Synthesis of butyrate using a heterogeneous catalyst based on polyvinylpolypyrrolidone

Article abstract of DOI:10.1515/chempap-2015-0243

A heterogeneous polyvinylpolypyrrolidone supported Br?nsted acidic catalyst ([PVPP-BS]HSO₄) was used to synthesize butyrate in this paper. The prepared catalysts were characterized by FT-IR, TG, and FESEM and their catalytic activity in butyric acid esterification with benzyl alcohol was investigated. The influencing factors such as the amount of catalyst, reaction temperature, and reaction time were carefully studied. Under the optimized condition with the butyric acid to benzyl alcohol mole ratio of 1 : 1.2 and the reaction temperature of 130°C, the yield of benzyl butyrate reached 96.8 % within 4 h in the presence of 8 mass % of catalyst. Moreover, the catalyst could be reused six times without noticeable drop in activity. This catalyst was also used to synthesize other kinds of butyrates achieving the butyrate yield above 90 %.

Full text of DOI:10.1515/chempap-2015-0243

Chemical Papers 70 (5) 538–544 (2016)
DOI: 10.1515/chempap-2015-0243
ORIGINAL PAPER
Synthesis of butyrate using a heterogeneous catalyst based
on polyvinylpolypyrrolidone
Song Wang*, Qian-Qian Chang, Nazar Shawgi, San-Xi Li, Lin-Nan Zhang
School of Science, Shenyang University of Technology, Shenyang 110870, China
Received 17 June 2015; Revised 23 September 2015; Accepted 21 October 2015
A heterogeneous polyvinylpolypyrrolidone supported Brønsted acidic catalyst ([PVPP-BS]HSO4)
was used to synthesize butyrate in this paper. The prepared catalysts were characterized by FT-IR,
TG, and FESEM and their catalytic activity in butyric acid esterification with benzyl alcohol was
investigated. The influencing factors such as the amount of catalyst, reaction temperature, and
reaction time were carefully studied. Under the optimized condition with the butyric acid to benzyl
alcohol mole ratio of 1 : 1.2 and the reaction temperature of 130◦C, the yield of benzyl butyrate
reached 96.8 % within 4 h in the presence of 8 mass % of catalyst. Moreover, the catalyst could be
reused six times without noticeable drop in activity. This catalyst was also used to synthesize other
kinds of butyrates achieving the butyrate yield above 90 %.
c
ꢀ 2015 Institute of Chemistry, Slovak Academy of Sciences
Keywords: butyrate, esterification, polyvinylpolypyrrolidone, catalyst
Introduction
et al., 2007). The application of ionic liquids, includ-
ing alkane sulfonic acid IL used in the temperature-
controlled liquid–solid separation system (Bates et al.,
2002), double SO3H-functionalized ILs (Zhang et al.,
2007), protonated N-alkylimidazolium ILs (Zhi et al.,
2009), and ILs with acidic counter anions (Liu et al.,
2011) for esterification has been reported. IL catalysts
were also reported for the butyl butyrate synthesis us-
ing N-methylimidazole and 1,3-propane sultone (Han
& Zhou, 2011). Unfortunately, the use of ionic liq-
uids to prepare catalysts leads to long reaction times,
large reaction volume, high viscosity of the catalyst
(Sahoo et al., 2009; Zhu et al., 2009). Recently, poly-
mer supported catalysts were developed for esterifi-
cation reactions. Specifically, a novel Brønsted acidic
heteropolyanion-based polymeric hybrid catalyst was
synthesized and applied to various esterification pro-
cesses (Leng et al., 2008). However, the preparation of
this kind of catalyst has some disadvantages such as
complex preparation and high cost.
Butyrate, as an alternative of the conventional in-
termediate in chemical industry, has drawn consider-
able attention in recent years due to its biodegrad-
ability and toxicity. Generally, butyrate is produced
by butyric acid esterification with alcohols catalyzed
by homogeneous catalysts such as H2SO4 and H3PO4,
which suffer from corrosiveness, difficult recovery and
environmental hazards. To overcome the above prob-
lems, the development of solid acid catalysts such as
acidic resins, supported mineral acids, and zeolites has
attracted much attention (Dijs et al., 2002; Fang et al.,
2006). However, most solid acid catalysts have dis-
advantages related to high mass transfer resistance,
product selectivity, and the tendency to deactivation
in practical application of the esterification process.
Ionic liquids with excellent thermal stability, neg-
ligible volatility, and a variety of structures are rec-
ognized as an alternative of conventional catalysts
and they have been extensively studied in the field
of organic reactions, especially esterification (Wasser-
scheid & Keim, 2000; Visser et al., 2001; Chowdhury
Polyvinylpolypyrrolidone (PVPP) is usually used
as an adsorbent to remove haze-active polyphenols
from beer and wine by forming hydrogen bonds or
*Corresponding author, e-mail: 1259669134@qq.com
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S. Wang et al./Chemical Papers 70 (5) 538–544 (2016)
539
Fig. 1. Preparation of polymeric IL [PVPP-BS]HSO4.
Van der Waals interactions (Laborde et al., 2006).
Because of its nontoxicity, hydrophilicity, and insol-
ubility, PVPP is gaining considerable attention as
a catalyst. Polyvinylpolypyrrolidone-supported boron
trifluoride has been studied for the synthesis of
1,8-dioxooctahydroxanthenes and 1,8-dioxodecahyd-
roacridines and the results indicated that the polyvin-
ylpolypyrrolidone-supported boron trifluoride com-
plex is a high loaded polymer supported Lewis
acid, which is stable and retains its effective ac-
tivity (Mokhtary & Langroudi, 2014). Consequently,
this paper attempted to develop an efficient, envi-
ronment friendly, low-cost polymeric acidic catalyst
([PVPP-BS]HSO4) synthesized by coupling SO3H-
functionalized PVPP with H2SO4 for the synthesis of
butyrate. In addition, the optimum conditions of bu-
tyric acid esterification with benzyl alcohol, as well as
the catalytic activity and reusability of this catalyst
are also discussed in this paper.
the heating rate of 10◦C min−1 under nitrogen atmo-
sphere. Elemental analyses and surface morphologies
of [PVPP-BS]HSO4, PVPP-BS and PVPP were in-
vestigated by a Hitachi SU8000 (Tokyo, Japan) field
emission scanning electron microscope (FESEM). The
BET surface area was measured at the liquid-nitrogen
temperature using a Micromeritics SSA4200 analyzer
(Beijing, China). The samples were degassed at 100◦C
to the vacuum of 0.13 Pa before the BET surface area
analysis. The acid value of [PVPP-BS]HSO4 was de-
termined by acid–base titration (Kafuku et al., 2010;
Shah et al., 2014).
PVPP-BS and [PVPP-BS]HSO4 were prepared ac-
cording to the following procedure. In a 250 mL round-
bottomed flask, BS (6 g) was added to PVPP (10 g)
dispersed in toluene and the resulting mixture was
slowly stirred and heated to 80◦C for about 24 h. Upon
completion, the mixture was cooled down to the room
temperature and filtrated. After filtration, the zwitte-
rion (PVPP-BS) was washed with ethyl acetate three
times and dried in vacuum at 60◦C.
Experimental
The obtained PVPP-BS was dispersed first in
methanol; then, sulfuric acid (4.32 g, 2.4 mL) in
equimolar amount to BS was added to the mixture
at 0◦C and stirred for 24 h. On completion, the mix-
ture was washed three times with methanol to remove
nonionic residues. Then, methanol was removed from
the mixture in vacuum at 60◦C and the final prod-
uct [PVPP-BS]HSO4 was obtained. The preparation
process is shown in Fig. 1.
Commercially available PVPP was purchased from
Gobekie New Materials Science & Technology Co.
(Shanghai, China). 1,4-Butane sultone (BS, 99 %)
and sulfuric acid (AR grade) were purchased from
Aladdin (Shanghai, China). FT-IR spectra measure-
ments were performed on a PRESTIGE-21 FT-IR
absorption spectrometer using KBr in the 4000–
400 cm−1 region. Thermal decomposition point was
obtained by TGA Q50 (New Castle, DE, USA) at
Typical butyric acid esterification with benzyl al-
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S. Wang et al./Chemical Papers 70 (5) 538–544 (2016)
Fig. 3. TGA patterns of PVPP (a), PVPP-BS (b), and
Fig. 2. Comparative FT-IR spectra of PVPP (a), PVPP-BS
[PVPP-BS]HSO4 (c).
(b), [PVPP-BS]HSO4 (c), and H2SO4 (d).
cohol was conducted as follows: butyric acid (7.0488
g), benzyl alcohol (10.3814 g), cyclohexane (8 mL, as a
water-carrying agent), and catalyst [PVPP-BS]HSO4
(1.394 g) were put in a three-necked flask equipped
with a thermometer and a water segregator with a re-
flux condenser. The resulting mixture was stirred at
90◦C in an oil bath for 3 h. Upon completion, the re-
action mixture was cooled to room temperature and
the obtained ester was separated from the mixture.
Chemical analysis of the products was done us-
ing a gas chromatograph Agilent 7890A GC (Palo
Alto, CA, USA) with an HP 5 capillary column (30
m × 0.32 mm × 0.25 m) and an FID detector. The
butyrate yield was calculated from the concentration
of butyrate as described in literature (Liang, 2013;
Wang et al., 2008).
polymeric cations and HSO−4 are combined by strong
ionic interactions and that a PVPP-based polymeric
hybrid was produced through the combination of
SO3H-functionalized PVPP with H2SO4 via ionic
linkages.
Thermal analysis of PVPP, PVPP-BS, [PVPP-BS]
HSO4 achieved by TG is presented in Fig. 3; thermal
decomposition temperature of PVPP was observed
to be about 350◦C. Also, the drastic mass loss of
PVPP-BS and [PVPP-BS]HSO4 in Fig. 3 (curves b
and c) in the temperature range of 350–500◦C corre-
sponds to the thermal decomposition of PVPP in the
catalyst. In Fig. 3 (curve b), an approximately 4.5 %
mass loss of PVPP-BS was observed between 150◦C
and 190◦C, and an approximately 3 % mass loss of
[PVPP-BS]HSO4 occurred between 200◦C and 240◦C
(curve c). The results indicate lower decomposition
temperature and higher mass loss of PVPP-BS com-
pared to [PVPP-BS]HSO4, thus H2SO4 is immobilized
on PVPP-BS as a ionic hybrid.
In the recycling tests, the catalyst [PVPP-BS]
HSO4 was reused after being heated in vacuum at
60◦C for 2 h. The recovered catalyst was directly used
in the next run.
Fig. 4 presents the results of field emission scanning
electron microscopy (FESEM) of PVPP, PVPP-BS,
and [PVPP-BS]HSO4. In Fig. 4a, amorphous PVPP
particles with the diameter of 3–5 m were ag-
gregated together. After the reaction with BS or
H2SO4, the surface morphology of PVPP-BS (Fig. 4b)
or [PVPP-BS]HSO4 (Fig. 4c) changed and was not
as smooth as that of PVPP; also, small particles
appeared on the surface of PVPP in both cases.
Specifically, the BET surface area of PVPP-BS and
[PVPP-BS]HSO4 was much higher than that of PVPP
(see Table 1). Moreover, the results of relative el-
ement content in PVPP-BS and [PVPP-BS]HSO4
(see Table 1) showed that the content of sulfur in-
creased in [PVPP-BS]HSO4. All these findings demon-
strate that BS and H2SO4 had already reacted with
PVPP.
Results and discussion
Characterization of [PVPP-BS]HSO
A comparison of the FT-IR spectra recorded for
PVPP, PVPP-BS, [PVPP-BS]HSO4, and H2SO4 is
presented in Fig. 2; three characteristic peaks at
1290 cm−1 (C—N), 1438 cm−1 (C—C), 1654 cm−1
—
—
(C O) can be observed in the PVPP spectrum
(Fahmy et al., 2009). As for PVPP-BS (Fig. 2;
curve b), the band at 1035 cm−1 was assigned to
—
—
the S O symmetric stretching vibrations of the -
SO3H group. For H2SO4, the symmetric stretch-
ing vibration of the S—O band was shifted from
610 cm−1 to 617 cm−1 compared with that in the
[PVPP-BS]HSO4 spectrum. This result indicates that
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541
Fig. 4. SEM images of PVPP (a), PVPP-BS (b), and [PVPP-BS]HSO4 (c).
Table 1. Characterization data of PVPP, PVPP-BS, and [PVPP-BS]HSO4
Aciditya
mg g−1
BET surface area
m2 g−1
wib/mass %
Sample
S
O
N
C
PVPP
PVPP-BS
[PVPP-BS]HSO4
–
–
3.84
6.28
6.56
–
0.27
0.42
11.33
18.61
25.72
12.14
17.59
22.91
76.53
63.53
50.95
274.89
a) Determined as KOH mass consumed for neutralization; b) relative element mass percentage obtained by elemental analysis using
FESEM.
Effect of reaction conditions on esterification
highest yield of benzyl butyrate obtained was 96.8 %
at the benzyl alcohol to butyric acid at mole ratio of
1.2 : 1 within 4 h. However, further increase of the
benzyl alcohol to butyric acid mole ratio did not in-
crease the yield of benzyl butyrate. This result is in
a good agreement with the literature that the excess
benzyl alcohol dissolves [PVPP-BS]HSO4 (Huang et
al., 2007; Han & Zhou, 2011). Thus, the optimum mole
ratio of BS to PVPP was chosen to be 1.2 : 1 in this
experiment.
Fig. 5 shows the influence of the mole ratio of ben-
zyl alcohol to butyric acid on the yield of benzyl bu-
tyrate; the mole ratio of benzyl alcohol to butyric acid
varied from 1 : 1 to 1.5 : 1 with excessive addition of
the reactant, benzyl alcohol, to increase the yield of
benzyl butyrate. Due to the different mass ratios of
benzyl alcohol to butyric acid, the yield of benzyl bu-
tyrate varied from 94 % to approximately 97 %. The
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S. Wang et al./Chemical Papers 70 (5) 538–544 (2016)
Fig. 7. Yield of benzyl butyrate at different temperatures (re-
action conditions: benzyl alcohol (96 mmol), butyric
acid (80 mmol), [PVPP-BS]HSO4 (8 mass %), 4 h).
Fig. 5. Yield of benzyl butyrate at different mole ratios of
reactants (reaction conditions: [PVPP-BS]HSO4 (8
mass %), 130◦C, 4 h).
Fig. 6. Yield of benzyl butyrate using different amounts of the
catalyst (reaction conditions: benzyl alcohol (96 mmol),
butyric acid (80 mmol), 130◦C, 4 h).
Fig. 8. Yield of benzyl butyrate at different reaction times (re-
action conditions: benzyl alcohol (96 mmol), butyric
acid (80 mmol), [PVPP-BS]HSO4 (8 mass %), 130◦C).
Influence of the amount of [PVPP-BS]HSO4 on the
yield of benzyl butyrate is presented in Fig. 6; the
yield of benzyl butyrate changed with the increase in
the amount of [PVPP-BS]HSO4 and a 96.8 % yield
of benzyl butyrate was obtained in the presence of 8
mass % of [PVPP-BS]HSO4 within 4 h of the reaction.
However, when the amount of the catalyst exceeded 8
mass %, the yield of benzyl butyrate decreased slightly
probably due to the solubility of the catalyst in ben-
zyl alcohol and its low solubility in benzyl butyrate.
Solubility of the catalyst was also restricted by the
degree of ester and benzyl alcohol mixing. Similar re-
sults were reported by other authors (Huang et al.,
2007; Han & Zhou, 2011). Thus, the optimum cata-
lyst amount of [PVPP-BS]HSO4 used in this reaction
was 8 mass %.
the yield of benzyl butyrate changed with the temper-
ature increase from 115◦C to 135◦C reaching 96.8 % at
130◦C. However, at the reaction temperatures above
130◦C, the benzyl butyrate yield did not increase fur-
ther. Therefore, the optimum reaction temperature for
this reaction was 130◦C.
The effect of reaction time on the benzyl butyrate
yield is shown in Fig. 8. It is evident that the reaction
yield increased with the reaction time increase from
1 h to 4 h reaching 96.8 % after 4 h. However, when
the reaction time exceeded 4 h, the yield of benzyl
butyrate decreased slightly. Therefore, the optimum
reaction time of 4 h was selected for this experiment.
Catalytic activities and reusability of different
catalysts
Fig. 7 depicts the changes of benzyl butyrate yield
at different temperatures. The results indicate that
Catalytic performance of different catalysts in the
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Table 2. Esterification of butyric acid and benzyl alcohol with
different catalystsa
Entry
Catalyst
Phenomenon
Yieldb/%
1
2
3
4
–
Homogeneous
Homogeneous
Homogeneous
Liquid–solid
37.5
85.5
89.2
96.8
H2SO4
p-CH3C6H4SO3H
[PVPP-BS]HSO4
a) Esterification conditions: benzyl alcohol (96 mmol), butyric
acid (80 mmol), 130◦C, 4 h, [PVPP-BS]HSO4 (1.39 g) or H2SO4
(0.34 g, with a similar proton content as [PVPP-BS]HSO4)
or p-CH3C6H4SO3H (1.19 g, with a similar proton content as
[PVPP-BS]HSO4); b) yield of butyrate based on the results of
GC analysis.
Fig. 9. Reusability of [PVPP-BS]HSO4 in the synthesis of ben-
butyric acid esterification with benzyl alcohol is pro-
vided in Table 2. According to the data, it can be
concluded that the benzyl butyrate yield reaches just
37.5 % without using catalysts, which indicates that
the esterification reaction is difficult to proceed with-
out catalysts. When H2SO4 and p-CH3C6H4SO3H
participated in the esterification reaction as catalysts,
the unsatisfying yield of 85.5 % and 81.9 %, respec-
tively, was achieved. Also, the homogeneous reaction
system complicates the separation of these catalysts.
In contrast, [PVPP-BS]HSO4 as a catalyst participat-
ing in the esterification reaction showed a high yield
of 96.8 %. Moreover, this catalyst can be easily sepa-
rated by vacuum filtration from the liquid–solid reac-
tion system. These contradictory results indicate that
[PVPP-BS]HSO4 has more advantages than the other
two catalysts studied.
Recycling of [PVPP-BS]HSO4 after the butyric
acid esterification with benzyl alcohol is illustrated in
Fig. 9; [PVPP-BS]HSO4 was recycled and reused in
six runs. In the first run, the yield of benzyl butyrate
reached 96.8 %, while it slightly decreased to 91.2 %
in the sixth run. During the six runs, only a slight
decrease in its catalytic activity was observed, which
can be ascribed to the loss of HSO−4 ions as reported
in literature (Miao et al., 2011).
zyl butyrate.
alyst in the esterification reaction. Table 3 presents
the results of butyric acid esterification with different
alcohols catalyzed by [PVPP-BS]HSO4. It is evident
that [PVPP-BS]HSO4 possesses high catalytic activ-
ity for the esterification of butyrate providing yields
of above 90 % in all investigated reactions. Therefore,
[PVPP-BS]HSO4 can be applied to various esterifica-
tion reactions as a catalyst.
Conclusions
A new heterogeneous catalyst based on polyvinyl-
polypyrrolidone was prepared, and the experiments
showed that the optimum reaction conditions of bu-
tyric acid esterification with benzyl alcohol are the
butyric acid to benzyl alcohol mole ratio of 1 : 1.2, re-
action temperature of 130◦C, reaction time of 4 h and
the amount of catalyst of 8 mass %. Under the opti-
mized conditions, the yield of benzyl butyrate reached
96.8 %. Reusability of the [PVPP-BS]HSO4 catalyst
was also studied in this work, excellent stability and
catalytic activity of the [PVPP-BS]HSO4 catalyst has
been proved, as it can be reused six times without
noticeable decrease of its catalytic activity. Moreover,
this catalyst can be efficiently applied in the butyric
acid reactions with other alcohols and the yield of bu-
Butyric acid and different alcohols as the reactants
were also tested using [PVPP-BS]HSO4 as the cata-
lyst to clarify the scope and limitations of this cat-
a
Table 3. Esterification of butyric acid with different alcohols in the presence of [PVPP-BS]HSO4
Entry
Carboxylic acid
Alcohol
Temperature/◦C
Yieldb/%
1
2
3
4
5
butyric acid
butyric acid
butyric acid
butyric acid
butyric acid
butanol
118
125
112
125
130
96.9
90.8
91.6
93.4
93.8
amyl alcohol
isoamyl alcohol
hexyl alcohol
benzyl alcohol
a) Alcohol (96 mmol), carboxylic acid (80 mmol), [PVPP-BS]HSO4 (8 mass %), 3 h; b) yield of butyrate based on the results of
GC analysis.
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S. Wang et al./Chemical Papers 70 (5) 538–544 (2016)
tyrate can be maintained at above 90 %. Thus, the
polymeric ionic liquid catalyst [PVPP-BS]HSO4 is an
attractive candidate for industrial butyrate synthesis.
Liang, X. Z. (2013). Novel acidic ionic liquid polymer for
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acetic acid using double SO3H-functionalized ionic liquids as
recoverable catalysts. Green Chemistry, 13, 697–701. DOI:
10.1039/c0gc00732c.
Acknowledgements. This work was financially supported by
the Shenyang Science and Technology Project (No.F15-199-1-
12) and by the Key Laboratory for Catalyst Synthesis of Poly-
mer of the Liaoning Province (No. 2010-36), China.
Miao, J. M., Wan, H., & Guan, G. F. (2011). Synthesis of immo-
bilized Brønsted acidic ionic liquid on silica gel as heteroge-
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Mokhtary, M., & Langroudi, S. A. M. (2014). Polyvinylpolypyr-
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1,8-dioxodecahydroacridines. Monatshefte fu¨r Chemie, 145,
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