Synthetic Ionophores. Part 20: Synthesis and Ionophore Character of 2-Aminothiophenol and 1,3-/1,4-Phenylene Based Silver Selective Receptors

Abstract

Nucleophilic displacements of 1,3- and 1,4-bis(bromomethyl)benzenes with 2-aminothiophenol provide 1,3- and 1,4- bis(2-aminophenylthiomethyl)benzenes 3 and 11 which undergo intermolecular cyclodehydrochlorination with thiodiglycolyl dichloride and isophthaloyl dichloride to give respectively 6, 8 and 12,13. The diamine 3 and its N,N'-dibenzyl derivative 4 with pyridine-2,6-dicarbonyl dichloride give 7 and 5, respectively. The extraction and transport behaviour of these receptors have been determined towards alkali (Li+, Na+, K+),alkaline earth (Mg2+, Ca2+, Sr2+, Ba2+), Tl+, Ag+ and Pb2+ picrates.The participation of various ligating sites in binding have been evaluated through 13 NMR studies. The acyclic receptors 3, 4 and 11 show higher Ag+ selectivity than the cyclic analogs 6 and 12. In the case of acyclic receptor 3 the organisation induced by the 1,3-phenylene spacer and 2-aminophenylthio units and its flexibility generates optimal binding and selectivity towards Ag+. However, in cyclicreceptors 3 and 12 though the three thioether unitsare better organised, the inward placement of the NHamide units restricts the entry of Ag+ into the cavity and lowers both the order of binding and selectivity. The lack of binding ability in 7due to an intramolecular NHamide–-Npy H-bond isrestored in the N-benzyl derivative 5.