Calix[4]arene-based Mannich and Schiff bases as versatile receptors for dichromate anion extraction: synthesis and comparative studies

A series of novel calix[4]arene-based Mannich (5 and 6) and Schiff base (9-11) receptors have been synthesized and characterized by various analytical techniques. Competitive two-phase extraction experiments of these novel calix[4]arene amine- and imine-containing derivatives revealed a strong affinity for dichromate anions (Cr2O72−/HCr2O7−). The protonated alkylinium form of 5, 6 and 9-11 proved to be effective extractants for transferring the dichromate anions from an aqueous into an organic phase. Moreover, the extraction of dichromate anions by 5 and 9 in the presence of competitive anions such as F−, Cl−, Br−, NO3−, NO2−, PO43− and SO42− showed that 5 and 9 could be selective anion receptors for dichromate anions in the presence of those anions.