Novel caesium-selective, 1,3-alternate calix[4]arene-bis(crown-6-ethers) with proton-ionizable groups for enhanced extraction efficiency

摘要

Synthesis of a series of novel 1,3-alternate calix[4]arene-bis(crown-6-ethers) with a proton-ionizable group (PIG)nlocated in front of one crown ether cavity is reported. Variation of the X group in the N-(X-sulfonyl)carbamoylnsubstituent on the calixbiscrowns provides variation of acidity of the PIG. NMR spectroscopic studies demonstratenthat the position of the PIG within the molecule allows it to participate in cooperative metal ion coordination bynthe ligand. In solvent extraction of alkali metal cations from aqueous solutions of varying pH into chloroform, thennovel ionophores possess enhanced efficiency relative to a non-ionizable analog, while retaining high Csnu0001 selectivity.nThe Csnu0001 extraction constants of the proton-ionizable calixbiscrowns are proportional to their acidities. Under thenconditions employed, 1 : 1 complexes of the ionized calixbiscrowns with Csnu0001 are the dominant species extracted intonthe organic phase.