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alcohol/toluene alkylation, which indicates a competition between
these acid-catalysed processes, which was particularly evidenced
under flow conditions.
Notes and references
1 J. C. Hayes, R. T. Mitsche, R. E. Rausch and F. C. Wilhelm,
US3751502, 1973, (Universal Oil Products Co.).
The stability of the Fe catalyst, particularly to Fe leaching, was
subsequently investigated under the reaction conditions. With this
purpose, ICP-MS was conducted on the final reaction mixture as
well as on the HNO3-treated Fe catalyst after several hours of
reaction (ca. 8 h) to ascertain the truly heterogeneous contribution
of the catalyst to the selected alkylation processes. Results
indicated a minimum leaching into solution (0.02 wt.% Fe) could
be only detected after several hours of reaction, a value which
correlates well with a final 0.22 wt.% Fe measured in the spent
catalyst after reaction. These findings support the high stability of
the mechanochemically synthesized Fe catalyst under continuous
flow conditions, in good agreement with a recent report by our
laboratories on stable and active Fe-based materials in aerobic
oxidations.14
2 (a) D. Das, J.-F. Leeb and S. Cheng, Chem. Commun., 2001,
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Haas Company).
3 For articles reviewing developments of solid acid-catalysts: (a) J.
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4 For a selection of articles investigating Friedel–Crafts alkyla-
¨
tions under continuous flow using scCO2, see: (a) R. Glaser and
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N. Aribert, S. Camy, Y. P. Lucchese, J. S. Condoret and
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6 K. Okumura, J. Jpn. Pet. Inst., 2009, 52, 219–230.
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8 (a) A. Pineda, A. M. Balu, J. M. Campelo, R. Luque, A. A. Romero
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M. Balu, D. Dallinger, D. Obermayer, J. M. Campelo, A.
A. Romero, D. Carmona, F. Balas, K. Yoshida, P. L. Gai,
C. Vargas, C. O. Kappe and R. Luque, Green Chem., 2012, 14,
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A. Romero and R. Luque, Green Chem., 2013, 15, 1232–1237.
Importantly, the proposed protocol could also be extended to
related acid-catalysed processes such as alkenylation and alkynyla-
tions of activated aromatic rings (e.g. substituted phenols), with
high activities and promising shape-selectivities to target products
under similar flow conditions (100–120 uC, 0.2–0.5 mL min21
)
depending on the nature of the support (e.g. zeolites favour the
formation of the p-product as compared to the o-isomer
preferentially observed in mesoporous materials). A full account
of these chemistries and preliminary results will be reported in
due course.
In summary, a highly active and stable mechanochemically
synthesized low-loaded Fe-based catalyst was able to provide good
to excellent yields of alkylated products in the alkylation of toluene
with benzyl chloride and benzyl alcohol, promoted by Lewis and
Brønsted acid sites, respectively. The increase in acidity (particu-
larly Lewis), as well as the accessibility of acid sites in Fe-
containing materials as compared to its parent support, seems to
be the key for the observed enhanced activities. Further studies are
currently expanding the proposed methodology to related Fe-
containing materials (e.g. Fe-hierarchical zeolites) aiming to
achieve shape-selectivities to isomers.
˜
9 (a) M. Guisan-Ceinos, F. Tato, E. Bunuel, P. Calle and D.
J. Cardenas, Chem. Sci., 2013, 4, 1098–1104; (b) S. Haldar and
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D. Carmona, F. Balas, J. Santamaria and R. Luque,
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Acknowledgements
This work was supported by a grant from the Christian
Doppler Research Society (CDG). Rafael Luque gratefully
acknowledges the Spanish MICINN for financial support via
the concession of a RyC contract (ref: RYC-2009-04199) and
funding under project CTQ2011-28954-C02-02. Both institu-
tions gratefully acknowledge support from MICINN under an
Integrated Action Austria-Spain (ES 09/2010; AT2009-0031).
12 P. Kalita, N. M. Gupta and R. Kumar, J. Catal., 2007, 245,
338–345.
13 T. N. Glasnov and C. O. Kappe, Chem.–Eur. J., 2011, 17,
11956–11968.
14 D. Obermayer, A. M. Balu, A. A. Romero, W. Goessler, R. Luque
and C. O. Kappe, Green Chem., 2013, 15, 1530–1537.
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