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961.
The direct synthesis of secondary amines from the corresponding primary amines by alkylation has been widely used. The major drawback, however, consists of polyalkylation. Several procedures exist for the solution of the problem. Some of the early methods involve reduction3, or alkylative hydrolysis4 of Schiff base. Other methods include acid hydrolysis of alkylated formanilides prepared from primary aromatic amine and trialkyl orthoformate5, or acid hydrolysis of N-alkylated phosphinamides6, or zinc cleavage of N-alkylated phenacylsulfonamides7, or reductive deprotection of N-alkylated trifluoromethanesulfonamides7. This latter method is analogous to the Gabriel synthesis of 相似文献
962.
963.
Alternating droplet generation and controlled dynamic droplet fusion in microfluidic device for CdS nanoparticle synthesis 总被引:1,自引:0,他引:1
A multifunctional and high-efficiency microfluidic device for droplet generation and fusion is presented. Through unique design of the micro-channels, the device is able to alternately generate droplets, generating droplet ratios ranging from 1 ratio 5 to 5 ratio 1, and fuse droplets, enabling precise chemical reactions in several picoliters on a single chip. The controlled fusion is managed by passive control based on the channel geometry and liquid phase flow. The synthesis of CdS nanoparticles utilizing each fused droplet as a microreactor for rapid and efficient mixing of reagents is demonstrated in this paper. Following alternating droplet generation, the channel geometry allows the exclusive fusion of alternate droplets with concomitant rapid mixing and produces supersaturated solution of Cd2+ and S2- ions to form CdS nanoparticles in each fused droplet. The spectroscopic properties of the CdS nanoparticles produced by this method are compared with CdS prepared by bulk mixing. 相似文献
964.
The title compounds ( 3 , 8 , 9 and 10 ) were efficiently synthesized, and their substitution reactions with various nucleophiles were carried out. The effects of leaving group, sulfur‐substituent, solvent, reaction temperature, and the nature of the nucleophiles on the reactivity and SN2/SN2′ regioselectivity were studied and rationalized with semi‐empirical calculations. 相似文献
965.
This study integrates maintenance and production programs with the economic production quantity (EPQ) model for an imperfect process involving a deteriorating production system with increasing hazard rate: imperfect repair and rework upon failure (out of control state). The imperfect repair performs some restorations and restores the system to an operating state (in-control state), but leaves its failure until perfect preventive maintenance (PM) is performed. There are two types of PM, namely imperfect PM and perfect PM. The probability that perfect PM is performed depends on the number of imperfect maintenance operations performed since the last renewal cycle. Mathematical formulas are obtained for deriving the expected total cost. For the EPQ model, the optimum run time, which minimizes the total cost, is discussed. Various special cases are considered, including the maintenance learning effect. Finally, a numerical example is presented to illustrate the effects of PM, setup, breakdown and holding costs. 相似文献
966.
Hung WY Liu B Shou W Wen TB Shi C Sung HH Williams ID Lin Z Jia G 《Journal of the American Chemical Society》2011,133(45):18350-18360
The electrophilic substitution reactions of metallabenzynes Os(≡CC(R)═C(CH(3))C(R)═CH)Cl(2)(PPh(3))(2) (R = SiMe(3), H) were studied. These metallabenzynes react with electrophilic reagents, including Br(2), NO(2)BF(4), NOBF(4), HCl/H(2)O(2), and AlCl(3)/H(2)O(2) to afford the corresponding bromination, nitration, nitrosation, and chlorination products. The reactions usually occur at the C2 and C4 positions of the metallacycle. These observations support the notion that metallabenzynes exhibit aromatic properties. 相似文献
967.
N. D. Hung Y. Segawa Y. H. Meyer P. Long L. H. Hai 《Applied physics. B, Lasers and optics》1996,62(5):449-455
Diffraction and transform-limited picosecond tunable pulses are generated from Spectro-temporal-Selection (STS) dye lasers by using a new extra-cavity filter. This filter is based on a grazing-incident grating and arranged in the configuration of a folded dispersive delay line. Thus, it provides both high spectral selectivity and controllable temporal compensation for elimination of pulse broadening. Direct production of diffraction- and transform-limited picosecond dye laser (10 µJ, 50 ps) pulses spectrally adjustable between 398 and 702 nm is demonstrated in a compact device, with 8 ns pump pulses from a nanosecond nitrogen laser. 相似文献
968.
The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter acceleration are studied. In particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (a) gravity gradient-dominated, (b) equally weighted between gravity gradients and jitter, and (c) gravity jitter-dominated accelerations are considered. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient and jitter accelerations are also investigated. 相似文献
969.
Yu‐Shen Lin Chun‐Yi David Lu Prof. Yann Hung Dr. Chung‐Yuan Mou Prof. 《Chemphyschem》2009,10(15):2628-2632
Well‐ordered mesoporous silica nanoparticles with uniform hexagonal disk shapes are synthesized under dilute alkaline conditions with a two‐step process, separating the nucleation and growth process. The resulting monodisperse hexagons can be arranged in a 2‐dimensional (2D) ordered periodical super‐structure. The hexagonal symmetry is similar in both scales. A statistical mechanical cell model is applied to analyze consequences of the interesting packing structure, including osmotic bulk modulus, phase separation and defects. 相似文献
970.
The mathematical formulation of the Dewar container sloshing dynamics for a partially filled liquid of cryogenic superfluid
helium II driven by the gravity gradient or jitter accelerations associated with slew motion in a microgravity environment
are studied. The numerical computation of sloshing dynamics is based on the non-inertia container bounded frame and the solution
of time-dependent, three-dimensional partial differential equations subjected to the initial and boundary conditions. This
study discloses that the capillary effect of sloshing dynamics governs the liquid-vapor interface fluctuations driven by the
gravity gradient or jitter accelerations associated with slew motion in a microgravity environment. The peculiar behavior
of superfluid helium in response to sloshing dynamics is also investigated. 相似文献