Lewis acid-catalyzed conjugate addition-cyclization reactions of ethenetricarboxylates with substituted propargyl alcohols: stereoselectivity in the efficient one-pot synthesis of methylenetetrahydrofurans

Oxygen-containing heterocyclic systems are important structures in organic chemistry because of their presence in many biologically active compounds. In this work, a Lewis acid-catalyzed cyclization of ethenetricarboxylate derivatives 1 with substituted propargyl alcohols to give methylenetetrahydrofurans was investigated. Reaction of 1 and gamma-silicon-substituted propargyl alcohols 4 with ZnBr2 at 80-110 degrees C led to (Z)-silicon-substituted products stereoselectively. Reaction of 1 and gamma-ester-substituted propargyl alcohol 7 in the presence of various Lewis acids gave ester-substituted methylenetetrahydrofurans stereoselectively. Interesting Lewis acid dependency on stereoselectivity for the reaction of 7 was found. Reaction of alpha-substituted propargyl alcohols also gave cyclized products.     

Zinc- and indium-promoted conjugate addition-cyclization reactions of ethenetricarboxylates with propargylamines and alcohol: novel methylenepyrrolidine and methylenetetrahydrofuran syntheses

A new zinc- and indium-promoted conjugate addition-cyclization reaction to afford nitrogen- and oxygen-containing five-membered heterocycles has been developed. Reaction of ethenetricarboxylates with propargylamines (1 equiv) in the presence of ZnBr2 or InBr3 afforded methylenepyrrolidines in high yields. The stoichiometric use of ZnBr2 or InBr3 at room temperature and the catalytic use of InBr3-Et3N at 80 degrees C were effective. Reaction of ethenetricarboxylates with propargyl alcohol in the presence of ZnBr2 or InBr3 afforded methylenetetrahydrofurans.     

Efficient synthesis of methylenetetrahydrofurans and methylenepyrrolidines by formal [3+2] cycloadditions of propargyl substrates

Recent developments concerning the synthesis of methylenetetrahydrofurans and methylenepyrrolidines by one-pot formal [3+2] cycloadditions involving propargylic (and allylic) alcohols and amines with electrophilic alkenes are described. The synthetic methods provide powerful tools to prepare highly functionalized oxygen- and nitrogen-containing five-membered ring systems. The reactions can be effectively promoted by base, base/transition metals, and Lewis acids, depending on the substrates.     

Reaction of 3-formyl-2-methoxy-1,6-dioxaspiro[4.4]nonanes with 3-amino-1,2,4-triazole: synthesis of 2-(1,2,4-triazolo[1,5-a]pyrimid-6-yl)methylenetetrahydrofurans

The reaction of 3-formyl-2-methoxy-1,6-dioxaspiro[4.4]nonanes with 3-amino-1,2,4-triazole gives 2-(1,2,4-triazolo[1,5-a]pyrimid-6-yl)methylenetetrahydrofurans in 51–65% yields.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2004–2005, November, 1993.     

Correction of pH of diluted solutions of electrolytes by electrodialysis with bipolar membranes

The current efficiencies of the water dissociation water and the voltage-current characteristics of the bipolar (asymmetric bipolar) membranes were measured in a two-chamber electrochemical cell. The cell was formed of an MB-3 bipolar membrane or an asymmetric bipolar membrane, which is an MA-40 heterogeneous membrane with a thin surface layer in the form of a cation-selective homogeneous film and MA-40 and MA-41 heterogeneous monopolar membranes. The dissociation of water on MA-40 in 0.01 M sodium chloride decreased the current efficiency of the acid and alkali both in the channel with a bipolar membrane and in the channel with an asymmetric bipolar membrane. The effective ion transport numbers across MA-40 and MA-41 at different pH values were determined. The water dissociation rate on MA-40 decreased at pH > 9.5. A kinetic model of the electrodialysis of a dilute solution of sodium chloride in a two-chamber unit cell with a bipolar and anionite membranes was suggested.     

A study of the long-term strength of repair bandages made of composite rings of unidirectional structure

The interference stress relaxation in a composite repair bandage formed on a cylindrical metal surface was studied. The creep of a repair ring bandage under the action of interference stresses was evaluated. The results of the calculation of the creep and the interference stress relaxation of a composite ring on a sample made of a segment of a metal pipe in time are presented.     

C60笼内内陷粒子的运动

研究C60笼内内陷粒子的量力力学运动, 导出运动能量与波函数, 以内陷CO分子为例做了计算, 解释了分子对微波的吸收现象。     

Simulation of the flow of polymer blends in convergent channels

The method for the simulation of various cases of collisions between spherical solid particles in suspensions or emulsions (for example, in mixtures of polymers) moving in convergent flows is proposed. These flows arise in many technological schemes for the processing of polymers. The derived formulas make it possible to relate interparticle distances with the dimensions of particles and their volume fraction. The effect of the distribution of particles with respect to their dimensions and distances between them is considered. The flow lines are proposed to be described by two functions: (i) a parabolic dependence for a reservoir and (ii) a logarithmic dependence at a capillary inlet. The height of the conjugation of the above dependences appears to be similar for both flow lines. Under similar conditions, the number of collisions between particles and their rate dramatically increase after passage from a reservoir to a capillary as well as with a decrease in the radius of the particles (at a constant volume fraction). The experiment on microimaging of the frozen emulsion of PMMA in PS at different regions of convergent flow shows a fair qualitative correlation between experimental and calculated data.     

Study of the mechanism of the photoisomerization and photooxidation of bilirubin using a model for the phototherapy of hyperbilirubinemia

Liquid chromatography was employed for a study of photochemical degradation of bilirubin in the complex with human albumin, using a model system in the presence of riboflavin. The concentrations of bilirubin, the photoisomers and biliverdin were monitored. The reaction mechanism was verified using a quantified mathematical model and was represented by a reaction scheme. Photoisomerization is the initial process, followed by photooxidation to degradation products of the tetrapyrrole skeleton, with formation of biliverdin as an intermediate. The blood of newborns that were irradiated for treatment of hyperbilirubinemia was studied for the sake of comparison. The effect of some biochemically important substances was followed, in view of possible inhibition of the processes. The experimental results demonstrate that riboflavin acts as a catalyst, even at the concentrations typical for its occurrence in blood. The results are discussed from the point of view of the mechanism of bilirubin degradation during phototherapy.     

Effect of electron donors on polymerization of propylene in the presence of titanium-magnesium catalysts

The effect of internal and external electron donors on the polymerization of propylene in a liquid monomer or a hydrocarbon diluent (hexane) in the presence of a titanium-magnesium nanocatalyst activated with an organoaluminum compound (triethylaluminum, triisobutylaluminum) and the properties of the resulting PP are studied. The polymerization of propylene in the absence of internal and external donors yields atactic PP, whereas, in the presence of a catalyst containing an aryl internal donor, isotactic PP is formed. The activity and stereospecificity of the catalytic system substantially depends on the method of electron-donor introduction. The thermal treatment of the catalyst with an electron donor affects its activity and stereospecificity.     

Study of the electrochemical reduction of dioxygen in acetonitrile in the presence of weak acids

The electrochemical reduction of dioxygen has been studied in acetonitrile at glassy-carbon electrodes. The initial step is the reversible one-electron reduction to form superoxide. In the presence of hydrogen-bond donors (water, methanol, 2-propanol), the superoxide forms a complex with the donor resulting in a positive shift in the potential that can be analyzed to obtain formation constants for these complexes. Stronger acids result in protonation of the superoxide followed by reduction to produce HO2-. In the absence of hydrogen-bond donors, the reduction of superoxide occurs at very negative potentials, and this second reduction peak is very much drawn-out along the potential axis, indicating a small value of the transfer coefficient, alpha. The addition of hydrogen-bond donors, HA, brings about a positive shift in this peak, without a noticeable change in shape. The reaction occurring at the second peak is a concerted proton and electron transfer (CPET) in which the electron is transferred to superoxide and a proton is transferred from HA to the superoxide, forming HO2- and A- in a concerted process. An estimation of the standard potential for this reaction shows that the second reduction always occurs at a high driving force, which explains the small value of alpha that is observed. Consistent with a CPET, a kinetic isotope effect, HA versus DA, was detected for the three hydrogen-bond donors. The increasing positive shift of the second peak with increasing water concentration has been interpreted as being a consequence of the change in the formal potential, as water is both a reactant in the process and a participant through the hydrogen-bond stabilization of the anions.     

Drawing of single-crystal mats of linear polyethylene

Drawing of single-crystal mats of linear polyethylene has been investigated. Drawing is possible at temperatures higher than about 90°C. The drawing is accompanied by distinct necking, with a large decrease in the thickness of the mat and a very high maximum draw ratio, sometimes over 30. The maximum draw ratio is approximately proportional to the thickness of the lamellae. This behavior strongly suggests the unfolding of chains during drawing. A change of orientation of crystal axes occurs before necking without change of lamellar orientation. The a axis orients in the drawing direction; the b axis orients perpendicular to the direction of drawing; and the chain axis tilts away from the thickness direction of the mat. The structure of films drawn from mats is characterized by a distinct double orientation of crystals. This biaxial orientation in the drawn films has a high degree of correlation with the orientation of crystal axes observed before necking, and suggests that necking takes place in such a way that the chain tilts gradually about the b axis and ultimately unfolds. The postulate of formation of transitory two-dimensional crystals in necking seems useful in explaining the double orientation in the drawn film. The orientation behavior of crystal axes observed before necking is not always similar to that observed in the deformation of a single crystal. The difference is thought to be due to the effect of forces induced by drawing that act in the direction normal to the lamellae within a mat.     

Effects of reprocessing of oxobiodegradable and non-degradable polyethylene on the durability of recycled materials

The use of plastics is steadily increasing in our daily lives, and plastics are the fastest-growing component of the waste stream. Although the efficiency of plastic recycling is increasing, plastics are often seen as a permanent environmental problem because of littering. The introduction of oxobiodegradable polyolefins (OBDs), containing prodegradant additives, is considered to be a way to reduce this problem by enabling the fast degradation of plastics in the environment. The prodegradant additives form radicals that attack the polymer chains, causing chain scissions and generation of low molecular mass oxidation products that can be consumed by microorganisms. There is, however, a concern that the prodegradant additives will present a problem if OBD materials end up in the conventional plastic recycling streams. The present study therefore highlights the impact of mixing OBD materials with conventional polyolefins to evaluate the impact on the remaining service life of the recyclates.The study included the use of two different OBDs, mixed in different proportions (10% and 20%) in a conventional polyethylene. The remaining service life of the mixtures was evaluated by monitoring the reduction in tensile strain after exposure to thermo-oxidative degradation at 70 °C, compared with a pure polyethylene. The impact of stabilizer content in the mixtures was also evaluated together with the effect of mixing partially degraded OBDs into the recyclate.The results show that the incorporation of minor fractions of OBD materials in the existing recycling streams will not create a severe effect on the service life of the recyclates as long as the polymer mixture possesses a reasonable degree of stabilization.     

Heats of Mixing of Mixed Solvent Solutions of Alkali Metal Salts of Substituted Benzenesulfonic Acids

The enthalpy change on mixing solutions of methyl-substituted benzenesulfonic acids and their salts, with salts having a common cation or anion, at constant ionic strength in mixtures of 1,4-dioxane with water, were measured at 25°C. The heat effects of mixing solutions having a common anion increase almost linearly with the reciprocal value of the dielectric constant of the solvent. The heat effects of mixing solutions having a common cation, which are all negative in water-rich solutions, become endothermic after a certain value of the dielectric constant is passed. The results are discussed in terms of the solute-solvent structural properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature and concentration dependence of the activity of quinones of presumed inhibiting action

The inhibiting properties of a series of organic compounds with a quinonoid structure have been electrochemically studied. The effect of the area and the structure of the organic molecule on the activity of the quinones has been followed. The compounds studied inhibit mild steel's corrosion in model cooling water and prove to be inhibitors of a cathodic type. The degree of corrosion inhibition is a function of the temperature, the concentration and the nature of the substance. The protective effect of the quinones is explained with their adsorption on the corroding surface. The adsorption itself is facilitated by the presence of π-electron systems and conjugated bonds in the molecules as well as by the increase of the molecule's size. Some differences in the behaviour of the p- and o-compounds studied are observed.     

Regularities of binary condensation of vapors when one of them is undersaturated

Simple analytical expressions are derived for the stationary concentration of a binary solution in a markedly supercritical droplet growing exothermically in diffusion or free-molecular regimes in mixed vapors when one of condensing vapors is supersaturated and present in a small amount and another vapor is slightly undersaturated and present in a large amount. The condensation of sulfuric acid and water vapors on a droplet under the conditions of Earth atmosphere is considered as an example of practical importance. Under isothermic conditions, analytical expressions are obtained for the time of establishing a power law for variations in a droplet radius with time under the diffusion and free-molecular regimes of the droplet growth. The power laws are derived in an explicit form under these regimes, which describe the rapid establishment of a stationary concentration of a solution in a growing droplet.     

Chemical methods of dispergation of metallic phases

The results of a cycle of works on the chemical dispergation of intermetallic compounds and alloys were summarized and analyzed. The chemical dispergation occurs in a hydrogen or ammonia atmosphere in the temperature range from 20 to 500 °C and a pressure of 0.5–2.0 MPa. The phase transformations were studied. The conditions suitable for the production of polymetallic phase powders of various degrees of dispersity were determined.     

Chemical modification of the surface of a sulfonated membrane by formation of a sulfonamide bond

This paper describes a novel approach for the surface modification of a cation-exchange membrane, bearing sulfonate groups, by a cationic layer. The modification procedure involved the chlorosulfonation of the sulfonate groups of the base membrane with thionyl chloride, followed by a reaction with a diamine to yield a sulfonamide bond and a terminal amine. The latter could be quaternized by reaction with methyl iodide or protonated by soaking in acidic media. The membranes were characterized in detail by attenuated total reflectance Fourier transform infrared and X-ray photoelectron spectroscopies as well as elemental analysis to confirm that the above reactions occurred. The selectivity of these membranes toward the electrochemically assisted transport of protons versus Zn2+ metallic cations was determined during an electrodialysis in a two-compartment electrochemical cell. The data indicate a significant decrease of the transport of the metallic cations following modification of the membrane with the cationic layer. The later allows for the transport of protons from the catholyte to the anolyte compartment with much improved selectivity since the divalent cations are excluded from the membrane due to the electrostatic barrier of the cationic layer.     

Enhancement of the reducing properties of metallic mercury in presence of complex forming ions

The reducing properties of metallic mercury in solutions containing ions forming precipitates or complexes with mercuric or mercurous ions have been studied.The reducing power of mercury in the presence of thiocyanate is greatly enhanced, and it is similar to that in the presence of hydrochloric acid. The effects of the thiocyanate and ferric concentrations have been examined. To reduce a 0.01 M solution of ferric ion without forming a precipitate of mercurous thiocyanate, a concentration of thiocyanate of at least 0.05 M is required. The action of mercurythiocyanate system on some oxidising substances has been studied. The most important reaction is the reduction of ferric ions. The method has been applied to the determination of iron on macro and semimicroscale and good results have been obtained.The reducing power of metallic mercury in the presence of cyanide has also been examined. In general it acts as a strong reducer in alkaline medium. Atmospheric oxygen is reduced partially to water and hydrogen peroxide. Ferricyanide is reduced quantitatively to ferrocyanide. The action of metallic mercury in the presence of cyanide on other oxidising substances has also been examined.     

Optimization of parameters of a system for continuous activation analysis of liquids

Mathematical considerations on the optimization of the flow and mechanical parameters of a system for continuous analysis of liquids are presented. The system in question contains a pump, an activation vessel placed in the vicinity of a neutron generator target, a pipeline and a vessel for the measurement of the induced activity. The following parameters of the system were taken into consideration: volumes of the activation and measurement vessels, position of the activation vessel with respect to the neutron generator target, shape of the activation vessel, and flow rate of the pumped fluid. The system is adapted for continuous and interrupted mode of operation of the neutron generator. The results of the theoretical considerations were verified in practice with the use of the above system and the reaction¹⁶O (n, p)¹⁶N. The agreement of theory and experiment was proved.