One-Pot Synthesis of Renewable Phthalic Anhydride from 5-Hydroxymethfurfural by using MoO3/Cu(NO3)2 as Catalyst

Article abstract of DOI:10.1002/cssc.201902590

Herein, a synthetic pathway to renewable phthalic anhydride (PA) from 5-hydroxymethfurfural (HMF) in one pot is reported. The commonly available catalysts MoO₃ and Cu(NO₃)₂ play a crucial role in integrating the multiple steps of the reaction, namely decarbonylation of HMF to active furyl intermediate (AFI), oxidation of HMF to maleic anhydride (MA), Diels–Alder cycloaddition of AFI and MA, and subsequent dehydration, in one pot. Under mild reaction conditions, a 63.2 % yield of PA is obtained from HMF. Compared with the currently reported route to renewable PA based on the Diels–Alder cycloaddition of biomass-derived MA and furan, this convenient one-pot synthesis represents a great improvement in efficiency.

Full text of DOI:10.1002/cssc.201902590

Accepted Article
Title: One pot Synthesis of Renewable Phthalic Anhydride from 5-
Hydroxymethfurfural using MoO3/Cu(NO3)2 as Catalyst
Authors: Wenlong Jia, Yong Sun, Miao Zuo, Yunchao Feng, Xing
Tang, Xianhai Zeng, and Lu Lin
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To be cited as: ChemSusChem 10.1002/cssc.201902590
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ChemSusChem
10.1002/cssc.201902590
FULL PAPER
One pot Synthesis of Renewable Phthalic Anhydride from 5-
Hydroxymethfurfural using MoO
3
/Cu(NO
3
)
2
as Catalyst
[a]
*[a], [b], [c]
[a]
[a]
[a]
[a]
[a]
Wenlong Jia, Yong Sun,
Miao Zuo, Yunchao Feng, Xing Tang, Xianhai Zeng, Lu Lin
Abstract: Herein, we reports a renewable synthetic pathway of
Nielsen et al. reported an early investigation on the furfural
oxidation to MA.12 In 2012, Ojeda et al.13 achieved MA yield of up
to 73 % through selective gas phase oxidation of furfural at 593 K
in a tubular fixed-bed reactor. Several studies describes liquid
phase catalytic oxidation of furfural to maleic anhydride with
heterogeneous catalysts.14, 15 Although the reaction condition is
mild, the oxidation efficiency is relatively lower. As for the
oxidation of HMF to MA, Zhang et al. developed heterogeneous
catalytic systems using vanadium-based solid catalysts for the
oxidation HMF to MA, achieving a yield of 52 % at the condition
phthalic anhydride (PA) from 5-hydroxymethfurfural (HMF) in one pot
3 3 2
for the first time. The commonly available catalysts MoO /Cu(NO )
played a crucial role in integrating the multistep reactions, namely
decarbonylation of HMF to active furyl intermediate (AFI), oxidation of
HMF to maleic anhydride (MA), Diels-Alder cycloaddition of AFI and
MA and subsequent dehydration, in one pot. Under a mild reaction
conditions, a 63.2 % yield of PA was obtained from HMF. Compared
to the currently reported route to renewable PA based on the Diels-
Alder cycloaddition of biomass-derived MA and furan, this convenient
one-pot synthesis pathway presents great advantage in efficiency.
of 1 Mpa O
, 100 C and 4 h.16 There still are some reports on the
2
preparation of MA from HMF, while the yield of MA was hardly
over 52 %.1
7, 18
Introduction
Phthalic anhydride (PA) is a versatile intermediate for the
chemical industry with a global production of over 3 million tons
1
per year, serving a vast range of industries including phthalate
2
resins,3
dyestuffs,4
esters
plasticizers,
polyester
5
pharmaceuticals, and so on. Currently, PA is primarily produced
via catalytic oxidation of naphtha or ortho-xylene, which is refined
from petroleum or coal.6, 7 In consideration of current concern on
fossil fuel depletion and environmental footprint, limited progress
has been made to seek sustainable solutions for the production
8
of chemicals from renewable biomass. Alternative routes to PA
Scheme 1. The synthesis pathway of PA
9
from renewable starting materials have been explored. In 2014,
Lobo et al.10 envisaged a renewable route to PA using biomass-
derived maleic anhydride (MA) and furan based on Diels-Alder
Furan is commercially produced by the decarbonylation of furfural
(
is necessary to point out here that the vapor-phase
decarbonylation usually requires higher reaction temperature
(
D-A) and following dehydration reaction, establishing an
FF) in vapor or liquid phase using supported Pd catalysts.19, 20 It
approach for transforming abundant renewable biomass
resources into PA (Scheme 1).
Industrially, MA is manufactured by the oxidation of petroleum-
derived benzene, butane, or butadiene.11 It can also be produced
from the aerobic oxidation of 5-hydroxymethylfurfural (HMF) or
furfural, a biomass-derived platform molecules.12-18 In 1949,
(
over 300 C) than the liquid-phase decarbonylation, whereas the
latter usually causes deactivation of catalysts and polymerization
of feedstock and product.17, 20
From the studies described above, we note that the current
renewable route to produce PA from HMF or FF needs to undergo
four steps: decarbonylation of FF to furan, oxidation of HMF or FF
to MA, D-A cycloaddition of furan and MA, and following
dehydration reaction of D-A adduct.21 It is considered as a
promising sustainable strategy for the production of PA. Whereas
it is worth noting that multistep reactions result in low efficiency
for the production of PA from HMF or FF. To make renewable PA
cost-competitive compared to the traditional synthetic route, a
simpler process is expected.21
[
[
a]
b]
W. L. Jia, Y. Sun, M. Zuo, Y. C. Feng, X. Tang, X. H. Zeng, L. Lin
Xiamen Key Laboratory of Clean and High-valued Utilization for
Biomass
College of Energy, Xiamen University
Xiamen, 361102, P. R. China
Y. Sun
Fujian Engineering and Research Center of Clean and High-valued
Technologies for Biomass
Xiamen University
Xiamen, 361102, P. R. China
E-mail: sunyong@xmu.edu.cn
Y. Sun
Hubei Key Laboratory of Pollutant Analysis & Reuse Technology
Hubei Normal University
Huangshi, 435002, Hubei, P. R. China
To the best of our knowledge, one-pot and straightforward
procedure capable of directly producing PA from HMF has not
been reported. This challenging goal would be of clear
significance and interest, the key to success is to develop a highly
advanced and versatile catalyst system that can integrate four
independent reactions mentioned-above in one pot. Herein, we
[c]
Supporting information for this article is given via a link at the end of
the document.
report such a combined catalyst of MoO
unexpectedly exhibited the excellent catalytic activities in
3 3 2
/Cu(NO ) , which
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ChemSusChem
10.1002/cssc.201902590
FULL PAPER
decarbonylation, oxidation, D-A cycloaddition and dehydration,
enabling the one pot process. It spured us to reveal the intrinsic
reaction pathway in this one pot process of HMF to PA in detail.
8
9
1
VOSO
4
/Cu(NO
3
)
2
91
93
95
97
100
99
98
89
100
-
34.0
36.0
36.0
54.4
20.0
55.0
57.8
57.8
63.2
-
13.0
23.0
5.0
<1
<1
4.0
7.0
<1
49.0
<1
<1
<1
<1
-
2 5
V O /CuO
0
3
VOCl /CaO
Results and Discussion
11
MnO
MnO
MnO
MoO
MoO
MoO
-
2 3 2
/Cu(NO )
[
b]
b]
One pot Synthesis of Renewable Phthalic Anhydride form 5-
Hydroxymethfurfural. Building upon the previous work of
preparing 2, 5-diformylfuran (DFF) from HMF using
12
2
2
3
3
3
/Fe
2
O
O
3
/Cu(NO
/Cu(NO
3
)
2
2
9.0
<1
[
1
1
3
4
/Fe
3
4
3
)
Fe(NO
with the assistant of K
3
)
3
/Cu(NO
3
)
2
as catalyst, a 99 % yield of DFF was obtained
in acetonitrile.22 When adding water
[b]
/CeO
2
/Cu(NO
3
)
2
<1
2
2 8
S O
[b]
into the reaction, PA was unexpectedly found with a yield of 8 %,
along with a substantial drop in the yield of DFF (Table 1, entry
15
/Fe
3
O
4
/Cu(NO
)
3 2
<1
1
1
6
7
/Cu(NO
)
3 2
<1
1
). Spurred by this result, we sought to identify a superior catalyst
that could promote the conversion efficiency of HMF to PA by
using K as oxidant. the investigation was initiated by
[c]
-
2
2 8
S O
examining a series of multi-metallic catalysts, including transition
elements of iron, copper, vanadium, manganese or molybdenum.
The results showed that most catalysts led to a high HMF
conversion in 7 h, moreover the iron-based catalysts appeared to
be more favorable to the generation of DFF (Table 1, entries 2-7).
[a] Reaction conditions: 0.63 g HMF (5 mmol), 10 wt % catalyst (the mass ratio of each metallic
catalyst was controlled as 1:1), 40 ml mixed solvents of water and acetonitrile (33:7), 5 mmol
o
K
2
S
2
O
8
, 90 C, 7 h; [b] 10 wt% catalyst (the mass ratio of each metallic catalyst was controlled
as 1:1:1); [c] without catalyst.
In study, the significant effect of water on product distribution was
25
also observed. The works performed by Otto et al. and Thomas
et al. 26 showed aqueous solvent tended to enhance the reaction
rate and selectivity of D-A reaction. The effect of water on D-A
reaction is attributed in part to the benefit of decreasing
hydrophobic surface area, as well as the hydrogen-bond donating
capacity.27-29 Obviously, compared with sole water, the common
polar aprotic solvents, including MeCN, DMSO, dioxane, MIBK,
toluene, carbon tetrachloride chloride and dichloromethane,
achieved lower conversion of HMF and yield of PA. The low
conversion of HMF indicated low catalytic activity of catalysts for
the oxidation of HMF to PA in these polar aprotic solvents. In
these reactions, the dominant product, either DFF or MA, was
obtained. Even if at the condition of high MA concentration in
these polar aprotic solvents (Table 2, entries 2, 4-6), the yield of
PA was lower than that obtained in sole water. Once Water/MeCN
was used as solvent, the yield of PA was substantially increased
3 3
It should be noted that chloride salts, such as FeCl or VOCl used
in this reaction, were inclined to produce by-product 5-
chloromethyl furfural (CMF) (Figure S1), contributing to the low
selectivity to the target product PA, as well as the intermediates
DFF and MA (Table 1, entries 2, 10). Generally, vanadium-based
oxides are reported as effective catalysts for the oxidation of
hydroxyl to ketones or oxidative decarboxylation.23, 24 In this case,
the vanadium oxides demonstrated a moderate selectivity to PA
with almost complete conversion of HMF (Table1, entries 8-10).
Then, several molybdenum oxides and manganese oxides
catalysts combined with cupric nitrate were examined
respectively.
MoO /Cu(NO
HMF to PA, with isolated yields of 54.4 % and 63.2 % respectively
Table1, entries 11, 16). It is further noteworthy that iron oxides
and cerium oxide caused negative effect on the generation of PA
3 2
to some extent (Table1, entries 12-15). In sum, MoO /Cu(NO )
In
wonder,
both
MnO
2
/Cu(NO
3
)
2
and
3
3 2
) gave promising results for the one-pot conversion
(
(
Table 2, entries 9-10). These results suggest that water
3
facilitated the oxidation of HMF, D-A cycloaddition and following
dehydration of adduct. Therefore, the lower PA yields obtained by
these aprotic organic solvents employed in this study is
reasonably ascribed to the less contribution in their hydrogen-
bond donating capacity.
are preferred catalysts for the one-pot conversion of HMF to PA.
Table 1. Effect of Catalysts on the Catalytic Oxidation of HMF.[a]
Sele.(%)
Entry
Catalyst
Conv.(%)
Despite obvious benefits, water as solvent alone only obtained
PA
MA
5.0
<1
DFF
70.0
25.0
61.0
50.0
40.0
43.0
3.0
37.6 % yield of PA. It ignited the speculation that water insoluble
intermediates were generated in the reaction, eventually effecting
the yield of PA. In view of this assumption, the mixed solvents of
water with MeCN or dioxane, were examined in the investigated
reaction based on the results that MeCN and dioxane preformed
relatively better than other organic solvents. As we expected,
water/organic solvents performed better than sole water,
moreover the high-water-content mixed solvent of water/MeCN
(5:1) obtained a relatively high PA yield of 63.2 % (Table 2, entry
1
2
3
4
5
6
7
Fe(NO
3
)
3
/Cu(NO
)
3 2
90
93
58
25
78
97
95
8.0
3
FeCl /CuO
20.0
22.0
12.0
<1
Fe
Fe
Fe
Fe
Fe
3
2
2
3
3
O
4
/CeO
2
<1
O
O
O
O
3
3
4
4
/CaO
<1
/Nb
2
O
5
<1
10). This result appeared to demonstrate the scenario mentioned
/CuO
<1
18.4
56.0
above. To further confirm this result, the D-A reaction of furan and
MA was conducted in water based on the low water-solubility of
furan. As expected, no PA and MA were obtained in water (Figure
/Cu(NO
)
3 2
28.0
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ChemSusChem
10.1002/cssc.201902590
FULL PAPER
S2), whereas by contrast, a little PA and a large quantity of MA
were obtained in the mixed solvents (Table 2, entries 13-15).
These results underscore the critical importance of the dispersity
of reactant or intermediate in reaction solvent, which facilitates
product yield. Therefore, it is in reason that the mixed solvent
performed well in the oxidation of HMF to produce PA.
generate PA is not detected, motivating our curiosity to investigate
the reaction pathway.
Table 2. Effect of Solvents on the Catalytic Oxidation of HMF.[a]
Sele.(%)
[b]
Entry
Solvent
Conv.(%)
PA
MA
DFF
1
2
3
4
5
6
7
8
9
Water
MeCN
DMSO
100
78
37.6
23.2
12.0
17.0
14.4
12.6
-
5.0
44.3
8.0
21.0
23.0
35.0
-
4.0
31.5
78.0
9.0
12.0
8.0
14.0
15.0
8.0
<1
56
Dioxane
43
MIBK
61
Figure 1. Effect of reaction parameters on the conversion of HMF to PA. a)
Effect of the dosage of K S O ; b) Effect of the dosage of catalyst; c) Effect of
2 2 8
reaction time; d) Effect of reaction temperature. Reaction conditions: 5 mmol
HMF, 40 ml mixed solvent of water and acetonitrile (33:7). a) 10 wt% catalyst
Toluene
59
Carbon tetrachloride
Dichloromethane
Water/MeCN(1:1)
Water/MeCN(5:1)
Water/Dioxane(1:1)
Water/Dioxane(5:1)
Water/MeCN(2:1)
Water/MeCN(1:5)
Water
100
100
100
100
100
100
100
100
100
o
(
themass ratio of MoO
ratio of MoO /Cu(NO
wt% catalyst (the mass ratio of MoO
, 90 oC; d) 10 wt% catalyst (the mass ratio of MoO
controlled as 1:1), 5 mmol K , 7 h.
3
/Cu(NO
3
)
2
was controlled as 1:1), 90 C, 7 h; b) themass
o
3
3
)
2
was controlled as 1:1, 5 mmol K
/Cu(NO
2
S
2
O
8
, 90 C, 7 h; c) 10
-
-
3
3
)
2
was controlled as 1:1), 5 mmol
/Cu(NO was
K
2
S
O
2 8
3
3 2
)
45.0
63.2
38.0
44.6
8.0
11.0
5.0
28.0
32.0
85.0
73.0
-
2 2 8
S O
1
1
1
1
1
1
0
1
2
3
4
5
<1
Reaction Pathway Study on the one-pot conversion of HMF
to PA. Generally, aldehyde tends to form corresponding acid
under an oxidation atmosphere, especially in the presence of
transition metal catalyst. At the outset of our work, several
experiments were devised with several downstream oxidation
derivatives of HFM, such as 2, 5-diformylfuran (DFF), 5-
hydroxymethyl-2-furancarboxylic acid (HFCA), 5-formyl-2-
furancarboxylic acid (FFCA), 2, 5-furandicarboxylic acid (FDCA)
as starting materials, to figure out the reaction pathway of the one-
pot conversion of HMF to PA. Only DFF achieved a better PA
yield than HMF, whereas FFCA, HFCA and FDCA were hardly
converted (Table 3, entries 1-4), indicating that DFF was an
essential intermediate for the conversion of HMF to PA. The
kinetic study in the above section also identified DFF as a
dominant intermediate. These results confirm that the conversion
of HMF to PA certainly underwent the intermediate DFF as the
dominant route.
<1
[
[
[
c]
c]
c]
-
4.0
-
-
-
[
a] Reaction conditions: 0.63 g HMF (5 mmol), 10 wt% catalyst (the mass ratio of MoO
3
3 2
/Cu(NO )
o
2 2 8
was controlled as 1:1), 5 mmol K S O , 90 C, 7 h; [b] 40 ml solvent; [c] Using furan as substrate.
To establish optimal reaction conditions, effects of reaction
parameters, including dosage of oxidant, amount of catalyst,
reaction time and temperature, were investigated, as showed in
the Figure 1. The results revealed that excess oxidant and high
temperature caused decline in the PA yield (Figure 1a and d).
The experiments using nonometallic or bimetallic catalysts to
oxidized HMF to PA demonstrated strong synergy between MoO
and Cu(NO in this catalytic reaction (Figure 1b). No MA was
3
Table 3. Effect of starting materials on the production of PA.[a]
3 2
)
observed within 1 h during the oxidation of HMF, whereas
prolonging the reaction time to 2 h, MA was gradually detected
accompanied by a drop in the yield of 2, 5-diformylfuran (DFF).
The product distribution with the prolonged reaction time infers
that the conversion of HMF to PA appears to undergo an
intermediate oxidation step of HMF to DFF, subsequently to MA
Yield (%)
Entry
Reactant 1
Reactant 2
Time (h)
PA
MA
4.2
M acid
14.4
1
2
3
4
DFF
-
-
-
-
5
5
5
5
77.2
FDCA
FFCA
HFCA
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
(
Figure 1c), amply substantiating that target PA is generated
through a stepwise reaction. Nevertheless, another essential
intermediate furan, together with MA, for the D-A reaction to
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ChemSusChem
10.1002/cssc.201902590
FULL PAPER
to MA (Table 3, entry 1). Moreover, no PA was detected when
furan used as substrate (Table 3, entries 7), only a little PA was
obtain when using furan and MA as substrates (Table 3, entries
5
6
7
8
9
Furan
Furan
Furan
M acid
MA
MA
2
2
3
2
2
7
8
7
4.3
4.8
0.0
0.0
0.0
0.0
4.0
18.6
187.0
169.0
86.0
0.0
<1
<1
<1
0.0
0.0
M acid
5), MA was dominant instead in these reactions. However, when
-
formic acid was added into the reaction, a obvious increase in the
PA yield was observed, suggesting that formic acid probably
involved to the formation of dehydrant, which improved the
dehydration of the D-A adduct to PA (Table 3, entry 12). The low
PA yield obtained by furan and MA as substrates was probably
caused by a lack of dehydrant, leading to the retro-D-A reaction.
Eventually, most furan was oxidized to MA. In the kinetic study
above, MA yield reached to a relatively high level in initial 3 h,
while PA yield was low than 10 %. It was gradually raised after 4
h. These results show that HMF firstly is oxidized to MA. However,
the reaction rate to MA become slow with the increase of MA,
resulting in the oxidation of DFF tends to form AFI. Menawhile the
increasing dehydrant with the course of reaction improves the
dehydration of adduct to PA, facilitating the D-A cycloaddition of
AFI and MA to form the adduct. Base on analysis above, it is
inferred that HMF is simultaneously oxidized to MA and AFI via
DFF. Meanwhile, AFI can also be oxidized to MA based on the
result of the easy oxidation of furan to MA.
-
98.3
-
100.0
0.0
10
FF
-
-
[
b]
11
FFA
23.0
＞70
[
c]
1
2
Furan
MA
147.8
0.0
[
a] Reaction conditions: 5 mmol reactant 1, 5 mmol reactant 2, 10 wt% catalyst (mass ratio of
MoO
3
/Cu(NO
3
)
2
was controlled as 1:1), 40 ml mixed solvent of water and acetonitrile (33:7), 5
o
mmol K
2
S
2
O
8
, 7 h, 90 C, 100% conversion for all reactions, except that FDCA, FFCA, HFCA,
MA and FF were hardly converted; [b] The yield of FF; [c] Adding 0.5 mmol formic acid 2.5 mmol
(the amount of K was reduced by half.)
K
2
S
2
O
8
2
S
2
O
8
;
Commonly, diene and dienophile are essential for the D-A
reaction characterized by cycloaddition 30, being a critical step for
the formation of PA. MA, a key dienophile, was detected as
intermediate in the course of the reaction, whereas diene was
never found so far. Initially, furan was considered as the diene
involved in the D-A reaction. Whereas in fact, less than 4.3 % PA
yields were obtained from the reaction of furan and MA or maleic
acid (M acid), along with the dominant product of MA (Table 3,
entries 5-6). Moreover, M acid also was converted to MA,
indicating that this reaction system facilitated dehydration to form
anhydride (Table 3, entry 8). Since furan was not detected in the
reaction, we inferred that the diene should be an active
intermediate associated with furan. To capture this active furyl
intermediate, the electrophilic reagent HBr was dropwise added
into the reaction solution. As a result, 2-bromofuran (BF) came
from the trapping of the active furyl intermediate by HBr was
successfully detected by GC-MS (Scheme 2 & Figure S3),
making us believe that the cleavage of the C−C bond between
In the study of the oxidation of biomass-based furfural to MA by
H
5
PV
2
Mo10
O
40
,
Yin et al.18 deemed that the catalytic
transformation should be initiated from the furfural radical
intermediate generated from the abstraction of the hydrogen atom
at the 5-position of furfural by H PV Mo10O40. However, in this
5 2
study, when furfural (FF) was used as starting material, no
conversion was observed (Table 3, entry 10). It was probably
attributed to lack enough catalytic activities to not only abstract
the hydrogen atom at the 5-position, but also decarbonylate at the
2-position due to the π-conjugation of aldehyde group and furyl
ring. Moreover, employing furfuralcohol (FFA) as the starting
material, more than 70 % yield of FF was obtained, along with
23 % MA and 4 % PA generated (Table 3, entry 11), indicating
that the C−C bond of hydroxymethyl group adjacent to furyl group
can be directly cleaved in this reaction system. Whereas, the low
yield of MA shows that it is only the minor reaction route. Several
studies on the oxidation of HMF to MA also show that the C–C
bond adjacent to the hydroxymethyl group in HMF molecule is
easily broken under an oxidation condition.17, 31 Therefore, it is
inferred that the direct oxidation of HMF to MA also takes place
as the minor reaction pathway.
3
the carbonyl group and furan sketch of DFF by MoO yielded the
active furyl intermediate (AFI). In addition, free radical inhibitor 4-
tertbutylphenol was added into the reaction solution to induce the
reaction. As expected, no MA or PA was detected, even if DFF as
substrate. These results suggest that the free radical reaction
should be involved in this catalytic conversion of HMF to PA,
followed by an electron transfer process.
In the previous report, Lobo et al.10 regarded that the D-A
cycloaddition of furan and MA to PA underwent the adduct exo-4,
10-dioxa-tricyclo[5.2.1.0]dec-8-ene-3,5-dione
(oxanorbornene
dicarboxylic anhydride, ODA) and subsequent dehydration.
Whereas hitherto, ODA was not detected in our study. We
speculated that the D-A adduct in this study was possibly an
active intermediate (named AODA) associated with ODA. Then,
an attempt was made to identify it by the analogy with the
1
0
dehydration mechanism of ODA put forward by Lobo et al. . In
reported literature, mixed sulfonic-acetic anhydride was regarded
as an effective dehydrant for the conversion of ODA to PA.
Scheme 2. Trapping of active furyl intermediate by HBr
Generally, K
sulfate, sulfur trioxide and oxygen at a temperature of 30-
200 °C.32 Considering K
was used as oxidant, sulfonic group
2 2 8
S O can be readily decomposed to potassium
Notably, MA together with M acid were detected with a total yield
of over 18.6 %, suggesting that DFF could be facilely converted
2
2 8
S O
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ChemSusChem
10.1002/cssc.201902590
FULL PAPER
was regarded to come from sulfur trioxide, while carboxylic
dihydrofuran-2-carbaldehyde. Then, decarbonylation of 5-oxo-2,
5-dihydrofuran-2-carbaldehyde and following 1, 4-rearrangement
led to 5-hydroxyl-2(5H)-furanone. Actually, 5-hydroxyl-2(5H)-
furanone was oxidized to MA. Therefore, based on the reported
mechanism and results obtained in this study, the reaction
pathway for the one-pot conversion of HMF to PA was proposed,
as illustrated in Scheme 3. Initially, HMF is oxidized to DFF in the
(
formate) should generate from the decarbonylation or oxidation
of HMF to AFI or MA. Sulfur trioxide and formic acid formed mixed
sulfonic-formic anhydride (Scheme 3).33 Much to our delight,
formic acid was detected in the reaction solution (Figure S4). The
pH of the reaction solution after the reaction decreased from 7.3
to 0.1 indicated the formation of acids, such as H
2 4
SO generated
from the reacion of SO with water and formic acid came from the
3
2 2 8
mixed solution of water/acetonitrile with K S O as oxidant. Then,
oxidation of aldehyde group in DFF (Table S1).
DFF undergo decarbonylation at the 2-position to form furfuran
radical or at the 2 and 5-position of furan ring simultaneously to
form AFI. Meanwhile, Furfuran radical and AFI is oxidized to MA.
The increase of MA in the reaction slows the conversion rate of
DFF to MA. More DFF tends to be oxidized to AFI. Eventually, AFI
and MA involves in the essential D-A cycloadditio to generate PA
though the dehydration of an active intermediate AODA by mixed
sulfonic-formic anhydride.
To confirm this inference, the effect of dehydrants on the
dehydration of ODA to PA was investigated (Table 4). When
using separate sulfuric acid, formic acid or maleic acid, no PA was
detected in the dehydration of ODA, whereas MA was found as
dominant product because of the retro-D-A reaction (Table 4,
entries 1-3). The similar results was also obtained by the mixed
acids of sulfuric acid and maleic acid (Table 4, entries 5 and 7),
suggesting that maleic acid was not suitable to use as dehydrant
for the dehydration of ODA. Using the mixed acids of sulfuric acid
and formic acid, only 2 % PA was obtained (Table 4, entry 4). By
comparison, after the mixed acids were reacted for 3 h, the
resulting acid solution was used for the dehydration of ODA, as a
result, an obvious enhancement in the yield of PA was achieved
(
Table 4, entry 6). These results suggest that sulfuric acid and
formic acid formed mixed sulfonic-formic anhydride, promoting
the dehydration of ODA to PA. More importantly, when additional
K S O was added to the reaction using separate formic acid or
2 2 8
the mixed acids of sulfuric and formic acid as dehydrant, a
significant increase in the PA yield was obtained (Table 4, entries
2 2 8
8-9). These results amply demonstrates K S O actually played
an essential role in the conversion of HMF to PA similar to mixed
sulfonic-acetic anhydride. The similar dehydration mechanism
also indirectly verifies the existence of the active intermediate
AODA in the conversion of HMF to PA.
Scheme 3. Reaction pathway of the one-pot conversion of HMF
to PA
Process Development for HMF to PA in one pot with O
oxidan. According to the decomposition equation of K , only
mol oxygen atom was released by 1 mol K to involve the
2
as
Table 4. Effect of dehydrant on the conversion of ODA to PA.[a]
2 2 8
S O
1
2 2 8
S O
Yield (%)
oxidation of HMF to PA, which was considerably less than the
required oxygen for the complete conversion of HMF to PA.
Hence, it was reasonably doubted that the air remained in the
reactor involved in the oxidation of HMF to PA. To gain more
Entry
Dehydrant
PA
MA
79.0
82.0
99.0
63.0
99.0
20.0
89.0
7.0
M acid
11.0
7.0
1
2
3
4
5
5 mmol Sulfuric acid
-
10 mmol Formic acid
-
insight into the intrinsic function of K
substituting K with O and H SO in the one pot conversion
of HMF to PA were carried out. One amazedly found that
/H SO also made it possible to oxidized HMF into PA in one-
2 2 8
S O , the studies of
2
S
2
O
8
2
2
4
5 mmol Maleic acid
-
99.0
11.0
99.0
34.0
96.0
-
5 mmol Sulfuric acid and 10 mmol Formic acid
5 mmol Sulfuric acid and 5 mmol Maleic acid
5 mmol Sulfuric acid and 10 mmol Formic acid
5 mmol Sulfuric acid and 5 mmol Maleic acid
10 mmol Formic acid
2.0
-
O
2
2
4
pot (Table 5), confirming the speculation that the oxygen in the
reactor also took part in the oxidation of HMF to PA. It is
worthwhile to point out here that excess oxygen resulted in high
selectivity to MA, instead of PA (Table 5, entry 2). By contrary,
insufficient oxygen also led to weak oxidizing power,
accompanied by low selectivity of PA and MA (Table 5, entries 1
and 3). Once an amount of oxygen was controlled at a reasonably
level, an obvious enhancement in the PA yield was observed
[
b]
6
7
8
9
17.0
-
[b]
[
c]
48.0
9.0
[d]
5 mmol Sulfuric acid and 10 mmol Formic acid
35.0
30.0
[
a] Reaction conditions: 5 mmol ODA, 40 ml mixed solvent of water and acetonitrile (33:7), 10 wt%
o
catalyst (mass ratio of MoO
reacted for 3 h, then 5 mmol ODA was added to react for another 2 h; [c] After 10 mmol formic acid and
mmol K were mixed for for 3 h, 5 mmol ODA was added to react for another 2 h; [d] After 5 mmol
3 3 2
/Cu(NO ) was controlled as 1:1), 90 C, 5 h; [b] After the mixed acids were
(
Table 5, entries 4-7). Apart from the effect of oxygen, appropriate
5
2
S
2
O
8
acidity was also a vital factor to facilitate the conversion of HMF
to PA (Table 5, entries 5-7). Summarily, an efficient conversion of
Sulfuric acid, 10 mmol Formic acid and 1 mmol K
react for another 2 h.
2 2 8
S O were mixed for 3 h, 5 mmol ODA was added to
HMF to PA using MoO
3 3 2
/Cu(NO ) as catalyst, oxygen as oxidant
Previous studies14, 18 on the oxidation of furfuran and HMF to MA
showed that formation of furfural radical was major route, followed
by hydration and 1, 4-rearrangement to form 5-oxo-2,5-
and H SO as accelerator was realized in one pot.
2
4
Table 5. Conversion of HMF to PA in one pot with oxygen as oxidant.[a]
This article is protected by copyright. All rights reserved.

ChemSusChem
10.1002/cssc.201902590
FULL PAPER
Sele. (%)
research funds from Hubei Key Laboratory of Pollutant Analysis
Entry
Oxidant
Conv. (%)
&
Reuse Technology (Hubei Normal University).
DFF
MA
43
78
24
46
15
57
42
PA
6
1
Air
100
100
45
28
-
[
b]
2
3
4
5
6
7
O
2
10
-
Keywords: Renewable phthalic anhydride • 5-
N
2
36
-
Hydroxymethfurfural• Oxidation • Diels-Alder reaction
O
O
O
O
2
2
2
2
100
100
100
100
18
56
26
24
[
[
[
c]
-
1
.
.
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d]
-
b][c]
11
2
[
a] Reaction conditions:
5
mmol HMF,
5
mmol
H
2
SO
4
10 wt% catalyst (mass ratio of
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358.
MoO /Cu(NO ) was controlled as 1:1), 40 ml mixed solvent of water and acetonitrile (33:7), 90
3
3
2
o
4. P. Eversfield, W. Liu and E. Klemm, Catalysis Letters, 2017, 147, 785-791.
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1
In summary, we demonstrated for the first time a highly efficient
protocol for directly synthesizing renewable PA from HMF through
an one-pot procedure mediated by MoO /Cu(NO ) . With
3 3 2
characteristics of green and sustainable feedstock, commonly
available catalysts, mild reaction temperature and high yield of
product, the pathway put forward in this study realized the
integration of multistep (decarbonylation of HMF to AFI, oxidation
of HMF to MA, D-A cycloaddition of AFI and MA and subsequent
9
233.
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The process in detail consisted of the initial oxidation of HMF to
DFF, followed by the direct oxidation of DFF to MA and indirect
oxidation of DFF to MA via intermediate AFI. Subsequently, the
active intermediate related to ODA was formed by the crucial D-
A cycloaddition of AFI and MA. Eventually, PA was generated by
the following dehydration. The catalyst system played a vital role
in making the efficient conversion of HMF to PA possible. Under
a mild reaction condition, PA yield of 63.2 % was obtained. This
convenient one-pot synthesis pathway exhibits great potential to
produce renewable PA in a cost-competitive fashion compared to
the current multistep synthesis approach.
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Synthesis procedures of PA form HMF, analysis of PA can be found in
Supplemental Information.
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Acknowledgements
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This work was supported by the National Natural Science Fund of
China (Nos. 21978246, 21776234), the Fundamental Research
Funds for the Central Universities of China (20720190127), the
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ChemSusChem
10.1002/cssc.201902590
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This article is protected by copyright. All rights reserved.