Copolymers of vinyl chloride obtained by polymer-analogous reactions of polyvinyl chloride with sodium salts of heteroaromatic H-N acids

By a reaction of PVC with sodium salts of pyrazole and 3,5-dimethylpyrazole we obtained copolymers possessing paramagnetic properties with a concentration of paramagnetic centers 10¹⁷–10¹⁹ spin g^?1 and g-factor of 2.0024-2.0044.     

Formation of the cobalt hydrogenation catalysts at the action of lithium aluminum hydride and lithium tri(tert-butoxy)aluminohydride and their properties

The interaction of Co(acac)₂₍₃₎ with LiAlH4 or LiAlH(t-BuO)₃ was studied using NMR, UV, IR, ESR spectroscopy, electron microscopy, and volumometry. The basic stages of formation of cobalt catalysts for hydrogenation were suggested. The formation of the nanoparticles that are active in the hydrogenation process is shown to occur at a ratio of reagents 5 ?? Red/Co ?? 12. The nanoparticles are stabilized by an excess of LiAlH₄ or LiAlH(t-BuO)₃, as well as by the products of their catalytic decomposition under the action of cobalt in the reduced state. At the ratio LiAlH₄ / Co> 12 to obtain the particles active in catalysis their activation by a proton-donor compound is required.     

Coupled (localized+delocalized) electron spins dynamics in polymer phase of RbC60 fulleride

The transverse response (transverse dynamic susceptibility) of coupled localized (s) and delocalized (e) electron spins of a metal paramagnet as well as the longitudinal dynamic response of such a system (to be registered by a longitudinal coil) to the modulation of microwave power saturating electron spin resonance (ESR) are calculated. The ESR spectrum is analytically decomposed into two Lorentzians with normal resonance frequencies and decay rates of the coupled localized +delocalized electron spin system. In the case of relaxationally coupled s- and e-spins the longitudinal response is decomposed into two “relaxational” Lorentzians squared with amplitudes containing ESR lineshapes with above-mentioned shifted frequencies and linewidths as well as enhancement-suppression coefficients of magnetization evolution. These results are essential for the interpretation of experiments on longitudinal response in metal paramagnets, the latter being the source of important information on longitudinal electron relaxation; in particular, for extraction of information from longitudinal response experiments in the polymer phase of RbC₆₀ fullende, where the obtained results describe the observed form of the ESR spectrum and the main features of the longitudinal response.     

Electrochemical behavior of tantalum(V) oxide in chloride-fluoride melts

Electrochemical behavior of KCl-KF-Ta₂O₅ melts is studied by cyclic voltammetry. It is a Ta(V) oxyfluoride (KTaO₂F₂, K₃TaO₂F₄, or K₃TaOF₆), yielded by the Ta₂O₅-KF interaction in the melt, that presumably participates in the electrochemical process, rather than Ta₂O₅ proper. The Ta(V) oxyfluoride complex is reduced to tantalum metal at 973 K via three irreversible diffusion-controlled stages. The product of the electrokinetic transfer coefficient and the number of electrons participating in the third stage is determined. The Ta(V) reduction becomes one-staged at 1073 K. Tantalum-containing ternary systems with molybdenum, cobalt, or silicon are prepared by electrolyzing Ta₂O₅-containing melts.     

EPR and longitudinal response signals in spin systems consisting of localized (<Emphasis Type="Italic">s</Emphasis>=1/2) and delocalized spins

The spin system of many new promising materials, such as high-temperature superconductors, fullerenes, fullerides, or manganites with colossal magnetoresistance, consists of localized spins (s-spins of impurity paramagnetic centers) and delocalized spins (e-spins of charge carriers). The two sorts of spins are coupled by exchange interaction, which leads to coupled precession of the corresponding magnetizations. When the materials mentioned above are investigated by EPR methods, the measured longitudinal (T₁) and transverse (T₂) relaxation times provide the most valuable information. However, the presence of inhomogeneous broadening of the EPR of s-spins often makes it difficult to measure T₂, while small values of T₁ do not allow one to measure it by conventional methods. Atsarkin and colleagues [4, 7, 8] proposed a new version of the method for measuring T₁ by longitudinal response signals induced in a longitudinal spin coil (oriented along the constant magnetic field) under low-frequency modulation of the microwave power, which saturates the EPR, even though very weakly. Earlier, the results obtained in experiments on measuring the longitudinal response for samples containing interacting s-and e-spins were interpreted using formulas for an individual sort of spins. In this paper, the magnetization of s-and e-spins that precess under the condition of relaxational coupling is considered, which is characteristic, for example, of fullerides. The complete EPR susceptibility is represented in a form that makes it possible to determine the origin (from s-or e-spins) of two Lorentzians, each of which is characterized by one of the normal decay rates of two coupled oscillators (i.e., of precessing transverse magnetization components). The common EPR line analytically decomposed into those Lorentzians, and special factors take into account the influence of the other sort of spins on the amplitude of the signal generated by the sort under consideration. Similarly to the EPR absorption signals, the expressions for the longitudinal response are decomposed into parts originating from s-and e-spins, and each part is proportional to the form factor of one of the modes (s-or e-like). The qualitative comparison shows good agreement with experimental data in terms of EPR and longitudinal response in a fulleride.     

Free-radical cooligomerization of N-vinyl-4,5,6,7-tetrahydroindole with butyl vinyl ether

Oligo(N-vinyl-4,5,6,7-tetrahydroindole-co-butyl vinyl ethers) have been synthesized through free-radical cooligomerization with a yield of 84%. The copolymers are readily soluble in organic solvents (benzene, 1,4-dioxane, chloroform, and tetrahydrofuran), stable up to 380–400°C, and paramagnetic. (The concentration of paramagnetic centers is 10¹⁴ spin/g.) In addition, the copolymers exhibit the properties of organic semiconductors. (After being doped with iodine, σ = 1.1 × 10^?7 S/cm.) The analysis of the ¹H and ¹³C NMR spectra has shown that the oligomerization reaction is complicated by intramolecular cyclization involving carbon atoms located at the 2-position of pyrrole rings.     

Photochemical reactions of acyl iodides with aryl halides

Photochemical reactions of acyl iodides RC(O)I (R = Me, Ph) with aryl halides, fluoro-, chloro-, and bromobenzenes, 1,4-dibromobenzene, 2- and 3-bromotoluenes, and 4-bromo-1,2-dimethylbenzene, were studied. Acetyl iodide reacted with chloro- and bromobenzenes and 1,4-dibromobenzene according to the exchange pattern to give iodobenzene and 1,4-diiodobenzene, respectively. No halogen exchange was observed in the reactions of acetyl iodide with fluorobenzene and hexafluorobenzene. Benzoyl iodide failed to react with chloro- and brombenzene under UV irradiation but underwent polycondensation with formation of black nonfusible oligomers which were found to possess paramagnetic and semiconducting properties. Ultraviolet irradiation of a mixture of MeCOI with 2- or 3-bromotoluene, as well as with 4-bromo-1,2-dimethylbenzene, also led to the formation of polymeric products as a result of polycondensation of aryl iodides formed initially via replacement of bromine by iodine. Irradiation of benzoyl iodide in 2- or 3-bromotoluene involved recombination of benzoyl radicals to give benzil as the only product.     

A mechanistic study of arabinigalactan sulfation with potassium persulfate in dimethyl sulfoxide

The mechanism of polysaccharide arabinogalactan sulfation was studied. Potassium persulfate in dimethyl sulfoxide was used as a sulfating agent. Sulfation of the biopolymer proceeds via its reaction with the SO₃—DMSO complex, which is formed upon the reduction of the persulfate anion in DMSO.     

13C-13C spin-spin coupling constants in structural studies: XLIII. Stereochemical study on functionalized 3-iminopyrrolizines

Three 1-ethylsulfanyl-3-imino-3H-pyrrolizine-2-carboxamides were synthesized by intramolecular cyclization of substituted (2Z)-2-cyano-3-ethylsulfanyl-3-(1H-pyrrol-2-yl)prop-2-enamides. The products were assigned syn configuration at the C=N bond and preferential s-cis orientation of the carbamoyl group on the basis of the experimental ¹³C-¹³C coupling constants and high-level nonempirical quantum-chemical calculations.