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@PHDTHESIS{Stobrawe:50009,
author = {Stobrawe, Annika},
othercontributors = {Leitner, Walter},
title = {{K}atalytische {F}estphasensynthese in {G}egenwart von
komprimiertem {K}ohlendioxid},
address = {Aachen},
publisher = {Publikationsserver der RWTH Aachen University},
reportid = {RWTH-CONV-112574},
pages = {100 S. : graph. Darst.},
year = {2008},
note = {Aachen, Techn. Hochsch., Diss., 2008},
abstract = {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.},
keywords = {Festphasensynthese (SWD) / überkritisches CO2 (SWD) /
Pauson-Khand Reaktion (SWD) / Baylis-Hillman Reaktion (SWD)},
cin = {154110 / 150000},
ddc = {540},
cid = {$I:(DE-82)154110_20140620$ / $I:(DE-82)150000_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-opus-22704},
url = {https://publications.rwth-aachen.de/record/50009},
}
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