Cation complexation by chemically modified calixarenes. Part 7. Transport of alkali cations by p-tert-butylcalix[n]arene esters and amides

Abstract

The co-transport of alkali thiocyanates, at 20 °C, from an aqueous source solution into an aqueous receiving solution through a bulk liquid dichloromethane solution, is facilitated by p-tert-butylcalix[n]arene esters of lower rim calixarene acetic acids, named ethyl esters (n= 4, 5, 6, 8), by p-dealkylated calix[6]arene ethyl ester and the diethyl and pyrrolidine amides of a p-tert-butylcalix[4]arene. The transport rates show that all derivatives, except the octamer, are efficient and selective neutral ionophores for alkaline cations. The amides are better carriers than the esters and the pyrrolidinyl amide is more efficient for Li⁺, Na⁺ and K⁺ than the diethyl amide. Among the esters, the most efficient, by far, is the pentamer. The tetra- and penta-esters are selective for Na⁺, the hexaester for Cs⁺ and the tetraamides for K⁺. The Cs⁺/Na⁺ selectivity of the hexaester is increased by dealkylation in the para position. The same is shown to be displayed in extraction. The data are compared with existing stability constant values in methanol and extraction equilibrium constants for alkali picrates, from water to dichloromethane. New extraction data are provided for alkali thiocyanates.