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 calixarenebased extractant 5, which has been synthesized from5,11,17,23-tetra-tert-butyl-25,27-bis(chlorocarbonyl-methoxy)-26,28-dihydroxycalix[4]arene(4) by treatment with isoniazid (isonicotinic acid hydrazide) in the presence ofpyridine. 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^-/Cr₂O₇^2- anions. The complexing properties of 5 toward selected alkali/transition metal cationsand 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 formfor transferring the HCr₂O₇^-/Cr₂O₇^2- anions from an aqueous into adichloromethane layer.