Abdulkadir Sirit

A Calix[4]arene Oligomer and Two Beta‐cyclodextrin Polymers: Synthesis and Sorption Studies of Azo Dyes

Two insoluble β‐cyclodextrin polymers were synthesized by reacting β‐cyclodextrin with hexamethylene diisocyanate (HMDI) or 4,4′methylene bis phenyldiisocyanate (MPDI) as a crosslinking agent and a calix[4]arene‐based oligomer was prepared by the condensation of p‐tert‐butylcalix[4]arene with HMDI and utilized to remove selected water‐soluble azo dyes from aqueous solution. Oligomer 2 was found to be a poor sorbent for the azo dyes. The influence of several parameters (pH, contact time, and NaCl concentration) on the sorption capacity was evaluated using the batch and recycling column methods. The proposed sorption mechanism involved several kinds of interactions: physical adsorption, hydrogen bonding and formation of an inclusion complex due to the β‐CD molecules through host‐guest interactions.

Synthesis and dichromate anion sorption of silica gel-immobilized calix[4]arenes

Three new silica gel-immobilized calix[4]arene polymers 9-11 have been prepared via modification of calix[4]arene mono amido derivatives 3-5 with 3-aminopropyl triethoxysilane (APTES) and activated silica gel, respectively. The polymers were characterized by Fourier transform infrared spectroscopy, elemental analysis and thermal gravimetric analysis. The solid-liquid extraction properties of ligands 3-5 along with their immobilized derivatives 9-11 towards dichromate (HCr(2)O(7)(-)/Cr(2)O(7)(2-)) anions were reported. It was found that these calix[4]arene-based polymers have high extraction abilities towards dichromate anions as compared to their monomeric precursors.

Synthesis and Metal Ion Recognition Properties of a Novel Chiral Calix[4](azoxa)crown-7

A novel chiral calix[4](azoxa)crown-7 (9) has been synthesized and its metal ion recognition properties investigated. The starting reagents, chiral diamine 5 and calix[4]arene diacid chloride derivative 8, were prepared according to literature methods. 1H and 13C NMR data show that 9 exists in a cone conformation. In liquid–liquid extraction experiments, 9 exhibits selectivity for Li+ among the other alkali metals and a good extraction ability for transition metal cations, suggesting its potential use in different fields, such as a sensor for ions as well as for chiral molecules.

Polymer supported calix[4]arene schiff bases : A novel chelating resin for Hg2+ and dichromate anions

This article describes the synthesis and characterization of two new calix[4]arene Schiff bases and their polymeric resins. The extraction properties of these “proton switchable extractants” with alkali, transition, post transition metal cations and for dichromate anions are reported. The two new calix[4]arene based Schiff bases (5 and 6) have been synthesized from 5,17‐diformyl‐25,27‐dipropoxy‐26,28‐dihydroxycalix[4]arene (4) by treatment with 3‐amino‐methylpyridine and 1,8‐diaminooctane in two separate reaction flasks following the same procedure. Compounds 5 and 6 have been appended to a polymeric resin by treatment with Merrifield resin through a nucleophilic substitution reaction. The receptor compounds (3 and 5–8) do not extract alkali metal cations, but show some selectivity toward transition metal cations, and a particularly high selectivity to Hg2+ and Pb2+. The protonated forms of all of the calixarene‐based receptors are good extractants for transferring Cr2O7 2−/HCr2O7 − anions from an aqueous into a dichloromethane layer.

Application of L‐proline derivatives as chiral shift reagents for enantiomeric recognition of carboxylic acids

Four proline-derived chiral receptors 5-8 were readily synthesized starting from L-proline. The enantiomeric recognition ability of chiral receptors was examined with a series of carboxylic acids by (1) H NMR spectroscopy. The molar ratio and the association constants of the chiral compounds with each of the enantiomers of guest molecules were determined by using Job plots and a nonlinear least-squares fitting method, respectively. The Job plots indicate that the hosts form 1:1 instantaneous complexes with all guests. The receptors exhibited different chiral recognition abilities toward the enantiomers of racemic guests. Among the chiral receptors used in this study, prolinamide 6 was found to be the best chiral shift reagent and is effective for the determination of the enantiomeric excess of chiral carboxylic acids.

Calixarene-based highly efficient primary amine–thiourea organocatalysts for asymmetric Michael addition of aldehydes to nitrostyrenes

The synthesis of calix[4]arene-based chiral bifunctional primary amine–thiourea catalysts has been described from p-tert-butylcalix[4]arene for the first time. The calix[4]arene-based catalysts were successfully applied to promote Michael addition of aldehydes with nitroalkenes affording preferentially the (R)- or (S)-adducts in high yields (up to 95%) and excellent enantioselectivities (up to 99% ees).

Synthesis of 1,3-(distal) Diamide Substituted Calix[4]arene Based Receptors for Extraction of Chromium (VI)

The synthesis of novel diamide derivatives of calix[4]arene by aminolysis of calix[4]arene diesters was reported. The 1H and 13C NMR, data showed that the synthesized compounds exist in the cone conformation. The complexation properties of these calix[4]arenes have been studied towards anions and it has been found that the protonated alkyl ammonium forms of calix[4]arene diamide derivatives (5,11,17,23-tetra-tert-butyl-25,27-(diethylpiperidineacetamido)26,28-dihydroxy-calix[4]arene 3 and 25,27-(diethyl-piperidineacetamido)26,28-dihydroxycalix[4]arene 4) are effective extractants for transferring anions.

Chiral calix[4]arenes bearing amino alcohol functionality as membrane carriers for transport of chiral amino acid methylesters and mandelic acid.

Novel chiral calix[4]arene derivatives bearing amino alcohol moieties at the lower rim have been synthesized from the reaction of p-tert-butylcalix[4]arene diester with various amino alcohols. The transport of amino acid esters (phenylglycine, phenylalanine, and tryptophan methyl esters hydrochloride) and mandelic acid were studied through chloroform bulk liquid membrane system using chiral calix[4]arenes 15-20. All these receptors have been found to act as carriers for transport of aromatic amino acid methylesters and mandelic acid from the aqueous source phase to the aqueous receiving phase. The influence of calixarene and guest structures upon transport through liquid membrane is discussed.

Synthesis of calix[4]arene mono and diamide derivatives and selective complexation of alkali and alkaline earth cations

The synthesis of mono and diamide derivatives of the p‐tert‐butylcalix[4]arenes/calix[4]arenes from the reaction of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐diethoxycarbonyl‐methoxy‐26,28‐dihydroxycalix[4]arene 1 and 25,27‐diethoxycarbonyl‐methoxy‐26,28‐dihydroxycalix[4]arene 2 with various primary amines were reported. The effect of reaction time and steric hindrance of the primary amines used on the reactions have been investigated. All the amide derivatives of calix[4]arene are in a cone conformation according to the 1H‐NMR doublet–doublet pattern of the protons of the methylene groups between the aromatic rings. The complexing properties of these compounds toward selected alkali and alkaline earth metal cations are also studied. It has been observed that receptor 8 is a selective extractant for Cs+ and Sr2+ cations.

A novel calix[4]arene-based bifunctional squaramide organocatalyst for enantioselective Michael addition of acetylacetone to nitroolefins

A new chiral calix[4]arene-based organocatalyst 3 bearing bis-squaramide moieties was designed and synthesized from p-tert-butylcalix[4]arene. This bifunctional squaramide organocatalyst was used in the enantioselective conjugate addition of acetylacetone to β-nitrostyrenes. The corresponding adducts were obtained in good to excellent yields with high enantioselectivities (up to 94% ee).