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141.
The spectrophotometric determination of ammonium ion in water by flow-injection analysis with a membrane-separator and a pH indicator for detection is studied in detail. The relations derived facilitate the selection of appropriate solution compositions or the prediction of sensitivity. It is shown that 1.5×10?5 M bromocresol purple (pH 6.8) as acceptor solution gives the maximal sensitivity in the flow system with a laboratory-made separation unit. Application of ultrasonic radiation in the separation step and the use of different flow rates for the donor and acceptor streams may result in increased permeation of ammonia and a correspondingly high sensitivity. By modifying the acceptor solution so that the sensitivity is decreased, more concentrated samples such as urine can be analyzed by direct injection without prior dilution. In this procedure, the sample rate was 60 h?1 for ammonium concentration of more than 10?5 M and 30–40 h?1 for concentrations in the range 3×10?7?10?5 M. The detection limit was about 3×10?7 M. 相似文献
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Enantioselective copper-catalyzed 1,4-additions of dialkylzincs to enones were carried out in the presence of 1 mol % of Cu(OTf)2 and 2.5 mol % of an N,N,P-ligand possessing a tert-butyl group at the adjacent position of the nitrogen of pyridine to afford the corresponding 1,4-adducts in up to 98% ee. 相似文献
144.
Dr. Jing Li Dr. Martin J. Lear Prof. Yujiro Hayashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(19):5901-5905
Cyclopropanes are traditionally prepared by the formal [2+1] addition of carbene or radical based C1 units to alkenes. In contrast, the one-pot intermolecular cyclopropanation of alkanes by redox active C1 units has remained unrealised. Herein, we achieved this process simply by exposing β-aryl propionitriles and C1 radical precursors (N-oxy esters) to base and blue light. The overall process is redox-neutral and a photocatalyst, whether metal- or organic-based, is not required. Our findings support that single electron transfer (SET) from the α-cyano carbanion of the propionitrile to the N-oxy ester is facilitated by blue-light via their electron donor–acceptor (EDA) complex. The α-cyano carbon radical thus formed can then lose a β-proton to form a π-resonance stabilised radical anion that preferentially couples at the benzylic β-position with a decarboxylated C1 radical unit. This new transition metal-free chemistry tolerates both electron rich and electron deficient (hetero)aryl systems, even sulfide or alkene functionality, to afford a range of cis-aryl/cyano cyclopropanes bearing congested tetrasubstituted quaternary carbons. 相似文献
145.
Akihiko Ishii Masashi Saitoh Tetsuhiko Kawai Masami Murata Juzo Nakayama 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8-9):2025-2026
The reaction of isolable dithiirane 1-oxides with (Ph 3 P) 2 Pt( m 2 -C 2 H 4 ) provided the title complexes in high yields. 31 P NMR spectroscopy of the phosphine ligands of the complexes and x-ray crystallographic analysis of a complex were reported. 相似文献
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O. I. Lebedev † J. Verbeeck G. Van Tendeloo N. Hayashi T. Terashima M. Takano 《哲学杂志》2013,93(36):3825-3841
Thin films of SrFeO3??? x (0?≤?x?≤?0.5) (SFO) grown on a (LaAlO3)0.3 (SrAl0.5Ta0.5O3)0.7 (LSAT) substrate by pulsed laser deposition have been structurally investigated by electron diffraction and high resolution transmission electron microscopy for different post-deposition oxygen treatments. During the deposition and post-growth oxidation, the oxygen-reduced SFO films accept extra oxygen along the tetrahedral layers to minimize the elastic strain energy. The oxidation process stops at a concentration SFO2.875 and/or SFO2.75 because a zero misfit with the LSAT substrate is reached. A possible growth mechanism and phase transition mechanism are suggested. The non-oxidized films exhibit twin boundaries having a local perovskite-type structure with a nominal composition close to SFO3. 相似文献
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For a spatial characteristic, there exist commonly fat-tail frequency distributions of fragment-size and -mass of glass, areas enclosed by city roads, and pore size/volume in random packings. In order to give a new analytical approach for the distributions, we consider a simple model which constructs a fractal-like hierarchical network based on random divisions of rectangles. The stochastic process makes a Markov chain and corresponds to directional random walks with splitting into four particles. We derive a combinatorial analytical form and its continuous approximation for the distribution of rectangle areas, and numerically show a good fitting with the actual distribution in the averaging behavior of the divisions. 相似文献