Di-substituted azocalix[4]arenes containing chromogenic groups: synthesis, characterization, extraction, and thermal behavior

In this study, the synthesis of chromogenic di-substituted azocalix[4]arene derivatives is described. Six novel azocalix[4]arenes (4a-f)were prepared by linking 4-methoxy, 4-methyl, 4-ethyl, 4-chloro, 4-bromo, and 4-nitroaniline to 25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)calix[4]arene through a diazo-coupling reaction, and were characterized by elemental analysis, FTIR, 1H NMR spectra and thermogravimetric analysis (TGA). The complexing properties of these compounds were studied by the liquid-liquid extraction of selected metal cations (Sr2+, Ag+, Hg+, Hg2+, Co2+, Ni2+, Cu2+, Pb2+, Cr3+, Al3+). It has been observed that di-substituted azocalix[4]arenes showed a high affinity for Ag+, Hg+, and Hg2+ ions, but almost no affinity to other metals. The colors of these azocalix[4]arenes were compared with respect to effect of varying pH on the absorption ability. Thermal behaviors of these compounds were also reported by means of thermogravimetry (TG) and thermal analysis (DTA).