Abstract
The metal-ion extraction abilities of calix[4]arene derivatives1and2are largely dependent on the type of the amide group forming the cation-binding site. Tertiary-amide derivative2was shown to be an excellent extractant for most alkali and alkaline earth cations.
Highlights
The complexes with secondary-amide derivative (1) were observed to have much lower stabilities than those with tertiary-amide derivative (2). This was presumably mostly caused by the presence of intramolecular NHÁ Á ÁOQC hydrogen bonds in the former case
In the course of the extraction process, the latter hydrophilic groups penetrate to the aqueous layer, whereas the hydrophobic calixarene basket remains in a non-polar organic layer
We present the syntheses of calix[4]arene amide derivatives with diethylene glycol functionalities appended to amide groups at the lower rim, and the study of their complexation affinities towards alkali and alkaline earth metal cations in two solvents with different solvation and hydrogen-bonding abilities
Summary
Several ethylene glycol-based calixarene derivatives have been reported previously.1,32–39 The first oxyalkylated p-tertbutylphenol-formaldehyde oligomers (both linear and cyclic) were developed as demulsifiers for the petroleum industry.1 Calixarene crown ethers with ethylene glycol substituents at the lower rim were shown to selectively bind sodium, potassium, and cesium cations.32,33 Another interesting group of compounds are bis-calixarenes, known as calix-tubes, which possess two calixarene skeletons bridged by ethylene glycol or various polyethylene glycol (PGE) chains.34 Calixarene derivatives with a large number of attached (poly)ethylene glycol groups have increasedPaper hydrophilic character, and have found application as agents for the extraction of metal cations from aqueous to organic phases.35–37 In order to optimize the structure of calix[4]arene derivatives for metal-ion biphasic extraction and phase-transition catalysis, Shinkai et al.35 prepared several amphiphilic calix[4]arene derivatives by introducing hydrophobic groups at the upper calixarene rim and oligo(ethylene glycol) chains at the lower rim. Extraction and complexation of alkali and alkaline earth metal cations by lower-rim calix[4]arene diethylene glycol amide derivatives† The complexation affinities of these compounds towards alkali and alkaline earth metal cations were studied at 25 1C in acetonitrile and methanol by means of spectrophotometric, conductometric, and potentiometric titrations.
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