Hydrierung im invertierten Zweiphasensystem scCO 2/H 2 O

Catalysis using an inverted scCO2/H2O biphasic system where the catalyst is immobilized in scCO2 as stationary phase and the substrate and product are contained in the aqueous phase, offers an interesting alternative to classical biphasic systems and enables the conversion of polar substrates, using scCO2 as solvent. As many fine chemicals and biological active compounds are hydrophilic in nature, a method for synthesizing these products without the problems of isolation and catalyst recycling forms an attractive possibility. The use of scCO2 as solvent reduces gas-liquid-liquid mass transfer limitations and eliminates cross-contamination of organic solvents into the aqueous layer. The catalyst is easily recycled without depressurising the autoclave by removal of the aqueous layer via a needle valve followed by addition of the next batch of substrate using a HPLC pump. The aim of this thesis was to examine the application of an inverted scCO2/H2O biphasic system. After allocation of an applicable catalyst and set-up of the reactor, the general practice of the system and the ability to recycle the catalyst was tested in case of the hydrogenation of itaconic acid as model substrate. Several CO2-philic rhodium-complexes were used. The best results were achieved using the fluorinated phosphine ligand 3-H2F6TPP and [Rh(cod)2]BF4. With a rodium:ligand:substrate ratio of 1:5:200, a conversion of 95% after 1 h reaction time was reached. Under the chosen conditions, the catalyst could be recycled at least three times. A turnover number of 800 was reached. After this, the optimization of reaction parameters occurred and other polar substrates were used. Then, enantioselective Hydrogenation was accomplished, leading to excellent results when (R,S)-3-H2F6-BINAPHOS-modified rhodium complexes were used. Hydrogenation of itaconic acid led to an enantiomeric excess of 97-98% ee (S) at full conversion and with recycling of the catalyst. Hydrogenation of Methyl-2-acetamidoacrylate gave full conversion and an enantiomeric excess of >98% ee (R) for at least five cycles. Another subject was the determination of solubility in scCO2, as the catalyst solubility plays an important role for the application of the inverted scCO2/H2O biphasic system. Therefore a simple method for qualitative estimation of the solubility, requiring only small amounts of compound was developed and applied on different materials and substances.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2006

Author dc:creator

• Burgemeister, Katja

Contributors dc:contributor

• Leitner, Walter

• info:eu-repo/classification/ddc/660
• Technische Chemie
• Katalytische Hydrierung
• Zweiphasensystem
• Kohlendioxid
• Asymmetrische Synthese
• überkritisches CO2
• Hydrogenation
• biphasic media
• supercritical CO2
• enantioselective synthesis

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-122556%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:60869