Selective Transport of Alkali Metal Cations in Solvent Extraction by Proton-Ionizable Dibenzocrown Ethers

Abstract

Lipophilic crown ethers with pendant proton-ionizable groups are novel metal complexing agents for use in solvent extraction of alkali metal cations. A variety of dibenzocrown ether carboxylic acids and dibenzo crown phosphonic acid monoesters have been examined to probe the effect of structural variation within the complexing agent upon selectivity and efficiency in solvent extraction. Results from competitive solvent extractions of alkali metal cations from aqueous solutions into chloroform are summarized.     

New lipophilic crown ethers with intraannular carboxylic acid groups: Synthesis and alkali metal cation extraction

A six‐step synthetic route to four lipophilic crown ethers with intraannular carboxylic acid groups and ring sizes of 15‐crown‐4, 18‐crown‐5, 21‐crown‐6 and 24‐crown‐7 is described. Eight new polyether compounds that bear inward‐facing bromo and formate ester substituents are prepared as synthetic intermediates. Selectivities and efficiencies of the four new lipophilic crown ether carboxylic acids in competitive alkali metal cation extraction from aqueous solutions into chloroform are evaluated.     

Separation of metals by liquid surfactant membranes containing crown ether carboxylic acids

A water-in-oil-in-water emulsion liquid membrane system is used to transport alkali metal and alkaline earth cations from an external alkaline aqueous source phase through an organic membrane containing a crown ether carboxylic acid and into the internal acidic aqueous phase of the emulsion droplet. The influence of varying the crown ether carboxylic acid structure upon the selectivity and efficiency of competitive metal ion transport is examined.     

Selective separation of alkali metal cations by bulk chloroform membranes containing lipophilic crown ether phosphonic acid monoethyl esters

A series of crown ether phosphonic acid monoethyl esters with crown ether ring size variation from 12-crown-4 to 24-crown-8 is used in bulk chloroform membranes to separate alkali metal cations from mixtures. Selective proton-coupled transport of alkali metal cations from weakly alkaline aqueous phases is achieved. With individual ionizable crown ether carriers, transport selectivity for Li⁺, Na⁺, K⁺, and Rb⁺-Cs⁺ is achieved. A closely related lipophilic phosphonic acid monoethyl ester derivative with a cyclohexyl unit in place of the crown ether exhibits transport selectivity for Li⁺. However, the corresponding phosphonic acid diethyl ester is devoid of transport activity. Effects of structural variation within the carrier upon the selectivity and efficiency of competitive alkali metal cation transport are assessed.     

Effect of structural variations of dibenzocrown ether resins and their acyclic analogues upon ion-pair sorption of alkali metal salts from aqueous and aqueous methanol solutions

Abstract

Ion-pair sorption of alkali metal salts from aqueous and aqueous methanol solutions by acyclic and cyclic dibenzopolyether resins possessing different side arm groups such as hydroxy, methoxy and carboxy has been investigated. The results reveal that both sorption selectivity and efficiency are influenced by: (1) the methanol content of the aqueous sample solution; (2) the acyclic or cyclic nature of the polyether unit; (3) the conformational positioning of the side arm group with respect to the crown ether cavity; and (4) the identity of the counteranion species of the alkali metal salt. For sym-(C₃H₇)(R′)dibenzo-16-crown-5 resins, the sorption selectivity and efficiency increased as the R′ group was varied: -OCH₃ < -OH < -OCH₂CO₂H. The highest sorption efficiency and Na⁺ selectivity was obtained for sym-(propyl)dibenzo-16-crown-5-oxyacetic acid resin (7) in which the pendent carboxylic acid group is oriented over the crown ether cavity. The use of a less hydrated anion in the alkali metal salt species enhances the ion-pair efficiency: SO₄ ^2- < NO₃ ^?, Cl^?, Br^? < I^? < SCN^?. Monovalent metal selective sorption was noted for competitive ion-pair sorption of NaCl, KCl, MgCl₂ and CaCl₂ by resin 7.     

AFM observation of cation complexation of dibenzocrown ethers adsorbed on highly oriented pyrolytic graphite

The cation complexation behavior of dibenzocrown ethers adsorbed on highly oriented pyrolytic graphite substrates was investigated by means of atomic force microscopy using probe tips modified chemically with ammonium ion by silane coupling. The specific adhesion force based on the intermolecular force between dibenzocrown ether and ammonium ion was observed via force curve measurements in ethanol at the interface between the substrate and tip. The observed specific force decreased in the presence of the alkali metal ion in solution, indicating that the cation in solution interferes with the complexation of the crown ethers adsorbed on the substrate with the ammonium ion immobilized on the tip. The blocking effect of metal ions in solution on the observed force depended on the sizes of both the blocking cation and crown ether ring, suggesting that the surface-adsorbed dibenzocrown ethers possess a selective cation-complexing ability similar to that in their bulk state and that the adhesion force measurements using cation-modified tips allow evaluation of the cation-complexing ability of crown ethers under cation-competitive conditions.     

Competitive transport of alkali metal ions from aqueous media into toluene solutions of 2-(sym-dibenzo-16-crown-5-oxy)-decanoic acid. A comparative study

Competitive permeation of alkali metal ions from an alkaline source phase into or through a toluene phase facilitated by the lipophilic crown ether carboxylic acid 2-(symdibenzo-16-crown-5-oxy)-decanoic acid is studied in liquid—liquid extraction, bulk liquid membrane transport, and emulsion liquid membrane transport. Most rapid transport was obtained in emulsion liquid membrane experiments. Some differences in selectivity orders for alkali metal permeation were observed for the three separation techniques.     

New lariat ether carboxylic and hydroxamic acids: Synthesis and lanthanide ion complexation

Twenty-six new lariat ether carboxylic and hydroxamic acids based upon dibenzo-13-crown-4, dibenzo-14-crown-4, dibenzo-16-crown-5 and dibenzo-19-crown-6 ring systems are synthesized and the solid-state structure for a dibenzo-19-crown-6 lariat ether hydroxamic acid is determined. The efficiency and selectivity for lanthanide ion extraction into chloroform by these proton-ionizable lariat ethers is strongly influenced by the crown ether ring size, lipophilic group attachment site and identity of the acidic function. In general, the lariat ether hydroxamic acids were more efficient and selective lanthanide ion extractants than the corresponding lariat ether carboxylic acids. The ¹H nmr and ir binding studies indicate that both the macrocyclic polyether unit and the proton-ionizable group are involved in lanthanide ion complexation.     

Side arm participation in lariat ether carboxylate-alkali metal cation complexes in solution

Lariat ether carboxylic acids of structure CECH₂OCH₂C₆H₄-2-CO₂H with crown ether (CE) ring sizes of 12-crown-4, 15-crown-5 and 18-crown-6 are prepared and converted into alkali metal-lariat ether carboxylate complexes. Absorptions for the diastereotopic benzylic protons in the ¹H NMR spectra of the complexes in CDCl₃ are utilized to probe the extent of side arm interaction with the crown ether-complexed metal ion as a function of the crown ether ring size and identity of the alkali metal cation.     

Solvent extraction and bulk liquid membrane transport of Co(II) and Ni(II) ammine cations by proton-ionizable crown ethers

Separation efficiencies and selectivities in solvent extraction of Co(II) and Ni(H) ammine cations from aqueous solutions into chloroform and toluene and in transport through bulk toluene membranes by proton-ionizable crown ethers have been determined. Six proton-ionizable crown ethers with differing lipophilicities, polyether cavity sizes and ionizable groups (carboxylic and sulfonic acid functions) were examined. Higher selectivity and efficiency for Co(II) ammine cation extraction was observed for the more lipophilic, proton-ionizable crown ethers. Highly lipophilic crown carboxylic acids provided effective and selective transport of Co(II) ammine cations through bulk toluene membranes.Presented in part at the 6th International Symposium on High Purity Materials in Science and Technology: Preparation, Characterization and Application of Well-Defined Materials, Dresden, GDR, May 1985, Poster D91, Poster Abstracts, pp. 144, 145.All extraction and transport experiments were conducted at this location.     

Transport of alkali metal cations across liquid membranes by crown ether carboxylic acids

Competitive alkali metal transport from an alkaline aqueous source phase through a chloroform phase to an acidic aqueous receiving phase facilitated by nine crown ethers with pendant carboxylic acid groups has been investigated. Transport selectivity is controlled by the size of the polyether cavity of the carrier. Increasing the lipophilicity of the carrier, while maintaining a constant polyether cavity size, enhances the total transport rate but does not affect the selectivity. There is poor agreement between the results of competitive transport and the behavior anticipated on the basis of single cation transport studies.     

Effect of structural variation within sym-(R)dibenzo-16-crown-5-oxyacetic acid resins upon the selectivity and efficiency of alkali-metal cation sorption

Five new crown ether carboxyhc acid resins have been prepared by condensation polymerization of sym-(R)dibenzo-16-crown-5-oxyacetic acids with formaldehyde. Competitive alkali-metal cation sorption by these novel resins, which contain both ion-exchange and crown ether binding sites for metal ions, has been investigated. As the R-group was varied (methyl, ethyl, propyl, butyl, hexyl and decyl) both the alkali-metal cation sorption selectivity and efficiency were affected. The highest efficiency (loading) and Na⁺ sorption selectivity were obtained when R = methyl, ethyl and propyl. The longer alkyl groups were found to be detrimental to both sorption efficiency and selectivity.     

Lead selective lipophilic acyclic diionizable polyethers

A structural series of acyclic polyether dicarboxylic acids with n-butyl and n-tetradecyl alkyl side chains at the alpha-position of the carboxylic acid units, as well as varying lengths of the ethylene glycol ether linkage connecting two benzo units were prepared. In terms of stability constants, competitive solvent extraction and cation transport experiment by bulk liquid membrane toward transition metal ions, ligand 3 with a monoethylene glycol unit and n-butyl side chains provide the best selectivity for the lead ion.     

腙型双冠醚对碱金属的配位性能

本文报道了五个腙型双冠醚的合成。电导测定结果表明含苯并-15-冠-5单元的双冠醚与四苯基硼酸钾、铷、铯,含苯并-18-冠-6单元的双冠醚与四苯基硼酸铯生成2:1夹心型配合物(冠醚单元:金属离子)。并用这些双冠醚的氯仿溶液萃取苦味酸碱金属盐水溶液,测定了萃取百分率和计算了萃取平衡常数,结果表明腙型双冠醚的萃取能力及选择性优于相应的单冠醚。     

Synthesis of a fluorescent 14-crown-4 derivative bearing a proton-dissociable moiety and its use for selective lithium-ion extraction

The fluorescent 14-crown-4 derivative possesses a p-(1,8-naphthalenedicarboxi-mido) phenol moiety as the proton -dissociable fluorophore; its synthesis is described. Highly selective extraction of lithium is achieved with the crown ether, based on a proton/metal ion-exchange mechanism. Extraction is accompanied by significant changes in the absorption and fluorescence spectra of the organic phase. Extraction equilibrium constants for the lithium and sodium ions are evaluated, the Li⁺/Na⁺ selectivity ratio being 200; other alkali metal ions were not extracted. The Li⁺ extraction quenched the fluorescence intensity of the crown ether, in correlation with the initial cation concentration in the aqueous phase.     

Cation exchange properties of crown ether-phosphotungstic acid precipitates

Precipitate formation between phosphotungstic acid and crown ethers is a general phenomenon, producing solids with selective ion exchange behavior for the alkali metal ions. Distribution coefficients for Li⁺, Na⁺, K⁺, and Cs⁺ were measured for a series of these precipitates with different crown ethers. The sorption data are more complicated than for the corresponding phosphomolybdates and indicate a variability in the number of exchangeable sites with H⁺ and M⁺ concentration. The crown ether used markedly affects the cation selectivity of the phosphotungstate precipitates.     

Influence of medium polarity upon selectivity and efficiency of alkali metal cation sorption by polyether carboxylic acid resins

The influence of medium polarity upon competitive sorption of alkali-metal cations from aqueous and aqueous methanolic solutions by the polymethacrylic acid resin Amberlite CG-50, two acyclic polyether carboxylic acid resins, and six sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid resins has been investigated. Addition of methanol was found to strongly depress the selective Li(+) sorption of CG-50 and one of the acyclic polyether carboxylic acid resins. Enhancement of metal ion-crown ether interactions as the percentage of methanol in the medium was increased accentuates the Na(+) sorption selectivity for the lariat ether carboxylic acid resins. The highest Na(+) sorption selectivity was obtained for sym-(alkyl)-dibenzo-16-crown-5-oxyacetic acid resins with ethyl and propyl groups in 80% methanol-20% water.     

Alkali cation binding of polymers with different sized crown ethers and photodimerizable units

The polymers which have different sized crown ethers as alkali cation binding sites and photodimerizable cinnamoyl units were prepared by the cationic copolymerization of corresponding monomers. The crown–cation complexation ratio (1:1 or 2:1) was investigated by measuring quantum yields ? of the photodimerization of the crown-connected cinnamoyl units in the presence of alkali metal chlorides and also by measuring the shift of λ_max of alkali metal picrates in THF on addition of the crown polymers. A significant 1:2 complex formation of alkali cations with two different sized crown ether units in the side chain of the polymers was confirmed. The alkali metal cation binding ability and selectivity of the polymers, which were studied by a method of picrate salts extraction, were markedly different from those expected from the combination of polymers of same ring-size crown ether units. When irradiated with ultraviolet (UV) light, the cinnamic acid ester groups of the polymers caused dimerization even in dilute solutions. The cation binding ability of the polymers was largely enhanced by the photodimerization of the cinnamoyl moieties with suitable template cations.     

Molecular Design of Crown Ethers. 22. Synthesis of Benzocrown Ether Derivatives and Their Solvent Extraction with Univalent／Bivalent Metal Picrates

Three novel benzocrown ether derivatives have been synthesized and their cation binding behavior with uniand bi-valent metal ions was evaluated by the solvent extraction of aqueous metal picrates. The obtained results indicate that the size-fit of crown ether and metal cation, and electron effect of the side arm attached to benzocrown ethers affect their cation binding ability and selectivity.     

Alkali metal cation complexation by 1,3-alternate,mono-ionisable calix[4]arene-benzocrown-6 compounds

Alkali metal cation extraction behaviour for two series of 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds is examined. In Series 1, the proton-ionisable group (PIG) is a substituent on the benzo group of the polyether ring that directs it away from the crown ether cavity. In Series 2, the PIG is attached to one para position in the calixarene framework, thereby positioning it over the crown ether ring. Competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform shows high Cs⁺ efficiency and selectivity. Single-species extraction pH profiles of Cs⁺ for Series 1 and 2 ligands with the same PIG are very similar. Thus, association of Cs⁺ with the calixcrown ring is more important than the position of the PIG relative to the crown ether cavity. Solid-state structures of two unionised ligands from Series 2 are presented. Also described is a crystal containing two different ionised ligand–Cs⁺ complexes.