Sorption of alkali metals and silver nitrates from binary and multicomponent solutions by a crown-containing polymer

The equilibrium in the systems containing a polymer based on dibenzo-18-crown-6 and binary or multicomponent aqueous solutions of NaNO₃, KNO₃, RbNO₃, and AgNO₃ was studied. The constants of the sorption of the individual electrolytes from solution into the polymer were determined. Preliminary calculations of the phase composition on sorption of 11 mixtures of electrolytes with a common anion from the data on the equilibria in the systems with one electrolyte are possible.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 464–466, March, 1993.     

Characterization of the solid phases of paracetamol and fenamates at equilibrium in saturated solutions

Differential scanning calorimetry (DSC), supported by hot stage microscopy, IR spectroscopy and X-ray powder diffractometry, was used to investigate the characteristics of the solid phases of mefenamic, niflumic, and flufenamic acids and of paracetamol, before and after equilibration with saturated solutions in different solvents. Mixtures of Lewis base (dioxane and ethyl acetate) and amphiprotic solvents (ethanol and water) were prepared for evaluating the influence of both nature and polarity of the solvents. Solid-state analysis performed on the original samples (commercial products) made it possible to establish that paracetamol, mefenamic acid and flufenamic acid were in their respective Form I. No polymorphic modifications are known for niflumic acid. Paracetamol, niflumic and mefenamic acids did not show any change after equilibration with the various solvents or solvent mixtures, regardless of their different chemical nature. In contrast, DSC, IR and X-ray analyses revealed the partial recrystallization of flufenamic acid into its polymorphic Form III in solid phases at equilibrium with ethanol, ethyl acetate and their blends, as well as in dioxane-water mixtures containing 30 to 100% dioxane and in ethanol-water mixtures with a water content less than 50%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of group II metal cations on catecholate oxidation.

The unexpected effects of Ca(2+) on the free-radical chain reactions of dopamine, norepinephrine, isoproterenol, and pyrocatechol oxidation are studied using oxygen consumption measurements, EPR-spectroscopy, UV/VIS spectrophotometry, and by potentiometric titration. It is found that the formation of Ca(2+)-catecholate complexes is accompanied by an increase in the dissociation constants (K(ai) ) of their phenolic hydroxyls. At pH>pK(ai) and in the presence of alkaline-earth metal cations, the rate of catecholate oxidation increases (Ca(2+), Mg(2+)> Sr(2+), Ba(2+)), whereas on addition of Zn ions the rate decreases. The effects of Group II metal cations on catecholate autoxidation are concomitant with a transient increase of the EPR signal for metal-semiquinonate complexes. Therefore, the effects of Ca(2+) and other alkaline-earth metal cations on catecholate autoxidation can be defined as 1) additional deprotonation of catechol OH-groups involved in the formation of M(2+)-catecholate complexes, the latter exceeding catechols in the susceptibility to dioxygen-induced oxidation and 2) formation of relatively stable free-radical intermediates responsible for chain propagation.     

Solid-solute phase equilibria in aqueous solution. VI. Solubilities,complex formation,and ion-interaction parameters for the system Na+−Mg2+−ClO 4 − −CO2−H2O at 25°C

The stoichiometric solubility constant of eitelite (NaMg _0.5 CO ₃ +2H⁺ ⇄ Na⁺+0.5Mg ²⁺ +CO ₂ (g)+H ₂ O, log^*K _pso ^I =14.67±0.03 was determined at I=3 m (mol kg⁻¹) (NaClO ₄ ) and 25°C. The stability of magnesium (hydrogen-)carbonato complexes in this ionic medium was explicitely taken into account. Consequently, trace activity coefficients of free ionic species, calculated from the Pitzer model with ion-interaction parameters from the literature, were sufficient for an evaluation of the thermodynamic solubility constants and Gibbs energies of formation for eitelite (−1039.88±0.60), magnesite (−1033.60±0.40), hydromagnesite (−1174.30±0.50), nesquehonite (−1724.67±0.40), and brucite (−835.90±0.80 kJ-mol ⁻¹ ). The increasing solubilities of nesquehonite and eitelite at higher sodium carbonate molalities were explained by invoking a magnesium dicarbonato complex (Mg²⁺+2CO ₃ ²⁻ ⇄ Mg(CO₃) ₂ ²⁻ , log β_z = 3.90 ± 0.08). A set of ion-interaction parameters was obtained from solubility and dissociation constants for carbonic acid in 1 to 3.5 m NaClO ₄ media which reproduce these constants to 0.02 units in log K. The following Pitzer parameters are consistent with the previously studied formation of magnesium (hydrogen-)carbonato complexes in 3m NaClO ₄ . The model and Gibbs functions of solid phases derived here reproduce original solubility data (−log [H⁺], [Mg ²⁺ ] _tot ) measured in perchlorate medium within experimental uncertainty. Presented at the XXII International Conference on Solution Chemistry, July 14–19, 1991, Linz, Austria.     

马来酸酐与1，2－环己烷二羧酸二异丁酯的气液平衡

采用小沸点仪测定了马来酸酐和1,2－环己烷二羧酸二异丁酯二元系统在不同配料组成条件下的温度与压力数据，并通过内插法得到不同压力下的温度与配料组成的数据.进一步采用单纯形法优化NRTL方程参数，推算了平衡气液相组成，发现该二元系统具有最高压力恒沸点，且该恒沸点随压力的变化显著.当压力降低至20 kPa时, 由温度随气相组成的变化趋势知该恒沸点将趋于消失.     

A thermodynamic analysis on the coincidence of extrema conditions in the sorption equilibrium for ternary polymer systems

Flory-Huggins theory of polymer solutions has been used to express the condition of extrema values in the total sorption, as well as the inversion point in the preferential adsorption parameters for termary polymer systems. Two approaches have been followed, the first considers the binary and ternary interaction parameters independent of polymer concentration and solvent composition. In the second one, this dependence has been introduced. Our attention is focused on the volume fraction of solvent mixture dependence of the above parameters, in order to confirm or not the coincidence between the extrema values and the inversion point. Several cosolvent and cononsolvent ternary polymer systems, have been used to test the validity of the equations obtained. Also, it has been verified, from an experimental point of view, that in cosolvent ternary polymer systems there is coincidence in both compositions while in cononsolvent ternary polymer systems, such coincidence does not appear.     

Ionization of aqueous toluic acids: Conductance and thermodynamics

Conductivities of aqueous solutions ofortho-, meta-, andpara-toluic acids have been measured for the concentration range 0.1–2 millimolar and at 5° intervals from 5 to 100°C. At each temperature pK _a(m) andA ₀ have been calculated using the paired ion model recently described by Fuoss. Thermodynamic parameters have been calculated for the ionization of each acid, and Walden products for the anions. Results are discussed in terms of contributions to acidity by enthalpy and entropy changes as well as by hydration of the various solute species.     

极性非质子溶剂与甲醇或1,2-二氯乙烷的汽液平衡

使用双沸点仪测定了丙酮、乙酸乙酯、对二氧六环、乙腈或三乙胺与甲醇或1,2→二氯乙烷以及二者混合物等十一组二元体系在99.3 kPa下的汽液平衡数据(T,x,p), 计算了有关体系的过量吉布斯自由能。结果表明, 六种非质子溶剂与甲醇组成的二元系GE>0; 乙腈或三乙胺与1,2-二氯乙烷组成的二元系GE>0, 而丙酮、乙酸乙酯或对二氧六环与1,2-二氯乙烷的二元混合物GE<0。从同种分子间或不同种分子间的缔合作用对上述结果进行了讨论。本文还在固定极性非质子溶剂(第三组分)物质的量浓度的条件下, 测定了非质子溶剂+1,2-二氯乙烷+甲醇三元混合物的汽液平衡数据, 考察了非质子溶剂的加入对甲醇+1,2-二氯乙烷二元系GE的影响。     

Growth transition and morphology change in polypropylene

The growth rate of isotactic polypropylene is deduced from microscopic observations during isothermal crystallizations. A change in the growth regime is observed at 138 C and interpreted as a Regime III Regime II transition, according to Hoffman's kinetic theory of polymer crystallization. A Regime II Regime I transition is also theoretically predicted at 155 C, i. e. at a temperature outside the investigated temperature range. The Regime III Regime II transition is related to the positive to negative change in the spherulite birefringence, which is generally attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae atT _c < 138 C (Regime III) and preferentially radiating lamellae atT _c > 138 C (Regime II). It is suggested that such a morphological change could be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. This interpretation could also explain the interspherulitic ruptures observed in negative spherulites.     

Solubility of carbazole in binary chloroalkane + dibutyl ether solvent mixtures

Solubilities are reported for carbazole in three binary chloroalkane + dibutyl ether solvent mixtures at 25°C. Results of these measurements are compared with solution models developed for solubility in systems containing specific solute-solvent interactions. A simple model based on a single 1:1 carbazole:dibutyl ether complex described the solubility data, though the calculated equilibrium constant was about one-half of values published previously. A more sophisticated solution model, which assumes both carbazole:dibutyl ether and carbazole:chloroalkane complexes, was needed to thermodynamically describe the systems studied. Equilibrium constants for three presumed carbazole:chloroalkane complexes are calculated from measured carbazole solubilities.