Search

Your search keyword '"Theyssen, Nils"' showing total 35 results
Start Over Author "Theyssen, Nils"
35 results on '"Theyssen, Nils"'

5. Synthetic ferripyrophyllite: preparation, characterization and catalytic application

Author

Qiao, Yunxiang, primary, Theyssen, Nils, additional, Spliethoff, Bernd, additional, Folke, Jan, additional, Weidenthaler, Claudia, additional, Schmidt, Wolfgang, additional, Prieto, Gonzalo, additional, Ochoa-Hernández, Cristina, additional, Bill, Eckhard, additional, Ye, Shengfa, additional, Ruland, Holger, additional, Schüth, Ferdi, additional, and Leitner, Walter, additional

Published
2021
Full Text
View/download PDF

16. Concerning the Role of Supercritical Carbon Dioxide in SN1 Reactions.

Author

Qiao, Yun X., Theyssen, Nils, Eifert, Tobias, Liauw, Marcel A., Franciò, Giancarlo, Schenk, Karolin, Leitner, Walter, and Reetz, Manfred T.

Subjects
*CARBON dioxide, *CARBOCATIONS, *SOLVENTS, *IONIZATION (Atomic physics), *NOBLE gases
Abstract

A series of SN1-type reactions has been studied under various conditions to clarify the role of supercritical carbon dioxide (scCO2) as reaction medium for this kind of transformations. The application of scCO2 did not result in higher yields in any of the experiments in comparison to those under neat conditions or in the presence of other inert compressed gases. High-pressure UV/Vis spectroscopic measurements were carried out to quantify the degree of carbocation formation of a highly SN1-active alkyl halide as a function of the applied solvent. No measureable concentration of carbocations could be detected in scCO2, just like in other low polarity solvents. Taken together, these results do not support the previously claimed activating effect via enhanced SN1 ionization due to the quadrupolar moment of the supercritical fluid. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

17. Selektive Oxidationsreaktionen mit molekularem Sauerstoff in komprimiertem Kohlendioxid

Author

Theyssen, Nils and Leitner, Walter

Subjects
Acetaldehyd, Alkene, Kohlendioxid, ddc:540, Selektive Oxidation, Oxidation, Überkritischer Zustand, Alkane, Chemie, Sauerstoff, Polycarnonate, überktritisches Kohlendioxid
Abstract

The present dissertation is divided into two research projects. In the first one the possibility for a synthesis of organic carbonates starting from alkenes, oxygen, carbon dioxide and aldehydes as coreductants was investigated. The first part of the consecutive reaction sequence-the stainless steel initiated synthesis of epoxides using O2/aldehyde mixtures in supercritical carbon dioxide-was successively performed by Loeker.[1] This result bares the potential for an in situ synthesis of organic carbonates by the addition of suitable catalysts. However, established catalysts of different structure and mode of operation for CO2 insertion proved not to be compatible with the reaction conditions of the epoxidation reaction. The coexistence of Lewis-base and a Brönsted-acid sites was identified as a main difficulty for the development of active and resistant catalysts. In the second project the coupled oxidation of cycloalkanes or alkylarenes with acetaldehyde (2.0 equiv.) and molecular oxygen (2.1 equiv.) was for the first time found to occur effectively in compressed carbon dioxide (16 equiv.) under mild multiphase conditions.[2] No catalyst is required but high pressure ATR-FT-IR online measurements show that the free radical reaction is heterogeneously initiated by the stainless steel of the reactor walls. Since experiments in a titanium autoclave led to comparable conversions, the initiation seems to be relative independent in terms of the reactor material. For secondary carbon atoms a high keto to alcohol ratio is observed (3.5-7.9), most probably due to the fast consecutive oxidation of alcoholic intermediates. Since C-C-scission reactions are detected only to a very small extend, tertiary carbon atoms are transformed to the corresponding alcohols with high selectivity. The obtained product distributions suggest that the strong influence of acetaldehyde is related to its function not only the determining oxygen activator and an efficient H-atom donating agent for peroxo and oxo radicals, but also a crucial reductant for hydroperoxo intermediates. In comparison with compressed N2 or Ar carbon dioxide was proven to increase the yields of alkane oxygenates under identical reaction conditions. Although the experimental results allow at present no full explanation for the enhanced conversion in CO2, a set of exclusive effects in CO2 as a reaction medium were described which are believed to play an important role for the enhanced performance in this medium. [1] F. Loeker, W. Leitner, Chem. Eur. J., 2000, 6, 2011-2015. [2] N. Theyssen, W. Leitner, Chem. Commun., 2002, 410-411.

Published
2003

26. Synthesis and Characterisation of Nonclassical Ruthenium Hydride Complexes Containing Chelating Bidentate and Tridentate Phosphine Ligands

Author

Prechtl, Martin H. G., primary, Ben‐David, Yehoshoa, additional, Giunta, Daniela, additional, Busch, Stefan, additional, Taniguchi, Yuki, additional, Wisniewski, Wolfgang, additional, Görls, Helmar, additional, Mynott, Richard J., additional, Theyssen, Nils, additional, Milstein, David, additional, and Leitner, Walter, additional

Published
2007
Full Text
View/download PDF

35. Concerning the Role of Supercritical Carbon Dioxide in S N 1 Reactions.

Author

Qiao YX, Theyssen N, Eifert T, Liauw MA, Franciò G, Schenk K, Leitner W, and Reetz MT

Abstract

A series of S N 1-type reactions has been studied under various conditions to clarify the role of supercritical carbon dioxide (scCO 2 ) as reaction medium for this kind of transformations. The application of scCO 2 did not result in higher yields in any of the experiments in comparison to those under neat conditions or in the presence of other inert compressed gases. High-pressure UV/Vis spectroscopic measurements were carried out to quantify the degree of carbocation formation of a highly S N 1-active alkyl halide as a function of the applied solvent. No measureable concentration of carbocations could be detected in scCO 2 , just like in other low polarity solvents. Taken together, these results do not support the previously claimed activating effect via enhanced S N 1 ionization due to the quadrupolar moment of the supercritical fluid., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Published
2017
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results