From lignocellulosic biomass to furans via 5-acetoxymethylfurfural as an alternative to 5-hydroxymethylfurfural

Article abstract of DOI:10.1002/cssc.201403252

A facile pathway to furan derivatives from lignocellulosic biomass via 5-acetoxymethylfurfural (AMF) was developed. AMF possesses advantageous properties due to its less-hydrophilic acetoxymethyl group relative to the hydroxymethyl group of 5-hydroxymethylfurfural (HMF). The hydrophobicity and chemical stability of AMF allowed practical isolation and purification to afford a highly pure product of up to 99.9 %. AMF was produced in good to excellent yields under mild conditions from 5-chloromethylfurfural (CMF) and alkylammonium acetates, both of which could be obtained directly from lignocellulosic biomass. Heterogeneous reactions with polymer-supported alkylammonium acetates were also established; this showed the feasibility of a continuous process for this pathway. AMF could be transformed into various promising furanic compounds, such as 2,5-furandicarboxylic acid (FDCA), 2,5-furandimethanol (FDM), and 5-hydroxymethyl-2-furanoic acid (HFA), in high yields.

Full text of DOI:10.1002/cssc.201403252

DOI: 10.1002/cssc.201403252
Full Papers
From Lignocellulosic Biomass to Furans via 5-
Acetoxymethylfurfural as an Alternative to 5-
Hydroxymethylfurfural
[a]
[a]
[a]
[b]
[b, c]
Eun-Sil Kang, Yeon-Woo Hong, Da Won Chae, Bora Kim, Baekjin Kim,
Yong
[b, c]
[b, c]
[a]
Jin Kim,
Jin Ku Cho,*
and Young Gyu Kim*
A facile pathway to furan derivatives from lignocellulosic bio-
mass via 5-acetoxymethylfurfural (AMF) was developed. AMF
possesses advantageous properties due to its less-hydrophilic
acetoxymethyl group relative to the hydroxymethyl group of
both of which could be obtained directly from lignocellulosic
biomass. Heterogeneous reactions with polymer-supported al-
kylammonium acetates were also established; this showed the
feasibility of a continuous process for this pathway. AMF could
be transformed into various promising furanic compounds,
such as 2,5-furandicarboxylic acid (FDCA), 2,5-furandimethanol
(FDM), and 5-hydroxymethyl-2-furanoic acid (HFA), in high
yields.
5-hydroxymethylfurfural (HMF). The hydrophobicity and chemi-
cal stability of AMF allowed practical isolation and purification
to afford a highly pure product of up to 99.9%. AMF was pro-
duced in good to excellent yields under mild conditions from
5-chloromethylfurfural (CMF) and alkylammonium acetates,
Introduction
Current issues involving energy and the environment are
prompting us to replace fossil-based resources with renewable
ethoxymethylfurfural (EMF; Figure 1), which can be used in
[3]
a variety of applications.
[
1]
and sustainable ones. Biomass-derived carbohydrates photo-
synthesized from atmospheric carbon dioxide are attracting
much attention due to their abundance and availability. Re-
cently, considerable efforts have been made to transform bio-
mass-derived carbohydrates into fuels and value-added chemi-
Until now, most efforts toward the production of HMF have
used simple hexoses, primarily fructose and glucose. These
edible starting materials are relatively easy to convert into val-
uable products in good yields, whereas noncrop-based ligno-
cellulosic biomass has been notoriously difficult to convert. For
example, the conditions under which the constituent saccha-
rides in the raw lignocellulosic biomass are transformed into
HMF are normally ineffective, and a laborious multiple-step
process is required: 1) chemical and biological pretreatment
for the removal of lignin, 2) hydrolysis of cellulose and hemicel-
lulose into glucose, 3) isomerization of glucose into fructose,
and 4) dehydration of fructose into HMF. This is why HMF pro-
duction from the most abundant lignocellulosic biomass on an
industrial scale is generally considered to be inefficient and un-
[
2]
cals.
One of the beneficial pathways in the chemical conversion
of carbohydrates is their dehydration into a broad range of in-
teresting compounds, especially furan-based ones. 5-Hydroxy-
methylfurfural (HMF) is the most well-known platform chemical
for the preparation of furanic compounds, such as 2,5-furandi-
carboxylic acid (FDCA), 2,5-furandimethanol (FDM), and 5-
[4]
[
a] E.-S. Kang, Y.-W. Hong, D. W. Chae, Prof. Dr. Y. G. Kim
Department of Chemical and Biological Engineering
Seoul National University, 1 Gwanak-ro
Gwanak-gu, Seoul 151-742 (Korea)
economical.
Promising results obtained by Zhao et al., who used chromi-
[5a]
um catalysts in alkylimidazolium chloride ionic liquids (ILs),
marked a breakthrough in the dehydration of sugar to form
HMF, and encouraged other groups to search for improved sol-
utions for the IL-mediated direct conversion of oligo- and poly-
saccharides to HMF. Work on di- and polysaccharide dehydra-
tion by the Dumesic group resulted in a 38% yield of HMF
with 85% conversion from cellobiose and a 36% yield of HMF
E-mail: ygkim@snu.ac.kr
[
b] B. Kim, Prof. Dr. B. Kim, Prof. Dr. Y. J. Kim, Prof. Dr. J. K. Cho
Green Material and Process R&D Group
Korea Institute of Industrial Technology (KITECH)
8
9 Yangdaegiro-gil, Ipjang-myeon, Cheonan 331-822 (Korea)
E-mail: jkcho@kitech.re.kr
[
c] Prof. Dr. B. Kim, Prof. Dr. Y. J. Kim, Prof. Dr. J. K. Cho
Department of Green Process and System Engineering
Korea University of Science and Technology (UST)
[5b]
with 91% conversion from starch. Binder and Raines report-
ed that N,N-dimethylacetamide (DMA) containing 10 wt% LiCl
[5c]
8
9 Yangdaegiro-gil, Ipjang-myeon, Cheonan 331-822 (Korea)
was a good solvent for this challenging goal. Considering
lignocellulosic feedstock transformations, the yields varied
from 16 to 47%. Although such studies have achieved desira-
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201403252. It contains detailed experi-
mental procedures for the direct conversion of lignocellulosic biomass
[5]
1
ble conversion of lignocellulosic biomass into HMF, low feed
concentrations were used and, in most cases, the product
into CMF and spectral data of the synthesized compounds ( H and
1
3
C NMR spectroscopy).
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of chloride and the exceptional stabilization of the
[11]
a carbon to the aromatic ring furan. It could be
easily transformed into the much more stable EMF
(
Figure 1) simply by stirring it in a solution in ethanol
[10]
at room temperature. In addition, deformylation of
the resulting furfural derivatives can take place in the
presence of water to give some decomposition prod-
[12]
ucts, such as levulinic acid derivatives. We also ob-
served a color change to deep brown when the syn-
thesized CMF was stored on a bench top for one
day; this could be attributed to its sensitivity to air
and/or moisture. It is necessary to keep CMF cold
and dry for long-term storage. Thus, the high reactivi-
ty of CMF makes it difficult to handle and to isolate
from the reaction mixture.
Therefore, we tried to modify CMF into a more
stable compound through a simple process and we
focused on the synthesis of an acetyl derivative of
HMF, namely, AMF. It can be efficiently produced
from CMF and alkylammonium acetates, both of
which could be obtained directly from lignocellulosic
biomass raw materials by using biphasic reactions
and anaerobic fermentation, respectively (Figure 2).
AMF offers some important advantages over HMF for indus-
trial production. Compared with the hydroxymethyl group of
HMF, the acetoxymethyl group makes AMF hydrophobic, less
reactive, and more readily isolable from the aqueous reaction
mixture, whereas HMF is known to be relatively unstable
Figure 1. HMF as a platform chemical and potential uses for its derivatives.
yields were quantified only by HPLC. Additional limitations are
due to the difficulty of separation and in making the produc-
tion cost effective. The development of viable methods for
HMF isolation and purification combined with the recycling of
expensive ILs also remains a challenge.
Herein, we propose 5-acetoxymethylfurfural (AMF) as an al-
under acidic conditions and is difficult to isolate from the
[
6]
[6,13]
ternative to HMF, which is the well-known precursor for furan
compounds, and a facile pathway to produce some furan de-
rivatives from lignocellulosic biomass via AMF.
aqueous reaction mixture.
AMF is as chemically versatile as
Results and Discussion
The dehydration of carbohydrates into HMF under acidic con-
ditions is often accompanied by a series of side reactions,
which decrease the efficiency of the processes. The most prev-
alent byproducts are levulinic and formic acids, which result
[
7]
from hydrolysis of HMF, and insoluble polymeric substances
called humins, which are formed by aldol addition and/or con-
[
8]
densation of decomposed HMF.
One strategy to prevent these undesirable side reactions,
first reported by Mascal and Nikitin, was to use a biphasic
system for the HCl-catalyzed carbohydrate conversion of HMF
[9]
to its chloro derivative, 5-chloromethylfurfural (CMF). This
practical method enabled direct conversion of lignocellulosic
biomass-derived carbohydrates (cellulose) into CMF in higher
yields than other methods used for the production of HMF. We
[
10]
applied the modified method of Mascal and Nikitin to other
polymeric carbohydrates, such as agarose, and even untreated
lignocellulosic biomass raw materials, including straws, rape
stem, grass, reed, paper, and fiberboard, which readily afforded
CMF in a single pot with moderate to good yields (see the Ex-
perimental Section and Supporting Information).
However, CMF is quite reactive toward even weak nucleo-
philes, such as alcohols, due to the better leaving-group ability
Figure 2. Proposed pathway for the production of AMF by using CMF and
alkylammonium acetate obtained directly from lignocellulosic biomass.
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HMF and can be transformed into promising precursors, such
as FDCA, FDM, 5-hydroxymethyl-2-furanoic acid (HFA), for bio-
based furan polymers (see below, Scheme 3). It is also consid-
ered to be a promising biofuel candidate with a high energy
The alkylammonium acetates required in the reaction could
be obtained from the reactive extraction of fermented acetic
acid. These days, acetic acid is generating interest as a biobased
platform chemical to replace petroleum-based C2 chemicals.
Particularly in terms of the bioconversion of lignocellulosic bio-
ꢀ
1
density of 8.7 kWhL , which is comparable to regular gasoline
ꢀ
1
ꢀ1 [14]
(
8.8 kWhL ) or diesel (9.7 kWhL ). Moreover, it is important
mass into a C chemical, the anaerobic production of acetic
2
[17]
to note that HMF shows a weak cytotoxicity and mutagenicity
acid by the microorganism acetogen is more beneficial than
ethanol production through traditional yeast fermentation for
[15]
in humans, whereas AMF is neither cytotoxic nor mutagenic.
To date, there have only been four reports, including three
patents, detailing the conversion of CMF into AMF, in which
AMF was produced by the substitution reaction of CMF with
the following reasons: 1) acetogen converts all xylose (C ) and
5
glucose (C ) sugars, 2) it tolerates all breakdown products of
6
lignocellulosic biomass, 3) it operates in harsh environments,
[16]
acetic acid in the presence of a weak inorganic base. The
treatment of acetic acid or other carboxylic acids in DMF or
acetonitrile with potassium carbonate afforded AMF or the cor-
responding ester derivatives of HMF in moderate to good
yields. The resulting carboxylated products were used as build-
ing blocks of therapeutic agents for osteoporosis or protein ty-
rosine phosphatase 1B (PTP1B) inhibitors. However, these pro-
cedures seem to be limited in scope due to relatively long re-
action times (5 h to overnight) and the limited use of a high
boiling and polar solvent, such as DMF, for solubilizing the in-
organic bases, from which the isolation of AMF looks rather
complicated.
and 4) it produces no CO as a byproduct. A variety of feed-
2
stocks, such as municipal solid waste, sewage sludge, forest
product residues, wood waste, and inedible energy crops, can
be converted into acetic acid by anaerobic fermentation.
Although salt formation is not favored from an environmen-
tal point of view, reactive extraction is proposed to be an effi-
cient and eco-friendly process for the recovery of fermented
carboxylic acids from the aqueous solution among several sep-
aration methods, such as crystallization, precipitation, distilla-
[18]
tion, ion exchange, reverse osmosis, and electrodialysis. It is
a separation process that uses the reaction between extrac-
tants and the materials extracted. The extractant in the organic
phase reacts with the material in the aqueous phase and the
reaction complexes formed are then solubilized in the organic
phase. Extractants, such as hydrocarbon, phosphorous, and ali-
phatic amine, are mainly used in the reactive extraction of car-
boxylic acids. The advantages of this process are as follows:
1) increased reactor productivity, 2) ease in reactor pH control
without base addition, 3) low process waste and production
costs through using a high substrate concentration, 4) reuse of
the extracting solvent, and 5) reduction of downstream proc-
Several patents detailing the production of alkoxymethyl
[14]
ethers and esters of HMF, including AMF, have been filed
that addressed the acid-catalyzed dehydration of carbohy-
drates into AMF in IL/acetic acid. However, low concentrations
of fructose, glucose, or disaccharides are used as starting mate-
rials, and a low to moderate level of the product selectivity
was obtained: For example, in 1-ethyl-3-methylimidazolium
chloride ([EMIm]Cl)/acetic acid (1:4 w/w), 4 wt% of glucose was
reacted in the presence of CrCl (4 wt%) at 1008C for 3 h to
2
[
14c]
[19]
yield 1.3% of HMF and 5.1% of AMF.
essing load and recovery cost.
The results found in the conversion of lignocellulosic bio-
mass into CMF led us to recognize that 1) the chloride leaving
group of CMF was reactive enough to be substituted by
a weak nucleophile, and 2) the chloride ion cleaved from CMF
needed to be sequestered to avoid undesired further reactions.
In our study, alkylammonium acetates were employed as effec-
tive reagents for the reaction. The acetate anion and the alky-
lammonium cation act as a nucleophile and as a countercation
for the liberated chloride, respectively (Scheme 1). Ionic reac-
tants are often insoluble in organic solvents, but the alkylam-
monium cation helps to solubilize the salts in the organic
phase, which allows for less-polar organic solvents to be used.
The reactivity of alkylammonium acetates in the conversion
of CMF into AMF was investigated according to the alkyl sub-
stituents (Table 1). Negligible conversion of CMF was observed
with ammonium acetate due to its poor solubility in organic
solvents (Table 1, entry 1), whereas alkyl-substituted ammoni-
um acetates reacted with CMF to produce the desired AMF in
good to excellent yields. AMF was obtained in 84 and 67%
with tetramethylammonium acetate (TMAA) and tetraethylam-
monium acetate (TEAA) (Table 1, entries 2 and 3), respectively.
Relatively low yields with TEAA could be attributed to the
presence of water in the reagent. TBAA performed excellently
in converting CMF into AMF (Table 1, entry 4). A nearly quanti-
tative yield of AMF was obtained at room temperature within
[16d]
5–10 min. Compared with the previous studies,
this 30-fold
increase in the reaction rate clearly indicates that the reactivity
of acetate anions is enhanced by the alkylammonium cations.
A similar role of substituted ammonium salts was reported in
[20]
the esterification of carboxylic acids with benzyl chloride.
Because commercially available alkylammonium acetates are
relatively more expensive than alkali metal acetates, a more
economic process was examined. We assumed that the substi-
tution reactions would also proceed with alkali-metal acetates
in the presence of a catalytic amount of TBAA. Indeed, CMF
was successfully converted into AMF in 94% yield with the cat-
Scheme 1. Conversion of CMF into AMF with alkylammonium acetate.
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or THF, resulted in lower AMF yields of 71–76% after longer re-
action times (>2–5 h; not listed in Table 1).
Table 1. Reactivity of alkylammonium acetates in the conversion of CMF
into AMF.
[
a]
The acetate salt of Aliquat 336 (a mixture of tri-n-octylme-
thylammonium and tri-n-decylmethylammonium), which is
widely used as an extracting reagent for the reactive extraction
of carboxylic acids, also afforded a good yield of AMF (89%;
Table 1, entry 11). Tri-n-octylammonium acetate (the acetate
salt of Alamine 336) gave a moderate yield (56%; Table 1,
entry 12). This indicates that tetrasubstituted ammonium ace-
tates are more effective than trisubstituted ammonium acetate
in the conversion of CMF into AMF. On the other hand, N-alky-
limidazolium acetates were less effective than alkylammonium
acetates (Table 1, entries 13 and 14).
Entry
R
R’
Reaction time Yield of
[
b]
[min]
AMF [%]
1
2
ꢀH
ꢀH
60
10
10
10
240
240
15
45
20
15
15
trace
84
67
96
94
93
90
81
86
85
89
56
36
37
ꢀCH
ꢀCH
3
ꢀCH
ꢀCH
3
[c]
3
4
5
6
7
8
9
0
2
CH
3
2
CH
3
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
2
2
2
2
2
2
2
2
2
)
)
)
)
)
)
)
)
)
3
3
3
3
3
3
3
7
7
CH
CH
CH
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
3
3
3
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
ꢀ(CH
2
2
2
2
2
2
2
)
)
)
)
)
)
)
3
3
3
3
3
3
3
CH
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
3
[
[
[
[
[
[
d]
e]
f]
g]
h]
i]
1
1
1
/ꢀ(CH
2
)
9
CH
3
ꢀCH
ꢀH
3
12
13
14
15
25
25
N-methylimidazole
N-methylimidazole
ꢀCH
2
CH
CH
3
Evaluation of the extraction of alkylammonium acetate
ꢀ(CH
2
)
3
3
To evaluate the reactive extraction of alkylammonium acetates,
[a] Unless otherwise noted, alkylammonium acetate (1.1 equiv) was used
their partition ratios (K ) were investigated based on the sub-
in acetonitrile as a solvent at room temperature. [b] Yields obtained after
purification by using column chromatography [c] Tetrahydrate form. [d] A
catalytic amount of tetra-n-butylammonium acetate (TBAA; 0.2 equiv)
was used with excess sodium acetate (3.3 equiv) at 408C. [e] A catalytic
amount of TBAA (0.2 equiv) was used with a stoichiometric amount of
sodium acetate (1.1 equiv) at 408C. [f] Crude CMF was used as a starting
material. [g] 1,1,2-Trichloroethane (TCE) was used as a solvent. [h] 1,2-Di-
chloroethane (DCE) was used as a solvent. [i] Dichloromethane was used
as a solvent.
D
stituted alkyl groups of the ammonium ion and the extracting
organic solvents (Figure 3).
alytic process (Table 1, entry 5). This is likely to be due to the
ability of alkylammonium cations to function as a phase-trans-
fer catalyst (PTC). Tetra-n-butylammonium chloride produced
by the substitution reaction then reacts with insoluble sodium
acetate to yield TBAA in situ. TBAA is thus generated continu-
ously and enters the next catalytic cycle. In other words, the
regeneration of quaternary ammonium acetates renders the
acetate anion soluble and sufficiently nucleophilic. Interesting-
ly, the use of a stoichiometric amount of sodium acetate under
the same reaction conditions also provided AMF in 93% yield,
with no difference in the reaction time (Table 1, entry 6). The
result is favored from an ecological point of view and is ame-
nable to industrial scaleup of the processes. This observation is
also in good agreement with the results obtained from a similar
reaction that the reaction rate was found to be first order in
Figure 3. Partition ratios (K ) of alkylammonium acetates to extracting sol-
vents.
D
The K values of TMAA with C alkyl chains and TBAA with
D
1
C4 alkyl chains ranging from 0.04 to 0.12, were insufficient for
[
21]
the concentrations of the substrate and catalyst.
extraction,. However, the K values of the acetate salts of Ali-
D
Moreover, crude CMF obtained without purification immedi-
ately after removal of the solvent from the organic phase in
the biphasic reaction was converted into AMF in 90% yield
quat 336 and Alamine 336 with C alkyl chains were enhanced
8
approximately 15–50 times compared with those of TMAA and
TBAA. Furthermore, the acetate salt of Aliquat 336 was effec-
tively extracted from simulant culture medium prepared with
yeast extract (Bacto). Thus, the acetate salt of Aliquat 336
could be recovered quantitatively by extraction, and it success-
fully reacted with CMF to afford AMF in high yield (90%). Un-
known components from yeast extract were extracted togeth-
er with the acetate salt of Aliquat 336, and no negative effect
was found for the AMF synthesis. Quantitative extraction of
the acetate salt of Aliquat 336 could be confirmed by the ab-
sence of any acetic acid in the NMR spectra of the aqueous
layer. Although the best result for the conversion of CMF to
AMF was obtained with TBAA, the acetate salt of Aliquat 336
(Table 1, entry 7). By taking integration of the two reactions (bi-
phasic reaction for CMF+substitution reaction for AMF) into
account, various chlorinated solvents were also evaluated in
the biphasic reaction for CMF synthesis. The use of TCE or
[
10]
DCE as a reaction solvent led to 81 and 86% yield of AMF,
[22]
respectively (Table 1, entries 8 and 9). Dichloromethane gave
5% yield of AMF (Table 1, entry 10). Although the reaction
8
was a little slower in the chlorinated solvents, insignificant de-
creases in yield were found relative to those in acetonitrile.
The reactions in other solvents, such as acetone, ethyl acetate,
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could not be excluded as a potential acetylating reagent for
use in an industrial process.
Synthesis of AMF under heterogeneous conditions
In the next study, in the pursuit of a continuous process, we
examined a heterogeneous reaction for the concise prepara-
tion of AMF from CMF by using polymer-supported alkylam-
monium acetates (Scheme 2).
Figure 4. Reusability test of acetate-exchanged Amberlite IRA-900. Reaction
conditions for each run: CMF (133 mg), Amberlite IRA-900 (3.7 mL), acetoni-
trile (2 mL), 508C, 12 h.
Scheme 2. Heterogeneous conversion of CMF into AMF by using polymer-
supported alkylammonium acetate.
Two commercially available anionic exchange resins (Amber-
lites IRA-400 and IRA-900) loaded with tetraalkylammonium
groups on the polystyrene resin were selected, and their coun-
teranions were exchanged with acetate prior to use (see the
Experimental Section).
As expected, a longer reaction time (12 h) and slightly
higher temperature (508C) were required to increase the reac-
[
23]
tion rate of the heterogeneous reactions.
Nevertheless,
a high yield of AMF (90%) was obtained in the reaction with
acetate anion-exchanged Amberlite IRA-900 after removal of
the polymer-supported alkylammonium chloride, through
simple filtration followed by concentration.
D
Figure 5. Comparison of the partition ratios (K ) of AMF and HMF in extract-
ing solvents.
The separated resin could be regenerated with additional
acetic acid or sodium acetate, and it was reused consecutively
at least five times. No clear changes in the conversion of CMF
and the selectivity of product were observed (Figure 4).
ether, and 99% could be recovered from ethyl acetate (see the
Experimental Section).
The polarity of the molecules also determines the forces of
intermolecular attraction. As the polarity of AMF decreases, its
boiling point becomes lower than that of HMF. HMF boils at
[19a]
110 8C at 0.02 torr (1 torr=133.32 Pa).
Among the several
Physical properties of AMF
purification methods available, vacuum distillation of HMF is
not an option because HMF is susceptible to thermal decom-
position. Yields of only 45–60% of pure HMF were reported
As briefly mentioned above, AMF showed different chemical
and physical properties to those of HMF due to its acetoxy-
methyl group, relative to the hydroxymethyl group of the
latter. It is not surprising that a decrease in both the hydrophil-
ic character and polarity results. Less hydrophilic AMF was
sparingly soluble in water (approximately 70 mL was needed
to dissolve 1 g of AMF), whereas more hydrophilic HMF was
freely soluble in water (approximately 3 mL was needed to dis-
[25]
when the crude product was distilled. Low-temperature dis-
tillation under a high vacuum is preferred in terms of the cost
of operations and manufacturing efficiency. Meanwhile, the
thermal behavior of AMF deserves special mention. In our
hands, less polar and more stable AMF could be distilled in
high yield (89%) from the crude reaction mixture at similar
temperatures (103–1078C) at 5 torr. Neither significant decom-
position nor a color change were observed. This remarkable
property of AMF, which is distinct from HMF, made another ef-
[
24]
solve 1 g of HMF). The enhanced hydrophobicity resulted in
a dramatic increase in the partition ratio of AMF (Figure 5). A
recovery of 89% could be obtained by extraction from diethyl
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fective and practical separation and purification strategy possi-
ble. Both extraction with a low-polar solvent and distillation
under pressure could easily be used to isolate and purify AMF.
In an effort to obtain highly pure HMF (>99%), Evonik Degus-
sa attempted the hydroxyl protection of HMF with an acetyl
open air on a bench top without color change or decomposi-
tion over two weeks.
Transformation of AMF into furanic monomers
[
26]
group. After fructose dehydration, the resulting HMF was re-
The possibility of using HMF as a versatile platform chemical in
the synthesis of several value-added compounds is derived
from the two functional handles attached to its furan ring. The
hydroxymethyl and formyl groups of HMF can be transformed
into a variety of other functionalities, such as a carboxylic acid
in FDCA or an alcohol in FDM. In recent years, furan-based
polymers have garnered much attention as substitutes for pe-
troleum-based aromatic polymers, such as poly(ethylene ter-
acted with acetic anhydride and 4-(N,N-dimethylamino)pyridine
(DMAP) to provide AMF as a stable intermediate. It was puri-
fied by fractional distillation at 106–1108C at 5 mbar (1 bar=
5
1
ꢁ10 Pa), and a subsequent basic hydrolysis of AMF gave
highly pure HMF.
Separation and purification of AMF
[29]
ephthalate) (PET). As a result, considerable effort has been
dedicated to the efficient conversion of HMF into furanic mon-
omers, such as FDCA, as a replacement for terephthalic acid
The separation and purification of HMF is still a challenging
issue, even though it is crucial for industrial production. The
use of IL solvent systems for the conversion of lignocellulosic
biomass into HMF showed positive results to some extent, but
extremely the low vapor pressure of ILs means that extraction
is the only purification method available. Additionally, the
vacuum distillation of heat-sensitive HMF caused a serious
[30]
(TPA).
With this in mind, we explored the transformation of AMF
into useful furanic monomers to demonstrate its utility
(Scheme 3). Although a number of papers on the transforma-
[
25]
yield drop due to decomposition and oligomerization.
Solvent extraction is conventionally used for the isolation of
organic products from an aqueous mixture, but it is inefficient
in the case of HMF because of the high affinity of HMF for
both water and a range of organic solvents. Recently, an inter-
esting purification method that used water extraction was re-
[
27]
ported, but it was only applicable to crude HMF obtained
[28]
from the dehydration of fructose in a low-boiling solvent.
On the other hand, hydrophobic AMF, with enhanced stabili-
ty, as mentioned in the previous section, allowed for effective
separation and purification from the crude reaction mixture.
Various purification methods, including column chromatogra-
phy, recrystallization, extraction, and vacuum distillation, were
attempted (see the Experimental Section).
Simple recrystallization (Method B) gave a comparable yield
(
(
90%) and purity (99%) of AMF to column chromatography
Method A; Figure 6a). As a simpler method, direct extraction
Scheme 3. Transformation of AMF into useful furan derivatives.
tion of HMF into these furanic monomers have been pub-
lished, to the best of our knowledge, few attempts at function-
al-group transformation, other than those reported in patents,
[31]
have been made for AMF.
Air oxidation of AMF in the presence of a catalytic amount
[32]
of Pt/C gave FDCA in 82% yield, and reduction with NaBH4
led to the desired diol of FDM in 92% yield. Notably, a Canniz-
zaro reaction of AMF was successfully performed to produce
both FDM and HFA. The Cannizzaro reaction simultaneously
yields an equimolar mixture of both a primary alcohol and
Figure 6. Appearance of purified AMF after (a) recrystallization (Method B)
and (b) vacuum distillation (Method D).
[33]
a carboxylic acid from an aldehyde.
Therefore, it can be
of AMF from the crude reaction mixture with hexane/diethyl
ether (1:1; Method C) afforded AMF in higher purity (96%). Re-
markably, extremely pure AMF (99.9%) could be obtained by
vacuum distillation (Method D) without a significant loss of
yield (89%; Figure 6b). Purified AMF could be stored in the
a highly expedient one-pot route to two different furanic mon-
omers from a single starting material, AMF. Another advantage
over standard reduction or oxidation conditions that employ
relatively expensive, reactive, and/or toxic reagents is the use
of an inexpensive and nontoxic hydroxide reagent. Treatment
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of AMF with an aqueous solution of 5n NaOH under mild and
benign conditions (room temperature and ambient atmos-
phere) afforded two furanic monomers simultaneously, and the
AMF purity was determined by GC/MS (HP 6890 GC Systems with
5
973 MSD). The percentage yields of all products were calculated
by dividing the amount of the desired product obtained after pu-
rification by the theoretical yields.
[33a]
yields were comparable to a previous report on using HMF.
Therefore, AMF could be considered as a substitute for HMF
because it can be converted into useful furan derivatives with-
out significant modification compared with earlier reports on
the reactions of HMF.
General procedure for the conversion of polymeric carbohy-
drates and lignocellulosic biomass raw materials into CMF
Hexose-containing biomass (100 mg) was placed in each of the 12
heavy-walled tubular reactors with a screw cap in a Carousel 12
Plus Reaction Station, and then concentrated HCl (3 mL) and TCE
Conclusions
(
3 mL) were added to each reactor. The resulting mixture was
A facile pathway for the production of useful biobased furan
derivatives from the most abundant noncrop-based lignocellu-
losic biomass was developed via AMF. This key intermediate
was produced in good to excellent yields under mild condi-
tions from CMF and alkylammonium acetates, both of which
could be obtained directly from lignocellulosic biomass. The
heterogeneous production of AMF from CMF by using poly-
mer-supported alkylammonium acetates showed the feasibility
for a continuous process of this pathway. As an alternative
platform chemical to well-known HMF, AMF possesses privi-
leged properties that arise from its less-hydrophilic acetoxy-
methyl group instead of the hydroxymethyl group of HMF.
Both the hydrophobicity and improved stability of AMF ena-
bled its practical isolation and purification to afford highly
pure product (up to 99.9%) in fairly high yield. The purified
AMF could be stored in the open air at room temperature
without any changes in purity over two weeks. Because of its
simple purification and improved stability, AMF could be evalu-
ated as an alternative precursor to HMF to synthesize com-
modity chemicals in industry. Finally, further transformations of
AMF into useful furan derivatives, such as FDCA, FDM, and
HFA, were achieved in a successful manner. These results indi-
cate that AMF can play an important role in exploring efficient
and sustainable pathways toward furan derivatives from the
most abundant lignocellulosic biomass. However, the produc-
tion and conversion of AMF through this pathway could also
bring some other issues caused by multiple steps to prepare
furan derivatives and harsh acidic reaction conditions during
biphasic reactions. Further studies on the integration of bipha-
sic and substitution reactions, milder reaction conditions, recy-
cling of solvents and reagents, and the utilization of waste are
currently ongoing.
heated to 908C and stirred at 700 rpm for 1 h. After cooling to
room temperature, the TCE layer was separated by pipette. Addi-
tional fresh TCE (3 mL) was added to the aqueous layer, and the
mixtures were stirred for 15 min before the organic layer was sepa-
rated. The extraction process was repeated twice. Each collected
organic layer was dried over MgSO and the solvent was evaporat-
ed. The crude mixture was purified by filtration through silica gel
(
4
dichloromethane) to give a yellowish liquid. In case of Barley
straw, a 68% yield of CMF was obtained based on hexose content.
Detailed results are given in the Supporting Information.
General procedure for the preparation of AMF from CMF
and alkylammonium acetate
Alkylammonium acetate (11 mmol) was added to a solution of
CMF (1.450 g, 10 mmol) in acetonitrile (20 mL). The resulting mix-
ture was stirred at room temperature, and the reaction was moni-
tored by TLC. In the case of TBAA, the reaction was completed
within 5–10 min.
Separation and purification of the resulting AMF was carried out
by one of the following procedures after evaporation of acetoni-
trile (reaction solvent) under reduced pressure.
Method A: The crude mixture was diluted with hexane/ethyl ace-
tate (10 mL, 4:1) and filtered over Celite, and the filtrate was con-
centrated under reduced pressure. The residue was purified by
column chromatography over silica gel with a gradient solvent
mixture (hexane/ethyl acetate from 4:1 to 2:1) to give AMF as
a pale-yellow to off-white solid (96% yield, 99% purity). The alkyl-
ammonium chloride salt could be recovered by washing the Celite
with organic solvents, such as dichloromethane and ethyl acetate.
Method B: The crude mixture was diluted with hexane/ethyl ace-
tate (10 mL, 4:1) and filtered over Celite, and the solvent of the fil-
trate was concentrated under reduced pressure. Recrystallization
with ethyl acetate (40 mL) provided AMF as a pale-yellow to off-
white solid (90% yield, 99% purity).
Experimental Section
Method C: The crude mixture was directly extracted (ꢁ3) with
hexane/diethyl ether (30 mL, 1:1), and then the supernatant was
decanted. The combined supernatants were concentrated in vacuo
to yield AMF as a pale-yellow solid (90% yield, 96% purity).
General
Unless otherwise noted, materials were obtained from commercial
sources and were used without further purification. Analytical TLC
was performed by using Merck 60 F254 glass plates precoated with
a 0.25 mm thickness of silica gel. Melting points were determined
with an open capillary melting point apparatus (Electrothermal
IA9100). NMR spectra were measured on a Bruker AVIII400 instru-
Method D: The crude mixture was directly distilled at 103–1078C
under high vacuum (5 torr) to yield AMF as a white solid (89%
yield, 99.9% purity).
The related results obtained from with other alkylammonium ace-
tates are summarized in Table 1.
ment as solutions in CDCl with tetramethylsilane (TMS) as an inter-
3
1
13
nal standard ( H at 400 MHz and C at 100 MHz), unless otherwise
stated and data were reported as follows in ppm (d) from TMS:
chemical shift (multiplicity, coupling constant in Hz, integration).
1
M.p. 548C; H NMR: d=9.64 (s, 1H), 7.26 (d, J=3.2, 1H), 6.63 (d,
13
J=3.2, 1H), 5.14 (s, 2H), 2.11 ppm (s, 3H); C NMR: d=177.5,
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1
69.9, 155.2, 152.6, 121.6, 112.3, 57.5, 20.3 ppm; HRMS: m/z calcd
the regenerated resin was tested with Amberlite IRA-900, and it
could be reused at least five times with little effect on the yield
+
for C H O [M +H]: 169.0501; found: 169.0501.
8
9
4
(1st run: 90%, 2nd run: 85%, 3rd run: 86%, 4th run: 85%, 5th run:
8
3%).
Investigation into the partition ratio of alkylammonium ace-
tates
Investigation into the partition ratios of AMF and HMF
All extraction experiments were conducted at room temperature.
The alkylammonium acetate (200 mg) was dissolved in an organic
solvent (20 mL), and the resulting solution was mixed with an
equal volume of deionized water or an aqueous solution of Bacto
yeast extract (5 gL ). The mixture was gently shaken for 1–2 min
and then allowed to separate. Each phase was recovered and con-
centrated under reduced pressure. After weighing each residue,
All extraction experiments were conducted at room temperature.
AMF (200 mg) or HMF (200 mg) were dissolved in an organic sol-
vent (20 mL) and the resulting solution was mixed with an equal
volume of deionized water. The mixture was gently shaken for 1–
ꢀ1
2
min and then allowed to separate. Each phase was recovered
and concentrated under reduced pressure. After weighing each
residue, the partition ratio, K , was determined from Equation (1).
the partition ratio, K , was determined as shown in Equation (1). In
D
D
In this step, phase volume changes were not measured. The
amount of AMF or HMF in each organic layer is reported in
Table 3.
this step, phase volume changes were not measured and the re-
sults were only approximate on a mass basis, but they gave an in-
dication of the merits of various organic solvents.
½
alkylammonium acetateꢁ
organic
KD¼
½
alkylammonium acetateꢁ
Table 3. Amount of AMF or HMF in each organic layer, as calculated
from Equation (1).
aqueous
ð1Þ
ðmg of alkylammonium acetateÞ
organic
aqueous
¼
ðmg of alkylammonium acetateÞ
Intermediate
Massorg/massaq
diethyl ether
ethyl acetate
AMF
HMF
178:22
51:149
197:3
113:87
The amount of alkylammonium acetate obtained in each organic
layer is reported in Table 2.
Transformation of AMF into FDCA
Table 2. Amount of alkylammonium acetate obtained in each organic
layer, as calculated from Equation (1).
The 10 wt% Pt/C (975 mg, 0.5 mmol) was added to a solution of
AMF (840 mg, 5 mmol) in a saturated aqueous solution of NaHCO3
Alkylammonium
acetates
Massorg/massaq
diethyl ether
(10 mL). The solution was stirred with molecular oxygen bubbling
dichloromethane
ethyl acetate
through the liquid aqueous phase for 2 h at 708C. Completion of
the reaction was confirmed by TLC. The platinum catalyst was then
filtered off, and the filtrate was acidified with a 1n aqueous solu-
tion of HCl. After concentration under reduced pressure, the crude
mixture was dissolved in methanol, dried over Na SO , filtered, and
TMAA
TBAA
Aliquat 336
Alamine 336
8:192
17:183
141:59
171:29
20:180
21:179
121:79
167:33
6:194
16:184
136:64
143:57
2
4
concentrated under reduced pressure. The residue was purified by
recrystallization from mixed solvents (5:1 dichloromethane/metha-
nol) to give FDCA as a white solid (640 mg, 82%). M.p. 340–3428C;
Preparation of AMF under heterogeneous conditions
1
13
H NMR (CD OD): d=7.26 ppm (s, 2H); C NMR (CD OD): d=159.5,
3
3
+
1
47.4, 118.0 ppm; HRMS: m/z calcd for C H O [M +H]: 157.0137;
6 5 5
Before the reaction, commercially available anionic exchange resins
found: 157.0140.
ꢀ
1
(
Amberlite IRA-400: 4.8 mL, 1.4 meqmL by wetted bed volume;
ꢀ1
Amberlite IRA-900: 3.7 mL, 1.0 meqmL by wetted bed volume)
were treated with 10n sodium acetate in water (100 mL) for 1 h to
replace their anions with the acetate anion. Then, the resins were
washed with water (2ꢁ100 mL), acetonitrile (2ꢁ100 mL). CMF
Transformation of AMF into FDM
NaBH4 (85 mg, 2.26 mmol) was added to a solution of AMF
(475 mg, 2.82 mmol) in MeOH (3 mL) at room temperature, and
the mixture was stirred for 30 min. After concentration in vacuo,
the residue was dissolved in water (5 mL) and then neutralized at
08C with a 1n aqueous solution of HCl until pH 6–7. The solution
was extracted with ethyl acetate (2ꢁ50 mL), and the combined or-
(
173 mg, 1.2 mmol for Amberlite IRA-900; 133 mg, 0.92 mmol for
Amberlite IRA-400) was dissolved in acetonitrile (2 mL), and the re-
sulting solution was added to the resin prepared as described
above. The mixture was shaken for approximately 12 h at 508C,
and the completion of the reaction was confirmed by TLC. The
mixture was filtered and the filtrate was concentrated under re-
duced pressure. The crude mixture was purified by column chro-
ganic layers were dried over MgSO , filtered, and concentrated
4
under reduced pressure. The residue was purified by column chro-
matography on SiO with a gradient solvent mixture (hexane/ethyl
matography on SiO with a gradient solvent mixture (hexane/ethyl
2
2
acetate from 4:1 to 2:1) to give AMF (182 mg, 90% from Amberlite
IRA-900; 75 mg, 49% from Amberlite IRA-400) as a pale-yellow to
off-white solid. Recycling of the recovered resins after completion
of the reaction was performed by repeating the anion-exchange
procedure described above. The 10n aqueous solution of sodium
acetate was reused without further treatment. The recyclability of
acetate from 1:2 to 1:4) to give FDM (334 mg, 92%) as an off-white
1
solid. M.p. 76–788C; H NMR (300 MHz, [D ]acetone): d=6.20 (s,
6
1
3
2H), 4.49 (d, J=6 Hz, 4H), 4.31 ppm (t, J=6 Hz, 2H); C NMR
(75 MHz, [D ]acetone): d=154.9, 107.5, 56.5 ppm; elemental analy-
6
sis calcd (%) for C H O (128.13): C 56.24, H 6.29; found: C 56.17, H
6
8
3
6.02.
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Full Papers
Transformation of AMF into FDM and HFA (Cannizzaro reac-
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[
Powdered NaOH (1.446 mg, 26.158 mmol) was added to a stirred
solution of AMF (1.216 g, 7.232 mmol) in water (7.2 mL) at 08C.
Excess NaOH was used to accelerate the reaction rate, although
three equivalents were sufficient to promote the reaction. The re-
sulting mixture was stirred vigorously at room temperature, and
the reaction was monitored by TLC. At the end of the reaction, it
was neutralized at 08C with a 1n aqueous solution of HCl until
pH 7–8. The resulting solution was extracted with ethyl acetate
[
(
3ꢁ200 mL). Each collected organic layer was dried over Na SO , fil-
2 4
tered, and concentrated in vacuo. Purification by recrystallization
with ethyl acetate (1 mL) afforded FDM (400 mg, 86%) as a pale-
yellow to off-white solid.
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from the abovementioned solution, until the pH of the aqueous
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solid. M.p. 165–1668C; H NMR ([D ]acetone): d=7.17 (d, J=3.2 Hz,
6
13
1
H), 6.49 (d, J=3.2 Hz, 1H), 4.61 ppm (s, 2H);
C NMR
(
[D ]acetone): d=160.1, 158.6, 144.1, 118.6, 108.7, 56.5 ppm; ele-
6
mental analysis calcd (%) for C H O (142.11): C 50.71, H 4.26;
6
6
4
found: C 51.19, H 4.73.
0
0
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Full Papers
[
26] D. Reichert, M. Sarich, F. Merz, (Evonik Degussa GmbH), EP 1958944,
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Bowers, K. R. Parker, A. Shaikh, L. R. Partin, C. E. Sumner Jr., (Eastman
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2
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[
AMF into FDCA, see: a) A. J. Sanborn, E. J. Howard, US 2009/156841,
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Received: November 10, 2014
Morrow, B. R. Bowers, K. R. Parker, A. Shaikh, L. R. Partin, J. C. Jenkins, P.
Published online on && &&, 0000
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FULL PAPERS
E.-S. Kang, Y.-W. Hong, D. W. Chae,
B. Kim, B. Kim, Y. J. Kim, J. K. Cho,*
Y. G. Kim*
&& – &&
From Lignocellulosic Biomass to
Furans via 5-Acetoxymethylfurfural as
an Alternative to 5-
Alternative routes: A facile pathway to
furan derivatives from lignocellulosic
biomass via 5-acetoxymethylfurfural
vantageous properties to well-known 5-
hydroxymethylfurfural (HMF) and can
be transformed into various promising
furanic compounds in high yields.
Hydroxymethylfurfural
(AMF) is reported. AMF possesses ad-
ChemSusChem 0000, 00, 0 – 0
www.chemsuschem.org
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These are not the final page numbers! ÞÞ