Quantum Chemical Study of Addition–Elimination Reactions of Dimethyl Carbonate with Methylamine

The mechanisms of noncatalytic and autocatalytic addition–elimination reactions of dimethyl carbonate with methylamine have been studied in terms of wB97XD/6-311++G(df,p), M06/6-311++G(df,p), and PBE0/6-311++G(df,p) quantum chemical methods, and thermodynamic and activation parameters of these reactions have been calculated. The rate-determining stage is the formation of tetrahedral carbon intermediate. The addition–elimination mechanism is preferred over the autocatalytic S_N2 mechanism determined by enhanced donor–acceptor and acid–base properties of amine complexes with alcohol associates in comparison to amines.     

Thiodiglycol-based oligomers

Sulfur-containing oligoethers were prepared by polycondensation of thiodiglycol in the presence of acid catalysts. These oligoethers are oligomers with terminal hydroxy groups, comprised of oxyalkyl sulfide units.     

Stability of Oligomeric α-Alkoxyhydroperoxides

The thermal decomposition of oligomeric -alkoxyhydroperoxides (I) is described by a first-order rate law and characterized by an activation energy equal to 19.7 kJ/mol. A chain mechanism and a rate law for this reaction are proposed. The effect of amine and phenolic stabilizers on decomposition is studied, the efficiency of phenolic stabilizers is examined, and the effective rate constant of the acid-catalyzed decomposition of compounds I is determined.     

Oligomerization of cyclic imines N-carboxamides by the action of anion type catalyst

Using methods of nuclear magnetic resonance, gel-permeation chromatography, and differential-scanning calorimetry, we showed that N-carboxamides were capable of polymerization. The polymerization mechanism of N-carboxamides in the presence of ?-caprolactam sodium salt was suggested.     

Heat exchange between phases and kinetics of condensation relaxation for different regimes of droplet growth

The mathematical model and numerical solution of the problem relevant to the heat exchange between a droplet and a vapor-gas medium are described for different regimes of the condensation droplet growth. The effect of the heat exchange between phases on the kinetics of the condensation relaxation after supersaturation is instantaneously generated in a vapor-gas mixture is studied based on the results obtained. Cesium-argon and ethane-helium mixtures are considered, with the droplet growth regime being free-molecular in the former case and varying from transient to continual in the latter case. The data obtained in terms of the general formulation of the problem and those resulting from the assumptions simplifying the behavior of droplet temperature are compared to determine the applicability domain of the aforementioned assumptions.     

Structure of the product of interaction of N-vinylcaprolactam with 3-chlorophenylisocyanate

The [2+2]-cycloaddition reaction of N-vinylcaprolactam with 3-chlorophenylcyanate yielding 1-(3-chlorophenyl)-4-[1H-perhydroazepinone-2]-azetidinone-2 is studied. The structure of the obtained compound is determined by single crystal XRD.     

Thermodynamic parameters of the thermal decomposition of dimethyl toluylenedicarbamates to toluylene diisocyanates

By B3LYP/6-311++G(df,p) quantum-chemical method complete thermodynamic characteristics (enthalpies, entropies, total Gibbs energies, equilibrium constants) were evaluated for separate stages of the thermal decomposition of dimethyl toluylene-2,4- and dimethyl toluylene-2,6-dicarbamates with the formation of 2,4- and 2,6-diisocyanates and methanol. The temperature ranges providing the equilibrium yield of 2,4- and 2,6-toluylene diisocyanates equal to 95?C99% were estimated. Principal possibility of obtaining practically pure 2,4- and 2,6-toluylene diisocyanates while decomposing the mixture of dimethyl toluylene-2,4- and -2,6-dicarbamates due to the regulation of temperature of the process was shown.     

Molding loose metal particles into briquettes with the use of short pulses of high density current

Theoretical estimates and experimental investigations were carried out on the process of molding a mixture of metal particles and a dielectric (air) into briquettes with the use of short pulses of high density current. Four groups of specimens were studied consisting of metal fragments and the dielectric in various proportions. In the experiments and the current and voltage oscillograms, the electrical resistance and the temperature of the specimens before and after passing the current were measured and their ultimate strength was determined. It has been found that the processes affecting the distribution of the current over the specimen cross section and the specimen inductance during the current pulse play an important role in molding briquettes of sufficient strength for transportation and processing.     

Effect of pH of a medium on the direction of reactions of isothiocyanates with amino acids

The interaction of isothiocyanates with amino acids may proceed to yield both low-molecular-mass products and polymer compounds. The structure of these compounds depends on the nature of isothiocyanate, and amino acid is strongly affected by the basicity of the medium.