A kinetic study of methane conversion by a dinitrogen microwave plasma

Conversion of CH₄ with a N₂ microwave plasma (2.45 GHz) is studied. The experiments cover the absorbed microwave power range 300–700 W with 17–62% of methane in the gas mixture, with pressures of 10–40 mbar and flow rates of 140–650 ml· min^–1. The yields of C₂ hydrocarbons and dihydrogen are analyzed by gas chromatography. The distance of methane addition downstream of the plasma plays an important role on the composition and the concentration of the products obtained. This distance mainly determines the energy concentrated in the active species of the plasma when they react with methane. Different behaviors for acetylene formation, on the one hand, and for ethane and ethene formation, on the other hand, have been observed, and this finding allows us to propose a kinetic mechanism for the decay of methane and for the formation of C₂ hydrocarbons.     

1,1,4,4-Tetranitrobutane-2,3-diol and its derivatives. 5. Reaction of 1,1,4,4-tetranitrobutane-2,3-diol with formaldehyde; synthesis and crystal structure of 4,4-dinitro-2,3-dihydroxytetrahydrofuran

1,1,4,4-Tetranitrobutane-2,3-diol reacts with formaldehyde, forming 2,2-dinitropropane-1,3-diol or a cyclic ether — 4,4-dinitro-2,3-dihydroxytetrahydrofuran — as a function of the reaction conditions.Institute of Chemical Physics, Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2755–2759, December, 1992.     

循环流化床(CFB)煤/焦气化反应的研究 Ⅰ.操作气速、固体循环速率对循环流化床气化反应的影响

报道了山西西山焦煤飞灰，在小型循环流化床气化反应器上，以二氧化碳为气化介质，在不同操作条件下（气速、固体循环速率）的气化反应。研究结果表明，ＣＯ出口浓度及碳转化率随着ＣＦＢ操作气速减小、固体颗粒循环速率的增加而增加。即在ＣＦＢ床中，提高气体、固体停留时间（床内固体颗粒浓度）有利于ＣＦＢ气化的进行。ＣＯ浓度及碳转化率沿床高的变化趋势与床内颗粒浓度分布一致。     

Highly diastereoselective chemoenzymatic synthesis of (2′R)- and (2′S)-2′-deoxy[2′-H]guanosines

In an effort to develop an efficient synthetic method of highly diastereoselective (2′R)- and (2′S)-2′-deoxy[2′-²H]guanosines, chemoenzymatic conversion was investigated. The synthesis of (2′R > 98% de)-2′-deoxy[2′-²H]guanosine was achieved by biological transdeoxyribosylation using (2′R > 98% de)-2′-deoxy[2′-²H]uridine, 2,6-diaminopurine, and Enterobacter aerogenes AJ-11125, followed by treatment with adenosine deaminase. (2′S > 98% de)-2′-Deoxy[2′-²H]guanosine was synthesized from (2′S > 98% de)-2′-deoxy[2′-²H]uridine and 2,6-diaminopurine using thymidine phosphorylase and purine nucleoside phosphorylase instead of E. aerogenes AJ-11125.     

Reactions of 4-Aryl-2-hydrazino-3-nitro-6-R-quinolines with HNO2

The reaction of 4-aryl-2-hydrazino-3-nitro-6-R-quinolines with NaNO₂ in AcOH gives the corresponding tetrazolo[1,5-a]quinolines. In contrast to tetrazolo[1,5-c]pyrimidines they cannot be converted to 6-R-4-phenyl[1,2,5]oxadiazolo[3,4-b]quinoline-3-oxides by heating in THF, toluene, or AcOH. Total energy quantum-chemical calculations using the MINDO/3 and MNDO methods show that [1,2,5]oxadiazolo[3,4-b]quinoline-3-oxides are significantly higher in energy (230-280 kcal/mol) than the mentioned tetrazolo[1,5-a]quinolines and hence their formation is unlikely.     

The length of the polymethine chain and the spectral-luminescent properties of symmetrical cyanine dyes

The general characteristics that relate the length of the polymethine chain of symmetrical cyanine dyes to their spectral-luminescent properties depending on the electron-donor character of the heterocycles and the nature of the solvent are formulated. For various types of symmetrical cyanines, the Stokes shifts decrease with the elongation of the polymethine chain due to weakening of the vibronic interactions. The vinylene shifts of the band maxima are essentially constant and fall within the range 100 to 130 nm depending on the nature of the heterocycles and the solvent. When the polymethine chain elongates the fluorescence quantum yields first increase and then decrease. The greater the effective length of the heterocycle the stronger the decrease. The fluorescence decay occurring when the polymethine chain gets longer is associated with intensification of the internal conversion. For symmetrical cyanines, the changes in the shapes of the electronic bands (their width, asymmetry, excess, and fine structure) as the chain elongates are governed by the competing effects of the vibronic and intermolecular interactions. The former decrease as the chain lengthens, causing the narrowing of the absorption bands for the lower vinylogs. On the other hand, the latter increase as chain lengthens, which leads to broadening of the bands for the higher vinylogs. The higher the solvent nucleophilicity and the greater the deviation of the electron-donor ability of the heterocycle from the average value the greater the broadening. Any elongation of the polymethine chain of symmetrical cyanines causes only narrowing of the bands and an increase in the asymmetry, excess, and structuring in the fluorescence spectra, which, unlike the absorption spectra, is independent of the electron-donor character of the heterocycles and the nature of the solvent. These effects are caused by the fact that, in contrast to absorption, changes in the shape of emission bands with increasing chain length are governed predominantly by vibronic rather than by intermolecular interactions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1227–1239, July, 1994.     

聚(4-偶氮磺酸苯乙烯-co-4-乙烯基吡啶)与本征态聚苯胺的氢键自组装及其光电转换性能

合成了一种新的共聚体——聚(4-偶氮磺酸苯乙烯-co-4-乙烯基吡啶), 它含有吡啶环, 能作为氢受体与本征态聚苯胺进行氢键自组装. 在紫外光照下, 组装膜通过偶氮磺酸基的光解, 形成稳定的共价交联结构, 在电解质水溶液中也不被破坏, 可用作光电转换膜, 并能在盐水溶液中直接测定它的光电流. 结果表明含有本征态聚苯胺的自组装膜是一种良好的光电转换材料.     

Effect of H2S-uptake on the conversion of cyclohexene on Ru- and Pd-promoted molybdena-alumina catalysts

The effect of H₂S on the activity and selectivity of catalysts (Ru/Al₂O₃, Pd/Al₂O₃ and Ru and Pd promoted molydena-alumina) was different (on differnt catalysts and different conversions of cyclohexene). Ru-containing catalysts showed higher sulfur sensitivities than the Pd-containing ones. The sequence of catalysts by their H₂S uptake related to mass of catalyst was PdMo/Al₂O₃RuMo/Al₂O₃Mo/Al₂O₃>Pd/Al₂O₃Ru/Al₂O₃.     

Fast and reversible migrations of N,S-centered groups around the perimeter of cyclopropene and cycloheptatriene rings

The kinetics and mechanism of circumambulatory rearrangements of N-centered (NCS) and S-centered (SPh, SC₃Ph₃, SC(OEt)=S) groups in corresponding derivatives of 1,2,3-triphenylcyclopropene and cycloheptatriene were studied by dynamic¹H and¹³C NMR spectroscopy. Migrations of the isothiocyanate group occur by the dissociation-recombination mechanism with intermediate formation of a tight ionic pair. Migrations of the phenylthio group around the perimeter of cyclopropene and cycloheptatriene rings occur by the 1,2-shift mechanism. It was found that rearrangements of theO-ethyl dithiocarbonate group inS-(1,2,3-triphenylcyclopropen-3-yl)-O-ethyl dithiocarbonate occur by the 3,3-sigmatropic shift mechanism. The molecular and crystal structure ofO-ethylS-(1,2,3-triphenylcyclopropen-3-yl) dithiocarbonate was studied by X-ray analysis.     

Theoretical Study of the Photochemical Reaction Mechanism of Bicyclo [4.1.0 ] heptane

IntroductionPhotochemical reactions, which involve a three-membered ring, have been of great interest to experi-mental photochemists[1—10]. A main reason for thisphenomenon is that the cyclopropane ring exhibits somereaction characteristics of double bon…