Extraction of sodium picrate into nitrobenzene in the presence of dicyclohexyl-18-crown-6

From extraction experiments and -activity measurements, the extraction constant corresponding to the equilibrium Na⁺(aq)+A^–(aq)+L(nb)NaL⁺(nb)+A^–(nb) taking place in the two-phase water-nitrobenzene system (A^–=picrate, L= dicyclohexyl-18-crown-6; aq-aqueous phase, nb=nitrobenzene phase) was evaluated as logK _ex(NaL⁺, A^–)=2.6.Further, the stability constant of the dicyclohexyl-18-crown-6-sodium complex in nitrobenzene saturated with water was calculated: _nb(NaL⁺)=7.8.     

Thermodynamics of molecular interactions in ethyl iodide+toluene mixtures

The excess Gibb's free energy of mixing, G^E, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The H^E and G^E values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and G^E>H^E. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A₂B molecular species describes well (within±10 J-mol^–1 in the worst case) the general dependence of H^E on X_A (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A AB and 2A+BA₂B reactions along with the enthalpies of formation of AB and A₂B molecular species have been calculated.     

Isotope exchange between alkaline earth metal hydroxide and HTO water in the equilibrium state

In order to reveal to what extent tritium (³H or T) can be incorporated into hydroxides, the isotope exchange reaction (OT-for-OH exchange reaction) between each alkaline earth metal hydroxide (M(OH)₂), where M means alkaline earth metal (M=Ca, Sr or Ba) and HTO water was observed homogeneously at 30 °C under equilibrium after mixing. Consequently, the followings were obtained: (1) a quantitative relation between the electronegativity of each M ion and the ability (of the M ion) incorporating OT^– into the M hydroxide can be found and the ability is small when the temperature is high, (2) the exchange rate for the OT-for-OH exchange reaction is small when the electronegativity of the M ion in the M hydroxide in great, (3) as for the dissociation of HTO water, it seems that fomula (HTOT⁺+OH^–) is more predominant than the fomula (HTOH⁺+OT^–) when the temperature is high and (4) the method used in this work is useful to estimate the reactivity of a certain alkaline material.     

Stability of complex of Cs+ with valinomycin in nitrobenzene saturated with water

From extraction experiments and -activity measurements, the extraction constants corresponding to the equilibrium Cs⁺(aq)+Cl^–(aq)+L(nb)CsL⁺(nb)+Cl^–(nb) in the two-phase water-nitrobenzene system (L=valinomycin; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as log K_ex(CsL⁺, Cl^–)=2.2. Further, the stability constant of the valinomycin-cesium complex in nitrobenzene saturated with water was calculated: log _nb(Csl⁺)=10.1.     

Composition and structure of zirconium complexes in tributyl phosphate extracts of Zr from concentrated nitric acid solutions

Using quantitative difference IR spectroscopy we have found that the tibutyl phosphate & acts of zirconium from 12–15 M HN03 contain ionic associates [(TBP)₂H⁺]Zr(NO₃)₅ ^– (I) and [TBP· H₃0⁺ (H₂0)_n]Zr(N0₃)₅ ^– (II), where n = 1, 2, as well as the Zr(N0₃)₄(TBP)₂ complex at a lower concentration than (I) and (I.). The equilibrium I II is shifted toward II at higher C_{HNo 3} ⁰ and lower c_Zr ⁰. The structure of associates I and II is discussed.Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, D. I. Mendeleev Moscow Chemical Technological Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 80–89, September–October, 1993.Translated by L. Smolina     

Complex formation followed by internal electron transfer: The reaction between cysteine and iron(III)

Summary A kinetic study of the anaerobic oxidation of cysteine (H₂ L) by iron(III) has been performed over thepH-range 2.5 to 12 by use of a stopped-flow high speed spectrophotometric method. Reaction is always preceded by complex formation. Three such reactive complex species have been characterized spectrophotometrically: FeL ⁺ (_max=614 nm, =2 820 M^–1cm^–1); Fe(OH)L (_max=503 nm; shoulder at 575 nm, =1 640 M^–1cm^–1); Fe(OH)L ₂ ^2– (_max=545 nm; shoulder at 445 nm, =3 175 M^–1 cm^–1). Formation constants have been evaluated from the kinetic data: Fe³⁺+L ^2– FeL ⁺: logK ₁ ^M =13.70±0.05; Fe(OH)²⁺+L ^2– Fe(OH)L: logK ₁ ^MOH =10.75±0.02; Fe(OH)L+L ^2– Fe(OH)L ₂ ^2– ; logK ₂ ^MOH =4.76±0.02. Furthermore the hydrolysis constant for iron(III) was also obtained: Fe(OH)²⁺+H⁺ Fe _aq ³⁺ : logK ^FeOH=2.82±0.02). Formation of the mono-cysteine complexes, FeL ⁺ and Fe(OH)L, is via initial reaction of Fe(OH)²⁺ with H₂ L (k=1.14·10⁴M^–1s^–1), the final product depending on thepH. FeL ⁺ (blue) formed at lowpH decomposes following protonation with a second-order rate constant of 1.08·10⁵M^–1s^–1. Fe(OH)L (purple) decomposes with an apparent third order rate constant ofk=3.52·10⁹M^–2s^–1 via 2 Fe(OH)L+H⁺ products, which implies that the actual (bimolecular) reaction involves initial dimer formation. Finally, Fe(OH)L ₂ ^2– (purple) is remarkably stable and requires the presence of Fe(OH)L for electron transfer. A rate constant of 8.36·10³M^–1s^–1 for the reaction between Fe(OH)L and Fe(OH)L ₂ ^2– is evaluated.Dedicated to Prof. Dr. mult. Viktor Gutmann on the occasion of his 70th birthday     

Preparation and properties of chiral complexes of Cu(II) with (S)-2-[(N-benzylprolyl)amino]benzaldehyde oxime,catalysts of azlactone hydrolysis

Two Cu(II) complexes of (S)-2-[(N-benzylprolyl)amino]benzaldehyde oxime (L) were isolated. The complex Cu[(LH^–1)(Cl)] is green, whereas Cu₂(LH₂)_–2 is red-brown. The structure of these complexes was proved by elemental analysis, IR and UV spectroscopy. The average molecular masses ( ) of the complexes in ethanol were determined by precision ebulliometry. The concentration dependence of the values of these complexes is consistent with the existence of the following equilibria in ethanol: Cu[(LH_–1)(Cl)] + EtOH Cu[(LH_–1)(HOEt)]⁺+Cl⁺ and [Cu₂(LH_–2)₂] + EtOH 2[Cu(LH-_–2)(HOEt)]. The equilibrium constants of these two reactions were determined. Both [Cu(LH_–1)(Cl)] and [Cu₂(LH_–2)₂] catalyze with equal efficiency the hydrolysis of 2-methyl-4-benzyl-5(4H)-oxazolone in aqueous solutions at a given pH. The UV spectra of both complexes in water at similar pH values are identical. Thus, both complexes must be interconvertible in aqueous solutions. Furthermore, the absence of any electrophoretically mobile particles in neutral aqueous buffers is an indication that the complexes [Cu₂(LH^–2)₂] and [Cu(LH^–2)(H₂O)] are the predominant species in solution under these conditions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2270–2275, October, 1991.     

An aqueous thermodynamic model for Ca2+−SO 3 2− ion interactions and the solubility product of crystalline CaSO3·1/2H2O

The solubility of CaSO₃·1/2H₂O(c) was studied under alkaline conditions (pH>8.2), in deaerated and deoxygenated Na₂SO₃ solutions ranging in concentration from 0.0002 to 0.4M and in CaCl₂ solutions ranging in concentration from 0.0002 to 0.01M, for equilibration periods ranging from 1 to 7 days. Equilibrium was approached from both the over- and the under-saturation directions. In all cases, equilibrium was reached in <1 days. The aqueous Ca²⁺–SO ₃ ^2– ion interactions can be satisfactorily modeled using either ion-association or ion-interaction aqueous thermodynamic models. In the ion-association model, the log K°=2.62±0.07 for Ca²⁺+SO ₃ ^2– CaSO ₃ ⁰ . In the Pitzer ion-interaction model, the binary parameters (⁰) and (¹) for Ca²⁺–SO ₄ ^2– were used, and the value of (²) was determined from the experimental data. As expected given the strong association constant, the value of (⁰) was quite small (about –134). We feel a combination of the two models is most useful. The logarithm of the thermodynamic equilibrium constant (K°) of the CaSO₃·1/2H₂O(c) solubility reaction (CaSO₃·1/2H₂O(c)Ca²⁺+SO ₃ ²⁺ +0.5H₂O) was found to be –6.64±0.07.     

Kinetics and mechanism of formation and dissociation of copper(II) and nickel(II) complexes of the Schiff base bis(acetylacetone)ethylenediimine in aqueous-organic solvent media

Summary In NH₄NO₃+NH₄OH buffered 10% (v/v) dioxan-water media (pH 7.0–8.5), thePseudo-first-order rate constant for the formation of the title complexes M(baen),i.e. ML, conforms to the equation 1/k_obs=1/k+1/(kK_o.s · T_L), where T_L stands for the total ligand concentration in the solution, K_o.s is the equilibrium constant for the formation of an intermediate outer sphere complex and k is the rate constant for the formation of the complex ML from the intermediate. Under the experimental conditions the free ligand (pK_a>14) exists virtually exclusively in the undissociated form (baenH₂ or LH₂) which is present mostly as a keto-amine in the internally hydrogen-bonded state. Although the observed formation-rate ratio k^Cu/k^Ni is of the order of 10⁵, as expected for systems having normal behaviour, the individual rate constants are very low (at 25°C, k^Cu=50 s^–1 and k^Ni=4.7×10^–4s^–1) due to the highly negative S values (–84.2±3.3 JK^–1M^–1 for CuL and –105.8±4.1 JK^–1M^–1 for NiL); the much slower rate of formation of the nickel(II) complex is due to higher H value (41.2±1.0 kJM^–1 for CuL and 78.2±1.2 kJM^–1 for NiL) and more negative S value compared to that of CuL. The K_o.s values are much higher than expected for simple outer-sphere association between [M(H₂O)₆] and LH₂ and may be due to hydrogen bonding interaction.In acid media ([H⁺], 0.01–0.04 M) these complexes M(baen) dissociate very rapidly into the [M(H₂O)₆]²⁺ species and baenH₂, followed by a much slower hydrolytic cleavage of the ligand into its components,viz. acetylacetone and ethylenediamine (protonated). For the dissociation of the complexes k_obs=k₁[H⁺]+k₂[H⁺]². The reactions have been studied in 10% (v/v) dioxan-water media and also ethanolwater media of varying ethanol content (10–25% v/v) and the results are in conformity with a solvent-assisted dissociativeinterchange mechanism involving the protonated complexes.     

Pseudohalogen compounds of astatine: Synthesis and characterization of At/I/-tricyanomethanide-and At/I/-azide-compounds

Reactions of At//⁺, At^o.H₂O, AtCl ₂ ^– and AtBr₂ with the pseudohalogenides tricyanomethanide and azide are described. Information on the compound formation of astatine with C/CN/ ₃ ^– and N ₃ ^– could be obtained on the basis of electromigration investigations under variation of the conditions /composition of the electrolyte, pH, exchange reactions of ligands/. For the reaction: [At/H₂O/C/CN/₃]+C/CN/ ₃ ^– [At/C/CN/₃/₂]+H₂O at 301 K and u=0.075 mol.l^–1 K₂=/675±25/ [1.mol^–1] and u^o=–/3.50±0.10/×10^–4 [cm².s^–1.V^–1]. According to this astatine/I/-tricyanomethanide is classified between AtI ₂ ^– and At/SCN/ ₂ ^– . First investigations in azid-containing systems confirm the formation of astatine/I/-azide-compounds. Their composition is probably At/N₃/ ₂ ^– . There is no dependence of the ion mobility of astatine/I/-azide in the investigated range on azide concentration which is due to its high stability.     

Potentiometric Determination of the First Hydrolysis Constant of Gallium(III) in NaCl Solution to 100°C

The hydrolysis equilibrum of gallium (III) solutions in aqueous 1 mol-kg^–1 NaCl over a range of low pH was measured potentiometrically with a hydrogen ion concentration cell at temperatures from 25 to 100°C at 25°C intervals. Potentials at temperatures above 100°C increased gradually because of further hydrolysis of the gallium(III) ion, followed by precipitation. The results were treated with a nonlinear least-squares computer program to determine the equilibrium constants for gallium(III)–hydroxo complexes using the Debye–Hückel equation. The log K (mol-kg^–1) values of the first hydrolysis constant for the reaction, Ga³⁺ + H₂O GaOH²⁺ + H⁺ were –2.85 ± 0.03 at 25°C, –2.36 ± 0.03 at 50°C, –1.98 ± 0.01 at 75°C, and –1.45 ± 0.02 at 100°C. The computed standard enthalpy and entropy changes for the hydrolysis reaction are presented over the range of experimental temperatures.     

Kinetics of base hydrolysis of trans-{Cr([15]aneN4)Cl2}+ ([15]aneN4 = 1,4,8,12-tetra-azacyclopentadecane)

Summary Reaction of CrCl₃(DMF)₃ with [15]aneN₄ (L; L = 1,4,8,12-tetra-azacyclopentadecane) gives the green trans-{Cr([15]-aneN ₄)Cl₂}Cl in high yield. The base hydrolysis kinetics of the cations [CrLCl₂]⁺ and [CrLCl(OH)] ⁺ have been investigated over a temperature range. For the dichloro complex, k _OH = 1.03 dm³ mol^–1 s^–1] at 25° C with H =30.4 kJmol^–1 and S _inf298 ^sup = -143 JK^–1 mol^–1. The substantial negative entropy of activation implies more association of water in the loss of Cl^– from the conjugate base in a D_CB mechanism. The kinetic parameters for the chlorohydroxo complex are k _OH = 1.9 × 10^–2dm³mol^–1 s^–1 at 25°C with H = 78.3kJmol^–1 and H _inf298 ^sup = -15 J K^–1 mol ^–1. The chlorohydroxo complex probably has the trans VI configuration with the chloride ligand on the same side of the equatorial plane as the four chiral sec-NH groups. The visible spectra of a variety of complexes trans-[Cr(L)XY] ⁿ⁺ (X = Y = Cl, OH, OH₂; X = Cl, Y = OH) have been determined.     

Coordination and spectral-luminescence characteristics of Ce3+ in nonaqueous solutions

By means of luminescence spectroscopy, through the characteristics of interconfiguration transitions 4f^n–1 5d 4fⁿ, a study has been made of the composition and structure of the coordination sphere of Ce³⁺ in anhydrous alcohols in the presence of the inorganic anions ClO^– ₄, Cl^–, Br^–, and SCN^–. For solutions of CeCl₃ - or CeBr₃ or Ce(SCN)₃ ^–, it has been shown that the inner-sphere complexes Ce(R - OH)_8–XA_X ^{3 -x} dominate (where R 0B is a solvent molecule; A is an anion) in the concentration interval from 10^–4 to 10^–2 M, x = l. In solutions of Ce· (ClO )₄ in addition to the inner-sphere complex' an anion-freer form Ce(R³⁺ OH)_{6 3+} has been found. In the solutions that were investigated, dynamic equilibrium constants were determined, and also the absorption and luminescence characteristics of the individual species.A. N. Sevchenko Scientific-Research Institute of Applied Physics Problems, Belorussian University, Minsk. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. l, pp. 114–119, January–February, 1991. Original article submitted May 3, 1990.     

Extraction of certain actinide and lanthanide elements from different acid media by polyurethane foams loaded with di-(2-ethylhexyl)phosphoric acid (HDEHP)

The effect of added TBP on the extraction of uranium(VI) with a solution of di-(2-ethylhexyl)-phosphoric acid (HDEHP) in o-dichlorobenzene from nitric acid solutions has been investigated at varying concentrations of nitric acid, HDEHP, TBP and uranium(VI). The mechanism of the synergistic effect of TBP is discussed on the basis of the results and can be summarized in the following equation: UO _2(aq) ²⁺ +0.67(HX)_3(o)+2TBP_(o)UO₂X₂·2TBP_(o)+2H _(aq) ⁺ where HX denotes HDEHP and the HDEHP loaded on the foam is trimerized.     

A thermodynamic surface model for caesium sorption on bentonite

Caesium sorption on Wyoming bentonite MX-80 has been studied in solutions of NaCl, KCl, MgCl₂, CaCl₂, NaNO₃ and Ca (NO₃)₂ of concentrations varying between 0.025 and 1 mol/L, as well as in a weakly saline (I=0.004 ml/L) and a strongly saline (I=0.46 mol/L) natural groundwater. These experiments have been used to derive a thermodynamic model for the interaction of caesium with the bentonite surface in accordance with a surface chemical model, including acid/base reactions developed recently for montmorillonite. The sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant obtained for the reaction NaX+Cs⁺CsX+Na⁺ (where X represents the ion exchange sites on montmorillonite) is log₁₀K⁰_ex=1.6. Impurities in the bentonite, influencing the concentrations of competing cations, such as Na⁺, K⁺, Mg²⁺ and Ca²⁺, have a crucial impact on the sorption of caesium. This impact can be adequately quantified with the present model. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. Distribution coefficients from the literature obtained from both batch and diffusion experiments and varying over four orders of magnitude are reproduced and explained successfully by the model.     

Effect of the Nature of a Sodium-Conducting Solid Electrolyte on the Impedance of Its Interface with the SmCo0.8Ti0.2O3 Oxide Electrode in an Oxygen Atmosphere

Impedance spectroscopy is employed for studying the behavior of the interface of the SmCo_0.8Ti_0.2O₃ semiconducting oxide electrode with a sodium-conducting solid electrolyte (Na⁺–SE) in atmospheres of argon and oxygen. Compounds with the susceptibility to hydration decreasing in the row Na₅TbSi₄O₁₂ Na₃Zr₂Si₂PO₁₂ Na₃Sc₂(PO₄)₃ are used as the Na⁺–SE. Only the systems containing the Na₅TbSi₄O₁₂ solid electrolyte, the grain surfaces of which acquire boundary layers formed by hydration products, are sensitive to oxygen. The exchange current of the electrode reaction O₂ (g) + e O₂ ^– increases from 1.8 to 19 mA/cm² in the temperature interval 250–300°C. The systems with Na⁺–SE that are not prone to hydration remain inactive in the oxygen atmosphere probably due to quick blocking of the active centers by nonconducting products of the secondary chemical reaction Na⁺ + O₂ ^– NaO₂.     

Copper(II) and nickel(II) complexes of N,N′-bis(2-cyanoethyl)-5, 7-dioxo-1,4,8,11-tetra-azacyclotetradecane

Summary Reaction of 5,7-dioxo-1,4,8,11-tetra-azacyclotetradecane with acrylonitrile gives the dicyanoethylated ligand (L). The Cu^II complex [CuLH_-2]·2H₂O has been isolated from basic solution where the macrocycle is deprotonated and acts as a dinegative quadridentate ligand. The ligand L is protonated in acidic solution and the ionisation equilibria can be summarised as LH _inf2 ^sup2+ LH⁺ +H⁺; K₁ LH⁺ L + H⁺; K₂ where pK₁ = 3.05 and pK₂ = 5.94 at 25 °C and I = 0.1 mol dm^-3 (NaNO₃). Complexation with Cu^II can be represented by the equilibria at 25 °C. Cu²⁺ + L [CuLH_-1]⁺ + H⁺; log_{11 – 1} = -3.43 Cu²⁺ + L [CuLH_-2] + 2H²⁺; log_{11 – 2} = -9.18 For Ni^II only the single equilibrium is of importance. Ni²⁺ + L [NiLH_-2] + 2H²⁺; log_{11 – 2} = -14.45     

Stability of the valinomycin-rubidium complex in water saturated nitrobenzene

From the extraction experiments and -activity measurements, the extraction constant corresponding to the Rb⁺(aq)+CsL⁺(nb)RbL⁺(nb)+Cs⁺(aq) equilibrium in the two-phase water-nitrobenzene system (L=valinomycin; aq=aqueous phase, nb=nitrobenzene phase) was evaluated in the form logK _ex (Rb⁺, CsL⁺)=0.9. Further, the stability constant of the valinomycin-rubidium complex in nitrobenzene saturated with water was calculated as log _nb(RbL⁺)=11.7.     

Kinetic studies on the formation of N-nitroso compounds IX. Nitrosyl acetate as a nitrosating agent

A study of the nitrosation of N-methylaniline and piperazine by nitrous acid in acetate buffer supports a mechanism covering both reactions, whose effective pathway depends on the relationship between the concentrations of nitrite ion, acetate ion, and nitrosatable substrate. In the case of N-methylaniline the only nitrosating agent is nitrosyl acetate, whereas in the nitrosation of piperazine the nitrous acidium ion and dinitrogen trioxide are also involved.The results obtained seem to show that nitrosation by nitrosyl acetate is diffusion controlled. On this assumption, the equilibrium constant of the reactionAcOH + HNO₂ AcONO + H₂O has been estimated from kinetic measurements as approximately 1.4 · 10^–8 M ^–1. This means that the concentration of nitrosyl acetate in the medium must be extremely small, which explains the virtual impossibility of detecting it in aqueous solution except by kinetic methods.

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Kinetische Untersuchungen zur Bildung von N-Nitroso-Verbindungen, 9. Mitt.: Nitrosylacetat als Nitrosierungsreagens

Zusammenfassung Die Untersuchung der Nitrosierung von N-Methylanilin und Piperazin mit Salpetriger Säure in Acetat-Puffer unterstützt einen für beide Fälle geltenden Mechanismus, dessen effektiver Ablauf von den Konzentrationsverhältnissen des Nitritions, des Acetations und der nitrosierbaren Substanz abhängt. Im Fall des N-Methylanilins ist das einzige Nitrosierungsagens Nitrosylacetat, während bei der Nitrosierung von Piperazin das Nitrit-Acidium-Ion und Distickstofftrioxid ebenfalls beteiligt sind.Die erhaltenen Resultate scheinen zu zeigen, daß die Nitrosierung durch Nitrosylacetat diffusionskontrolliert ist. Unter dieser Annahme kann die Gleichgewichtskonstante der ReaktionAcOH + HNO₂ AcONO + H₂O aus kinetischen Messungen zu etwa 1,4 · 10^–8 M ^–1 abgeschätzt werden. Das bedeutet, daß die Konzentration von Nitrosylacetat im Medium extrem gering sein muß; das erklärt die praktische Undetektierbarkeit dieser Spezies in wäßriger Lösung, ausgenommen mit kinetischen Methoden.

     

Catalytic properties of trinuclear thio complexes of rhenium in hydrogenation of m-nitrobenzoic acid

Trinuclear thio complexes of rhenium based on Re₃S₇ and Re₃S₄ cluster groupings have been synthesized and studied as catalysts in liquid-phase hydrogenation of m-nitrobenzoic acid. Thio complexes containing as Re₃S₇ cluster surrounded by hydroxo groups are the most active. Complexes with an Re₃S₄ cluster are less active. Reversible Re₃S₇ Re₃S₄ + S₈ transitions were found to be possible in solution.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 239–242, May–June, 1992.