Extraction of technetium by DB18C6 and 18C6 into nitrobenzene and acetylacetone from an aqueous phase containing NaBH4

The extraction of technetium by DB18C6 and 18C6 into nitrobenzene and different solvents from aqueous phase containing NaBH₄ was investigated. The experimental data indicate that the main extracted species have the formulas TcO/OH/₂.CE or 2TcO/OH/₂.3CE, where CE refers to the crown ethers. The effects of crown ether concentration, pH and organic solvent on the distribution ratio are discussed. The extent of extraction from different solvents decreases in the order nitrobenzene >acetylacetone>1-butanol>toluene> benzene.     

Dilute Solution Properties of Poly(Vinyl Chloride)

Light scattering and viscosity studies were made on dilute solutions of poly(vinyl chloride) (PVC) in three solvents: cyclo-hexanone, cyclopentanone, and tetrahydrofuran. Eight samples of PVC (M_w = 25,400 to 145,000) were used to determine the intrinsic viscosities, molecular weights, and the polymer-solvent interaction parameters over a range of temperatures. The solutions were found to behave normally and to exhibit no evidence of aggregate formation. The molecular weights obtained in all three solvents were independent of temperature and agreed well within the experimental errors. The interaction parameters observed were independent of concentration and molecular weight, and functions only of temperature. The intrinsic viscosities were related to molecular weight by the Mark-Houwink equation between 20 and 50°C. The temperature coefficient of the interaction parameter obtained by light scattering agrees well with that found by viscometry. Cyclohexanone, cyclopentanone, and tetrahydrofuran are all good solvents for PVC, and the order of solvent quality is cyclohexanone > cyclopentanone > tetrahydrofuran.     

Kinetics of nitrobenzene hydrogenation on spongy nickel and catalyst with supported palladium in 2-propanol aqueous solutions with acid or base additives

The effect acetic acid and sodium hydroxide additives in a 2-propanol aqueous solution of azeotrope composition have on the rate of nitrobenzene (NB) hydrogenation over spongy nickel and supported palladium catalysts is studied. Analysis of the experimental data indicates that adding acid slows the rate more than adding a base during NB hydrogenation on spongy nickel. The observed rate for spongy nickel falls in a series of solvents: 2-propanol–water (0.68 mole fraction) > 2-propanol–water (0.68 mole fraction) + NaOH (0.01M) > 2-propanol–water (0.68 mole fraction) + CH₃COOH (0.01 M). When a palladium catalyst is used, the addition of acid has less of an effect on slowing the rate of the reaction than that of the base: 2-propanol–water (0.68 mole fraction) > 2-propanol–water (0.68 mole fraction) + CH₃COOH (0.01 M) > 2-propanol–water (0.68 mole fraction) + NaOH (0.01 M).     

Competitive transport of seven metal cations through bulk liquid membrane using 5,12-di(phenoxymethyl)-1,4-dioxa-7, 10-dithiacyclododecane-2,3-dione as carrier

The competitive metal ion transport of copper(II), cobalt(II), zinc(II), cadmium(II), silver(I), chromium(III) and lead(II) with a S-O donor compound was examined. Competitive transport experiments involving the metal cations from an aqueous source phase through an organic membrane into an aqueous receiving phase have been carried out using 5,12-di(phenoxymethyl)-1,4-dioxa-7,10-dithiacyclododecane-2,3-dione as the ionophore present in the organic phase. Fluxes and selectivities for competitive metal cations transport across bulk liquid membranes have been determined in a variety of chlorinated hydrocarbon and aromatic hydrocarbon solvents. The membrane solvents include: dichloromethane (DCM), chloroform (CHCl₃), 1,2-dichloroethane (1,2-DCE), and nitrobenzene (NB) and also in chloroform-dichloromethane (CHCl₃-DCM) and chloroform-nitrobenzene (CHCl₃-NB) binary mixtures. Although the selectivity for silver(I) cation in all of these organic solvents is fundamentally similar, but the most transport rate for Ag(I) was obtained in dichloromethane. The sequence of transport rate for silver ion in organic solvents was: DCM > CHCl₃ > 1,2-DCE > NB. A linear relationship was observed between the transport rate of silver ion and the composition of CHCl₃-DCM, but a non-linear behavior was observed in the case of CHCl₃-NB binary solution. The influence of the stearic, palmetic and oleic acids as surfactant in the membrane phase on the transport of the metal cations was also investigated.     

The extraction behavior of some dicarbollylcobaltate crown extraction systems

The extraction of cesium, strontium and barium by a nitrobenzene solution of dicarbollylcobaltate in the presence of various crown ethers has been investigated and the influence of the substituent of crown to the extraction possibility has been observed. It has been found, that the addition of DB15C5, DB18C6 and DB21C7 (but not DB24C8 and DCH24C8) increases the distribution ratio of Cs by one order of magnitude. The fivemembered crowns are usually more efficient extractants for strontium than DCH18C6, which is widely used for strontium separation. The distribution ratio of strontium D_Sr decreases in the order 15-crown-5>benzo-15-crown-5>2-hydroxymethyl-15-crown-5>cyclohexyl-15-crown-5 >dibenzo-15-crown-5> nitrobenzo-15-crown-5. The selectivity α(Sr/Ca) decreases in the order 15C5>B15C5>DB15C5>2HM15C5>CH15C5. A selectivity factor α(Sr/Ca)≥1000 can be reached in the presence of 15C5 and B15C5. Six-membered and four-membered crowns extract strontium worse than most of the five-membered crowns. The selectivity factors α(Sr/Ca)≈100 have been reached for six-membered crowns and α(Sr/Ca)<1 has been found for 12C4. The extraction of barium by a nitrobenzene solution of dicarbollylcobaltate in the presence of 15C5 is even more efficient as the extraction of strontium. In that system D_Sr>10⁴ and D_Ba>10⁴ have been found for the extraction of Sr and Ba by a 0.01M nitrobenzene solution of dicarbollylcobaltate (c_B=0.01 mol/l) from 0.1M HNO₃. Maximal values of separation factor α(Ba/Sr) have been found in the system containing DB21C7.     

Effect of solvent on the amount of tetraoxane produced in the solution polymerization of trioxane catalyzed by BF3·O(C2H5)2

The amounts of tetraoxane produced in the polymerization of trioxane catalyzed by BF₃·O(C₂H₅)₂ were measured in various solvents. The maximum amount of tetraoxane produced depends on the nature of solvent used. This amount was independent of the initial concentration of the catalyst in ethylene dichloride and in nitrobenzene. On the other hand, in benzene, the amount of tetraoxane produced decreased slightly with increasing initial catalyst concentration. This result was explained by the reaction of tetraoxane produced with the residual catalyst as well as with the active center. The maximum amount of tetraoxane produced decreased, other conditions being similar, in the order, nitrobenzene > ethylene dichloride > benzene solvent. This order may be explained in terms of a longer lifetime of the active center in the more polar solvent, leading to the formation of tetraoxane.     

Effect of Solvent on Competitive Bulk Membrane Transport of Transition and Post Transition Metal Cations Using Decyl-18-crown-6

A series of competitive metal ion transport experiments have been performed. Each involved transport from an aqueous source phase across an organic membrane phase into an aqueous receiving phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), cupper(II), zinc(II), cadmium(II), silver(I) and lead(II) metal cations. The membrane phase incorporated ionophore, decyl-18-crown-6. The membrane solvents include: chloroform, dichloromethane, 1,2-dichloroethane, nitrobenzene and chloroform–nitrobenzene binary solvents. A good transport efficiency and selectivity of Pb²⁺ transport from aqueous solutions are observed in this investigation. The selectivity order for competitive bulk liquid membrane transport of the studied transition and post transition metal cations through chloroform is: Pb²⁺>Co²⁺>Ni²⁺>Ag⁺>Cd²⁺, but in the case of dichloromethane, 1,2-dichloroethane and nitrobenzene as liquid membranes, the selectivity sequences were found to be: Pb²⁺>Co²⁺>Cd²⁺>Cu²⁺>Ag⁺>Ni²⁺>Zn²⁺, Pb²⁺>Co²⁺>Ag⁺>Ni²⁺>Zn²⁺ and Pb²⁺>Co²⁺>Ni²⁺>Zn²⁺>Cd²⁺>Ag⁺, respectively. The transport rate of the metal cations in chloroform–nitrobenzene binary solvents is sensitive to the solvent composition. The transport processes were studied in absence and presence of the stearic acid and the results show that the sequence of selectivities and ion transport rates change in the presence of stearic acid.     

The effect of solvents on asymmetric induction cationic copolymerization of l-menthyl vinyl ether with indene

Cationic copolymerization of l-menthyl vinyl ether (l-MVE) with indene (IN) was carried out in several solvents with BF₃OEt₂ as catalyst at 0°C. The solvents used in this study were selected toluene (Tol), chloroform (CHCl₃), chlorobenzene (BzCl), 1,2-dichloroethane (EtCl₂), and nitrobenzene; (BzNO₂)/Tol = 65/35 mixture solvent. l-Methyl residue, which is an optically active side chain of copolymer produced by cationic copolymerization, was removed with dry hydrogen bromide gas by ether cleavage reaction. The copolymer [vinyl alcohol(VA)–lN], produced by the ether cleavage reaction, also showed optical rotation. From this result, therefore, it was concluded that asymmetric induction takes place in the copolymer main chain. The efficiency of asymmetric induction was determined by the measurement of optical rotation of VA–IN copolymer after the ether cleavage reaction. The efficiency of asymmetric induction in the copolymer main chain developed from the variation on polymerization solvents; the order was Tol > EtCl₂ > BzCl > CHCl₃ > BzNO₂/Tol (65/35) mixture solvent.     

An analysis on the transmission of electron density through sulphur atoms in the quaternization reactions of benzothiazoles

The kinetics of quaternization of a number of 2-substituted benzothiazoles with alkyl iodides and phenacyl bromide have been studied in nitrobenzene. The order of reactivity of different substituted benzothiazoles has been found to be -H > NO₂ > Cl. The relative reactivity of 2-amino and 2-methyl derivatives has been ascribed to a solvation phenomenon. The analysis of rho values from the Hammett equation suggests two possible routes for the transmission of electron density.     

Study on the Solvent Extraction with Radio-Tracers. I. Extraction Study on Protactinium-233 with the Noyltrifluoroacetone

Protactinium-233, separated from the irradiated thorium, was used as a tracer for the extraction study with thenoyItrifluoroacetone. From the results obtained by the variation of acidities of HCl with the constant concentration of TTA in benzene, a slope of ?2 was obtained by plotting the distribution coefficients against acidities. With a definite acid concentration of HCl in the aquous solution and by the variation of TTA concentration, a slope of 4 was obtained by plotting the distribution coefficients against the concentration of β-diketone. With these results, species extracted by the organic layer was assumed to be Pa[TTA]₂[HTTA]₂. If the composition of the organic layer was changed by the addition of the following solvents into the TTA in benzene solution, the order of the extraction was found as follows: n-amyl alcohol > cyclohexane > chloroform > n-hexane > carbon tetrachloride > benzene > nitrobenzene > hexone > cyclohexanone > n-butyl alcohol.     

Symmetrical electrochemical cell for determination of coextraction constants of metal salts for ion-selective polymeric membranes

A symmetrical electrochemical cell has been developed to perform cyclic voltammetric study of a plasticised poly(vinyl chloride) (PVC) membrane. The plasticised PVC membrane of ca. 100 μm thickness was mounted in a specially laboratory-made electrochemical cell for voltammetric analysis on exposure to various sodium salt and metal chloride solutions. Symmetrical cyclic voltammograms were obtained when the sample and internal solutions contained same kind of metal salts. The coextraction constant of a metal salt for the plasticised PVC could be determined from either the positive or negative potential scans of a cyclic voltammetry. In addition, two coextraction constants could also be simultaneously obtained when the membrane was exposed to two different metal salts in the sample and internal solutions, respectively. It was observed that the more lipophilic of the cations or anions, the larger the coextraction constants of these ions for the plasticised PVC membrane. The results followed the Hofmeister sequence of ClO₄⁻>NO₃⁻>Br⁻>Cl⁻>OAc⁻ for anions and the ease of extraction of cations was in the order of Cs⁺>K⁺>Na⁺>Li⁺. The proposed method provides a simpler, faster and more convenient method to obtain the coextraction constants of metal salts for plasticised polymeric membranes.     

Thermal degradation studies in poly(vinyl chloride)/poly(methyl methacrylate) blends

The miscibility, morphology, and thermal properties of poly(vinyl chloride) (PVC) blends with different concentrations of poly(methyl methacylate) (PMMA) have been studied. The interaction between the phases was studied by FTIR and by measuring the glass transition temperature (T_g) of the blends using differential scanning calorimetry. Distribution of the phases at different compositions was studied through scanning electron microscopy. The FTIR and SEM results show little interaction and gross phase separation. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of the first and second stage of degradation in PVC in the presence of PMMA were higher than the pure. The stabilization effect on PVC was found most significant with 10 wt% PMMA content in the PVC matrix. These results agree with the isothermal degradation studies using dehydrochlorination and UV-vis spectroscopic results carried out on these blends. Using multiple heating rate kinetics the activation energies of the degradation process in PVC and its blends have been reported.     

Potentiometric determination of coextraction constants of potassium salts in ion-selective electrodes utilizing a nitrobenzene liquid membrane phase

A theoretical treatment of potentiometric data is applied to calculate coextraction constants (K_IA) for three potassium salts from water into a liquid nitrobenzene phase. The experiment involves treating nitrobenzene as a membrane and contacting it with two aqueous solutions of different ion activities. In the presence of either a cation or anion exchanger, the ratio of activities of ions in the two aqueous phases gives rise to a potential difference across the membrane that depends upon the nature and charge of the counter ion of the ion-exchanger in excess. Here, the cation exchanger was chosen to be potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and the anion exchanger was tetradodecylammonium chloride (TDDACl). TDDACl was incrementally added to the nitrobenzene phase containing a fixed concentration of KTpClPB, and the corresponding emf was recorded as a function of concentration of TDDACl. The membrane changes from one with cation exchanger properties (excess KTpClPB) to one with anion exchanger properties (excess TDDACl). The potential difference and shape of the titration curve can be predicted by theory based on the phase boundary potential model. Log(K_IA) values calculated for KCl, KNO₃ and KClO₄ in nitrobenzene were found as: −10.53 (± 0.09), −8.16 (± 0.05) and −5.63 (± 0.03) respectively, in accordance with the Hofmeister series of lipophilicity, and similar to those observed in PVC membranes containing other plasticizers. The method presented here offers the advantage over other methods to calculate K_IA, in that it is relatively experimentally simple without compromising the accuracy of the calculated coextraction constants. The ability to titrate directly into the liquid membrane phase affords a higher precision compared to the preparation of a series of PVC/plasticizer membranes with different compositions.     

Study of Kryptofix5 Complexation with La<Superscript>3+</Superscript> Cation in Several Individual and Binary Nonaqueous Solvents Using Conductometric Method

Complexatio of the La³⁺ cation with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane(Kryptofix5) was studied in pure solvents acetonitrile (AN), methanol (MeOH), nitrobenzene (NB), tetrahydrofuran (THF), methyl acetate (MeOAC) and in various binary solvent mixtures of AN–MeOH, AN–NB, AN–THF, and AN–MeOAC systems at different temperatures using the conductometric method. The stoichiometry of the complex was found to be 1 : 1 (ML). In all cases, the variation of the log kf with composition of the solvent was non-linear. This behavior is probably due to a change in the structure of these binary mixed solvents as the composition of the medium is varied. The stability order of the complex in pure nonaqueous solvents at 25°C increases in the order: AN > THF > MeOAC > MeOH > NB. The values of thermodynamic data (ΔH _c °,ΔS _c °) formation of (Kryptofix5.La)³⁺ complex are definitely solvent dependent.     

Excess Molar Volumes and Partial Molar Volumes of Binary Mixtures Containing Diethylcarbonate with Benzene and Substituted Benzenes at 293.15 K

Densities of the binary mixtures of diethylcarbonate with benzene and substituted benzenes, namely toluene, bromobenzene, chlorobenzene and nitrobenzene have been measured as a function of the composition, at 293.15 K and atmospheric pressure using a bicapillary pycnometer with an accuracy of 4 parts in 10⁴.The calculated excess molar volumes, V ^E were correlated with Redlich-Kister equation. The excess molar volumes are negative over the entire range of composition for the systems diethylcarbonate with benzene, toluene, bromobenzene and nitrobenzene. An inversion of the sign of V ^E is observed over some concentration for mixtures of diethylcarbonate with chlorobenzene. Partial molar volumes, V_i are also evaluated and their values have been extrapolated to zero concentration to obtain the limiting value at infinite dilution, V^o _i . The numerical values of the excess molar volumes for binary mixtures decrease in the order: chlorobenzene > benzene > bromobenzene ≈ toluene > nitrobenzene. The results are explained in terms of dissociation of the self-associated solute molecules and the formation of aggregates between unlike molecules.     

Thermal degradation of γ-irradiated poly(vinyl chloride)

The thermal degradation of unstabilized poly(vinyl chloride) irradiated with γ-rays has been investigated by dynamic thermogravimetry in a nitrogen atmosphere. The overall effect of irradiation is to render PVC more susceptible to thermal degradation. The change in activation energy of degradation with dose showed a behavior parallel with the change of intrinsic viscosity with dose. The minimum and maximum E_a values were found to correspond with the minimum and maximum observed on [η] versus dose curves. This behavior indicates an inverse relationship between the rate of thermal degradation and molecular size.     

Mathematical models of the initial stage of the thermal degradation of poly(vinyl chloride). II. The thermal degradation of poly(vinyl chloride) with effective removal of HCl

The dehydrochlorination of different samples of PVC under vacuum with continuous removal of HCl by freezing, has been studied at 180–210°C. The comparison of the kinetic curves of the dehydrochlorination of various samples of PVC which were obtained by us and other investigators, with the theoretical curves for the thermal degradation of idealized PVC in the absence of HCl has been carried out. This had made it possible to evaluate the influence of unstable fragments present in the original polymer on the initial rate of PVC degradation quantitatively. It has been shown that the distinction between the stationary rates of the dehydrochlorination of various samples of PVC is determined by the difference of the values of the average length of dehydrochlorination chain, l_av. The most probable interval of the values of l_av has been ascertained to be 4–12. It is established that the most probable value of the constant of the rate of dehydrochlorination of normal links of PVC, k₀, is 2.1 × 10^?7?2.5 × 10^?7 s^?1 at 200°C. © 1993 John Wiley & Sons, Inc.     

Effect of solvent on glass transition temperature in chemically modified polyvinyl chloride (PVC)

Polyvinylchloride has been chemically modified with sodium benzene thiolate at different temperatures, in solvents promoting the formation of polymer gels, in solvents favoring light polymer interactions and in the absence of solvent, that is, in the melt. From the¹³C-NMR results it is shown that the substitution reactions on PVC, in all media and temperatures studied, are stereospecific and the nature of substituted chlorines the same.The glass transition temperature of modified polymers has been studied by differential scanning calorimetry. The glass transition temperature of the modified polymers in the absence of solvent decreases linearly with degree of substitution. When the reaction is carried out in solvents containing carbonyl groups, such as diethyl malonate, cyclohexanone and 2-butanone, the evolution of the glass transition up to about 25% substitution does not follow the above behavior. At higher levels of substitution the evolution ofT _g is similar to that in the melt. For the ether-containing solvents, such as tetrahydrofurane and dioxane, the evolution lies between the two previous curves.When the reactions of PVC with sodium benzene thiolate are carried out in cyclohexanone at different temperatures, between 15–90°C, the evolution of the glass transition temperature with conversion is different for each temperature, and if the reaction temperature increases, the slope of the initial part moves to that in the absence of solvent.These results are related to the formation of PVC gels or interactions. As the nature and percentage of substituted chlorine for a given chemical composition are the same in all the solvents and conditions studied, we propose that Cl-atoms of isotactic and/or heterotactic configurations are implied in the formation of PVC gels or interactions.     

Effect of chelation on the polycondensation of monomers having an active ester group

Various amino acid esters and dicarboxylic acid esters having a β-thioether group have been synthesized and their polycondensation with diamine was found to occur at room temperature to form polyamide thioether. The effect of solvents or chelating agents on their polycondensation reaction was investigated. Metal acetylacetonates or inorganic salts had a great influence on the rate of the polycondensation reaction, and the catalytic activity of metal acetylacetonates M(AcAc)_n or inorganic salts decreased in the following order: Mg(AcAc)₂?Th(AcAc)₄>Cu(AcAc)₂>Li(AcAc)>None>Zr(AcAc)₄, MgCl₂·6H₂O>CuCl₂·.2H₂O>ZnCl₂>MgCl₂>None. It was also found that the amount of polyamide thioether was dependent on solvents or the presence of chelating agents because the polycondensation rate and the apparent equilibrium between ring and chain structures were both greatly influenced by solvents or chelating agents. These effects of solvents or chelating agent on the polycondensation may be attributable to formation of a complex with the thioether group which enhances the reactivity of ester.     

Investigation of stabilizing action of mixtures of organic phosphites with trialkyl(aryl)tin isocyanates in the thermal degradation of poly(vinyl chloride)

Investigation was made on the effects of mixtures of organic phosphites (tributyl-, trioctyl-, diphenylisooctyl) with isocyanates (triethyl-, tributyl-, triphenyl-, tribenzyltin) upon the rate of dehydrochlorination and crosslinking, and on the absorption spectrum of PVC during degradation in evacuated ampoules at 180°. The effectiveness of stabilizing action of these synergistic mixtures depends on the chemical structures of both phosphite and isocyanate. The activity of isocyanates in mixtures with phosphites decreases in the order: Bz₃SnNCO, Ph₃SnNCO > Bu₃SnNCO > Et₃SnNCO. At 180°. triphenyltin isocyanate decomposes with formation of tetraphenyltin and diphenyltin diisocyanate; parallel with disproportionation, decarboxylation of triphenyltin isocyanate occurs, during which carbon dioxide and N,N′-bis(triphenyltin)carbodiimide are generated. N,N′-bis(triphenyltin)carbodiimide is a stabilizer for PVC in thermal degradation and gives synergistic mixtures with organic phosphites.