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31.
Zinc powder was found to be a highly efficient catalyst for the synthesis of aromatic ethers using microwave heating in the presence of N,N-dimethylformamide as well as under stirring in an oil-bath using tetrahydrofuran as solvent without any inorganic base. This method can be used for selective mono-, di- or tri-O-alkylations. 相似文献
32.
R. Krishna Mohan Rao Kallury Pramod V. Upadhyaya Tumbalam G. Surendra Nath Vankipuram R. Srinivasan 《Journal of mass spectrometry : JMS》1977,12(5):307-312
The mass spectra of eight 1,2,4-triazole derivaties have been recorded and found tao reveal extensive hydrogen and skeletal migrations. The structures of the fragments have been confirmed by deuterium labelling and exact mass measurement. The compounds revealed striking differences in their spectra depending on the nature of the substituents. 相似文献
33.
Syntheses and structures of isomeric [6.6]- and [8.8]cyclophanes with 1,4-dioxabut-2-yne and 1,6-dioxahexa-2,4-diyne bridges 总被引:1,自引:0,他引:1
Srinivasan M Sankararaman S Hopf H Dix I Jones PG 《The Journal of organic chemistry》2001,66(12):4299-4303
All three isomers (ortho, meta, and para) of [8.8]cyclophane bearing 1,6-dioxahexa-2,4-diyne bridges have been synthesized and structually characterized by single-crystal X-ray crystallography to determine the conformation of the cyclophanes and their cavity dimensions. The three isomeric [6.6]cyclophanes bearing 1,4-dioxabut-2-yne bridges have also been synthesized from but-2-yne-1,4-diol ditosylate and the isomeric dihydroxybenzenes. The [6.6]orthocyclophane has been structurally characterized by single-crystal X-ray crystallography. The energy-minimized structures from the semiempirical AM1 calculations of these cyclophanes compare very well with the structures obtained by X-ray crystallography. 相似文献
34.
The kinetics and mechanism of thermal polymerization of acrylonitrile initiated by Mn(III) pyrophosphate — poly(ethylene glycol) (PEG, molecular weight 6000) redox system in aqueous sulfuric acid medium was studied in the temperature range 30–60°C. The overall rates of polymerization and the disappearance of Mn3+ were determined. The polymerization was initiated by the organic free radical produced from the Mn3+-PEG reaction and the termination was by the metal ions. The rate of polymerization of acrylonitrile was found to be directly proportional to the square of the monomer concentration and first power of PEG concentration, and inversely proportional to the concentration of Mn3+. The rate of manganic ion disappearance was found to be directly proportional to manganic ion concentration and PEG concentration, and independent of the monomer concentration. Based on these observations, a plausible reaction scheme was suggested and suitable kinetic expressions were evaluated. 相似文献
35.
T. Ashok Reddy M. Srinivasan 《Journal of polymer science. Part A, Polymer chemistry》1988,26(4):1051-1061
Novel polybenzimidazoles containing thiaxanthone heterocyclic units were synthesised from 2,7-thiaxanthonedicarboxylic acid-5,5′-dioxide and 2,8-thiaxanthonedicarboxylic acid-5,5′-dioxide and two aromatic tetramine hydrochlorides by PPA solution polycondensation in 60–70% yield. Two model compounds, 2,7-bis(2-benzimidazolyl)thiaxanthone-5,5′-dioxide and 2,8-bis(2-benzimidazolyl)thiaxanthone-5,5′-dioxide, were prepared and characterized by spectral methods. The polybenzimidazoles have inherent viscosities in the range 1.13–1.50 dL/g and decomposition temperatures of 495–560°C. The effect of thiaxanthone units on polymer properties are discussed. 相似文献
36.
A primal transportation algorithm is devised via post-optimization on the costs of a modified problem. The procedure involves altering the costs corresponding to the basic cells of the initial (primal feasible) solution so that it is dual feasible as well. The altered costs are then successively restored to their true values with appropriate changes in the optimal solution by the application of cell or area cost operators discussed elsewhere. The cell cost operator algorithm converges to optimum within (2T – 1) steps for primal nondegenerate transportation problems and [(2T + 1) min (m, n)] – 1 steps for primal degenerate transportation problems, whereT is the sum of the (integer) warehouse availabilities (also the sum of the (integer) market requirements) andm andn denote the number of warehouses and markets respectively. For the area cost operator algorithm the corresponding bounds on the number of steps areT and (T + 1) min (m, n) respectively.This report was prepared as part of the activities of the Management Sciences Research Group, Carnegie—Mellon University, under Contract N00014-67-A-0314-0007 NR 047-048 with the U.S. Office of Naval Research. 相似文献
37.
La2O(CN2)2 was synthesized from a 1:1:2 molar reaction mixture of LaCl3, LaOCl, and Li2(CN2) at 650 °C. Well developed single crystals were grown from a LiCl‐KCl flux. The crystal structure was refined as monoclinic (space group C2/c, Z = 2, a = 13.530(2) Å, b = 6.250(1) Å, c = 6.1017(9) Å, β = 104.81(2)°) from single crystal X‐ray diffraction data. The La3+ and (CN2)2— ions in the crystal structure of La2O(CN2)2 can be compared to Fe3+ and S22— ions in the cubic pyrite structure, being arranged like in a distorted NaCl type structure with their centers of gravity. In addition, the O2— ions in La2O(CN2)2 are occupying 1/4 of the tetrahedral voids formed by the arrangement of metal ions. 相似文献
38.
Summary Copper has been determined gravimetrically as its bis-salicylaldehyde-ethylenediamine complex of the composition C16H14O2N2 · Cu, dried at 100–120° C. The complex is completely precipitated in theph range of 10.5–13.5, adjusted with ammonia or caustic alkali. It is stable in presence of excess ammonia, 0.1 N alkali, ammonium salts and complexing agents as tartrate, citrate, sodium-thiosulphate, fluoride, thiourea, triethanolamine and EDTA. In presence of tartrate and ammonia the ions of alkali metals, alkaline earths, Ag+, Tl+, Tl3+, Pb2+, Cd2+, Co2+, Mn2+, Pd2+, Al3+, Cr3+, La3+, Ce3+, Au3+, Pt4+, Ti4+, Zr4+, Th4+, UO2
2+ and anions as VO3
–, MoO4
2–, WO4
2–, CrO4
2–, PO4
3–, AsO4
3– do not interfere. Ni2+ and Hg2+ are masked by tartrate, EDTA and ammonia; As3+, Sb3+ and Sn2+ are separated using fluoride as the complexing agent; at an alkalinity of 0.1 N caustic alkali in presence of tartrate As3+, Sb3+, Sn2+, Bi3+, Zn2+ and Fe3+ are separated. Fe3+ can also be separated using triethanolamine as the masking agent at aph of about 13.0. Copper can be separated from almost all the ions, thus affording a highly selective method for the determination of copper.
Part I: Singh, B. R., and S. Kumar: Z. analyt. Chem. 185, 211 (1962). 相似文献
Zusammenfassung Es wird eine gravimetrische Methode zur Bestimmung von Kupfer beschrieben, die auf der Bildung des Bis-salicylaldehyd-äthylendiaminkomplexes beruht. Dieser hat die Zusammensetzung C16H14O2N2 · Cu. Die Fällung wird imph-Bereich 10,5–13,5 (mit Ammoniak oder Alkalilauge eingestellt) vorgenommen und der Niederschlag bei 100°–120° C getrocknet. Der Komplex ist beständig in Gegenwart von überschüssigem Ammoniak, 0,1 n Alkali, Ammoniumsalzen sowie Tartrat, Citrat, Natriumthiosulfat, Fluorid, Thioharnstoff, Triäthanolamin und ÄDTA. In Gegenwart von Tartrat und Ammoniak stören nicht: Alkalien, Erdalkalien, Ag+, Tl+, Tl3+, Pb2+, Cd2+, Co2+, Mn2+, Pd2+, Al3+, Cr3+, La3+, Ce3+, Au3+, Pt4+, Ti4+, Zr4+, Th4+, UO2 2+ sowie VO3 –, MoO4 2–, WO4 2–, CrO4 2–, PO4 3– und AsO4 3+. Ni2+ und Hg2+ können mit Tartrat, ÄDTA und Ammoniak maskiert werden, As3+, Sb3+ und Sn2+ mit Fluorid. In 0,1 n ätzalkalischer Lösung in Gegenwart von Tartrat können As3+, Sb3+, Sn2+, Bi3+, Zn2+ und Fe3+ abgetrennt werden. Fe3+ kann ebenfalls mit Triäthanolamin beiph 13,0 maskiert werden. Das beschriebene Verfahren erlaubt somit eine Abtrennung des Kupfers von fast allen anderen Ionen.
Part I: Singh, B. R., and S. Kumar: Z. analyt. Chem. 185, 211 (1962). 相似文献
39.
Damodaran S 《Analytical and bioanalytical chemistry》2003,376(2):182-188
A new circular dichroism (CD) spectroscopy technique for studying conformational changes in proteins in situ at the air-water interface is described. By using this technique, conformations of four proteins, viz., beta-casein, bovine serum albumin (BSA), lysozyme, and fibrinogen in the adsorbed state at the air-water interface have been studied. beta-Casein, which is predominantly in a disordered state in solution, assumes a beta-sheet conformation at the air-water interface. On the other hand, lysozyme and fibrinogen, which are alpha+beta-type proteins in solution, become beta-type proteins by completely transforming their alpha-helix structure into beta-sheets. Bovine serum albumin, which is an alpha-type protein in solution, loses its alpha-helix and becomes a disordered protein at the air-water interface. The results indicated that during unfolding and film formation at the interface, structural changes in proteins, regardless of their initial native state, follow the course of increasing beta-sheet and disordered structure and decreasing alpha-helix content. Although this seems to be the general trend, the exceptional case of BSA suggests, however, that this is not universal. 相似文献
40.
Wong PS Srinivasan N Kasthurikrishnan N Cooks RG Pincock JA Grossert JS 《The Journal of organic chemistry》1996,61(19):6627-6632
Membrane introduction mass spectrometry (MIMS) allows on-line monitoring of the products of photolysis (254 nm) of benzyl acetate in aqueous methanol and 3,5-dimethoxybenzyl acetate in water. The reaction mixture is continuously exposed to a silicone membrane through which analyte molecules permeate into a triple quadrupole mass spectrometer for qualitative and quantitative analysis. Ionization is achieved by either isobutane or ammonia chemical ionization, and ions characteristic of the reactant ester and its products are monitored simultaneously and continuously. Three products, benzyl methyl ether, ethylbenzene, and bibenzyl are observed in the benzyl acetate photolysis. Two products, 3,5-dimethoxybenzyl alcohol and 3,5-dimethoxyethylbenzene, are formed in the photolysis of 3,5-dimethoxybenzyl acetate. Quantitation is achieved through calibration using external standard solutions and, in the case of benzyl methyl ether, tandem mass spectrometry is used to verify product identification. During the photolysis of benzyl acetate, benzyl methyl ether and ethylbenzene are produced at onset with similar efficiencies. For the 3,5-dimethoxy ester photolysis, performed in aqueous solution, the efficiency of formation of the polar product 3,5-dimethoxybenzyl alcohol is about 300 times greater than that of the nonpolar product 3,5-dimethoxyethylbenzene. The results show that the relative reaction rates are dependent on the solvent and on the photon intensity and are consistent with earlier off-line experiments by Pincock et al. which showed that the photolysis proceeds through both ion and radical pair intermediates. To the best of our knowledge, the work reported here describes the first analysis of the photochemistry of an aralkyl ester in water and the first use of on-line mass spectrometry in a mechanistic study. 相似文献