Synthesis and evaluation of a novel ionophore based on a thiacalixarene derivative bearing imidazole units†
O-Alkylation of the flexible thiacalixarene 1 with 2-chloromethyl-1-methyl-1H-imidazole 2 in the presence of Na2CO3 or K2CO3 afforded mono-O-alkylation product 3 in 29–51% yield, along with recovery of the starting compound. In contrast, the same reaction in the presence of Cs2CO3 gave only one pure stereoisomer, namely 1,3-alternate-4; other possible isomers were not observed. Alkali metal salts such as Na2CO3 and Cs2CO3 can play an important role in the conformer distribution via a template effect. The conformations of the receptors, mono-O-alkylation product 3 and that of 1,3-alternate-4, have been confirmed by X-ray crystallography. Furthermore, the complexation properties of the receptor 1,3-alternate-4 toward selected alkali/transition metal cations are reported. The two-phase solvent extraction data indicated that 1,3-alternate-4 exhibited a stronger extraction efficiency for transition metals over alkali metals. The dichromate anion extraction ability of 1,3-alternate-4 showed that it could serve as an efficient extractor of HCr2O7−/Cr2O72− anions at low pH.