Aminocalix[4]arene derivatives as extractant for chromate ion

Abstract

This work consisted of the study of extraction properties of 25,27-N,N-di-((2-ethoxy) benzyl) propylenediamine-p-tert-butylcalix[4]arene dichloride (1b), 25,27-{2,2’-[2,2’-((2,5,8-triammonium)nonyl)diphenoxyl]diethyl}-p-tert-butylcalix[4]arene trichloride (2b),25,27-di((2-ethoxy)benzylamine)-calix[4]arene (3) and 3,3’-dihexylurea azobenzene (4) as extractant towards oxyanions, particularly towards Cr(VI) which plays the important role in biology and environment. The influence of several parameters such as extraction time, pH, extractant concentration and mediums has been investigated in order to determine the optimal conditions for extractions. The results showed that the protonated forms of1b and 2b were effective hosts for Cr(VI) while 3 and 4 showed no significant extraction from aqueous solution into chloroform layer. The highest extraction ability of Cr(VI) was found in a 0.01 M choride medium at pH 2.37. Effects of other oxyanions were also studied at five-fold excess of K₂CrO₄. The relative affinities of three oxyanions to 1b and 2b were in the order of NO₃⁻˃H₂PO₄⁻≈SO₄²⁻. The extraction mechanisms were determined by the classical slope analysis method, from which 1:1 complex formation was indicated. The anion extracted might be either HCrO₄⁻ or Cr₂O₇²⁻. The solid-phase extraction studies with dynamic coating of 1b and 2b on silica as solid-support showed higher extraction efficiencies than liquid-liquid extraction. Compounds 1b and 2b retained quite high extraction ability at seven and three extraction cycles for liquid-liquid extraction and solid-phase extraction, respectively.