Metal-free oxidative synthesis of succinic acid from biomass-derived furan compounds using a solid acid catalyst with hydrogen peroxide

Article abstract of DOI:10.1016/j.apcata.2013.03.033

Green oxidation of 2-furaldehyde (furfural) and its homologues were investigated using solid acid catalyst and hydrogen peroxide (H ₂O₂) in aqueous media to form succinic acid (SA), a key chemical that affords wide applications in macromolecular, pharmaceutical and agrochemical industries. Amberlyst-15, a strongly acidic ion-exchange resin, functioned as an efficient solid acid catalyst for a highly selective SA production in the furfural oxidation reaction. The synthesized SA was simply isolated in high purity (supported by NMR spectral data). Furthermore, the utilization of Amberlyst-15 with H₂O₂ was also useful in oxidizing carbonyl derivatives of furan (furfural, 5-hydroxymethyl-2- furaldehyde, furoic acid) to a one carbon less linear di-carboxylic acid such as SA and 2-oxoglutaric acid (OGA) under moderate conditions. This catalytic oxidation process with an acid catalyst and H₂O₂ promises to be a viable route for SA syntheses since they have the advantages of easy handling and simple purification decreasing the cost for the production, as compared to the current state of art.

Full text of DOI:10.1016/j.apcata.2013.03.033

Applied Catalysis A: General 458 (2013) 55–62
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Metal-free oxidative synthesis of succinic acid from biomass-derived
furan compounds using a solid acid catalyst with hydrogen peroxide
Hemant Choudhary, Shun Nishimura, Kohki Ebitani∗
School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Green oxidation of 2-furaldehyde (furfural) and its homologues were investigated using solid acid cat-
alyst and hydrogen peroxide (H2O2) in aqueous media to form succinic acid (SA), a key chemical that
affords wide applications in macromolecular, pharmaceutical and agrochemical industries. Amberlyst-
15, a strongly acidic ion-exchange resin, functioned as an efficient solid acid catalyst for a highly selective
SA production in the furfural oxidation reaction. The synthesized SA was simply isolated in high purity
(supported by NMR spectral data). Furthermore, the utilization of Amberlyst-15 with H2O2 was also use-
ful in oxidizing carbonyl derivatives of furan (furfural, 5-hydroxymethyl-2-furaldehyde, furoic acid) to a
one carbon less linear di-carboxylic acid such as SA and 2-oxoglutaric acid (OGA) under moderate condi-
tions. This catalytic oxidation process with an acid catalyst and H2O2 promises to be a viable route for SA
syntheses since they have the advantages of easy handling and simple purification decreasing the cost
for the production, as compared to the current state of art.
Received 22 December 2012
Received in revised form 5 March 2013
Accepted 22 March 2013
Available online xxx
Keywords:
Biomass
Succinic acid
Heterogeneous acid catalyst
Oxidation
Furans
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
pentose in hemicellulose) into bio-products [6]. Furan derivatives
obtained by removal of three water molecules from monosaccha-
Green plants offer a means of harnessing solar energy via photo-
synthesis, and it conveniently serves storage of the biomass energy
around the world. The biomass energy source is far more widely
available than fossil fuels and, with good management practices,
can be the only renewable resource of energy and organic carbon
for our industrialized society [1,2]. The huge number of publications
and intellectual property rights clearly demonstrates the potential
of biomass to displace petroleum in the production of chemicals
and transportation fuels. However, when the edible biomass con-
verts to the valuable chemical materials, it may concern about
the result in food crisis and increase in food prices, especially in
developing countries. In addition, the deforestation of classical for-
est for the plantation of fuel-crops raises the serious issues of
global warming and biodiversity in the world. These issues inspired
researchers to develop techniques to use more abundant lignocel-
lulose, cheaper and inedible biomass.
ride are one of the useful intermediates in the bio-refinery. For
example, 5-hydroxymethylfurfural (HMF) and 2-furaldehyde (fur-
fural) obtained by the acid-catalyzed dehydration of glucose and
xylose, respectively, have been synthesized by various promising
approaches as reported in the literatures [7]. 2-Furoic acid (FuA)
was produced by the Cannizaro reaction from furfural [8] and oxi-
dation of furfural by using KMnO4 [9], Ag2O [10], or mixtures of iron
or copper oxide with platinum oxides [11]. Moreover, the synthesis
of 2,5-furandicarboxylic acid (FDCA) from HMF using a conven-
tional HNO3 oxidant [12] or molecular oxygen with the hydrotalcite
supported Au nanoparticles catalyst [13] was also reported. Herein,
we studied the oxidative synthesis of succinic acid (SA) from these
biomass-derived furan compounds by using a heterogeneous acid
catalyst with hydrogen peroxide (H2O2) under metal-free condi-
tions.
SA is the 1,4-dicarboxylic acid, and it has become a chemi-
cal of significance in recent years; SA was identified as one of
the top 12 value-added chemicals to be produced from biomass
in a report released by the US Department of Energy [14]. SA is
used as a C4 building block [15] for fuel additives [16], solvents
[17], food/cosmetic/pharmaceuticals [18], biopolymers/polyesters
[19], polyurethane [20], plasticizers [21], and fine chemicals [22].
Production of SA through the fermentation of glucose, fructose, lac-
tose, maltose, mannitol, mannose, sucrose, xylose, and cellobiose
by A. succinogenes has been known [23]. Hydrogenation of maleic
acid (MA) using Pd/C [24], Zn/Hg [25], and H3PO2 [26] to pro-
duce SA has been reported earlier. Other studies demonstrated
Lignocellulose, a polymeric material is composed of cellu-
lose, hemicellulose and lignin [3–5]. Various researchers have
reported fermentation and chemical processes for the conver-
sion of glucose (a major hexose in cellulose) and/or xylose (a
Abbreviations: SA, succinic acid; MA, maleic acid; FA, fumaric acid; FuA,
2-furoic acid; OGA, 2-oxoglutaric acid; LA, levulinic acid; HMF, 5-hydroxymethyl-
2-furaldehyde; FDCA, 2,5-furandicarboxylic acid.
∗
Corresponding author. Tel.: +81 761 51 1610; fax: +81 761 51 1149.
E-mail address: ebitani@jaist.ac.jp (K. Ebitani).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.03.033

56
H. Choudhary et al. / Applied Catalysis A: General 458 (2013) 55–62
the electrolytic reduction of aqueous or aqueous-alcoholic sulfu-
ric acid/benzenesulfonic acid/hydrochloric acid media [27], spongy
nickel [28], lead [29], and TiO2 cathodes [30] producing SA in mod-
erate yields. A vapour-phase catalytic process has been patented
for oxidation 2-butene to MA, followed by hydrogenation to SA in
good yield [31]. The oxidation of furfural to SA using Na2MoO4 [32],
Pd(NO3)2 [33], H2SO4 [34], and Hg(NO3)2 [35] was also examined.
Interestingly, Tachibana et al. have studied a two-step generation
of SA from furfural involving formation of FA using NaClO3 and
V2O5 in water at 368 K followed by the reduction of FA with Pd/C
in an autoclave (433 K, 13 MPa), affording SA in 46.6% overall yield
[17,36]. Although industrialized methods [37] have been proposed
in good yield, their practicability is limited by several factors: the
requirement of a supporting electrolyte in the electrochemical cell,
need for costly and hazardous reagents, and separation of elec-
trolyte and catalyst from the reaction mixture/product. The use of
homogeneous metal for the reaction progress is highly undesir-
able because of the depleting mineral resources and metal toxicity
concerns.
synthesized in the laboratory according to the previous literature
[52].
2.2. General procedure for oxidation
2.2.1. General procedure for oxidation of furfural, HMF, FuA and
FDCA
Furfural, HMF, FuA and FDCA oxidation were carried out in a
Schlenk glass tube attached with a reflux condenser. In each reac-
tion solid acid and/or solid base catalyst(s) and reactants were
loaded in the reactor followed by the addition of 30% H2O2 oxidant
and water solvent. The reaction was performed with stirring under
atmospheric pressure at a range of temperatures. After the reac-
tion, the resultant reaction mixture were diluted 10–20 times with
water and the catalyst was filtered off using Millex®-LG 0.20 ␮m.
The recovered catalyst was washed by 50 mL of water, and dried
in vacuo at room temperature before further reuses.
2.2.2. Isolation of SA for the case of furfural
SA obtained by the oxidation of furfural was isolated by simple
crystallization technique after evaporating water from the reaction
mixture using rotary evaporator. The removal of water (bp. 373 K)
under reduced pressure at 328 K also removed the impurities of MA
(bp. 408 K) and formic acid (bp. 373.8 K), confirmed by TLC and pH
of the evaporated solution. The slurry obtained after evaporation
was dissolved in small volume of water and filtered, followed by
cooling the solution in refrigerator overnight to afford pure SA as
white crystalline solid after drying in vacuo for 48 h. 1H NMR (D2O,
The oxidation reactions of furans by H2O2 have been widely
investigated [38–40]. For instance, the oxidation of furfural to
MA [41], fumaric acid (FA) [17] or furan-2(5H)-one [42] had been
extensively reported. The oxidation of HMF with molecular oxy-
gen serves 2,5-diformylfuran (DFF) [43] and FDCA [13] in the
presence of noble metals. Fructose is converted into levulinic
acid (LA) using acid catalyst via HMF formation [44]. The oxida-
tion of other furan derivatives using H2O2 is well summarized
by Badovskaya and Povarova [45]. However, the oxidation of two
acid derivatives of furan, FuA and FDCA, has never been reported.
The formation of oxoglutarate had been found in the literature
using pseudomonas species on FuA [46]. An effective methodol-
ogy of producing commodity chemicals in an environmentally
benign process involves the replacement of homogeneous cata-
lyst by a combination of resins supported sulfonic acid and H2O2
pair. The efficiency of those pairs in a wide variety of oxida-
tion of organic compounds was reported by various researchers
[47]. Interestingly, the activity of resin-supported sulfonic acid
was generally found to be superior to those of the conventional
homogeneous acid catalyst. Very recently, we communicated an
alternative approach for the selective oxidation of furfural to SA
in good yields and high purity using Amberlyst-15, solid acid
catalyst in the presence of H2O2 [48]. Amberlyst-15 is a macro-
reticular sulfonated polystyrene-based ion-exchange resin with
20% divinylbenzene and acidic sulphonic groups [49]. In this paper,
we extended this catalytic system to oxidation of various furan
compounds including furfural, HMF, FuA and FDCA to the SA and/or
2-oxoglutaric acid (OGA), and the reaction pathway has been pro-
posed.
400 MHz): ı 2.60 ppm (s, 4H, CH2
28.84 ppm ( CH2 ), 177.12 ppm (C O).
)
13C NMR (D2O, 400 MHz): ı
2.3. Analytical procedures
2.3.1. HPLC analysis
The filtrate was analyzed by high performance liquid chro-
matography (HPLC, WATERS 600) using an Aminex HPX-87H
column from Bio-Rad Laboratories, Inc. attached to a RI detec-
tor. The column was run at 0.5 mL min−1 at 323 K with 10 mM
H2SO4 aq. as the mobile phase. The conversion and selectiv-
ity were determined with a calibration curve method. The HPLC
retention time for each compounds was observed as 10.9 min for
OGA, 11.5 min for MA, 14.7 min for SA, 17.4 min for formic acid,
18.3 min for FA, 35.4 min for Furan-2(5H)-one, 39.2 min for HMF,
39.5 min for FuA and 58.8 min for furfural. These products were
also confirmed by NMR analysis comparing with those of authentic
samples.
Conversions of all substrates were calculated by using
the following formulae: [{(substrateinput − substrateremained)/
substrateinput} × 100], whereas the product yield was calculated
by [(productdetected/substrateinput) × 100] with the HPLC analysis.
2. Experimental
3. Results and discussion
2.1. Materials
3.1. Oxidation of furfural by solid acid catalyst and H2O2 oxidant
Nafion NR50, Nafion SAC13, Amberlyst-15, FuA and HMF were
purchased from Sigma–Aldrich, Inc. Furfural and FDCA were pro-
cured from Acros Organics and Tokyo Chemical Industry Co., Ltd.,
respectively. ZrO2, conc. H2SO4, conc. HCl and p-toluenesulphonic
acid (p-TsOH) and 2,6-di-tert-butyl-p-cresol were obtained from
Kanto Chemical Co., Inc. Wako Pure Chemical Industries, Ltd. sup-
plied 30% H2O2 [50,51], Nb2O5 and Sulphated Zirconia (SO4/ZrO2).
Süd-Chemie Catal. Jpn. Inc. provided H-ZSM5 (JRC-Z-5-90H(1),
SiO2/Al2O3 = 90). ␥-Aluminum oxide (␥-Al2O3, JRC-ALO-8) was
served by Sumitomo Chemical. Distilled water (Yamato WG202)
was used in the reaction. Hydrotalcite (HT, Mg/Al = 3) was supplied
from Tomita Pharmaceutical Co. Ltd. Hydroxyapatite (HAP) was
The oxidation of carbonyl furans in water was performed
using various heterogeneous and homogeneous acid catalysts. Oxi-
dation of furfural, as one of the suitable source for the linear
1,4-dicarboxylic acids such as FA, SA or MA, was studied initially
[17,32–35,41]. The efficiencies of various acid catalysts for the oxi-
dation of furfural to SA in the presence of H2O2 under mild reaction
parameters are listed in Table 1. Amberlyst-15 displayed the high-
est activity for selective oxidation of furfural to SA (entry 1) among
all the solid acid catalysts. The major products formed in competi-
tion with SA were identified as FA, MA, and FuA by HPLC. Nafions,
␥-Al2O3 and Nb2O5 were moderately active (entries 2–5) whereas

H. Choudhary et al. / Applied Catalysis A: General 458 (2013) 55–62
57
Table 1
Furfural oxidation using various acid catalysts in the presence of hydrogen peroxidea
.
Entry
Catalyst
Furfural conv. (%)
SA selec. (%)
Yield (%)
SA
FA
MA
FuA
1
2
3
4
5
6
7
8
9
10
11
12
13g
14g
Amberlyst-15
Nafion NR50
Nafion SAC13
>99
>99
>99
>99
>99
>99
>99
97
>99
>99
>99
69
74
41
29
26
25
17
17
10
72
49
45
<1
0
74
41
28
26
24
17
17
10
72
49
45
<1
0
<1
<1
<1
2
5
2
2
4
<1
3
<1
1
11
11
10
4
5
2
5
6
11
11
6
2
2
2
<1
0
0
0
0
1
0
c
␥-Al2O3
Nb2O5
ZSM-5e
ZrO2
SO4/ZrO2
p-TsOHf
HClf
f
H2SO4
0
18
0
Blank
Amberlyst-15
Blank
5
0
0
34
23
0
0
0
0
0
a
Reaction conditions: Furfural (1 mmol), H2O (3 mL), Catalyst (50 mg), 30% H2O2 (4 mmol, determined by iodometric titration), 353 K, 24 h, 500 rpm.
JRC-ALO-8.
SiO2/Al2O3 = 90, JRC-Z-5-90H(1).
1 mmol.
Without H2O2.
c
e
f
g
the other solid acid catalyst had very low activities for the oxidation
at least three runs for furfural oxidation with approximately 70%
yields of SA for each run (Fig. 1). Additionally, a scale-up reaction for
furfural (20 mmol) was tested with Amberlyst-15 (1.0 g) and 30%
H2O2 (80 mmol) in water (30 ml) at 353 K. The SA was obtained
in 68% isolated yield with >99% conversion of furfural after 36 h
reaction.
into di-carboxylic acids (entries 6–8). Among homogeneous acid
catalysts (entries 9–11), p-TsOH exhibited the best catalytic activ-
ity. In the absence of either the Amberlyst-15 (entry 12) or H2O2
(entry 13), SA was not obtained but a noticeable amount of furfural
was consumed. The presence of H2O2 alone formed FuA along with
MA in major amounts as compared to SA (entry 12) [53]. The max-
imum yield for FuA was obtained when H2O2 was used without
Amberlyst-15 (entry 12). Besides, the use of Amberlyst-15 alone
(entry 13) or without Amberlyst-15 and H2O2 (entry 14) as well
any products could not be detected using HPLC [54]. These results
in Table 1 clearly demonstrate that the simultaneous presence of
both H2O2 and Amberlyst-15 is essential for the selective conver-
sion of furfural to SA. The efficiency of H2O2 utilization was found
to be 85% under this catalytic system.
The presence of SO3H (protonic type) functional group in solid
acid catalysts like Amberlyst-15 and Nafion enhanced the selectiv-
ity for SA in oxidation of furfural as compared to other acid products.
The high acidic strength of homogeneous acid catalyst like H2SO4
and HCl forced the oxidation with decent selectivity for SA. The
moderate acidic strengths of p-TsOH and Amberlyst-15 (H0 = −2.2)
gave the significant activities (>70% yields). The presence of both
3.2. Oxidation of HMF over solid acid Amberlyst-15 catalyst and
H2O2 oxidant
Oxidation of HMF was also conducted by using Amberlyst-15
acid catalyst and H2O2 oxidant system in water. In this case, not
only SA but also 2-oxoglutaric acid (OGA) was obtained as a major
product. The yields for OGA and SA during the oxidation of HMF by
using Amberlyst-15 and H2O2 are plotted in Fig. 2. FA and MA were
also detected in the reaction mixture but they were not plotted in
a
SO3H functional group and a tolyl ring in Amberlyst-15 and p-
TsOH supposedly enhance their catalytic activities for oxidation of
furans to SA with H2O2. It seems that the ␲–␲ interaction between
a tolyl ring of catalyst and a furan ring favored a suitable confor-
mation via five-membered ring intermediate involving the sulfur
atom of SO3H group to form furan-2(3H)-one type intermedi-
ate and thus catalyzing the synthesis of SA selectively (Scheme 1).
The lack of such structural features in Nafion NR50, Nafion SAC13
and H2SO4 may explain their moderate activities in comparison to
Amberlyst-15 and p-TsOH.
Amberlyst-15 not only exhibited a remarkable catalytic activity
but also an excellent reusability for the furfural oxidation. The cata-
lyst was recovered by simple filtration, washed by water to remove
any adsorbed reaction mixture, and dried in vacuo at room temper-
ature. No SO3H leaching from Amberlyst-15 occurred during the
reactions because the reproducible yields of SA were obtained for
Fig. 1. Reusability of Amberlyst-15. Reaction conditions: Furfural (1 mmol), H2O
(3 mL), Amberlyst-15 (50 mg), 30% H2O2 (4 mmol, determined by iodometric titra-
tion), 353 K, 24 h, 500 rpm.

58
H. Choudhary et al. / Applied Catalysis A: General 458 (2013) 55–62
Scheme 1. Proposed reaction mechanism for production of SA from furan compounds with Amberlyst-15 as solid acid catalyst in the presence of H2O2.
Fig. 2 because their yields were below 1% in all time. After 12 h, the
conversion for HMF reached to >99%. Interestingly, the yield of OGA
was always higher than that of SA. Formation of LA was expected
through a hydration of HMF in the presence of acid catalyst [44],
however, no LA was detected in the reaction mixture at any stage
of the reaction progress. OGA is not produced from LA because of
the stability of LA under present condition (vide infra). According to
these results, it is inferred that the oxidation reaction of HMF to OGA
does not proceed via hydration reaction of HMF to LA and successive
oxidation of LA to OGA, but by oxidative cleavage of furan ring of
HMF, as illustrated by the proposed reaction pathway (Scheme 1).
Table 2 shows the effect of reaction temperature in the oxidation
of HMF. The yield of OGA increased with an increase of the reaction
temperature from 313 K to 348 K and the yields of SA shows similar
tendency but the maximum SA yield was obtained at 353 K.
Fig. 3 shows the effect of amount of H2O2 for the oxidation
of HMF. It was found that lower H2O2 concentration favored the
formation of OGA whereas the SA yield increased and OGA yield
decreased at higher concentrations of H2O2. Interestingly, LA was
found to form in small amount (2.7% yield) in the absence of
H2O2; i.e. hydration of HMF to LA by acid catalysis was observed
in the absence of oxidant. Fig. 4 throws light on the effect of cat-
alyst amount on the HMF oxidation. The yield of OGA increased
with the increasing acid amount with a maximum yield of 38%
for 50 mg (0.24 mmol) of acid. The yield of SA increased ini-
tially with the increase in acid amount to 37.5 mg (0.18 mmol)
thereafter the yield decreased. According to these results, we
confirmed that yields of OGA and SA from HMF were influ-
enced by the amounts of H2O2 and acidic site in the reaction
mixture.
Table 2
Effect of reaction temperature on the oxidation of HMF catalyzed by Amberlyst-15a
.
Entry
Temperature (K)
HMF conv. (%)
Yield (%)
OGA
SA
FA
MA
LA
Formic acid
1
2
3
4
5
6
7
313
333
343
348
353
363
373
39
98
4
22
28
31
27
18
11
0
10
16
18
19
17
15
0
0
0
0
0
0
0
0
0
31
52
59
60
47
25
19
Trace
Trace
Trace
Trace
Trace
Trace
Trace
Trace
Trace
Trace
Trace
Trace
>99
>99
>99
>99
>99
a
Reaction conditions: HMF (1 mmol), H2O (5 mL), Amberlyst-15 (50 mg), 30% H2O2 (4 mmol, determined by iodometric titration), 24 h, 500 rpm, LA is levulinic acid.

H. Choudhary et al. / Applied Catalysis A: General 458 (2013) 55–62
59
Table 3
OGA
SA
HMF
35
30
25
20
15
10
5
Control experiment with OGA and LAa.
100
90
80
70
60
50
40
30
20
10
0
Entry
Substrate
Conv. (%)
Product (yield (%))
1
2
OGA
LA
>99
2
SA (97.2)
No product (0)
a
Reaction conditions: Substrate (100 mg), Amberlyst-15 (50 mg), 30% H2O2
(4 mmol, determined by iodometric titration), H2O (5 mL), 353 K, 24 h, 500 rpm.
␣-keto-acids) to SA (or carboxylic acid) in the reaction pathway.
OGA was oxidized almost completely to SA in the presence of
H2O2 and Amberlyst-15 (Table 3, entry 1). However, under the
same reaction conditions, LA remained inert and no significant
conversion was observed (Table 3, entry 2) [55]. Bunton reported
the oxidation of ␣-diketones and ␣-keto-acids by H2O2 in alkaline
medium involves the breaking of the C C bond between the
carbonyl carbon and the carboxyl groups [56]. We found that the
transformation of OGA to SA is achieved in acid medium over
Amberlyst-15 with H2O2 oxidant system. The result in Table 3
supported that OGA formation from HMF via hydration to LA and
successive oxidation is impossible under the present conditions
[55]. This also explains the increase in yield of SA with increasing
amount of H2O2 or with the higher acid amount; since SA is formed
as a secondary oxidation product for the HMF oxidation.
0
0
5
10
15
20
25
30
35
40
Reaction time/h
Fig. 2. Reaction progress for oxidation of HMF. Reaction conditions: HMF (1 mmol),
H2O (5 mL), Amberlyst-15 (50 mg), 30% H2O2 (3 mmol, determined by iodometric
titration), 348 K, 500 rpm.
30
100
90
80
70
60
50
40
30
20
10
0
OGA
SA
HMF
25
20
15
10
5
Amberlyst-15 could be recycled efficiently for HMF oxidation
with about 18% SA and 27% OGA yield in each run (Fig. 5). The
catalytic system employed for the oxidation of HMF in the scale
up reaction with 10 mmol of HMF oxidized HMF (98% conv.) to
generate products in the similar yield to that in small scale.
3.3. Oxidation of FuA over solid acid Amberlyst-15 catalyst and
H2O2 oxidant
Trudgill [46] reported the oxidation of FuA to oxoglutarate using
pseudomonas F2 species in 1969, but since then no further improve-
ment have been reported. In this work, the oxidation of FuA to alkyl
carboxylic acids was also examined over solid acid Amberlyst-15
catalyst and H2O2 oxidant in water solvent. In the case of FuA oxi-
dation reaction, SA can be formed via C O bond cleavage of FuA
skeleton and OGA can be possibly formed as a competition product
although OGA production was minor.
0
0
1
2
3
4
5
Amount of H2O2/mmol
Fig. 3. Effect of variation of H2O2 on oxidation of HMF. Reaction conditions: HMF
(1 mmol), H2O (5 mL), Amberlyst-15 (50 mg), 24 h, 348 K, 500 rpm. H2O2 amounts
were determined by iodometric titration.
Table 4 enlists the effect of temperature for the oxidation of FuA.
Amberlyst-15 actively converted FuA to SA mainly with a forma-
tion of minor amount of OGA. MA and FA were the side products
Production of SA via successive oxidative cleavage of C C bond
of OGA was confirmed by the following reactions using OGA and
LA as a reactant. The results of this control experiment supported
the proposed C C bond cleavage of OGA (or ␣-diketones and
OGA
30
SA
100
90
80
70
60
50
40
30
20
10
0
25
40
35
30
25
20
15
10
5
OGA
SA
HMF
20
15
10
5
0
0
1
2
3
0
10
20
30
40
50
Number of runs
Catalyst amount/mg
Fig. 4. Effect of acid amount on the oxidation of HMF. Reaction conditions: HMF
(0.5 mmol), H2O (5 mL), Amberlyst-15, H2O2 (2 mmol, amount determined by iodo-
metric titration), 24 h, 348 K, 500 rpm.
Fig. 5. Recyclability of Amberlyst-15 for oxidation of HMF. Reaction conditions: HMF
(1 mmol), H2O (5 mL), Amberlyst-15 (50 mg), H2O2 (3 mmol, amount determined by
iodometric titration), 24 h, 348 K, 500 rpm.

60
H. Choudhary et al. / Applied Catalysis A: General 458 (2013) 55–62
Table 4
Effect of temperature for the oxidation of FuAa
.
Entry
Temperature (K)
FuA conv. (%)
Yield (%)
SA
OGA
MA
FA
Furan-2-one
1
2
3
4
5
313
333
343
353
363
3
20
26
33
59
2
4
6
10
23
1
3
4
5
10
0
11
12
12
16
0
1
2
2
8
0
0
0
2
2
a
Reaction conditions: FuA (1 mmol), H2O (5 mL), Amberlyst-15 (50 mg), 30% H2O2 (4 mmol, determined by iodometry titration), 24 h, 500 rpm.
Scheme 2. Summary of the reactions of furan-2(5H)-one, MA and FA in the presence of Amberlyst-15 and H2O2. Reaction conditions: Substrate (1 mmol), H2O (3 mL),
Amberlyst-15 (50 mg), 30% H2O2 (4 mmol, determined by iodometry titration), 353 K, 24 h, 500 rpm.
in traces. OGA was not formed as major product but instead SA
was formed in decent yields in all temperatures. Unlike Trudgill’s
report, the presence of H2O2 H+ promoted the migration of one of
the adjacent carbons to an electron deficient oxygen atom (i.e., the
Baeyer–Villiger oxidation) forming SA as a major product [46]. The
yield of SA was found to increase continuously with increasing tem-
perature up to 363 K. Furan-2-one was also formed at high reaction
temperatures in small amounts. FuA is highly stable, therefore, it
required high temperature and long-time reaction for conversion
(59% conv., 23% SA yield) [57]. Comparing among furfural, HMF and
FuA oxidations, the oxidative cleavage of FuA required more severe
conditions.
A large scale oxidation of FuA (15 mmol) was tried to demon-
strate the strength and nature of reaction with Amberlyst-15 (0.6 g)
in water (30 ml) in the presence of 30% H2O2 (75 mmol). The 22%
yield of SA was obtained with 90% conversion of FuA after 24 h
reaction at 373 K.
3.4. Plausible reaction pathway
The reactivity of furans toward oxidative cleavage was explored.
Furfural was found to be the easiest substrate for this reaction both
in terms of conversion and selectivity for SA. At temperatures lower
than that required for furfural, HMF is oxidized to generate SA and
Scheme 3. Reaction pathway for SA from furfural, HMF, FuA and FDCA in the presence of Amberlyst-15 and H2O2.

H. Choudhary et al. / Applied Catalysis A: General 458 (2013) 55–62
61
OGA. FuA, on the other hand, was experienced to be a stable com-
pound. The order of reactivity based on the conversion can be given
as following: furfural ∼ HMF > FDCA > FuA [58].
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A plausible acid-catalyzed reaction pathway was proposed for
oxidation of furan compounds, involving the Baeyer–Villiger oxi-
dation based on the report by Kul’nevich et al. [59] (Scheme 1). The
pathway was well supported by adequate experiments showing
that furan compounds could be oxidized to SA via furan-2(3H)-one
type intermediate. The experiment revealed that MA is obtained
from furan-2(5H)-one [48]. SA was not obtained from MA, FA and
furan-2(5H)-one under the present reaction conditions (Scheme 2).
Therefore, we suppose that SA is formed from furan-2(3H)-one.
The reaction was proposed to be initiated via formation of five
membered ring intermediate of furans and Amberlyst-15 which
results in selective production of SA from furfural and FuA, whereas
OGA from HMF. This intermediate was responsible for high con-
sumption of furans in the initial stages of the reactions. The sulphur
atoms with a maximum co-ordination number of 6 and bonding
in the cis configuration leads to the formation of the ring inter-
mediate. The special situation for the two types of configurations
may appear due to the contribution of the ␲-bonds between the
p-electron pairs on neighboring atom [60]. The reaction pathway
for each furan compound to SA is summarized in Scheme 3.
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4. Conclusions
We have demonstrated selective formation of SA from inedi-
ble biomass-based various furan carbonyls using heterogeneous
acid catalysts. SA was selectively formed by oxidation of furfural
in the presence of Amberlyst-15 as a solid acid catalyst and H2O2
as a green oxidant in aqueous media. Dependences of SA yield and
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conversion of furfural at 353 K in presence of 4 mmol of H2O2 oxi-
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The advantages of high yield, reusability of catalyst and simple
isolation of SA from the reaction mixture promises to be a viable
alternative to current state of art of SA. Other furan carbonyls like
HMF, FuA and FDCA [58] were also effectively converted under
ambient reaction conditions using water as solvent to produce 30%,
45% and 42% SA yields, respectively. The C C bond cleavage of OGA
(␣-keto-acids) into SA was also achieved over Amberlyst-15 with
H2O2 oxidant system.
The solid acid catalyst with SO3H group and an aromatic ring
assisted the ␲–␲ interaction along with the strong covalent bond-
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enhanced activity of the catalyst. Such ␲–␲ interaction was pro-
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catalytic activity of Amberlyst-15. Therefore, the acid catalyst in
combination with H2O2 was found to be an effective system for
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Acknowledgement
This work was supported by a Grant-in-Aid for Scientific
Research (C) (No. 22560764) of the Ministry of Education, Culture,
Sports, Science and Technology (MEXT), Japan.
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