Wyniki wyszukiwania dla: Ján Cvengroš

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Mild Stereoselective Intermolecular Acetoxylation and Azidation of α‐C−H Bonds in Tröger's Bases

Raul Pereira, Pavol Ondrisek, Alžbeta Kubincová, Elisabeth Otth, więcej

Advanced Synthesis & Catalysis > 358 > 17 > 2739 - 2744

Introduction of oxygen and nitrogen into organic molecules is one of the fundamental strategies for their functionalization. Traditional approaches rely on the formation of an activated intermediate, which is then modified in a subsequent step. Here we report a simple direct oxidative α‐acetoxylation and azidation of α‐C−H bonds in Tröger's base analogues promoted by N‐bromosuccinimide (NBS) and palladium(II)acetate...

artykuł

Accessing N‐Stereogenicity through a Double Aza‐Michael Reaction: Mechanistic Insights

Sonja Kohrt, Nico Santschi, Ján Cvengroš

Chemistry – A European Journal > 22 > 1 > 390 - 403

Further development of the chemistry and applications of chiral compounds that possess configurationally stable stereogenic nitrogen atoms is hampered by the lack of efficient strategies to access such compounds in an enantiomerically pure form. Esters of propiolic acid and chiral alcohols were evaluated as cheap and readily available Michael acceptors in a diastereoselective synthesis of N‐stereogenic...

artykuł

Flocculation Using Polyacrylamide Polymers for Fresh Microalgae

Jozef Mikulec, Gabriela Polakovičová, Ján Cvengroš

Chemical Engineering & Technology > 38 > 4 > 595 - 601

Flocculation‐sedimentation of five microalgae species was tested with high‐molecular‐weight cationic polyacrylamide flocculants. An apparent difference in the shape of flocculated particles was detected when comparing flocculation with increasing pH of the microalgae culture to that with polyacrylamide. In the case of flocculation with pH adjustment, the surface charge of the cells is neutralized...

artykuł

Chemo‐ and Stereoselective NBS‐Promoted Intermolecular Oxygenation and Nitrogenation of α‐C–H Bonds of Tertiary Diamines

Raul Pereira, Elisabeth Otth, Ján Cvengroš

European Journal of Organic Chemistry > 2015 > 8 > 1674 - 1679

A new method for the activation of the non‐benzylic α‐C–H bonds in tertiary diamines has been developed. The protocol relies on an N‐bromosuccinimide (NBS)‐mediated oxidation of carbon atoms next to the nitrogen atoms in the presence of a catalytic amount of Pd(OAc)₂ followed by an intermolecular reaction with oxygen‐ or nitrogen‐centered nucleophiles. Mechanistic studies hint towards a radical intermediate,...

artykuł

Rapid and Selective Electrophilic Trifluoromethylation of the 4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) Scaffold

Nico Santschi, Ján Cvengroš, Coraline Matthey, Elisabeth Otth, więcej

European Journal of Organic Chemistry > 2014 > 29 > 6371 - 6375

This report deals with the rapid functionalization of the 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) scaffold by means of electrophilic trifluoromethylation. Subjecting dye 2 to the disclosed protocol led to the successful isolation of 3‐trifluoromethylated derivative 9. Subsequent comparison of structural and electronic properties allowed for the characterization of changes imparted by the...

artykuł

Tröger's Base Derived Phosphanes for Suzuki–Miyaura and Buchwald–Hartwig Cross‐Coupling Reactions

Raul Pereira, Ján Cvengroš

European Journal of Organic Chemistry > 2013 > 20 > 4233 - 4237

A library of bis(phosphane) ligands based on the 2,8‐substituted Tröger's base scaffold was synthesized through an efficient two‐step protocol by starting from a commercially available aniline. The new ligands proved their efficiency in palladium‐catalyzed Suzuki–Miyaura cross‐coupling reactions and Buchwald–Hartwig aminations of aryl chlorides and bromides.

artykuł

Standard methyl esters from used frying oils

Andrea Kleinová, Zuzana Cvengrošová, Ján Cvengroš

Fuel > 2013 > 109 > Complete > 588-596

Used frying oils (UFO) are an interesting and important source material for manufacturing of methyl esters (ME) as alternative fuels. The technology of methyl ester preparation from UFO (abbreviated as UFOME) is similar as in the case of fresh oils. However, in spite of a high degree of acylglycerol conversion into methyl esters, UFOME frequently exhibit insufficient methyl ester content, increased...

artykuł

Novel motif for bidentate P,N ligands. Application to Pd-catalyzed Suzuki cross-coupling reactions

Raul Pereira, Ján Cvengroš

Journal of Organometallic Chemistry > 2013 > 729 > Complete > 81-85

A library of novel C ₂ -symmetric P,N ligands based on a Tröger’s base backbone was prepared via a concise two-step synthesis starting from a commercially available aniline derivative. X-ray crystallography and ³¹ P NMR studies confirm that a single ligand molecule can accommodate two palladium atoms via coordination to nitrogen and phosphorus. Preliminary results proved the synthetic...

artykuł

Oxidative stability of FAME prepared from oxidatively degraded rapeseed oils

Andrea Kleinová, Zuzana Cvengrošová, Ján Cvengroš

Fuel > 2013 > 106 > Complete > 749-756

The present paper contains induction period (IP) values obtained from Rancimat and peroxide value (PV) tests of oxidatively degraded rapeseed oils. Methyl esters of fatty acids (FAME), prepared freshly from these oxidatively degraded oils and two months after the preparation are simultaneously evaluated for the samples kept in open transparent bottles at laboratory temperature, without agitation during...

artykuł

Simulation of a new regeneration process of solvents with ionic liquid by short-path distillation

Marek Blahušiak, Štefan Schlosser, Ján Cvengroš

Separation and Purification Technology > 2012 > 97 > Complete > 186-194

A new promising process for the regeneration of solvents with ionic liquid (IL) by short-path distillation (SPD) has been proposed and its application potential analyzed by simulation. Main advantage of this process compared to classical stripping with alkali solution is that the product is in form of free acid, not its salt and the consumption of chemicals is reduced. The model loaded solvent with...

artykuł

Catalytic role of lignocellulosic materials in triacylglycerol cracking

Eduard Buzetzki, Katarína Sidorová, Zuzana Cvengrošová, Ján Cvengroš

Journal of Analytical and Applied Pyrolysis > 2011 > 92 > 2 > 314-323

Cracking of vegetable oils and animal fats carried out with a view to preparing fuels or fuel components for diesel engines is one of the options of reducing high molecular weight and viscosity of natural triacylglycerols (TAG). We have found out that lignocellulose shows a surprisingly high catalytic activity in TAG cracking comparable and equivalent to that achieved with zeolite catalysts NaY and...

artykuł

Effects of oil type on products obtained by cracking of oils and fats

Eduard Buzetzki, Katarína Sidorová, Zuzana Cvengrošová, Ján Cvengroš

Fuel Processing Technology > 2011 > 92 > 10 > 2041-2047

This paper deals with cracking of vegetable oils and animals fats in the presence of zeolite catalysts, the objective being preparation of liquid products similar in their properties to fossil diesel. The effects of oil/fat type on the liquid condensate yields and parameters were monitored. The tests were carried out with rapeseed, sunflower, soybean and jatropha oils as well as with used frying oils...

artykuł

The influence of zeolite catalysts on the products of rapeseed oil cracking

Eduard Buzetzki, Katarína Sidorová, Zuzana Cvengrošová, Alexander Kaszonyi, więcej

Fuel Processing Technology > 2011 > 92 > 8 > 1623-1631

The article is devoted to the study of rapeseed oil cracking in the presence of zeolite catalysts in order to prepare the liquid fraction with the properties close to fossil diesel.To evaluate the cracking products, the chromatographic methods GL and GC/MS were used, together with the determination of viscosities, acid values and densities. The cracking of rapeseed oil in the presence of zeolite-type...

artykuł

New approach to regeneration of an ionic liquid containing solvent by molecular distillation

Marek Blahušiak, Štefan Schlosser, Ján Cvengroš, Ján Marták

Chemical Papers > 2011 > 65 > 5 > 603-607

A promising new process for the regeneration of solvents with ionic liquid by molecular distillation has been proposed. The main advantage of this process compared with the classic stripping of acids with alkali solution is that the volatile organic acid is recovered with a yield of about 88 % in the form of free acid, not as its salt. Furthermore, improvement on the yield of the stripping can be...

artykuł

P‐Stereogenic Ferrocene‐Based (Trifluoromethyl)phosphanes: Synthesis, Structure, Coordination Properties and Catalysis

Aline Sondenecker, Ján Cvengroš, Raphael Aardoom, Antonio Togni

European Journal of Organic Chemistry > 2011 > 1 > 78 - 87

Diastereoselective ortho‐hydroxymethylation of (R)‐(1‐ferrocenylethyl)dimethylamine and Brønsted‐acid‐mediatednucleophilic substitution with phenyl(trifluoromethyl)phosphane affords an epimeric mixture of P‐stereogenic amine–phosphanes 4a and 4b, which are readily separated by crystallization from methanol. Subsequent substitution of the dimethylamino group with diphenylphosphane occurs without epimerization,...

artykuł

Thermooxidative stability of vegetable oils refined by steam vacuum distillation and by molecular distillation

Peter Šimon, Ján Cvengroš

European Journal of Lipid Science and Technology > 112 > 11 > 1236 - 1240

Semi‐refined rapeseed and sunflower oils after degumming and bleaching were refined by deodorization and deacidification in two ways, i.e., by steam vacuum distillation in the deodorization column Lurgi and by molecular distillation in the wiped‐film evaporator. The oxidative stability of the oils before and after the physical refining has been evaluated using non‐isothermal differential scanning...

artykuł

Totalsynthese des marinen Antibiotikums Pestalon und seine einfache Umwandlung in Pestalalacton und Pestalachlorid A

Nikolay Slavov, Ján Cvengroš, Jörg‐Martin Neudörfl, Hans‐Günther Schmalz

Angewandte Chemie > 122 > 41 > 7751 - 7754

Überraschend: Die Totalsynthese des marinen Naturstoffes Pestalon (1), eines hoch substituierten Benzophenons mit starker antibiotischer Aktivität, gab Einblicke in die überraschende Neigung dieses und verwandter Moleküle, intramolekulare Cannizzaro‐Tishchenko‐Reaktionen einzugehen. Pestalon kann mit Ammoniak bei pH 8 in Pestalachlorid A (2) überführt werden, einen stark antimykotischen Metaboliten...

artykuł

Total Synthesis of the Marine Antibiotic Pestalone and its Surprisingly Facile Conversion into Pestalalactone and Pestalachloride A

Nikolay Slavov, Ján Cvengroš, Jörg‐Martin Neudörfl, Hans‐Günther Schmalz

Angewandte Chemie International Edition > 49 > 41 > 7588 - 7591

Surprise, surprise! The total synthesis of the marine natural product pestalone (1), a highly substituted benzophenone with strong antibiotic acitivity, has provided insight into the surprising tendency of this and related molecules to undergo intramolecular Cannizzaro–Tishchenko‐type reactions. Pestalone can be readily converted into pestalachloride A, a strongly antifungal metabolite isolated from...

artykuł

New hypervalent iodine reagents for electrophilic trifluoromethylation and their precursors: synthesis, structure, and reactivity

Katrin Niedermann, Jan M. Welch, Raffael Koller, Ján Cvengroš, więcej

Tetrahedron > 2010 > 66 > 31 > 5753-5761

Several new five- and a six-membered heterocyclic monochloroiodanes, including two cationic species, were synthesized. Three of which were used for the preparation of corresponding trifluoromethylation reagents. These compounds were characterized by X-ray crystallography for a comparative structural study. A reactivity study on the trifluoromethylation of para-toluenesulfonic acid has been conducted...

artykuł

Second generation diesel fuel from renewable sources

Jozef Mikulec, Ján Cvengroš, Ľudmila Joríková, Marek Banič, więcej

Journal of Cleaner Production > 2010 > 18 > 9 > 917-926

The study is devoted to the issue of direct transformation of triacylglycerols (TAG) to diesel fuels applying a commercially available NiMo and NiW hydrorefining catalysts. It was proved that during hydrodesulphurisation also hydrodeoxygenation occurs and TAG can be converted to the fuel biocomponent by adding 6.5 % vol. of TAG to atmospheric gas oil. In this way, after hydroprocessing at mild conditions...

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angielski (23)
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Elsevier (13)
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European Journal of Organic Chemistry (4)
Fuel (2)
Fuel Processing Technology (2)
Tetrahedron (2)
Advanced Synthesis & Catalysis (1)
Angewandte Chemie (1)
Angewandte Chemie International Edition (1)
Biomass and Bioenergy (1)
Chemical Engineering & Technology (1)
Chemical Papers (1)
Chemistry – A European Journal (1)
European Journal of Lipid Science and Technology (1)
Journal of Analytical and Applied Pyrolysis (1)
Journal of Cleaner Production (1)
Journal of Organometallic Chemistry (1)
Separation and Purification Technology (1)
Tetrahedron Letters (1)
The Chemical Engineering Journal and The Biochemical Engineering Journal (1)
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