Some regularities of chlorosilanes etherification

The influence of reagents, solvent polarity, and temperature on the etherification of chlorosilanes ClCH₂SiCl₃, VinSiCl₃, PrSiCl₃, and Ph₃SiCl with ethanol was studied. Influence of reaction temperature on the ratio of the synthesized alkoxysilane and related side-product siloxane is revealed. Use of excess alcohol is shown to increase the content of siloxane. Introduction of FeCl₃ does not affect the synthesis. Solvents are shown to influence the reaction rate: the rate constant increases with increasing ? parameter of the solvent. The rate constant of etherification of chlorosilanes with ethanol falls in the series: ClCH₂SiCl₃ > VinSiCl₃ > PrSiCl₃. An explanation of the regularities is suggested.     

Single bubble growth during water electrolysis under microgravity

Single bubble evolution on a micro-electrode (Pt, φ = 0.2 mm) was observed in 0.36 M KOH solution under terrestrial (1-G) and microgravity (μ-G) environments. The bubble size during galvanostatic electrolysis (j = −2.6 × 10³ A m⁻²) was measured by CCD images, which allowed us to calculate the gas evolution efficiency, f_G, by comparison with the consumed charge. The efficiency under μ-G increased until 1 s after starting electrolysis and then reached constant value (f_G = 0.85), while, under 1-G, it showed a lower value and remarkably decreased 2 s after the beginning of the measurement. Such differences between μ-G and 1-G were explained by the mass transfer rate of the dissolved gas. Bubble-induced microconvection dominated the mass transfer under μ-G without any buoyancy force, on the other hand, the single-phase free convection (microscopic natural convection) influenced the bubble growth under 1-G.     

Some consequences of thermodynamic feasibility for chemical reaction networks

Power law dynamics is used to describe the stability behavior in metabolic networks such as chemical reaction networks (CRN’s). These systems allow multiple steady states within a single stoichiometric class. On the other side thermodynamic constraints such as loop-less fluxes represented by the Gorban theorem of alternatives applied to these networks reveal considerable restrictions to their dynamics by eliminating multistability of CRN’s in general. Thermodynamic feasible CRN’s are contained in the class of injective CRN’s. We can give an alternative proof of the detailed balance with Brewer’s Fixed Point Theorem. Furthermore we can derive by the loop-less principle the extended detailed balance. This paper establishes a link between recent research in CRN theory and thermodynamic basics. The result has also consequences for the picture of multiple steady states as assumed for cell differentiation and regulation. CRN’s provide from their perspective not enough means to maintain multistability without regulation or external control.

     

Kinetic regularities in reaction of methanethiol with methanol

The kinetics of the reaction of methanethiol with methanol has been studied under gradientless conditions. A mechanism is postulated according to which, under the effect of methanol the surface is rapidly methoxylated and then CH₃O groups react with methanethiol or methanol to produce dimethyl sulfide and dimethyl ether. The kinetic equations obtained describe fairly well the reaction on the inhomogeneous catalyst surface.

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. , CH₃O , . , .

     

Self-propelled motion of a fluid droplet under chemical reaction

We study self-propelled dynamics of a droplet due to a Marangoni effect and chemical reactions in a binary fluid with a dilute third component of chemical product which affects the interfacial energy of a droplet. The equation for the migration velocity of the center of mass of a droplet is derived in the limit of an infinitesimally thin interface. We found that there is a bifurcation from a motionless state to a propagating state of droplet by changing the strength of the Marangoni effect.     

The regularities of polyurethane foam chemical degradation with thiodiglycol

A pattern was studied of the process of chemical degradation of elastic polyurethane foam under the action of thiodiglycol and its mixture with oxypropylated oligopolyol. It was established that in the systems simulating the process of polyurethane degradation the introduction of sulfur atoms in the hydrocarbon chain of glycol reduced its activity in the reaction with the urethane and reduced the thermodynamic stability of the urethanes formed. On the basis of recycled sulfur-containing oligoether-urethane a polyurethane sealant resistant against oil and petrol was obtained.     

Kinetic regularities of the reaction of dimethyldioxirane with cyclic acetals

Kinetic regularities of the reactions of dimethyldioxirane (1) with 1,3-dioxolane, 2-propyl-1,3-dioxolane, 2-i-propyl-1,3-dioxolane, 2-phenyl-1,3-dioxolane, and 2,2-pentame-thylene-1,3-dioxolane (RH) in acetone have been studied spectrophotometrically in the temperature range from 15 to 48°C. The reaction rate d[1] /dt=k[1]·[RH] does not depend on the oxygen concentration in the reaction mixture. The activation parameters in the reaction with 1,3-dioxolane have been determined: lgk=(5.13±0.6)−(10.07±0.82)/Q, where Q=2,303 RT kcal/mol.     

Some regularities of of laser pyrolysis of polyphenylene- and polyamidocarboranes

Data of laser pyrolysis of carborane-containing polymers are presented in this paper. The main directions of chemical transformations of polyphenylene- and polyamidocarboranes by laser pyrolysis are established. It is proposed to make use of IR laser irradiation for synthesis of secondary polymer structures with specific properties.     

Some regularities of interface formation in solid-contact potentiometric surfactant-selective sensors

The regularities of interface formation in solid-contact potentiometric sensors for surfactants of different types were found. It was shown that the nature of electronic conductors and ionophores, the state of ionophores in aqueous and organic media, and the composition and ratios of membrane components had the decisive effect on the electroanalytical properties of these sensors.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 316–322.Original Russian Text Copyright © 2005 by Kulapin, Chernova, Kulapina.     

Kinetics of cluster aggregation in competition with a chemical growth reaction

The kinetics of abundances and the distribution in size of clusters at a given time are obtained by numerical simulation in the case where a chemical growth competes with the coalescence of clusters originating from isolated monomers. To take into account the size dependence of cluster reactivity, it is assumed that the chemical reaction occurs only beyond a critical valuen _c . The kinetics of the total cluster concentration are unchanged by addition of the reactant but the size distribution is suddenly perturbed for sizes beyondn _c . The decay of the reactant, the kinetics of a cluster of a given nuclearity and the distribution of sizes at a given time depend on the relative values of the rates of coalescence and of growth due to the reactant. It is shown how the initial conditions control the kinetics and the amplitude or the time of the maximum cluster abundance. The case of an attack by a chemical reactant on clusters, restricted to low values ofn, is also considered. The concentration kinetics (for all size clusters) display much lower amplitudes than for pure coalescence case. No parity effects are observed.     

Fundamental physicochemical regularities of the chemical vapor deposition of nickel oxide layers

Physicochemical regularities of the chemical vapor deposition (CVD) of nickel oxide layers in the (EtCp)₂Ni–O₃–O₂–Ar reaction system at a reduced pressure were studied. Dependences of growth rate of NiO layers on deposition temperature, linear gas flow velocity, and roughness were derived. A mass-spectrometric study of the composition of the reaction gas phases formed in these systems provided evidence about the fundamental physicochemical regularities of the CVD process, which is important for solving applied problems associated with the development of technological equipment and industrial technology for deposition of NiO layers.     

Photoassisted reaction of chemical warfare agent VX droplets under UV light irradiation

A photoassisted reaction of O-ethyl S-[2-(diisopropylamino) ethyl] methylphosphonothioate (VX) droplets in air was carried out. The experimental results indicated that VX droplets could be easily and chemically transformed into other compounds under irradiation of a germicidal lamp over sufficient time. Quantum chemical calculation results demonstrated that UV light less than 278 nm wavelength could possibly initiate photoreaction of VX and that both P-S and P=O bonds in the VX molecule were lengthened. The identification of reaction products by gas and liquid chromatography mass spectroscopy and NMR revealed that the VX molecule in air under UV light irradiation could undergo isomerization of S-esters to O-esters, cleavage of P-S, S-C, and C-N bonds, and ozonation of tertiary amines.     

Gas-phase halo alkylation of C60-fullerene by ion-molecule reaction under chemical ionization

Chemical ionization (CI) mass spectra of C₆₀-fullerene were studied using 1,2-dibromoethane and 1,2-dichloroethane as CI reagents. The ion-molecule reaction between C₆₀ and C₂H₄X⁺ (X=Br and Cl) leads to the formation of (C₆₀+C₂H₄X)⁺ adducts. The collision-induced dissociation of the adducts reveal gas phase halo alkylation of C₆₀-fullerence involving the C?C bond formation.     

The reaction between silylene and ammonia: Some gas-phase kinetic and quantum chemical studies

Time-resolved kinetic studies of the reaction of silylene, SiH₂, generated by 193 nm laser flash photolysis of silacyclopent-3-ene, have been carried out in the presence of ammonia, NH₃. Second order kinetics were observed. The reaction was studied in the gas phase at 10 Torr total pressure in SF₆ bath gas at each of the three temperatures, 299, 340 and 400 K. The second order rate constants (laser pulse energy of 60 mJ +) fitted the Arrhenius equation:noindent Experiments at other pressures showed that these rate constants were unaffected by pressure in the range 10–100 Torr, but showed small decreases in value at 3 and 1 Torr. There was also a weak intensity dependence, with rate constants decreasing at laser pulse energies of 30 mJ +. Ab initio calculations at the G3 level of theory, show that SiH₂+NH₃ should form an initial adduct (donor-acceptor complex), but that energy barriers are too great for further reaction of the adduct. This implies that SiH₂+NH₃ should be a pressure dependent association reaction. The experimental data are inconsistent with this and we conclude that SiH₂ decays are better explained by reaction of SiH₂ with the amino radical, NH₂, formed by photodissociation of NH₃ at 193 nm. The mechanism of this previously unstudied reaction is discussed.