Synthesis of azo-functionalized calix[4]arenes and its application to chloride-selective electrode as ionophores

Azo-functionalized calix[4]arenes as ionophores for chloride-selective electrode, 5,11,17,23-Tetra-tert-butyl-25.27-bis[(N,N-dimethyl-aniline-azo-phenylthioureido)ethyl]oxy-26,28-dihydroxycalix[4]arene (4a) and 5,11,17,23-Tetra-tert-butyl-25,27-bis[(N,N-dimethyl-aniline-azo-phenylthioureido)ethyl]oxy-26,28-dimethoxycalix[4]arene (4b) were synthesized. The PVC membrane electrode based on azo-functionalized calix[4]arene 4a with o-NPOE exhibits a linear stable response over a wide concentration range (1.5 x 10(-4) 1.0 x 10(-1)) with a slope of -52.0 mV/decade and a detection limit of log[Cl-] = -4.02. This ionophore-based membrane exhibited improved selectivity for chloride anion compared with classical Hofmeister series.