Sustainable production of pyromellitic acid with pinacol and diethyl maleate

Article abstract of DOI:10.1039/c6gc03576k

Herein, we report an unprecedented and sustainable route to synthesize pyromellitic acid (PMA), a monomer of polyimide, with pinacol and diethyl maleate which can be derived from lignocellulose. Analogously, a sustainable route to trimellitic acid (TMA) was also developed using pinacol and acrylate as the feedstocks.

Full text of DOI:10.1039/c6gc03576k

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Sustainable production of pyromellitic acid with pinacol and
diethyl maleate†
Yancheng Hu,a Ning Li,*a,b Guangyi Li,a Aiqin Wang,a,b Yu Cong,a Xiaodong Wanga and Tao Zhang*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Herein, we report an unprecedented and sustainable route to
synthesize pyromellitic acid (PMA), a monomer of polyimide, with
pinacol and diethyl maleate which can be derived from
lignocellulose. Analogously, a sustainable route to trimellitic acid
(TMA) was also developed using pinacol and acrylate as the
feedstocks.
With the increasing of the social concern about energy and
environmental problems, the substitution of fossil resources (such
as coal, petroleum and natural gas) with renewable and CO2 neutral
biomass as the feedstock for fuels1 and chemicals2 is drawing more
and more attention. Lignocellulose is the main component of
agricultural and forestry wastes. Compared with fossil feedstock,
lignocellulose is richer in oxygenic groups. Therefore, the selective
conversion of lignocellulose and its derivates to high value
oxygenates3, 4 has great significance.
Polyimide (PI), Kapton for example, has high mechanical
strength, unique electrical properties, excellent chemical- and heat-
resistance. Thus, it is widely used in many areas, such as
engineering plastics, microelectronics, flat panel displays,
separation membranes, and aerospace.5 Pyromellitic acid (PMA) is a
monomer that is used in the production of PI. Nowadays, PMA is
usually produced by the oxidation of durene.6 However, the
approaches towards durene, including separation of durene from
C10 aromatics, methylation of xylenes or pseudocumene, and
disproportionation of pseudocumene, are strongly dependent on
non-renewable fossil feedstock (Scheme 1). In this context, the
Scheme 1 A comparison of fossil and bio route to pyromellitic
acid (PMA).
Pinacol is an important vic-diol which can be formed by the
metal-mediated coupling7 or electrolytic reduction8 of acetone from
the acetone-butanol-ethanol (ABE) fermentation of lignocellulose.9
Besides,
a sustainable approach towards pinacol, involving
photocatalytic coupling of isopropanol and acetone over
heterogeneous catalyst, has been reported.10 This method is
exploration of
a sustainable route to synthesize PMA with
-1
efficient (10.87 mmol gcat h-1) and feasible because the hydrogen
lignocellulose or its derivates is highly demanded.
generated during the ABE fermentation can be used to hydrogenate
the acetone to isopropanol.9 Diethyl maleate is the esterification
product of cellulosic ethanol and maleic anhydride (MA), which can
be produced by the oxidation of furfural,11 5-hydroxylmethylfurfural
(HMF)12 or levulinic acid (LA)13 from the hydrolysis/dehydration of
hemicellulose or cellulose (Scheme 1). Herein, we develop an
unprecedented three-step route for the synthesis of renewable
PMA with pinacol and diethyl maleate (Scheme 1). In the first step,
pinacol and diethyl maleate were directly transformed into diethyl
4,5-dimethylcyclohex-4-ene-1,2-dicarboxylate (i.e. compound 8) by
a one-step dehydration/D-A reaction cascade. As reported in the
a.State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese
Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
E-mail: taozhang@dicp.ac.cn; lining@dicp.ac.cn.
b.iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian
Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
†Electronic Supplementary Information (ESI) available: Experimental details and
copies of GC chromatograms and NMR spectra. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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literature,14 the selective pinacol dehydration to 2,3- influence on the reaction patterns. With the ViniecwreAratiscilenOgnlionef
DOI: 10.1039/C6GC03576K
dimethylbutadiene is very challenging due to the predominance of ChCl/HCOOH molar ratio from 1:1 to 2:1, the carbon yield of
pinacol rearrangement (a textbook reaction). However, this compound 2 varied a little, while that of unexpected compound 3
problem was first solved in this work by employing a choline significantly decreased from 22% to 12% (Table 1, entries 8 and 18).
chloride (ChCl) based deep eutectic solvent (DES) ChCl/HCO2H. This result further proved that the presence of ChCl restrained the
Choline chloride is
a
non-toxic, cheap, renewable and pinacol rearrangement. Based on this result, we fixed the
biodegradable ammonium salt which can be synthesized by the ChCl/HCOOH molar ratio in the DES as 2:1 in the following work.
Table 1 Effect of solvents on the dehydration of pinacol.a
neutralization of choline (a water-soluable vitamin). Formic acid is
the side-product in the production of levulinic acid by the
hydrolysis/dehydration of cellulose.15 Thus, the whole reaction
system is sustainable and renewable. In the second step, the
following dehydrogenation and hydrolysis were successfully
integrated into a one-pot reaction, providing 4,5-dimethylphthalic
acid (i.e. compound 11) in a high efficiency. Finally, aerobic
oxidation under the catalysis of N-hydroxyphthalimide
(NHPI)/Co(OAc)2/Mn(OAc)2 system afforded PMA in an excellent
yield.
Carbon
yield of yield of
2 (%)
Carbon
Entry
Catalyst
Solventb
3 (% )
1
2
Amberlyst-15
‒
Trace
88
Initially, we investigated the effect of solvents on the
dehydation of pinacol using Amberlyst-15 resin (a commercial solid
acid which has been used for many dehydration reactions) as the
catalyst. As we can see from the entries 1 and 2 of Table 1,
pinacolone (i.e. compound 3) was identified as the main product
from the dehydration of pinacol under solvent-free condition or
using toluene as solvent. Only trace amount of 2,3-
dimethylbutadiene (i.e. compound 2) was detected (Fig. S1†).
Compound 3 was generated by pinacol rearrangement, which was
more preferred than 1,2-elimination of H2O.14 It is very interesting
that evident improvement in the carbon yield of 2,3-
dimethylbutadiene was observed when we used some polar aprotic
solvents such as tetrahydrofuran (THF), dimethyl sulfoxide (DMSO)
and N-methyl pyrrolidone (NMP) (Table 1, entries 3-5). Notably, the
dehydration in DMSO and NMP provided compound 2 as the main
product, although pinacol was not completely consumed (Fig. S2†).
These results indicate that higher solvent polarity is benefical for
1,2-elimination of H2O. Because both DMSO and NMP are non-
renewable, great efforts were devoted to enhancing the diene
selectivity in renewable reaction media. ChCl-based deep eutectic
solvents (DESs) are a new class of cheap and biodegradable green
solvents which have strong electrostatic force and hydrogen-bond
interactions.16 In view of this fact, we surmised that the dehydration
of pinacol in DESs possibly could give better results. As expected,
higher carbon yields (66% and 51%) of compound 2 were achieved
over Amberlyst-15 resin in neutral DESs which were formed with
ChCl and biomass derived polyols (such as ethylene glycol (EG) and
glycerol) (Table 1, entries 6 and 7).
To make the system more renewable, we also explored the
dehydration in a series of acidic DESs which were formed with ChCl
and biomass derived carboxylic acids (at molar ratio of 1:1)
according to the method developed by Abbott et al..16 Among the
investigated systems, the DES ChCl/HCOOH exhibited the best
performance (Table 1, entries 8-15). A high carbon yield (69%) of
compound 2 was achieved in this medium. From the blank
experiments using HCOOH or ChCl alone (Table 1, entries 16 and
17), no compound 2 was obtained, indicating that the synergism
effect of HCOOH and ChCl (or the formation of DES) is necessary for
the excellent performance of ChCl/HCOOH. Moreover, it is noticed
that the molar ratio of ChCl and HCOOH in DES also exerted a great
Amberlyst-15
Toluene
THF
Trace
14
97
81
15
21
20
33
22
4
3
Amberlyst-15
4
Amberlyst-15
DMSO
NMP
31
5
Amberlyst-15
39
6
Amberlyst-15
ChCl/EGc (1:1)
ChCl/glycerol
(1:1)
ChCl/HCOOH
66
7
Amberlyst-15
51
8
‒
‒
‒
‒
‒
‒
‒
‒
‒
‒
‒
‒
69
(1:1)
9
ChCl/HOAc (1:1)
26
ChCl/levulinic
acid (1:1)
ChCl/oxalic acid
(1:1)
ChCl/succinic
acid (1:1)
ChCl/adipic acid
(1:1)
ChCl/tartaric
acid (1:1)
ChCl/citric acid
10
11
12
13
14
15
16
17
18
19e
19
4
17
35
32
13
40
36
N.R.d
80
12
13
58
44
43
31
(1:1)
ChCl
N.R.d
Trace
68
HCOOH
ChCl/HCOOH
(2:1)
ChCl/HCOOH
83
(2:1)
aReaction conditions: pinacol (1.0 g), Amberlyst-15 (100 mg or 0
o
mg when acidic DESs were used), solvent (4.0 g), 120 C, 12 h.
bThe ratio in parenthese is the molar ratio of choline chloride
(ChCl) to the other component. cEG = ethylene glycol. dN.R. = no
e
reaction. The dehydration of pinacol (1.0 g) was carried out in
ChCl/HCOOH (2:1, 8 g) at 140 oC for 12 h.
2 | J. Name., 2012, 00, 1-3
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The influence of ChCl/HCOOH (2:1) dosage on the dehydration
of pinacol was studied. According to Fig. S5†, the carbon yield of
compound 2 increased with the increment of ChCl/HCOOH dosage,
reached the maximum (78%) when 8.0 g ChCl/HCOOH was used,
then stabilized with further increasing the dosage. In contrast, it is
noticed that the dosage of DES had no evident effect on the carbon
yield of compound 3.
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DOI: 10.1039/C6GC03576K
We also investigated the effect of reaction temperature on the
carbon yields of compounds 2 and 3. As shown in Fig. S6†, with the
increasing of reaction temperature, the carbon yield of compound 2
slightly increased, reached the maximum (83%) when the pinacol
dehydration was performed at 140 oC (Table 1, entry 19), then
decreased with further increment of the temperature. This can be
rationalized because high temperature led to the self D-A reaction
of compound 2 (Fig. S4†), which decreased its carbon yield or
selectivity.
Scheme 2 The reaction pathways for the D-A reaction of
compound
2 and maleic anhydride (or diethyl maleate),
followed by dehydrogenation.
Another advantage of this DES system is the easier separation
of the product. At the beginning, pinacol and ChCl/HCOOH merge
100
Conversion of compound 8
o
together at 140 C, the reaction system is monophasic (Fig. S7a†).
Carbon yield of compound 9
Carbon yield of compound 10
After the completion of the reaction, the mixture spontaneously
separates into two phases: the upper layer is compound 2 and the
lower layer consists of DES and water (Fig. S7b†). Remarkably, when
submitting the mixture to a low temperature, the DES layer became
solid while the upper layer still remained as liquid, thus allowing a
facile separation of compound 2 just by decantation (Fig. S7c†). In
real application, this is highly advantageous.
The reusability of the DES system was also checked. To do this,
the ChCl/HCOOH (2:1) was repeatedly used for the pinacol
dehydration. After each usage, the upper layer was removed by
decantation. The lower layer (i.e. the mixture of water and DES
system) was recovered by desiccation and reused for the next cycle.
From the result shown in Fig. S8†, the ChCl/HCOOH system can be
conveniently recycled for at least four times without significant
decline in the carbon yield of compound 2. Moreover, we also
checked the thermal stability of formic acid under the investigated
conditions. According to the blank experiment result illustrated in
Fig. S9†, the formic acid was stable under the investigated
conditions. No decomposition of formic acid was noticed during the
reaction.
80
60
40
20
0
Pd/C (48 h)
Raney Ni
Ru/C
Pd/C
Ni/C
Rh/C
Pt/C
Fig. 1 Conversion of compound 8 and the carbon yields of
compounds 9 and 10 over different catalysts. Reaction conditions:
compound 8 (10 mmol, 2.5 g), catalyst (250 mg), 220 oC for 24 h.
Besides compound 9, small amount of compound 10 was
observed as the main side product in the dehydrogenation step (Fig.
S12†). As proposed in Scheme 2, compound 10 was generated by a
three-step process, including the retro D-A reaction of compound 8,
isomerization of the obtained diethyl maleate to diethyl fumarate,
and D-A reaction of compound 2 and diethyl fumarate. This
hypothesis was verified by two experimental facts. 1) According to
the blank test, diethyl maleate was isomerized to diethyl fumarate
over the Pd/C catalyst under the dehydrogenation condition (Fig.
S16†). 2) The dehydrogenation of compound 10, which can be
easily prepared by the D-A reaction of compound 2 and diethyl
fumarate (Fig. S11†), was slower than that of compound 8. Under
the same condition, lower substrate conversion (87% vs. 100%) and
carbon yield of compound 9 (66% vs. 80%) were achieved from the
dehydrogenation of compound 10 (Fig. S13†).
Subsequently, we explored the synthesis of PMA precursors (i.e.
compounds 6 and 9 in Scheme 2) with compound 2 and maleic
anhydride (or diethyl maleate) by the D-A reaction and
dehydrogenation. It is noticed that the D-A reaction can take place
spontaneously under thermal condition without using solvent or
catalyst (Fig. S10†, S24† and S25†). After the reaction was carried
out under mild conditions (60 oC for 1.5 h or 120 oC for 6 h),
compound 2 and maleic anhydride (or diethyl maleate) were nearly
quantitatively converted to the corresponding D-A adducts (i.e.
compound 5 or 8). However, evident difference was observed for
o
the following solvent-free dehydrogenation step (Pd/C, 220 C, 24
h). When compound 5 was used as the substrate, no aromatic
compound 6 was detected in the products. In contrast, a high
carbon yield (80%) of compound 9 was obtained from the
dehydrogenation of compound 8. Based on this result, we can see
that the esterification is favorable for the dehydrogenation of D-A
adducts.
The catalytic performances of Raney Ni and a series of active
carbon loaded metal catalysts in the dehydrogenation step were
compared. As shown in Fig. 1, the Pd/C exhibited evidently higher
activity than those of other catalysts such as Raney Ni, Ni/C, Pt/C,
Rh/C and Ru/C. After prolonging the reaction time to 48 h, 84%
carbon yield of compound 9 was obtained. However, we still think
24 h is better from the point view of economic.
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same reaction conditions, a high overall carbon yieldVoiefwTAMrtiAcle(O5n8l%ine)
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).
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Green Chemistry
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DOI: 10.1039/C6GC03576K
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Sustainable production of pyromellitic acid with pinacol and diethyl
maleate
Yancheng Hu, Ning Li,* Guangyi Li, Aiqin Wang, Yu Cong, Xiaodong Wang and Tao Zhang*
An unprecedented and sustainable route to synthesize pyromellitic acid (PMA), a monomer of polyimide, with
bio-derived pinacol and diethyl maleate was developed.