Crown ether, alkali metal

Onium salts, crown ethers, alkali metal salts or similar chelated salts, quaternary ammonium and phosphonium are some of the salts which have been widely used as phase transfer catalysts (PTC). The choice of phase transfer catalysts depends on a number of process factors, such as reaction system, solvent, temperature, removal and recovery of catalyst, base strength etc. 

Crown Ether/Alkali Metal Base Catalysts. 155... 

McPhee, M. M. Kern, J. T. Hoster, B. C. Kerwin, S. M, (2000) Propargylic sulfone-armed lariat crown ethers alkali metal ion-regulated DNA cleavage agents Bioorg. Chem. 8, 98-118. 

The dicyanophosphide(l-) ion was first prepared by reduction of P(CN)3. It is more conveniently obtained from white phosphorus in a nucleophilic disproportionation by an ammonium, phosphonium, or crown ether alkali metal cyanide. ... 

Bribre, K.M. Detellier, C. Metal interchange of crown ether-alkali metal cation complexes in solution. Li Nuclear magnetic resonance study of the exchange kinetics of lithium 15-crown-5 and lithium monobenzo-15-crown-5 in nitromethane. J. Phys. Chem. 1992. 96 (5), 2185-2189. 

The TCID method was systematically used to examine crown ether-alkali-metal-ion (Li+-Cs+) complexation energies (Table For comparison with the tetra- to hexadentate crown ethers, binding data were also determined for smaller ethers, that is, monodentate dimethylether (DME) and bidentate dimethoxyethane (DXE). In solution, each crown ether binds most strongly to that alkali cation which fits best into the crown s cavity. For example, K+ is most strongly bound to 18-crown-6, while Na prefers 15-crown-5. With the gas-phase data in hand, the vahdity of this best fit model can be tested under environment-free conditions. 

Membranes with steric recognition Layers with intermolecular channels Calixarenes crown ethers Alkali metal ions... 

Molecular mechanics calculation (MM) is the computational method most familiar to bench chemists (6, 7). Many kinds of software are on the market and are successfully used to address the conformational properties of various organic molecules. Since the programs have some limitations in dealing with weak interactions, crown ether-alkali metal complexes and related systems have hardly been examined. We applied the "extended MM2 program" (CAChe Scientific, version 3.0) to design Ag(I) ion-specific carriers (8). Because interaction between Ag(I) and donor atoms of the carrier is adequately strong, the MM2 calculation is applicable in such a case. 

A. Arnold et al. determined the crystal structure of the same crown ether 4-NaI complex (20), Since their estimated bond lengths were comparable to those predicted, the density functional method is believed to be applicable for crown ether - alkali cation complex. We attempted to apply MM2 and MNDO calculations for several crown ether-alkali metal cation complexes f27). Since the parameters for weak interactions between alkali metal cations and neutral donor atoms have not been optimized completely, these calculations sometimes gave results which differ from those in experiments. 

Suparne, S., Crown-ethers-alkali metal complexes as catalyst of e-caprolactam polymerization, Polymer J., 13, 313, 1981. 

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