New phenol-containing bis(azacrown ether)s: synthesis and complexing properties

Abstract

A simple synthesis of phenol-containing bis(azacrown ethers) by the treatment of N-methoxymethyl-substituted azacrowns with phenols has been elaborated. Temperature conditions have been found for selectively introducing into one phenolic ring both one and two monoazacrown ether substituents. New symmetric 14a–e and asymmetric 15 phenol-bridged bis(azacrown ether)s exhibited strong complexation abilities towards both alkali and especially alkaline-earth metal cations. All measurements have been carried out using the pH-metric titration technique. Complexation constant values in neutral (K₁) and in alkaline (K₂) media are in the order: monocyclic 1b–d < bicyclic ligands 14a–c. In all cases, K₂ > K₁. These results show participation of phenolic ions in the complex formation process. In an alkaline medium, bis(azacrown ether)s 14b, 14e and 14d showed high selectivity towards Li⁺, Ba⁺² and Sr⁺², respectively.