Efficient conversion of furfuryl alcohol into alkyl levulinates catalyzed by an organic-inorganic hybrid solid acid catalyst

Article abstract of DOI:10.1002/cssc.201000231

A clean, facile, and environment-friendly catalytic method has been developed for the conversion of furfuryl alcohol into alkyl levulinates making use of the novel solid catalyst methylimidazolebutylsulfate phosphotungstate ([MIMBS]₃PW₁₂O₄₀). The solid catalyst is an organic-inorganic hybrid material, which consists of an organic cation and an inorganic anion. A study for optimizing the reaction conditions such as the reaction time, the temperature and the catalyst loading has been performed. Under optimal conditions, a high n-butyl levulinate yield of up to 93 % is obtained. Furthermore, the kinetics of the reaction pathways and the mechanism for the alcoholysis of furfuryl alcohol are discussed. This method is environmentally benign and economical for the conversion of biomass-based derivatives into fine chemicals. Size zero waste: A clean, facile, and environment-friendly catalytic method has been developed for the conversion of furfuryl alcohol into alkyl levulinates, making use of the novel solid catalyst methylimidazolebutylsulfate phosphotungstate ([MIMBS]₃PW ₁₂O₄₀). Under the optimal conditions, a high n-butyl levulinate yield of up to 93 % was obtained, with easy work-up procedures and minimal waste generation.

Full text of DOI:10.1002/cssc.201000231

DOI: 10.1002/cssc.201000231
Efficient Conversion of Furfuryl Alcohol into Alkyl
Levulinates Catalyzed by an Organic–Inorganic Hybrid
Solid Acid Catalyst
[a, c]
[a, c]
[a, b]
Zehui Zhang,*
Kun Dong,
and Zongbao (Kent) Zhao
A clean, facile, and environment-friendly catalytic method has
been developed for the conversion of furfuryl alcohol into alkyl
levulinates making use of the novel solid catalyst methylimida-
zolebutylsulfate phosphotungstate ([MIMBS] PW O ). The
time, the temperature and the catalyst loading has been per-
formed. Under optimal conditions, a high n-butyl levulinate
yield of up to 93% is obtained. Furthermore, the kinetics of
the reaction pathways and the mechanism for the alcoholysis
of furfuryl alcohol are discussed. This method is environmental-
ly benign and economical for the conversion of biomass-based
derivatives into fine chemicals.
3
12 40
solid catalyst is an organic–inorganic hybrid material, which
consists of an organic cation and an inorganic anion. A study
for optimizing the reaction conditions such as the reaction
Introduction
Alkyl levulinates are known to have widespread applications
for example as plasticizing agents, solvents, odorous substan-
[
1]
ces, and fuel additives. In addition, alkyl levulinates contain
two functional groups (a ketone group and an ester group),
which make them versatile building blocks for the synthesis of
Scheme 1. Conversion of furfuryl alcohol into alkyl levulinates.
[
2]
[3]
various chemicals and drugs . Alkyl levulinates were mainly
obtained by direct esterification of levulinic acid with alcohols
in the presence of acid catalysts, and enzymatic methods were
[
4]
also documented recently.
use of mineral acids usually leads to discharge of highly toxic
waste to the environment, corrosion to the instruments, and
difficulties in separation. Therefore, the use of heterogeneous
catalysts has attracted much more attention, because such
techniques are easy to work up and the quantity of waste is
With diminishing resources of fossil fuels as well as global
heating warnings caused by greenhouse gas emissions, much
effort has been devoted to the identification of attractive
chemical transformations to convert biomass into organic bulk
[
5]
[11]
chemicals. One attractive option is the conversion of lignocel-
reduced significantly. Recently, Lange and co-workers carried
[6]
[12]
lulosic biomass to levulinic acid by treatment with acid. How-
ever, acid hydrolysis processes yield an aqueous mixture con-
taining levulinic acid, formic acid, furans (5-hydroxymethylfur-
out pioneering work in furfuryl alcohol alcoholysis. They re-
ported a good yield of ethyl levulinate, which was obtained by
the reaction of furfuryl alcohol with ethanol catalyzed by vari-
ous solid acid catalysts, including acidic ion-exchange resins
and zeolites.
[
7]
fural and furfural), and some polymers. Because water inhibits
the esterification reaction process effectively, one obvious dis-
advantage is that a large amount of energy is needed for the
water evaporation when using the hydrolysis solution. Even
though water has been removed to form a concentrated
syrup, after esterification, the separation of the products from
the remaining mixture is complex and time-consuming. There-
fore, the development of a more facile method to produce
alkyl levulinates is strongly demanded.
In recent years, organic–inorganic hybrid materials have at-
tracted much attention due to the flexible adaptability of both
[13]
the organic and the inorganic groups. Among the hybrid
materials, the counter anions in common ionic liquids, such as
ꢀ
ꢀ
Cl or BF4 , are replaced by Keggin heteropolyanions to form
[
a] Dr. Z. Zhang, K. Dong, Prof. Z. K. Zhao
Furfuryl alcohol can be readily obtained from furfural by hy-
Dalian Institute of Chemical Physics, CAS
[
8]
drogenation. An atom-economic and convenient method for
the synthesis of alkyl levulinates can be envisioned by alcohol-
ysis of furfuryl alcohol in the presence of acid catalysts
4
57 Zhongshan Road Dalian (PR China)
Fax: (+86)411-84379211
E-mail: zhangzehui@dicp.ac.cn
[
9]
[
b] Prof. Z. K. Zhao
(
Scheme 1). As furfuryl alcohol readily polymerizes to form
Dalian National Laboratory for Clean Energy
Dalian 116023 (PR China)
oligomeric products in the presence of strong mineral acids,
the alcoholysis of furfuryl alcohol is always carried out in a
moderate yield by addition of furfuryl alcohol to a large excess
[
c] Dr. Z. Zhang, K. Dong
Graduate School of the Chinese Academy of Sciences
Beijing 100039 (PR China)
[
10]
of alcohols in order to inhibit polymerization. However, the
112
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2011, 4, 112 – 118

Conversion of Furfuryl Alcohol into Alkyl Levulinates
special ionic liquids that demonstrate some unique
advantageous properties. Wang and co-workers developed a
novel Keggin-type phosphotungstate functionalized catalyst
and applied this catalyst to the esterification of n-butanol with
Influence of the catalyst amount
Initially, the effect of the catalyst amount on the alcoholysis of
furfuryl alcohol in n-butanol was investigated. The experiments
were carried out at 1108C for 10 h with a catalyst dosage in
the range of 1–5 mol% based on furfuryl alcohol (Figure 2). It
[
14]
citric acid with good performance.
Herein we report on the behavior of an organic–inorganic
hybrid solid acid catalyst in the alcoholysis of furfuryl alcohol
to alkyl levulinates. The catalyst loading, the reaction tempera-
ture and the water content were found to have significant ef-
fects on this catalytic system. Under the optimal conditions, a
high yield of n-butyl levulinate of up to 93% was obtained. An
important intermediate was also identified by investigating the
reaction kinetics. On the basis of this intermediate, a new
mechanism was proposed, which might lead to further insights
into furfuryl alcohol alcoholysis.
Results and Discussion
Catalyst characterization
The structure of the prepared catalyst was confirmed by NMR
and FTIR (Figure 1) spectroscopy. The Keggin structure has four
different kinds of oxygen atoms; oxygen atoms bound to
Figure 2. Influence of the catalyst amount on furfuryl alcohol alcoholysis. Re-
action conditions: Furfuryl alcohol (1.13 mmol) and catalyst (set amount) in
n-butanol (5 mL), T=110 8C.
can be seen that the yield of n-butyl levulinate increased with
an increasing reaction time for all different catalyst dosages.
However, at the same reaction time point, the more the cata-
lyst dosage was, the higher the n-butyl levulinate yield was.
Under the reaction conditions, 5 mol% of catalyst was required
to reach a maximum n-butyl levulinate yield of 87% within
10 h with a furfuryl alcohol conversion of 100% (data not
given). The increase in the n-butyl levulinate yield with an in-
creasing catalyst dosage should be attributable to an increase
in the availability and number of catalytically active sites.
Figure 1. FTIR spectrum of the catalyst.
Influence of the temperature
Temperature is known to have a profound effect on both the
reaction rate and the product yield. To determine the influence
of the temperature on the furfuryl alcohol alcoholysis, the ex-
periments were carried out at 70, 90, and 1108C, respectively.
Figure 3 shows the temporal evaluation of the results. When
the reaction was performed at 708C, the rate for the n-butyl
levulinate formation was rather slow. Even with a prolonged
reaction time, we only obtained it in a low yield of 7% within
12 h. As discussed in the mechanistic part (see below), the al-
coholysis of furfuryl alcohol with n-butanol requires the forma-
tion of 2-butoxymethylfuran firstly, which then was converted
into the final product. In our experiment, large amount of fur-
furyl alcohol remained unchanged (data not given), indicating
that the first reaction step of the required intermediate
formation was difficult at 708C.
three metal atoms M and to the heteroatom X (O ), bridging
a
[15]
oxygen atoms (O and O ), and terminal oxygen atoms (O ).
b
c
d
The symmetric and asymmetric vibration spectra showed
ꢀ
1
peaks for PꢀO bonds (1080 and 1044 cm ), bridging WꢀO
a
b/c
ꢀ
1
bonds (897 and 806 cm ), and terminal WꢀO bonds
d
ꢀ
1
(
979 cm ), indicating that the Keggin structure was main-
ꢀ1
tained in the catalyst. Two bands at 1230 and 1170 cm were
assigned to S=O stretching vibrations, indicating that a sulfonic
ꢀ
1
group was present. In addition, the band at 622 cm was
attributed to the bending vibration of the CꢀH bond in
imidazole.
ChemSusChem 2011, 4, 112 – 118
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113

Z. Zhang et al.
Figure 3. Influence of the reaction temperature on furfuryl alcohol alcoholy-
sis. Reaction conditions: Furfuryl alcohol (1.13 mmol) and catalyst (5 mol%)
in n-butanol (5 mL), specified temperature.
Figure 4. Influence of the n-butanol volume on the n-butyl levulinate yield.
Reaction conditions: Furfuryl alcohol (1.13 mmol) and catalyst (5 mol%) in
n-butanol (set amount), T=110 8C.
When the reaction temperature was elevated to 908C, the
furfuryl alcohol conversion and the n-butyl levulinate yield
both enhanced significantly. In comparison with the reaction
at 708C, the yield of n-butyl levulinate within 12 h increased
sharply, from 7% to 75%. When the reaction temperature was
further increased to 1108C, its influence was much more evi-
dent. As depicted in Figures 3 and 6, furfuryl alcohol was
almost completely converted into the intermediate 2-butoxy-
methylfuran (data not given) within just 1 h at 1108C, and the
intermediate was almost entirely converted into the product
within 8 h in a yield of 87%. The results demonstrated that the
optimal reaction temperature for the alcoholysis of furfuryl
alcohol was 1108C.
By further increasing the n-butanol volume to 5 mL and
7 mL, the chance of furfuryl alcohol polymerization decreased
significantly, and the n-butyl levulinate yields reached a maxi-
mum of 88% and 82% within 12 h, respectively. Comparison
of the profile with 5 mL of n-butanol to that with 7 mL n-buta-
nol shows that the yield of n-butyl levulinate was higher in
5 mL n-butanol at the same reaction time point. This could be
explained through recognition of the reaction pathway (see
below). The intermediate 2-butoxymethylfuran was formed
quickly by the reaction of furfuryl alcohol with n-butanol, but
the rate for the conversion of the intermediate into the prod-
uct is low. When the reaction was performed in 7 mL of
n-butanol, the content of the intermediate was lower than
that obtained in 5 mL of n-butanol. Therefore, as long as the
n-butanol volume was high enough to inhibit the furfuryl
alcohol polymerization, a higher n-butanol volume caused a
Influence of the n-butanol volume
It is reported that furfuryl alcohol readily polymerizes at a high
lower reaction rate, corresponding to a lower n-butyl
[
16]
concentration to form oligomeric products.
Consequently,
levulinate yield at the same reaction time point.
by keeping the amount of furfuryl alcohol constant, the
amount of n-butanol should have a profound effect on the
product yield. Figure 4 schematically depicts the influence of
the n-butanol volume on the n-butyl levulinate yield. When
using 1.5 mL of n-butanol, the yield of n-butyl levulinate was
lower than that obtained with 3 mL of n-butanol at the same
reaction time point. During the reaction process, the reaction
system quickly turned black in 1.5 mL of n-butanol. This indi-
cated that furfuryl alcohol readily polymerized to form oligo-
mers under the relatively high concentration in 1.5 mL of n-bu-
tanol. Only a n-butyl levulinate in a maximum yield of 56%
within 12 h was obtained, although the conversion of furfuryl
alcohol reached 100%. When the n-butanol volume was in-
creased to 3 mL, the rate of the n-butyl levulinate formation
was much higher than that observed with 1.5 mL of n-butanol
and a high yield of 79% was obtained within 12 h. All of these
results indicated that the furfuryl alcohol polymerization was
inhibited to some degree when the n-butanol volume was
increased from 1.5 mL to 3 mL.
Substrate screening
Furthermore, we carried out the alcoholysis of furfuryl alcohol
with different alkyl alcohols in order to explore the scope of
this method (Table 1). All of the reactions were performed at
reflux temperatures. When methanol was used, methyl levuli-
nate was only obtained in a yield of 5% (Table 1, entry 1). Be-
cause the reaction temperature using methanol was below
708C, a large amount of furfuryl alcohol could not be convert-
ed into the intermediate, leading to the low methyl levulinate
yield. A similar result was observed with an n-butyl levulinate
formation at 708C, which was discussed previously (see
above). In contrast to the methyl levulinate formation, treat-
ment of furfuryl alcohol with n-propanol or isopropanol at
reflux temperature, the yields of n-propyl levulinate and iso-
propyl levulinate increased significantly to 80% and 66%
within 12 h, respectively (Table 1, entries 2 and 3). The large
differences should attributable to the boiling points of the dif-
114
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ChemSusChem 2011, 4, 112 – 118

Conversion of Furfuryl Alcohol into Alkyl Levulinates
Table 1. Reaction of furfuryl alcohol with different alcohols to form alkyl
levulinates.
Table 2. The result of furfuryl alcohol alcoholysis in n-butanol to form
n-butyl levulinates with different catalysts.
[
a]
[a]
Entry
Substrate
Yield [%]
Entry
Catalyst
Time [h]
Yield [%]
[
b]
1
2
3
4
5
6
methanol
5
80
66
88
36
4
1
2
3
4
5
HY-Zeolite
NKG-9
[MIMBS]
12
4
12
2
3
73
0
58
88
n-propanol
isopropanol
n-butanol
isobutanol
tert-butanol
n-butanol
H
3
PW12
O
40
[BmimSO
3
H]
3
PW12
O
40
12
[
b]
[a] Reaction conditions: Furfuryl alcohol (1.13 mmol) and catalyst
5 mol%) in n-butanol (5 mL), heated at reflux temperature. [b] Catalyst
7
65
(
[
(
a] Reaction conditions: Furfuryl alcohol (1.13 mmol) and catalyst
5 mol%) in alkyl alcohol (5 mL), reflux temperature, t=12 h. [b] The
amount was 30 mg.
catalyst was reused.
er, the structure of NKG-9 was seriously destroyed. The catalyst
spheres were pulverized during the reaction, therefore separa-
tion and recycling of the NKG-9 catalyst was difficult. Furfuryl
alcohol alcoholysis was further attempted with methylimidazo-
lebutylsulfate ([MIMBS]), the precursor of [MIMBS] PW O , as a
ferent alkyl alcohols. The high reflux temperatures of n-propa-
nol (978C) and isopropanol (838C) greatly promoted the furfur-
yl alcohol reaction with these alcohols to the intermediates,
which were then converted into alkyl levulinates. The differ-
ence between the n-propyl levulinate and isopropyl levulinate
formation was that it was not only depended on the reaction
temperature, but also had some correlation with steric effects.
The steric effect was much more obvious when using n-bu-
tanol, isobutanol, or tert-butanol (Table 1, entries 4, 5, and 6).
With increasing molecular volume, the reactions of furfuryl al-
cohol with the butanols to the corresponding intermediate as
well as the subsequent conversion of the intermediates into
the products became much more difficult. When furfuryl alco-
hol reacted with n-butanol, the furfuryl alcohol and the inter-
mediate had almost disappeared after 1 and 8 h, respectively.
However, the conversion was much lower in the reaction with
isobutanol and even lower with tert-butanol.
3
12 40
catalyst but did not give any n-butyl levulinate (Table 2,
entry 3). The reason for this was that methylimidazolebutylsul-
fate was a neutral salt, which could not catalyze this reaction.
This also indicated that furfuryl alcohol was stable under neu-
tral condition. When H PW O was used as a catalyst, a homo-
3
12 40
geneous reaction mixture was obtained. Moreover, the reac-
tion proceeded very quickly, with a furfuryl alcohol conversion
of 100% within half an hour. However, the maximum yield of
butyl levulinate was only 58% within 2 h (Table 2, entry 4).
During the reaction process, the reaction mixture became
dark, indicating that furfuryl alcohol seriously polymerized to
form oligomeric condensation products.
[MIMBS] PW O exhibited the best catalytic performance of
3
12 40
all the screened catalysts (Table 2, entry 5). In contrast to the
H PW O , the butylsulfate group in the organic cation pro-
One of the main advantages of heterogeneous catalysts
over homogeneous catalysts is that the former can be recov-
ered and reused. Recycling of the catalyst was also investigat-
ed (Table 1, entry 7). The yield of n-butyl levulinate decreased
from 83% to 65% for the second run, indicating that the cata-
lyst lost some activity during the reaction process, which was
3
12 40
vides the active acid site responsible for the high performance.
Moreover, the heteropolyanions, with high valence and large
volume, are able to endow the novel ionic liquids with a high
melting point.
[
17]
also reported for a previous study. The reasons for the cata-
[
18]
lyst deactivation were complex. One important reason may
be that some insoluble substances, such as oligomeric prod-
ucts from the furfuryl alcohol polymerization, were absorbed
on the solid catalyst.
Reaction pathway and possible mechanism
During the reaction process, the intermediately formed 2-bu-
toxymethylfuran was separated off by chromatography on
silica gel and the structure was confirmed by NMR spectrosco-
py and MS (see Experimental Section for data). To better un-
derstand the alcoholysis of furfuryl alcohol in n-butanol, we in-
vestigated the time course of the intermediate and the prod-
uct formation. The alcoholysis of furfuryl alcohol requires two
Catalyst screening
Furthermore, we carried out the furfuryl alcohol alcoholysis
with different catalysts in order to compare them with our pre-
pared catalyst. HY-Zeolite, a commercial solid acid catalyst, was
used to catalyze the alcoholysis of furfuryl alcohol (Table 2,
entry 1). It showed little catalytic activity and gave only a poor
yield of 3% within 12 h. This effect is attributable to the weak
acidity of the catalytic site. A sulfate functionalized ion-ex-
change resin NKG-9, a strong solid acid catalyst, was also used
to catalyze the reaction. As expected, a high butyl levulinate
yield of 73% was achieved within 4 h (Table 2, entry 2). Howev-
steps. In the first step, furfuryl alcohol (t =1.75 min) reacted
R
with n-butanol (t =1.35 min) to form the intermediate 2-bu-
R
toxymethylfuran (t =1.49 min), and then the intermediate was
R
slowly converted into n-butyl levulinate (tR =2.09 min;
Figure 5).
Comparing the relative area of each compound to the
internal standard (t =3.76 min; Figure 6), the reaction can be
R
described by the following Equations (1)–(3):
ChemSusChem 2011, 4, 112 – 118
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115

Z. Zhang et al.
Figure 5. Typical gas chromatogram of the reaction mixture after 1 h.
Reaction conditions: Furfuryl alcohol (1.13 mmol) and catalyst (4 mol%) in n-
butanol (5 mL), T=110 8C.
Figure 6. The relative peak area of furfuryl alcohol, the intermediate, and
n-butyl levulinate compared to an internal standard. Reaction conditions:
Furfuryl alcohol (1.13 mmol) and catalyst (5 mol%) in n-butanol (5 mL),
T=110 8C.
k1
furfuryl alcohol ƒ! intermediate þ H O
ð1Þ
ð2Þ
ð3Þ
2
Influence of water content on the 2-butoxymethylfuran
conversion
k2
intermediate þ H O ƒ! alkyl levulinate
2
Even though we have identified the intermediate 2-butoxyme-
thylfuran during the reaction of furfuryl alcohol with n-butanol,
further experiments using the intermediate as a substrate were
also carried out in order to confirm that the product was
formed directly from the intermediate. As discussed in the
k3
furfuryl alcohol or intermediate ƒ! byproduct
As shown in Figure 6, it only took 2 h for a complete conver-
sion of the furfuryl alcohol. However, the conversion of the in-
termediate into n-butyl levulinate was much slower. Hence,
the reaction rate was controlled by Equation (2) (k >k ). In
mechanistic section, H O was needed for the conversion of the
2
intermediate into alkyl levulinates. Hence, the influence of the
1
2
addition, some byproducts were formed by nonsequential
reactions, which might derive from furfuryl alcohol and the
intermediate.
H O amount was investigated. As shown in Figure 7, the yield
2
of n-butyl levulinate was less than 23% when no water was
added. However, it increased to 85% within 11 h when one
Several studies on the mechanism of furfuryl alcohol alcohol-
ysis have been published. One possible mechanism was that a
dehydration of furfuryl alcohol to a-angelica lactone takes
place, which was in turn readily
equivalent H O was added to the reaction mixture. When the
2
amount of H O was further increased to two equivalents, the
2
attacked by alcohols to form
[
19]
alkyl levulinates.
However, as
discussed for the reaction path-
way, the reaction of furfuryl alco-
hol with n-butanol to form 2-bu-
toxymethylfuran was an impor-
tant step (Scheme 2). The next
intermediate A was formed by a
1,4-addition. Subsequent depro-
tonation and the discharge of
alkyl alcohol gave rise to the 1,3-
diene B. Protonation of this
diene yielded the cyclic oxonium
C. By electron-pair transfer, the
cyclic oxonium compound was
converted into exocyclic oxoni-
um D, which was attacked by
water to form compound E,
which then isomerized to form
the product.
Scheme 2. Possible mechanism for the conversion of furfuryl alcohol to alkyl levulinates.
116
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ChemSusChem 2011, 4, 112 – 118

Conversion of Furfuryl Alcohol into Alkyl Levulinates
Figure 7. Influence of the water content on the conversion of 2-butoxyme-
thylfuran into n-butyl levulinate. Reaction conditions: 2-butoxymethylfuran
Figure 8. Influence of the water content on the conversion of furfuryl alco-
hol alcoholysis into n-butyl levulinate. Reaction conditions: furfuryl alcohol
(1.13 mmol), water (set amount), and catalyst (5 mol%) in n-butanol (5 mL),
T=110 8C.
(90 mg), water (set amount), and catalyst (5 mol%) in n-butanol (5 mL),
T=110 8C.
reaction rate increased significantly compared to that with one
equivalent of H O. All of the experiments confirmed that water
as the catalyst was investigated. This work demonstrated that
[MIMBS] PW O is an efficient catalyst for the alcoholysis of
2
reacted with the intermediate to form alkyl levulinates.
3
12 40
furfuryl alcohol. Under the optimal conditions, n-butyl levuli-
nate was obtained in a high yield of 93% within 12 h. After
the reaction, the catalyst could easily be separated from the re-
action mixture for reuse. As furfuryl alcohol can be produced
from renewable resources, this method is environmentally
benign and economical for the conversion of biomass-based
derivates into fine chemicals. Further research and application
of this solid acid catalyst in sustainable chemistry should be
developed in the future.
Influence of the water content on the furfuryl alcohol
alcoholysis
It is known that furfuryl alcohol also reacts with water to form
[
20]
levulinic acid under acidic conditions. Following the above
discussion, it should be noted that water promotes the conver-
sion of the intermediate into alkyl levulinates. As the conver-
sion of furfuryl alcohol into the intermediate was a fast step,
we believed that water would also have some effect on the
furfuryl alcohol alcoholysis. Therefore, a control experiment
was carried out with an extra addition of one equivalent of
water into the reaction system, and the result is shown in
Figure 8. Compared to the reaction system without water,
water largely promotes the conversion of furfuryl alcohol to n-
butyl levulinate at the early stage especially during the first
Experimental Section
Materials
Keggin-type phosphotungstic acid was purchased from the Tianjin
Damao Chemical Reagent Factory (Tianjin, China) and N-methylimi-
dazole (99%) from Zhejiang Kaile Chemicals Co. Ltd. (Hangzhou,
China). 1,4-Butane sultone (99%) was supplied by Wuhan Fengfan
Chemical Co., Ltd (Wuhan, China) and furfuryl alcohol (98%) by
Beijing Chemicals Co. Ltd. (Beijing, China). Methyl palmitate (99%)
was purchased from Sigma (St Louis, USA). All alkyl alcohols were
freshly distilled before use.
2
h, and levulinate acid was not detected under these condi-
tions. It was also interesting to see that a slightly higher yield
of n-butyl levulinate of up to 93% was obtained compared to
that of 88% achieved without water. This indicated that water
promoted the desired reaction rather than the competing re-
action with n-butanol to form levulinate acid under our reac-
tion conditions. One important reason for this was that n-buta-
nol was used in excess. Another important reason should be
attributable to the fact that the furfuryl alcohol conversion into
the intermediate was a fast step, whereas the reaction of the
intermediate with water to form alkyl levulinates was a slow
step. This finding once again confirmed the proposed mecha-
nism in which water took part in the reaction to some degree.
Catalyst synthesis
The catalyst was prepared according to the known procedure with
[14]
some modifications (Scheme 3).
Methylimidazole (10.3 g,
0.125 mol) and 1,4-butane sulfone (17.1 g, 0.125 mol) were added
into a 100 mL round bottom flask and the mixture was stirred at
5
08C for 24 h under nitrogen atmosphere. During this process, a
white precipitate (MIMBS) formed. The slurry mixture was filtered
and the obtained solid was washed with ethyl acetate (3ꢁ50 mL),
then dried in vacuum. MIMBS (3.3 g, 0.015 mol) was added to an
Conclusions
ꢀ1
aqueous solution of H PW O (11.4 g, 0.005 mol, 144 mgmL )
3
12 40
The production of alkyl levulinates by alcoholysis of furfuryl al-
cohol using a novel organic–inorganic hybrid [MIMBS] PW O
and the mixture was stirred at room temperature for 24 h. Water
was removed in vacuum, and the final product, [MIMBS] PW O ,
3
12 40
3
12 40
ChemSusChem 2011, 4, 112 – 118
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117

Z. Zhang et al.
Keywords: alcohols · biomass · heterogeneous catalysis ·
solvolysis · sustainable chemistry
[
1] a) H. J. Bart, J. Reidetschlager, K. Schatka, A. Lehmann, Ind. Eng. Chem.
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EP2065025 A2;
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d) L.
Clark,
A.
Felix-Moore,
J. J. J.
Louis,
Scheme 3. Synthesis of the catalyst.
[
[
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Characterization
1
[
MIMBS] PW O : H NMR (400.3 MHz, D O): d=8.65 (s, 1H), 7.53
3
12 40
2
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(
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2
2
3
.92–2.90 (t, 2H), 2.10–2.06 (m, 2H), 1.77–1.73 ppm (m,
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3
H); C NMR (100.6 MHz, D O): d=135.7, 124.1, 122.6, 50.3, 49.3,
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2
31
6.0, 28.5, 21.3 ppm; P NMR (160.1 MHz, D O): d=ꢀ15.2; FTIR
2
(
KBr): n¯ =1230, 1170 (both S=O), 1080, 1044 (both PꢀO ), 979 (Wꢀ
a
ꢀ1
O ), 897, 806 (both PꢀO ), 622 cm (CꢀH).
d
b/c
1
2
6
1
-Butoxymethylfuran: H NMR (400.3 MHz, CDCl ): d=7.44 (s, 1H),
3
.38–6.37 (d, 1H), 6.35–6.34 (d, 1H), 4.46 (s, 2H), 3.52–3.49 (t, 2H),
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1, 2356–2358; b) J. Bozell, G. R. Petersen, Green Chem. 2010, 12, 539–
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554.
(
100.6 MHz, CDCl ) d=152.1, 142.7, 110.4, 108.9, 70.1, 64.8, 31.7,
3
+
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9.3, 13.9. HRMS calcd. for C H O Na [M+Na] : 177.0891;
9 14 2
found: 177.0889.
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is as follows: Furfuryl alcohol (110.7 mg, 1.130 mmol), n-butanol
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(
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round bottom flask equipped with a reflux condenser. The mixture
was heated at 1108C with vigorous stirring. At different time inter-
vals, samples (100 mL) were withdrawn, diluted with an internal
[
ꢀ
1
standard solution containing methyl palmitate (12 mgmL ), centri-
[21]
fuged at 10000 rpm for 5 min, and then analyzed.
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4
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Analysis of Products
The products were analyzed on by gas chromatography (GC) on a
890F instrument (Techcomp Scientific Instrument Co., Ltd., China)
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7
[
[
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with a crosslinked capillary FFAP column (30 mꢁ0.32 mmꢁ0.4 mm)
equipped with a flame ionization detector. Operating conditions
were as follows: The flow rate of the N carrier gas was
2
ꢀ
1
4
0 mLmin , the injection port temperature was 2508C, the oven
temperature was 1908C, and the detector temperature was 2808C.
The peaks were identified by comparison of the retention time of
the unknown compounds with those of standard compounds and
quantified based on the internal standard method.
1380–1387.
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Acknowledgements
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[
[
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Financial support provided by the National High-Tech Research
and Development Program of China (2007AA05Z403) and the
Knowledge Innovation Program of CAS (KGCXZ-YW-336) are
greatly acknowledged.
2021.
Received: July 25, 2010
118
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