Russian Chemical Bulletin最新文献

This review summarizes results of the research on the rare class of organophosphorus compounds, namely, mixed phosphonium-iodonium ylides, highlighting their structural features and modification of their key molecular sites. Particular attention was given to the mechanistic aspects of the main heterocyclization processes involving mixed phosphonium-iodonium ylides, with a focus on the influence of the substituent nature in key structural fragments on the reaction pathways.

The patterns of the formation of geopolymers based on naturally enriched kaolin (KR-1 brand, Eleninskoe deposit, Russia) were studied under conditions of its alkaline activation in a reaction medium (10 M NaOH and water glass) with different silicate modulus (SiO₂/Al₂O₃). The prepared samples were examined by X-ray phase diffraction, scanning electron microscopy, and low-temperature nitrogen adsorption/desorption. The mechanical strength of the samples for compression and bending was determined. When the silicate modulus ranges from 2.0 to 2.5, zeolite NaY crystallizes in the studied systems accompanied by a decrease in the strength of the samples (2–3 MPa for compression and 2.7 MPa for bending) and an increase in their specific surface area (170 m² g⁻¹). At SiO₂/Al₂O₃ ranging from 2.5 to 3.0, an X-ray amorphous phase of the geopolymer with high strength characteristics (compressive strength reaches 67 MPa, bending strength is 7.5 MPa) and a low specific surface area (30 m² g⁻¹) is formed. At higher values of the silicate modulus (3.0 < SiO₂/Al₂O₃ < 3.5), an X-ray amorphous phase consisting of a geopolymer and unreacted water glass is formed, while the compressive strength of the material decreases (25–40 MPa).

By the reaction of dibenzo[b,h][1,5]naphthyridine-7(5H)-ones with sodium borohydride in acetic acid, their N-ethyl dihydro derivatives were obtained. A study of their photophysical properties showed that these compounds are fluorophores emitting in the yellow-green region of the spectrum with a fluorescence quantum yield of up to 0.25 and a Stokes shift of up to 162 nm.

The first representatives of 1,2,4-oxadiazoles bearing the oxydiazene oxide moieties at positions 3 or 5 were synthesized and characterized.

The thermal sensitivity of a random copolymer of N-isopropylacrylamide with maleic acid (CPL) was studied at its constant concentration of 0.5 • 10⁻² g cm⁻³ in aqueous solutions containing NaCl at concentrations of 0, 0.15, and 0.5 mol L⁻¹ depending on temperature and pH. When heated, CPL solutions exhibited thermal sensitivity, which was manifested in the occurrence of phase separation. It was found that the pH sensitivity is observable in the acidic region: the phase separation temperature increased with increasing pH. The introduction of NaCl into solutions led to a decrease in the phase separation temperature. An analysis of the composition of scattering structures existing in aqueous solutions without and with NaCl additions far from the phase transition temperature and upon heating was carried out. In the region of phase separation, large aggregates are formed, the size of which decreases with increasing NaCl concentration.

The effect of medium polarity, varied by the addition of ethanol, on counterion condensation processes in aqueous solutions of chitosan aspartate (a weakly charged polyelectrolyte) was studied. It was determined that the dielectric permittivity, specific conductivity, and viscosity index of the polymer system decrease, while the pH increases with increasing ethanol content. This indicates the effects of counterion association with the polycation, leading to the formation of ion pairs and multiplet ionic structures; the addition of EtOH significantly accelerates the associative transformations on macrochains. The influence of the concentration of chitosan aspartate in the system and EtOH in the water-alcohol mixture on the size characteristics and surface charge of the nanoparticles formed during phase segregation of the polymer substance was revealed. A method for spray selective precipitation of a polyelectrolyte solution is proposed with the aim of accelerating the counterion association. It was determined that spherical-, ovoid-, or ellipsoid-shaped nano(micro)particles can be obtained by varying the nature of precipitating liquid (EtOH, BuⁿOH, PrⁱOH, or Me₂CO). The potential benefits of using ionomer nano(micro)particles in biomedical applications and in the field of agrobiotechnology are discussed.

Convenient syntheses of functionalized aminomethylene bisorganophosphorus acids and their derivatives have been developed. Trimethylsilyl esters of trivalent phosphorus acids react with iminium salts in the presence of effective catalysts, trimethylsilyl triflate or boron trifluoride etherate, to afford new functionalized aminomethylene bisorganophosphorus acids and their derivatives with P—C—P units. The resulting substances, organophosphorus analogs of amino carboxylic acids and natural pyrophosphates containing various functional groups are structural analogs of active plant growth regulators and can be of interest as biologically active substances and effective polydentate ligands.

Silanes and silatranes containing an 1-aza dienyne moiety, Ph—C≡C—CH=C(SR) C(H)=N—, were synthesized by the reaction of (3-aminopropyl)triethoxysilane and 1-(3-aminopropyl)silatrane with 2-en-4-ynals. Upon storage for 2–4 days at 25 °C in CHCl₃, these compounds cyclize to CCl₃-containing pyrroles. The structure and stereoisomeric composition of the products were confirmed by elemental analysis, IR and NMR spectroscopy, and mass spectrometry.

The mechanism of thermal solvation of the PtBr₆²⁻ complex in methanol and the photochemistry of PtBr₆²⁻ in methanol in the presence of free bromide ions were studied. It was established that thermal solvation of PtBr₆²⁻ in methanol is a two-stage process with an autocatalytic second stage, which gives rise to S-shaped kinetic curves displaying the changes in the UV absorption spectra of PtBr₆²⁻ solutions. A qualitative mechanism of the reaction is proposed. Steady-state photolysis and laser flash photolysis studies revealed that photoexcitation of PtBr₆²⁻ in methanol in the presence of free Br⁻ ions is accompanied by competing reactions, namely, photosolvation and two-electron photoreduction. The photoreduction is due to electron transfer from both solvent molecules and free bromide ions to the photoexcited complex to produce dihalide radical anions Br₂^•−. The reaction with the starting complex affording a pentavalent platinum intermediate contributes largely to the Br₂^•− decay. The values of the rate constant for this reaction in methanol and in water are discussed.