Synthesis, conformations and extraction properties of new chromogenic calix[4]arene amide derivatives

Abstract

The synthesis of a new series of chromogenic calix[4]arene derivatives is described. p-Tetrakis(phenylazo)calix[4]arenes substituted with tertiary amide groups at the lower rim were obtained. The O-substitution of 25,26,27,28-tetrahydroxy-11,23-bis(phenylazo)calix[4]arene (2) and 25,26,27,28-tetrahydroxy-5,17,11,23-tetrakis(phenylazo)calix[4]arene (3) to provide 26,28-bis{[(diethylamino)carbonyl]methoxy}-25,27- dihydroxy-11,23-bis(phenylazo)calix[4]arene (4), 26-{[(diethylamino)carbonyl]methoxy}-25,27,28-trihydroxy- 5,11,17,23-tetrakis(phenylazo)calix[4]arene (5), 25,26,27,28- tetrakis{[(dialkylamino)carbonyl]methoxy}-5,11,17,23- tetrakis(phenylazo)calix[4]arene [alkyl = ethyl (6a), methyl (7)] and 26,28-bis{[(diethylamino)carbonyl]methoxy}-25,27- dihydroxy-5,11,17,23-tetrakis(phenylazo)calix[4]arene (8a) have been carried out by treatment of the precursors 2 and 3 with either α-chloro-N,N-diethylacetamide or α-chloro-N,N- dimethylacetamide. A potassium complex of 8 (8b) was isolated. The structures of these compounds have been studied by NMR spectroscopy. In addition, the conformations have been confirmed by single-crystal X-ray analysis in the cases of tetra-O-substituted azocalix[4]arenes (6a and 7) and bis(O-substituted) azocalix[4]arenes (8a and 8b). The resolved structures of 6a and 7 show 1,3-alternate conformations while the bis (O-substituted) analogues 8 display cone conformations, their packing showing a zigzag chain of molecules for 8a and a dimer for 8b. Moreover, the extraction properties of 6a, 6b and 8a towards different metal ions have been studied by liquid-liquid extraction and atomic absorption spectrometry and found to exhibit K+ selectivity. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2002.