Catalytic oxidative C-C bond cleavage route of levulinic acid and methyl levulinate

Article abstract of DOI:10.1039/c6ra16149a

Recently, obtaining value-added chemicals from biomass resources has attracted considerable attention. Levulinic acid is one of the most important biomass platform compounds, which could be obtained from carbohydrate biomass. In this work, levulinic acid was selectively converted into C4 product, including succinic anhydride, via catalytic oxidation with a manganese catalyst in acetic anhydride. Moreover, an unexpected product of maleic anhydride was obtained, which greatly differs from that of levulinate ester. The pathway for formation of maleic anhydride was studied by monitoring and confirming intermediates α-angelica lactone and its derivative 2-methyl-5-oxotetrahydro-2-furanyl acetate. Based on the obtained mechanistic information, the different behaviour between the oxidative cleavage of levulinic acid and levulinate ester was further discussed.

Full text of DOI:10.1039/c6ra16149a

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Catalytic oxidative C-C bond cleavage route of levulinic acid and
methyl levulinate
Fei Xia,a,b Zhongtian Du,c Junxia Liu,a Yangyang Ma,a,b and Jie Xu*a
Received 00th January 20xx,
Accepted 00th January 20xx
Obtaining value-added chemicals from biomass resources has attracted much attention recently. Levulinic acid is one of
the most important biomass platform compounds, which could be obtained from carbonhydrate biomass. In this work,
levulinic acid was selectively converted into C4 product including succinic anhydride via catalytic oxidation with
manganese catalyst in acetic anhydride. Besides an unexpected product of maleic anhydride was obtained which differs
greatly from that of levulinate ester. The pathway for formation of maleic anhydride was studied by monitoring and
confirming intermediates α-angelica lactone and its derivative 2-methyl-5-oxotetrahydro-2-furanyl acetate. Based on
obtained mechanistic information the different behaviour between the oxidative cleavage of levulinic acid and levulinate
ester was further discussed.
DOI: 10.1039/x0xx00000x
www.rsc.org/
valerolactone34,35 and 1,4-pentadiol.36,37
Introduction
Levulinic acid contains carbonyl and carboxyl group;
structurally similar to that of succinic acid.38 Therefore
Succinic acid is an versatile platform chemical which can be
utilized for the preparation of a variety of value-added
downstream products such as succinate ester, succinamide, γ-
butyrolactone, 1,4-butanediol, tetrahydrofuran, 2-pyrrolidone
and N-methyl-2-pyrrolidone.1,2 Succinic anhydride is the
precursor of succinic acid, both of which are important
monomers for biodegradable material poly (butylene
succinate).3-5 Succinic acid and succinic anhydride were
traditionally produced from hydrogenation of maleic
anhydride6-12 which was obtained from catalytic oxidation of
fossil derived feedstocks such as benzene13-15 and butane16-18
However, the raw materials applied in these procedures are
short of oxygen atom, therefore extra oxygen resource was
needed.
production of succinic acid from the oxygenation of levulinic
acid is preferable considering the atom economy.39,40
To date, there are few reports on catalytic conversion of
levulinic acid to succinic acid or succinic anhydride with
molecular oxygen. The first example was a patent in 1954 that
described V2O5 catalysed succinic anhydride and succinic acid
production from levulinic acid at a high temperature of 200-
400 °C.41 Recently Podolean et al. reported the use of noble
metal Ruthenium for the conversion of levulinic acid to
succinic acid at 150 °C.42
However, it is still a challenge to develop a catalytic
procedure characterized by using dioxygen under mild
conditions. Our group reported in 2013 the first example of
manganese-catalysed selective oxidation of levulinate to
succinate in 58.6% yield with O2 under mild conditions. Mn(III)
acetate was disclosed as an efficient catalyst for the oxidative
C-C cleavage of methyl levulinate at the terminal methyl-
carbonyl position.38 The oxidation of substrate methyl
levulinate in our previous research was carried out in acetic
anhydride. However, the use of methyl levulinate is not
arbitrary. When levulinic acid was oxidized under the similar
conditions remarkably different results were observed.
As a renewable oxygen-containing carbon resource, biomass
has attracted extensive attention in recent years. Lots of
studies have focused on the conversion of saccharides such as
cellulose, hemicellulose, glucose, and fructose to value-added
chemicals and platform chemicals,19-27 among which levulinic
acid is an important C5 biomass platform compound that can
be obtained by hydrolysis of cellulose, glucose and 5-
hydroxymethylfurfural.28-32 Levulinic acid could be converted
to various useful chemicals, including levulinate esters,33 γ-
Succinic anhydride (
decreased dramatically compared with that of methyl
levulinate; whereas, a certain amount of maleic anhydride (
1), as a succinate series C4 product,
a. State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese
Academy of Sciences, Dalian National Laboratory for Clean Energy, Dalian,
116023, P. R. China. E-mail: xujie@dicp.ac.cn; Fax: +86-411-8437-9245; Tel: +86-
411-8437-9245.
2
)
was detected as a maleate series C4 product. In addition the
route for levulinic acid oxidation is vague as well.
b. University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
c. School of Petroleum and Chemical Engineering, Dalian University of Technology,
Panjin, 124221, P. R. China.
Hitherto, no report has been published on oxidation of
levulinic acid to succinic anhydride with manganese
compounds as catalyst. Nor did any relevant study on the
significant difference of the oxidation behaviour between the
† Electronic Supplementary Information (ESI) available: Details of characterization
of products and the calculation methods for the experiments. See
DOI: 10.1039/x0xx00000x
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two levulinates been investigated thoroughly. On the basis of was charged to 0.5 MPa. The autoclave was heated to 90 °C
previous study, herein we investigated the reaction process and kept for the desired reaction time.
and confirmed the possible intermediates, besides the
Product analysis
difference between the oxidation of levulinic acid and
levulinate ester was also discussed.
The autoclave was cooled to room temperature after the
reaction. The liquid products were transferred into
a
volumetric flask followed by addition of internal standard for
analysis. The liquid reaction mixture was analysed by GC
calibration curve.
Experimental
Materials and methods
As for the substrate of methyl levulinate, all the liquid
Levulinic acid, dimethyl malonate and dimethyl oxalate were
obtained from Aladdin chemistry Co. Ltd.. Methyl levulinate, α-
angelica lactone were obtained from TCI (Shanghai)
Development Co. Ltd.. Succinic acid was purchased from
Sigma-Aldrich. Dimethyl succinate, dimethyl maleate were
supplied by Alfa Aesar. Maleic anhydride was purchased from
Shenyang chemical reagent Co. Ltd.. Succinic anhydride was
obtained from Sinopharm chemical reagent Co. Ltd.. 2-Methyl-
5-oxotetrahydro-2-furanyl acetate was separated from the
experiments by column chromatography and characterized on
a Bruker 400 MHz spectrometer. Methanol, acetic acid, ethyl
acetate, DMF, DMSO, dichloromethane, acetonitrile and
cyclohexane were purchased from Tianjin Kermel chemical
reagent Co. Ltd.. Methanol, acetic acid, ethyl acetate, DMF,
DMSO, dichloromethane, acetonitrile and cyclohexane were
analytical grade and dried by activated 3A molecular sieve
before used. Mn(OAc)3·2H2O and Mn(acac)3 were purchased
from Alfa Aesar. Mn(OAc)2·4H2O was obtained from aladdin
chemistry Co. Ltd.. Deionized water was purified by Milli-Q
system (Millipore). All the other reagents were commercially
available and used as received.
reaction mixture was transferred into
a 50 mL round-
bottomed flask, then BF3·Et2O (150 mg) and absolute methanol
(20 mL) were added and reflux for 6 h. This method is verified
experimentally and similar methods are also employed for
analysis of carboxylic acid in the previous reports.38,43 GC
measurements were conducted on an Agilent 7890A GC
equipped with an auto sampler and a flame ionization
detector. DB-225 (30m × 250μm × 0.25μm) and DB-17 (30m ×
320μm × 0.25μm) capillary columns were employed for
analysis of reaction mixtures of levulinic acid and methyl
levuinate respectively. Identification of main products was based
on GC-MS (Agilent 7890A/5975C) system equipped with an
Agilent HP-5ms (30m × 250μm × 0.25μm) as well as by
comparison with authentic samples. 1,2,4,5-Tetramethylbenzene
(TMB) was used as the internal standard. The product distribution
was shown on the molar basis.
The conversion (mol%) of levulinates and yield (mol%) of
main products were calculated as follows:
Moles of levulinate in product
Conversion of levulinate = ꢀ1- Moles of levulinate loaded initiallyꢁ ×100%
Moles of Pi in product
Yield of Pi = Moles of Pi formed theoratically ×100%
Typical Procedure for Catalytic Oxidation
In
a typical experiment, Levulinate (2.5 mmol) and Pi: Succinic anhydride, maleic anhydride, angelica lactones, 2-
Mn(OAc)3·2H2O (5 mol%) and 2 mL solvent were added into a methyl-5-oxotetrahydro-2-furanyl acetate, dimethyl succinate,
25 mL teflon-lined stainless steel autoclave equipped with dimethyl malonate, dimethyl oxalate and dimethyl maleate.
magnetic stirrer, pressure gauge and automatic temperature
control apparatus. After purged for 6 times to exclude air, O2
Table 1. Catalytic oxidation of levulinic acida
O
O
O
O
O
O
O
—
Mn(OAc)3 2H2O, O2
O
O
O
O
O
O
O
OH
+
+
+
+
+
Others
O
Acetic anhydride,
90 oC, 10 h
O
1
2
3
4
5
Yield of main products [mol%]
Entry
Catalyst
Conv. [mol%]
Others
1
2
3+4
5
C4-C5 products
1
2
3
4
Mn(OAc)3·2H2O
Mn(acac)3
None
Mn(OAc)2·4H2O
Mn(OAc)3·2H2O
Mn(OAc)3·2H2O
Mn(OAc)3·2H2O
97.6
97.7
96.1
96.8
97.8
97.9
61.8
6.8
6.6
0.9
4.9
5.3
9.4
7.1
14.8
15.3
2.0
12.7
8.8
5.8
6.5
3.5
1.4
3.9
1.2
4.7
38.3
31.5
83.7
44.2
61.7
1.0
65.7
59.9
90.1
63.2
79.7
37.6
28.8
31.9
37.8
6.0
33.6
18.1
60.3
33.0
5b
6c
7d
26.0
17.0
-
a Reaction conditions: Levulinic acid (2.5 mmol), catalyst (5 mol% Mn), acetic anhydride (2 mL), 90 °C, 0.5 MPa O2, 10 h. Data were analysed by GC. b 10
mol% Mn. c 20 h. d Substrate: 5 (2-methyl-5-oxotetrahydro-2-furanyl acetate). Others refer to those cannot be quantified through calibration curve but
conformed by GC-MS, including 1,2,3,5-tetra-O-acetylpentofuranose, acetoxy acetic acid, 1,3-cyclopentanedione, 1,1-ethanediol diacetate, 4-hydroxy-
2-pentenoic acid and 1,1,2-ethanetriol triacetate.
2 | J. Name., 2012, 00, 1-3
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Results and discussion
Comparison of oxidation of levulinic acid and methyl levulinate
Our group previous study focused on the manganese (III)
catalysed aerobic oxidation of methyl levulinate to dimethyl
succinate in acetic anhydride, and 95.3% conversion with
58.6% yield of succinate was obtained.38 In this study, when
levulinic acid was oxidised under the same reaction conditions,
Scheme 1. Dehydration of levulinic acid to angelica lactones and
its derivative.
two substrates while methyl levulinate may be more
preferable for the production of succinate through catalytic
oxidation compared with levulinic acid.
97.6% of levulinic acid was converted whereas the yield of
1
decreased dramatically to 6.8% (Table 1, entry 1). In addition,
reaction catalysed by Mn(acac)3 showed the similar results:
In order to investigate the differences, controlled
experiments were carried out. In the oxidation of levulinic acid
97.7% conversion with negligible yield of
detected compared with 92.4% conversion and 49.8% yield of
succinate from that of methyl levulinate. was observed in
1 (6.6%) were
catalysed by Mn(OAc)3·2H2O and Mn(acac)3 respectively, 2 was
2
obtained unexpectedly as one of the main C4 products with
yield of 14.8 and 15.3% (Table 1, entries 1 and 2). In contrast,
succinate was given as the only C4 product in the oxidation of
methyl levulinate,38 which further confirmed different reaction
routes existed for the oxidation of levulinic acid and methyl
levulinate. According to the GC-MS results, α-angelica lactone
both systems. Based on these results, it was suggested that
there might exists a different conversion pathway between the
(α-AL,
methyl-5-oxotetrahydro-2-furanyl acetate (
during the oxidation (Fig. S1,S3,S13). About 6% of ALs (α,β-AL)
with more than 30% of were obtained after 10 h of reaction
3
), β-angelica lactone (β-AL,
4
) and its derivative 2-
5
) were detected
(a)
5
under the catalysis of Mn(III) (Table 1, entries 1 and 2). To
further explore the reaction mechanism, comparative
experiments of these two substrates were carried out under
the same conditions while samples were taken periodically at
different time along the reaction course while possible
intermediates and products were monitored and confirmed by
GC (Fig. 1) and GC-MS (Fig. S1-S3). The products of oxidation of
levulinic acid and methyl levulinate were traced and shown in
20h
15h
10h
8h
4h
3h
2h
90min
80min
70min
60min
50min
40min
30min
20min
10min
0min
Fig. 1(a) and (b), suspected intermediates
3 and its isomer 4 as
well as its derivative 5 generated during the reaction of
7
8
9
10
11
12
13
14
15
16
17
t (min)
levulinic acid. The dramatic difference between the oxidation
behaviour of levulinic acid and methyl levulinate illustrated
that there exist a “non-oxidative” consumption of levulinic acid
(Scheme 1). During that process it generates
3 through
dehydration cyclization with the aid of acetic anhydride. This
was followed by an addition reaction with acetic acid that
derived from the dehydration process of acetic anhydride to
(b)
form 5. And the yield of 5 was in relatively large quantity
especially without any catalysts (83.7%, Table 1, entry 3). This
is in agreement with former researches. Mascal et al. reported
recently the dehydration of levulinic acid under the catalysis of
60min
e
solid acid to give 3 44
methyl levulinate with acetic anhydride under a nitrogen
atmosphere respectively (Fig. 2) showed that products and
generated due to the dehydration process of levulinic acid,
.
The treatment of levulinic acid and
s
r
u
o
c
n
30min
o
i
t
c
a
e
r
3, 4
10min
5
7
8
9
10
11
12
t (min)
13
14
15
16
17
whereas no such products were obtained for that of methyl
levulinate. These indicated that acetic anhydride promoted the
dehydration of levulinate substrates while the ester group of
methyl levulinate prohibited the process from generating
Fig. 1. (a) GC trace at different reaction time of the oxidation of
levulinic acid. The retention time correspond to the following
compounds: 7.37 min (α-angelica lactone), 10.42 min (maleic
anhydride), 11.68 min (β-angelica lactone), 15.83 min (2-methyl-
5-oxotetrahydro-2-furanyl acetate), 16.06 min (succinic
anhydride). (b) GC trace of the first period of the oxidation of
methyl levulinate (methyl levulinate retention time: 10.6 min).
intermediate
3, 4 and 5. On the basis of former reports and
our results, we can come to the conclusion that the
dehydration of levulinic acid generates 3 which undergo
isomerization to 445 and further addition reaction with acetic
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Dehydration of levulinic acid
Dehydration of methyl levulinate
Scheme 2. Plausible protocol of oxidation of levulinic acid and methyl
levulinate.
6
7
8
9
10
11
12
13
14
15
16
17
A
2. In order to figure out the relationship between the
formation of
controlled experiments were needed. When
to the similar conditions; about 13.1% of and less than 1%
and were detected within 1 h, which was in quite
2
and the generation of the intermediate
3, extra
Fig. 2. Controlled experiments of dehydration of levulinic acid and
methyl levulinate. The retention time correspond to the following
compounds: 7.37 min (α-angelica lactone), 7.92 min (inner
standard: 1,2,4,5-tetramethylbenzene (TMB)), 10.41 min (methyl
levulinate), 11.68 min (β-angelica lactone), 15.83 min (2-methyl-
5-oxotetrahydro-2-furanyl acetate).
3
was subjected
2
1
5
resemblance as the oxidation of levulinic acid. Neither of
which could be associated with the oxidation of methyl
levulinate where succinate (58.6%) consisted exclusively the
majority of the final products without any maleate or other
acid to form 5. However, the reaction of methyl levulinate
does not undergo this route nor does it give any ALs or its
derivatives as intermediates under the same conditions (Fig.
1b and 2).
As shown in Fig. 1(a), ALs formed instantly by dehydration of
levulinic acid in acetic anhydride during the reaction, thus
resulted in the increase of ALs at the first 20 min followed by
the decrease of which to a relatively stable level as the
detectable C4 products.38 As for the oxidation of
3, the
conversion reached more than 99%. We assumed that these
results may due to its high activity and instability, especially
under the specific conditions with a high concentration. As
shown in Fig. 1(a), during the oxidation of levulinic acid, quite
small amount of ALs were formed through the dehydration
process and the concentration of which kept at a relatively low
level during the whole reaction course. The concentration
difference of ALs between the two systems and the high
reaction went on to
intermediate rapidly increased to a high level within the first
1 or 2 h. When the reaction time was prolonged to 3 h and
longer, an increasing amount of dehydration product was
detected after 10 or 15 h while the amount of almost kept in
2 h. Meanwhile, the quantity of
5
3
activity and instability of
3 might account for the low
5
selectivity of target C4 product. Some of the products were
confirmed and shown in Fig. S14-S18.
a relative stable level. As for this abnormal phenomenon, it is
supposed that this was partially due to the decreasing
consumption of which due to the deactivation of the catalyst
Mn(III) by trace water formed during the reaction process. This
can be demonstrated by the decline in quantity of
Consequently, a plausible reaction route for the Mn(III)-
catalysed oxidation of levulinic acid and methyl levulinate in
acetic anhydride was proposed as summarized in scheme 2.
The dehydration of levulinic acid with the aid of solvent acetic
anhydride played an important role, in which the substrate
was dehydrated to ALs followed by the subsequent oxidation
intermediate
3 and 5 as well as increase of products 1 and 2
when adding fresh catalyst to the system and prolonged the
reaction for another 5 h. Whereas doubling the catalyst
amount at the beginning of the reaction did not increase any
ring opening to give
supported the hypothesis that
derivative were the specific intermediates in the catalytic
2. The controlled experiments of
3 further
of the main C4 products except by-product
Besides, prolonging the reaction time showed some positive
effects especially on (26.0%) with nearly trace of detected
(Table 1, entry 6), which indicated that intermediate could
be further convert to and . This was also evidenced by
oxidation of as the substrate under our reaction system
5 (Table 1, entry 5).
3
and its isomer as well as
4
5
2
5
oxidation of levulinic acid which differed from that of methyl
levulinate.
5
1,
2
3
5
The solvent effect on the oxidation of levulinate
(Table 1, entry 7) in which a similar products distribution was
obtained; other side products can be confirmed by GC-MS (Fig.
S3-S12).
Since the generation of intermediates and
2 were closely
related to the dehydration role of acetic anhydride solvent,
therefore solvent effect on the manganese catalytic oxidation
of levulinic acid and methyl levulinate should be considered.
The results in different solvents are summarized in Table 2 in
which products were analysed after esterification with excess
of methanol in order to facilitate detection and comparison.
The studies of oxidation behaviour of levulinic acid and
methyl levulinate proved that
3 and its derivatives were key
intermediates during the reaction in the presence of acetic
anhydride. However, it is still vague on the formation route of
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Table 2. Solvent effect on the oxidation of levulinic acid and methyl levulinate.a
Yield of important products [mol%]b
Entry
Solvent
Subatrate
Conv. [mol%]
Succinate
Trace
5.2
-
Maleate
Malonate
Oxaliate
levulinic acid
methyl levulinate
levulinic acid
methyl levulinate
levulinic acid
methyl levulinate
levulinic acid
methyl levulinate
levulinic acid
methyl levulinate
levulinic acid
methyl levulinate
levulinic acid
methyl levulinate
levulinic acid
82.1
26.9
75.9
29.8
24.1
11.4
46.3
17.9
19.6
Trace
31.4
5.7
2.5
-
7.2
-
-
1
2
3
4c
5
6
7
8
Acetic acid
DMF
3.9
0.5
8.5
-
0.4
2.5
0.1
2.1
3.5
2.0
-
2.2
1.7
0.2
1.0
2.5
1.3
-
-
-
-
1.4
1.2
-
1.4
1.9
Ethyl acetate
Methanol
Acetonitrile
Cyclohexane
DMSO
-
-
-
-
-
-
-
-
-
-
-
-
-
-
7.9
14.0
1.8
-
-
6.4
2.0
-
0.6
18.0
7.9
19.5
3.8
-
-
-
-
-
3.5
-
Dichloromethane
methyl levulinate
a Reaction conditions: Levulinate (2.5 mmol), Mn(OAc)3·2H2O (5 mol% Mn), slolvent (2 mL), 90 °C, 0.5 Pa O2, 10 h. b Data detected by GC after esterification. c Data
in second row of entry 4 was from reference [38].
When oxidation of levulinic acid was carried out in acetic acid
and DMF separately, only 2.5 and 7.2% of dimethyl maleate
Conclusions
with trace amount of dimethyl succinate were obtained
though the conversion did not vary significantly (82.1 and
74.8% respectively) (Table 2, entries 1 and 2). In other solvents
like ethyl acetate, methanol, acetonitrile, cyclohexane, DMSO
and dichloromethane, the conversion of levulinic acid range
from 18.0 to 46.3% while the yield of succinate was less than
3% with trace or even no amount of maleate. As for methyl
levulinate, when the oxidation was carried out in solvents like
acetic acid, DMF and methanol,38 the conversion dramatically
reduced to 26.9, 29.8 and 17.9 from 95.3% that obtained in
acetic anhydride respectively and the yield of succinate was
less than 6.0% (Table 2, entries 1,2,4). Results in other solvents
like ethyl acetate, acetonitrile, cyclohexane, DMSO and
dichloromethane (Table 2, entries 3-8) indicated that the
majority of methyl levulinate maintained unconverted and
negligible succinate and even no maleate were detected as the
C4 products. Both levulinic acid and methyl levulinate yielded
some portion of oxaliate or malonate as by-products in these
solvents.
In summary, catalytic oxidative cleavage of the biomass
derived platform compound levulinic acid was carried out
using manganese (III) as catalyst with molecular oxygen to give
succinic anhydride. Moreover maleic anhydride was obtained.
This process differs greatly from the oxidation of methyl
levulinate under the same reaction conditions, which afforded
the only C4 product succinate. The pathway for levulinic acid
oxidation was disclosed by confirming the intermediates α and
β-angelica lactone and 2-methyl-5-oxotetrahydro-2-furanyl
acetate for the generation of maleic anhydride and low
selectivity of succinic anhydride. Acetic anhydride was proved
to be a key solvent in the oxidation conversion reaction for
dehydration of levulinic acid and maintaining the activity of
Mn(III) catalyst. This study provides an insight into the
comparison in catalytic oxidation of levulinic acid and methyl
levulinate thus indicated the protection of ester group of
methyl levulinate in its oxidative conversion to succinate.
Further study on the transformation of levulinic acid is
currently underway.
Compared with other solvents, therefore, acetic anhydride
played a key role in the oxidation of levulinic acid for the
generation of dehydration products
3 which further oxidized
to 2. In addition, acetic anhydride was the appropriate solvent
Acknowledgements
for the Mn(III)-catalytic oxidation of methyl levulinate to
succinate, since small amount of water produced during the
oxidation process could be absorbed by acetic anhydride thus
keeping the Mn(III) catalyst effective by avoiding it from
disproportionation.46 This was confirmed by the results of
replacing Mn(OAc)3·2H2O with Mn(OAc)2·4H2O, which the
conversion of methyl levulinate dropped to 12.9 from 95.3%
and yield of succinate decreased from 58.6 to 7.7%.38 To the
best of our knowledge, this is the first report on insights of the
mechanism comparison of the Mn(III)-catalysed aerobic
oxidation of levulinic acid and methyl levulinate under mild
conditions.
This work was supported by the National Natural Science
Foundation of China (21233008 and 21473184), Liaoning
Natural Science Foundation of China (2015020587) and the
“Strategic Priority Research Program-Climate Change: Carbon
Budget and Related Issues” of the Chinese Academy of
Sciences (XDA05010203).
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TOC
The difference of catalytic oxidative cleavage route between levulinic acid and
methyl levulinate were intensively investigated.