Kinetics of the disproportionation reaction of HIO2 in acidic aqueous solutions

We review and discuss kinetic studies of the disproportionation reaction of iodous acid (HIO₂) in the presence of excess of Hg²⁺‐ions. The reactions are followed at different temperatures in water solution with strongly defined acidity. The rate constants of disproportionation are determined between 285 and 303 K based on kinetic data obtained under steady‐state conditions. The calculated rate constants increase with increasing temperature and acid concentration. The corresponding values of activation energy as well as enthalpy and entropy of activation for this reaction have been calculated. The enthalpy of activation as well as entropy is higher at higher sulfuric acid concentration. Also, it was considered that the values of Gibbs energy of formation of HgI⁺ are generated during the process. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 687–691, 2010     

Potentiodynamic passivation of zinc in aqueous KOH solutions

The potentiodynamic oxidation of an upward-facing, horizontal zinc electrode in unstirred KOH solutions at concentrations in the range 1.0–5.0 M has been studied. Besides electrochemical treatment of the experimental data, the morphological evolution of the electrode surface during the oxidation has been followed by means of a scanning electron microscope. In the initial dissolution region, the Tafel slopes are near 40 mV dec⁻¹(25°C) and the reaction orders with respect to the OH⁻ion about 3, these results being consistent with the mechanisms already proposed by Bockris and by Chang and Prentice. The experimental results suggest that the passivation of zinc takes place by a dissolution-precipitation mechanism. However, the rate determining step for passivation appears to be the resistance of the solution in the pores formed by the precipitation and spreading of a film presumably composed of Zn(OH)₂, which is supposed to be the result of a local supersaturation with Zn(OH)²⁻₄.     

Kinetics of lecithin oxidation in liposomal aqueous solutions

The peculiarities of egg phosphatidylcholine (lecithin) oxidation with molecular oxygen in aqueous media are investigated. Under the action of ultrasound, lecithin forms multilamellar liposomes or vesicles in aqueous solutions. Lecithin is oxidized through a chain free-radical mechanism. The nonlinear dependence of the rate of oxygen absorption on the substrate concentration and the imitation of the linear termination of the oxidation chain are observed. The study of the inhibited oxidation of phosphatidylcholine suggests that catecholamines, such as dopamine, noradrenalin, and adrenalin, are markedly more efficient antioxidants than quercetin and α-tocopherol. Phosphate buffer solution is shown to strongly influence the ways of adrenalin transformation in reactions with peroxyl radicals.     

Kinetics of synthesis of monomeric betaines in aqueous solutions

In the nucleophilic addition of N-(3-dimethylaminopropyl)methacrylamide to acrylic acid (1 : 1) in aqueous solutions, forming monomeric β-propiobetaine, the dependence of the initial rate on the starting reagent concentration was found to have a pronounced maximum (whose position does not depend on the temperature at 30–70°С). In the case of the addition of N,N-dimethylaminoethyl methacrylate, the dependence was exponential. The dependences of equilibrium conversions on the starting reagent concentrations were of the same type and had a maximum for both systems. The detected concentration effects are related to the peculiarities of the pre-reaction association of the reagents.     

Kinetics of silver nanoparticle growth in aqueous polymer solutions

Silver nanoparticles were prepared in aqueous AgNO₃ solution by using hydroquinone and sodium citrate as reducing agents with neutral polymers poly(vinylpyrrolidone) and poly(vinyl alcohol) as stabilizers. The rate of particle formation was determined with a diode array UV-Vis spectrophotometer. The effects of the polymer concentration on the reaction rate, the size, and the size distribution of the particles formed were studied by transmission electron microscopy. Both the reaction rate and the size of silver nanoparticles decreased with increasing polymer concentration in the range 0.07–0.50 w/v%.     

Specific features of the bulk etching of single-crystal semiconducting silicon in aqueous KOH solutions

Bulk chemical etching of single-crystal semiconducting silicon in aqueous alkaline solutions of KOH was studied at various solution temperatures, alkaline component concentrations, and microscopic amounts of a potassium ferricyanide additive. Specific effects of these factors on the process of silicon etching are explained by comparing the corresponding activation energies. The possibility of using alkaline aqueous solutions of KOH with a potassium ferricyanide additive for fabrication of elements in microsystem technology devices is assessed.     

Dissolution of chitin in aqueous KOH

Our NMR experiments show that chitin can dissolve well in aqueous KOH through a freeze-thawing process, and the dissolution power of the alkali solvent systems is in the order of KOH > NaOH > LiOH aqueous solution, which is totally contrary to that of cellulose in the alkali aqueous solution (i.e., LiOH > NaOH ? KOH). In this work, we systematically study the dissolution process in KOH and KOH/urea aqueous solutions. Chitin has good solubility (solubility ~80 %) in 8.4–25 wt% KOH aqueous solution at ?30 °C. The role of urea also has been investigated: unlike aqueous chitin-NaOH solutions, urea indeed enhances the solubility of chitin in KOH aqueous solutions, but the increased degree becomes unobtrusive with decreasing temperature and increasing dissolution time; the DA decline curves of chitin-KOH and chitin-KOH/urea aqueous solutions are nearly overlapping, indicating that the effect of the urea on the degree of acetylation of chitin in KOH aqueous solutions is small, similar to the NaOH/urea solvent.     

Kinetics of oxidation of dioxanes by ozone in aqueous solutions

The kinetics of oxidation of dioxanes by ozone was investigated by a spectrophotometric method in the temperature interval of 281-311 K. The activation parameters of the reaction were determined.     

Kinetics of DC discharge-induced degradation of phenol in aqueous solutions

The influence of discharge parameters and phenol concentration on the kinetics of phenol degradation in an aqueous solution by the action of direct-current discharge with an electrolyte cathode has been studied. The degradation rate constants of phenol as a function of its initial concentration at different discharge parameters and volumes of the treated solution have been obtained. The energy efficiency of the degradation process has been determined, and the dependences of the rate constants on the concentration, the discharge current, and the volume of the solution have been explained.     

Kinetics of wetting and spreading by aqueous surfactant solutions

Interest in wetting dynamics processes has immensely increased during the past 10-15 years. In many industrial and medical applications, some strategies to control drop spreading on solid surfaces are being developed. One possibility is that a surfactant, a surface-active polymer, a polyelectrolyte or their mixture are added to a liquid (usually water). The main idea of the paper is to give an overview on some dynamic wetting and spreading phenomena in the presence of surfactants in the case of smooth or porous substrates, which can be either moderately or highly hydrophobic surfaces based on the literature data and the authors own investigations. Instability problems associated with spreading over dry or pre-wetted hydrophilic surfaces as well as over thin aqueous layers are briefly discussed. Toward a better understanding of the superspreading phenomenon, unusual wetting properties of trisiloxanes on hydrophobic surfaces are also discussed.     

Kinetics and mechanism of acid-catalyzed decomposition of triazenes in aqueous ethanolic solutions

The kinetics and nature of the end products of the acid decomposition of triazenes (R-N=N-NHR, where R is aryl, and R is aryl or alkyl) in aqueous ethanolic solutions of varying composition have been studied. A hydrolysis mechanism which includes protonation of the triazene molecule (R-N+H=NH-R), formation of an _N-transition stafte (R-N=N-N+H₂-R), and dissociation of this state has been proposed to explain the literature data and the opposite ionic effects observed in the present study. This mechanism explains the roles of the acid anion and the water molecule in the hydrolysis of triazenes. An analytical expression has been obtained from the hydrolysis constant which agrees with the experimental results.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 1, pp. 23–30, January–February, 1993.     

Kinetics of Ca2+ complexation with some carbohydrates in aqueous solutions

For solutions of four saccharides in water with alkaline-earth chlorides added ultrasonic attenuation spectra between 100 kHz and 2 GHz are reported and compared to those for carbohydrate solutions without salt. Calcium chloride does not alter the relaxation times in the spectra of D-glucose and D+-maltose solutions, reflecting the exocyclic hydroxymethyl group rotation, a saccharide-saccharide association, and, with the disaccharide, also motions of both rings of a molecule relative to one another. The spectra of D-xylose and D-fructose solutions are substantially changed by the salts. With both saccharides an additional term with relaxation time around some nanoseconds exists which is assigned to a rearrangement of a carbohydrate-cation complex. Other relaxation terms of these saccharide solutions are also subject to noticeable changes by the salt, indicating specific carbohydrate-cation interactions. The ultrasonic spectra show that such interactions may exist also with carbohydrates which do not display the particular hydroxyl group sequences that are considered to promote complexation with cations.