pb.sup.2+ concentration reductions were not as great. In particular. the plain silica gel column performed quite poorly under conditions where cations other than Pb.sup.2+ were present at much greater concentrations than that of Pb.sup.2+. The effect of silica gel or sand interaction with ions flowing through the column can be minimized by blocking the majority of the .OH sites present with trimethylsilyl groups.

The same 18-crown-6 bonded silica gel column has also been tested for its ability to selectively remove Sr.sup.2+ from a solution containing 1 M MgCl.sub.2 and 0.001 M SrCl.sub.2. The molar concentrations of Sr.sup.2+ in the aqueous stream coming out of the bottom of the column vs. the corresponding volumes of solution which have been flowed through the column are plotted as the exponential points in FIG. 7. A predicted Sr.sup.2+ concentration vs. volume plot is also shown (solid line). The predicted plot was obtained by numerically solving the partial differential mass balance equation for the column using the equilibrium constant for Sr.sup.2+ could be removed from the aqueous source phase.

Once the desired ion(s) are attached to the silica gel column they must be removed using a small volume of a receiving phase so that a concentrated and purified product is obtained. In the Pb.sup.2+ and Sr.sup.2+ recovery tests described, 99% of the purified Pb.sup.2+ or Sr.sup.2+ was recovered from the column using 25 ml of a concentrated basic solution of either ethylenediamine tetraacetate (EDTA), citrate or acetate. These reagents form stronger complexes with the ion(s) that the macrocycle does. Hence, they can effectively strip ion(s) from the macrocycle. These ion-receiving phase reagent complexes are easily broken by adding acid to the solution. These species can be recovered as a solid if desired. For example, the Pb.sup.2+ can be recovered as a solid by using H.sub.2 SO.sub.4 as the acid and, hence, precipitating PbSO.sub.4.

An example of the use of these materials and processes is the quantitative and selective removal of undesired heavy metals such as Pb.sup.2+ from blood. The silica-gel bonded macrocycle 18-crown-6 (FIG. 2. A-- F= oxygen, n= 1) selectively complexes Pb.sup.2+ over K.sup.+, Na.sup.+, Ca.sup.2+, Fe.sup.3+, proteins and other materials necessary in the body by at least 2 orders of magnitude.

Although the invention has been described and illustrated by reference to certain specific macrocyclic ligands and processes of using them, analogs of these macrocycles are within the scope of the compounds and processes of the invention as defined in the following claims.