Presence Of Crown Ether Research Articles

New polymer architectures: Recent results with polyrotaxanes

AbstractRecent results from our laboratory have shown that the formation of polyester and Polyurethane rotaxanes by polymerization in the presence of crown ethers is driven by hydrogen bonding of the OH groups with the oxygen atoms of the macrocycles. Here we summarize these findings. Then we describe the application of this type of self assembly for the production of polyrotaxanes by threading preformed macromolecules and for the controlled synthesis of branched and crosslinked systems. These latter protocols comprise a new and novel way to prepare mechanically linked, elastomeric materials. Rheological properties of main chain polyrotaxanes are compared to simple linear backbones; the rotaxanes display higher intrinsic viscosities and lower melt viscosities, reflecting larger hydrodynamic volumes and less entanglement, respectively; these are potentially useful aspects in terms of processability of this new class of polymeric materials.

Influence of Crown Ethers and Macrocyclic Kryptands upon the Percolation Phenomena in AOT/Isooctane/H2O Microemulsions

The influence of several additives upon the properties of the system AOT/isooctane/water has been investigated. The presence of crown ethers (18-crown-6) and kryptand complexes (kryptand 222, kryptand 221 and kryptand 211) have an important effect upon the electrical percolation phenomena. Low macrocyclic concentrations hinder the electrical percolation phenomenon. This effect seems to be due to the ability of macrocycles to complex ions and transfer them to the interface. Medium and high macrocyclic concentrations favor the electrical percolation, and this effect is related to their interfacial association to the AOT head groups. The observed behavior has been explained in terms of critical packing parameter, and it is compared with the influence of small additives as electrolytes or small organic molecules.

Studies of the Formation of Poly(ester rotaxane)s from Diacid Chlorides, Diols, and Crown Ethers and Their Properties

The formation of poly(alkylene sebacate−crown ether pseudorotaxane)s by condensation of linear alkylene diols and sebacoyl chloride in the presence of crown ethers in the neat state has been studied. It was found that the average number of crown ether molecules per repeat unit in the polypseudorotaxane was a function of (a) the ring size and (b) the stoichiometric ratio of macrocycle to diol but independent of (i) the equilibration time of the diol and crown ether prior to addition of the diacid chloride, (ii) the length of the diol, and (iii) the temperature of equilibration and polycondensation. All of these observations are consistent with the involvement of hydrogen bonding between the diol and the crown ether as a driving force for threading, except the lack of temperature dependence. Dethreading of the isolated polypseudorotaxanes was shown to be extremely slow. Therefore, it was reasoned that the lack of temperature dependence was due to dethreading during the polymerization, inasmuch as once the ester bond has formed there is no strongly attractive force between the linear and cyclic species and the low molecular weights of the growing oligomeric esters would permit relatively facile dethreading. Based on this idea, a bulky tetraphenylmethane-based bisphenol was employed to make a copolymer (1:4) with 1,10-decanediol; indeed, the purified polyrotaxane contained more than twice as much crown ether as the polypseudorotaxane from the linear diol, confirming that dethreading does occur during the polymerization process. The polyrotaxanes all were capable of extracting metal ions from aqueous solutions. In the cases with high loadings of crown ether two distinct crystalline phases were detected by DSC: one due to the polyester backbone and one due to the crown ether; glass transitions were also observed for the crown ether component of the polyrotaxanes. Polyrotaxanes possess higher intrinsic viscosities than the backbone polymers of the same molecular weight due to increased hydrodynamic volume brought about by the macrocyclic components. However, differential solvation of the backbone and cyclic components of the polyrotaxanes was demonstrated; the intrinsic viscosity of the polyrotaxane decreased in a good solvent for the crown ether. The temperature dependence of the melt viscosity of a polyrotaxane was essentially the same as that of the polyester model backbone, but the absolute melt viscosity was much lower due to reduced chain entanglement.

Selective Dealkylations of Alkyl Aryl Ethers in Heterogeneous Basic Media under Microwave Irradiation.

Ethyl isoeugenol and 2-ethoxyanisole could be selectively deethylated using potassium t-butoxide in the presence of crown ether under solvent-free conditions. By addition of ethylene glycol, selectivity was reversed to demethylation. In both cases, strong enhancements were observed under focused microwaves. © 1997 Published by Elsevier Science Ltd.

Synthesis of F−-containing LTA-type GaPO4 in the presence of crown ethers as organic templates

The use of crown ethers as templating agents in the system Ga2O3-P2O5-HF-H2O was investigated. The LTA-type gallophosphate could be obtained in the presence of the K+ 18-crown-6 ether complex and with aza-crown ethers (Kryptofix 22 and Kryptofix 222). These crown ethers are occluded in the structure (8 molecules per unit cell). The products were characterized by elemental analysis, SEM, XRD and solid-state NMR spectroscopy.

SYNERGISTIC SOLVENT EXTRACTION OF TRIVALENT LANTHANIDES WITH MIXTURES OF 3-PHENYL-4-BENZOYL-5-ISOXAZOLONE AND CROWN ETHERS

ABSTRACT Synergistic solvent extraction of trivalent lanthanides such as Nd, Eu and Tm has been studied using mixtures of 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and 18-crown-6; 15-crown-5, benzo-15-crown-5, or dibenzo-18-crown-6. The results demonstrate that these trivalent metal ions are extracted into chloroform as Ln(PBI)3 with HPBI alone and as Ln(PBI) 3. CE in the presence of crown ethers (CE). The equilibrium constants of the above species are found to increase monotonically with the decreasing ionic radii of these trivalent lanthanides. The addition of a crown ether to the metal chelate system significantly enhances the extractability of these trivalent metal ions.

30] High-performance liquid chromatographic determination of biotin in biological materials after crown ether-catalyzed fluorescence derivatization with panacyl bromide

This chapter aims to quantify biotin by high-performance liquid chromatography (HPLC) after precolumn derivatization of the carboxylic group with fluorescent panacyl bromide [ p -(9-anthroyloxy)phenacyl bromide] in the presence of crown ether. The analytical procedure should be applicable to biological samples containing biotin in picomolar amounts and in free as well as protein-bound form. To characterize the panacyl esters of biotin and dethiobiotin, 1 H nuclear magnetic resonance (NMR) spectra of the derivatization product is recorded. The substances are dried under a nitrogen stream and subsequently dissolved in [ 2 H]chloroform. From the spectra of the panacyl esters of biotin and dethiobiotin, it could be concluded that only the carboxylic function of biotin participates in the formation of the panacyl ester whereas the amide functions of the molecule could still be detected at 5.8 and 6.3 ppm. Both reversed-phase and normal-phase HPLC are well suited to achieve complete separation of the panacyl esters of biotin and dethiobiotin within 7 min. The fluorescence maxima of both derivatives are found to be 380 and 470 nm for excitation and emission wavelengths, respectively, in both mobile phases.

Silicon and Aluminum Ordering in Frameworks of FAU and EMT Aluminosilicate Zeolites Crystallized in the Presence of Crown Ethers

The siting pattern of Si and Al atoms in the frameworks of a FAU zeolite, an EMT zeolite, and a FAU/EMT structural intergrowth crystallized in presence of 15-crown-5 ethers and 18-crown-6 ethers and with an Al/(Si+Al) ratio of 0.217 is determined using a combination of 29Si MAS NMR and model generation by computer algorithm. In the three zeolite samples, the Si(nAl) distributions determined with 29Si MAS NMR are very similar. They are compared with hypothetical distributions in computer-generated models of framework fragments comprising 1440 T-atoms. The model building starts from a pure silicon dioxide framework. The appropriate number of Al atoms are substituted for Si, one atom at a time, according to selection rules with a physical basis. A model of random Al siting obeying the Löwenstein rule is in disagreement with the experimental Si(nAl) distribution. A framework model that allows one to fit the experimentally obtained 29Si MAS NMR spectra takes into account the position of the crown ether molecules in the zeolite cavities and allows Al-enrichment in the six-membered rings perpendicular to 111CUB or 001HEX crystallographic directions and Si-enrichment in the remaining T-sites, which are in positions near the hydrophobic ethane bridges of the crown ether molecules. This model classifies different sets of the 12-membered rings as siliceous or aluminum-rich and consequently explains the experimentally observed anomalous population of sodium cations at the different cation sites in sodium-exchanged samples.

Synthesis and characterization of high-silica EMT and FAU zeolites prepared in the presence of crown-ethers with either ethylene glycol or 1,3,5-trioxane

EMT- and FAU-type zeolites were prepared by using a mixture of organic molecules, i.e., crown-ether + ethylene glycol or crown-ether + 1,3,5-trioxane. The products were characterized by elemental analysis, XRD, SEM, thermal analysis, n-hexane adsorption, and n.m.r. spectroscopy. Depending on the method used to prepare the starting gel, the solids obtained showed different characteristics. D.t.a. proved to be a good tool to determine, from the thermal decomposition of the organic templates the presence of structure defects in the EMT and FAU samples.

ＦＡＢ質量スペクトルを用いる競争的条件下でのクラウンエーテル錯形成現象の解析

Complexation behavior of crown ethers with lithium and sodium ions under competitive conditions has been assessed by use of FAB mass spectrometry and shown to correlate with the results obtained in the competitive transport experiments in presence of crown ethers and phosphoric acid esters. The FAB/MS technique gave information about competitive complexation by using relatively small quantities of the ligands.

On the formation of permethylcyclopolysilanes in the w�rtz-type reaction of Me2SiCl2: The influence of solvent and complexing agent

Permethylcyclopolysilanes are most often prepared by Wurtz-type coupling of Me2SiCl2 with Na K alloy in THI: When nonpolar solvents like benzene were used, only linear polysilanes (Me2Si)n were produced, but the addition of a catalytic amount of crown ether 18-crown-6 was found to increase significantly the amount of cyclic oligomers. The ratio of (Me2Si)6 to (Me2Si)5 decreased from 18:1 to 6:1 in the presence of crown ether in a typical synthesis in THF. An explanation based on solvated electron theory has been proposed.

Molecular recognition by artificial receptors

Abstract

Effect of Solvent on the Complexation and Thermal Stability of Benzenediazonium Tetrafluoroborate in the Presence of Crown Ethers.

Effect of Solvent on the Complexation and Thermal Stability of Benzenediazonium Tetrafluoroborate in the Presence of Crown Ethers.

Simultaneous determination of Zn(II) and Ni(II) in the presence of crown ether by dc polarography

The simultaneous determination of Zn(II) and Ni(II) was studied in the presence of a crown ether by dc polarography. Addition of this reagent caused the difference in the halfwave potentials between the two ions to increase from 0.01 to 0.34 V. The relationship between the concentration of the ion and the wave current was linear for both ions, which suggests the feasibility of a simultaneous determination of Zn(II) and Ni(II) in the presence of a crown ether.

Hydrosilylation of carbonyl compounds catalysed by alkali metal fluorides in the presence of crown ethers

Hydrosilylation of the C=O bond with dimethylphenylsilane proceeds readily in low-polarity solvents (dichloromethane, benzene, THF) in the presence of the catalytic pair MF/18-crown-6 (M = Cs, Rb, K), with caesium and rubidium fluorides being the most active. Using the CsF/18-crown-6 pair, the hydrosilylation of a number of aromatic and heteroaromatic aldehydes and ketones has been carried out. Silyl ethers of the corresponding alcohols have been prepared in good yields.

Generation and Trapping of Cyclopropenes from 2-Alkoxy-1,1-dichlorocyclopropanes

In presence of crown ether, 2-alkoxy-1,1-dichlorocyclopropanes react with t-BuOK/THF preferentially via ring opening to 2-chloroalk-2-en-1-ones and alkynones or to chlorocyclopropenes. The latter may be intercepted with 1,3-diphenylisobenzofuran, but in the absence of trapping agent, the rearrangement to vinylcarbenes does not occur.

An Efficient Procedure for the 1-Alkylation of 2-Nitroimidazoles and the Synthesis of a Probe for Hypoxia in Solid Tumours

The N-alkylation of 2-nitroimidazole through its 'naked' anion, formed from its alkali metal salts in the presence of crown ethers and in homogeneous solution, is shown to be a useful preparative procedure. The reactions of α,ω-dihaloalkanes can be controlled to afford either the mono- or diheteroarylalkane. The procedure has been used to alkylate theophylline and to prepare a compound of use as a probe to identify, locate and quantify hypoxia in sections from solid tumours.

Rapid synthesis of radiolabeled phenylethanolamine

AbstractA method for the rapid synthesis of [14C]‐phenylethanolamine (PEOH) amenable to the preparation of [11C]‐PEOH was developed under anhydrous conditions. Reaction of benzaldehyde with [14C]‐NaCN in the presence of crown ethers in THF yielded [14C]‐cyanohydrin which was reduced to [14C]‐PEOH with borane in the same solvent. The overall chemical and radiochemical yields were 33%.

ChemInform Abstract: Phase‐Transfer of Potassium Hydroxide into Toluene in the Presence of Crown Ethers.

ChemInform Abstract: Phase‐Transfer of Potassium Hydroxide into Toluene in the Presence of Crown Ethers.

A kinetic study of acetoxylation of benzyl chloride—a model of activated allylic chlorides in PVC—using a crown ether complex

AbstractBenzyl chloride has been used in a kinetic study of chlorine replacement by acetoxy groups to model the behaviour of allylic chlorine during the acetoxylation of poly(vinyl chloride). Chlorine substitution was carried out in tetrahydrofuran at 30°C using a potassium acetate‐crown ether complex with methanol to ensure homogeneous solution. The process followed an SN2 mechanism. The orders of reaction with respect to benzyl chloride and potassium acetate were close to one, and the second order velocity constant was 4.2 x 10−5 litre mol−1 s−1 when the molar ratio of crown ether to potassium acetate was approximately unity. Higher ratios caused a slight increase in rate constant. Substitution was followed by NMR spectroscopy which also revealed a proton exchange between methanol and acetate anion with an equilibrium constant 9.4 x 10−2. This observation has suggested an explanation for the effect of some free‐radical inhibitors on the rate of acetoxylation of poly(vinyl chloride) by potassium acetate in the presence of crown ether.