Catal Lett (2010) 138:155–159
DOI 10.1007/s10562-010-0406-0
Microwave-Assisted Nafion-H Catalyzed Friedel–Crafts Type
Reaction of Aromatic Aldehydes with Arenes: Synthesis
of Triarylmethanes
•
Surya G. K. Prakash Gabriella Fogassy
•
George A. Olah
Received: 12 May 2010 / Accepted: 20 June 2010 / Published online: 2 July 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A new solid acid Nafion-H, a perfluorinated
sulfonic acid resin, catalyzed microwave-assisted synthesis
of triarylmethanes is described. Various benzaldehydes
react readily with arenes to provide the corresponding tri-
arylmethanes in good to excellent yields. The reactions
were carried out under solvent free conditions under
microwave irradiation in a pressure vessel. The solvent free
microwave irradiation methods appears to be an environ-
mentally friendly synthetic protocol providing products in
significantly shorter reaction times over traditional heating
methods carried out in a pressure tube.
readily occurs under highly acidic conditions for example
over 2 equivalent of AlCl3 at 60 °C [8] to give a number of
products such as triphenylmethane, diphenylmethane, tri-
phenylmethanol and anthracene in yields varying from 30
to 60% [9]. Further work showed that substituted trip-
henylmethanes and anthracenes were formed by the
reactions of other aromatic aldehydes with aromatic
hydrocarbons such as toluene and xylenes in presence of
excess AlCl3 [10–13]. The initial step in these reactions
was considered to be the decarbonylation of the aldehydes,
the reverse of a Gattermann–Koch reaction [14–17], rather
than a transformylation reaction. The aldehyde derived
from a transformylation reaction was not detected. The
carbon monoxide produced by the decarbonylation was
presumed to react with the aromatic hydrocarbons in some
unspecified way to produce the triarylmethanes and
anthracenes. To ascertain the mechanism, a number of
aromatic aldehydes with a variety of arenes and Lewis and
Brønsted acid catalysts were examined [18]. In many
reactions, triarylmethanes were observed that did not
contain the aromatic moiety corresponding to the original
aldehydes. This might be interpreted as evidence for initial
formation of the ‘‘other aldehydes’’ by transformylation,
followed by subsequent addition reactions to produce the
triarylmethanes.
Keywords Nafion-H ꢀ Microwave irradiation ꢀ
Arylation ꢀ Triarylmethanes ꢀ Benzaldehyde
1 Introduction
Over the past two decades, microwave-assisted organic
synthesis has emerged as an important area that has
attracted significant attention as indicated by extensive
number of publications [1–3]. It is a convenient and time
saving method, which promotes the application of envi-
ronmentally benign approaches such as solvent free and
heterogeneous catalytic reaction conditions [4, 5].Triar-
ylmethanes constitute an important class of compounds
that are ubiquitous in materials, medical, and dyestuff
fields [6]. Acid-catalyzed condensation of benzaldehyde
with benzene is known since 1886 [7]. This classic reaction
To establish the mechanism, different acids were studied
at room temperature [19]. For example in 100% H2SO4
(H0 = -12) [20] benzaldehyde did not react with benzene
at room temperature. In trifluoromethanesulfonic acid
(H0 = -14) however, the reaction is complete in 30 h,
giving a 90% yield of triphenylmethane at room tempera-
ture. Addition of 1% SbF5 to trifluoromethanesulfonic acid
(H0 = -16) enhanced the reaction rate, and the reaction
was completed in 18 h at room temperature. In stronger
acid, CF3SO3H2?B(OSO2CF3)4- (H0 = -18), the reaction
S. G. K. Prakash (&) ꢀ G. Fogassy ꢀ G. A. Olah
Donald P. and Katherine B. Loker Hydrocarbon Research
Institute and Department of Chemistry, University of Southern
California, University Park, Los Angeles, CA 90089-1661, USA
e-mail: gprakash@usc.edu
123