Perchlorate Media Research Articles

Studies on the Reaction Kinetics and Mechanism of Iron(II) Reduction of the cis-Halogeno(cetylamine)bis(ethylenediamine)cobalt(III) Complex Ion in Aqueous Perchlorate Medium

The electron-transfer kinetics of the ionic surfactant complex cis-chloro/bromo(cetylamine)bis(ethylenediamine)cobalt(III) by iron(II) in aqueous perchlorate medium at μ=1.0 mol⋅dm−3 ionic strength have been studied at 303, 308 and 313 K by spectrophotometry under pseudo-first-order conditions using an excess of the reductant. The effects of [H+], ionic strength and [Fe2+] on the rate were determined. The reaction was found to be second order and showed to be independence of the acid concentration in the range [H+]=0.05–0.25 mol⋅dm−3. The second order rate constant increased with surfactant–cobalt(III) concentration and the occurrence of aggregation of the complex itself altered the reaction rate. Activation and thermodynamic parameters have been computed. It is suggested that the reaction of Fe2+(aq) with the cobal (III) complex proceeds by an inner-sphere mechanism. The critical micelle concentration (CMC) values of these surfactant–metal complexes were obtained in aqueous solution from conductance measurements. Specific conductivity data (at 303, 308 and 313 K) served for the evaluation of the temperature-dependence of the critical micelle concentration (CMC) and the thermodynamics of micellization (ΔGmo,ΔHmo and ΔSmo).

Effect of the composition of water-acetone solvent and benzhydrazine structure on their efficiency during cadmium electrodeposition from perchlorate media

The feasibility of controlling the degree of retardation of a cathodic process by changing the ratio of the components in the liquid phase and nature of electron shifts in additive molecule (benzhydrazine) is discussed. The minimum electrode reaction rate is observed in a range of water structure stabilization under conditions of the predominant adsorption of organic molecules. The highest efficiency are achieved using an additive with an electron-donating substituent in the molecule. The highest rate of the electroreduction of Cd2+ and the lowest efficiency of the additives are registered in the region of the loosening of the structure of the mixed solvent, causing selective ion solvation to become possible, which results in an abrupt increase in the adsorption activity of ClO4− anions on the cathode and is the main reason for the ψ’ effect during the electroreduction of metal ions.

Voltammetric behavior of perfluorocarboxylic acids and their corresponding ethyl esters on glassy carbon electrode: surface effects

Voltammetric responses of trifluoroacetic acid, perfluorobutyric acid, perfluorohexanoic acid, and perfluorooctanoic acid (PFOA) were studied in acetonitrile/tetra-n-butylammonium perchlorate medium on glassy carbon electrode. All the four acids gave two voltammetric waves. PFOA exhibits blocking effects. In the presence of excess water, the first cathodic peak current increases, and the second peak disappeared. Very small quantity of triethylamine (TEA; 1–2 mM) was found to be effective in suppressing the first cathodic peak. Both the peak current and peak potential values were sensitive to water and TEA content. The ester derivatives of all the four perfluorocarboxylic acids (PFCAs), however, gave well-defined cathodic reduction peak around −2.3 V. This peak appears to be the best choice for quantitative estimation of PFCAs.

Kinetics and mechanism of oxidation of β-Alanine by N-bromophthalimide in the presence of Ru(III) chloride as homogenous catalyst in acidic medium

The kinetics of Ru(III) chloride-catalyzed oxidation of β-Alanine (NH3+CH2CH2COOH, β-Ala) by N–bromophthalimide (NBP) in aqueous perchloric acid medium was studied at 35 °C. The rate law followed a first-order and zero-order dependence with respect to [NBP] and [β-Ala], respectively. The reaction followed first-order kinetics with respect to [Ru(III)] chloride at a range of low concentrations while the order changed from first- to zero-order at high concentration of [Ru(III)] chloride; demonstrating the catalytic effect for the oxidation of β-Ala by NBP. The rate decreased with increase in acidity. Chloride ions positively influenced the rate of the reaction. Neither phthalimide (NHP) nor Hg(II) influenced the reaction rate. Ionic strength (I) and dielectric constant (D) of the medium had no significant effect on the rate. Activation parameters of the reactions were determined by studying the reaction at different temperatures (30–50 °C). The colorimetric, FTIR, and GC-MS techniques were used to identify methyl cyanide (CH3CN) and CO2 as products of the reaction. In the reaction, approximately 2.3 moles of NBP oxidized one mole of β-Ala. A reaction scheme of the oxidation of β-Ala by NBP in the presence of Ru(III) chloride was found to be in consistent with the rate law and the reaction stoichiometry.

Oxidation of iodide and iodine on birnessite (δ-MnO 2) in the pH range 4–8

The oxidation of iodide by synthetic birnessite (δ-MnO 2) was studied in perchlorate media in the pH range 4–8. Iodine (I 2) was detected as an oxidation product that was subsequently further oxidized to iodate (IO 3 −). The third order rate constants, second order on iodide and first order on manganese oxide, determined by extraction of iodine in benzene decreased with increasing pH (6.3–7.5) from 1790 to 3.1 M −2 s −1. Both iodine and iodate were found to adsorb significantly on birnessite with an adsorption capacity of 12.7 μM/g for iodate at pH 5.7. The rate of iodine oxidation by birnessite decreased with increasing ionic strength, which resulted in a lower rate of iodate formation. The production of iodine in iodide-containing waters in contact with manganese oxides may result in the formation of undesired iodinated organic compounds (taste and odor, toxicity) in natural and technical systems. The probability of the formation of such compounds is highest in the pH range 5–7.5. For pH <5 iodine is quickly oxidized to iodate, a non-toxic and stable sink for iodine. At pH >7.5, iodide is not oxidized to a significant extent.

Kinetics and Mechanistic Study on the Reaction of Iodo(diethylenetriamine) Platinum(II) with L-Cystine

Substitution reactions of the complex [Pt(dien)I]+, where dien = diethylenetriamine or 1,5-diamino-3-azapentane, with the sulfur-containing rescue agent l-cystine have been studied in a 1.0 × 10–1 mol dm–3 aqueous perchlorate medium at various temperatures (25–50°C) and pH (2.30–1.00) using a UV-visible spectrophotometer. The products were characterized by their infrared and 1H NMR data at various temperatures. These data indicate that [Pt(dien)I]+ formed a complex with l-cystine through Pt–S bonds at pH 1.00–2.30. This Pt–S bond is observed at 50°C with ring closure of the dien (δ 3.8–3.9, 2H, CH2) and with open-ring dien (δ 3.2, 3.6–3.8 (dien), 2H, CH2). All reactions follow the rate law –d[mixture]/dt = (k1 + k2[Nu])[PtII], where k2 denotes a second-order rate constant and [Nu] is the total concentration of nucleophile. The product formation rate constant and activation parameters Ea, ΔH#, and ΔS# have been determined.

Kinetics and mechanism of uncatalyzed and silver(I) catalyzed oxidation of lysine by cerium(IV) in acid perchlorate medium

The kinetics of the uncatalyzed and silver(I) catalyzed oxidation of lysine with cerium(IV) has been st udied in perchloric acid medium. The reaction is second order, that is first order with respect to each reactant. The mode of electron transfer has been indicated through an adduct between Ag I and lysine via oxygen atom of the carboxyl group rather than the amino group. Uncatalyzed reaction simultaneously occurs with the siver(I) catalyzed reaction and the following rate law conforms to all experimental data observed in the reaction, k = k 1 [H + ]/k h +[H + ] + k 2 [Ag I ][H + ]/k h +[H + ] where, k is an observed second order rate constant. A reaction mechanism accounting for all these experimental observations has been suggested.

3‐Hydroxy‐2‐[1′‐phenyl‐3′‐( p ‐chlorophenyl)‐4′‐pyrazolyl]‐4‐oxo‐4 H ‐1‐benzopyran as a spectrophotometric reagent for trace determination of tungsten( vi )

3-Hydroxy-2-[1′-phenyl-3′-(p-chlorophenyl)-4′-pyrazolyl]-4-oxo-4H-1-benzopyran solution in acetone forms a yellow-coloured complex with tungsten(vi) in perchloric acid medium which is extractable into chloroform after equilibration. In this study, tests were carried out on this compound and it was found to be quite stable and to obey Beer’s law. Interactions with various ions were studied and the molar absorptivity, Sandell’s sensitivity and relative standard deviation were also investigated. Job’s method, the mole ratio method and the equilibrium-shift method were also used. The ratio of metal to ligand was measured using a method that was simpler, more accurate, sensitive, rapid and selective as compared with existing methods. This method is applicable to the analysis of various samples of varied composition.

Homoligand and mixed-ligand complexes of mercury(II) with aspartic acid and iminodiacetic acid and its derivatives

The formation of homoligand mercury(II) complexes with aspartic acid (H2Asp) and aspartate-chelant mixed-ligand mercury(II) complexes with iminodiacetic acid (H2Ida, IDA), 2-hydroxyethyliminodiacetic acid (H2Heida, HEIDA), and nitrilotriacetic acid (H3Nta, NTA) in an aqueous perchlorate medium was studied by spectrophotometry and pH-potentiometric titration. The following complexes were identified: [Hg(OH)Asp]−, [HgAsp2]2−, [Hg(Asp)Ida]2−, [Hg(Asp)Heida]2−, and [Hg(Asp)Nta]3−. The logarithms of their stability constants are, respectively, 11.74 ± 0.12, 20.18 ± 0.17, 20.11 ± 0.10, 19.82 ± 0.09, 19.48 ± 0.11, and 20.58 ± 0.07 (μ = 0.1 (NaClO4), t = (20 ± 2)°C). The hydrogen and hydroxyl competition regions were located in the systems, and relationships between the molar yields of complex species and the reactant concentrations were established. The protonation and dissociation constants of aspartic acid were derived from pH-potentiometric titrations. Experimental data were analyzed using mathematical models allowing one to judge the existence of various complex species in the solution and to identify the species that are sufficient to reproduce the observed data.

Ruthenium(III)-catalyzed and uncatalyzed kinetic studies on the oxidation of sulfanilic acid by chloramine-T in perchloric acid medium: a mechanistic approach

The kinetics of the oxidation of sulfanilic acid (SAA) by sodium N-chloro-p-toluenesulfonamide (CAT) in the presence and absence of ruthenium(III) chloride have been investigated at 303 K in perchloric acid medium. The reaction shows a first-order dependence on [CAT]o and a non-linear dependence on both [SAA]o and [HClO4] for both the ruthenium(III)-catalyzed and uncatalyzed reactions. The order with respect to [RuIII] is unity. The effects of added p-toluenesulfonamide, halide, ionic strength, and dielectric constant have been studied. Activation parameters have been evaluated. The rate of the reaction increases in the D2O medium. The stoichiometry of the reaction was found to be 1:1 and the oxidation product of SAA was identified as N-hydroxyaminobenzene-4-sulfonic acid. The ruthenium(III)-catalyzed reactions are about four-fold faster than the uncatalyzed reactions. The protonated conjugate acid (CH3C6H4SO2NH2Cl+) is postulated as the reactive oxidizing species in both the cases.

Nonionic Micellar Catalyzed Oxidation of Vitamins by Chloramine-T in HClO4 Medium: A Kinetic Study

The kinetics of oxidation of vitamin B1 (thiamine hydrochloride) and vitamin B6 (pyridoxine hydrochloride) by chloramine-T (CAT) in perchloric acid medium and in presence of a non ionic surfactant (Triton x-100) have been investigated. A catalytic effect of the nonionic micelle on the rate of oxidation has been observed and rate is found to be proportional to 7lcub;k′ + k″ [Triton x-100]}, where k′ and k″ are the rate constants in absence and presence of surfactant, respectively. The rate shows a first-order, a fractional order and a zero order dependence on [Chloramine-T]o, [Vitamin]o and [H+]0, respectively in absence as well as in presence of surfactant. A mechanism involving association/binding between the oxidant and the surfactant micelle, which is supported by spectrophotometric evidence has been proposed. The binding parameters have also been evaluated using a pseudo-phase kinetic model.

The Kinetics of Oxidation of L-Tryptophan by Water-Soluble Colloidal Manganese Dioxide

The kinetics of the oxidation of L-tryptophan by water-soluble colloidal MnO2 (prepared from potassium permanganate and sodium thiosulfate solutions) has been carried out in aqueous perchloric acid medium at different temperatures. Monitoring the disappearance of the MnO2 spectrophotometrically at 390 nm was used to follow the kinetics. The first-order kinetics with respect to [L-tryptophan] at low concentrations shifted to zero-order at higher concentrations. The reaction followed first-order with respect to [MnO2] but fractional-order with respect to [HClO4]. Adding trapping agents enhanced the rate of the reaction. The Arrhenius and Eyring equations were found valid for the reaction between 35°C and 55°C and different activation parameters (Ea, ΔH#, ΔS#) have been evaluated. On the basis of various observations and product characterization a plausible mechanism has been envisaged for the reaction taking place at the colloid surface. The results suggest formation of an adsorption complex between L-tryptophan and MnO2. The complex decomposes in a rate-determining step, leading to the formation of free radical, which again reacts with the colloidal MnO2 in a subsequent fast step to yield products. Freundlich isotherm is used to explain the adsorption of L-tryptophan on the colloidal MnO2.

Complexation thermodynamics and the formation of the binary and the ternary complexes of tetravalent plutonium with carboxylate and aminocarboxylate ligands in aqueous solution of high ionic strength

The stability constants of the binary and the ternary complexes of Pu 4+ have been measured for certain carboxylate and aminocarboxylate ligands in aqueous solution of I = 5.0 M (1 M perchloric acid + 4 M ionic strength perchlorate media) and temperatures of 0–45 °C by the solvent extraction technique. The stability constants of the binary and the ternary complexes increased with increased temperature. The complexation enthalpy and entropy of the binary Pu–Ox and the ternary Pu–EDTA–Ox and DGA complexes indicated the stability of these complexes is due to the highly favorable entropy contribution while complexation enthalpies either oppose complexation or are weakly favorable.

Effect of Inorganic Ligands and Hydrogen Peroxide on ThO2 Dissolution. Behaviour of Th0.87Pu0.13O2 during Leaching Test

The dissolution of ThO2 powdered samples was examined in various conditions of pH and concentration of anions in the leachate. The first part of this paper describes the influence of pH on the dissolution of ThO2 in both nitric and hydrochloric media. The partial order relative to the proton concentration and the apparent normalized dissolution rate constants were determined. The second part of the paper describes the influence of other ligands such as perchlorate, chloride, sulfate, and hydrogen peroxide on the dissolution kinetics (at pH 1). An increase of RL was observed correlatively with the increase of complexing affinity of the ligand with Th. While nitric and hydrochloric media, which are weakly complexing, lead to RL values with the same order of magnitude as those for perchlorate media, the presence of sulfate or peroxide in the leachate significantly enhances the dissolution of ThO2. Consequently, the dissolution mechanism can be explained by the weakening of Th-O bonds through the formation of surface complexes at the solid/liquid interface, which enhance the detachment and thus accelerate the global dissolution. In addition, the dissolution of Th 0.87Pu 0.13O2 solid solution was also examined. The increase of the dissolution kinetics of Th 0.87Pu 0.13O 2, in comparison with that of ThO2, is considered to be caused by the presence of hydrogen peroxide formed by radiolysis of the leachate. Moreover, the redox properties of plutonium in acidic media, like disproportionation of Pu(IV) and Pu(V) and reduction of Pu(VI) and Pu(IV) in Pu(III) by H2O2, probably increase the dissolution of plutonium.

Solvent Extraction Behavior of Neptunium (IV) Ions between Nitric Acid and Diluted 30% Tri‐butyl Phosphate in the Presence of Simple Hydroxamic Acids

Formo‐ and aceto‐hydroxamic acids are very effective reagents for stripping tetravalent actinide ions such as Np(IV) and Pu(IV) ions from a tri‐butyl phosphate phase into nitric acid. Distribution data for Np(IV) in the presence of these hydroxamate ions have now been accumulated and trends established. Stability constants for aceto‐hydroxamate complexes of Np(IV) and Np(V) ions have also been determined in a perchlorate medium, and these reaffirm the affinity of hydroxamate ligands for actinide (IV) ions over actinyl (V,VI) ions.

Kinetics and mechanism of oxidation of pyruvic acid by peroxomonophosphate in acid perchlorate medium

Kinetics of oxidation of pyruvic acid by peroxomonophosphate (PMP) has been studied in a wider pH range. The stoichiometry corresponds to the reaction as represented by the eq. (1) CH 3 COCO 2 H + H 3 PO 5 → CH 3 CO 2 H + H 3 PO 4 (1) The pattern of reactivity of peroxomonophosphate species has been delineated. A plausible reaction mechanism is suggested. The energy and entropy of activation were calculated to be (72 ± 7) kJ mol -1 and (-40 ± 4) JK -1 mol -1 respectively.

Kinetics and mechanism of electron transfer reactions oxidation of mannitol by chromium(vI) in acid perchlorate medium

Kinetics and mechanism of electron transfer reactions oxidation of mannitol by chromium(vI) in acid perchlorate medium

Kinetics and electrochemical studies of uranium in acetate and formate media by cyclic voltammetry

SummaryThe cyclic voltammetric behavior of uranyl ion was investigated at hanging mercury drop electrode in perchlorate supporting electrolyte. The standard heterogeneous electron transfer rate constant “ks” for the reduction of uranyl ion in perchlorate medium was (2.74±0.03)×10−3cm s−1while in acetate and formate medium the value ofkswas (2.83±0.02)×10−3and (2.66±0.02)×10−3cm s−1, respectively. The effect of temperature on the values ofkswas investigated and thermodynamic constants ΔH*, ΔS* and ΔG298* were evaluated. The values of ΔH*, ΔS*; and ΔG298* were 8.06±0.03 kJ mol−1, −23.42±0.05 J mol−1K−1and 15.02±0.07 kJ mol−1in simple perchlorate medium and 3.67±0.02 kJ mol−1, −38.04±0.05 J mol−1K−1, and 15.01±0.03 kJ mol−1in acetate medium and 0.79±0.02 kJ mol−1, −48.24±0.04 J mol−1K−1and 15.17±0.02 kJ mol−1in formate medium, respectively. The thermodynamic data showed that the process of reduction of uranyl ion at hanging mercury drop electrode was endothermic and non-spontaneous. The stability constants of uranyl acetate and uranyl formate were calculated from an analysis of the shift in peak potential data. The logβ1and logβ2values for 1:1 and 1:2 uranyl acetate complexes were 2.67±0.04 and 4.71±0.01, respectively. The values of logβ1and logβ2of uranyl formate complex were 1.61±0.02 and 2.57±0.01, respectively, which are reported for the first time.

A Lead‐Selective Membrane Electrode Based Upon a Phosphorylated Hexahomotrioxacalix[3]Arene

AbstractSolvent extraction of a mixture of PbII, MnII, FeIII, CoII, NiII and CdII in aqueous perchlorate medium by a phosphorylated hexahomotrioxacalix[3]arene (calix‐3) in dichloromethane shows a significant selectivity towards lead ions. The ligand can also be incorporated into a membrane to provide a new lead ion‐selective electrode (PbII‐ISE). A plasticized PVC membrane containing 30% PVC, 53.5% ortho‐nitrophenyloctylether (NPOE), 4.5% sodium tetraphenylborate (NaTPB) and 12% ionophore was directly coated on a graphite rod. This sensor gave a good Nernstian response of 29.7 ± 0.7 mV decade−1 over a concentration range of 1 × 10−8 – 1 × 10−4 M of lead ions, independent of pH in the range 3‐7, with a detection limit of 0.4 × 10−8 M. The dynamic response time of the electrode to achieve a steady potential was very fast and found to be less than 7 s. The selectivity relative to Ag+, NH4+, Li+, Na+, K+, Ca2+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Fe3+, La3+, Sm3+, Dy3+, Er3+, Y3+ and Th4+ was examined. The electrode exhibits adequate stability with good reproducibility (with a slope of 29.6 ± 1.5 mV for 8 weeks). The characteristics of the sensor are compared with those of a tetraphosphorylated calix[4]arene (calix‐4) based PbII‐ISE, reported recently. The electrode was successfully used as an indicator electrode for a potentiometric titration of a lead solution using a standard solution of EDTA. The applicability of the sensor for lead ion measurements in various synthetic samples was also investigated.

Silicate complexation of NpO2 + ion in perchlorate media

Complexation behavior of NpO2+ with ortho-silicic acid (o-SA) has been studied using solvent extraction at ionic strengths varying from 0.10 to 1.00M (NaClO4) at pcH 3.68±0.08 and 25 °C with bis-(2-ethylhexyl) phosphoric acid (HDEHP) as the extractant. The stability constant value (log β1) for the 1:1 complex, NpO2(OSi(OH)3), was found to decrease with increase in ionic strength of the aqueous phase [6.83±0.01 at I=0.10M to 6.51±0.02 at I = 1.00M]. These values have been fitted in the SIT model expression and compared with similar values of complexation of the metal ions Am3+, Eu3+, UO22+, PuO22+, Np4+, Ni2+ and Co2+. The speciation of NpO2+-o-silicate/carbonate system has been calculated as a function of pcH under ground water conditions.