Synthesis of monoazacrown ethers under phase-transfer catalysis

A procedure has been proposed for the synthesis of monoazacrown ethers by reaction of N-benzyldiethanolamine with oligo(ethylene glycol) bis-p-toluenesulfonates in a two-phase system aromatic hydrocarbon-50% aqueous alkali, followed by removal of the benzyl group by catalytic hydrogenolysis. The maximal yields of N-benzylaza-12-crown-4, -18-crown-6, and -21-crown-7 were achieved by adding 4?C10 equiv of LiCl, BaBr₂, and CsCl, respectively, to the reaction mixture, which probably indicated template effect.     

Partial molar volumes of organic solutes in water. XXVI. 15-Crown-5 and 18-crown-6 ethers at temperatures (298 to 573) K and pressures up to 30 MPa

Densities of dilute aqueous solutions of two cyclic ethers, viz. 15-crown-5 and 18-crown-6, measured over the temperature range from (298 to 573) K and at pressures up to 30 MPa using an automated flow vibrating-tube densimeter are reported. Standard molar volumes were evaluated from the measured data. Present data were combined with those obtained previously for several cyclic ethers and predictions of standard molar volumes based on group contribution approach were tested and analysed.     

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ligands: synthesis and high divalent metal ion extraction selectivity

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ethers in the cone conformation are synthesized with their conformation and regioselectivity verified by NMR spectroscopy. The new ligands are efficient extractants with high selectivity for Ba²⁺ in competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform.     

A Polarographic Study on Some Complexes of Pb2+ and Cd2+ with Macrocyclic Polyethers (Crown Ethers)

Abstract

Complexation constants of Pb²⁺ and Cd²⁺ nitrates with five crown compounds (18-crown-6, dicyclohexyl-18-crown-6, benzo-15-crown-5, dibenzo-24-crown-8 and 12-crown-4), have been determined by d.c. and a.c. polarographic measurements in aqueous medium using 0.1 M HNO₃ as supporting electrolyte. The complexes of lead with 18-crown-6 and dicyclohexyl-18-crown-6 are very stable which may be attributed to the partially covalent bonds formed by this metal ion.     

A polarographic study of some complexes of Tl(I) with polyoxa macrocyclic ligands

The log β₁ values at 25° for the reaction in aqueous solution of Tl(I) with 15-crown-5, benzo-15-crown-5, 18-crown-6 and dicyclohexyl-18-crown-6 (isomer cis-syn-cis) have been determined by d.c. and a.c. polarographic measurements.     

Polarographic Eiectroreduction of Some Complexes of Uranium with Macrocyclic Polyethers

Abstract

The polarographic behaviour of uranium(VI) in aqueous C. 1 N nitric acid medium, in the presence of some polyoxa macrocyclic ligands (15-crown-5, benzo-15-crown-5, 18-crown-6, dicyclohexyl-18-crown-6), at 25°C, was investigated. Both in the absence and in the presence of the polyoxa macrocyclic ligands, the reduction of hexavalent uranium in aqueous medium takes place in two steps, each of which involving the transfer of an electron. Under diffusion-controlled conditions, the two steps of the reduction in acid medium proceed reversibly. The results of the polarographic measurements enabled to estimate the ratio of the stability constants of the complex ions of U(111) and of U(IV) with macrocyclic polyethers.     

Volume Changes on Complex Formation of 18-Crown-6 with Amino Acids in Aqueus Solutions

The densities of 18-crown-6-water and 18-crown-6-amino acid-water solutions at 298.15 K were determined. These values were used to estimate the partial molar volumes of 18-crown-6 in water and 0.15 M aqueous solutions of amino acids, as well as the volumes of transfer of 18-crown-6 from water to aqueous solutions of amino acids. The interaction of 18-crown-6 with amino acids involves H bonds and electrostatic forces. A conclusion was drawn that the nature and arrangement of side groups in amino acids affect their complex formation with the crown ether.     

Extraction of strontium from nitric acid solutions by selected crown ethers

The extraction of Sr from nitric acid solutions by the crown ethers, 12-crown-4, 15-crown-5, 18-crown-6 and DB 18-crown-6 dissolved in chloroform has been investigated. Sr is reasonably well extracted by 18-crown-6 compared to other crown ethers from different nitric acid solutions. The extraction is strongly dependent on the concentration of HNO₃ and nitrate salts. Preliminary studies indicate that¹³⁷Cs is also extracted to a limited extent by 18-crown-6 from nitrate medium. Stripping of Sr was achieved by an aqueous solution of low acidity, the crown ether being regenerated for subsequent extraction.     

Effect of the Type of Glycosidic Linkage on the Selective Interactions of Maltose and Cellobiose with Some Crown Ethers in Dilute Aqueous Solutions

Titration calorimetric and densimetric measurements have been applied to study the selective interactions of two disaccharides composed of two glucose units, maltose and cellobiose, with 15-crown-5 and 18-crown-6 in dilute aqueous solutions. Maltose and cellobiose form thermodynamically stable complexes with different stoichiometries with 18-crown-6 but not with 15-crown-5. The obtained results are explained by the different states of the disaccharides in aqueous solution due to effect of the type of linkage between glucose units     

Inclusion [2]complexes based on the cryptand/diquat recognition motif

Seven diquat-based inclusion [2]complexes were studied by proton NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray analysis. The hosts used in these inclusion [2]complexes are bis(5-hydroxymethyl-1,3-phenylene)-32-crown-10, a bis(m-phenylene)-26-crown-8-based cryptand, and five bis(m-phenylene)-32-crown-10-based cryptands. Bis(m-phenylene)-32-crown-10-based cryptands have been proved to be able to complex diquat much more strongly than bis(m-phenylene)-32-crown-10 itself and one containing a pyridyl moiety has one of the highest K_a values reported to date. These hosts form 1:1 complexes with diquat in solution and in the solid state. It was found that the improved binding from bis(m-phenylene)-32-crown-10 to bis(5-hydroxymethyl-1,3-phenylene)-32-crown-10 was due to a supramolecular cryptand structure formed by chelation of the two terminal OH moieties of bis(5-hydroxymethyl-1,3-phenylene)-32-crown-10 with a water molecule as a hydrogen-bonding bridge.     

A PGSE diffusion and electrophoretic NMR study of Cs+ and Na+ dynamics in aqueous crown ether systems

Multinuclear pulsed gradient spin-echo (PGSE) NMR diffusion and linewidth measurements were used to probe binding and transport in aqueous Na+-15-crown-5, Na+-18-crown-6, Cs+-15-crown-5 and Cs+-18-crown-6 systems. Since direct PGSE observation of many alkali cations is precluded by either low inherent sensitivity or rapid relaxation (or both), the feasibility of proton-detected electrophoretic NMR (ENMR) measurements to complement PGSE data was investigated. ENMR measurements were performed on aqueous Cs+-, Li+-, Na+-, K+-, and Rb+- 18-crown-6 systems. The data analysis is based on a two-site binding model and its corresponding association constants. Cs+ was found to bind considerably more tightly to 18-crown-6 (K=8 M-1) than to 15-crown-5 (K approximately 2 M-1), whereas Na+ had almost equal affinity (K approximately 4.5 M-1) for 15-crown-5 and 18-crown-6. The difficulties encountered in analysing the NMR parameters, methodological limitations and the implied need for more complicated binding models are discussed.     

Luminescent terbium(III) complexes with pendant crown ethers responding to alkali metal ions and aromatic antennae in aqueous solution

The luminescence lifetime of TbL2 with a pendant 15-crown-5 increased by 65% to 2.95 ms with an [Na+] concentration of 0.13 M in aqueous solution; the maximum amplification of the luminescence intensity of TbL1 containing aza-15-crown-5 reached a factor of 47 upon addition of the aromatic antenna p-chlorobenzoate 1.     

Di-ionizable calix[4]arene-1,2-crown-5 and -crown-6 ethers in cone conformations: synthesis and divalent metal ion extraction

Two series of di-ionizable calix[4]arene-1,2-crown-5 and -crown-6 ethers in cone conformations are synthesized. The ionizable groups are oxyacetic acid moieties and N-(X)sulfonyl oxyacetamide units with X=methyl, phenyl, 4-nitrophenyl, and trifluoromethyl, which ‘tunes’ their acidity. For competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform, the new ligands with N-(X)sulfonyl carbamoyl groups are efficient extractants with Ba²⁺ selectivity. On the other hand, the dicarboxylic acid analogues exhibit little selectivity in extraction of alkaline earth metal cations. For single species extractions of Pb²⁺, the ligands with both types of ionizable groups show very good extractions abilities. In single species extractions of Hg²⁺, the N-(X)sulfonyl carboxamide ligands are highly efficient, in contrast to the dicarboxylic acid compounds. Influences of the ionizable group identity, the crown ether ring size, and the presence of upper-rim p-tert-butyl groups on divalent metal ion extraction are explored.     

The Effect of Crown Ethers on the Oxidation of Triethylamine by Ferricyanide Ion in Aqueous Solutions at Different pH Values

The effect of benzo-15-crown-5,15-crown-5 and 12-crown-4 on the oxidation of triethylamine by aqueous ferricyanide ion has been studied at pH 4, 7 and 11. The crown ethers retard the normal oxidation process at all pH values, the effect depending on the crown ether concentration. The three crown ethers show the same retardation effect at pH 4 and 7, while at pH 11 the retardation decreases in the order B15C5 > 12C4 > 15C5.     

Excess enthalpies and apparent molar volumes of aqueous solutions of crown ethers and cryptand(222) at 25°C

The enthalpies of dilution and densities of aqueous solutions of 12-crown-4, 15-crown-5, 18-crown-6, 1,10-diaza-18-crown-6 and cryptand (222) were measured at 25°C. The excess enthalpies and enthalpic coefficients of solute-solute interactions were calculated by the McMillan-Mayer theory formalism. Values for the apparent molar volumes at infinite dilution were determined by extrapolation. The contributions of the-CH₂CH₂O-group to values of h₂ and to the limiting partial molar volume were calculated for the series of crown ethers studied. It is concluded that the hydrophobic hydration and the hydrophobic solute-solute interaction are predominant in the solutions investigated.     

Extraction of some lanthanides by nitrobenzene solutions of dicarbolide in the presence of 18-crown-6

The extraction of¹⁴⁴Ce and^152,154Eu microamounts by nitrobenzene solutions of bis-1,2-dicarbollylcobaltate in the presence of 18-crown-6 from aqueous solutions of nitric acid has been investigated. The protonisation constants of 18-crown-6 in water and in nitrobenzene were determined and the corresponding equilibrium constants for cerium and europium extraction were evaluated.     

Thermodynamics of complexation of aqueous 18-crown-6 with potassium ion: apparent molar volumes and apparent molar heat capacities of aqueous 18-crown-6 and of the (18-crown-6 + potassium chloride) complex at temperatures (278.15 to 393.15) K, at molalities (0.02 to 0.3) mol · kg, and at the pressure 0.35 MPa

We have measured the densities at temperatures T = (278.15 to 363.15) K and heat capacities at T = (278.15 to 393.15) K of aqueous solutions of 18-crown-6 and of (18-crown-6 + KCl) at molalities m = (0.02 to 0.3) mol · kg⁻¹ and at the pressure 0.35 MPa. We have calculated apparent molar volumes V_? and apparent molar heat capacities C_p,? for 18-crown-6(aq), and we have applied Young’s Rule and have accounted for chemical speciation and relaxation effects to resolve V_? and C_p,? for the (18-crown-6: K⁺,Cl⁻)(aq) complex in the mixture. We have also calculated estimates of the change in volume Δ_rV_m, the change in heat capacity Δ_rC_p,m, the change in enthalpy Δ_rH_m, and the equilibrium quotient log Q for formation of the complex at T = (278.15 to 393.15) K and m = (0 to 0.3) mol · kg⁻¹.     

Evolution of Organized Lariat Ether Alcohol and Diol Hydrate Macrostructures in the Solid State

Lariat ether alcohols and diols derived from dibenzo-14-crown-4crystallize in the anhydrous form or as hydrogen-bondedmonohydrates or networks depending upon thepolyether ring substitutents and the composition of the aqueous organic crystallization solvent. Supramolecular structures are created when the lariat ether alcohol sym-(hydroxy)dibenzo-14-crown-4 (1) with ``sticky ends' of ether oxygens and hydroxyl protons, hydrogen bond to each other via bridging water molecules to form three-dimensional networks. For crystallization of 1 from 30% aqueous acetonitrile, this self-association is sufficiently strong to spontaneously generate a supramolecular structure with water channels.     

Structures of 18-crown-6, 15-crown-5 and their metal complexes in methanol solution as studied by Raman spectroscopy

Raman spectra of 18-crown-6, 15-crown-5, and their complexes with Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺ and Ba²⁺ have been investigated in methanol solution. Normal coordinate calculations are presented for the D_3d⁻ and C_i-symmetric structures of 18-crown-6. Analysis of the Raman spectra gives information on the ring conformations of the crown ethers and the stoichiometry of complexation. The uncomplexed ethers adopt diverse conformational states in methanol at room temperature, the D_3d state being the most stable in 18-crown-6 and various states equally stable in 15-crown-5. Most of the cations form 1:1 or 2:1 crown—metal complexes depending on the cation size relative to the hole size of crown. Exceptionally, Cs⁺ forms both 1:1 and 2:1 complexes with 18-crown-6. The ring structures in complexes of 18-crown-6 are not much distorted from the D_3d one, though the distortion is rather large in the 2:1 Cs²⁺ and 1:1 Ca⁺ complexes. Complexes of 15-crown-5 exhibit for types of ring structure depending on the size and charge of the cation. These structures are likely to involve distortion from the gauche or gauche′ conformation about the CC bonds and various conformation about the CO bonds.     

Ion-pair extraction of tetravalent plutonium from hydrochloric acid medium using crown ethers

Ion-pair extraction behaviour of plutonium (IV) from varying concentrations of HCl solution was studied employing crown ethers (benzo-l5-crown-5 (B15C5), 18-crown-6, (18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6, (DC18C6), dibenzo-24-crown-8 (DB24C8) and dicyclohexano-24-crown-8 (DCH24C8)) in nitrobenzene as the extractant. Ammonium metavanidate was used as the holding oxidant in the aqueous phase and the conditions necessary for the quantitative extraction of the tetravalent ion were found. The co-extraction of species of the type [HL⁺].[HPu(Cl) ₆ ^– ] and [HL⁺]2·[Pu(Cl) ₆ ^2– ] as ion-pairs (where L represents the crown ether) is suggested.