Vol 68, No 8 (2019)

The best examples of catalysts and catalytic systems for the oxidative functionalization of alkanes and mechanisms of their action are considered. The prospects for industrial application of homogeneous catalysis in the synthesis of key petrochemical products, diff erent oxygenated organic compounds based on natural and associated petroleum gases, are outlined. Special attention is given to transformations of methane.

Under conventional conditions of styrene oxide conversion catalyzed by perchloric acid in an alcohol solution (Bu^tOH-chlorobenzene (9 : 1 by vol.), 343 K), an iminium ylide absorption band (λ_max ≈ 460–470 nm) was recorded in the presence of pyridine trap, which corresponds to the adduct of pyridine and phenylmethylene. In the presence of oxygen, another intermediate product was detected, the absorption band of which (λ_max ≈ 400 nm) coincides with the corresponding carbonyl oxide absorption. A similar observation was made earlier for the acid-catalyzed conversion of styrene oxide in the presence of p-toluenesulfonic acid in alcohol and acetonitrile solutions. Thus, the obtained results confirm formation of active intermediate species of carbene nature in two epoxide-acid systems.

Various mechanisms of the primary act of gas-phase monomolecular thermal decomposition of nitrobenzene were studied theoretically. The following reactions were considered: radical decomposition with dissociation of the C-N bond, nitro-nitrite rearrangement to trans-phenyl nitrite and cis-phenyl nitrite, elimination of nitrous acid, as well as formation of 6(S)-7-oxa-8-azabicyclo[4.2.0]octa-1(8),2,4-triene 8-oxide were studied theoretically. Calculations were carried out for different temperatures using a number of density functional theory methods (B3LYP, wB97XD, CAM-B3LYP, MN12L, and PBE0) and basic sets (6-31G(d,p) and 6-31+G(2df,p)). The transition state of homolytic dissociation of the C-N bond was localized using the method of search for the structure corresponding to maximum value of the Gibbs free energy along the reaction coordinate. The structure thus found was used to evaluate the rate constants and the activation parameters at different temperatures. It was shown that not only radical decomposition, but also isomerization to trans-phenyl nitrite (at low temperatures) and cis-phenyl nitrite (at high temperatures) can contribute to the effective rate constant.

Efficient electrosynthesis of silver nanoparticles (AgNPs) in bulk solution of a two-phase water—isooctane system is carried out by electrolysis in an undivided cell in the presence of methylviologen (MV²⁺) used as a mediator. Silver nanoparticles are formed in the aqueous phase of the system as a result of the electroreduction of Ag⁺ ions generated in situ by dissolving the Ag anode at potentials of the redox couple MV²⁺/MV^·+. The obtained AgNPs are stabilized by an anionic surfactant, sodium dioctyl sulfosuccinate, and are distributed throughout both the aqueous and the organic phases. All the nanoparticles would transfer to the organic phase after the obtained solution was kept in the dark for 48 h. In addition to dissolution, the Ag anode undergoes dispersion during electrolysis, therefore the total current yield of the obtained AgNPs is 175%. According to electron microscopy, the formed AgNPs are polydisperse and their size ranges from 5 to 71 nm. A surface plasmon resonance of AgNPs in the solution obtained after electrolysis was observed in the region of 418–463 nm.

commo-Ferracarboranes and [8-{(nido-7″,8″-C₂B₉H₁₁-9″(11″)-)Ph₂PCH₂CH₂PPh₂}-commo-3,3′-Fe-{1,2-C₂H₉B₁₀}{1′2′-C₂B₉H₁₁}] were prepared as minor products in the metallation reaction of [K]⁺[nido-7,8-C₂B₉H₁₂]⁻ with the 14-electron iron complex [Ph₂P(CH₂)₂PPh₂]FeCl₂. The structures of the complexes were determined by single-crystal X-ray diffraction.

(Chloromethyl)silanes ClCH₂SiMe_n(OMe)_3-n (n = 0—2) react with methylamine at room temperature to give a mixture of secondary N-methyl-N-(silylmethyl)amines MeNHCH₂SiMe_n(OMe)_3-n and tertiary N-methy1-N, N-bis(silylmethyl)amines MeN[CH₂SiMe_n(OMe)_3-n]₂ (n = 0—2). The product ratio depends on the ratio of the starting reactants. At the methylamine : silane ratio of 5 : 1, the main products are tertiary amines, while the increase in the proportion of methylamine (methylamine : silane = 25 : 1) leads to predomination of the secondary amines.

A series of new electrochromic derivatives of 3-aryl-4,5-bis(pyridin-4-yl)isoxazole was synthesized. Their electrochemical characteristics were studied by cyclic voltammetry, and a low eff ect of the substituents in the isoxazole and pyridinium cycles on the positions of the oxidation and reduction peaks was shown. The electrochromic cells prepared on the basis of the synthesized compounds were reversibly colored into brown upon the application of a voltage of 1.5 V. The spectral properties of the synthesized compounds under the electric field application and their stability for cycling from 0 to 2 V were studied.

Anionic five-coordinate complexes with two bis-O,O’-chelating ligands bearing α-hydroxy acid moieties, dicyclohexylammonium salts \(\text{Cy}_{2}\text{NH}_{2}{^+}\{\text{PpnCH}_2\text{Si}[\text{OCR}_2\text{C}\text{(O)O]}_2\}^-\) (Cy is cyclohexyl, PpnCH₂ is 4-methyl-2,5-dioxopiperazin-1-ylmethyl, R = Me, Ph), were synthesized by esterification of alkoxysilane PpnCH₂Si(OMe)₃ with α-hydroxy acids (dimethyl- and diphenylgylcolic acids) in the presence of dicyclohexylamine. The five-coordinated state of the silicon atom in the resulting compounds in solution was confirmed by ²⁹Si NMR spectroscopy. According to the X-ray diffraction data, the synthesized compounds contain the SiCO₄ coordination unit.

The influence of the structure of high-molecular-weight alkoxyamines (obtained in situ from C-phenyl-N-tert-butylnitrone and 2-(benzylideneamino)-2-methyl-1-phenylpropanol-1-N-oxide) and their low-molecular-weight analogs on styrene polymerization in the temperature range 70—110 ° was analyzed. The controlled synthesis of polystyrene in the presence of low-molecular-weight alkoxyamines was revealed to occur most efficiently at 110 °. The use of high-molecular-weight alkoxyamines makes it possible to perform the controlled process under lower-temperature conditions (70—90 °), when the constant polymerization rate and linear increase in the molecular weight with conversion are observed, and the synthesis of polymers with fairly low polydispersity (M_w/M_n ~ 1.26) is also possible. The quantum chemical calculations showed that the energy of the C-ON bond in alkoxyamines is determined by the length of the chains at the nitroxide fragment rather than the structure of the substituents. It is found that the equilibrium dissociation constants of high-molecular-weight alkoxyamines are caused by both the structure of the nitroxide fragment and molecular weights.

Organic-inorganic composites filled with nanoscale graphene and tungsten disulfide particles using thermoelastoplastic multiblock co-poly(urethane-imide)s as polymer matrices were obtained. The matrix polymers were the products of the polycondensation of 1,3-bis-(3′,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(aminophenoxy)diphenyl sulfone, and two aliphatic polyesters terminated by 2,4-toluene diisocyanate, namely, polypropylene glycol (M_n = 2300) and poly(ethylene adipate) (M_n = 2700). The weight fraction of aromatic segments in samples of co-poly(urethane-imide)s differed by a factor of two. Obtained composites were investigated by TGA, DSC, and DMA methods.

A new pharmacologically active nanostructured silicon—zinc—boron-containing glycerohydrogel was synthesized by the sol—gel method using silicon, zinc, and boron glycerolates as biocompatible precursors. The hydrogel composition and structural features were investigated by transmission electron microscopy, powder X-ray diffraction, IR spectroscopy, atomic emission spectrometry, and elemental analysis; a structural model was proposed. It was found that the 3D framework of the gel is formed by the products of hydrolysis and subsequent (co)condensation of silicon- and boron-containing precursors. Meanwhile, the major part of zinc monoglycerolate does not undergo hydrolytic transformations during gelation, being present in the 3D framework cells as amorphous nano-sized particles. The dispersion medium of the gel is an aqueous glycerol solution of silicon and boron glycerolates, products of their hydrolytic transformations, and water-soluble products of hydrolytic transformations of zinc monoglycerolate. The silicon—zinc—boron gel is nontoxic and possesses wound-healing and antimicrobial activities; it can be considered as a nanostructured dispersed system promising for biomedical applications, which is prepared in a simple and cost-effective way without using catalysts or toxic organic solvents.