Synthesis of functionalized crown ethers and cation complexation by crown ethers

Date

1983-08

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Publisher

Texas Tech University

Abstract

Several crown ethers with pendant ionizable groups such as carboxylic and phosphonic groups were synthesized from corresponding hydroxy crown ethers. Efficient and inexpensive synthetic methods were developed to produce diphenols directly from catechol. Facile syntheses of hydroxy crown ethers were achieved by the reaction of epichlorohydrin with a diphenol in alkaline aqueous media. These hydroxy crown ether provided a convenient route to ionizable crown ethers with pendant carboxylic acid groups. Various crown ether carboxylic acids with different crown ether cavity sizes and different "arm" length connecting the ionizable group to the crown ether framework were prepared. Synthetic pathways have been established for the preparation of a crown ether phosphonic acid which has a more acidic ionizable group compared with crown ether carboxylic acids.

Shaking concentrated aqueous acids with methylene chloride solutions of 18-crown-6 or 12-crown-4 produced stable, solid, nonhygroscopic hydronium ion-crown ether complexes. The complexes were characterized by elemental analysis, proton NMR spectroscopy and infrared spectroscopy. The effects of polyether and anion variation upon the stoichiometry and properties of resultant hydronium ion-crown ether complexes were examined. From nitric acid and 18-crown-6, a complex composed of two nitric acid monohydrate species and one molecule of 18-crown-6 was isolated.

Interaction of NOBF4 and NOPF5 with 18-crown-6, 15-crown-5, and 12-crown-4 in dichloromethane, acetonitrile and nitromethane were probed by a combination of proton magnetic resonance spectroscopy, infrared spectroscopy and conductance measurements. The stoichiometries of the crown ether-nitrosonium salt complexes were one mole of 18-crown-6 per mole of nitrosonium salt and two moles of 12-crown-4 per mole of nitrosonium salt in all solvents. For 15-crown-5, the one-to-one stoichiometry observed in acetonitrile and nitromethane changed to two moles of crown ether per mole of nitrosonium salt in dichloromethane. The nature of these complexes is discussed.

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