Vol 57, No 3 (2016)

The enthalpy and activation energy of reactions involving attack by MeO₂^• and MeO₂^• on CH₂ groups of 2-butyl nitrite and 2-nitrosobutane have been calculated by quantum chemical methods. The abstraction of a hydrogen atom is accompanied, in the former case, by concerted N–O bond breaking and, in the latter case, by concerted C–N bond breaking, resulting in NO• formation. On the basis of the results obtained, an algorithm has been developed within the intersecting parabolas model for calculating the enthalpies, activation energies, and rate constants of these types of reactions involving alkyl, alkoxyl, aminyl, peroxyl, phenoxyl, thiyl, and hydroxyl radicals.

The specific features of the association of cobalt octahydroxyphthalocyanine in aqueous alkaline solutions have been investigated by electron spectroscopy. The kinetic parameters of the oxidation of n-propylmercaptan by the phthalocyanine complex of cobalt in the absence of oxygen have been determined. The association leads to a decrease in the activity of the complex and to changes in activation parameters.

The mechanism of the initial stage of the ozonolysis of a series of olefins and trans-1,3-butadoiene has been investigated by the B3LYP density functional theory (DFT) method, B2PLYP double hybrid method based on DFT and the MP2 approximation, and CCSD coupled cluster method. Two possible butadiene and olefin ozonolysis mechanisms are considered: concerted 1,3-cycloaddition, which yields a primary ozonide (Criegee mechanism) and stepwise ozone addition via a biradical transition state (DeMore mechanism). The geometries of the initial and transition states and the energies of the elementary steps of the reaction have been determined. The geometric structures of the stationary states determining the rate constant of the reaction have been completely optimized using the above methods and the aug-cc-pVDZ basis set. The rate constants for both reaction pathways have been calculated. For butadiene, the contribution from nonconcerted addition can reaches 25%. According to the MRMP2 method, the overall rate constant (which includes both reaction pathways) is 1778 L mol^–1 s^–1; according to B2PLYP, 1640 L mol^–1 s^–1; according to CCSD, 1424 L mol^–1 s^–1 (aug-cc-pVDZ basis set). These results are in good agreement with experimental data (k = 3 × 10³ L mol^–1 s^–1 and with earlier calculations. The data calculated for olefins are also in agreement with experimental data.

An efficient and simple oil bath method for rapid synthesis of graphene/BiOI as visible light active photocatalyst was described. The resultant graphene/BiOI composites were characterized by different techniques, including scanning electron microscopy, X-ray diffraction, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activity of the as-prepared graphene/BiOI composites for methyl orange degradation was also investigated under visible light irradiation. The results show that BiOI and graphene taken with a mass ratio of 100: 1 exhibited the highest photocatalytic efficiency, which is two times that of pure BiOI. Part of this effect results from higher specific surface area that provides an increased number of active sites. A relatively narrow band gap (2.08 eV) formed in the heterostructure can also contribute to this effect. A suggestion of the photocatalytic mechanism was also offered.

Nonwoven chitosan (CS) nanofiber mats were successfully prepared by the electrospinning of the mixture of CS and poly(ethylene oxide) (PEO) in acetic acid aqueous solution. The CS/PEO fiber mats were treated with glutaraldehyde aqueous solution to stabilize fibers in solution. The concentration of glutaraldehyde is important for incorporating swelling properties in the cross-linked CS/PEO fiber mats. The cross-linked CS/PEO fibers (CCS/PEO fibers) were then used as supports for palladium catalysts in the Mizoroki–Heck reaction. The results of the study demonstrated that the catalytic activities of Pd catalyst supported on CCS/PEO fiber (Pd-CCS/PEO fiber) were highly dependent on the concentration of glutaraldehyde in the cross-linking process. Density functional theory (DFT) calculations indicated that the Schiff bond formed between CS and glutaraldehyde could reduce the energy needed to form a chelate complex between the CCS/PEO fibers and palladium active species. This in turn could decrease the activation energy of the Mizoroki–Heck reactions which occur in the presence of the Pd-CCS/PEO fiber catalysts. The optimized Pd-CCS/PEO fiber catalyst was very efficient and stable in the Mizoroki–Heck reaction of aromatic iodides with olefins.

The change in the surface composition of a MoB catalyst in the epoxidation of 1-octene with tert-butyl hydroperoxide and the effects of the reactant concentrations and reaction products (tert-butanol and 1,2-epoxyoctane) on this process have been studied.

It has been demonstrated experimentally and theoretically that the essentially different inhibiting effects of fullerene C₆₀ on the initial stage of the polymerizations of styrene and methyl methacrylate (including complete hampering of styrene polymerization throughout a long induction period) are of common kinetic nature. The difference arises from the competition between C₆₀ and the monomer not for initiating radicals but for radicals originating from the monomer; that is, the difference stems from the competition between the chain propagation reactions and the termination reactions on fullerene molecules. As a consequence, the further development of the process is determined by the relative reactivities of the radicals toward C₆₀ and towards their parent monomers.

This work continues a series of our studies on the synthesis of nanostructured carbon (NSC) by the pyrolysis of H₂ + C₃–C₄ alkane mixtures on nickel and cobalt metal catalysts supported on chemically diverse inorganic materials (aluminosilicates, alumina, carbon) having different textural characteristics (mesoporous and macroporous supports) and shapes (granules, foamed materials, and honeycomb monoliths). Here, we consider Ni catalysts supported on granular mesoporous silica (SiO₂). It has been elucidated how the yield of synthesized carbon depends on the Ni/SiO₂ catalyst preparation method (homogeneous precipitation or impregnation) and on the composition of the impregnating solution, including the molar ratio of its components—nickel nitrate and urea. The morphology of catalytic NSC and Ni distribution in the silica granule have been investigated using a scanning electron microscope with an EDX analyzer. Carbon-containing composite supports (NSC/SiO₂) have been employed as adsorbents for immobilizing microbial lipase. The enzymatic activity and stability of the resulting biocatalysts have been estimated in transesterification reactions of vegetable (sunflower and linseed) oils involving methyl or ethyl acetate, esterification, and synthesis of capric acid–isoamyl alcohol esters in nonaqueous media.