Selectivity changes towards steroids in packed column supercritical fluid chromatography (SFC) induced by temperature and pressure variation

Summary Pressure/temperature variation in SFC was shown to influence selectivity towards steroids. Major changes were observed for polar column packings compared to non-polar packings and variation of the amount of modifier showed that this is valid over the whole investigated range. The effect is underlined by a fall in resolution in the low density range (low pressure/high temperature) for polar stationary phases and appears to be significantly larger than for non-polar phases. Major selectivity shifts induced by variation of the physical properties of the mobile phase are considered to be due to the greater effect of polar modifiers on the nature of polar stationary phases than on non-polar phases.     

Synthesis of Dimethyl Carbonate from CO2 , Methanol, and Epoxides Using Re（CO） 5 Cl/K2 CO3 as Catalyst System

IntroductionOver the past few years, dimethyl carbonate(DMC) has been proven to be an efficientmethylating,methoxylating, and methoxycarbonylating agent inorganic syntheses, in which DMC is used to replace thetoxic methyl halides, dimethyl sulfate or carb     

Fluoride effect on the palladium–phenanthroline catalyzed carbonylation of nitroarenes to carbamates

Fluorides promote the palladium–phenanthroline catalyzed carbonylation of nitroarenes to carbamates. The effect is more evident on the rate of the reaction at short reaction times, but a positive effect on selectivity is also observed under certain conditions. The effect is observed even under conditions under which chloride inhibits the reaction. Tetraethylammonium is a better countercation than sodium. Copyright © 2007 John Wiley & Sons, Ltd.     

Fourier transform spectroscopy of CH3OH: rotation-torsion-vibration structure for the CH3-rocking and OH-bending modes

High-resolution Fourier transform spectra of CH₃OH have been investigated in the infrared region from 930 to 1450 cm⁻¹ in order to map the torsion-rotation energy manifolds associated with the ν₇ in-plane CH₃ rock, the ν₁₁ out-of-plane CH₃ rock, and the ν₆ OH bend. Upper-state term values have been determined from the assigned spectral subbands, and have been fitted to power-series expansions to obtain substate origins and effective B-values for the three modes. The substate origins have been grouped into related families according to systematic trends observed in the torsion-vibration energy map, but there are substantial differences from the traditional torsional patterns. There appears to be significant torsion-mediated spectral mixing, and a variety of “forbidden” torsional combination subbands with |Δυ_t|>1 have been observed, where υ_t denotes the torsional quantum number (equivalent to υ₁₂). For example, coupling of the (υ₆,υ_t)=(1,0) OH bend to nearby torsionally excited (υ₇,υ_t)=(1,1) CH₃-rock and (υ₈,υ_t)=(1,1) CO-stretch states introduces (υ₆,υ_t)=(1,0)←(0,1) subbands into the spectrum and makes the ν₇+ν₁₂−ν₁₂ torsional hot band stronger than the ν₇ fundamental. The results suggest a picture of strong coupling among the OH-bending, CH₃-rocking, and CO-stretching modes that significantly modifies the traditional energy structure and raises interesting and provocative questions about the torsion-vibration identity of a number of the observed states.     

激光溅射Ni等离子体与气相CH3OH团簇的反应

用激光溅射 分子束技术研究了气相中Ni的等离子体与甲醇分子团簇的反应 .观察到Ni+ (CH3 OH) n、NiO+ (CH3 OH) n、H+ (CH3 OH) n、H3 O+ (CH3 OH) n 四个种类的团簇正离子和CH3 O-(CH3 OH) n(n≤ 2 5 )一种团簇负离子 .详细考察了激光烧蚀等离子体作用于脉冲分子束的不同位置时 ,对团簇产物种类和团簇尺寸大小的影响 .发现NiO+ (CH3 OH) n 是由Ni+ (CH3 OH) n 团簇内的脱甲烷反应生成的 ,而H+ (CH3 OH) n、H3 O+ (CH3 OH) n主要是激光等离子体中的电子与甲醇团簇碰撞电离产生的     

甲醇在不同形态ZrO2上吸附行为的FTIR研究

用FTIR技术考察了甲醇在不同形态氧化锆上的吸附和活化转化行为.甲醇吸附在无定型和四方氧化锆上生成线式和桥式甲氧基物种,而在单斜氧化锆上还出现锥桥式甲氧基物种.在单斜和无定性氧化锆上的桥式羟基活泼而四方氧化锆上的线式羟基活泼.氧化锆表面吸附的甲氧基物种在晶格氧的作用下进一步转化,在单斜和无定性氧化锆上生成甲酸盐,并且可以进一步氧化为碳酸盐物种;而在四方氧化锆表面,甲氧基物种可以直接氧化为碳酸盐物种,这表明四方氧化锆的晶格氧比其他两种氧化锆上的更为活泼.     

Tandem silylformylation-allyl(crotyl)silylation: a new approach to polyketide synthesis

Tandem intramolecular silylformylation-allyl(crotyl)silylation reactions have been developed that allow the highly efficient synthesis of polyketide fragments. The substrates are subjected to Rh(I)-catalyzed silylformylation to afford β-(diallyl)silyl aldehydes which undergo spontaneous uncatalyzed allylsilylation. This unusual spontaneous allylsilylation reaction is driven by strain release Lewis acidity, which arises from the ∼95° O-Si-C bond angle in the oxasilacyclopentane product of the silylformylation reaction. The methodology has been developed both for alkene and alkyne substrates, may be used to establish as many as three stereocenters, and has been shown to be amenable to use in an iterative fashion.     

Synthesis of the ethyl ester of the mononitrile of malonic acid by the catalytic carbonylation of benzenesulfonyloxyacetonitrile

A new method has been developed for the synthesis of the ethyl ester of the mononitrile of malonic acid by the carbonylation of benzenesulfonyloxyacetonitrile in absolute ethanol in the presence of cobalt carbonyl. The yield of the desired product was 30% with 60–90% conversion of the starting compound. The effects of temperature, pressure, and reaction time were studied.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. S. M. Kirov Urals Polytechnical Institute, Ekaterinburg. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 215–216, January, 1992.     

Electrocatalytic activity of ordered intermetallic PtSb for methanol electro-oxidation

Ordered intermetallic PtSb had been synthesized by arc-melted and then sintering treatment. The electro-oxidation of liquid methanol on PtSb was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results are compared to those at a polycrystalline platinum electrode surface. It was found that PtSb intermetallic was catalytically more active than pure platinum according to the onset potential and current density. X-ray diffraction (XRD) and XPS technologies had been used to investigate the crystal structure and electron effect.