Highly Selective Coextraction of H + /SO 4 2- Using a Strapped Calix[4]pyrrole.

We report on the synthesis of a cage-type calix[4]pyrrole ( 1 ) bearing an additional basic pyridinebisthiazolamine group on the strap. The receptor in its protonated form shows strong affinity and selectivity for sulfate over a wide range of inorganic anions. With receptor 1 as a liquid-liquid extractant, H + /SO 4 2- in the form of H 2 SO 4 is almost quantitatively extracted from an aqueous solution containing HNO 3 at a high concentration to CH 2 Cl 2 in a recyclable manner.