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Asymetryczne reakcje pericykliczne katalizowane kompleksami magnezu

Czombik Anna

Wiadomości Chemiczne

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2022

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[Z] 76, 9-10

755--788

EN

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.

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Lewis acids immobilized in ionic liquid – application for the acetal synthesis

Janus E.

Polish Journal of Chemical Technology

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2013

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Vol. 15, nr 3

78-80

EN

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.

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Badania nad nowymi poliketanilami

Wolska B., Rzymski W. M.

Prace Naukowe Instytutu Technologii Organicznej i Tworzyw Sztucznych Politechniki Wrocławskiej. Konferencje

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2001

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Vol. 50, nr 23

178-181

PL

Poszukując nowych metod sieciowania nasyconych elastomerów stwierdziliśmy, że uwodorniony >99% mol. kauczuk butadienowo-akrylonitrylowy można usieciować za pomocą kwasów Lewisa generowanych in situ w reakcji odpowiednio dobranego tlenku metalu(II) z polimerem zawierającym reaktywne atomy chloru, np. chlorosulfonowanym polietylenem. Szybkość i stopień usieciowania zależą od stężenia tlenku metalu i zawartości donora aktywnego chloru oraz od proporcji tych składników w mieszaninie z kauczukiem. Z badań FT-IR wynika, że sieciowanie kauczuku w omawianym przypadku związane jest z powstawanie kompleksów kwasu Lewisa z grupami nitrylowymi, katalizowaną przez kwas hydrolizą grup nitrylowych pod wpływem wilgoci oraz reakcjami powstających w ten sposób grup amidowych i karboksylowych z grupami chlorosulfonowymi, z utworzeniem wiązań poprzecznych o budowie >C-SO2-NH-CO<. Opisana niekonwencjonalna metoda sieciowania umożliwia wytwarzanie wulkanizatów HNBR o zróżnicowanym stężeniu i strukturze węzłów sieci.

EN

Investigations show that hydrogenated nitrile rubber becomes crosslinked due to the action of Lewis acid formed in situ during heating of rubber-chlorosulphonated polyethylene-ZnO blend. The rate and degree of crosslinking depend both on concentration of ZnO and CSM, sa well as on their proportion in the blend. The crosslinking of rubber is connected with the formation of Lewis acid, the formation of is complex with the nitrile groups of the rubber, the hydrolysis of -CN-groups to amide and carboxyl groups and their reactions with chlorosulphonated groups. These reactions lead to formation of complex and sulphonamide >C-SO2-NH-CO-C< crosslinks in the rubber network.