Contribution to the thermodynamics of complexes of alkali metal cations with hexaethyl p-tert-butylcalix[6]arene hexaacetate in the water—nitrobenzene extraction system

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M⁺(aq)+CsL⁺(nb)⇔ML⁺(nb)+Cs⁺(aq) taking place in the two-phase water-nitrobenzene system (M⁺ = Li⁺, Na⁺, K⁺, Rb⁺; L = hexaethyl p-tert-butylcalix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) were determined. Moreover, the stability constants of the ML⁺ complexes in water saturated nitrobenzene were calculated; they were found to increase in the cation order Rb⁺<Cs⁺<K⁺<Na⁺<Li⁺.     

Individual extraction constants of some divalent metal cations in the two-phase water–nitrobenzene system

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M²⁺(aq) + Sr²⁺(nb) ? M²⁺(nb) + Sr²⁺(aq) taking part in the two-phase water–nitrobenzene system (M²⁺ = Mg²⁺, Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, ${\text{UO}}_{2}^{2 +} $ , Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the individual extraction constants of the M²⁺ cations in the mentioned two-phase system were calculated; they were found to increase in the following cation order: ${\text{UO}}_{2}^{2 + } $  < Zn²⁺, Ni²⁺ < Cu²⁺, Cd²⁺ < Co²⁺ < Mg²⁺ < Ca²⁺ < Mn²⁺, Fe²⁺ < Sr²⁺ < Pb²⁺ < Ba²⁺.     

Individual extraction constants of some organic cations in the two-phase water–nitrobenzene system

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium C⁺(aq) + Cs⁺(nb) ⇔ C⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (C⁺ = organic cation; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the individual extraction constants of 15 organic cations in the mentioned two-phase system were calculated.     

Proton NMR study of the stoichiometry, stability and thermodynamics of complexation of Rb+ ion with 18-crown-6 in binary dimethylsulfoxide–nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Rb⁺ ion with 18-crown-6 (18C6) in a number of binary dimethylsulfoxide (DMSO)–nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 18C6 was fast on the NMR time scale and only a single population average ¹H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift mole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of formation constants. In all solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. The ?H° versus T?S° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reaction.     

Individual extraction constants of some univalent cations in the two-phase water–phenyltrifluoromethyl sulfone system

The preparation and characterization of three different phases of zirconium phosphate (ZrP) have been carried out using XRD, SEM, EDX, and FTIR spectroscopy. The phases exchange and sorption properties with three different radioisotope ²³⁴Th, ²³⁸U, and ¹³⁴Cs were investigated.     

Hydrophobic supramolecular complexes of various cations with 18-crown-6 as the ligand and N-methoxy-picramide as the anion pair in a water/methylene chloride two-phase system: complexes with α-amino acids,their characteristics and conditions for formation

α-Amino acids (arginine, valine, glycine, isoleucine, alanine, leucine, and phenylalanine), as amphionic species, were extracted from water into methylene chloride as neutral, hydrophobic, red supramolecular complexes of the type (CE-AmAc)⁺A⁻ where CE is 18-crown-6, AmAc is RCH(NH₃)⁺ COOH, and A⁻ is the N-methoxy-2,4,6-trinitroanilinium anion, where the latter gives rise to the red colour of the complexes (λ_max = 462 nm). The extraction constants (K_exs) of the α-amino acids from water to methylene chloride as supramolecular complexes were determined in relationship to the aqueous ionic strength (I).     

Enthalpy parameters for interaction of small peptides with 18-crown-6 and aza-18-crown-6 in water at 25°C

Enthalpies of dilution have been determined for binary aqueous solutions of 1-aza-18-crown-6 as well as for ternary aqueous solutions containing glycine, glycylglycine, glycyl-L--alanine, L--alanyl-glycine, L--alanyl-L--alanine, DL--alanyl-DL--alanine, trialanine and 18-crown-6 and/or 1-aza-18-crown-6 and or 1,10-diaza-18-crown-6 at 25°C. The results have been treated by the McMillan-Mayer approach in order to obtain enthalpic virial coefficients for homotactic and heterotactic interactions. A significant exo-effect is demonstrated by the enthalpically favorable interaction between peptides and the 18-crown-6. The additivity of the positive alanyl group contribution toh _xy has been confirmed on the basis of oligomeric data. The influence on the enthalpy of the 18-crown-6-peptide interaction of the methyl group position, in relation to the ammonium group in peptides, has been found to result in the exo-effect decreasing with a decrease of this distance. Some decrease in enthalpy of L--alanyl-L--alanine and DL--alanyl-DL--alanine by 18-crown-6 has been observed as well.Deceased.     

Study of isotope effect upon lithium iodide complexation with benzo-15-crown-5 in water–chloroform extraction system

Extraction characteristics of chloroform–water system in lithium iodide extraction with benzo-15-crown-5 (B15C5) were studied. The complexation of the crown ether with LiI in organic phase was shown by IR spectroscopy. Isotope effect multiplication was performed by extraction chromatography technique. The magnitude of isotope separation factor (α) for ⁶Li-⁷Li pair was 1.017. The light lithium isotope is concentrated in organic phase.     

Lithium isotope effects in extraction of lithium chloride by benzo-15-crown-5 in the 1,1,7-trihydrododecafluoroheptanol–water system

The extraction characteristics of the 1,1,7-trihydrododecafluoroheptanol water system have been studied for lithium chloride as the salt to be extracted and benzo-15-crown-5 as the extracting agent, as well as blank extraction of lithium chloride in this system. Single-stage lithium isotope separation factors (a) have been measured at various lithium chloride concentrations in water, and the isotope effect has been multiplied by extraction chromatography. The value of a for the Li⁶–Li⁷ pair was 1.024. The light lithium isotope is concentrated in the organic phase.     

Stability of dicyclohexyl‐18‐crown‐6‐hydrogen complex in nitrobenzene saturated with water

From extraction experiments with 22 Na as a tracer, the extraction constant corresponding to the equilibrium H⁺ (aq)+NaL ⁺(nb) HL⁺ (nb)+Na ⁺ (aq) in the twophase waternitrobenzene system (L = dicyclohexyl18crown6; aq = aqueous phase, nb = nitrobenzene phase) wasevaluated in the form log K ex (H⁺ , NaL⁺ ) = 0.2. Further, the stability constant of the complex HL⁺ in nitrobenzene saturated with water wascalculated for a temperature of 25 °C : log bnb (HL⁺ ) = 7.7.     

Calorimetric investigation of the complex formation reaction of 18-crown-6 ether with d,l-alanine in water–ethanol mixtures

The standard thermodynamic parameters (Δ_r G°, Δ_r H°, and TΔ_r S°) of the reaction of molecular complex formation of 18-crown-6 ether (18C6) with d,l-alanine (Ala), [Ala18C6], have been obtained from calorimetric titration experiments carried out using the microcalorimetric system TAM III (TA Instruments, USA) at T = 298.15 K in water–ethanol (H₂O–EtOH) solvents at X _EtOH = 0 ÷ 0.6 mol fractions. Results show that the increase of the EtOH concentration in solvent brings about an increase of the [Ala18C6] complex stability and of the exothermicity of the reaction of complex formation. The solvation contributions of 18C6, Ala, [Ala18C6] to Δ_r G° and Δ_r H° at various X _EtOH values are also analyzed.     

Extraction of triply charged metal cations in aqueous phase-separating system antipyrine–sulfosalicylic acid–water

Extraction of macro amounts of triply charged metal cations (0.01–0.05 mol L^?1) in aqueous phase-separating system antipyrine–sulfosalicylic acid–water containing no organic solvent is studied. Optimum conditions for phase separation are established and the influence of the concentrations of the major components, inorganic acids (H₂SO₄, HCl), salting-out agents, and the volume of the aqueous phase on the process in question is determined. It was found that the optimum antipyrine/sulfosalicylic acid ratio in the system was (1.5–2.0): 1.0. The introduction of inorganic salting-out agents causes the volume of the organic phase (0.8–1.8 mL) to increase to 2 mL and more. The extractability series of triply charged metal ions is as follows: Tl > Fe > Sc > In > Ga. It was shown that inorganic salts and hexamine influence the degree of extraction of metal cations and that inorganic acids and water affect the distribution mechanism and the composition of the complexes. The half-extraction pH values (pH₁/₂) of the cations are calculated and correlations between the pH₁/₂ values, the ionic radii of the cations, and the polarization ability of the metal ions are established.

     

Solvent extraction of silver trifluoromethanesulfonate from water into nitrobenzene in the presence of silver ionophore?IV

Abstract  

From extraction experiments in the two-phase water/nitrobenzene system, the stability constant of the silver ionophore IV (i.e., 5,11,17,23-tetra-tert-butyl-25,27-bis[2-(methylthio)ethoxy]calix[4]arene)–Ag⁺ complex in nitrobenzene saturated with water was determined. Furthermore, the most probable structure of the resulting complex was derived by means of density functional level of theory calculations.     

Oxygen permeability and the state of water in Nafion® membranes with alkali metal and amino sugar counterions

The mobility of hydration water and the dissolved oxygen permeability through different cation forms of the Nafion^® membranes were determined. Two alkali metals (Na and K) and two amino sugars (an equivalent molar mixture of d-glucopyranosyl-α(1′ → 6)-2-amino-2-deoxy-d-mannitol and its sorbitol (GPA)and d-glucosamine (GLU)) were used as counterions. Based on the two-state model, the content and mobility of hydration water were determined using DSC and ¹⁷O NMR. The dissolved oxygen permeability through the Nafion^® membrane containing GPA was the lowest value in this study because, for the membrane, the fraction of hydration water was the greatest and the mobility of hydration water was the lowest. The amount and location of the hydrophilic group contained in substances as well as the kind of hydrophilic group affected the fraction and mobility of hydration water and dissolved oxygen permeability through the membranes.     

Contribution to the system Europium — boron — carbon

By means of chemical preparation techniques and x-ray analysis the ternary system EuBC was studied, with special emphasis on the technologically important sections EuB₆C and EuB₆B₄C. It was possible to prove the existance of a hexaboride-carbon solid solution EuB_6−xC_x (0 ⩽ x ⩽ 0.25), a ternary phase EuB₂C₂, the europlum carbides EuC_x (⪡Eu₂C⪢), EuC₂, as well as another carbide of the approximate composition Eu₂C₃.     

Solvation thermodynamics of benzene,nitrobenzene, and aniline in water–acetonitrile mixtures

The enthalpies of dissolution of benzene, nitrobenzene, and aniline in water–acetonitrile mixtures are determined via calorimetry. The concentration dependences of the standard enthalpies of solvation of solutes are calculated. It is found that the concentration dependences of the standard enthalpies of solvation pass through maxima. The height of the observed maxima is shown to depend largely on the nature of the substituent. In the presence of a hydrophilic amino group capable of forming strong hydrogen bonds with water molecules, the value of a maximum falls; in the presence of a nitro group, it rises. The enthalpy parameters of pair interaction between molecules of water and benzene and its derivatives are calculated.     

Separation of microamounts of yttrium from strontium in the two‐phase water/nitrobenzene system

A rapid and very effective separation of carrierfree 90 Y in the aqueous phase of the water/nitrobenzene system from an 90 Y/90 Sr generator is proposed. After a twostage extraction separation, the radionuclide impurity of 90 Sr in the final aqueous phase containing carrierfree 90 Y is approximately 10 16%, while the chemical yield of 90 Y in this phase is practically 100%.     

Phase and extraction equilibria in the water—ethoxylated nonylphenol—sodium sulfate system

Russian Chemical Bulletin - Phase equilibria in the water-ethoxylated nonylphenol (neonol AF 9–12)-sodium sulfate system were studied at 25 °C using isothermal titration and isothermal...