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.     

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.     

Transport of trivalent lanthanides in a H2O-CHCl3H2O liquid membrane system containing a crown ether carboxylic acid

Neutral crown ethers do not transport trivalent lanthanide cations in a H₂O-CHCl₃-H₂O liquid membrane system. With the addition of a carboxylate group to a macrocyclic polyether, as in the case of sym-dibenzo-16-crown-5-oxyacetic acid, high efficiencies of transporting trivalent lanthanides were observed across the H₂O-CHCl₃-H₂O liquid membrane. The crown ether carboxylic acid also showed significant selectivity for the lanthanides studied in this system.     

Metal ion separations with proton-ionizable crown ethers and their polymers

Abstract

Lipophilic crown ethers with pendent proton-ionizable groups are novel complexing agents for use in metal ion separations by solvent extraction. For a series of structurally related, lipophilic dibenzocrown ether carboxylic acids, the efficiency and selectivity of competitive alkali metal cation extraction for aqueous solution into chloroform is found to be strongly influenced by the crown ether ring size and the lipophilic group attachment site. Reaction of dibenzocrown ether carboxylic acids with formaldehyde in formic acid produces condensation polymers which possess both ion-exchange and cyclic polyether binding sites for metal ion complexation. These resins exhibit excellent exchange kinetics for competitive alkali metal cation sorption from aqueous solution and subsequent stripping and may be used in concentrator columns for the recovery of these metal ions from very dilute aqueous solution. Cation selectivity in the sorption and stripping steps is controlled by the structure of the crown ether monomer unit.     

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.     

Synthesis of new proton-ionizable and neutral macrocyclic,macrobicyclic and macrotricyclic crown compounds containing dibenzo-16-crown-5 units

Fifteen new macrocyclic, macrobicyclic and macrotricyclic crown ether compounds with sym-dibenzo-16-crown-5 units have been prepared. The series includes macrocyclic polyether and bis(crown ether) compounds with proton-ionizable carboxylic or phosphonic acid monoethyl ester groups and bis(crown ether) and macrotricyclic polyether compounds with two sym-dibenzo-16-crown-5 units linked by amide, diamide, or diester functions.     

Retardation of dibenzo polyether-formaldehyde resin formation by alkali-metal cations

Macrocyclic polyethers are well-known complexing agents for alkali-metal and alkaline earth-metal cations. The influence of alkali-metal cations upon the polycondensation rate of acyclic and cyclic dibenzo polyethers with formaldehyde in formic acid and alkali-metal cation sorption by some of the resultant resins have been investigated. For certain dibenzo polyether and alkali-metal cation combinations, polymer formation is markedly reduced. The alkali-metal cation that provides the best fit for the macrocyclic polyether cavity produces the greatest retardation of polymer formation. It is proposed that metal ion complexation renders the dibenzo polyether monomer inert to polymerization under the reaction conditions. No template effect for alkali-metal cation sorption by dibenzo polyether carboxylic acid resins was observed. © 1995 John Wiley & Sons, Inc.     

Separation and Removal of Metal Ionic Species by Polymer Inclusion Membranes

Competitive alkali metal cation transport across polymer inclusion membranes (PIMs) containing sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid carriers provides excellent selectivity for Na⁺ transport with the total fluxes being strongly influenced by the length of the alkyl chain that is attached geminal to the functional side arm in the lariat ether. Removal of chromium(VI) anions by PIMs from acidic aqueous phases was also investigated. Using tri-n-octylamine (TOA) as the ion carrier, Cr(VI) was removed by a PIM to decrease the source phase metal concentration from 1.0 to 0.010 ppm after 30 hours of transport. Competitive transport of Cr(VI) and Cr(III) ions from acidic source phases through PIMs and supported liquid membranes (SLMs) containing TOA and tri-n-octylphosphine oxide (TOPO) as carriers was evaluated and a very high Cr(VI)/Cr(III) separation ratio of 4800 was achieved with a PIM containing TOA. Competitive transport of Zn(II), Cd(II), and Cr(VI) from acidic aqueous solutions through PIMs containing TOA was investigated. The selectivity order for metal ion transport was: HCrO₄ ^–>CdCl₄ ^2–+CdCl₃ ^–>ZnCl₄ ^2–+ ZnCl₃ ^–. Non-contact atomic force microscopy was used to obtain images of the pores in cellulose triacetate membranes containing a plasticizer.     

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.     

冠醚配合物的热力学性质的研究 III. 碱金属离子与18C6甲基衍生物配位反应的电导研究

The coordination reaction of Na+, K+, Rb+ and Cs+ with benzo- 15-crown-5, 18-crown-6 and the newly synthesized cyclic polyethers 2, 3-benzo-8, 15-dimethyl-18-crown-6, 2, 3-benzo-8, 11, 15-trimethyl-18-crown-6 in methanol at 25`C has been studied by conductometric titration. The stability constants for the 1:1 coordination compounds were calculated. The marked selectivity of 18-crown-6 toward alkali metal ions was not found in its methyl derivatives. The induction effect of the benzene ring and methyl group on polyether ring reduced the stability of the coordination compounds. In methanol, the stability sequence of te compounds of alkali metal ions with 18-crown-6 was K+>Rb+>Cs+>Na+, that of its dimethyl derivative was K+>Rb+>Na+>Cs+ and that of its trimethyl derivative was K+>Na+>Rb+>Cs+, that is, the methyl substituent had a weaker influence on the stability of Na+ compound than on that of Rb+ or Cs+ compound. In the range of concentration studied, decrease in equivalent conductance is in agreement with the prediction on the basis of the structure of the complexes. The above results may give a clue for modifying the structure of a crown ether for specified selectivity.     

Extraction of sodium and potassium picrates with 16-crown-5 into various diluents. Elucidation of fundamental equilibria determining the extraction selectivity for Na(+) over K(+)

The constants of the overall extraction equilibrium (K(ex)), the partition for various diluents having low dielectric constants (K(D,MLA)), the aqueous ion-pair formation (K(MLA)), and the dimer formation in CCl(4) of 16-crown-5 (16C5)-alkali metal (Na, K) picrate 1:1:1 complexes were determined at 25 degrees C; the distribution constants of 16C5 were also measured at 25 degrees C. The logK(MLA) of Na and K are 4.14+/-0.19 and 3.05+/-0.28, respectively. The partition behavior of 16C5 and its 1:1:1 complexes with the alkalimetal picrates can be explained by regular solution theory, except for CHCl(3); the molar volumes and solubility parameters of 16C5 and the 1:1:1 complexes were determined. The magnitude of K(ex) largely depends on that of K(MLA). For every diluent, 16C5 always shows Na(+) extraction-selectivity over K(+). The K(MLA) value most contributes to the extraction selectivity of 16C5 for Na(+) over for K(+) among the three fundamental equilibrium constants, the aqueous 1:1 complex-formation constant of 16C5 with the alkali metal ion, K(MLA), and K(D,MLA). Furthermore, correct contributions of a methylene group to distribution constants of organic compounds between diluents of low dielectric constants and water were determined by the distribution constants of 16C5 and 15-crown-5; the additivity of the contributions of functional groups to the partition constant of a crown ether was verified.     

Density Functional Theoretical Investigation of Remarkably High Selectivity of the Cs(+) Ion over the Na(+) Ion toward Macrocyclic Hybrid Calix-Bis-Crown Ether

Density functional theoretical analysis was performed to explore the enhanced selectivity of the Cs(+) ion over the Na(+) ion with hybrid calix[4]-bis-crown macrocyclic ligand compared to 18-crown-6 ether. The calculated selectivity data for Cs(+)/Na(+) with hybrid calix[4]-bis-crown ligand using the free energy of extraction employing thermodynamical cycle was found to be in excellent agreement with the reported solvent extraction results. The present study further establishes that the selectivity for a specific metal ion between two competitive ligands is primarily due to the complexation free energy of the ligand to the metal ions and is independent of the aqueous solvent effect but strongly depends on the dielectricity of the organic solvents and the presence of the coanion.     

Extraction of sodium and potassium picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (lariat 16C5) into various organic solvents. Elucidation of fundamental equilibria which determine the extraction ability for Na(+) and K(+) and the selectivity

To quantitatively elucidate the effects of the side chains and diluents on the extraction selectivity for sodium and potassium picrates of 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L16C5) from the viewpoint of equilibrium, the constants for the overall extraction (K(ex)), the partition for various diluents of low dielectric constants (K(D,MLA)), and the aqueous ion-pair formation (K(MLA)) of L16C5-sodium and -potassium picrate 1:1:1 complexes were determined at 25 degrees C; the distribution constants of L16C5 were also measured at 25 degrees C. The log K(MLA) values for Na(+) and K(+) are 2.74+/-0.29 and 1.70+/-0.36, respectively. In going from 16-crown-5 (16C5) to L16C5, the side chains decrease the K(MLA) value, but do not increase the difference in K(MLA) between Na(+) and K(+). The distribution behavior of L16C5 and its 1:1:1 complexes with the alkali metal picrates closely obeys regular solution theory, except for chloroform. Molar volumes and solubility parameters of L16C5 and the 1:1:1 complexes were determined. The magnitude of K(ex) is mainly governed by the K(M(L16C5)A) value. For every diluent, L16C5 shows Na(+) extraction selectivity over K(+). The Na(+) extraction selectivity of L16C5 is determined completely by K(M(L16C5)A). The extraction ability and selectivity for sodium and potassium picrates by L16C5 are compared with those of 16C5 on the basis of the fundamental equilibrium constants.     

Effect of solvent upon competitive liquid-liquid extraction of alkali metal cations by isomeric dibenzo-16-crown-5-oxyacetic acids

The selectivity and efficiency of competitive liquid-liquid extraction of alkali metal cations into organic solvents containingsym-(octyl)dibenzo-16-crown-5-oxyacetic acid (2) andsym-bis[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid (3) have been determined. Solvents examined include: dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,1-trichloroethane, benzene, toluene,p-xylene, chlorobenzene, 1,2-dichlorobenzene, and 1,2,3,4-tetrahydronaphthalene. The Na⁺/K⁺ and Na⁺/Li⁺ extraction ratios are highest in chloroform. The extraction selectivity is found to correlate with the diluent parameter (DP) of the organic solvent.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Substitution effect,absorption, and fluorescence behaviors of 11,12-benzo-1,7,10,13-tetraoxa-4-aza- cyclopentadec-11-ene (benzoaza-15-crown-5) derivatives upon cation complexation in solvent extraction

Substitution effect, absorption, and fluorescence behaviors of some benzoaza-15-crown-5 derivatives upon cation complexation in solvent extraction were studied. The introduction of a substituent on the nitrogen atom in benzoaza-15-crown-5 enhanced extractabilities in the solvent extraction of aqueous alkali metal picrates. The nondonating substituents raised the cation selectivity for Na(+) over K(+), but the donating substituents reduced the cation selectivity. The absorption and fluorescence spectral behavior was different with the alkali metal cations.     

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.     

Polyurethane foam extraction of platinum-tin halide complexes

The sorptive capacity of the polyether-based foam was determined to be between 0.85 and 0.92 moles/kg for the platinum-tin(II) chloride complex. At hydrochloric and hydrobromic acid concentrations up to 3.0M, the platinum-tin(II) bromide complex had higher extraction efficiencies than the platinum-tin(II) chloride complex. Sorptions were optimized at 5.0M hydrochloric acid and 3.0M hydrobromic acid and distribution ratios as high as 2.0 x 10(5) 1./kg were observed at high foam:platinum ratios. The percent of platinum extracted increased when the alkali metal cations are added in the order K(+) < Na(+) < Li(+) for polyether foam, and decreased in the order K(+) > Na(+) > Li(+) for polyester foam. Also, the sorption efficiencies increased as the proportion of poly(ethylene oxide) of the foam was increased. A Scatchard plot analysis shows that there is a 2:1 ratio of loosely bound platinum to tightly bound platinum with the polyether foam, however, the experimental results are consistent with a weak-base anion exchange mechanism as the prominent method of sorption. For polyester foam, results are consistent with a solvent-like ion-pair sorption mechanism.     

Potentiometric Selectivities of Dibenzo-16-crown-5 Compounds for Alkali and Alkaline Earth Metal Cations and Ammonium Ions

Potentiometric selectivities toward alkali and alkaline earth metal cations and ammonium ions are utilized to probe the complexation of these cationic species by dibenzo-16-crown-5 lariat ethers. Attachment of one or two pendant groups to the central carbon of the three-carbon bridge in dibenzo-16-crown-5 markedly alters the potentiometric responses of the ionophores when incorporated in solvent polymeric membrane electrodes. Results obtained for dibenzo-16-crown-5 compounds with coordinating side arms containing ether, carboxylic acid, ester, and amide groups provide insight into the role of the side arm in metal ion complexation by lariat ether compounds.     

Probing ionophore selectivity in argon-tagged hydrated alkali metal ion-crown ether systems

Crown ethers are an important family of compounds that are closely related to naturally occurring ionophores. Thus, crown ethers are useful in modeling the size-selective behavior of ionophores. Using a combination of infrared predissociation spectroscopy and density functional theory calculations, we have investigated M(+)(18-crown-6 ether)(H(2)O)(1-4) Ar complexes, where M = Li, Na, K, Rb and Cs in the gas phase. The argon-tagging technique was used to lower the internal energies (effective temperatures ~100 K), yielding well-resolved spectra in the OH stretching region for systems containing up to three waters. Spectral changes were monitored as both the size of the ion and degree of hydration were varied. While there is not a particular spectroscopic signature of gas-phase selectivity reported in this work, the unique role that K(+) plays in the systems studied, as a "bridge" between the smaller and larger alkali metal ions, is consistent with the well-known special affinity for K(+) by 18-crown-6 ether in the aqueous phase.     

Template-assisted self assembly of two lipophilic polyion aggregates derived from sodium tetraphenyl imidodiphosphinate-complexes containing sodium ions in four different coordination environments

The molecular structures of two lipophilic polyion aggregates derived from tetraphenyl imidodiphosphinate are described: [Na(crown ether)][MNa(2)[Ph(2)P(O)NP(O)Ph(2)](4)] with crown ether = 15-crown-5 for 1and benzo-15-crown-5 for (M = Na(+) for 1 and Na(H(2)O)(+) for 2).