A bithiazole-containing calix[4]arene podand as versatile ligand for copper(I) and copper(II)

A new calix[4]arene-based bithiazole podand designed to complex copper(I) or copper(II), and the corresponding complexes, have been synthesised and characterised. Structural information was notably obtained for the copper(I) complex by a ¹H¹⁵N HMBC NMR experiment.     

Calixarenes 30. Calixquinones

Chlorine dioxide and thallium trifluoroacetate are shown to be useful reagents for the preparation of calixquinones. p-H-Calix[4]arene( 1a ),p-H-calix[5]arene ( 1b ), and p-H-calix[6]arene ( 1c ) are oxidized in modest yields by ClO₂ to the fully quinonoid compounds calix[4]tetraquinone ( 2a ), calix[5]pentaquinone ( 2b ), and calix[6]hexaquinone ( 2c ), respectively. Although Tl(OCOF₃)₃ is less effective for the oxidation of 1a-c , it proves to be the reagent of choice for converting partially etherified or esterified calixarenes carrying p-tert-butyl groups directly to partially quinonoid calixarenes. Thus, monosubstituted calix[4]arenes yield triquinones; disubstituted calix[4]arenes yield diquinones; trisubstituted calix[4]arenes yield monquinones; and tetrasubstituted calix[6]arenes yield diquinones. The structures of the calixquinones have been established by elemental analysis, ¹H NMR spectroscopy, mass spectroscopy, and in the case of 2c by X-ray crystallography. Since the starting materials are readily accessible, the calixquinones become easily available compounds for further study.     

Electrochemical oxidation of <Emphasis Type="Italic">p</Emphasis>-sulfonated calix[8]arene

The water-soluble p-sulfonated sodium salt of calix[8]arene (III) was synthesized. The product was characterized by FT-IR, NMR and UV–Vis spectra.Then the electrochemical behaviors of p-sulfonated sodium salt of calix[8]arene in NaAc+HAc (pH = 4) buffer solution was studied. In aqueous solution, p-sulfonated calix[8]arene can be oxidized when the potential is more than 0.7 V vs SCE. It was confirmed that the reaction was a two-electron irreversible electrochemical reaction. The transfer coefficient, α, was measured as 0.7. At 25°, the diffusion coefficient of p-sulfonated calix[8]arene was determined as 8.6 × 10⁻⁷ cm² s⁻¹. The diffusion activation energy of p-sulfonated calix[8]arene was 18.9 kJ mol⁻¹ at pH = 4.     

Extraction of Pb2+ with p-tert-butylcalix [4]-, [5]-, [6]Arene Carboxylic Acid Ligands and their Monomeric Counterpart: A Thermodynamic Approach

Studies on extraction equilibrium constants at different temperatures and thermodynamic parameters of solvent extraction of Pb²⁺ ion with carboxylic acid derivatives of different ring size calixarenes and structure related monomeric compound have been carried out. The extraction equilibrium constants corresponding to calix[n]arene (n?=?4, 5, 6) derivatives decrease in the order [5]arene > [6]arene > [4]arene. In all cases, the complexation process is primarily enthalpy driven. The favorable enthalpic contribution for extraction of Pb²⁺ is in the order hexamer ≈ monomer > tetramer > pentamer. However, the unfavorable entropic loss follows the order: monomer > hexamer > tetramer > pentamer. Overall stability of the host-guest complex is the function of entropy-enthalpy compensation and the free energy of complexation is minimum for the pentamer, followed by tetramer ≈ hexamer and monomer. Although the carboxylic acid derivative of calix[4]arene is more preorganized than the calix[5]arene derivative, extraction of Pb²⁺ ion with the tetramer passes through greater entropic loss than that with the pentamer and the degree of preorganization of calix[4]arene derivative is far from perfect for the complexation and extraction of Pb²⁺ ion. As compared to tetrameric and hexameric counterparts, the structural features of the carboxylic acid derivative of calix[5]arene prior to complexation contribute much to interact with the Pb²⁺ ion and form a thermodynamically stable complex. Supplementary materials are available for this article. Go to the publisher's online edition of Solvent Extraction and Ion Exchange to view the supplemental file.     

Stretchable calix[4]arene-based gels by induction of water

This study focused on controlling the stretching property of gels. This resilience is dependent on the water content in the calix[4]arene-based gel solvent system, where the stretching property of gels could be controlled upon the addition of water. The storage (G′) and loss (G″) moduli of the calix[4]arene-based gels prepared in solvent systems with different water contents were investigated via rheological measurements. By the strain sweeps, the values of G′ decreased, while tan-delta increased with water content in the solvent system. In addition, a significant changes in the G′ and G″ values were observed upon the addition of water by frequency sweeps. In particular, the decrease in the G″ value of the gel prepared from the 1,3-alternated calix[4]arene derivative ( HC4 ) and diisocyanate linker ( HDI ) in DMSO/H₂O mixed solvent (8:2 v/v) was approximately 5-fold larger than that of the gel prepared in 100% DMSO. Thus, this novel approach would useful for the development of new soft materials with finely controllable mechanical properties.     

Selective Extraction of Fe3+ Cation by Calixarene-Based Cyclic Ligands

Abstract

The selective liquid-liquid extraction of Fe³⁺ cation from the aqueous phase to the organic phase was carried out by using p-tert-butylcalix[4]arene [L₁], ca-lix[4]arene [L₂], p-nitro-calix[4]arene [L₃], calix[4]arene p-sulfonic acid [L₄], p-(diethylamino)methylcalixt4]arene [L₅], tetramethyl-p-tert-butylcalix[4]arene tet-raketone [L₆], 25,27-dimethyl-26,28-dihydroxy-p-tert-butylcalix[4]arene diketone [L₇], calix[4]arene-bearing dioxime group on the lower rim [L₈], and a monooxime [L₉]. The effect of varying pH upon the extraction ability of calixarenes substituted with electron-donating and electron-withdrawing groups at their p-position was examined. Observed results were compared with those found for unsubstituted calix[4]arene.     

Synthesis and characterization of calix[4]arene-based copolyethers and polyurethanes. Ionophoric properties and extraction abilities towards metal cations of polymeric calix[4]arene urethanes

Copolyethers and polyurethanes containing lower and upper rim calix[4]arene units in the fixed cone conformation were prepared in good yield by polycondensation reactions of distal calix[4]arene diols with bisphenol-A/dibromomethane and 2,4-tolylendiisocyanate (TDI), respectively. In a similar way were prepared calix[4]arene-crown-5 and -crown-6 polyurethanes in the fixed 1,3-alternate conformation by condensation of TDI with lower rim calixcrown-5 and calixcrown-6 diols. However, the poor solubility in common organic solvents of the copolyether derivatives (M_w=11,100-11,600 g/mol) hampered further studies on their ionophoric properties. Aiming to obtain model compounds for the investigation of both extraction abilities and ionophoric properties of the polyurethane materials, several bis-urethanes were also synthesized by reaction of the calix[4]arene diols with p-tolylisocyanate (TI). The extraction ability measurements of monomeric and polymeric calix[4]arene urethanes (M_w=12,300-83,500 g/mol) towards alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and Ag⁺showed a remarkable efficiency and selectivity of calixcrown-6 polyurethane toward Rb⁺, Cs⁺and Ag⁺.     

Selective Complexation and Membrane Transport of Guanidinium Salts by Calix[6]arene Amides

The p-tert-butylcalix[6]arene hexamide 2 and syn-1,3,5–trimethoxy-2,4,6-triamide 4 were synthesized by reaction of α-chloro-N,N-diethylacetamide and the corresponding calix[6]arenes 1 and 3 , respectively. ¹H NMR spectroscopy shows that 2 is a mixture of different conformations whereas 4 is fixed in a cone conformation. Extraction experiments, (S-L) and (H₂O–CDCl₃) with picrate salts, indicate that 2 complexes both alkali metal (1:2 complex) and guanidinium salts (1:1 complex) but 4 complexes only guanidinium (1:1 complex). Incorporated in supported liquid membranes (Accurel^® / o-nitrophenyl n-octyl ether) the calixarenes 2 and 4 transport guanidinium salts. The hexamide 2 is a more efficient carrier of guanidinium but the syn-1,3,5-trimethoxy-2,4,6-triamide 4 is much more selective. Both 2 and 4 are sufficiently lipophilic to give membranes that are stable over longer periods (weeks).     

Preparation and antibacterial activity of C2-benzaldehyde-C6-aniline double Schiff base derivatives of chitosan

C₂-benzaldehyde-C₆-aniline double Schiff base derivatives of chitosan were synthesized with positioning protection method for the first time. The structures and properties of the new synthesized products were characterized by Fourier transform infrared spectroscopy, ¹³C nuclear magnetic resonance, scanning electron microscope image, X-ray diffraction, and elemental analysis. The elemental analysis results indicated that the degrees of substitution of the products were from 39.6% to 48.2%. The synthesized compounds exhibited an excellent solubility in organic solvents. The antibacterial activities of all of the derivatives were tested in the experiment, and the results showed that the prepared chitosan derivatives had significantly improved antibacterial activity of chitosan and C₂-benzaldehyde Schiff bases of chitosan toward Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 35218). Antibacterial activity of the Schiff bases against E. coli differs from the substituent at the same position of different anilines and increases as the sequence aniline?>?p-toluidine?>?o-toluidine, and the antibacterial activity of the Schiff bases against S. aureus increases as the sequence p-toluidine?>?aniline?>?o-toluidine. The I_C50 of the C₂-benzaldehyde-C₆-aniline double Schiff base derivatives of chitosan against E. coli and S. aureus is 0.0035 and 0.0031?mg?L^?1, respectively, much lower than that of chitosan (0.0064?mg?L^?1) and C₂-benzaldehyde Schiff bases of chitosan (0.0054?mg?L^?1). The cytotoxicity test showed that compared with chitosan and C₂-benzaldehyde Schiff bases of chitosan, the prepared chitosan derivatives had lower cytotoxicity against SCG-7901. This paper provided a new method for the synthesis of Schiff bases of chitosan, which was enlightening.     

Arsenate and Dichromate Removal Efficiency of a New Calix[4]arene Impregnated Resin

This article highlights a newly synthesized 5,11,17,23-tetra-tert.butyl-25,26,27,28-tetrakis(hydrazidecarbonylmethoxy)-calix[4]arene (3) impregnated resin 4 and it's sorption ability for the removal of selected oxoanions, i.e., (arsenate and dichromate) from aqueous environment. Resin 4 was characterized by using FT-IR spectroscopy, scanning electron microscope (SEM), elemental, and thermogravimetic (TGA) analyses techniques. Sorption study was carried out through static and dynamic methods with continuous flow operation to evaluate the potency of resin 4 under various conditions. Several parameters, such as effect of sorbent dosage, contact time, pH, and initial concentration were optimized through batch experiments. Results justify that % sorption of these oxoanions is highly dependent on pH of the solution. Equilibrium was achieved in 45 min, while sorption efficiency of resin 4 can be better explained by Langmuir and Temkin isotherm models. Furthermore, kinetically both oxoanions follow pseudo second order model. Additionally, sorption of arsenate more appropriately could be explained by Moris-Weber diffusion kinetic model. For the dynamic method, Thomas model was used to calculate the kinetic coefficient (k_TH) and maximum sorption capacity (q_o) of resin 4 which are 3.84 and 5.94 ml mg^?1 min^?1 and 0.185, 0.160 mg g^?1 for As (V) and Cr (VI) respectively. Furthermore, resin 4 has been found as potential sorbent for removal of these oxoanions from contaminated surface water samples.     

Synthesis of a Novel Macroporous Silica-Calix[4]arene-Crown Supramolecular Recognition Material and its Adsorption for Cesium and some Typical Metals in Highly Active Liquid Waste

Abstract

A novel macroporous silica-based 25,27-bis(iso-propyloxy)calix[4]arene-26,28-crown-6 (BiPCalix[4]C6) supramolecular recognition material, BiPCalix[4]C6/SiO₂-P, was synthesized. It was prepared by impregnation and the immobilization of the BiPCalix[4]C6 molecule into the pores of the macroporous SiO₂-P particles. The adsorption of Cs(I) and some typical elements Na(I), K(I), Rb(I), Sr(II), Ba(II), Ru(III), Mo(VI), La(III), and Y(III) onto the BiPCalix[4]C6/SiO₂-P material was investigated. The effects of the HNO₃ concentration, contact time, and temperature on the adsorption of the tested metals were studied. It was found that at the optimum concentration of 3.0 M HNO₃, BiPCalix[4]C6/SiO₂-P exhibited excellent adsorption ability and high selectivity for Cs(I) over all the tested elements, which showed weak or almost no adsorption except Rb(I). A pseudo-second-order model was found to be able to describe the adsorption kinetics of Cs(I). The chemical complexation of Cs(I) with BiPCalix[4]C6/SiO₂-P was considered to be the rate-controlling step. Meanwhile, the thermodynamic parameters of the Cs(I) adsorption, ΔH?, ΔG?, and ΔS? were determined. The adsorption of Cs(I) onto BiPCalix[4]C6/SiO₂-P was exothermic. It was demonstrated that in 3.0 M HNO₃, the novel macroporous BiPCalix[4]C6/SiO₂-P material shows promise for the partitioning of Cs(I) from highly active liquid waste.     

Removal of Chromium(VI) and Chromium(III) from Aqueous Solution by Grainless Stalk of Corn

Abstract

Grainless stalk of corn (GLSC) was tested for removal of Cr(VI) and Cr(III) from aqueous solution at different pH, contact time, temperature, and chromium/adsorbent ratio. The results show that the optimum pH for removal of Cr(VI) is 0.84, while the optimum pH for removal of Cr(III) is 4.6. The adsorption processes of both Cr(VI) and Cr(III) onto GLSC were found to follow first-order kinetics. Values of k _ads of 0.037 and 0.018 min^?1 were obtained for Cr(VI) and Cr(III), respectively. The adsorption capacity of GLSC was calculated from the Langmuir isotherm as 7.1 mg g^?1 at pH 0.84 for Cr(VI), and as 7.3 mg g^?1 at pH 4.6 for Cr(III), at 20°C. At the optimum pH for Cr(VI) removal, Cr(VI) reduces to Cr(III). EPR spectroscopy shows the presence of Cr(V) + Cr(III)-bound-GLSC at short contact times and adsorbed Cr(III) as the final oxidation state of Cr(VI)-treated GLSC. The results indicate that, at pH ≈ 1, GLSC can completely remove Cr(VI) from aqueous solution through an adsorption-coupled reduction mechanism to yield adsorbed Cr(III) and the less toxic aqueous Cr(III), which can be further removed at pH 4.6.     

Transport of Chromium(VI) through a Supported Liquid Membrane Containing Tri-n-octylphosphine Oxide

ABSTRACT

In this study the transport of chromium(VI) from aqueous solutions of pH 2–4 through a supported liquid membrane (SLM) with tri-n-octylphosphine oxide (TOPO) dissolved in kerosene as a mobile carrier was investigated. The transport flux of Cr(VI) increased with an increase in the concentrations of Cr(VI) in the feed phase and of TOPO in the membrane phase, but with a decrease in pH of the feed phase. Considering the equilibria of various Cr(VI) species in the aqueous phase and of the Cr(VI)—TOPO complexes formed in the membrane phase, a permeation model including the aqueous film diffusion of HCrO₄ ^? and Cr₂O₇ ^2? toward the membrane, the interfacial chemical reaction between them and TOPO, and the membrane diffusion of the Cr(VI)—TOPO complexes (H₂CrO₄(TOPO) and H₂Cr₂O₇(TOPO)₃) was proposed to describe the transport of Cr(VI) through the SLM. By best fitting the transport flux equations of Cr(VI) with the experimental data using the Rosenbrock method, the apparent mass-transfer coefficients of HCrO₄ ^? and Cr₂O_7^. across the aqueous film, and those of H₂CrO₄(TOPO) and H₂Cr₂O₇(TOPO)₃ across the membrane phase, were obtained. This work helps to clarify the transport mechanism of Cr(VI) through an SLM.     

Oxidative conversion of thiourea and N-substituted thioureas into formamidine disulfides with acidified chloramine-T: a kinetic and mechanistic approach

The kinetics of oxidation of thiourea and N-substituted thioureas namely: N-methylthiourea, N-allylthiourea N-phenylthiourea and N-tolylthiourea to the corresponding formamidine disulfides by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in the presence of HClO₄ has been investigated at 278 K. The reactions follow identical kinetics for all thioureas, being first order each with respect to [CAT]_o, [Thiourea]_o and [H⁺]. Ionic strength of the medium and addition of p-toluenesulfonamide or halide ions have negligible influence on the rate. The solvent isotope effect has been studied using D₂O in the case of the oxidation of thiourea. Decrease in the dielectric constant of the medium by adding methanol decreases the rate. The reactions were studied at different temperatures, and the composite activation parameters have been computed. An isokinetic relationship was observed with β=314 K, indicating that enthalpy factors control the reaction rate. Under comparable experimental conditions, the rate of oxidation of thioureas increases in the order: N-allylthiourea>N-phenylthiourea>N-methylthiourea>thiourea>N-tolylthiourea. A mechanism involving the interaction of conjugate acid (CH₃C₆H₄SO₂NHCl) and substrate giving an intermediate complex, in a slow step, has been suggested. The derived rate law is in agreement with the observed kinetics.     

Removal of Cr(VI) From Aqueous Solution by Turkish Vermiculite: Equilibrium,Thermodynamic and Kinetic Studies

Abstract

The adsorption of Cr(VI) from aqueous solution by Turkish vermiculite were investigated in terms of equilibrium, kinetics, and thermodynamics. Experimental parameters affecting the removal process such as pH of solution, adsorbent dosage, contact time, and temperature were studied. Equilibrium adsorption data were evaluated by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Langmuir model fitted the equilibrium data better than the Freundlich model. The monolayer adsorption capacity of Turkish vermiculite for Cr(VI) was found to be 87.7 mg/g at pH 1.5, 10 g/L adsorbent dosage and 20°C. The mean free energy of adsorption (5.9 kJ/mol) obtained from the D–R isotherm indicated that the type of sorption was essentially physical. The calculated thermodynamic parameters (ΔG ^o , ΔH ^o and ΔS ^o ) showed that the removal of Cr(VI) ions from aqueous solution by the vermiculite was feasible, spontaneous and exothermic at 20–50°C. Equilibrium data were also tested using the adsorption kinetic models and the results showed that the adsorption processes of Cr(VI) onto Turkish vermiculite followed well pseudo-second order kinetics.     

Physical and electrochemical properties of 1-(2-hydroxyethyl)-3-methyl imidazolium and N-(2-hydroxyethyl)-N-methyl morpholinium ionic liquids

Various ionic liquids (ILs) were prepared via metathesis reaction from two kinds of 1-(2-hydroxyethyl)-3-methyl imidazolium ([HEMIm]⁺) and N-(2-hydroxyethyl)-N-methyl morphorinium ([HEMMor]⁺) cations and three kinds of tetrafluoroborate ([BF₄]⁻), bis(trifluoromethanesulfonyl)imide ([TFSI]⁻) and hexafluorophosphate ([PF₆]⁻) anions. All the [HEMIm]⁺ derivatives were in a liquid state at room temperature. In particular, [HEMIm][BF₄] and [HEMIm][TFSI] showed no possible melting point from −150 °C to 200 °C by DSC analysis, and their high thermal stability until 380-400 °C was verified by TGA analysis. Also, their stable electrochemical property (electrochemical window of more than 6.0 V) and high ionic conductivity (0.002-0.004 S cm⁻¹) further confirm that the suggested ILs are potential electrolytes for use in electrochemical devices. Simultaneously, the [HEMMor]⁺ derivatives have practical value in electrolyte applications because of their easy synthesis procedures, cheap morpholinium cation sources and possibilities of high Li⁺ mobility by oxygen group in the morpholinium cation. However, [HEMMor]⁺ derivatives showing high viscosity usually had lower ionic conductivities than [HEMIm]⁺ derivatives.     

Syntheses of inherently chiral monosulfinyltrithiacalix[4]arenes by the oxidation of one of the bridging sulfurs of a tetrathiacalix[4]arene fixed in the 1,3-alternate conformation

A new synthetic strategy for the construction of an inherently chiral, sulfur-bridged calix[4]arene molecular framework was presented by oxidation of one of the four epithio bonds of a tetrathiacalix[4]arene derivative of 1,3-alternate conformation: Tetra(carboxymethyl) ether of p-tert-butyltetrathiacalix[4]arene of 1,3-alternate conformation ( 7 ) was converted to the tetra(l-menthoxycarbonylmethyl) ether ( 8 ). Oxidation of the tetra l-menthyl ester 8 by treatment with NaBO₃ (1.1 molar equiv.) afforded a pair of diastereomers of the monosulfinyl derivatives ( 9 ) in 58% yield, which were readily separable by silica-gel column chromatography. Removal of the l-menthyl moieties followed by methyl esterification gave enantiomerically pure samples of inherently chiral (-)- and (+)-monosulfinyltrithiacalix[4]arene derivatives ((-) -10 and (+) -10 ) in 62 and 56% yield, respectively.     

Tetrapyrazolyl-calix[4]arene-based supramolecular architectures from [Pd16L4] macrocycle to three-dimensional microporous channels

By employing di-palladium complex [(bpy)₂Pd₂(NO₃)₂](NO₃)₂ (where bpy = 2, 2′-bipyridine) as corners and tetrapyrazolate calix[4]arene-based ligand (L^4 −) as linkers, a novel cavity-containing high-positively-charged polypyrazolate-bridged metallo-macrocycle [Pd₁₆L₄]^16 +·16NO₃ with Pd(II)⋯Pd(II) dimetal-coordination motifs has been synthesized by a directed coordination driven self-assembly with spontaneous deprotonation of the 1H-bipyrazole ligands in aqueous solution. The counter ions NO₃⁻ were trapped within the amphiphilic 3-D microporous channels in the solid state.     

The comprehensive investigation of the room temperature ionic liquid additives in PVC based polymer inclusion membrane for Cr(VI) transport

This study is to perform the comprehensive investigation of PVC based ionic plasticized membrane (IPM) production by using room temperature ionic liquid (RTIL)‐based additives and the membrane application of selective Cr(VI) removal. Some significant parameters related to membrane structures that are membrane thickness, plasticizer rate, and type, RTILs rate, and type, the average molecular weight of PVC were studied to define the excellent polymeric membrane film composition. After that, the PVC based polymeric film used in the Cr(VI) transport and initial mass transfer coefficient (J_o) were about 3.57 × 10^?7 mol s^?1 m^?2 by decyl substituted RTIL as an additive. Also, optimized membrane transport process has been considered as selective enough for Cr(VI) in the presence of the other heavy metal ions. Surface characterizations of the membranes have been performed to clarify the structural and the morphological assessment of IPMs at initial and end of Cr(VI) transport by SEM‐EDX, AFM, contact angle measurement and found a good relationship between the molecular structure of RTIL additive and membrane morphology. As we know that lots of researchers are still trying to find environmentally friendly, inexpensive and straightforward processes to remove toxic substances from industrial effluents or natural sources. At that point, our results can open a gate for cheap, novel and environmentally friendly Cr(VI) removal by PVC based membrane. J. VINYL ADDIT. TECHNOL., 25:E107–E119, 2019. © 2018 Society of Plastics Engineers     

Liquid–Liquid Extraction of Alkali Metal Cations by Calix[4]crowns with Pendant Groups

Abstract

The selective liquid–liquid extraction of alkali metal cations from the aqueous phase to the organic phase was carried out by using calix[4]crowns bearing two pendant groups with donor sites. It was found that calix[4]crown‐4 and calix[4]crown‐5 extractants with two pendant groups exhibit higher extraction efficiency than the parent compounds and possess obvious selectivity for Na⁺ and K⁺, respectively.