Synthesis and Extraction Studies of a Versatile Calix[4]arene-Based "Proton-switchable Extractant" for Toxic Metals and Dichromate Anions

The article describes the syntheses and extraction properties of a new calixarene based extractant 5, which has been synthesized from 5,11,17,23-tetra-tert-butyl-25,27-bis(chlorocarbonyl-methoxy)-26,28-dihydroxycalix[4]arene (4) by treatment with isoniazid (isonicotinic acid hydrazide) in the presence of pyridine. The compound 5 was converted to its methyl iodide salt (6) by refluxing 5 with methyl iodide in acetonitrile. In this synthesis it was thought to explore the role of pyridinium sites in the extraction of HCr2O7-/Cr2O72- anions. The complexing properties of 5 toward selected alkali/transition metal cations and HCr2O7-/Cr2O72- anions are reported. It has been observed that receptor 5 does not extract alkali metal cations but shows an excellent selectivity toward transition metals. The protonated pyridinium form of 5 is an effective form for transferring the HCr2O7-/Cr2O72- anions from an aqueous into a dichloromethane layer.