Aqueous Solutions Of Different Composition Research Articles

HYDROGEN ROLE IN SELECTIVITY OF SUBSTITUTED NITRO-AZOBENENES HYDROGENI-ZATION ON SKELETAL NICKEL IN 2-PROPANOL AQUEOUS SOLUTIONS

Elucidation of the substituted nitrobenzenes transformations sequence, in particular, containing several reactive groups and the development of approaches to the control of the selectivity of processes involving them is of interest from both theoretical and practical points of view. The article is devoted to the analysis of the hydrogenation kinetics of 2-nitro-2'-hydroxy-5'-methylazobenzene, 4-nitro-2'-hydroxy-5'-methyl-isobenzene, 4-nitroaniline, 4-amino-2'-hydroxy-5'-methylazobenzene on skeletal nickel in 2-propanol aqueous solutions of different composition, including with the addition of acetic acid or sodium hydroxide with various initial amounts of organic compound. The rise in the 4-nitro-2'-hydroxy-5'-methylazobenzene initial amount leads to increase in the nitro group transformation rate in the starting compound and to decrease in the azo-group transformation rate. The effect of sodium hydroxide additives in the 2-propanol aqueous solution on the nitro- and azo-groups conversion rate into 4-nitro-2'-hydroxy-5'-methyl-isobenzene is analogous to the change in the individual compounds hydrogenation rates (4-nitroaniline and 4-amino-2'-hydroxy-5'-methylazobenzene). Obtained results do not contradict the parallel-sequential scheme concept for the 4-nitro-2'-hydroxy-5'-methylazobenzene transformations. One of the directions is associated with the azo-group transformation into 4-nitro-2'-hydroxy-5'-methylazobenzene and 4-nitroaniline and 2-amino-4-methylphenol formation, and the second with the 4-nitro-2'-hydroxy-5'-methyl-isobenzene conversion through 4-amino-2'-hydroxy-5'-methyl-isobenzene by the nitro-group reducing. At the reaction end, all intermediate compounds are reduced to 2-amino-4-methylphenol and 1,4-phenylenediamine. When 2-nitro-2'-hydroxy-5'-methylazobenzene is hydrogenated, one of the directions leads to the 2-nitro-2'-hydroxy-5'-methylhydrazobenzene formation, and the second to the product containing the triazole cycle - N-oxide 2-2'-hydroxy-5'-methylphenylbenzotriazole. At the reaction end, these compounds are reduced to 2-2'-hydroxy-5'-methylphenylbenzotriazole and 2-amino-4-methylphenol and 1,2-phenylenediamine, respectively. In the solution at the sodium hydroxide presence, 2-nitro-2'-hydroxy-5'-methylhydrazobenzene transforms into the N-oxide 2-2'-hydroxy-5'-methylphenylbenzotriazole as a result of intramolecular rearrangement.

In Ukrainian

The production of stable dispersions of carbon nanotubes (CNTs), synthesized by CVD, in different liquids, is one of the methods of preparation of CNTs for introduction into polymeric matrix. The aim of this work is to produce composites of polyethylene (PE) – CNT, and the study of their structural characteristics, mechanical, thermodynamic, and kinetic properties as dependent on the concentration of multi-walled CNTs and the preliminary dispersion by several methods. Multi-walled CNTs were synthesized by catalytic pyrolysis (CCVD) using iron-containing catalyst in admixture with pyrogenic silica (grade A 300), which was prepared by coprecipitation of hydroxides of aluminum, magnesium and divalent iron. CNTs with a diameter of 10–20 nm were grown in a reactor with a volume of 24 dm 3 with a smooth mixing of the catalyst layers due to rotation of the reactor. Deagglomeration of CNTs was carried out by processing in an ultrasonic dispergator or in a device that combines the cavitation mixing and shear deformation in aqueous solutions of different composition. Composite samples of the of PE–CNT with different concentration of the filler obtained by hot pressing at the temperature of 140 °C and the pressure of 5 MPa of polyethylene powders. Their surface was pre-deposited CNTs from stable aqueous dispersions. The structural characteristics of the CNTs and the composite of PE–CNTs is determined by the methods of transmission electron microscopy (JEM-100CXII), X-ray diffraction (DRON-3M, λСо = 0.179 nm). Structural and phase transitions and the processes of destruction of polymer composites in air are investigated by methods of DTA and DTG on a derivatograph Q 1500 D (Hungary). Electric conductivity at low frequencies (0.1, 1 and 10 kHz) was measured by double contact method with an immittancemeter E7-14. The frequency dependence of complex electric conductivity of the composites was evaluated from calculations of the impedance spectra in the frequency range 10 -2 –10 6 Hz obtained by an impedance spectrometer Solartron SI 1260. The carbon nanotubes (CNTS) introduction in a matrix of polyethylene in small amounts (up to 5 wt. %) leads to a nonmonotonic change of the degree of crystallinity of the matrix. Their electrophysical and thermodynamic properties were studied. The percolation threshold in systems PE–CNTs from certain experimental data on the electrical conductivity is in the range 0.0015–0.0020 in volume. The content CNT to 2 % increases the temperature of the thermal oxidative degradation of the polymer by almost 60 °C. Influence of CNTs on the structure and properties of the composite is the more significant, the greater the degree of CNTs deagglomeration.

Studies on the kinetics and equilibrium of the solvent extraction of chromium(III) from alkaline aqueous solutions of different composition in the system with Aliquat 336

The kinetics and equilibrium of Cr(III) extraction with Aliquat 336 from the alkaline aqueous solutions containing anions of various complexing abilities and solvating properties, as: nitrates, or perchlorates, or sulphates, were studied and interpreted. Stoichiometry of Cr(III) complexes formed in the organic phases was also discussed. It was found that under the same conditions the yield and the rate of Cr(III) extraction as well as values of mass transfer coefficient increase in the following order of anions: perchlorates < nitrates < sulphates. The equilibrium of extraction of Cr(III) in the systems with nitrates and/or perchlorates differs significantly from that one established for the extraction of Cr(III) from the alkaline aqueous solutions of sulphates. Experiments with the modified Lewis cell and analysis of the experimental data by mathematic models appeared that the studied extraction of Cr(III) occurs in the mixed diffusion-kinetic regime, irrespective of the kind of anions present in the aqueous phase.

Spontaneous activation of fish eggs is abolished by protease inhibitors

During spawning, eggs of most fish species entering the aquatic environment remain fertilizable for a relatively short period of time. This is due to the "spontaneous egg activation" giving rise to the fertilization membrane, which prevents the penetration of excessive and foreign sperm into the egg during normal fertilization. This work demonstrates that the fertilization membrane formation and the loss of fertilizability in aqueous solutions of different composition are inhibited by protease inhibitors, in particular, leupeptin and aprotinin. The presence of natural protease inhibitors in the ovarian fluid that prevent spontaneous egg activation is proposed. The decrease in the concentration of these inhibitors as the ovarian fluid is diluted in aquatic medium during spawning can explain egg activation in the absence of sperm.

Visualization of the Reaction Zones Between Two Miscible Solutions with Potentiometric and Amperometric Microsensors

AbstractA strategy for visualizing the concentration gradients in the border zone between two miscible aqueous solutions of different composition is presented. To achieve this goal, potentiometric pH microsensors and disk‐shaped Pt microelectrode have been operated as scanning probes in a set‐up that combined conventional scanning electrochemical microscopy (SECM) equipment with an inverted optical microscope and a syringe pump for analyte injection. With the established system, complex gradients in proton concentration have been examined in the reaction zone between two aqueous solutions of different pH value, one of which being dispensed into the other at controlled flow rate. In addition to the local potentiometric measurements, Pt microelectrodes have been used as amperometric SECM tips to visualize the reaction zone at the diffuse boundary between a stream of H2O2 and a neighbouring catalase‐containing buffer solution.

On the Anomalous Cathodic Dissolution of Aluminum in Connection with Concentration Changes Near the Electrode

The peculiarities of the corrosion damage to cathodically polarized aluminum in aqueous solutions of different composition are discussed. A mathematical model, semiquantitatively describing and explaining the main regularities of the phenomenon under study, is worked out and analyzed. Additional data, strengthening the hypothesis about the determining role of concentration changes in the near-electrode layer, in particular, a significant increase in pH, are obtained.

Application of drop-weight interfacial tensiometry to the quantitative analysis of Cu/SiO 2 composite coatings

Interfacial tension γ was measured between several organic solvents—butanol, isobutyl methyl ketone and mixtures of the two (in volume ratios 3/1 and 5/1)—and aqueous solutions of different composition, applying drop-weight interfacial tensiometry. A method for quantitative analysis of silicon in Cu/SiO 2 composite coatings was improved by funding an organic solvent, suitable for quantitative extraction of silicon as silicomolybdic acid in higher concentrations. Interfacial tension measurement results allowed one to better understand the reason due to which, with the solvents reported in literature, the extraction is not complete. The dependence of γ on the aqueous phase composition was investigated and the influence of the Cu matrix and all other reagents present in solutions was established. The optimum time for extraction was determined on the basis of interfacial tension measurements.

Adsorption of cesium on, and desorption from, controlled porous glasses

Cesium contained in aqueous solutions of different composition was adsorbed in columns packed with controlled porous glasses (CPG) and then removed by means of 1M HCl. Recovery of cesium in the eluate was studied as a function of the solution composition and the kind of CPG.