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Wyszukujesz frazę "Lewis acid" wg kryterium: Temat


Wyświetlanie 1-6 z 6
Tytuł:
Complexation of polyaniline with Lewis acids - a Mössbauer spectroscopy study
Autorzy:
Bieńkowski, K.
Oddou, J.
Horner, O.
Kulszewicz-Bajer, I.
Genoud, F.
Suwalski, J.
Pron, A.
Powiązania:
https://bibliotekanauki.pl/articles/148872.pdf
Data publikacji:
2003
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
polyaniline
Lewis acid doping
Mössbauer effect spectroscopy
Opis:
Doping with Lewis acid is a new method for improving solution processibility of conductive polyaniline. We report here detailed Mössbauer spectroscopy studies of polyaniline complexed with Lewis acids containing Mössbauer active nuclei, namely SnCl4 and FeCl3. Films of Lewis acid doped polyaniline cast from nitromethane solutions show stoichiometries of PANI(MeCln)1(CH3NO2)1 (where n = 3 or 4, Me denotes Sn or Fe and PANI denotes one aniline repeat unit), which means that both types of polyaniline nitrogens (imine and amine) participate in the complexation reaction, and one solvent molecule is introduced in the polymer matrix per one Lewis acid molecule. Mössbauer parameters of polyaniline doped with SnCl4 are consistent with hexacoordinated Sn(IV) in an environment of non-equivalent ligands. The spectrum of PANI doped with FeCl3 consists of two doublets with distinctly different Mössbauer parameters, which can be ascribed to two types of complexing sites (amine and imine nitrogens). From the temperature dependence of the isomer shift and the recoil free absorption, we have calculated the Mössbauer lattice temperature, ?m, as probed by both complexing sites, which are 83 K for amine and 126 K for imine sites.
Źródło:
Nukleonika; 2003, 48,suppl.1; 3-7
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Lewis acids immobilized in ionic liquid – application for the acetal synthesis
Autorzy:
Janus, E.
Powiązania:
https://bibliotekanauki.pl/articles/778768.pdf
Data publikacji:
2013
Wydawca:
Zachodniopomorski Uniwersytet Technologiczny w Szczecinie. Wydawnictwo Uczelniane ZUT w Szczecinie
Tematy:
acetal formation
ionic liquid
Lewis acid
1,1-diethoxycyclohexane
Opis:
Catalytic systems composed of metal chloride (InCl3, ScCl3, YCl3, YbCl3, LaCl3, BiCl3, ZnCl3 and CuCl3) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)-imide, [C1C4Pyrr][NTf2] as ionic liquid were prepared. Catalytic activity of all the systems were compared in acetalization reaction between cyclohexanone and triethyl orthoformate. 1,1-Diethoxycyclohexane were formed with high yield and the selectivity at 0°C within 5 minutes. Selected metal chlorides immobilized in ionic liquid were recycled 5 times without a decrease in their activities.
Źródło:
Polish Journal of Chemical Technology; 2013, 15, 3; 78-80
1509-8117
1899-4741
Pojawia się w:
Polish Journal of Chemical Technology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Asymetryczne reakcje pericykliczne katalizowane kompleksami magnezu
Magnesium-catalyzed asymmetric pericyclic reactions
Autorzy:
Czombik, Anna
Powiązania:
https://bibliotekanauki.pl/articles/2200433.pdf
Data publikacji:
2022
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
chiralność
kataliza asymetryczna
reakcja pericykliczna
kwas Lewisa
magnez
chirality
asymmetric catalysis
pericyclic reactions
Lewis acid
magnesium
Opis:
II Group-metals, like magnesium, are one of the most widespread elements in the environment. The abundance of II-group metals in the Earth’s crust is over 108 times greater than the precious metals. For the industrial applications, the important factors are the low costs of production and higher accessibility of their compounds. This puts the spotlight on alkaline-earth metals competing with transition elements as catalysts in organic synthesis. Features of their derivatives, like mild Lewis acidity and strong Brønsted basicity enabled them to catalyze reactions where Lewis-acidactivation of the substrate is essential. In this review the emphasis was put on magnesium-catalyzed pericyclic reactions, which are recognized as one of the most important methods of new carbon-carbon or carbon-heteroatom bonds formation. Using the catalysts based on II-group metal cations and chiral ligands, a highly stereoselective conversion of achiral substrates into enantioenriched products is possible. The Mg-based catalysts have been used in Diels-Alder, ene and 1,3-dipolar additions. Described synthesis methods were characterized by high efficiency (chemical yields and enantiomeric excesses). Where applicable, the relationships between the structure of catalyst/substrates, conditions and efficiency were discussed. Just now there are a few applications, for example in synthesis of alkaloid (–)-manzacidine or antibiotic of algal origin – (–)-malyngolide.
Źródło:
Wiadomości Chemiczne; 2022, 76, 9-10; 755--788
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Comparative study of continuous-flow microreactors based on silica monoliths modified with lewis acid centres
Autorzy:
Ciemięga, A.
Maresz, K.
Malinowski, J. J.
Mrowiec-Białoń, J.
Powiązania:
https://bibliotekanauki.pl/articles/185145.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
flow chemistry
silica monolith
Lewis acid centres
MPV reduction
przepływ chemii
monolit krzemionkowy
Centra kwasu Lewisa
Redukcja MPV
Opis:
Silica multichannel monoliths modified with zirconia, titania and alumina have been used as reactive cores of microreactors and studied in chemoselective reduction (MPV) of cyclohexanon/benzaldehyde with 2-butanol as a hydrogen donor. The attachment of metal oxides to the silica surface was confirmed by FT–IR spectroscopy, and dispersion of metal oxides was studied by UV–Vis spectroscopy. the catalytic activity of the lewis acid centres in both chemical processes decreased in the order zirconia > alumina > titania. This activity is in good agreement with dispersion and coordination of metal species. good stability of zirconia-grafted reactors was confirmed. high porosity of the monoliths and the presence of large meandering flow-through channels with a diameter of ca. 30 mm facilitate fluid transport and very effective mixing in the microreactors. The whole synthesis process is perfectly in line with trends of modern flow chemistry.
Źródło:
Chemical and Process Engineering; 2018, 39, 1; 33--38
0208-6425
2300-1925
Pojawia się w:
Chemical and Process Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Synthesis of tetrahydroquinolines and quinoline derivatives through the Lewis acid catalysed Povarov reaction: A comparative study between multi step and multi-component methods
Autorzy:
Hellel, Djamila
Chafaa, Fouad
Nacereddine, Abdelmalek Khorief
Powiązania:
https://bibliotekanauki.pl/articles/35146220.pdf
Data publikacji:
2023
Wydawca:
Radomskie Towarzystwo Naukowe
Tematy:
quinoline
Lewis acid catalyst
Povarov
cycloaddition
imine
vinyl ethers
chinolina
kataliza kwasowa Lewisa
Powarow
cykloaddycja
iminy
etery winylowe
Opis:
In this work, we have synthesised a new disubstituted tetrahydroquinolines by the Povarov [4+2] cycloaddition reaction between imines derivatives and an electron-rich olefin such as vinyl ethers. These reactions were carried out in the presence of different acid catalysts in its two versions, multi-step reaction starting with imine synthesis and multi-component reaction in which the imine is formed in situ. The reactivity of the cycloaddition reaction is directly attributed to the nature of the reagents, the used synthetic strategy, in which the obtained yield is found in the case of multi-step reactions lower than that in the multi-component reaction one. Additionally, the multi-step reactions are faster kinetically in comparison with that of the multi-component one. The nature of the catalyst directly increases the rate and enhances the yield of the reactions.
Źródło:
Scientiae Radices; 2023, 2, 3; 295-308
2956-4808
Pojawia się w:
Scientiae Radices
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Wiązanie wodorowe i inne oddziaływania typu kwas Lewisa-zasada Lewisa
The hydrogen bond and the other Lewis acid-Lewis base interactions
Autorzy:
Grabowski, S. J.
Powiązania:
https://bibliotekanauki.pl/articles/171998.pdf
Data publikacji:
2011
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
wiązanie wodorowe
wiązanie halogenowe
wiązanie wodorkowe
oddziaływanie kwas Lewisa-zasada Lewisa
teoria Atomy w Cząsteczkach
hydrogen bond
halogen bond
hydride bond
Lewis acid-Lewis base interaction
atoms in molecules theory
AIM
Opis:
Hydrogen bond is analyzed very often since its importance in numerous chemical, physical and biological processes is very well known. It covers the broad range of various interactions; sometimes this is the subject of discussions and polemics if some of them may be classified as hydrogen bonds. This is because there are numerous definitions of hydrogen bond interaction, often they are hardly accepted since they are not univocal. For example one can mention different types of the proton acceptors for hydrogen bonds; one center electronegative atoms, multi-center acceptors such as đ-electrons or even ó-electrons. There are the other interactions which play the key role in various processes and phenomena. All are often named as no-covalent interactions but the other term, Lewis acid–Lewis base interactions seems to be more accurate. One can mention halogen bond, hydride bond or dihydrogen bond. These interactions may be treated as counterparts or competitors of hydrogen bond. The common characteristic for them, including hydrogen bond, is the electron charge transfer from the Lewis base to the Lewis acid. It was found that the amount of this transfer corresponds roughly to the strength of the interaction. In recent years the ó-hole concept was introduced and developed and it was applied to the Lewis base–Lewis acid interactions. According to this concept the atomic centers are characterized by the presence of the regions of positive and negative electrostatic potentials; very often both regions are detected even for atoms which are commonly known as electronegative ones. In such a way halogen atoms, especially if connected by covalent bond with carbon, may act as Lewis acids and also as Lewis bases. In the first case the halogen bond is formed, recently extensively studied. In this review the characteristics of different Lewis base–Lewis acid interactions are given as well as their common features are presented.
Źródło:
Wiadomości Chemiczne; 2011, 65, 11-12; 975-1001
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-6 z 6

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