Reactions of diethyl trichloromethylphosphonate with metallic zinc

Complexes of tetrachloroethylenediphosphonic acid tetraethyl ester and diethyl trichloromethylphosphonate (DETCMP) with ZnCl₂ are shown to be formed in the reaction of DETCMP with metallic zinc. The complexes undergo dealkylation and condensation reactions leading to the formation of zinc polypyrophosphonate:

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.Alcoholic solvents cause an increase of reaction rate.     

Initiation of electropolymerization of acrylamide and formaldehyde by metallic zinc in aqueous medium

The effect of postpolymerization (polymerization after current interruption) is observed and studied for electropolymerization composition based on acrylamide, N,N′-methylene bisacrylamide, formaldehyde, and zinc chloride. The possible causes of this phenomenon are considered. It is found that the main cause of postpolymerization is the catalytic effect of metallic zinc formed in the course of polymerization and initiation of further polymerization by metallic zinc after current interruption in an electrochemical cell. Kinetics and the mechanism of polymerization initiation by zinc are studied. It is shown that polymerization initiators may be other metals with the electrochemical potential in the studied solution sufficient for discharge of a zinc-acrylamide complex.     

Oxidative dissolution of copper and zinc metal in carbon dioxide with tert-butyl peracetate and a beta-diketone chelating agent

A series of beta-diketone ligands, R(1)COCH(2)COR(2) [tmhdH (R(1) = R(2) = C(CH(3))(3)); tfacH (R(1) = CF(3); R(2) = CH(3)); hfacH (R(1) = R(2) = CF(3))], in combination with tert-butyl peracetate (t-BuPA), have been investigated as etchant solutions for dissolution of copper metal into carbon dioxide solvent. Copper removal in CO(2) increases in the order tfacH < tmhdH < hfacH. A study of the reactions of the hfacH/t-BuPA etchant solution with metallic copper and zinc was conducted in three solvents: scCO(2) (supercrical CO(2)); hexanes; CD(2)Cl(2). The etchant solution/metallic zinc reaction produced a diamagnetic Zn(II) complex, which allowed NMR identification of the t-BuPA decomposition products as tert-butyl alcohol and acetic acid. Gravimetric analysis of the amount of zinc consumed, together with NMR studies, confirmed the 1:1:2 Zn:t-BuPA:hfacH reaction stoichiometry, showing t-BuPA to be an overall two-electron oxidant for Zn(0). The metal-containing products of the copper and zinc reactions were characterized by elemental analysis, IR spectroscopy, and, as appropriate, NMR spectroscopy and single-crystal X-ray diffraction [trans-M(hfac)(2)(H(2)O)(CH(3)CO(2)H) (1, M = Cu; 2, M = Zn)]. On the basis of the experimental results, a working model of the oxidative dissolution reaction is proposed, which delineates the key chemical variables in the etching reaction. These t-BuPA/hfacH etchant solutions may find application in a CO(2)-based chemical mechanical planarization (CMP) process.     

Defect-induced acceleration of a solid-state chemical reaction in zinc alkoxide single crystals

A family of dinuclear (salicylaldimato)zinc(micro(2)-alkoxide) complexes show unusual behavior, decomposing to olefins and the corresponding micro(2)-hydroxide complexes under very mild conditions in the solid state. The reaction in homogeneous solution is, on the other hand, not observable, even at elevated temperatures over extended periods of time. The reaction in the solid state occurs preferentially on one crystallographic face and displays kinetics characteristic of polymorphic transformations in single crystals.     

Electrodeposition of zinc + cobalt alloys.: Relation between the electrochemical response and the composition and morphology of the deposits

The electrodeposition of cobalt and zinc + cobalt alloy in aqueous chloride solution has been studied on vitreous carbon electrodes under different concentration conditions (total concentration of metallic ion 0.1 mol dm ⁻³, chloride ion 1 mol dm ⁻³, pH = 3), particularly during the initial stages of the deposition process. For the alloy a relation has been found between the shape of the current-time transients, the morphology of the deposits, the stripping analysis and the results of X-ray microanalysis. The different alloy phases present in the deposits were identified using X-ray microanalysis data, stripping voltammetry results and literature data.The results indicate that the electrocrystallization of cobalt is inhibited even at very low concentrations of zinc in solution: voltammetric and galvanostatic results indicate that the deposition potentials always correspond to more negative values than those for cobalt deposition. This inhibition depends strongly on both the metallic ion ratio in solution and the applied overpotential (or current density). For Zn(II)/Co(II) ratios greater than 1/9, low overpotentials (or low current densities) favoured homogeneous and compact deposits that were rich in zinc and were mainly composed of γ-phases of zinc + cobalt alloy. However, when high overpotentials or current densities were used and/or when the Zn(II)/Co(II) ratio was very low (< 1/9), dendritic and non-homogeneous cobalt-rich deposits were obtained.     

Interactions during the chlorination of a copper–zinc alloy

In this paper several aspects involved in the chlorination of a Zn 48% wt.–Cu alloy between 250 and 500 °C are investigated. The starting temperature for the chlorination of the alloy is determined, which is different from those of pure metals. Analysis of the chlorination thermogravimetric curves and reaction products reveal that there are interactions between reactants and products during the reaction, and that volatilization of ZnCl₂ is diminished during the alloy chlorination. Metallic copper is detected at intermediate stages of the chlorination, and this element, which is not present in the initial sample, appears during the chlorination reaction. An oxidation–reduction type reaction between copper chlorides and metallic zinc is proposed to explain the behaviour observed. The occurrence of this reaction at room temperature was confirmed in separate experiments. At the beginning of the reaction, formation of zinc oxichloride was detected that is being formed from the zinc oxide layer that covers the alloy surface. According to the results obtained, a reaction mechanism is presented for the alloy chlorination.     

Electroreduction of Mo(VI) Compounds in Ammonium–Acetate Solutions

The kinetics of cathodic reactions in ammonium acetate solutions proposed for electrodeposition of metallic molybdenum was studied. The reduction of molybdenum compounds in the oxidation state +6 was found to occur stepwise according to the scheme Mo(VI) → Mo(V) → Mo(III). The waves observed on the polarograms are complicated by adsorption effects. The reduction of molybdenum to the metallic state is possible only at high negative potentials of the cathode; under the polarographic analysis conditions, this wave was not recorded. The deposit that formed on the surface of the solid cathode during cathodic polarization (i = 0.5 A cm^–2) contains both molybdenum in the metallic state and molybdenum oxides. The ratio between the electrolysis products depends on the temperature of solution: a decrease in the temperature leads to an increase in the amount of metallic molybdenum.

     

Catalytic effect of zinc oxide on the reduction of barium sulfate by methane

Reduction of barium sulfate by methane was investigated in this work. The thermogravimetric method was used to obtain kinetic parameters of the reaction in the temperature range of 900–975 °C at atmospheric pressure. The kinetics of the reaction has been studied both in the absence and presence of zinc oxide as a catalyst. The conversion–time data have been interpreted by using the grain model, and the effect of catalyst on the kinetic parameters has been elucidated. It was found that zinc oxide acted as fairly strong catalyst for the reaction, especially at higher temperatures. At about 975 °C the reaction rate constant was increased more than 7 times by using 2% of zinc oxide. This enhancement in the rate constant is valuable for industries.     

Electrochemically induced growth of zinc oxide.

The electrolytically induced precipitation of zinc oxide from zinc nitrate solution on gold surfaces in the presence of water-soluble polymers was examined for reaction times between 0.5 and 600 seconds. Regardless of the additive, polycrystalline films of zinc oxide have formed after 30 seconds, but polymeric additives dramatically change the morphology of the ZnO films. Amperometric analysis and fitting the diffusion reduced the current density-time curve according to Avrami kinetics and it reveals that polymers bearing methacrylic acid groups result in spherical growth whereas such with sulfonic acid groups lead to a platelike growth of crystallites. Without additive prisms grow predominantly in one dimension. These findings are confirmed also by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis.     

Thermodynamic characteristics of the complex formation in the zinc(II) ion-L-serine-water system

Using calorimetric method we determined the thermal effects of reactions of the L-serine complex formation with the doubly charged zinc ion. The heat effects of the reaction of amino acid solution with a solution of zinc(II) were measured at temperatures 288.15, 298.15, and 308.15 K and ionic strengths 0.25, 0.50, and 0.75, against the background of KNO₃. The heats of dilution of zinc nitrate in the background electrolyte solution were determined under the same conditions, to introduce respective corrections. The thermochemical data were processed with accounting for all the possible equilibria. The standard thermodynamic characteristics of complex formation processes were calculated. The effects of concentration and temperature on the thermal effects of the complex formation of zinc(II) and L-serine in aqueous solution were estimated.     

Phase transitions of adsorbed carboxylic acids on zinc oxide and of zinc soaps. Infrared and X-ray diffraction investigations

Summary The reaction between carboxylic acids in benzene solution and suspended zinc oxide particles was investigated by means of infrared spectrometry. The results show how the carboxyl groups react with the zinc oxide forming zinc carboxylate groups at the chemisorption. The chemisorbed acid forms a multilayer at the surface, which gives a new explanation of the protective action of adsorbed acids against flocculation of the particles in nonpolar solvents. The temperature-dependence of the spectra showed transitions at the same temperatures and of the same kind as the corresponding zinc carboxylates, whose spectra were also recorded. The zinc soaps exhibited thermotropic behaviour, and lyotrophy is suggested as the explanation of the multilayer formation.

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Zusammenfassung Mit Hilfe der Infrarotspektrometrie wurde die Einwirkung von Stearins?ure und ?ls?ure auf Zinkoxid untersucht, das in Benzol suspendiert worden war. Durch Carboxylatbildung wird eine multimolekulare Schicht der S?uren auf der Oberfl?che der Zinkpartikel ausgebildet. Die Partikel werden dadurch von der Flokkulation in nichtpolaren L?sungsmitteln geschützt. Die Temperaturabh?ngigkeit der Spektren entspricht der der Zinkcarboxylate.

     

Convenient extraction method for quantification of thin zinc patina layers

Synthetic zinc patina was grown on galvanized steel sheets in supercritical carbon dioxide atmosphere. Different patina compounds were dissolved and quantified using a stepwise immersion and dissolution procedure. The distinct patina components, namely anhydrous zinc carbonate (a dense layer adjacent to metallic zinc) and zinc hydroxy carbonate (nanowires on the surface), were dissolved in glycine solutions, followed by quantification of Zn²⁺ in the solutes by X‐ray fluorescence. The zinc hydroxy carbonate nanowires were readily glycine soluble, and the anhydrous zinc carbonate showed scarce glycine solubility, which enabled their selective quantification. The amount of the remaining (anhydrous) zinc carbonate after glycine extraction was determined from the glycine‐soluble zinc oxide after calcination (heat treatment for 10 minutes at 350°C). The results were verified by scanning electron microscopy imaging and Fourier transform infrared spectroscopy measurements.     

Precipitation of zinc sulfide by the hydrolysis of thioacetamide

Zinc can be precipitated quantitavely as zinc sulphide using thioacetamide in a weakly acid solution. This is accomplished by carrying out the reaction in a sealed tube at 120⁰. The method, however, does not give a good separation from cobalt. Best separations are obtained by using a sulfate-bisulfate buffer containing ammonium thiocyanate with hydrogen sulfide as precipitant.     

Substoichiometric isotope dilution analysis of copper traces in zinc by adsorptive sampling

The spontaneous deposition of Cu²⁺ from aqueous solutions on a hydrogen-saturated platinum surface as a possibility for the substoichiometric sampling of copper is shown. A sensitive isotope dilution method has been developed for the determination of traces of copper in high purity zinc making use of the spontaneous deposition of microquantities of Cu²⁺ from aqueous solutions of zinc salts on a cathodically polarized platinum surface. If the same platinum surface is used in each run, the saturation values of the deposited copper are practically independent of the concentrations and contents of copper and zinc in the solution. The copper traces were labelled with the product of the⁶⁴Zn(n,p)⁶⁴Cu nuclear reaction. A copper content of 0.18±0.03 ppm in zinc was determined by this method.     

Sensitive spectrofluorimetric determination of zinc at ultra-trace levels

An ultra-trace method based on the reaction of zinc with salicylthiocarbohydrazone (SATCH) and Triton X-100 as a non-ionic surfactant was developed for the fluorimetric determination of zinc at the picogram level. The reaction is carried out in the pH range 4.4–4.7 in an aqueous ethanolic medium [52% (v/v) ethanol]. The influence of the reaction variables is discussed. The detection limit is 10 pg ml^?1 and the range of application is 0.01–500 μg l^?1, with an optimum range of 0.04–400 μg l^?1. The relative standard deviations are 0.68% (0.01–0.1 μg l^?1 of zinc), 0.41% (0.1–1.0 μg l^?1 of zinc), 0.64% (1–10 μg l^?1 of zinc), 0.82% (10–100 μg l^?1 of zinc) and 0.15% (100–500 μg l^?1 of zinc). The method is highly sensitive and selective in the presence of Cd^II and Hg^II. The effect of interferences from other metal ions and anions was studied; the masking action is discussed. The advantages of the proposed method include its high sensitivity, simplicity and selectivity.     

Photolysis of zinc azide in the solid state

The photolysis of anhydrous zinc azide prepared by (1) dehydration of Zn(N₃)₂·2H₂O and (2) precipitation by acetone from aqueous solution, under the action of high pressure mercury arc is reported here. The pressure of nitrogen developed during photolysis under steady-state conditions at constant intensity is a linear function of t^1/2 in both the samples. The rate of photolysis is a linear function of intensity at constant temperature. A detailed analysis of the dark rate suggests that the dependence on t^1/2 should be due to the diffusion of nitrogen from the reaction site to the surface of the solid azide. An appropriate mathematical analysis is presented. The linear dependence of the rate of photolysis on the intensity of irradiation is interpreted in terms of the reaction of a trapped exciton with an adjacent azide ion. Absence of any detectable photoconduction in the wavelength range of the irradiating radiation suggests that excitons are the most probable reactive species. The sample of zinc azide obtained by the first method decomposes faster than the other under identical conditions, and has a slightly lower energy of activation of 1.4 kcal/mole compared to 1.75 kcal/mole for the second. These differences are discussed in terms of the defect concentrations of the two azide samples.     

Photoelectrochemical kinetics of eosin y-sensitized zinc oxide films investigated by scanning electrochemical microscopy

Eosin Y is used as a sensitizer for nanoporous zinc oxide films for prospective applications in photoelectrochemical solar cells. The kinetics of the reduction of the intermittently formed photo-oxidized dye molecules by iodide ions in the electrolyte phase was investigated by using the feedback mode of scanning electrochemical microscopy (SECM). The bulk solution phase contained triiodide as electron transfer mediator, from which the ultramicroelectrode-generated iodide ions acted as electron donors for photo-oxidized Eosin Y molecules (D(+) (ads)) at the zinc oxide sample. Effective rate constants for the dye regeneration could be extracted from the SECM approach curves. The effective rate constants at different triiodide concentrations could be related to the rate constant for the reaction of the dissolved donor with photo-oxidized Eosin Y bound to ZnO, as well as to the overall rate of the photosensitization process. For the reaction D(+) (ads) + 1.5 I(-)-->D(ads) + 0.5 I(3) (-) a rate constant of k(ox) = (1.4+/-0.8)x10(8) cm(9/2) mol(-3/2) s(-1) was determined.     

Flow injection analysis for traces of zinc with immobilized carbonic anhydrase

A small column packed with immobilized bovine carbonic anhydrase is used for determination of traces of zinc in aqueous solution, based on the measurement of recovered esterase activity of the metal-free apoenzyme after taking up zinc from the sample solution. Conditions for the removal of zinc from the immobilized enzyme and for activity measurement are established. A linear calibration graph is obtained between 1 × 10^?8 and 4 × 10^?7 g of zinc. Then the method is successfully applied to the determination of zinc in tea, sediment and spring water.     

Functionalized manganese-doped zinc sulfide quantum dot-based fluorescent probe for zinc ion

We report on a simple strategy for the determination of zinc ion by using surface-modified quantum dots. The probe consists of manganese-doped quantum dots made from zinc sulfide and capped N-acetyl-L-cysteine. The particles exhibit bright yellow-orange emission with a peak at 598?nm which can be attributed to the ⁴T₁→⁶A₁ transition of Mn(II). This bright fluorescence is effectively quenched by modifying the sulfur anion which suppresses the radiative recombination process. The emission of the probe can then be restored by adding Zn(II) which causes the formation of a ZnS passivation layer around the QDs. The fluorescence enhancement caused is linear in the 1.25 to 30?μM zinc concentration range, and the limit of detection is 0.67?μM.

Foliar uptake of zinc by vascular plants: radiometric study

The aim of this paper was to obtain quantitative data of foliar uptake kinetics and long distance transport of zinc in tobacco (Nicotiana tabacum L.) and hop (Humulus lupulus L.) plants. Zinc was used as a model of microelement and toxic metal, tobacco and hop as a representatives of agriculturally important plants. A tip of leaf blade was immersed in the solution spiked with ⁶⁵ZnCl₂ and foliar uptake and translocation to other parts of the plant grown in nutrient solution was measured by gamma-spectrometry and autoradiography. We found that foliar zinc uptake by both plants is dependent on the initial metal concentration within the range C ₀ = 10–100 μmol dm⁻³ ZnCl₂. Zinc is immobilized mainly in immersed part of the contact leaf and only <1% is transported to non-immersed parts of the leaf. At C ₀ = 0.1 mmol dm⁻³ ZnCl₂ concentrations >2.5 mg/g Zn and 4.8 mg/g Zn (dry wt.) in immersed part of tobacco and hop leaf plant, respectively were found after 5 days of exposure. Low mobility of zinc entering the plant via the leaf surface can be attributed to the immobilization of zinc into Zn–ligand complexes with high stability constants log K at pH 6.0–8.0, such as the reaction products of Zn²⁺ ions with citric acid, histidine or phosphates. Zinc can be extracted from dried leaves by the solutions of inorganic salts, carboxylic acids, amino acids and synthetic complexing ligands such as EDTA. Anionic (SDS) and non-ionic (Tween 40) surfactants causes the decrease of the Zn foliar uptake, but not translocation of Zn from the contact leaf area. Obtained data are discussed from the point of view of possible limited efficiency of liquid formulations designed for practical applications as Zn foliar fertilizers.