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61.
Nguyen VD 《Analytical and bioanalytical chemistry》1996,354(5-6):738-741
An ion chromatographic measuring system for the off-line and on-line determination of some trace anions and cations in high-purity water is presented. The ng/L level of anions and cations in 20-130 mL high-purity water can be analyzed after preconcentration on ion exchange columns. The concentrated solutes are eluted by eluents from the trap column and separated using a Dionex analytical column. The quantification of each ion is achieved using the suppressor technique and conductivity detector. The influence of various parameters on the results is discussed. The detection limits of cations and anions are between 10 and 30 ng/L for chloride, bromide, nitrate, phosphate, sulphate, sodium, ammonium, potassium, magnesium and calcium ions. 相似文献
62.
Dense membranes were prepared from poly(vinyl alcohol)–poly(N-vinyl pyrrolidone) (PVA–PVP) blends of different compositions and studied in swelling and dehydration by pervaporation of three organic solvents contaminated by 5 wt% water. The swelling generally increases with the PVP content. No extraction occurs in water–tetrahydrofuran (THF) and water–methyl ethyl ketone (MEK) mixtures. In ethanol containing 10 wt% of water, there is no extraction for blends containing less than 40 wt% PVP and an increasing extraction beyond this PVP content. The pervaporation flux of the water–ethanol mixture increases drastically at the same threshold whereas the water permselectivity falls to a low level. The values of the diffusion and permeability coefficients determined from transient permeation of the test water–ethanol mixture exhibit a similar sudden increase at the same PVP content threshold. This singular behavior of the blend membranes is interpreted by a strong affinity of the PVP component to ethanol, combined with a disappearance of crystallites in the blend at this threshold. Consequently the amorphous membrane can swell freely according to the affinity of the PVP component, leading to the observed behavior. 相似文献
63.
Nguyen Thoai 《Journal of fluorine chemistry》1975,5(2):115-125
Perfluoroalkylmagnesium bromide, CnF2n+1MgBr (n = 2, 6, 8), reacts with α,β-unsaturated aldehydes to give allylic alcohols as the sole products. No attack on the β-carbon atom of the carbonyl was detected, even when the reaction was carried out in the presence of CuCl. Part of the Grignard reagent decomposes to trans-RFCFCFBr and trans-RFCFCFI. Neither a mechanism involving dissociation into R+F MgX- nor the formation of a carbene intermediate is capable of explaining the thermal decomposition of the Grignard reagent. 相似文献
64.
Existing theories of the motion of foam films in capillaries often assimilate the pressure drop over the foam films to the static capillary pressure obtained from the Young-Laplace equation. Hence, they ignore the contribution of dynamic effects associated with the rapid stretching and contraction of the foam films to the overall viscous dissipation. This paper reports an investigation of the motion of foam films in axisymmetric diverging-converging channels, taking into account surface viscosity and elasticity. First, a phenomenological theory for the motion of the foam films is developed using simple physical arguments. We show that the displacement of the film obeys a nonlinear second-order differential equation, which can be solved numerically for the (dimensionless) distance from the inlet and the pressure drop as a function of time. Experiments with foam film motion, conducted using glass diverging-converging channels (minimum radius = 3.00 +/- 0,01 mm, maximum diameter = 7,98 +/- 0,01 mm) and nitrogen foam stabilized with sodium dodecyl sulfate (SDS) in brine, are discussed. For a single film motion in the diverging channel, we find that (a) the static pressure drop is a concave-upward function of distance and decreases from 1.0 to about 0.3, whereas (b) the dynamic pressure drop is concave downward and increases from 1 to a maximum of 1.3 and then decreases to 0.7. In the converging channel both the static and dynamic pressure drops are concave-downward functions, but the dynamic pressure drop values are always higher than the static ones. For two films the motions were found to be rather sensitive to the initial arrangement in the channel. The experiments are found to be in excellent agreement with the theoretical predictions. These observations imply that the large flow resistance obtained during foam flow in granular porous media, where converging-diverging channels are abundant, is largely due to the surface elasticity and viscosity of the films. 相似文献
65.
A model system for the synthesis of phloroglucinol containing natural products was synthesized. Key steps include a manganic acetate-mediated cyclization and the facile conversion of an alkene into a β-bromoenone. 相似文献
66.
Yasuo Saegusa Sakayu Iida Shigeo Nakamura Nguyen Chau Yoshio Iwakura 《Journal of polymer science. Part A, Polymer chemistry》1984,22(5):1017-1023
Aromatic polythioamide-oxothioxoquinazolines were synthesized by the polycondensation of 2,2′-(m-phenylene)bis-1,3,4-thiadiazoline-5-thione with aromatic bis-o-amino esters. The polymerizations were carried out at 160°C in acidic media such as m-cresol, sulfolane, and polyphosphoric acid to produce polymers with reduced viscosities up to 0.5 dL/g. These polymers were soluble in polar aprotic solvents like N-methyl-2-pyrrolidone and some acidic media including m-cresol. The polythioamide-oxothioxoquinazolines showed relatively good thermal stability with 10% weight loss at 344–394°C in air. 相似文献
67.
Yinghong Sheng Jerzy Leszczynski Thuc-Quyen Nguyen Anu Bamgbelu 《Structural chemistry》2007,18(6):827-832
A theoretical study using density functional theory was performed to understand the structure/property relationship of the
cationic conjugated polyelectrolytes, poly[9,9-bis-(6′-N,N,N-trimethylammonium) hexyl] fluorene-alt-4,7-(2,1,3-benzothiadiazole)] (PFBT-X, where X = Br). The torsion angle between the fluorene and benzothiadiazole units in the PFBT monomer was found to substantially affect
the structural and electronic properties of the cationic PFBT monomer. The changes of geometrical parameter, HOMO and LUMO energy levels, and band gap, as well as the absorption maximum
are discussed in terms of the torsion in the PFBT monomer structure. For comparison, its neutral analogue, the monomer of
poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) was also studied. The length of conjugation backbone was also examined. 相似文献
68.
Hu C Chin RM Nguyen TD Nguyen KT Wagenknecht PS Nathan LC 《Inorganic chemistry》2003,42(23):7602-7607
The reactions between H(2)dc3 and Co(acac)(3) have been studied in the presence and absence of base. In the presence of base, a complex with an intramolecular Co-C bond, Co(dc3-C-(8))(H(2)O), 1, is formed, presumably through heterolytic C-H bond activation. An X-ray crystallographic study demonstrates the presence of a Co-C bond and shows that the diazacyclooctane (daco) subunit adopts the chair-boat conformation with respect to the metal. The cobalt-carbon bond induces strain in the macrocycle as demonstrated by bond angles significantly deviating from tetrahedral. The (13)C NMR resonance of the carbon atom bound to cobalt (-10.5 ppm) suggests significant ionic character in the cobalt-carbon bond. However, we were unable to cleave this bond in the presence of strong acid. In the absence of base, the reaction of Co(acac)(3) with H(2)dc3 resulted in C-N cleavage of the ligand and the formation of a complex of dioxocyclam, Co(dc)(acac), 2. This complex has subsequently been prepared in high yield by the reaction of Co(acac)(3) with dioxocyclam. An X-ray crystallographic study demonstrates that dioxocyclam adopts the heretofore unreported cis configuration, having folded along a N-Co-N axis that is perpendicular to the Co-acac plane. 相似文献
69.
Nguyen Chan Hung I. V. Anoshkin E. G. Rakov 《Russian Journal of Applied Chemistry》2007,80(3):443-447
Method of thermodynamic simulation was used to calculate the equilibrium parameters of reactions of graphite with anhydrous LiOH, NaOH, and KOH and with the alkalis in the presence of water vapor. The change in the specific surface area and mass loss were used to analyze the interaction of carbon nanofibers and multilayer carbon nanotubes produced by catalytic pyrolysis of CH4 with the alkalis. 相似文献
70.
Bose G Nguyen VT Ullah E Lahiri S Görls H Langer P 《The Journal of organic chemistry》2004,69(26):9128-9134
The Lewis acid mediated domino "[3+3]-cyclization-homo-Michael" reaction of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes allows an efficient one-pot synthesis of functionalized salicylates containing a halogenated side chain. A great variety of substitution patterns could be realized by variation of the starting materials and of the Lewis acid. The mechanism of the domino process was studied. 相似文献