Reductometric determination of manganese in presence of excess cobalt with Cobalt(II) salt in a medium of alkaline triethanolamine and cyanide

Summary Conditions have been worked out for the reductometric determination of Mn^II with cobalt(II)-nitrate solution in a medium of triethanolamine, cyanide and hydroxide. A large excess of cobalt and a number of other common elements does not interfere in this determination, which is well suited for practical purposes. The error is below 1%.

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Zusammenfassung Eine Methode wurde ausgearbeitet zur reduktometrischen Bestimmung von Mn^II mit Kobalt(II)-nitratlösung in Gegenwart von Triäthanolamin, Cyanid und Hydroxid. Ein großer Überschuß an Kobalt und eine Anzahl anderer Elemente stören diese für praktische Zwecke geeignete Methode nicht. Der Fehler ist kleiner als 1%.

     

Suspensions of biological tissues in alkaline medium for the determination of copper, manganese and cobalt by electrothermal atomic absorption spectrometry

Electrothermal atomic absorption spectrometry was applied to the determination of copper, manganese and cobalt in biological tissues of which small amounts are available only. The samples (10 mg of mice tissue) were suspended in 1 mL of water containing tetramethylammonium hydroxide, Triton X-100 and silicone antifoam. The sample was homogenized by heating to 60 °C for 5 min, submitted to dilution if necessary, and injected into the atomizer. Wall atomization was used for Cu and Mn, and platform atomization for Co. Calibration was carried out using aqueous standards for copper and manganese determination. The determination of cobalt suffered from a matrix effect and, in this case, calibration was enabled by using a suspension of a cobalt-free muscle sample. The detection limits are 25, 20 and 62 ng?g^?1. The results obtained for five certified reference materials demonstrated the reliability of the procedures for the determination of the three analytes in normal and dystrophic mice tissue.     

Back titration with mercuric ntrate in alkaline medium; potentiometric estimation of aluminium and manganese

Summary Mercuric nitrate has been successfully used for back titrating excess EDTA amounts than required for chelation with Al³⁺ or Mn²⁺ ions. This principle was the basis underlying the potentiometric determination of small amounts of both metals in the range of 10 g to 6 mg. End points are attended within 0.01 to 0.02 ml of titrant with fair accuracy and reasonable jumps ranging from 35 to 88 mv per 0.1 ml of titrant.     

Role of rhodium doping into lanthanum cobalt oxide (LaCoO3) perovskite and the induced bifunctional activity of oxygen evolution and reduction reactions in alkaline medium

Transition metal oxides, especially perovskites, have been considered effective electrocatalysts for the oxygen evolution (OER) and oxygen reduction (ORR) reactions in an alkaline solution. Here, a series of lanthanum cobalt rhodium oxide perovskites with the chemical formula LaCo_1-xRh_xO₃ (LCRO, 0.1 ≤ x ≤ 0.70) were prepared through the approach of solid-phase synthesis and their bifunctional electrocatalytic activity was assessed for both the OER and ORR. The crystallinity, morphology, surface, and electrocatalytic features of the LCRO were significantly correlated with the rhodium content. The LaCo_0.7Rh_0.3O₃ electrocatalysts with x = 0.3 showed enhanced electrocatalytic bifunctional performance with a substantially lower OER/ORR onset potential of 1.38/0.73 V vs HRE, smaller Tafel slope (116/90 mV/dec), and low charge-transfer resistance, which is the most efficient catalyst among the other studied ratios and superior to the pristine lanthanum cobalt oxide benchmark electrocatalysts. The LaCo_0.7Rh_0.3O₃ electrode exhibit good bifunctional electrocatalytic behavior and long-term durability with an OER and ORR onset potential gap (ΔE = E_OER ? E_ORR) of only 0.65 V, which could be credited to the enriched oxygen vacancies, lattice expansion and the improved electrical conductivity upon the doping of larger size of Rh ions. The LaCo_1-xRh_xO₃ catalysts are obtained from abundant materials that have the potential of highly-active bifunctional OER and ORR electrocatalysts.     

Kinetics and mechanism of the decomposition of dibridged cobalt dioxygen complexes of amino acid derivatives in alkaline medium

The kinetics and thermodynamics of the decomposition of dibridged μ(O₂²⁻, OH⁻)cobalt complexes with the linear tetradentate ⁻OOCCH(R)NHCH₂CH₂NHCH(R)COO⁻ (L = EBAA*) ligand have been studied in alkaline medium. Under these conditions, the dioxygen complex Co₂L₂O₂OH⁻ undergoes irreversible metal-centered autoxidation to form a CO(III) complex with the unchanged ligand and H₂O₂. The reaction is base-catalyzed, and a mechanism has been proposed in which deprotonation of a coordinated nitrogen activates the hydrolysis of the CO^IIIO₂ bond. From the enthalpy—entropy relationship, the isokinetic temperature β=274 K has been found.     

Synthesis, molecular and crystal structure of bis(triethanolamine)manganese(II) saccharinate: a seven-coordinate manganese complex with tri- and tetradentate triethanolamine ligands

The synthesis, molecular and crystal structure of bis(triethanolamine)Mn(II) saccharinate, [Mn(tea)₂](sac)₂ are reported. The configuration of the tea ligands results in an unusual example of coordination number seven for the Mn(II) ion. The two triethanolamine (tea) ligands coordinate to the Mn(II) ion forming a monocapped trigonal prism geometry, in which one of the tea ligands behaves as a tridentate ligand, while the other one acts as a tetradentate donor. The free and coordinated hydroxyl hydrogens of the tea ligands are involved in hydrogen bonding with the amine nitrogen, carbonyl and sulfonyl oxygens of the neighbouring sac ions to form a three-dimensional infinite network. A weak π–π interaction between the phenyl rings of the sac ions also occurs.     

Oxidation of some monosaccharides by hexavalent manganese in aqueous alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of some monosaccharides viz., D-ribose, D-xylose, and D-arabinose, D-glucose, D-fructose, D-galactose, 2-deoxyglucose, and α-methyl glucopyranoside by MnO₄^2? in aqueous alkaline medium have been studied. The rate of oxidation has been found to be first-order both with respect to [oxidant] and [sugar]. The rate is independent of [OH^?] under experimental conditions of [OH^?] > 0.5 M where the oxidant is stable. The effect of ionic strength is negligible on the rate. A mechanism involving the formation of a 5-membered cyclic intermediate complex between MnO₄^2? and 1,2-enediol form of the sugar is proposed. The intermediate complex decomposes to give products in the subsequent slow step. The involvement of 1,2-enediol form receives support from the reaction of α-methyl glucopyranoside, which exists in ring structure in alkaline solution reacting much slower than glucose with MnO₄^2? under similar conditions. Second-order rate constant k″ and activation parameters have been evaluated. The series of reactions exhibits a clear demonstration of applicability of isokinetic phenomenon where Arrhenius plots for all the reactions are found to intersect at a common point (295 K). © 1995 John Wiley & Sons, Inc.     

Surface poisoning during electrocatalytic monosaccharide oxidation reactions at gold electrodes in alkaline medium

In the present study, the surface poisoning of electrocatalytic monosaccharide oxidation reactions at gold electrodes were investigated. In the cyclic voltammetric studies, the electrocatalytic oxidation of aldohexose and aldopentose type monosaccharides, aminosugars, acetyl-glucosamine and glucronamide were observed at gold plate electrodes in alkaline medium. However, in controlled-potential electrolytic studies ranging −0.3 to −0.2 V in reaction solutions, current flows during electrolyses decreased quickly with time, except when glucosamine was used as a substrate.Results from surface enhanced infrared adsorption (SEIRA) spectroscopic measurements at an evaporated gold electrode for the electrocatalytic oxidation of glucose in 0.1 mol dm⁻³ NaOH at −0.3 V and Gaussian simulated spectra indicated that the gluconic acid as a 2-electron oxidation product and/or its analogs adsorbed onto the gold surface. Electrochemical quartz crystal microbalance (EQCM) measurement results, along with surface adsorption results from surface poisoning at the gold electrode during electrolytic reactions, suggested that gluconic acid and/or its analogs adsorbed vertically onto electrode surfaces in a full monolayer packing-like conformation. In the case of the electro oxidation of glucosamine in 0.1 mol dm⁻³ NaOH at −0.2 V, the obtained SEIRA spectra and EQCM results, clearly indicated that the glucosaminic acid as a 2-oxidation glucosamine product did not strongly bind onto the gold electrode surface.     

Oxidation of nucleic acid bases by hexavalent manganese in aqueous alkaline medium: a kinetic study

Oxidation of uracil or thymine by Mn^VI in aqueous alkali shows first order dependence on [MnO ₄ ²⁻ ] and fractional order dependence on [uracil] or [thymine]. The effect of ionic strength is negligible on the rate of oxidation. The product of oxidation is the 5,6-dihydroxy compound. A mechanism is proposed involving the formation of a 5-membered cyclic complex between the substrate and manganate in a fast step, which subsequently disproportionates to give the final products. The large negative values of the entropy of activation suggest the formation of an intermediate complex. The formation constants of the latter and the rate of its disproportionation have been calculated from the derived rate law. The rate of oxidation of thymine is faster than that of uracil.     

Influence of oxidation-reduction treatment on the formation of cobalt nanoparticles in the Zr-Co-H system

Continuous in situ magnetization measurements are used to study the dynamics of processes in the Zr-Co-H system during oxidation-reduction treatment (ORT). The oxidation of a ZrCoH _x sample after removal of hydrogen results in a significant rise in magnetization. ZrCoH _x oxidation in air leads to higher magnetizations compared to oxidation in a 5% O₂ + Ar mixture.     

Electrocatalytic oxygen evolution reaction of hierarchical micro/nanostructured mixed transition cobalt oxide in alkaline medium

Journal of Solid State Electrochemistry - In this work, different cobalt-based mixed transition metal oxides (MTMOs) were fabricated by hydrothermal process followed by calcination. Doping Co3O4...     

废碱锰电池焙烧干粉酸解条件的研究

碱性锌锰电池具有能量大、贮存性能优越、无记忆效应、成本低、可互换等优点,其产量和消费量都相当大[1],根据1995年日本松下电池公司川崎先生统计的数据推算,1997年全球各类一次性电池的总量近300亿节,其中碱性锌锰电池约80亿节,占电池总量的25%以上[2-3]。据资料介绍[4-5],2003年中国电池产量达209·3亿元,占世界电池总产量的50%以上,年消费量达100多亿节,其中大部分为锌锰和碱性锌锰电池,并且碱性锌锰电池正以30%的速度增长,预计到2005年碱性锌锰电池将达到50亿节,面对如此大的产量和用量,若不对用过的废旧电池采取有效措施,不仅会造成严…     

Determination of manganese with triethanolamine and o-tolidine by conventional and long-path photometry

A very sensitive method for the spectrophotometric determination of manganese is reported. To the sample is added triethanolamine (TEA) and sodium hydroxide to give a pH above 11; after atmospheric oxidation of manganese(II) to the green manganese(III)—TEA complex, sodium pyrophosphate is added and the solution is acidified. Manganese(III) thus forms a complex with pyrophosphate. Then o-tolidine is added and is oxidized in a 2e step to the intensely yellow quinonediimine, while manganese(III) is reduced to manganese(II). The absorbance is measured at 440 nm. The calibration curve is linear up to 1.6 μg Mn ml^-1 in the final solution; the limit of determination is 0.2 μg Mn ml^-1. For the 20-cm path cell, the respective data are 45 ng Mn ml^-1 and 2 ng Mn ml^-1. The only severe interferences are strong oxidants like dichromate or cerium(IV), which are readily reduced with sulfurous acid. Vanadium in amounts up to 2–3 times that of manganese can be dealt with by an appropriate blank solution; larger amounts of vanadium must be removed e.g. by a cupferron extraction.     

Studies of unusual oxidation states of transition metals III-kinetics and mechanism of oxidation of triethanolamine by diperiodatoargenate(III) ion in aqueous alkaline medium

The kinetics of oxidation of triethanolamine (TEA) by diperiodatoargenate(III) anion, [Ag(HIO₆)₂]^5?, has been studied in aqueous alkaline medium by conventional spectrophotometry. The reaction is pseudo-first-order in [Ag(III)] disappearance with k_obs = (k₁ + k₂[OH^?]) K₁K₂[TEA]/{[H₂IO₆^3?]_e + K₁ + K₁K₂[TEA]}, where k₁ = 8.05 × 10^?3 S^?1, k₂ = 0.46 M^?1 S^?1, K₁ = 6.15 × 10^?4 M, and K₂ = 537 M^?1 at 25°C, and μ = 0.30 M. Based on the inference that an inner-sphere complex is formed by indirect replacement of a ligand of [Ag(HIO₆)₂]^5? by a TEA molecule, a reaction mechanism has been proposed. The complex undergoes redox by two modes, both internal and one hydroxide ion assisted.