Tri-substituted hexahomotrioxacalix[3]arene derivatives bearing imidazole units: synthesis and extraction properties for cations and chromate anions

Abstract

The article describes the synthesis and extraction properties of the new hexahomotrioxacalix[3]arenebased derivatives cone- and partial-cone-2 bearing 1-methyl-1H-imidazole moieties at the lower rim. It has been demonstrated that O-alkylation of the flexible macrocycle 1 with 2-(chloromethyl)-1-methyl-1Himidazole hydrochloride affords tri-O-alkylated products with a cone or partial-cone conformation. Alkali metal salts such as NaH and Cs2CO3 can play an important role in the conformer distribution via a template effect. The conformation of receptors 2 has been confirmed by X-ray crystallographic analysis. Furthermore, the complexation properties of receptors 2 toward selected alkali/transition metal cations and alkylammonium ions are reported. The new 1-methyl-1H-imidazole-substituted hexahomotrioxacalix[3] arene frameworks are also efficient extractors of HCr2O7(-)/Cr2O7(2-) anions at low pH.

Synthesis and evaluation of a novel ionophore based on a thiacalix[4]arene derivative bearing imidazole units

“…A slight low field shift for the H 5 proton (À0.05 ppm) may be attributed to a longer distance between the H 5 proton and the ring current shielding effect. 15 X-ray crystallographic analyses confirmed the molecular structures of 3 and 1,3-alternate-4 as shown in Fig. 2 and 3.…”

“…This could be attributed to an ion-pair (hydrogen bonded) complex formed in the two-phase extraction system following proton transfer to the nitrogen atoms of the imidazole units in 1,3-alternate-4 and then complexation of Cr 2 O 7 2À /HCr 2 O 7 À . 15 However, the reference compound 6 showed almost no significant selective binding of dichromate anions even at low pH. Based on these results, it is concluded that the thiacalix[4]arene unit plays an important role in confirming cooperative participation of the peripheral imidazole groups.…”

“…analyses were performed with a Shimadzu gas chromatograph. 5,11,17,8,14,arcne-25,26,27,28-tetraol l was prepared from p-tert-butylphenol according to the reported procedure.…”

Selected applications of calixarene derivatives

“…53,54 The trivalent form Cr(III) is important for mammals in maintaining glucose, lipid and protein metabolisms, however the hexavalent form, Cr(VI) is toxic, e.g. it can diffuse as Cr 2 O 7 2-or HCr 2 O 7 -through human cell membranes, resulting in oxidized biological molecules.…”

“…it can diffuse as Cr 2 O 7 2-or HCr 2 O 7 -through human cell membranes, resulting in oxidized biological molecules. 53,55 Because Cr(VI) is a strong environmental pollutant, 55 for its removal from contaminated water a variety of separation techniques, e.g. nanofiltration, solvent extraction and adsorbing colloid flotation have been used.…”