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91.
G. A. Vorob'eva S. D. Chemerisov A. V. Kozintsev Ya. S. Lebedev 《Russian Chemical Bulletin》1997,46(2):284-288
A new simple method was developed for the preparation of organometallic bi- and triradicals by the heterogeneous reaction
of γ-Al2O3 or analogous oxides with free radicals generated in solution through the interaction of 3,6-di-tert-butyl-o-benzoquinone with 3,6-di-tert-butylpyrocatechol. An explanation was offered for the plus sign of the dipoledipole coupling constant observed previously
in the ESR spectra recorded in a superstrong field at low temperatures.
Deceased.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 298–302, February, 1997. 相似文献
92.
93.
D. L. Hoang A. Dittmar M. Schneider A. Trunschke H. Lieske K. -W. Brzezinka K. Witke 《Thermochimica Acta》2003,400(1-2):153-163
CrOx/La2O3 mixed oxides, prepared by impregnating La2O3 with appropriate aqueous solutions of (NH4)2CrO4 and calcining at 600 °C for 4 h, have been investigated by means of XRD, TPR, XPS, DRIFTS, and Raman spectroscopy (RS). The formation of the compounds La2CrO6, La(OH)CrO4 and LaCrO4 under these conditions was evidenced. Strong peaks at 864, 884, 913, and 921 cm−1, as well as weak peaks at 136, 180, 354, 370, and 388 cm−1 in the RS spectrum of CrOx/La2O3 have been assigned to La2CrO6. 相似文献
94.
G. S. Zakharova L. Yu. Buldakova V. L. Volkov L. S. Molochnikov E. G. Kovaleva 《Russian Journal of Electrochemistry》2006,42(1):53-58
Complex vanadium and titanium oxides modified by copper ions are studied by the electrochemical and ESR methods. Oxides Cu x V2?y Ti y O5?δ·nH2O (0<y<1.33) have a layered structure and oxides Cu x Ti1?y V y O5+δ·nH2O (0<y<0.25), an anatase structure. The intercalation of cations Cu2+ into the hydrates leads to oxidation of V4+. According to ESR data, V4+ exists in the oxides in the form of VO2+ and an octahedral surround of oxygen (V4+?O6), respectively. The electroreduction of ions of d-elements and chemisorbed oxygen in the oxides is analyzed. The intercalation of cations Cu2+ alters the content of V4+ and the chemisorption ability of the oxides. Possible reasons for this phenomenon are discussed. 相似文献
95.
We have theoretically examined the reaction course of the butadiene insertion into the arylNiII bond in the [NiII(η5-Cp)(η1-phenyl)(η2-butadiene)] complex (1), by employing a gradient-corrected DFT method. Critical elementary processes have been scrutinized, viz. monomer insertion, rotational allylic isomerization and allylic η1-σ→η3-π rearrangement. The first mechanism suggested by Lehmkuhl et al. was refined and supplemented with important details. The critical factors that determine the generation of anti-η3- and syn-η3-allyl isomers of the [NiII(η5-Cp)(1-benzyl-allyl)] product have been elucidated. This let us to rationalize the experimentally observed, almost exclusive formation of the anti-η3-allyl isomer. Butadiene preferably inserts in η2-mode into the η1-phenylNiII bond, initially giving rise to the η1(C3)-allyl product species, 3σ. The direct formation of the η3-allyl product species, 3π, along the alternative path for η4-butadiene insertion, however, is found to be almost entirely disabled kinetically. The thermodynamically favorable η2-trans form of 1 is also shown to be more reactive in accomplishing CC bond formation. Species 3σ is indicated to be a metastable intermediate, occurring in an appreciable stationary concentration. Its respective anti and syn isomeric forms are likely to be in equilibrium, due to the facile rotational isomerization. The subsequent allylic rearrangement into the thermodynamically strongly favorable η3-allylNiII coordination mode is shown to be the crucial elementary step that discriminates which of the isomeric η3-allyl forms is preferably generated. The higher reactivity of the anti isomer in this process decisively determines the almost exclusive formation of the anti-η3-allyl product species under kinetic control. The requirement of elevated temperatures for the anti-η3-allyl→syn-η3-allyl isomerization to occur, as revealed from experiment, is attributed to the pronounced thermodynamic stability of the η3-allylNiII coordination. 相似文献
96.
In the Claus process hydrogen sulfide reacts to elemental sulfur. Because the Claus reaction is thermodynamically limited, sulfur compounds are still present in Claus tailgas. To avoid air pollution, the tailgas has to be treated.Alfa- and gamma-alumina are being used either as a catalyst or as a support for an active component in the Claus process and some tailgas treatment processes. In order to elucidate the mechanism of the Claus reaction, the adsorption of sulfur dioxide on both of the above aluminas was investigated using Fourier transform infrared spectroscopy.Different adsorbed species displaying a different heat of adsorption were detected. A broad band near 3500 cm–1 is associated with the basic hydroxyl groups. This band is assigned to a hydrogen bond between the surface of alumina and a bisulfite species. As bisulfite species are reactive towards hydrogen sulfide, we assume that bisulfite species are active intermediates on alumina in the Claus reaction. 相似文献
97.
98.
Maria Grazia Bonicelli Gianfranco Ceccaroni Franco Gauzzi Giuseppe Mariano 《Thermochimica Acta》2005,430(1-2):95-99
Differential scanning calorimetry (DSC) and particle size measurements were carried out on disproportionation products of pure SnO to investigate the fusion and solidification behaviour of Sn droplets and their catalytic nucleation on Sn oxides. If disproportionation reaction takes place at T ≥ 798 K, the products are metallic Sn and SnO2; but for 523 < T < 798 K, SnO2 is replaced by an intermediate oxide (IO) SnxO(1+x). On melting, samples with IO show a drop of melting point of metallic tin due to Gibbs–Thomson effect; no lowering of melting point was observed in samples with SnO2. On the other hand, if solidification occurs in the presence of IO, Tin droplets always displayed three distinct exothermic solidification peaks, but if it takes place in the presence of SnO2, only one exothermic peak is observed. Undercooling values and contact angles were determined for each of the heterogeneous nucleation processes. The different behaviour of metallic Tin droplets was related to the different lattice symmetry of SnO2 and IO, which act as nucleation catalysts. 相似文献
99.
100.
A. S. Kulikov M. A. Epishina I. V. Ovchinnikov N. N. Makhova 《Russian Chemical Bulletin》2007,56(8):1580-1587
The conditions for the thermolysis of furoxans annulated with differently strained five-membered carbocycles (cyclopentafuroxan
1, norbornenofuroxan 2, and acenaphthofuroxan 3) to bis(nitrile oxides) in the presence of various dipolarophiles (diethyl acetylenedicarboxylate, benzoylformonitrile, and
ethoxycarbonylformonitrile) were optimized. It was found that the reactivities of the above furoxans as sources of bis(nitrile
oxides) decrease in the order 2 > 1 > 3. Among the furoxans studied, only norbornenofuroxan 2 can be recommended as a possible cross-linking reagent for polymers. The formation of di-N-oxides of 3,4-bis(cyanopropyl)-, 3,4-bis(cyanocyclopentyl)-, and 3,4-bis(cyanonaphthyl)furoxans was detected. They resulted
from intermolecular cyclodimerization of bis(nitrile oxides) initially formed in the thermolysis of furoxans 1–3.
Dedicated to Academician V. A. Tartakovsky on the occasion of his 75th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1521–1528, August, 2007. 相似文献