SYNTHESIS AND APPLICATION OF NOVEL CALIX[N]ARENE BASED RECEPTORS FOR THE EXTRACTION OF TOXIC IONS ESPECIALLY FLUORIDE ION FROM DRINKING WATER OF THAR DESERT

Abstract

During last three decades, calixarenes a family of macrocyclic oligophenols have attracted much attention because of their unique molecular structure, simple one-pot synthesis, stability and their application as recognition agents with high sensitivity toward the ionic as well as neutral guest molecules. However, the present study comprise the synthesis and derivatization of calix[n]arene based and/or simple polymeric resins by anchoring different groups (i.e. esteric, nitro, amino or thiourea) along with their analytical/environmental applications. The new synthetic compounds/resins were characterized by various analytical techniques (i.e. FT-IR, NMR, SEM, elemental analysis etc). In the first phase of study, the synthetic work was carried out by synthesizing 5,11,17,23-p-tert-butyl-25,26,27,28-tetrahydroxycalix[4]arene (i) and 5,11,17,23,29,35- hexa-tert-butyl-37,38,39,40,41,42-hexahydroxycalix[6]arene (ii) followed by their de- tert-butylation from para-positions and Williumsons’ etherification to obtain iii, iv and v, vi, respectively. The synthesis of iii and iv was achieved by the treatment of i and ii with AlCl3 in the presence of phenol. Compounds v and vi, were prepared by the reaction of bromoethyl acetate in the presence of K2CO3 in acetone while, the ligand v was immobilized on to Amberlite XAD-4 resin (vii). The 5,11,17,23-p-tetranitro- 25,26,27,28-tetrahydroxycalix[4]arene (viii) was also synthesized from i by treating H2SO4/ NaNO3 in chloroform. Furthermore, the ligand viii was used to obtain a new derivative, i.e. 5,11,17,23-p-tetranitro-25,26,27,28-tetramethoxycarbonylmethoxy- calix[4]arene (ix). The ligands (v,vi and ix) and resin (vii) were used in extraction (liquid-liquid and/or solid-liquid) studies for a series of metal cations (i.e, Li+, Na+, K+, Cs+, Mg2+, Ag+, Pb2+, Cu2+, Co2+, Cd2+, Ni2+, Hg2+, Al2+, Fe3+). The extraction results reveal that both vi and vii are highly suitable extractants selective for Pb2+ while ix is for Hg2+ even in the presence of other co-existing ions. Consequently, the anion receptors were also synthesized; the ligand viii was immobilized onto Marrifield resin to have x that was followed by catalytic reduction of p-nitro groups of x to obtain a modified resin xi with amino groups. Finally, the p-amino groups of xi were converted to thiourea binding sites in order to obtain resin xii. The Amberlite XAD-4 resin (xiii) was modified to have nitro groups onto its surface through nitration (xiv). The nitro groups were converted to amino groups by catalytic reduction (xv) followed by conversion into thiourea (xvi) groups. for comparison with above resins i.e. xi and xii. In order to evaluate the fluoride extraction efficiency of newly synthesized anionophoric resins (xi, xii, xv and xvi) solid-liquid extraction experiments were performed. From the results it has been concluded that all resins have significant extraction efficiency for fluoride from aqueous media. It has also been noticed that there is no significant effect of co-existing anions (Cl-, Br-, I-, NO32-, NO2-, SO32-, PO42-, CO32- and HCO3-) on the extraction behavior of these resins. A remarkable extraction efficiency for fluoride has been observed with the calixarene appended resins (xi and xii) as compared with the simply modified resins (xv and xvi). Moreover, the fluoride extraction efficiency of the resins was also found satisfactory when these were applied on real water samples collected from different places of Thar Desert. Thus, it has been deduced that the resins could be used as adsorbent material for the removal of fluoride from the ground water of Thar Desert.