Crown ethers using

The diffusion, location and interactions of guests in zeolite frameworks has been studied by in-situ Raman spectroscopy and Raman microscopy. For example, the location and orientation of crown ethers used as templates in the synthesis of faujasite polymorphs has been studied in the framework they helped to form [4.297]. Polarized Raman spectra of p-nitroaniline molecules adsorbed in the channels of AIPO4-5 molecular sieves revealed their physical state and orientation - molecules within the channels formed either a phase of head-to-tail chains similar to that in the solid crystalline substance, with a characteristic 0J3 band at 1282 cm , or a second phase, which is characterized by a similarly strong band around 1295 cm . This second phase consisted of weakly interacting molecules in a pseudo-quinonoid state similar to that of molten p-nitroaniline [4.298]. 

Okahara and his coworkers have made a number of contributions to the synthesis of crown ethers using a one-pot method (see Sect. 3.13). These methods have been applied largely to the preparation of simple aliphatic crown ether systems. In addition, this group has prepared macrocyclic ester compounds using a one-pot procedure. Although... 

Armstrong and Jin [15] reported the separation of several hydrophobic isomers (including (l-ferrocenylethyl)thiophenol, 1 -benzylnornicotine, mephenytoin and disopyramide) by cyclodextrins as chiral selectors. A wide variety of crown ethers have been synthesized for application in enantioselective liquid membrane separation, such as binaphthyl-, biphenanthryl-, helicene-, tetrahydrofuran and cyclohex-anediol-based crown ethers [16-20]. Brice and Pirkle [7] give a comprehensive overview of the characteristics and performance of the various crown ethers used as chiral selectors in liquid membrane separation. 

Figure 8.1 A phosphine-substituted crown ether, used as ligand and phase transfer reagent...

Dai, S., Ju, Y.H., and Barnes, C.E., Solvent extraction of strontium nitrate by a crown ether using room-temperature ionic liquids, /. Chem. Soc., Dalton Trans., 1201,1999. 

Cyclic dilactones can be prepared in high yields from the corresponding diadd chloride and diol, and have interesting cation binding properties (81JA1821). A useful method for their reduction to crown ethers using lithium aluminum hydride has recently been reported (82CC248). 

Gakh, A.A. Sumpter, B.G. Noid, D.W. Sachleben, R.A. Moyer, B.A. Prediction of complexation properties of crown ethers using computational neural networks. J. Inclusion Phenom. Mol. Recognit. Chem. 1997, 27 (3), 201-213. 

Dai, S., Ju, Y. H., Barnes, C. E. (1999), Solvent Extraction of Strontium Nitrate by a Crown Ether using Room-temperature Ionic Liquids, Dalton Trans. 1201-1202. 

Main-chain poly(styrene rotaxane)s <1997MM337, 1999PLM1823> were obtained by free radical polymerization of styrene in the presence of crown ethers using initiators incorporating bulky blocking groups to prevent dethreading of the macrocyclic components. 

A different type of crown ether used to separate enantiomers is the one derived from 18-crown-6 tetracarboxylic acid, covalently immobilized on silica gel via reaction between 18-crown-6 tetracarboxylic acid and amino propyl silica gel [76]. The structure of 18-crown-6 tetra carboxylic is presented in Figure 22-18 [77]. The enantioselectivity on this chiral phase is improved by the addition of triethylamine into the mobile phase and operating at high methanol concentrations however, enhanced selectivity may come at the expense of greatly increased retention times [78]. 

Figure 12.8 Chiral crown ether used in commercial LC chiral stationary phases.

Some chemical substances have been used in the past as switches to control ion transport. Several new molecular sensory devices, which are responsive crown ethers used for the dynamic control of cation and anion binding induced by changes in pH, redox potential, temperature, light, and magnetic and electrical field, have been developed. These new ligands possess chromophores or fluorophores linked to the macrocycle, and display drastic variations in their photochemical and/or luminescent properties upon cation complexation. 

Table 9.2 Some Typical Macrocyclic Crown Ethers Used in Coupled Transport. ...

T. Sata, M. Tanimoto, K. Kawamura and K. Matsusaki, Electrodialytic separation of potassium ions from sodium ions in the presence of crown ether using a cation exchange membrane, Colloid Polym. Sci., 2000, 278, 57. 

Several concepts (categories of action) that could result in cation enhanced fluorescence can be envisioned. Five examples are summarized here (a) the ion could cause subtle change(s) in energy levels or electron densities that lead to enhanced fluorescence, (b) the cation of interest could displace a quencher complexed by the crown, (c) the complexation of a cation could interrupt a quenching mechanism operable in the free crown, (d) complexation could adjust the conformation so that a new fluorescent excited state might form, (e) a crown ether used in an extraction method could promote the solubility of a fluorescent ion in a phase that is monitored for fluorescence. The literature of crown ethers contains examples employing each of these concepts (i-2i) with the possible exception of case (b). Seve concq)ts we have attempted to employ follow. 

Scheme 6.2 Structure of Fc-functionalized pyrrole crown ether used for the formation of Fc-crown polypyrrole films. This polymer is active as sensor for Ca and Ba ...

A. A. Gakh, B. G. Sumpter, D. W. Noid, R. A. Sachleben, and B. A. Moyer, /. Incltision Phenom. Mol. Recognit. Chem., 27, 201 (1997). Prediction of Complexadon Properties of Crown Ethers Using Computational Neural Networks. 

Figure 1. The structures of crown ethers used in this study.

The structures of crown ethers used in this study are shown in Figure 1, In table 1 are shown the results of the qualitative test by the paper disc method. Some alkylbenzocrown ethers (type II and III) and dicyclo-hexylcrown ethers (type IV) showed certain activity. On the other hand, unsubstituted crown ethers (type I) and benzocrown ethers with a polar substituent were inactive. Kryptofix 221 (VI) and Kryptofix 222B, which are highly selective to sodium and potassium, respectively, proved to be inactive, whereas Kryptofix 22DD, which has long alkyl chains, showed some activity. 

A Method for Catalytic Synthesis of Convenient Thioxanthone Crown Ethers Using Wells-Dawson, H EP WijO ], Preyssler Hj lNaPjWj O,],... 

Scheme 3.21 Synthesis of thioxanthone crown ethers using green method...

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