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Green Chemistry
Page 4 of 6
COMMUNICATION
Journal Name
DOI: 10.1039/C6GC03576K
was achieved.
Conclusions
In summary, we have developed an unprecedented three-step
route for the synthesis of PMA with pinacol and diethyl maleate
which can be derived from lignocellulose. Noteworthy features of
our protocol include a renewable and recyclable DES ChCl/HCOOH
for the one-step selective pinacol dehydration and D-A reaction
Scheme 3 The conversion of pinacol and diethyl maleate to
PMA precursor (i.e. compound 11) by two cascade reactions,
followed by catalytic aerobic oxidation.
with
diethyl
maleate,
an
integrated
one-pot
We also tried to combine the pinacol dehydration and the
following D-A reaction into one-step. Gratifyingly, submitting
pinacol and diethyl maleate to the DES ChCl/HCOOH at 140 oC could
directly produce the D-A adduct in 89% yield (the molar ratio of
compounds 8 and 10 is 7.1:1), which was similar as the one
obtained by the two-step method (Scheme 3, eqn 1). The product
can also be isolated by a simple decantation. Besides, we were
delighted to find that the subsequent dehydrogenation and
hydrolysis can also be conducted in a one-pot fashion, affording 4,5-
dimethylphthalic acid 11 in 73% yield (Scheme 3, eqn 1). These two
cascade reactions avoid the isolation of intermediates (i.e.
compounds 2 and 9), thus rendering the whole process shorter and
simpler.
dehydrogenation/hydrolysis cascade, and aerobic oxidation
catalyzed by NHPI/Co(OAc)2/Mn(OAc)2 system. An analogous route
to renewable TMA was also developed using pinacol and acrylate as
the feedstocks. This work paves a new way for the synthesis of
renewable polyimide with lignocellulosic platform compounds.
Meanwhile, this work also offers a practical and sustainable
approach towards 2,3-dimethylbutadiene, which is an important
precursor in organic synthesis and polymer science.19
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (no. 21690082; 21690084; 21506213;
21476229; 21277140), Dalian Science Foundation for Distinguished
Young Scholars (no. 2015R005), the Strategic Priority Research
Program of the Chinese Academy of Sciences (XDB17020100),
Department of Science and Technology of Liaoning Province (under
contract of 2015020086-101). Dr. Hu appreciates the Postdoctoral
Science Foundation of China (2015M581365) and the dedicated
grant for methanol conversion from DICP for funding this work.
Finally, the oxidation of compound 11 with oxygen (1 atm) in
the presence of a catalytic amount of Co(OAc)2 (4 mol%), Mn(OAc)2
(4 mol%), and N-hydroxyphthalimide (NHPI, 20 mol%) using acetic
o
acid as solvent at 120 C afforded PMA in 88% yield (Scheme 3, eqn
2).
Notes and references
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Scheme 4 The strategies for the synthesis of renewable PMA
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Based on what we found in this work, a three-step route for the
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Analogously, we also developed a route for the synthesis of
renewable trimellitic acid (TMA) with pinacol and ethyl acrylate
(Scheme 4). The detail information was given in ESI†. Under the
4 | J. Name., 2012, 00, 1-3
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