Selective Extraction of Heavy Rare-earth Metal Ions with a Novel Calix[4]arene-based Diphosphonic Acid

The selective extraction of heavy rare-earth metal ions is achieved by using a novel calix[4]arenediphosphonic acid 4, in which two phosphono groups are introduced directly at the lower rim of the calix skeleton through the Ullmann-type phosphonation of the 1,3-bistriflate ester of p-tert-butylcalix[4]arene 3 as a key step.