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TY - THES AU - Stobrawe, Annika TI - Katalytische Festphasensynthese in Gegenwart von komprimiertem Kohlendioxid CY - Aachen PB - Publikationsserver der RWTH Aachen University M1 - RWTH-CONV-112574 SP - 100 S. : graph. Darst. PY - 2008 N1 - Aachen, Techn. Hochsch., Diss., 2008 AB - In this work, the influence of compressed carbon dioxide on catalytic reactions on solid support was investigated. Pauson-Khand reactions (PKR) and hydrogenations were investigated representing reactions with gaseous substrates while the Baylis-Hillman reaction (BHR) was chosen because of its high negative reaction volume. For all reactions fast and effective coupling- and cleavage conditions were found. Reaction conditions were optimized allowing for comparing the reactions in organic solvent, expanded liquid (XPL) and supercritical carbon dioxide. Thus, evaluation of the influence of compressed carbon dioxide on the reaction was possible. For all three reactions, an enhancement of reaction rate in the presence of compressed CO2 compared to the reaction in organic solvent was observed. For PKR and hydrogenation, optimal conditions were found in XPL, whereas for BHR highest yields could be obtained using pure carbon dioxide. Apparently, for the reactions containing gaseous substrates, the gas availability and catalyst concentration is best in XPL. Switching to the supercritical phase leads to higher gas availability but at the same time to lower catalyst concentration as the supercritical phase occupies the entire reactor volume. In contrast, in the organic solvent, there is a high catalyst concentration accompanied by low gas availability as a result of the low gas solubility which is given in organic solvents. Such for the PKR as for the hydrogenation the optimum of these opposite trends seems to be given in XPL. Concerning the BHR, highest reaction rates were achieved in pure carbon dioxide. Detailed investigations on this reaction are pending. Hydrogenation of solid supported substrates in pure carbon dioxide was not possible, as the CO2-soluble ligand 3-H2F6TPP was deactivated by the support (Wang resin). In contrast, using the structurally similar ligand triphenyl phosphine (TPP) leads to a very active catalyst system with marginal deactivation by the Wang resin. Therefore, hydrogenation was performed in organic solvent and compared to the reaction using compressed carbon dioxide with organic co-solvent. Parallel reactions in the presence of compressed carbon dioxide could be realized for PKR. Different supported substrates were converted to the corresponding reaction products in the same high pressure reactor. Furthermore, a reaction sequence of BHR and hydrogenation was also realized. Excess substrate and catalyst of the first reaction step were removed from the reactor by extraction with scCO2. The reaction product of the whole sequence could be cleaved off in almost quantitative yields. In summary, it could be shown that compressed carbon dioxide can be used to overcome mass transfer limitation in solid phase organic synthesis with pressurized gaseous reagents (PKR and hydrogenation) and also to enhance reaction rates for reactions with negative activation volume (BHR). Thus, the use of compressed CO2 can significantly expand the range of catalytic reactions to generate molecular diversity via solid supported reactions. KW - Festphasensynthese (SWD) KW - überkritisches CO2 (SWD) KW - Pauson-Khand Reaktion (SWD) KW - Baylis-Hillman Reaktion (SWD) LB - PUB:(DE-HGF)11 UR - https://publications.rwth-aachen.de/record/50009 ER -