Reaction of 2,4,6-tri-tert-butylphenoxyl with oxygen in the presence of metal compounds

Conclusions A dependence was found for the isomer composition of the quinolide peroxides formed upon the oxidation of 2,4,6-tri-tert-butylphenol on the coordination capacity of the metal compounds used for the oxidation and the medium. Kinetic measurements showed that the reaction of 2,4,6-tri-tert-butylphenoxyl with oxygen is accelerated in the presence of manganese diacetate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 706–709, March, 1986.     

Reaction of <Emphasis Type="Italic">N</Emphasis>-alkyl(aryl)aminocarbonyl-1,4-benzoquinone monoimines with alcohols

Reactions of N-alkyl(aryl)aminocarbonyl-3,5-dimethyl-1,4-benzoquinone monoimines with alcohols led to the formation of products of 1,2-addition, quinolide compounds. They are the final products in reactions with alkyl derivatives, but in event of aryl derivatives they underwent cyclization with the subsequent elimination of the alcohol molecule to provide 4,7a-dimethyl-1-aryl-7,7a-dihydro-1H-benzimidazole-2,6-diones.     

Activated sterically strained C=N bond in N-substituted p-quinone mono- and diimines: XIII. Reactions of N-alkyl(aryl, trifluoromethyl)sulfonyl-, N-arylsulfinyl- and N-arylsulfanyl-1,4-benzoquinone monoimines with alcohols

Steric strains arising between the substituent atoms at nitrogen (S, SO, or SO₂) and the methyl group located in positions 3 or 5 of the quinoid ring of 3,5-dimethyl-substituted quinone monoimines lead to the increased angle C=N-S. As a result in these quinone monoimines the reactions of 1,2-addition become thermodynamically possible since the formation of quinolide structures with the sp³-hybridized carbon atom removes the steric strain.     

Activated Sterically Strained C=N Bond in N-Substituted <Emphasis Type="Italic">p</Emphasis>-Quinone Mono- and Diimines: XVI. Structural Characteristics

N-Substituted 1,4-quinone imines with an activated sterically hindered C=N bond characteristically react with nucleophiles via 1,2-addition to that bond with formation of quinolide compounds. The C=N–X bond angle in these quinone imines ranges from 130 to 145°, the upper limit being defined by their thermodynamic stability. According to the X-ray diffraction data, the real C=N–X can be smaller than 130°C, but in this case considerable deviations of the nitrogen atom and substituent attached thereto from the mean-square plane of the quinoid ring and twisting of the C=N bond are observed.     

Effect of Quinones on the Cobalt(II) Acetate–Catalyzed Mild Oxidation of Cyclohexane with Hydrogen Peroxide in Acetic Acid

The effects of free-radical reaction inhibitors (InH), hydroquinone (HQ) and quinone (Q), on the oxidation of cyclohexane catalyzed by cobalt(II) acetate Co(OAc)₂ · 4H₂O and on the decomposition of hydrogen peroxide in acetic acid (HOAc) at 303 K were studied. It was found that an increase in the concentration of HQ in the starting reaction mixture containing cyclohexane, the catalyst, and H₂O₂ dissolved in HOAc resulted in an exponential decrease in the yields of the target products of oxidation: cyclohexanol, cyclohexanone, and cyclohexyl hydroperoxide. In the presence of Q, the dependence of the yield of the target products on the initial inhibitor concentration exhibited a maximum at (1.8–2.5) × 10^–2 M Q. At (2.2–2.4) × 10^–2 M Q concentrations, the yield of the target products was 55–60% of that in an uninhibited process. Based on kinetic, spectrometric, and quantum-chemical data, the effect found was explained by the fact that under the experimental conditions highly active hydroxyl derivatives of radicals rather than a hydroxy quinolide hydroperoxide (the homolysis of which can produce species with a free valence, which are capable of initiating free-radical reactions) were largely formed from Q.     

Effect of the nature of the active component and support on the activity of catalysts for the hydrolysis of sodium borohydride

The effect of the nature of an active component and a support on the rate of hydrolysis of aqueous sodium borohydride solutions was studied. It was found that the activity of supported catalysts, which were reduced in a reaction medium of sodium borohydride, decreased in the order Rh > Pt ≈ Ru ? Pd regardless of the nature of the support (γ-Al₂O₃, a Sibunit carbon material, or TiO₂). The catalysts based on TiO₂ exhibited the highest activity. As found by UV-vis diffuse reflectance spectroscopy, the composition and structure of the supported precursor of an active component depend on the nature of the support. It is likely that rhodium clusters with different reaction properties were formed on various supports under the action of a reaction medium.     

Composition of the fatty acid fraction of zeins with various degrees of purification

It has been shown that maize zeins are associated with lipids mainly of saturated nature. The process of quantitative repression of prolamines in maize grain under the action of the mutant gene opaque-2 is accompanied by a change in the associative properties with substances of lipid nature. A covalent nature of the zein polypeptide-lipid (fatty acid) bond is suggested.Scientific-Research Institute of Biology, Dnepropetrovsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 187–189, March–April, 1990.     

Dependence of the relative retention of organic compounds on the nature and pressure of the carrier gas and on the thickness of the PEG-20M film in the capillary column

The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases: helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997.     

Effect of the Dopant Nature on the Response of Sensor Arrays Based on Polypyrrole

The effect of the nature of the dopant on the response of a sensor array based on films of polypyrrole under the influence of the vapor of various organic solvents was studied. It was found the electric conductivity of the polymer can both increase and decrease during the action of analytes on electropolymerized films of polypyrrole. It is suggested that the main factors determining the response of polypyrrole are the morphology of the films and the type of charge carriers in the polymer, which depend on the nature of the dopant anion, and also the polarity and nucleophilicity/electrophilicity of the analyte. The responses of polypyrrole and polyaniline are compared, and the effect of the nature of the conducting polymer on them is analyzed. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 265–271, September–October, 2005.     

Quantum-chemical investigation of the triplet-triplet absorption in photochromic indolinespiropyrans

The triplet-triplet absorption spectra of the initial and photoinduced forms of unsubstituted and methoxy- and nitro-substituted indolinespiropyrans were calculated by the CNDO/S method. An interpretation of the experimental data with respect to the absorption of indolinespiropyrans in the visible region is proposed on the basis of the results. The presence of long-wave triplet-triplet absorption in the spectral region > 800 nm is indicated. A suggestion is made about the nature of the kinetic changes in the absorption spectra of nitro-substituted indolinespiropyrans during the photochromic transformations. An explanation of the nature, the structure, and the complexity of the kinetics of decay of the absorption band in the region of 400–460 nm is given in terms of the cis-isomeric form, which is formed immediately after photoexcitation of the indolinespiropyran. The nature of the triplet-triplet absorption of the trans isomers of the colored form was established. An analysis is made of the orbital nature of the triplet states of the initial and photoinduced forms of unsubstituted and methoxy- and nitrosubstituted indolinespiropyrans.Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 24, No. 3, pp. 291–299, May–June, 1988.The authors express their gratitude to G. G. Konoplev for taking part in the discussion of the results.     

Use of the IR spectra of adsorbed ethane and propane molecules to characterize the strength of active sites in zeolites and to analyze the activation of C-H bonds in these paraffins

The adsorption and activation of ethane and propane on the hydrogen and cationic forms of mordenite, zeolite ZSM-5, and zeolite Y were studied by diffuse-reflectance IR spectroscopy. The effect of the polarization of these molecules by adsorption sites on the intensities and shifts of absorption bands due to C-H stretching vibrations were studied. It was found that weak adsorption species were formed on the hydrogen forms of the above zeolites. In this case, both the intensity distributions and the positions of absorption bands due to C-H stretching vibrations were almost independent of the nature of zeolites. However, both absorption band maximum positions and relative intensity distributions changed upon paraffin adsorption on the cationic forms. It was also found that relative intensity distributions and shifts of absorption bands due to C-H stretching vibrations strongly depended on the nature of cations and zeolites. In this case, the initially totally symmetrical C-H vibrations were found most strongly disturbed. The low-frequency shifts and relative intensities of absorption bands due to these vibrations for various cations and zeolites were found to increase in the following orders: H < Na < Ca < Mg < Zn and zeolite Y < Mord ≈ ZSM-5. The experimental results suggest that ethane and propane molecules can be used as molecular probes for acquiring information on the nature and properties of acidbase sites in zeolites. In this case, both the low-frequency shifts and the relative intensities of absorption bands due to C-H stretching vibrations can be used as measures to characterize the nature of cations and zeolites. However, the latter was found to be much more sensitive to the nature of active sites.     

On the resistance to the interpenetration between macromolecular coils of different segment densities

Using viscometry techniques on polymer fractions, we determine the critical concentrationc ^* (separating the dilute and semi dilute solutions). The same measurements have been conducted with mixtures of these fractions (mixtures 1:1 by weight of fractions differing in molecular mass and chemical nature, or fractions differing only in molecular mass). The determined values of critical concentrationc ^* of the mixtures are higher than the values calculated based on the critical concentrations of the corresponding fractions. This deviation from the additivity rule is attributed to the resistance in the interpenetration (delay to the attainment of the homogeneous state) between macromolecular coils of different chemical nature or of the same chemical nature but of different molecular mass. Higher values of the reduced viscosities of the mixture of the fractions, compared to the values calculated using the reduced viscosities of the corresponding fractions, are observed above the critical concentrationc ^*. In this concentration region the interaction parameter between two different polymers is calculated.     

Characterization of the Hf-NTA complex

Hafnium ion forms a strong complex with nitrilotriacetic acid (NTA). But there is a controversy about the nature of the complex on whether it is a 1:1 or a 1:2 complex. We have carried out an electrophoresis experiment and supplemented data to establish the nature of the complex. Our data indicates that it is a 1:2 complex i.e. [Hf(NTA)₂]^2- in which the coordination number 8 has been satisfied for hafnium.     

Effect of an oxidant on the nature of bulk defects in Li/CaO and its catalytic activity in the oxidative dimerization of methane

The nature of bulk defects formed in Li/CaO during the oxidative dimerization of methane with O₂ and N₂O as oxidants is studied with the use of ESR. Changing the oxidant from oxygen to nitrogen oxide results in changes in the nature of the bulk defects and the catalytic behavior of Li/CaO.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 599–601, March, 1993.     

Photopolymerization of methyl methacrylate with the use of tetrahydrofuran–bromine charge-transfer complex as the photoinitiator

The polymerization of MMA was kinetically studied in the presence of visible light (using a 125-W high-pressure mercury vapor lamp with fluorescent coating, without a filter), a THF—bromine charge-transfer complex being used as the photoinitiator. The initiator exponent was 0.5 in bulk polymerization. The monomer exponent varied from about 1.2 to about 2.5, depending on the nature of the solvent used; the initiator exponent also varied in diluted systems, depending on the nature and proportion of the solvent, the variation being from a value of 0.5 in bulk system to zero or almost zero at about 25% (v/v) solvent concentration. Other kinetic parameters, viz., k_p²/k_t and the activation energy for polymerization, were determined and are reported. Kinetic and other evidence indicates that the photopolymerization takes place by a radical mechanism and termination is bimolecular in nature in bulk systems; in dilute systems, termination by initiator complex assumes predominance, particularly at high solvent concentrations (≥25% v/v).     

Regularities of the processes of radiationless conversion in polyatomic molecules

The processes of radiationless conversion in aromatic and heteroaromatic molecules are investigated theoretically. The values of constant rates of internal conversion are calculated. The theoretical estimation of constant rates of S–T conversion aromatic hydrocarbon molecules and in their carbonyl-, thiocarbonyl-, and nitroderivatives and in azaheterocyclic molecules are given. The S-T conversion probability between the states of different orbital nature (nπ* and ππ*) is equal to ca. 10¹⁰–10¹¹ sec^?1 that is two to four orders higher than the conversion probability between the states of the same orbital nature. It is shown that the process of T-S conversion may be described in the second and in the highest orders of perturbation theory. The luminescent characteristics of molecules are connected with the relative position of electron states of different orbital nature and multiplicity and conversion characteristics.     

Nature of the centers on the surface of oxide catalysts and the forms of adsorbed toluene

IR spectroscopy has been used to analyze the forms of toluene adsorbed on various oxides, differing in the nature of their surface centers: TiO₂, CuO, V₂O₅/Al₂O₃, V₂O₅. The form of adsorption is found to depend on the nature of the surface centers of the oxide. When coordinationally saturated cations are involved complexes of toluene are formed, while if surface oxygen is involved benzoate structures are produced. The temperature at which the latter begin to be formed depends on the strength of the bond between oxygen and the surface. It was shown that the presence of acidic hydroxyl groups on the surface of the oxide leads to proton transfer to the aromatic compound to give carbonium ions. The nature of the interaction is then determined by the mobility of the proton on the surface and the basic strength of the adsorbed molecule. The possibility of identifying such compounds spectroscopically is discussed.Translated from Teoreticheskie i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 710–715, November–December, 1990.     

Poly(N-ethylmethacrylamide) thermally-sensitive microgel latexes: effect of the nature of the crosslinker on the polymerization kinetics and physicochemical properties

Thermally-sensitive crosslinked submicronic particles were prepared by an emulsion/precipitation process of N-ethylmethacrylamide (NEMAM), using potassium persulphate as initiator and four different crosslinkers; ethylene glycol dimethacrylate (EGDMA), 1,3-butanediol dimethacrylate (1,3-BDDMA), 1,4-butanediol dimethacrylate (1,4-BDDMA) and tetraethylene glycol dimethacrylate (TEGDMA). At first, polymerization kinetics was studied by NMR, revealing the negligible effect of the crosslinker nature. On the contrary, the water-soluble polymer amounts, the final hydrodynamic particle size, the swelling ability, the electrokinetic properties were found to be dependent upon the nature of crosslinker. The final latexes were found to be narrowly size distributed irrespective of the crosslinker agent’s chemical nature. In this study, the water solubility of the cross-linker was reported to be an important criterion, but other factors, such as diffusion and reactivity, have to be taken into consideration. To cite this article: P. Hazot et al., C. R. Chimie 6 (2003).     

Electrochemical reduction of oxygen in the presence of humic acids

The effect of the nature of humic acids (HAs), their modification by mechanochemical methods, and the pH of the medium on the electrochemical reduction of oxygen is determined. The mechanical activation of caustobioliths, regardless of their nature, is shown to increase the role of quinone moieties in the composition of HAs, thus promoting the initiation of the electrochemical reduction of O₂ in a basic medium. The conclusion is drawn that this changes not only the ratio of redox-active moieties in HAs, which determine the total antioxidant activity, but also their character.     

Influence of the nature of a curing agent on the peculiarities of formation of vulcanization networks in polysulfide sealants

The molecular mobility of vulkanizates of liquid thiokols cured with various vulcanizing agents was studied by the NMR method in a wide temperature interval. The influence of the nature of vulcanizing agents and the structure of the forming vulcanization network on the change in the character of molecular mobility in vulcanizates of polysulfide oligomers was established. The correlation of effective (υ_eff) and chemical (υ_ch) densities of vulcanization networks of thiokol sealants with parameters of the NMR spectrum of the latter was found. The influence of the nature of a curing agent on the peculiarities of the formation of vulcanization networks of polysulfide oligomers is discussed.