Kinetics and mechanism of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone-triphenylarsine oxide mixture in chloroform and aqueous nitrate medium

The kinetics of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone (HTTA) and triphenylarsine oxide (Ph₃AsO) mixture in chloroform and aqueous nitrate medium has been investigated using a stirred Lewis cell at ionic strength of 0.1M. The effect of the concentration of HTTA, Ph₃AsO, H⁺ and NO ₃ ^– on the rate of distribution of Am(III) and Eu(III) was studied. The results were interpreted by reaction mechanisms where the rate-determining steps are the parallel reactions of Am(OH)²⁺ or Eu(OH)²⁺ with one HTTA molecule and one Ph₃AsO molecule in the aqueous medium. The values at 25 °C of the rate constantk _HLL (HL=HTTA andL=Ph₃AsO) are 1.6±0.3·10⁶M^–2·s^–1 and 2.3±±0.3·10⁸M^–2·s^–1 for Am(III) and Eu(III), respectively.     

Studies on the equilibrium uptake of some metal ions on a mixed and doped hydrous oxide using radiotracers

A highly sensitive and rapid method has been developed for the extraction-spectrophotometric determination of ultra trace amounts of americium. Americium(III) is selectively extracted from 1–10M HNO₃ medium with a mixture of (0.3M HDEHP+0.1M P₂O₅), both dissolved in xylene, and finally estimated in the organic phase itself absorptiometrically employing Arsenazo-III as the chromogenic reagent. A 60% dioxaneethanol mixture was used for optium colour development. Beer's law is obeyed in the concentration range 0.1–0.7 g Am cm^–3 and as little as 0.11 g Am cm^–3 could be determined with a precision better than ±2%. The molar absorptivity based on Am content is (3.599±0.049)·10⁵ dm³·mol^–1·cm^–1 at 648 nm which is incidentally the highest value reported as yet for its determination. The optimum concentration range, evaluated by Ringbom's method is 0.1–0.6 ppm Am. Common contaminants such as Al³⁺, Co²⁺, Cr³⁺, Fe³⁺, Ni²⁺, Zr⁴⁺, F^–, NO₃ ^–, and SO ₄ ^2- in fairly large quantities and moderate amounts of Pu⁴⁺, Th⁴⁺ and UO ₂ ²⁺ cause no interference in the final assay. Colour development is almost instantaneous and its intensity remains virtually constant for at least 48 hours.     

Spectrophotometric and titrimetric determination of gallium in minerals and ores using semimethylthymol blue

The composition, overall stability constant and molar absorptivity of the chelate of gallium(III) ion with semimethylthymol blue, SMTB, were determined spectrophotometrically in acetate buffer (pH 4.5–5). A violet Ga(SMTB) chelate was formed with logarithmic overall stability constant of 18.0±0.1 (I=0.1) and molar absorptivity of 4.25×10⁴l mol^–1cm^–1 (_max 580 nm). SMTB is proposed as a new reagent for the spectrophotometric determination of micro-molar amounts of gallium(III). The colour development depends on time, temperature, pH and buffer species. The interference of different cations, anions and organic acids on gallium(III) determination was also investigated. Beer's law was obeyed for 3.5–31.3 gGa(III)/25ml (0.14–1.25 g ml^–1). SMTB was used for the spectrophotometric determination of gallium in different grade minerals and ores and the results were of acceptable error and relative standard deviation. Comparison between the two suggested methods and atomic absorption spectrometry for Ga(III) determination was carried out.     

Palladium(II)-kojic acid interaction

Summary The interaction of palladium(II) with the bidentate kojic acid compound, HL, was studied. The pk_L and pk_c (11) values 7.65±0.15 and 5.22±0.10 were determined in aqueous media in the presence of different solvents (dioxane, MeOH, EtOH, Me₂CO and DMF) at variable concentrations (20–50% v/v solvent/H₂O). A reddish brown square planar 11 solid palladium kojic acid complex, PdLCl·H₂O, was prepared and characterized.     

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.     

A comparative kinetic study of iridium(III) catalysis in cerium(IV) oxidation of dioxane in aqueous sulfuric acid and perchloric acid media

The kinetics and mechanism of IrIII-catalysed oxidation of dioxane by CeIV in both aqueous H2SO4 and HClO4 media have been studied at different temperatures under the conditions: [dioxane]T [CeIV]T [Ir]T (ca. 10–6–10–8moldm–3). In aqueous HClO4 media a slow uncatalysed path exists alongside the catalysed path, while in aqueous H2SO4 media the catalysed path is the only kinetically detectable path. In both media, the overall process shows a first-order dependence on [CeIV]T; the catalytic path is first order in [Ir]T and exhibits a non-linear dependence on [dioxane]T. The catalysed path probably involves a pre-equilibrium interaction between the catalyst and substrate leading to an outer-sphere complex followed by the electron transfer in the rate-determining step involving CeIV and an outer-sphere complex formed in pre-equilibrium steps. The catalytic path presumably involves the IrIII/IrIV cycle. In HClO4 media the catalytic efficiency is greater than in H2SO4 media. Activation parameters for different paths have been determined in order to rationalise the mechanistic steps.     

Potentiometric studies of the thermodynamics of iodine disproportionation from 4 to 209°C

The equilibrium constant for the disproportionation of iodine in aqueous solution was determined as a function of temperature from 3.8 to 209.0°C using emf measurements in low ionic strength media. The equilibrium constant and associated molal thermodynamic quantities at 25°C are: K₁=1.17±0.62×10^–47, H^o=273±3 kJ-mol^–1, S^o=16±9 J-K^–1-mol^–1, and C _p ^o =–1802±41 J-K^–1-mol^–1. Although the value of K₁ is in excellent agreement with a previous emf measurement at 25°C, these results conflict with the corresponding parameters obtained from the NBS tables. Moreover, at temperatures above ca. 100°C, our measured values for the equilibrium constant diverge strongly from all previous estimates and predictions.     

Spectrophotometric Determination of Iron(III) After Separation by Adsorption of its 2-Thenoyltrifluoroacetone Complex on Microcrystalline Naphthalene

Summary A new spectrophotometric method for the determination of iron (III) after adsorption of its red TTA complex onto microcrystalline naphthalene has been developed. Iron(III) reacts with 2-thenoyltri-fluoroacetone in pH range 2.4–5.2 to form a water-insoluble 13 red complex which is easily adsorbed onto microcrystalline naphthalene from its acetone solution. The naphthalene mixture is separated, dried and dissolved in 10 ml dioxane. The red organic phase has a plateau around 480–500 nm while the reagent has no absorbance beyond 420 nm. The system obeys Beer's law over 20–120g iron(III) in 10 ml of dioxane solution or 0.4–2.4 ppm aqueous. The molar absorptivity of the complex species is 3.9×10³·l·mol^–1·cm^–1, while the sensitivity for Fe(III) extends to 1.43×10^–2 g cm^–2 for 0.001 absorbance. Samples containing 80g of iron gave a relative standard deviation of 1.23%. The effects of experimental variables such as pH, amount of reagents, shaking and digestion time, aqueous volume and diverse ions have been examined. The method has been applied to the determination of iron(III) in standard reference and environmental samples and results compared with other standard colorimetric procedures.

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Spektrophotometrische Bestimmung von Eisen(III) nach Adsorption seines 2-Thenoyltrifluoraceton-Komplexes an mikrokristallines Naphthalin

Zusammenfassung Eine neue spektrophotometrische Methode zur Bestimmung von Eisen (III) nach Adsorption seines roten TTA-Komplexes an mikrokristallines Naphthalin wurde ausgearbeitet. Fe(III) reagiert mit 2-Thenoyltrifluoraceton bei pH 2,4-5,2 unter Bildung eines roten, wasser-unlöslichen 13-Komplexes, der sich aus seiner acetonischen Lösung leicht an mikrokristallines Naphthalin adsorbieren läßt. Das Naphthalin-Gemisch wird abgetrennt, getrocknet und in 10 ml Dioxan gelöst. Die rote organische Phase hat ein Adsorptions-Plateau bei 480–500 nm, während das Reagens jenseits 420 nm nicht adsorbiert. Das System entspricht dem Beerschen Gesetz von 20–120g Fe(III) in 10 ml Dioxan-Lösung bzw. 0,4–2,4 ppm in wäßriger Lösung. Die molare Extinktion der Komplexverbindung beträgt 3,9× 10³l·mol^–1·cm^–1. Die Empfindlichkeit für Fe(III) entspricht 1,43×10^–2 g cm^–2 für 0,001 Absorptionseinheiten. Proben mit 80g Fe(III) zeigen eine rel. Standardabweichung von 1,23%. Die Wirkung variabler Versuchsbedingungen pH, Reagensmenge, Zeit, Volumen und diverse Fremdionen wurden geprüft. Das Verfahren wurde an Standardsubstanzen geprüft und seine Ergebnisse mit denen anderer kolorimetrischer Verfahren verglichen.

     

Alkylation of nucleic acids and their components

Guanosine, cytidine, inosine, and thymine react with 4-[N-(-chloroethyl)-N-methylamino]-benzaldehyde to give 7-alkylguanosine, 3-alkylcytidine, 1-alkylinosine, and 1-alkylthymine, respectively. The order of reactivities of the nucleosides with respect to 4-[N-(-chloroethyl)-N-methylamino] benzaldehyde in 36% aqueous dioxane at 50°C and pH 5–6 is guanosine > inosine > cytidine > thymine. Inosine, cytidine, and thymine are 36%, 21%, and 13% as reactive as guanosine. Adenosine and uridine do not react under these conditions. The ratio of the rate constant for the alkylation of guanosine by 4-[N-(-chloroethyl)-N-methylamine]-benzaldehyde and the rate constant for the hydrolysis of the latter in 17% aqueous dioxane at 50° and pH 5–6 is 10.5±0.5 mole^–1. The alkylation of guanosine at pH 7.5 is accompanied by cleavage of the imidazole ring of the 7-alkylguanosine, which proceeds at a higher rate than the rate of the limiting step — ionization of 4-[N-(-chloroethyl)-N-methylamino]benzaldehyde. The transformations of the alkylated nucleosides in acids and alkalis were studied, and the rate constants of these transformations were determined.See [26] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 109–116, January, 1972The authors thank D. G. Knorre for discussing the kinetic results of this research.     

Aquation of α-cis-chloroaquoethylenediamine-N,N'-diacetatocobalt(III) in aqueous and in mixed solvents: A mechanistic study

Summary The displacement of chloride ligands from -cis-chloro-aquoethylenediamine-N,N-diacetatocobalt(III) in nonacidic aqueous solutions was followed conductimetrically at 30–45° and the products of aquation were characterised by conductance, spectral and ion-exchange techniques. The rate constants for aquation in aqueous media and in 1 : 4 v : v mixed solvents at 25° are: 4.0 × 10^–5 s^–1 in H₂O, 2.71 × 10^–5 s^–1 in MeOH : H₂O, 2.74 × 10^–5 s^–1 in EtOH: H₂,O and 2.58 × 10^–5 s^–1 n in Me₂CO : H₂O. The corresponding H* and S* values have also been evaluated. Solvent polarity has a marked influence on the rate of chloride ion release. The aquation rate constants and the activation parameters have been correlated with solvent parameters,e.g. D, Y-values, Dimroth's E_T and Kosower's Z-values and, based on these correlations, a dissociative interchange (I_d) mechanism is proposed rather than dissociative as observed for some other cobalt(III) complexes.Senior author.     

Kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) in aqueous solution

Summary The kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) ion in aqueous solution in the presence ofo-phenanthroline was studied spectrophotometrically. The first-order rate constant (k ) at 30° C [I=1 M(NaCl)] for the thermal reaction is (1.49±0.13)×10^–6 s^–1 with H =(158±7)kJ mol^–1 and S=(42±4) JK^–1 mol^–1. The initial quantum yield for the photochemical reaction at pH=7 is independent of the light intensity and is (1.49±0.33)×10^–2 mol einstein^–1.A communication on this subject was presented at the XVI Latinamerican Chemistry Congress held at Rio de Janeiro. Brasil, October 14–20, 1984.     

Thermodynamics of Cm(III) in Concentrated Salt Solutions: Carbonate Complexation in NaCl Solution at 25°C

The carbonate complexation reactions of Cm(III) were studied by time-resolved laser fluorescence spectroscopy in 0–6 m NaCl at 25°C. The ionic strength dependence of the stepwise formation constants for the carbonato complexes Cm(CO₃) _n ^3–2n with n = 1, 2, 3, and 4 is described by modeling the activity coefficients of the Cm(III) species with Pitzer's ion-interaction approach. Based on the present results and literature data for Cm(III) and Am (III), the mean carbonate complexation constants at I = 0 are calculated to be: log ₁₀₁ ^o =8.1 ±0.3, log ₁₀₂ ^o =13.0 ± 0.6, log ₁₀₃ ^o =15.2 ± 0.4, and log ₁₀₄ ^o =13.0 ± 0.5. Combining these equilibrium constants at infinite dilution and the evaluated set of Pitzer parameters, a model is obtained, that reliably predicts the thermodynamics of bivalent actinide An(III) carbonate complexation in dilute to concentrated NaCl solution.     

Colorimetric method for the simultaneous determination of chlorphenoxamine hydrochloride and anhydrous caffeine in pure and dosage forms with rose bengal

A rapid, simple and sensitive colorimetric method for the simultaneous determination of chlorphenoxamine HCl and anhydrous caffeine was developed, based on charge-transfer complex formation of the drugs with rose bengal in basic media of pH 9.0. The chlorphenoxamine HCl (I) complex was measured at 588 nm whereas anhydrous caffeine (II) was measured at 551 nm. The optimal experimental parameters for colour production were studied. Beer's law was obeyed in the concentration ranges 2–40 and 2–34 g ml^–1 for I and II, respectively. The Ringbom optimum concentration ranges were 3–36 and 3–30 g ml^–1 for I and II, respectively. The results obtained showed good recoveries of 100.2 ± 1.5 and 99.7 ± 1.3% with relative standard deviations of 0.37 and 0.47% for I and II, respectively. Applications of the method to representative pharmaceutical dosage forms are presented and the validity assessed by applying the standard addition technique.     

Effect of acrylamide concentration on the kinetics of oxidation of tartaric acid by cerium(IV) in sulfuric-perchloric acid media

The kinetics of oxidation of tartaric acid by Ce(IV) in the absence and presence of acrylamide has been investigated spectrophotometrically in aqueous H₂SO₄–HClO₄ media at a constant ionic strength 2.0M and 25°C. Oxidation of tartaric acid in both cases was first order with respect to Ce(IV). Kinetic data showed that the reaction involves the formation of an unstable complex and an intermediate free radical. The activation parameters were calculated to be E _a =91.3±0.4 kJ-mol^–1, S=20.2±1.0 J-mol^–1-K^–1, H=88.8±0.4 kJ-mol^–1. A polymerization mechanism is discussed.     

Decomposition kinetics ofbis(biguanide)silver(III) cation in acid perchlorate media

Summary In acid perchlorate media, the title complex undergoes intramolecular redox decomposition generating ultimately Ag⁺ ion and oxidation products of the ligand. The reaction follows a simple first-order process, and the observed pseudo-first-order rate constant is given by k_obs=k₀+kK_a/[H⁺] where K_a is the deprotonation constant of the parent complex; pK_a is approximately 5.9 at 30°. The values of 10⁵ k₀(s^–1) and 10⁷ kK_a (Ms^–1) at 30°, I=1.0 M, are 9.3±0.1 and 11.8±1.3; corresponding H (kJ/mol), S (JK^–1 M^–1) values are 105±0.5, 23±1 and 79±8,-96±5, respectively. The results are compared with those for similar reaction of (ethylenebisbiguanide)silver(III) and effect of change in ligand structure on kinetic behaviours of these complexes is discussed.     

Photolysis of water-carbon tetrachloride and water-chlorobenzene saturated solutions and their two-phase systems. Quantum yields of chloride ions

The quantum yields of formation of chloride ions were determined in photolysis (=254 nm) of watercarbon tetrachloride organic phase of CCl₄(Cl^–)=0.89±0.04 water-chlorobenzene (_PhCl(Cl^–)=0.137± ±0.005) two-phase systems and saturated aqueous solutions of carbon tetrachloride (_CCl4(Cl^–)=18.9±5.6 and chlorobenzene _PhCl(Cl^–)=0.56±0.03. The quantum yields of chloride ions obtained from these systems are compared with partial radiation yields in the same systems. A mechanism for formation of Cl^– ions is proposed.     

Temperature Dependence of Solubility for Ibuprofen in Some Organic and Aqueous Solvents

The thermodynamic functions—Gibbs energy, enthalpy, and entropy of solution—were evaluated from the solubilities of ibuprofen determined at several temperatures in the pure solvents: octanol, isopropyl myristate, chloroform, cyclohexane, and water. The organic solvent-saturated aqueous media and water-saturated organic solvents were also studied, except for cyclohexane. In aqueous media, the solubility was determined at pH = 7.4 and an ionic strength 0.15 mol-L^–1 (physiological values). The excess Gibbs energy and the activity coefficients of the solutes were also determined. The solubilities are higher in organic media such as chloroform and octanol than in aqueous media and cyclohexane.     

Potassium ferrocyanide as a spectrophotometric reagent for the determination of uranium

Potassium ferrocyanide gives a colour reaction with U(VI), which is suitable for its determination. The complex absorbs in the wavelength range of 390–397 nm. The optimum pH range for colour development was 1.5–3.5. The molar absorptivity was found to be 4.65·10³ 1·mol^–1·cm^–1. Most of the anions up to 1000 g did not interfere. The method was made selective by extracting U(VI) first with DOSO from the mixture of interfering cations from 1–2M HNO₃ medium and then determining uranium in the back-extracted solution by developing the colour with ferrocyanide. 20 g/10 ml of U(VI) in the final solution could be satisfactorily determined within an RSD of ±2%.     

Structure of tetraphenylarsonium tricyano- 2,2′,6′,2′′-terpyridylferrate(II), AsPh4[FeII(terpy)(CN)3]; and kinetics of oxidation of the complex anion by peroxodisulfate in water and in binary aqueous mixtures

The structure of the title compound has been determined by X-ray crystallography. The octahedral arrangement of ligands about the iron(II) centre is somewhat distorted, with the axial NC–Fe–CN bond angle being 174.3(4)°. The oxidation of the tricyano-2,2,6,2- terpyridylferrate(II) anion by the peroxodisulfate anion has been investigated in water and in binary aqueous mixtures. The reaction follows a second order rate law, with a second-order rate constant of 0.126± 0.001dm3mol–1s–1 at 295.2K. The enthalpy and entropy of activation in water are 51.3±1.8kJmol–1 and –89±5JK–1mol–1 respectively. The rate is retarded on addition of organic cosolvent. The transfer chemical potential of the initial state from water into mixed solvents has been determined from solubility measurements, and compared with the transfer potential of the transition state. Solvent effects on the reaction are discussed in terms of initial state versus transition state solvation.     

Nuclear magnetic resonance investigation of intramolecular scrambling processes in meso-(2,3-butylenediamine)tetraacetate. Diamagnetic complexes of transition metal ions

Summary The acetate scrambling processes (, conversion and N inversion) occurring in the complexes formed from meso-(2,3-butylenediamine)tetraacetic acid (BDTA) with zinc(II), cadmium(II), mercury(II), scandium(III), yttrium(III) and lanthanum(III) ions have been investigated by line shape analysis of their n.m.r. spectra. Between 308 and 373 K fast conversion between and isomers and slow nitrogen inversion occur except for mercury(II) and yttrium(III) in the latter case. H^* = 2.3±0.1 kJ mol^–1 and S^* = –6.9±0.2 mol^–1 J K^–1 for the mercury complex; H^* = 2.6 ±0.2 kJ mol^–1 and S^* = –5.5±0.5 mol^–1 JK^–1 for the yttrium complex. Exchange mechanisms proceeding through different reaction intermediates are discussed on the light of the results obtained in this work as well as previously on other polyaminepolycarboxylate complexes of the same ions.