Kinetics and mechanism of the reduction of μ-adi-di[N,N′-bis{salicylideneethylenediaminatoiron(III)}] by dithionate ion

The kinetics and mechanism of the reduction of the μ-adi-di[N,N′-bis{salicylideneethylenediaminatoiron(III)}] complex, [Fe₂adi], by dithionate ion, S₂O₆ ^2?, have been investigated in aqueous perchloric acid at 29 °C, I = 0.05 mol dm^?3 (NaClO₄) and [H⁺] = 5.0 × 10^?3 mol dm^?3. Spectrophotometric titrations indicated that one mole of the reductant was oxidized per mole of oxidant. Kinetic profiles indicated first-order rate with respect to [Fe₂adi] but zeroth-order dependence on [S₂O₆ ^2?]. The rate of reaction increased with increase in [H⁺], decreased with increased dielectric constant, but was invariant to changes in ionic strength of the medium. Addition of small amounts of AcO^? and Mg²⁺ ions did not catalyse the reaction. A least-squares fit of rate against [H⁺]² was linear (r ² = 0.984) without intercept. The reaction was analysed on the basis of a proton-coupled outer-sphere electron transfer mechanism.     

Kinetics and mechanism of the oxidation of tris(2,2′-bipyridine)iron(II) and tris(1,10-phenanthroline)iron(II) complexes by nitropentacyanocobaltate(III) in acidic aqueous medium

The kinetics of the oxidation of tris(2,2′-bipyridyl)iron(II) and tris(1,10-phenanthroline)iron(II) complexes ([Fe(LL)₃]²⁺, LL = bipy, phen) by nitropentacyanocobaltate(III) complex [Co(CN)₅NO₂]^3? was investigated in acidic aqueous solutions at ionic strength of I = 0.1 mol dm^?3 (HCl/NaCl). The reactions were carried out at fixed acid concentration ([H⁺] = 0.01 mol dm^?3) and the temperature maintained at 35.0 ± 0.1 °C. Spectroscopic evidence is presented for the protonated oxidant. Protonation constants of 360.43 and 563.82 dm³ mol^?1 were obtained for the monoprotonated and diprotonated Co(III) complexes respectively. Electron transfer rates were generally faster for [Fe(bipy)₃]²⁺ than [Fe(phen)₃]²⁺. The redox complexes formed ion-pairs with the oxidant with increasing concentration of the oxidant over that of the reductant. Ion-pair constants for these reaction were 160.31 and 131.9 dm³ mol^?1 for [Fe(bipy)₃]²⁺ and [Fe(phen)₃]^2+, respectively. The activation parameters measured for these systems have values as follows: ?H ^≠ (kJ K^?1 mol^?1) = +113.4 ± 0.4 and +119 ± 0.3; ?S ^≠ (J K^?1) = +107.6 ± 1.3 and 125.0 ± 1.6; ?G ^≠ (kJ K^?1) = +81 ± 0.4 and +82.4 ± 0.4; and E _a (kJ mol^?1) = 115.9 ± 0.5 and 122.3 ± 0.6 for LL = bipy and phen, respectively. Effect of added anions (Cl^?, $ {\text{SO}}_{4}^{2 - } $ and $ {\text{ClO}}_{4}^{ - } $ ) on the systems showed decrease in the electron transfer rate constant. An outer-sphere mechanism is proposed for the reaction.     

Mechanism of the oxidation of hydrazoic acid by tetrachloroaurate(III) ion

The oxidation of hydrazoic acid in perchloric acid in the absence of added chloride under pseudo first-order conditions ([HN₃] » [AuCl ₄ ^? ]) is first order in [Au(III)]. Michaelis–Menten type of dependence (linear plots of k _obs ^?1 vs [HN₃]^?1) is observed with respect to [HN₃]. The k _obs is independent of ionic strength and the plot between k _obs ^?1 and [H⁺] is linear. The inner-sphere mechanism is consistent with the formation of an axial complex (K = 25 dm³ mol^?1) between AuCl₃(HO)^? ion and HN₃ prior to its rate determining decomposition (k = 0.0182 s^?1). It is inferred that the free radicals N ₃ ^? do not oxidise Au(II). The reaction becomes outer-sphere in the presence of added Cl^? ions which are inferred to form a cage around the hydronium ion surrounding the AuCl ₄ ^? ions. The penetration of N ₃ ^? through the cage is rate controlling and within the cage, the electron transfer from N ₃ ^? ion to AuCl ₄ ^? is fast. The value of the rate determining constant k ₂ is 0.547 dm³ mol^?1 s^?1 and the equilibrium constant K _Cl for the cage formation is 5 dm³ mol^?1 at 25 °C. It is calculated that the minimum HN₃ concentration required before the reaction exhibits zero-order dependence in HN₃ is 0.31 mol dm^?3 when [H⁺] = 0.18 mol dm^?3 at 25 °C.     

Kinetics and Mechanism of the Formation of (1,5)bis(2-hydroxybenzamido)3- azapentaneiron(III) and its Reactions with Thiocyanate,Azide, Acetate,Sulfur(IV) and Ascorbic Acid in Solution,and the Synthesis and Characterization of (nitrato)bis- (2-hydroxybenzamido)3-azapentaneiron(III). The Role of Phenol–amide–amine Coordination

The complexation of iron(III) with (1,5)bis(2-hydroxybenzamido)3-azapentane (H₂L) under varying [H⁺]_T (0.01–0.1 mol dm^?3) and [Fe^III]_T (3.0 × 10^?4–1.7 × 10^?2, [L]_T=(0.5 - 1.0) × 10^-4 mol dm^?3) (I=0.3 mol dm^?3, 10% v/v, MeOH  + H₂O, 25.0 °C) was reversible and displayed monophasic kinetics; the dominant path involved FeOH²⁺ and H₃L⁺. The mechanism is essentially a dissociative interchange (I_d) and dissociation of the aqua ligand from the encounter complex, [Fe(OH₂)₅OH²⁺, H₃L⁺] is rate-limiting. Equilibrium measurements indicated that the ligand binds iron(III) in a bidentate, tetradentate and pentadentate fashion under varying pH conditions. Iron(III) promoted deprotonation of the phenol moieties, and sec-NH ₂ ⁺ of the dien unit are in tune with this proposition. The octahedral coordination of [Fe(HL/L})(OH₂)]^2+/+ is further supported by the aqua ligand substitution by AcO^?, NCS^?, N ₃ ^- /N₃H, SO ₃ ^2- /HSO ₃ ^- . However, marked pK perturbation of the bound ascorbate in [Fe(L)(HAsc/Asc)]^0/? (ΔpK_{{[Fe(L)(HAsc)] ? HAsc?}}=6) is compelling evidence for chelation of HAsc^?/Asc^2? leading to unusual hepta coordination of iron(III) in the ascorbate complexes. Despite the multidentate nature of the ligand, its iron(III) complexes remain sensitive to reduction by S^IV and ascorbic acid. The complex (nitrato){(1,5)bis(2-hydroxybenzamido)3-azapentane}iron(III) has been synthesised and characterised by elemental analysis, i.r. and u.v.–vis spectral measurements. The room temperature magnetic moment (μ_eff=4.2 BM) conforms to the intermediate spin state of iron(III) (S=3/2) which is further supported by e.s.r. measurements (77 K, g=4.2, 8.1) and the ⁵⁷Fe Mössbauer spectrum (δ=0.41 mm s^?1; ΔE_Q=0.78 mm/s). The cyclic voltametry (MeOH, TEAP as background electrolyte) display only one quasi-reversible peak in the ?0.254 to ?0.4 V range (vs. SCE), the irreversibility being due to the formation of an iron(II) complex which dissociates under the experimental conditions.     

Kinetics of oxidation of glutathione by an octahedral cobalt(III) complex with phenolate–amide–amine coordination

The reduction of the octahedral cobalt(III) complex Co^III(HL)·9H₂O, H₄L = 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane by glutathione (GSH) has been studied by conventional spectrophotometry at 25.0 ≤ t/°C ≤ 45.0, 0.02 ≤ [H⁺]/mol dm^?3 ≤ 0.20 and I = 0.3 mol dm^?3 (NaClO₄). The reaction is biphasic. The fast initial phase is attributed to the H⁺-induced formation of the mixed ligand complex, [Co^III(H₂L)GSH]⁺, for which the rate-limiting step is the chelate ring opening via Co^III–NH (amide–N) bond cleavage of the protonated species, [Co^III(H₂L)]⁺. Outer-sphere association equilibria between GSH/GSH₂ ⁺ and [Co^III(H₂L)]⁺ substantially retard the ring opening process and consequently the mixed ligand complex formation. This is then followed by a slow phase involving reduction of [Co^III(H₂L)GSH]⁺ by both GSH and GSH₂ ⁺. The final products are the corresponding Co(II) complex and the oxidized form of GSH, GS–SG. The kinetic data and activation parameters for the redox process are interpreted in terms of an outer-sphere electron transfer mechanism.     

Ferric Chloride Complexes in Aqueous Solution: An EXAFS Study

A series of concentrated aqueous solutions of ferric chloride with different chloride:iron(III) ratios has been studied by means of EXAFS to determine the structure around the iron(III) ion of the dominating species in such solutions. The dominating species in dilute acidic aqueous solution of ferric chloride, at less than 1 mmol·dm^?3, are the hydrated iron(III) and chloride ions, while in concentrated aqueous solution and in solutions with an excess of chloride ions, up to 1.0 mol·dm^?3, it is the trans-[FeCl₂(H₂O)₄]⁺ complex. Possible higher chloroferrate(III) or dimeric [Fe₂Cl₆] complexes at room temperature, as proposed in the literature, were not observed in any of the studied solutions in spite of an excess of chloride ions of 1 mol·dm^?3.     

Complex Formation Equilibria of Unusual Seven Coordinate Fe(III) Complexes with DNA Constituents

Seven-coordinate Fe(III) complexes [Fe(dapsox)(H₂O)₂]⁺, where [dapsox = 2,6-diacetylpyridine-bis(semioxamazide)] is an equatorial pentadentate ligand with five donor atoms (2O and 3N), were studied with regard to their acid–base properties and complex formation equilibria. Stability constants of the complexes and the pK _a values of the ligands were measured by potentiometric titration. The interaction of [Fe(dapsox)(H₂O)₂]⁺ with the DNA constituents, imidazole and methylamine·HCl were investigated at 25 °C and ionic strength 0.1 mol·dm^?3 NaNO₃. The hydrolysis constants of the [Fe(dapsox)(H₂O)₂]⁺ cation (pK _a1 = 5.94 and pK _a2 = 9.04), the induced ionization of the amide bond and the formation constants of the complexes formed in solution were calculated using the nonlinear least-squares program MINIQUAD-75. The stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1:1 and 1:2 complexes with DNA constituents supporting the hepta-coordination mode of Fe(III). The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated for interaction of [Fe(dapsox)(H₂O)₂] with uridine.     

Micelle-Catalyzed Interaction Between [Ni(II)-Gly-Gly]+ and Ninhydrin

The effect of cationic micelles of cetyltrimethyl ammonium bromide (CTAB) on the observed pseudo-first-order rate constant for the interaction of nickel dipeptide complex [Ni(II)-Gly-Gly]⁺ with ninhydrin has been studied spectrophotometrically. At constant temperature and pH, increase in the [CTAB] from 0.0 to 60.0 × 10^?3 mol dm^?3 caused nearly three-fold increase of the rate constant. The micellar catalysis is explained in terms of the pseudophase model. From the observed kinetic data, binding constants of micelle–[Ni(II)-Gly-Gly]⁺ (K _S), and micelle–ninhydrin (K _N) are evaluated, respectively, to be 5.3 mol^?1 dm³ and 84.0 mol^?1 dm³. The role of added inorganic (NaCl, NaBr, Na₂SO₄) and organic salts (NaBenz, NaSal) on the reaction rate has also been examined.     

Studies on synthesis,determination of CMC values,kinetics and the mechanism of iron(II) reduction of surfactant–Co(III)–ethylenediamine complexes in aqueous acid medium

The surfactant–Co(III) complexes of the type cis-[Co(en)₂AX]²⁺ (A?=?Tetradecylamine, X?=?Cl^?,?Br^?) were synthesised from corresponding dihalogeno complexes by the ligand substitution method. The critical micelle concentration (CMC) values of these surfactant complexes in aqueous solution were obtained from conductance measurements. The kinetics and mechanism of iron(II) reduction of surfactant–Co(III) complexes, cis-[Co(en)₂(C₁₄H₂₉NH₂)Cl](ClO₄)₂ and cis-[Co(en)₂(C₁₄H₂₉NH₂)Br] (ClO₄)₂ ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co(III) using an excess of the reductant under pseudo-first-order conditions: [Fe(II)]?=?0.25?mol?dm^?3, [H⁺]?=?0.1?mol?dm^?3, [μ]?=?1.0?mol?dm^?3 ionic strength in a nitrogen atmosphere at 303, 308 and 313?K. The reaction was found to be of second order and showed acid independence in the range [H⁺]?=?0.05–0.25?mol?dm^?3. The second-order rate constant increased with surfactant–Co(III) concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe(II)], [H⁺] and [μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of [Fe(II)] with Co(III) complex proceeds by an inner-sphere mechanism.     

Effect of surfactant micelles on the kinetics of oxidation of D‐fructose by cerium(IV) in sulfuric acid medium

Kinetics of the oxidation of D ‐fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first‐order kinetics each in [cerium(IV)] and [D ‐fructose] and inverse first order in [H₂SO₄]. The Arrhenius equation is found to be valid for the reaction between 30–50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant K_s that equals to 286 mol^?1 dm³ is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na₂SO₄, NaNO₃, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18–25, 2006     

Effects of alkyltrimethylammonium bromide surfactants on the kinetics of the oxidation of tris(1,10-phenanthroline)iron(II) by azido-pentacyanocobaltate(III) complex

The redox reaction between tris(1,10-phenanthroline)iron(II), [Fe(phen)₃]²⁺, and azido-pentacyanocobaltate(III), [Co(CN)₅N₃]^3? was investigated in three cationic surfactants: dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB) in the presence of 0.1?M NaCl at 35°C. Second-order rate constant in the absence and presence of surfactant, k_w and k_ψ, respectively, were obtained in the concentration ranges DTAB?=?0???4.667?×?10^?4?mol?dm^?3, TTAB?=?0–9.364?×?10^?5?mol?dm^?3, CTAB?=?0???6.220?×?10^?5?mol?dm^?3. Electron transfer rate was inhibited by the surfactants with premicelllar activity. Inhibition factors, k_w/k_ψ followed the trend CTAB?>?TTAB?>?DTAB with respect to the surfactant concentrations used. The magnitudes of the binding constants obtained suggest significant electrostatic and hydrophobic interactions. Activation parameters ΔH^≠, ΔS^≠, and E_a have larger positive values in the presence of surfactants than in surfactant-free medium. The electron transfer is proposed to proceed via outer-sphere mechanism in the presence of the surfactants.     

Kinetics and mechanism of the reduction of diaquotetrakis (2,2′-bipyridine)-µ-oxodiruthenium(III) ion by hypophosphorous acid in acidic medium

The kinetics and mechanism of the reduction of diaquotetrakis(2,2′-bipyridine)-µ-oxodiruthenium(III), [(H₂O)₂(bipy)₄Ru₂O]⁴⁺, by H₃PO₂ has been studied in aqueous acid at ionic strength = 0.5 mol dm^?3 (NaClO₄), [H⁺] = 5.0 × 10^?2 mol dm^?3 and temperature = 31 ± 1 °C. Measurement of the stoichiometry showed that 1 mole of [(H₂O)₂(bipy)₄Ru₂O]⁴⁺ was reduced by 1 mole of H₃PO₂. The reaction was found to be first order with respect to both [(H₂O)₂(bipy)₄Ru₂O⁴⁺] and [H₃PO₂], hence second order overall. Variations in the ionic strength and dielectric constant of the reaction medium had no effect on the rate. Also, addition of various ions to the reaction medium did not significantly alter the rate. Free radicals were identified during the course of the reaction by a polymerisation test. Spectroscopic information and Michaelis–Menten plots suggested the absence of an intermediate complex prior to electron transfer. [(H₂O)₂(bipy)₂Ru]²⁺, the reduction product of [(H₂O)₂(bipy)₄Ru₂O]⁴⁺, plus H₃PO₃, the oxidation product of H₃PO₂, were identified in the product solutions. It is suggested that the reaction proceeds through the outer sphere pathway. A mechanism for the reaction is proposed.     

DNA Binding and Equilibrium Investigation of the Interaction of a Model Pd(II) Complex with Some Selected Biorelevant Ligands

The Pd(DAP)Cl₂ complex, where DAP is 2,6-diaminopyridine, was synthesized and characterized. The stoichiometries and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(DAP)(H₂O)₂]²⁺ were investigated at 25 °C and at constant 0.1 mol·dm^?3 ionic strength. The concentration distribution diagrams of the various species formed were evaluated. A further investigation of the binding properties of the diaqua complex [Pd(DAP)(H₂O)₂]²⁺ with calf thymus DNA (CT-DNA) was investigated by UV–Vis spectroscopy. The intrinsic binding constants (K _b) calculated from UV–Vis absorption studies is 1.04 × 10³ mol·dm^?3. The calculated (K _b) value was found to be of lower magnitude than that of the classical intercalator EB (ethidium bromide) (K _b = 1.23 (±0.07) × 10⁵ mol·dm^?3), suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA.     

Isosaccharinate Complexes of Fe(III)

Prior to this study there were no thermodynamic data for isosaccharinate (ISA) complexes of Fe(III) in the environmental range of pH (>~4.5). This study was undertaken to obtain such data in order to predict Fe(III) behavior in the presence of ISA. The solubility of Fe(OH)₃(2-line ferrihydrite), referred to as Fe(OH)₃(s), was studied at 22?±?2?°C in: (1) very acidic (0.01?mol·dm^?3 H⁺) to highly alkaline conditions (3?mol·dm^?3 NaOH) as a function of time (11?C421?days), and fixed concentrations of 0.01 or 0.001?mol·dm^?3 NaISA; and (2) as a function of NaISA concentrations ranging from approximately 0.0001 to 0.256?mol·dm^?3 and at fixed pH values of approximately 4.5 and 11.6 to determine the ISA complexes of Fe(III). The data were interpreted using the SIT model that included previously reported stability constants for $ {{\text{Fe(ISA}})_{n}}^{3 - n} $ (with n varying from 1 to 4) and Fe(III)?COH complexes, and the solubility product for Fe(OH)₃(s) along with the values for two additional complexes (Fe(OH)₂(ISA)(aq) and $ {\text{Fe(OH)}}_{ 3} ( {{\text{ISA}})_{2}}^{2 - } $ ) determined in this study. These extensive data provided a log₁₀ K ⁰ value of 1.55?±?0.38 for the reaction $ ({\text{Fe}}^{ 3+ } + {\text{ISA}}^{-} + 2 {\text{H}}_{ 2} {\text{O}} \rightleftarrows {\text{Fe(OH}})_{ 2} {\text{ISA(aq}}) + 2 {\text{H}}^{ + } ) $ and a value of ?3.27?±?0.32 for the reaction $ ({\text{Fe}}^{ 3+ } + 2 {\text{ISA}}^{-} + 3 {\text{H}}_{ 2} {\text{O}} \rightleftarrows {\text{Fe(OH)}}_{ 3} ( {\text{ISA}})_{2}^{2 - } + 3 {\text{H}}^{ + } ) $ and show that ISA forms strong complexes with Fe(III) which significantly increase the Fe(OH)₃(s) solubility at pH?<~12. Thermodynamic calculations show that competition of Fe(III) with tetravalent ions for ISA does not significantly affect the solubilities of tetravalent hydrous oxides (e.g., Th and Np(IV)) in ISA solutions.     

Inner-sphere oxidation of a ternary dipicolinatochromium(III) complex involving a malonic acid co-ligand

The oxidation of a ternary complex of chromium(III), [Cr^III(DPA)(Mal)(H₂O)₂]^?, involving dipicolinic acid (DPA) as primary ligand and malonic acid (Mal) as co-ligand, was investigated in aqueous acidic medium. The periodate oxidation kinetics of [Cr^III(DPA)(Mal)(H₂O)₂]^? to give Cr(VI) under pseudo-first-order conditions were studied at various pH, ionic strength and temperature values. The kinetic equation was found to be as follows: \( {\text{Rate}} = {{\left[ {{\text{IO}}_{4}^{ - } } \right]\left[ {{\text{Cr}}^{\text{III}} } \right]_{\text{T}} \left( {{{k_{5} K_{5} + k_{6} K_{4} K_{6} } \mathord{\left/ {\vphantom {{k_{5} K_{5} + k_{6} K_{4} K_{6} } {\left[ {{\text{H}}^{ + } } \right]}}} \right. \kern-0pt} {\left[ {{\text{H}}^{ + } } \right]}}} \right)} \mathord{\left/ {\vphantom {{\left[ {{\text{IO}}_{4}^{ - } } \right]\left[ {{\text{Cr}}^{\text{III}} } \right]_{\text{T}} \left( {{{k_{5} K_{5} + k_{6} K_{4} K_{6} } \mathord{\left/ {\vphantom {{k_{5} K_{5} + k_{6} K_{4} K_{6} } {\left[ {{\text{H}}^{ + } } \right]}}} \right. \kern-0pt} {\left[ {{\text{H}}^{ + } } \right]}}} \right)} {\left\{ {\left( {\left[ {{\text{H}}^{ + } } \right] + K_{4} } \right) + \left( {K_{5} \left[ {{\text{H}}^{ + } } \right] + K_{6} K_{4} } \right)\left[ {{\text{IO}}_{4}^{ - } } \right]} \right\}}}} \right. \kern-0pt} {\left\{ {\left( {\left[ {{\text{H}}^{ + } } \right] + K_{4} } \right) + \left( {K_{5} \left[ {{\text{H}}^{ + } } \right] + K_{6} K_{4} } \right)\left[ {{\text{IO}}_{4}^{ - } } \right]} \right\}}} \) where k ₆ (3.65 × 10^?3 s^?1) represents the electron transfer reaction rate constant and K ₄ (4.60 × 10^?4 mol dm^?3) represents the dissociation constant for the reaction \( \left[ {{\text{Cr}}^{\text{III}} \left( {\text{DPA}} \right)\left( {\text{Mal}} \right)\left( {{\text{H}}_{2} {\text{O}}} \right)_{2} } \right]^{ - } \rightleftharpoons \left[ {{\text{Cr}}^{\text{III}} \left( {\text{DPA}} \right)\left( {\text{Mal}} \right)\left( {{\text{H}}_{2} {\text{O}}} \right)\left( {\text{OH}} \right)} \right]^{2 - } + {\text{H}}^{ + } \) and K ₅ (1.87 mol^?1 dm³) and K ₆ (22.83 mol^?1 dm³) represent the pre-equilibrium formation constants at 30 °C and I = 0.2 mol dm^?3. Hexadecyltrimethylammonium bromide (CTAB) was found to enhance the reaction rate, whereas sodium dodecyl sulfate (SDS) had no effect. The thermodynamic activation parameters were estimated, and the oxidation is proposed to proceed via an inner-sphere mechanism involving the coordination of IO₄ ^? to Cr(III).     

Effect of surfactants on the performance of hollow fiber renewal liquid membrane (HFRLM): a case study of uranium transfer

In this study the application of various surfactant agents on the performance of HFRLM for uranium transfer was investigated. Using Taguchi experimental design in recycling mode of HFRLM, maximum uranium recovery of 63.17% was obtained at 0.15 mol L^?1 H₂SO₄, 0.0125 mol L^?1 Alamine 336 and 0.25 mol L^?1 NH₄Cl in the donor, liquid membrane and acceptor phase, respectively. Also, the continuous mode experiments were conducted and HFRLM stability was compared with HFSLM. The uranium transfer would be improved by adding 0.05 mmol L^?1 of SDS, CTAB and LAE-7 to the donor phase and 10 mmol L^?1 of CTAB and LAE-7 to the acceptor phase.     

Transference Numbers in the H2O + NaCl + MgCl2 System at T = 298.15 K,Determined in a Five-Compartment Hittorf Cell

The concentration range of transference number measurements with the Hittorf cell has been extended up to a total concentration of c _T = 3.4 mol·dm^?3 for the H₂O + NaCl + MgCl₂ ternary system at (298.15 ± 0.05) °C. This was achieved with a redesigned Hittorf cell, by dividing each of the anodic/cathodic compartments into two subcompartments: one with a low concentration of H₂O + NaCl for the electrode reaction and another one in contact with the middle compartment with the ternary solution to be measured. Measurements of the transference numbers were also made for the corresponding H₂O + NaCl and H₂O + MgCl₂ binary systems. The experimental details and the results are described.     

Cocatalysis by ruthenium(III) in hydrogen ions catalyzed oxidation of iodide ions: A kinetic study

RuCl₃ further catalyzes the oxidation of iodide ion by K₃Fe(CN)₆, already catalyzed by hydrogen ions. The rate of reaction, when catalyzed only by hydrogen ions, was separated graphically from the rate when both Ru(III) and H⁺ ions catalyzed the reaction. Reactions studied separately in the presence as well as absence of RuCl₃ under similar conditions were found to follow second‐order kinetics with respect to [I^?], while the rate showed direct proportionality with respect to [Fe(CN)₆]^3?, [RuCl₃], and [H⁺]. External addition of [Fe(CN)₆]^4? ions retards the reaction velocity, while changing the ionic strength of the medium has no effect on the rate. With the help of the intercept of the catalyst graph, the extent of the reaction that takes place without adding Ru(III) was calculated and it was in accordance with the values obtained from the reaction in which only H⁺ ions catalyzed the reaction. It is proposed that ruthenium forms a complex, which slowly disproportionates into the rate‐determining step. Arrhenius parameters at four different temperatures were also calculated. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 545–553, 2004     

Flow Injection Spectrophotometric Determination of N-Acetylcysteine and Captopril Employing Prussian Blue Generation Reaction

A novel flow injection procedure to determine N-acetylcysteine and captopril in pharmaceutical formulations is proposed. The flow procedure developed was based on oxidation of the analytes by Fe(III) in acidic medium and subsequent reaction of the Fe(II) generated with excess hexacyanoferrate(III) to produce soluble Prussian blue (KFe[Fe(CN)₆]) measured at 700 nm. Detection limits of 1.0 × 10^?5 mol L^?1 and 3.0 × 10^?5 mol L^?1 for N-acetylcysteine and captopril, respectively, were found. The sample throughput was 70 h^?1 for both analytes and the results obtained were in agreement at a 95% confidence level with those obtained using reference methods.     

Base hydrolysis of tris(3-(2-pyridyl)-5,6-bis(4-phenyl sulphonic acid)-1,2,4-triazine)iron(II) in aqueous,SDS and CTAB media: kinetic and mechanistic study

The kinetics and mechanism of base hydrolysis of tris(3-(2-pyridyl)-5,6-bis(4-phenyl sulphonic acid)-1,2,4-triazine)iron(II), \({\text{Fe}}({\text{PDTS}})_{3}^{4 - }\) have been studied in aqueous, sodium dodecyl sulphate (SDS) and cetyltrimethyl ammonium bromide (CTAB) media at 25, 35 and 45 °C under pseudo-first-order conditions, i.e. \(\left[ {\text{OH}^{ - } } \right]\) ? \({\text{Fe}}({\text{PDTS}})_{3}^{4 - }\). The reaction is first order each in \({\text{Fe}}({\text{PDTS}})_{3}^{4 - }\) and hydroxide ion. The rate increases with increasing ionic strength in aqueous and SDS media, whereas this parameter has little effect in CTAB. In SDS medium, the rate-determining step involves the reaction between \(\left[ {\text{OH}^{ - } } \right]\) and \({\text{Fe}}({\text{PDTS}})_{3}^{4 - }\), whereas in CTAB medium, it involves reaction between a neutral ion pair, {\({\text{Fe}}({\text{PDTS}})_{3}^{4 - }\)·4CTA⁺} and \(\left[ {\text{OH}^{ - } } \right]\) ions. The specific rate constants and thermodynamic parameters (E _a, ΔH ^#, ΔS ^# and ΔG _35°C ^# ) have been evaluated in all three media. The near equal values of ΔG _35°C ^# obtained in aqueous and SDS media suggest that these reactions occur essentially by the same mechanism. Slightly lower ΔG _35°C ^# values in CTAB medium can be attributed to a higher concentration of reactants in the Stern layer. The reaction is inhibited in SDS medium but catalysed in CTAB. The former can be attributed to the anionic surfactant creating more repellent space between the reactants. Catalysis in CTAB medium is ascribed to electrophilic and hydrophilic interactions between hydroxide ion/substrate with the cationic Stern layer, resulting in increased local concentrations of both reactants.