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排序方式: 共有134条查询结果,搜索用时 562 毫秒
1.
J. Goworek W. Stefaniak Agnieszka Kierys Mariola Iwan 《Journal of Thermal Analysis and Calorimetry》2007,87(1):217-222
Mesoporous silica material of MCM-41 type was synthesized by co-condensation
of highly concentrated octyltriethoxysilane (OTEOS), octadecyltriethoxysilane
(ODTEOS) and tetraethoxysilane (TEOS). The obtained hybrid materials were
characterized using XRD, TG-DSC and low temperature adsorption/desorption
of nitrogen. It was shown that the applied method of synthesis allows to obtain
silica of MCM-41 type with a high degree of hydrocarbon saturation. 相似文献
2.
Mariola Koszytkowska-Stawińska 《Tetrahedron letters》2004,45(28):5437-5440
N-Pivaloyloxymethyl amides and sulfonamides, readily available from N-alkylation of both amides and sulfonamides with commercial chloromethyl pivaloate, were converted into acyclic azanucleosides via a one-pot base silylation/nucleoside coupling procedure. 相似文献
3.
Prof. Dr. José Luis García Ruano Dr. José Alemán Leyre Marzo Dr. Cuauhtémoc Alvarado Dr. Mariola Tortosa Dr. Sergio Díaz‐Tendero Dr. Alberto Fraile 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(27):8414-8422
We describe the unexpected behavior of the arylsulfonylacetylenes, which suffer an “anti‐Michael” addition of organolithiums producing their alkynylation under very mild conditions. The broad scope, excellent yields, and simplicity of the experimental procedure are the main features of this methodology. A rational explanation of all these results can be achieved by theoretical calculations, which suggest that the association of the organolithiums to the electrophile is a previous step of their intramolecular attack and is responsible for the unexpected “anti‐Michael” reactions observed for substituted sulfonylacetylenes. 相似文献
4.
Filip Ciesielczyk Przemysław Bartczak Karolina Wieszczycka Katarzyna Siwińska-Stefańska Magdalena Nowacka Teofil Jesionowski 《Adsorption》2013,19(2-4):423-434
The aim of this work was to obtain an inorganic oxide system containing silica and magnesium oxide, and characterized by specific physicochemical properties, in particular well-defined adsorption parameters. The preparation process was carried out according to a co-precipitation method using solutions of sodium silicate and selected inorganic magnesium salt. The oxide system obtained (MgO·SiO2) was used as a support (adsorbent) of nickel(II) ions, whose precursors were model solutions of nitrates. The effectiveness of the adsorption process was evaluated using many different analytical techniques, including atomic absorption spectroscopy, energy dispersive X-ray spectroscopy and equivalent point titration. Moreover the stability of adsorbent/adsorbate bonding was estimated. The oxide systems—adsorbents—used in the process were also analyzed according to their physicochemical properties, especially changes in adsorption parameters. The last part of the study involved evaluation of the kinetics of the adsorption process depending on time and the pH of the reaction system. 相似文献
5.
Alma Viso Roberto Fernández de la Pradilla Ana García Carlos Guerrero-Strachan Marta Alonso Mariola Tortosa 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5-6):1229-1234
Abstract Readily available p-tolylsulfinimines undergo highly stereoselective [3 + 2] cycloadditions with azomethine ylides generated from α -iminoesters and LDA to produce N-sulfinylimidazolidines. In the presence of Lewis acids, p-tolylsulfinimines react with glycine iminoester enolates to produce N-sulfinylimidazolidines, after cyclization of open chain intermediates. These mechanistically diverse processes take place with excellent regio-, stereo-, and facial selectivities, and the latter is opposite to most known reactions involving sulfinimines. Some of the resulting imidazolidines have been transformed into examples of a novel class of nonsymmetrical vicinal diamines using reductive and/or hydrolytic protocols. 相似文献
6.
The stereoselective synthesis of two epimeric penta-hydroxylated indolizidines was accomplished from 2,3:5,6-di-O-isopropylidene-α-d-mannofuranose and N-(2-methylpent-4-en-2-yl)hydroxylamine. The transformation of these substrates into the corresponding 7-oxa-1-azabicyclo[2.2.1]heptane by the intramolecular 1,3-dipolar cycloaddition was the key step of the synthesis. The adduct was transformed into the tricyclic ammonium salt by intramolecular N-alkylation. The tricyclic ammonium salt was converted to the target compounds by: (route 1) the catalytic hydrogenation; or (route 2) the reaction with sodium azide, followed by the enantioselective reduction of the resulting indolizidinone. 相似文献
7.
This article presents the investigations of the progress of conversion process of calcium aluminate hydrates formed during hydration of calcium aluminate cement at various temperature conditions occurring over time by thermal analysis method. Moreover, the differences of microstructure were also confirmed by SEM/EDS studies and X-ray diffraction analysis. On the basis of the obtained results, it is concluded that thermal analysis method is a very attractive and useful way to identify the structure of hydrated calcium aluminate cement matrix and allows estimating the degree of the conversion at different times of various process conditions. The conversion process of metastable calcium aluminate hydrates into stable hydrogarnet and gibbsite is strictly temperature dependent and could be completed at different times. Acceleration of the conversion is caused not only by the increasing external temperature of storage, but also the temperature inside the sample is very important. The self-heating, which could be strong in large sample, and occurring during first few hours of hydration of calcium aluminate cement, initiates the transformation. 相似文献
8.
Artur Wiktor Magdalena Chadzynska Katarzyna Rybak Magdalena Dadan Dorota Witrowa-Rajchert Malgorzata Nowacka 《Molecules (Basel, Switzerland)》2022,27(4)
In recent years, an increasing interest in reducing sugar consumption has been observed and many studies are conducted on the use of polyols in the osmotic dehydration process to obtain candied or dried fruits. The studies in the literature have focused on the kinetics of the process as well as the basic physical properties. In the scientific literature, there is a lack of investigation of the influence of such polyol solutions such as sorbitol and mannitol used as osmotic substances during the osmotic dehydration process on the contents of bioactive components, including natural colourants. Thus, the aim of the study was to evaluate the impact of polyols (mannitol and sorbitol) in different concentrations on the process kinetics and on chosen physical (colour and structural changes) as well as chemical (sugars and polyol content, total anthocyanin content, total polyphenol content, vitamin C, antioxidant activity) properties of osmotic-dehydrated organic strawberries. Generally, the results showed that the best solution for osmotic dehydration is 30% or 40% sorbitol solutions, while mannitol solution is not recommended due to difficulties with preparing a high-concentration solution and its crystallization in the tissue. In the case of sorbitol, the changes of bioactive compounds, as well as colour change, were similar to the sucrose solution. However, the profile of the sugar changed significantly, in which sucrose, glucose, and fructose were reduced in organic strawberries and were partially replaced by polyols. 相似文献
9.
(S)-trans-4-Phenylbut-3-en-2-ol has been obtained in excellent yields and with high enantiomeric excess in the reduction of trans-4-phenylbut-3-en-2-one using the comminuted roots of carrot (Daucus carota L.), celeriac (Apium graveolens L. var. rapaceum), and beetroot (Beta vulgaris L. subsp. Vulgaris) in isooctane. This is the first Letter of this bioreduction with plant tissue in an organic solvent. 相似文献
10.
[reaction: see text] The highly selective Claisen rearrangements of substrates bearing a sulfinyl moiety at C-5 allow for creation of up to two asymmetric centers and preserve a useful vinyl sulfoxide. 相似文献