Chemistry - A European Journal
10.1002/chem.201701060
COMMUNICATION
High Loading Crystals of Tetraaryladamantanes and the Uptake
and Release of Aromatic Hydrocarbons from the Gas Phase
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[a]
Pierre-Emmanuel Alexandre, Alexander Schwenger, Wolfgang Frey and Clemens Richert*
Abstract: Recent ly , a tetraphenyladamantane octamethylether was
shown to encapsulate a wide range of small molecules in its crystals.
Uptake and release from the liquid phase w ere demonstrated, and
crystalline inclusion complexes were prepared that act as
formulation for obnoxious reagents. Less than two equivalents of
guest molecules were found in the crystal structures, though. Here
we report the synthesis of 1,3,5,7-tetrakis(2,4-diethoxyphenyl)-
adamantane (TEO) and tw elve X-ray crystal structures that contain
up to 3.5 equivalents of guest molecules. After crystallization and
drying, TEO gives a material that absorbs 30 weight percent of p-
xylene reversibly through the gas phase, and releases it again at
aromatics, but only one molar equivalent of benzene or
trifluorobenzene w ere found in X-ray crystal structures, and just
0.5 equivalents of nitrobenzene w ere thus encapsulated.
Further, uptake and release of guest molecules occurred
through the solution phase, so that the release of captured
benzene required immersing the crystals in chloroform to
liberate the molecular cargo.
This made TDA unattractive for
molecular storage or environmental applications.
When w e studied closely related compounds, including
tetrakis(2-ethyl-4-methoxyphenyl)adamantane,
w hich
is
isoelectronic to TDA, they w ere found not to posses the same
55 °C, suggesting that it may be used for the capture and release of
propensity to crystallize as solvates, but other octaethers had
not been explored. Here w e report the synthesis of 1,3,5,7-
tetrakis(2,4-diethoxyphenyl)adamantane (2, TEO) and 1,3,5,7-
tetrakis(2,4-di-n-propyloxyphenyl)adamantane (3, TPO). The
former gives high-loading crystals w ith organic guest molecules,
w hereas the latter does not.
aromatic hydrocarbons.
Aromatic hydrocarbons are natural constituents of crude oil.
They are also components of w idely used fuels, such as
[
1]
gasoline and kerosene. Further, benzene, toluene and xylenes,
also know n as 'the BTX aromatics', are petrochemical starting
materials for a large number of industrial processes, including
those producing PET, polystyrene, and several plastic fibers.
But, benzene is also carcinogenic, and is one of the more
problematic volatile organic compounds that act as hazardous
[
2]
air pollutants.
Significant amounts of aromatics escape into
the environment, e.g. during the cold start of combustion
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3]
engines, and it is therefore interesting to ask w hether they can
be captured, ideally in a w ay that allow s feeding the captured
molecules into useful processes at minimal expense.
Know n adsorbents for the removal of organic pollutants
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4]
include activated carbon, mesoporous organosilica, sulfonated
[
5]
[6]
graphene, and metal-organic framew orks.
Neither of these
materials are simple organic crystals. Multicomponent organic
crystals are know n, though, and tuning their properties by crystal
[
7,8]
engineering is a developing art.
,3,5,7-tetrakis(2,4-dimethoxyphenyl)adamantane
crystallizes to form inclusion complexes w ith a w ide range of
We have recently found that
1
(1, TDA)
Scheme 1. Synthesis of tetraaryladamantanes.
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small organic molecules as guests.
When the guests are
Scheme 1 show s the route to 1-3. First, w e scaled up the
dangerous, labile and/or malodorous compounds, their
problematic properties can be masked. The TDA crystals can
thus act as a formulation or 'crystalline coating' for reactive
to ten gram batches to make sure that a
robust access to these molecules exists. For this, the volume of
1,3-dialkoxybenzene used in the arylation of 1,3,5,7-
tetrahydroxyadamantane (TOA, 4) w as adjusted, the reaction
time w as reduced to 72 h, and a process for recovering 95% of
the excess 1,3-dialkoxybenzene through vacuum distillation w as
established. An overall yield of 44% of 1 w as thus obtained.
The synthesis of the TDA derivatives 2 and 3 started w ith the
preparation of 1,3-diethoxybenzene (5) and 1,3-di-n-
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compounds.
The guests that w ere found in crystals of TDA include
[
[
a]
M.Sc. P.-E. Alexandre, Dipl.-Chem. A. Schwenger, Dr. W. Frey,
Prof. C. Richert,
Institut für Organische Chemie, Universität Stuttgart, 70569 Stuttgart
[
11]
propyloxybenzene (6) from resorcinol (7) on a 60-80 g scale in
(Germany),
Fax: (+49)711 608 64321
E-Mail: lehrstuhl-2@oc.uni-stuttgart.de
94% and 79% yield, follow ed by four-fold substitution to produce
and 3 in yields of 56% and 58%, respectively.
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These authors contributed equally to this work.
Crystals of tw o different solvate-free systems w ere found
Supporting information for this article is given via a link at the end of
the document.
when a solution of TEO in dichloromethane/ethanol (5:1) w as
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