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131.
Takayasu Yamauchi Hiroyuki Sazanami Yuuichi Sasaki Kimio Higashiyama 《Tetrahedron》2005,61(7):1731-1736
1,3-Oxazolidines were easily obtained by condensation of N-substituted (R)-phenylglycinol with aldehydes. Addition of organolithium reagents to 1,3-oxazolidines by complexation with the bulky Lewis acid aluminum tris(2,6-diphenylphenoxide) (ATPH) readily produced the corresponding chiral amines with good yield and high diastereoselectivity. The configuration of the new stereogenic center was shown to be opposite to that of adducts obtained for the same 1,3-oxazolidines using Grignard reagents. The best diastereoselectivity was achieved using N-isopropyl-1,3-oxazolidines. The mechanism of addition was deduced by determining the stereochemistry of the iminium-aluminum complex by NOE experiments. 相似文献
132.
A series of calixcrown ethers for which the cavity size of the crown ring is varied from crown-6 to crown-7 to crown-8 were examined for the transport abilities toward alkali metal ions. These ligands were incorporated into supported liquid membranes (SLMs) and into polymer inclusion membranes (PIMs) composed of cellulose triacetate (CTA) as a support and 2-nitrophenyl octyl ether (NPOE) and tris(2-butoxyethyl) phosphate (TBEP) as a plasticizer. In both membrane systems, calixcrown-6 showed the best selectivity toward a cesium ion over other alkali metal ions. The polymeric CTA membrane showed more rapid transport rate as well as higher durability than did the SLMs. 相似文献
133.
134.
Ming Guo Jue Wang Man Xiong Ronghui Wu Xuejuan Yang Jianzhong Zhou Minghui Li Jiajun Li 《大学化学》1986,35(12):237-246
In order to improve university laboratory teaching and practical education under the background of information technology, as well as overcome the difficulty for practical training, develop a virtual simulation experiment platform for rapid pyrolysis of natal materials and high-performance liquid chromatographic (HPLC) detection of its components. The experiment integrates the actual operation process of the plant to produce cleaved products by rapid pyrolysis of biomass with HPLC detection. The virtual experiment is divided into biomass sample pretreatment, rapid biomass pyrolysis, bio-oil extraction, and HPLC determination of complex components, making the biomass cleavage workshop "real" through simulation. This virtual simulation experiment fully integrates the utilization of biomass resources and basic chemistry courses (such as organic chemistry, instrumental analysis, chemical engineering principles, etc.), which are widely involved in agricultural and forestry majors with advantageous characteristics value. 相似文献
135.
136.
137.
I. Kuselman 《Accreditation and quality assurance》1998,3(3):131-133
It is argued that results of uncertainty calculations in chemical analysis should be taken into consideration with some caution
owing to their limited generality. The issue of the uncertainty in uncertainty estimation is discussed in two aspects. The
first is due to the differences between procedure-oriented and result-oriented uncertainty assessments, and the second is
due to the differences between the theoretical calculation of uncertainty and its quantication using the validation (experimental)
data. It is shown that the uncertainty calculation for instrumental analytical methods using a regression calibration curve
is result-oriented and meaningful only until the next calibration. A scheme for evaluation of the uncertainty in uncertainty
calculation by statistical analysis of experimental data is given and illustrated with examples from the author's practice.
Some recommendations for the design of corresponding experiments are formulated. 相似文献
138.
S. Fakirov Z. Sarac T. Anbar B. Boz I. Bahar M. Evstatiev A. A. Apostolov J. E. Mark A. Kloczkowski 《Colloid and polymer science》1997,275(4):307-314
This second part of a systematic study of the properties of crosslinked-oriented gelatin involves the effects of orientation
and water content on the glass transition temperature T
g and on the melting behavior. The samples were the same as those in the preceding study, and their transition temperatures
were determined by both differential scanning calorimetry and dynamic mechanical thermal analysis. The crosslinked gelatin
which had been room-conditioned showed two transition temperatures: the lower one was attributed to T
g of the water-plasticized gelatin, and the higher one was interpreted as T
g of dried gelatin superimposed by melting. A rather unusual situation arose because of the fact that the T
g and melting temperatures T
m (217 and 230 °C, respectively) are so similar. Using water as plasticizer not only decreases T
g but produces imperfect crystallites which melt below the T
g of the system. The presence of the amorphous phase in the glassy state would presumably make it essentially impossible to
define a melting point or crystallization temperature in the normal manner, as an equilibrium between crystalline and amorphous
phases.
Received: 8 October 1996 Accepted: 2 November 1995 相似文献
139.
The surface free energies of polyethylene terepthalate fibers with different draw ratios were experimentally determined by contact angle measurements inn-alkane/water systems. The dispersive component of the surface free energy increased with increasing draw ratio, whereas the nondispersive one remained almost constant. After heat treatment, the dispersive surface free energy increased, but was reduced above 140°C. The nondispersive component increased by heat treatment at 190°C. The increases in the density and birefringence of the fibres due to the drawing and heat treatment suggested that the increase in the dispersive surface free energy was caused by the increase in the atomic density at the fiber surface due to drawing and heat treatment. ESCA results indicated that the increment in the nondispersive surface free energy due to heat treatment was caused by the addition of functional groups to the fiber surface due to heat treatment. 相似文献
140.
Guo-xiang Xu Lu Qi Bi-tao Yu Lei Wen Department of Applied Chemistry College of Chemistry Molecular Engineering Peking University Beijing China Department of Inorganic Nonmetal Materials School of Materials Science Engineering University of Science Technology Beijing Beijing China 《高分子科学》2006,(3):307-313
PVC disulfide (2SPVC) was synthesized by solution crosslink and its molecular structure was confirmed by infrared spectrum. 2SPVC's specific area is 36.1 m2·g-1 tested by stand BET method, and granularity experiment gives out the particle size of d0.5= 11.3μm. With SEM (Scanning Electron Microscope) experiment the surface morphology and particle shape of 2SPVC were observed. Cyclic voltammetry (scan rate: 0.5 mV·s-1) shows that 2SPVC experience an obvious S-S redox reaction in charge-discharge process. When 2SPVC was used as cathode material for secondary lithium battery in a 1 mol·L-1 solution of lithium bis(trifluoromethylsulfonyl) imide (Li(CF3SO2)2N) in a 5:45:50 volume ratio mixture of o-xylene (oxy), diglyme (DG) and dimethoxymethane (DME) at 30℃, the first discharge capacity of 2SPVC is about 400.3 mAh·g-1 which is very close to its theoretical value (410.5 mAh·g-1) at a constant discharge current of 15 mA·g-1. It can retain at about 346.1 mAh·g-1 of discharge capacity after 30 charge-discharge cycles. So 2SPVC is a very promising cathode candidate for rechargeable lithium batteries. 相似文献