Flow-Injection Determination of Gold(III) Based on Its Catalytic Effect on the Peroxodisulfate Oxidation of Bromopyrogallol Red

It was found by derivative spectrophotometry that gold(III) ions exhibit a significant catalytic effect on the peroxodisulfate oxidation of Bromopyrogallol Red in slightly acidic chloride–citrate solutions. It was shown that if this catalytic reaction is implemented in a three-channel flow-injection system, the intensity of the signal due to a decrease in the reagent color is proportional to the concentration of gold(III) in the injected solution and depends on the reagent concentrations, pH, and the temperature of the solution as well as on the sample volume, flow rates, and the length of the reaction coil. The conditions assuring the kinetic masking of foreign ions in the injected solution were found. The possibilities of the flow-injection determination of 0.004–1.00 g/mL gold(III) in the presence of copper, iron, and many other concomitant elements were found. The average throughput of the analytical system is 200 h^–1 for a sample volume of 500 L. The performance characteristics of the procedure were estimated in the analysis of synthetic mixtures simulating the rinsing waters of gilding baths.     

Extraction-spectrophotometric determination of uranium(VI) with PAR and N-octylacetamide

A new and simple method for selective spectrophotometric determination of uranium(VI) with 4-(2-pyridylazo)resorcinol (PAR) and N-octylacetamide into benzene over pH 7.0–9.0 is described. The molar absorptivity of the complex with 9 different amides is in the range of (0.40–3.2)·10⁴ 1·mol^–1·cm^–1 at the absorption maximum. Out of these, the most sensitive compound N-octylacetamide (OAA) was chosen for detailed studies in the present investigation. The detection limit of the method is 0.008 g U·ml^–1. The system obeys Beer's law in the range of 0–5 g U·ml^–1. The method is free from interferences of most of the common metal ions except vanadium(V) and copper(II), which are masked by proper masking agents. The composition of the complex is determined by curve-fitting method. The method has been applied for the recovery of the metal from rock samples and synthetic mixtures.     

3-Hydroxy-2-(2"-Thienyl)-4H-Chromon-4-one as a Spectrophotometric Reagent for the Trace Determination of Zirconium in an Aqueous Phase

A rapid, simple, selective, and sensitive method for the trace determination of zirconium has been developed based on the reaction of 3-hydroxy-2-(2"-thienyl)-4H-chromon-4-one in an hydrochloric acid medium to form a yellow–colored complex which is rendered water soluble by the micellar action of Triton X-100 and measured at 415 nm. Most of the metal ions do not interfere with the determination. Beer's law is obeyed in the concentration range 0–2.0 g/mL and the molar absorptivity of the complex is 2.73 × 10⁴L mol^–1cm^–1; Sandell's sensitivity is found to be 0.0034 g cm^–2. The method has been applied for the determination of zirconium in various samples, and satisfactory results have been obtained.     

Mixed metal complexes in solution. Part 4. Formation and stability of heterobinuclear complexes of cadmium(II)-citrate with some bivalent metal ions in aqueous solution

Summary The systems, Cd-Ni-citrate, Cd-Mn-citrate and Cd-Zn citrate have been investigated pH-metrically at 25°C and I = 0.1 mol dm^–3 (KNO₃).As previously found for analogous citrate systems (namely for Cu-Ni-, Cu-Zn- and Ni-Zn-citrate) the existence of mixed metal complexes of the type [MM(cit)₂H_–2]^4– has been shown. In addition, the species [MM(cit)₂H_–1]^3– was also found to be present for Cd-Ni- and Cd-Zn-citrate systems The significance of the formation of such species is discussed.The existence of mixed metal complexes is also discussed in connection with the transport and the absorption of metal ions in biological systems.     

The nature of colloidal platinum in aqueous solution: features of catalytic reactions

The specific features of the catalytic reduction of methylviologen by dihydrogen in water in the presence of platinum colloids synthesized by various methods are studied. The colloids prepared by the radiation-chemical reduction of PtCl₄ ^2– in the presence of polyacrylate or polyphosphate as stabilizers and colloids prepared by the reduction with dihydrogen efficiently catalyze the reaction. The citrate colloids synthesized by the reduction of PtCl₆ ^2– with citric acid are characterized by a prolonged induction period after which these colloids also gain the catalytic activity. We assume that the citrate platinum colloids are giant clusters with the close-packed metal core containing the magic number of platinum atoms (Pt₅₆₁), which are coordinated by the ligand molecules blocking the surface of the metal particle. In the presence of H₂, the ligand molecules are decomposed or removed from the surface, which is accompanied by the appearance of the catalytic activity.     

Attack of cadmium(II) and palladium(II) on cis-(R,S)-[Pd(egta)]2−: coordination rearrangements facilitated by pendant carboxylates

Cd(H2O)2+6–8 reacts with cis-(R, S)-[Pd(egta)]2– producing equimolar amounts of [Cd(egta)]2– and [Pd2(egta)Cl2]2–. The progress of the reaction and products have been followed by recording 1H- and 13C-n.m.r spectra as a function of time. The PdII released in forming [Cd(egta)]2– is thousands of times more reactive than CdII, and intercepts another [Pd(egta)]2– to form the 2:1 complex [Pd2(egta)Cl2]2–; the 2:1 complex is not attacked by CdII. The role of pendant carboxylates below the PdN2O2 plane of cis-(R, S)-[Pd(egta)]2– in supplying a site for docking of an incoming CdII or PdII centre, and in leading the metal near the lone pair of rupturing Pd–N bond of [Pd(egta)]2–, or simply by increasing the residence time of CdII or PdII nearby to accelerate the number of collisions between the ruptured N-base and external metal ions, is described. Although mixed-metal [Cd(Pd)(egta)] intermediates are required for the reaction, no such species achieves a detectably large enough concentration to be seen by 1H-n.m.r. The observed spectra are the sum of the reactant, [Pd(egta)]2–, and products, [Cd(egta)]2– and [Pd2(egta)Cl2]2–, throughout the time-dependent change.     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.     

Spectrophotometric determination of mercury with 5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine by flow injection analysis

5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine (m-Cl-TPPS₄) was synthesized and used for the Spectrophotometric determination of mercury by flow injection analysis. A pseudo-first-order reaction kinetic mechanism was proposed with a rate constant of 0.8 min^–1 for Hg(II) withm-Cl-TPPS₄ in the presence of 8-hydroxyquinoline in a medium of 1.0M acetic acid and sodium acetate buffer solution (pH 6.22). In the optimum conditions of reaction temperature (85 ° C), stopped-flow time (60 s) and sampling volume (100 l), the method's relative standard deviation was 0.82% (n = 12) at 5.0 g ml^–1 mercury, with a linear range of 0–12.0 g ml^–1 and an analytical frequency of 60h^–1. The detection limit (3) was 0.025 g ml^–1. Interference studies showed that most metal ions co-existing with Hg²⁺ could be tolerated at 100-fold excess levels, but Zn²⁺, Cu²⁺ and Mn²⁺ needed to be masked. The method has been applied to the analysis of water samples with satisfactory results.     

Synthesis of phenoxypyridines under phase transfer catalysis conditions

Reactions of halopyridines with alkali metal phenoxides in a two phase liquid-solid catalytic system, rather than in a liquid-liquid phase transfer catalytic system, make it possible to prepare 2-, 3-, and 4-phenoxypyridines from unactivated bromo- or chloropyridines and 2-chloropicolines. In polyhalogenated pyridines only - and -halogen atoms undergo substitution. 7, 8-Dibromo-6-azaphenoxane has been prepared by the reaction of 2,3,5,6-tetrabromopyridine with the dipotassium salt of pyrocatechol.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 24, No. 3, pp. 356–360, March, 1988.     

Studies on the kinetics and mechanism of dissociation of copper(II) and nickel(II) complexes of the macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene in perchloric acid media

Summary Acid catalysed dissociation of the copper(II) and nickel(II) complexes (ML²⁺ of the quadridentate macrocyclic ligand 1, 5, 9, 13-tetraaza-2, 4, 4, 10, 12, 12-hexamethyl-cyclohexadecane-1, 9-diene (L) has been studied spectrophotometrically. Both complexes dissociate quite slowly with the observed pseudo-first order rate constants (k_obs) showing acid dependence; for the nickel(II) complex (k_obs)=k_O+k_H[H⁺], the k_o path is however absent with the copper(II) complex. At 60°C (I=0.1M) the k_H values areca 10^–4 M^–1 s^–1 for both complexes; k _H ^Cu /k _H ^Ni =ca. 3.9, comparable to some other square-planar complexes of these metal ions. The rate difference is primarily due to H values [copper(II) complex, 29.4±0.5 kJ mol^–1; nickel(II) complex, 35.6±1.5 kJ mol^–1] with highly negative S values [for copper(II), –215.5 ±6.1 JK^–1 mol^–1 and for nickel(II), –208.1 ±5.6 JK^–1 mol^–1] which are much higher than the entropy of solvation of Ni²⁺ (ca. –160 JK^–1 mol^–1) and Cu²⁺ (ca. –99 JK^–1 mol^–1) ions; significant solvation of the released metal ions and the ligand is indicated.     

Effects of Solvent, Structure, and Temperature on the Ionization Equilibrium Constants of Phenols and Pyridinium Ions in Mixtures of Water and 1,4-Dioxane

An extensive collection of data has been used to study the effects of solvent, structure, and temperature on the ionization equilibrium constants of some substituted phenols and pyridinium ions in water–1,4-dioxane mixtures (0–70% weight fraction in dioxane) and temperatures ranging from 10 to 50°C. The effects of structure and solvent are explained using Hammett's equation and the Marshall–Quist model at all temperatures. An equation allowing an analysis of the three effects together on the pK values has been developed. The pK data under all experimental conditions fit this equation well, with standard errors of less than 0.3 pH units. Hammett's reaction constant for the ionization of phenols and pyridinium ions has been obtained for all the experimental conditions. The pK and Hammett's reaction constants for the different ionizations in water–1,4-dioxane mixtures correlate well with Kamlet and Taft's solvatochromic parameters ^* and , which measure the dipolarity/polarizability and hydrogen-bonding capacity of the solvent, respectively. These correlations explain more thoroughly the different contributions and origin of the effects of the solvent on the pK.     

Effect of the chemical structure of nitroxyl radicals on their reactivity in the reaction with hydrazobenzene and tetranitromethane

The reaction rate constants of reduction of stable radicals of different classes by hydrazobenzene in hexane at 20C, in the range of 0.4–5·10³ M^–1sec^–1, were determined; a single scale of the oxidative properties of stable nitroxyl radicals was constructed. The rate constants of oxidation of a series of nitroxyl radicals by tetranitromethane in aqueous medium at 20C, in the range of 0.06–10 M^–1·sec^–1, were determined. It was shown that the oxidative properties of the nitroxyl group decrease slightly with an increase in its reducing properties for nitroxyl radicals of the piperidine and imidazoline series in reactions with ascorbic acid and tetra-nitromethane in aqueous medium, respectively.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2575–2582, November, 1990.     

Synthesis and investigation of styryl derivatives of 5,6-benzo-2, 2′-diquinolyl

By catalytic condensation of quinolidene--naphthylamine with benzalacetone and its derivatives, previously undescribed styryl-5, 6-benzo-2,2diquinolyls have been synthesized. Complexes of these compounds with univalent copper ions have been studied, the spectral characteristics of the reagents and complexes have been reported, and a hypothesis has been advanced on the relationship between the structure of the ligands and the intensity of coloration of the metal complexes.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1525–1527, November, 1985.     

Ternary Complexes of Cadmium(II) with Phenylalanine and Phenylalkylmalonates in Dioxane–Water Mixtures

The formation and stability of ternary complexes of cadmium(II) with phenylalanine and malonate, phenylmalonate benzylmalonate, 2-phenylethylmalonate, and 3-phenylpropylmalonate, have been studied by the potentiometric pH titration technique in 40% (v/v) dioxane–water at 25°C and 0.10—ionic strength (NaNO₃). All systems give stable ternary complexes, and the log K and _K values demonstrated that the complexes possess enhanced stability. The possible reasons that lead to these results are discussed in terms of –electron back donation from metal ions to ligands and intramolecular ligand–ligand aromatic ring-stacking interactions present in the complexes. The relative contribution of each interactions to the enhanced stability have also been evaluated.     

Photometry in a continuous flow system

Summary Sulphate in various environmental samples was determined by measuring the optical absorbance upon reaction with the barium(II) dimethylsulphonazo(III) complex. The measurement took place in a flow-through system. Interferences from phosphate, metal ions and others were eliminated. The results of a turbidimetric measurement, a spectrophotometric measurement with thorin, an automatic titration and the proposed method are compared. The latter allows the determination of sulphate in the range of 1.4–60 mol·l^–1. The standard deviation is 0.3–0.6 mol·l^–1, depending on the type of sample (water) analysed. A determination takes 1.5min.

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Photometric in einem DurchflußsystemBestimmung von Sulphat mit Dimethylsulfonazo(III) in Umweltmaterial mit Hilfe eines Durchflußsystems

Zusammenfassung Sulfat wurde in verschiedenen Umweltproben durch Messung der Extinktion nach Reaktion mit dem Barium(II)-dimethylsulfonazo(III)-komplex im Durchflußsystem bestimmt. Störungen von Phosphat, Metallionen, u.a. wurden beseitigt. Die Ergebnisse einer turbidimetrischen, einer photometrischen, einer automatischen Titration und der vorgeschlagenen Methode werden verglichen. Die Methode ermöglicht die Sulfatbestimmung im Bereich von 1,4–60 mol·l^–1. Die Standardabweichung beträgt 0,3–0,6 mol· l^–1 je nach Typ des Probematerials (Wasser). Eine Bestimmung erfordert 1,5min.

     

Electrochemical Properties and Analytical Applications of Keggin-type Phosphomolybdic Anions in Electrostatically Linked 2-Aminoethanethiol Self-Assembled Monolayers

A composite film containing a heteropolyanion was prepared on a 2-aminoethanethiol (AT) self-assembled monolayer film-modified gold electrode by attaching the Keggin-type phosphomolybdic anion. The surface structures and electrochemical properties of the composite films were characterized by using ATR-FTIR, AC impedance, cyclic voltammetry and chronocoulometry. FTIR studies indicated that there was some electrostatic interaction between Pmo₁₂O₄₂^7– and surface NH₃⁺. Three reversible redox couples were observed in 1.0molL^–1 H₂SO₄ in the potential range of 0–0.7V for the composite film modified electrode, which were attributed to two-electron and two-proton electrochemical processes of PMo₁₂O₄₂^7–. The diffusion coefficient is determined to be 2.04×10^–7cm²s^–1. The composite film shows good catalytic activities for the reduction of nitrite (NO₂^–) in acidic solution and the catalytic mechanisms are described. The modified electrode provides a linear response for NO₂^– in the concentration range of 1.0×10^–4 to 1.0×10^–7molL^–1 by differential pulse adsorptive stripping voltammetry with a correlation coefficient of 0.9965. The detection limit (three times the signal blank/slope) was 2.0×10^–8molL^–1. The modified electrode was used for the determination of NO₂^– in wastewater.     

Complexometric determination of copper(II) in ores,alloys and complexes using 2-mercaptoethanol as indirect masking reagent

A complexo-titrimetric method for the determination of copper(II) in the presence of other metal ions is described, based on the selective masking ability of 2-mercaptoethanol towards copper(II). Copper and other ions in a given sample solution are initially complexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10%) is then added, the mixture is shaken well and the released EDTA from the Cu-EDTA complex is titrated against standard zinc sulfate solution. The interferences of various ions are studied and the method is applied to the determination of copper in its ores, alloys and complexes. Reproducible and accurate results are obtained for 2.5–40 mg of Cu with relative errors 0.4% and standard deviations 0.04 mg.     

Pyrroles from ketoximes and acetylene 8. Synthesis of 4,5,6,7-tetrahydroindole and its 1-vinyl derivative

4,5,6,7-Tetrahydroindole or 1-vinyl-4,5,6,7-tetrahydroindole was obtained in 81 and 93% yields, respectively, by reaction of cyclohexanone oxime with acetylene at 90–140C in the presence of alkali metal hydroxides or alkoxides in dimethyl sulfoxide (DMSO) or mixtures of DMSO with low-polarity or nonpolar solvents. The reaction is effective both in an autoclave (initial pressure 8–16 gage atm) and at atmospheric pressure.See [1] for communication 7.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 197–199, February, 1979.     

Determination of palladium, platinum and gold by first derivative spectrophotometry

Summary The application of first-derivative spectrometry to the simultaneous determination of palladium(II), platinum(IV) and gold(III) is described. Light absorption of stable chlorocomplexes formed in 1 mol/l hydrochloric acid provides the basis of their determinations. A difference in the derivative amplitudes between two first-derivative zero crossing points of one metal A is read, corrected for the contribution of metal B and used for quantitation of metal C. Palladium (0.48–20 g ml^–1), platinum (0.16–24 g ml^–1) and gold (0.32–24 g ml^–1) have been determined with good precision and accuracy without any separations. Results are also presented for the simultaneous determination of the three precious metals in the presence of several major constituents.