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101.
102.
The first examples of direct palladium-catalyzed arylation and heteroarylation of cyclopropenes have been demonstrated. This method allows for efficient synthesis of various tetrasubstituted cyclopropenes, incuding nonracemic cyclopropenes, which are not available via known asymmetric cyclopropenation methods. Mechanistic studies strongly suggest an electrophilic path for this Heck-type transformation. 相似文献
103.
A simple, highly selective and sensitive method for the determination of 14 representative alkylphenols from phenol (C0) to nonylphenol (C9) in produced water is described. Solid-phase extraction (SPE) by anion-exchange sorbent is used to extract alkylphenols from produced water. The samples are then derivatised by pentafluorobenzoyl chloride and analysed on GC-MS (negative ion chemical ionisation, NCI). The derivatisation procedure has been validated by means of two-level factorial design (2(7-4)) experiments. Quantification is done with isotope dilution of five internal standards of different alkyl chain length. The detection limits were at low ng/l levels. A comparison with GC-MS analysis of non-derivatised alkylphenol samples revealed the advantage of derivatisation as described in the method. 相似文献
104.
Alexander L. Stroyuk Ivan V. Sobran Anna V. Korzhak Alexandra E. Raevskaya Stepan Ya. Kuchmiy 《Colloid and polymer science》2008,286(5):489-498
Photocatalytic activity of CdS and Cd
x
Zn1−x
S nanoparticles in the polymerization of acrylamide and acrylic acid in aqueous solutions has been found. It has been shown
that the most probable way of the photogeneration of primary radicals is the reduction of an adsorbed monomer by the conduction
band electrons of the semiconductor nanoparticles, a monomer oxidation by the valence band holes and atomic hydrogen addition
to a monomer being complementary photoinitiation routes. A correlation between the composition of CdxZn1-xS nanoparticles and their photocatalytic activity in the acrylamide polymerization has been established. It has been shown
that an increase in the quantum yield of the photopolymerization in a sequence СdS < Cd0.75Zn0.25S < CdS0.5Zn0.5S < Cd0.3Zn0.7S originates from a concurrent increase of the conduction band potential of the semiconductor nanoparticles. A kinetic equation
of the photocatalytic acrylamide polymerization has been derived. Quantum yields of the photoinitiation have been found to
be as small as 10−4 to 10−3. 相似文献
105.
Anna V. Korzhak Natalia I. Ermokhina Alexander L. Stroyuk Viktor K. Bukhtiyarov Alexandra E. Raevskaya Valentina I. Litvin Stepan Ya. Kuchmiy Vladimir G. Ilyin Piotr A. Manorik 《Journal of photochemistry and photobiology. A, Chemistry》2008,198(2-3):126-134
Na+ complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130–140 m2/g, pore diameter 5–9 nm and anatase content 70–90%. The mesoporous TiO2 samples prepared were found to have photocatalytic activity in CuII, NiII and AgI reduction by aliphatic alcohols. The resulting metal–semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water–alcohol mixtures, their efficiency being 50–60% greater than that of the metal-containing nano-composites based on TiO2 Degussa P25.The effects of the thermal treatment of mesoporous TiO2 upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO2/Ag0 to TiO2/Ni0 to TiO2/Cu0 was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal–semiconductor nanocomposites. 相似文献
106.
Location of Framework Al Atoms in the Channels of ZSM‐5: Effect of the (Hydrothermal) Synthesis 下载免费PDF全文
Dr. Veronika Pashkova Dr. Stepan Sklenak Petr Klein Dr. Martina Urbanova Dr. Jiří Dědeček 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):3937-3941
27Al 3Q MAS NMR and UV/Vis spectroscopy with bare CoII ions as probes of Al pairs in the zeolite framework were employed to analyze the location of framework Al atoms in the channel system of zeolite ZSM‐5. Furthermore, the effect of Na+ ions together with tetrapropylammonium cation (TPA+) in the ZSM‐5 synthesis gel on the location of Al in the channel system was investigated. Zeolites prepared using exclusively TPA+ as a structure‐directing agent (i.e., in the absence of Na+ ions) led to 55–90 % of Al atoms located at the channel intersection, regardless the presence or absence of Al pairs [Al?O?(Si?O)2?Al sequences in one ring] in the zeolite framework. The presence of Na+ ions in the synthesis gel did not modify the Al location at the channel intersection (55–95 % of Al atoms) and led only to changes in i) the distribution of framework Al atoms between Al pairs (decrease) and single isolated Al atoms (increase), and ii) the siting of Al in distinguishable framework tetrahedral sites. 相似文献
107.
Stepan A. Ukhanev Sergei V. Fedorov Leonid B. Krivdin 《Magnetic resonance in chemistry : MRC》2022,60(9):869-876
The substituent α-, β-, and γ-effects of the elements of the second and third periods on 19F NMR chemical shifts are evaluated including the establishment of stereochemical dependence of γ-effect, the latter particularly important in stereochemical studies of fluorine-containing compounds. Benchmark calculations performed for a series of 32 simple inorganic fluorine-containing molecules demonstrated a markedly good correlation between calculated and experimental fluorine chemical shifts characterized by a mean absolute error of 22.5 ppm in the range of about 900 ppm, which corresponds to a 2.5% error in the percentage terms. 相似文献
108.
Ivan Hevus Dean C. Webster John McNamara Nicole G. Ricapito Stepan Tymoshenko 《Journal of polymer science. Part A, Polymer chemistry》2021,59(8):665-674
The applicability of polyesters across a wide range of fields creates a demand for novel polyester structures that can offer advanced product performance. Two critical factors to the development of unique polymer architectures are the speed at which new polymeric systems can be synthesized and the available selection of monomers from which polymers are designed. Herein, we successfully demonstrate the applicability of a high-throughput (HT) approach to polyesterification reaction between dicarboxylic acids and diols in reaction conditions similar to those used in industry. Furthermore, we apply our HT design to a series of bio-based monomers whose unique structures offer potential for enhanced properties in polyester-based systems. Using a custom-built array of small-scale film reactors, we conducted a parallel screening of 13 bio-based dicarboxylic acids as potential monomers in the synthesis of polyester polyols through copolymerization with 1,6-hexanediol. The polyester polyols were characterized for their molecular weight and thermal properties. Carrying out polyesterification reactions in small-scale film reactors is seen as a quick and powerful tool for screening the effectiveness of a series of potential monomers, as this method offers highly controllable and reproducible reaction conditions in every reactor coupled with the ability to use a minimum amount of reagents. 相似文献
109.
110.
Daria Uryupina Nikolay Panov Maria Kurilova Anna Mazhorova Roman Volkov Stepan Gorgutsa Olga Kosareva Andrei Savel’ev 《Applied physics. B, Lasers and optics》2013,110(1):123-130
Complex experimental study of spectral, spatial and temporal behaviors of the IR shifted component observed under filamentation of the collimated femtosecond laser beam (80 GW, 50 fs, 805 nm) in molecular gases showed that this component behaves like a Raman soliton. Namely, it is confined in all domains: (a) it propagates within the filament core, (b) it has a stable duration of 30 fs along the filament, and (c) its spectrum shifts as a whole from 820 to 870 nm on the distance of 2 m from the filament start. A simple model explaining the origin of anomalous group velocity dispersion in the plasma channel of a filament is suggested. 相似文献