Polarography and preparative electrolysis are used to show that the electrochemical behavior of 1-ethyl-4-nitro-3-cyanopyrazole (1) in acidic aqueous-alcoholic solutions resembles the behavior of nitrobenzene. By varying the parameters of the electroreduction (ER) of compound 1, one can obtain either 1-ethyl-4-amino-3-cyanopyrazole (2) or 1-ethyl-4-amino-3-cyano-5-chloropyrazole (3). Compound 2 is formed during the ER of compound 1 in the presence of a mediator (titanium(III)) at temperatures below 10°C. Compound 3 is produced by the direct reduction of compound 1 on a lead electrode (30% ethanol, 10% HCl). The yield of amine chlorohydrates 2 and 3 is 56 and 92%, respectively. The mediated ER of compound 1 at catholite temperatures higher than 10°C yields a mixture of compounds 2 and 3; the proportion of the latter increases with temperature to become the major product at 60°C. Compound 3 is formed due to the rearrangement of the hydroxylamine derivative produced by the ER of compound 1, followed by the substitution of chlorine for the hydroxy group. 相似文献
Effect the morphology of the surface of the working electrode (PbS) exerts on the sensitivity of a low-temperature potentiometric hydrogen sulfide sensor is studied. The sensor, which is based on electrochemical cell NaxWO3/NASICON/PbS, may be used for fast selective detection of hydrogen sulfide in air in natural conditions. It is demonstrated that the sensors with PbS that are deposited out of solution have a faster response than the pressed-to ones. The dependence of EMF on the hydrogen sulfide concentration for the former is linear in semilogarithmic coordinates. Thus difference is explained by the microstructure of the lead sulfide layer. It is shown that the lead sulfide interaction with hydrogen sulfide involves a reversible partial reduction of sulfur and lead at the surface. The species that form in so doing contain sulfur atoms in lower oxidation degrees (poly-and oligo sulfides, sulfite). A mechanism of the sensor operation is proposed on the basis of data yielded by experiment and quantum-chemical simulation. The mechanism includes reversible transport of hydrogen from sulfur atoms to oxygen atoms. 相似文献
The anticorrosion properties of epoxy-polysiloxane coatings on the surface of the aluminum alloy D-16 were studied by a potentiodynamic
method. It was established that the use of the hybrid coating led to an increased corrosion resistance from 0.250 kΩm·cm2 for uncoated alloy to 0.396-0.996 kΩm·cm2 for the coated aluminum support. The yield of the sol fraction, the micro hardness, and the glass transition temperature
of the polymers were determined. 相似文献
Ditopic complex formation of silene H2SiCH2 with bidentate ligands Me2NCH2SiHnF3-n (n = 0-3) was studied at the MP4(SDQ(T)6-311G(d,p))//MP2/6-31G(d,p) levels of theory. The AIM and ELF analyses have shown that π-bonding in the silenic Si1C moiety in the relatively weak (H2Si1CH2)·(Me2NCH2Si2HnF3-n) (n = 2, 3) ditopic complexes is partially preserved. 相似文献
DFT (B3LYP, M06‐2X) and MP2 methods are applied to the design of a wide series of the potentially 10‐C‐5 neutral compounds based on 6‐azabicyclotetradecanes: XC1(YCH2CH2CH2)3N 1 – 3 , XC1(YC6H4CH2)3N 4 – 6 , XC1[Y(tBuC6H3)CH2]3N 7 – 9 and carbatranophanes 10 – 25 (X=Me, F, Cl; Y=O, NH, CH2, SiH2; Z=O, CH2, (CH2)2, (CH2)3). Carbatranophanes 10 – 25 are characterized by a sterical compression of their axial 3c–4e XC1←N fragment with respect to that in the parent molecules 4 – 6 . A magnitude of the revealed effect depends on a valence surrounding of the central carbon atom C1, the size and the nature of the side chains (Z) that link the “π‐electron cap” with a tetradecane backbone. This circumstance allowed us to obtain 10‐C‐5 structures with the configuration of the bonds around the C1 atom, which corresponds to practically an ideal trigonal bipyramid. In these compounds, the values of the covalence ratio χ of approximately 0.6 for the coordination C1←N contacts with a covalent contribution (atoms in molecules (AIM) and natural bond orbital (NBO)) are record in magnitude. These values lie close to a low limit of the interval of the χSi←D change (0.6–0.9) being characteristic of the dative and ionic‐covalent (by nature) Si←D bond (D=N, O) in the known 10‐Si‐5 silicon compounds. 相似文献
Thermostable heterocyclic polymers containing phenyl-substituted quinoxaline and both amide and imide units have been synthesized by low-temperature solution polycondensation of diaminophenyl-quinoxalines with diacid chlorides of certain aromatic acids containing preformed imide rings. Also, copolymers have been obtained in which a mixture of diaminophenylquinoxaline and diaminooxadi-azole or diaminobenzimidazole was used in the reaction with the same diacid chlorides. The thermal stability and the electrical insulating properties of these products are discussed and compared with related heterocyclic polymers. 相似文献
Epoxy-polysiloxane composites of cationic polymerization were synthesized based on epoxy resin and tetraethoxysilane. The thermophysical properties of the resulting polymers were studied. It was established that, as the filler content increases from 0.5 to 3 wt %, the molecular weight of an intermodal segment increases and the cross-linking density of an epoxy matrix and glass transition point reduce. The resulting polymers have a heterogeneous structure in which the regions of structuring with the corresponding glass transition points are segregated. 相似文献
The reaction of N-unsubstituted imines of 2-hydroxyacetophenones with trichloro(trifluoro)ethylidene nitromethanes in the presence of DABCO proceeds via tandem oxa-Michael/aza-Henry additions (in dichloromethane) or aza-Michael addition (in benzene) to give 4-methyl-3-nitro-2-trichloro(trifluoro)methyl-2H-chromenes or 1,1,1-trichloro(trifluoro)-3-nitro-N-[1-(2-hydroxyaryl)ethylidene]propan-2-amines, respectively. 相似文献
Phase analysis, spectroscopic, and light scattering methods are applied to investigate the peculiarities of the interaction of oligochitosan (OCHI) with native and preheated bovine serum albumin (BSA) as well as the conformational and structural changes of BSA in BSA/OCHI complex. As shown, untreated BSA binds with OCHI mainly forming soluble electrostatic nanocomplexes, with the binding causing an increase in BSA helicity without a change in the local tertiary structure and thermal stability of BSA. In contrast, soft preheating at 56 °C enhances the complexation of BSA with OCHI and slightly destabilizes the secondary and local tertiary structures of BSA within the complex particles. Preheating at 64 °C (below the irreversible stage of BSA thermodenaturation) leads to further enhancement in the complexation and formation of insoluble complexes stabilized by both Coulomb forces and hydrophobic interactions. The finding can be promising for the preparation of biodegradable BSA/chitosan-based drug delivery systems. 相似文献