Effective synthesis of cis-3-hexen-1-yl acetate via transesterification over KOH/γ-Al2O3: Structure and catalytic performance

Article abstract of DOI:10.1016/j.apcata.2013.01.015

Cis-3-hexen-1-yl acetate is a significant green note flavor compound and widely used in the food and cosmetic industry. In this research, a series of solid base KOH/γ-Al₂O₃ have been prepared and been utilized for the synthesis of cis-3-hexen-1-yl acetate via transesterification from cis-3-hexen-1-yl and ethyl acetate. The catalysts were also characterized by several physic-chemical techniques such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, N₂ adsorption, CO ₂-temperature-programmed desorption (CO₂-TPD), and X-ray fluorescence (XRF). 30%KOH/Al₂O₃ was suggested to be the best conversion due to the cis-3-hexen-1-ol conversion of 59.3% at a temperature 88 °C within 2 h. Characterization results showed that KOH transformed into Al-O-K and K₂O·CO₂ species during the calcination process. It was confirmed that K₂O·CO₂ disappeared and Al-O-K groups existed on the surface of the water-washing 30%KOH/Al ₂O₃ which was inactive for transesterification. K ₂O·CO₂ species might be the major active species on KOH/Al₂O₃, and Al-O-K groups was inactive for cis-3-hexen-yl acetate synthesis.

Full text of DOI:10.1016/j.apcata.2013.01.015

Applied Catalysis A: General 455 (2013) 1–7
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Effective synthesis of cis-3-hexen-1-yl acetate via transesterification
over KOH/␥-Al2O3: Structure and catalytic performance
Xiaoshuan Lia, Dinghua Yub,c, Wengui Zhangb, Zhengwen Lib, Xiaowei Zhangb,
He Huangb,c,∗
a School of Pharmaceutical Sciences, Nanjing University of Technology, Nanjing 210009, China
b College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210009, China
c State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Cis-3-hexen-1-yl acetate is a significant green note flavor compound and widely used in the food and
cosmetic industry. In this research, a series of solid base KOH/␥-Al2O3 have been prepared and been
utilized for the synthesis of cis-3-hexen-1-yl acetate via transesterification from cis-3-hexen-1-yl and
ethyl acetate. The catalysts were also characterized by several physic-chemical techniques such as X-
ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, N2 adsorption, CO2-temperature-
programmed desorption (CO2-TPD), and X-ray fluorescence (XRF). 30%KOH/Al2O3 was suggested to be
the best conversion due to the cis-3-hexen-1-ol conversion of 59.3% at a temperature 88 ◦C within 2 h.
Characterization results showed that KOH transformed into Al–O–K and K2O·CO2 species during the
calcination process. It was confirmed that K2O·CO2 disappeared and Al–O–K groups existed on the surface
of the water-washing 30%KOH/Al2O3 which was inactive for transesterification. K2O·CO2 species might
be the major active species on KOH/Al2O3, and Al–O–K groups was inactive for cis-3-hexen-yl acetate
synthesis.
Received 5 August 2012
Received in revised form 11 January 2013
Accepted 12 January 2013
Available online xxx
Keywords:
Cis-3-hexen-1-yl acetate
Cis-3-hexen-1-ol
Transesterification
KOH/␥-Al2O3
Flavor
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
considered as a kind of effective and green catalyst, which mini-
mizes the difficulty in separation and recovery processes usually
Hexyl esters (i.e. cis-3-hexen-1-yl acetate) are extremely aro-
matic compound with ‘green notes’ flavor and widely used in the
food and cosmetic industry [1,2]. The present demands for natural
flavors are estimated to be 5–10 metric tons annually at price of
2500–6000 US/kg, while the demands are not fulfilled by the cur-
rent production capacity [3]. Traditionally, they have been isolated
from high plants [3]. Nowadays, cis-3-hexen-1-ly acetate, caproate
and butyrate have been mostly synthesized via esterification pro-
cess over enzymes [3–8]. However, enzyme catalysts remain an
important consideration to the manufacturers for their high cost
and long reaction period (>24 h). In addition, some catalysts such as
metallic chlorides [9] and perchlorates [10] have been also devel-
oped for the synthesis of cis-hexen-1-yl esters via esterification,
while the removal of residual metallic salts in products becomes
a problem. Therefore, the synthesis of such esters needs to reduce
the product cost in most favorable conditions.
encountered with conventional base. From reported articles, solid
base has been tried extensively for biodiesel [11–13], diethyl car-
bonate [14,15], methy propyl carbonate [16,17], polycarbonate
diols [18], and other fine chemicals. Among the solid base cat-
alysts, modified ␥-Al2O3 has been widely used in a number of
base-catalyzed reactions as a heterogeneous base catalyst [19–21],
especially, transesterification [21–25]. K. Noiroj and W. Xie et al.
did excellent work in biodiesel production over ␥-Al2O3 modi-
fied by potassium salt [22,26–28], and found that high activity
for transesterfication could be attributed to the strongly basic
nature of catalysts. However, there are few reports on this alter-
ative synthesis of cis-3-hexen-1-yl acetate over solid base catalyst
from cis-3-hexen-1-ol and ethyl acetate catalyzed by a solid base
(Scheme 1).
In this research, solid base catalysts were prepared from a
commercial ␥-Al2O3 modified by KOH solutions and firstly used
for the production of cis-3-hexen-1-yl acetate (see Scheme 1).
KOH/Al2O3 was prepared by impregnation and applied to deter-
mine the optimum conditions for cis-3-hexen-1-yl acetate. Several
factors which may influence the quality of cis-3-hexen-1-yl acetate
were investigated, including wt% of KOH loading on Al2O3, amount
of catalyst, molar ratio cis-3-hexen-1-ol to ethyl acetate, reaction
time and temperature. Moreover, the stability of the catalyst and
Theoretically, cis-3-hexen-1-yl acetate also can be synthesized
via transesterification catalyzed by solid base. Solid base is always
∗
Corresponding author at: Nanjing University of Technology, No.5 Xinmofan
Road, Nanjing 210009, China. Tel.: +86 25 83172094; fax: +86 25 83172094.
E-mail address: biotech@njut.edu.cn (H. Huang).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.01.015

2
X. Li et al. / Applied Catalysis A: General 455 (2013) 1–7
Energy dispersive X-ray fluorescence (XRF) spectrometry was
performed using a Switzerland ARL9800 XRF.
2.3. Catalytic activity measurements
Scheme 1. Synthesis of cis-3-hexen-1-yl acetate via transesterification.
The transesterification of cis-3-hexen-1-ol (Nippon Zeon Co.,
Ltd) with ethyl acetate (Sinopharm Chemical Reagent Co., Ltd) was
carried out in a 100 mL jacketed two-necked glass round bottom
flask, equipped with a long spiral condenser connected to water
circulation and a temperature-controlled magnetic stirrer. The
desired amount of cis-3-hexen-1-ol, ethyl acetate and catalyst was
added into the flask. The reaction was carried out until it reached
the desired reaction time. After that, the reaction was stopped by
cooling the reactor to room temperature and the catalyst was sep-
arated from the liquid phase by filtration. All experiments were
performed under atmospheric pressure.
water-washing catalyst was also discussed. Furthermore, the active
sites of KOH/Al2O3 catalysts were discussed, and a plausible reac-
tion mechanism for transesterification was proposed.
2. Experimental
2.1. Catalyst preparation
KOH/␥-Al2O3 catalysts were prepared by wet impregnation
method. Powder ␥-Al2O3 was calcined in a muffle furnace at
500 ◦C for 3 h before catalyst preparation. Typically, 20 g ␥-Al2O3
was impregnated into 50 ml KOH solution at 40 ◦C for 3 h, and
water was removed under 90 ◦C. The precursor was dried at
120 ◦C overnight and stored in a vacuum desiccator. Prior to
the reaction, the precursor was activated in a muffle furnace at
500 ◦C for 3 h. For convenience, the catalysts were designated
as 10%KOH/Al2O3, 20%KOH/Al2O3, 30%KOH/Al2O3, 40%KOH/Al2O3.
30%KOH/Al2O3 was mean for 30 wt.% of KOH with respect to ␥-
Al2O3 and KOH.
Reusability tests were conducted over 30%KOH/Al2O3. The first
method was that the used 30%KOH/Al2O3 was filtered, dried at
120 ◦C overnight after each test. The second method was that the
used 30%KOH/Al2O3 was filtered, dried at 120 ◦C overnight, and
calcined at 500 ◦C for 3 h after each test. During the second method
procedure, after the first reused catalyst calcined at 500 ◦C for 3 h
was called 30%KOH/Al2O3-U1, after the second reused one was
30%KOH/Al2O3-U2, afterthethirdwas30%KOH/Al2O3-U3, andafter
the fourth was 30%KOH/Al2O3-U4. 30%KOH/Al2O3 was washed by
water, until the water going through the catalyst was neutral. The
washed catalyst was named 30%KOH/Al2O3-W, which was then
dried at 120 ◦C overnight, and calcined at 500 ◦C for 3 h.
2.4. Product analysis
Analysis of the reaction products were conducted by an Agilent
6890N gas chromatograph equipped with a flame ionization detec-
tor and a HP-FFAP column (30 m × 0.53 mm, film thickness 1 ␮m).
The carrier gas was N2 (2 mL/min, split). The GC oven temperature
was maintained at 60 ◦C for 2 min and then increased to 210 ◦C at a
rate of 10 ◦C/min and held for 4 min. The injector temperature was
fixed 250 ◦C and the detector temperature was at 240 ◦C. The GC
was connected to a chemstation which recorded the peak areas and
retention times in the chromatogram. Cis-3-hexen-yl acetate was
identified by the retention times. The cis-3-hexen-1-ol conversion
and the cis-3-hexen-1-yl acetate selectivity were calculated using:
Conversioncis-3-hexen-1-ol (%)
Minital cis-3-hexen-1-ol − Mfinal cis-3-hexen-1-ol
=
× 100
Minitial cis-3-hexen-1-ol
Selectivitycis-hexen-1-yl acetate (%)
Mcis-hexen-yl acetate
=
× 100
Minitial cis-3-hexen-1-ol − Mfinal cis-3-hexen-1-ol
where Minitial cis-3-hexen-1-ol refers to additional cis-hexen-1-ol,
Mfinal cis-3-hexen-1-ol refers to the cis-hexen-1-ol in the product after
reaction, and Mcis-hexen-1-yl acetate refers to the cis-hexen-1-yl from
cis-hexen-1-ol in the product after reaction. They were determined
by quantitative analysis using relative molar calibration factor.
2.2. Catalyst characterization
The XRD measurements were performed on a Philips X’Pro X-ray
diffractometer with a Cu K␣ irradiation, over a 2ꢀ range of 10–90◦
with a step size of 0.02◦. The X-ray source was operated at 40 kV and
40 mA. The phases were identified using the Powder Diffraction File
(PDF) database (JCPDS, International Centre for Diffraction Date).
FT-IR spectra were recorded on a Nicolet 670 spectrometer
during 4000–400 cm−1, with 2 cm−1 resolution. The KBr pellet tech-
nique was applied for preparing samples. All measurements were
conducted at room temperature.
3. Results and discussion
3.1. Catalyst characterization
3.1.1. X-ray diffraction
The XRD patterns of ␥-Al2O3, and KOH/Al2O3 were performed to
determine the change of crystal structure in the catalysts, and the
corresponding results were shown in Fig. 1. Fresh ␥-Al2O3 exhibited
the typical diffraction peaks of ␥-Al2O3 at 2ꢀ value of 37◦, 46◦, and
67◦. With the increasing amount of loaded KOH from 10% to 40%,
the intensities of the typical diffraction peaks (37◦, 46◦, and 67◦)
decreased, demonstrating the strong interaction between KOH and
␥-Al2O3 [27,28]. As the amount loading of KOH exceeded 20%, the
diffraction peak at 2ꢀ value of 37◦ almost disappeared and new
diffraction peaks at 2ꢀ value of 20◦, 29◦, 33◦, 34◦, 39◦, 41◦, 47◦,
59◦and 69◦ (JCPDS 01-089-8451) appeared, which were ascribed
to orthorhombic ␣-KAlO2 species formed on the catalyst surface
[29]. When the KOH amount was up to 40%, the new phase of ␣-
KAlO2 was obviously observed in Fig. 1. It could be deduced that
KOH reacted with ␥-Al2O3 generating new phase of Al–O–K groups
N2 adsorption/desorption isotherms were measured at −196 ◦C,
using a Micromeritics ASAP 2020 analyzer. The sample was pre-
treated at 250 ◦C in a vacuum for 48 h before measurements. Surface
areas were calculated using the Brunanuer–Emmett–Teller (BET)
model. Pore volumes were estimated from desorption branches of
nitrogen isotherms using the Barret–Joyner–Halenda (BJH) model.
Temperature-programmed desorption (TPD) of carbon dioxide
was performed in a BEL-CAT-B-82 equipment. The sample was first
calcined at 500 ◦C for 3 h and subsequently cooled to 100 ◦C under a
helium flow (30 mL/min), saturated with dry gaseous carbon diox-
ide (99.999%, 50 mL/min) at 100 ◦C for 30 min. The sample was then
purged with a helium flow (30 mL/min) for 30 min. The CO2-TPD
performed at a rate of 10 ◦C/min to 750 ◦C, and kept for 90 min at
750 ◦C.

X. Li et al. / Applied Catalysis A: General 455 (2013) 1–7
3
groups [22,32–34]. From the spectra of KOH/Al2O3, there were two
peaks at 1527 cm−1 and 1400 cm−1. The intensity of the band at
1400 cm−1 increased with increasing amount of KOH on the cat-
alyst, while its intensity at 1527 cm−1 decreased. The bands at
KAlO
Al O
2 3
2
100 (a.u.)
j
i
h
1527 cm−1 and 1400 cm−1 were due to CO3
ions (chemisorbed
2−
g
f
CO2) weakly bounded with K+ present on the surface of the catalyst
2−
[30,35]. The CO3
might be attributed to the chemical adsorbed
CO2 forming K2O·CO2 species like K2CO3 during the calcination of
the catalyst preparation. Therefore, K2O·CO2 species were responsi-
ble for the peaks of K2O not observed in the XRD patterns (see Fig. 1).
The bands at 778 cm−1 (AlO4 groups) and 582 cm−1 (AlO6 groups)
indicated the presence of Al–O–Al framework [32,36]. While the
shoulders at 778 cm−1 decreased and shifted to a lower wavelength
due to the effect of K+ on the Al–O bonds (the Al–O bands were on
AlO4 groups). As shown in Fig. 2, the spectra of used 30%KOH/Al2O3
showed the same spectra with that of fresh 30%KOH/Al2O3. How-
ever, there were not the bands at 1527 cm−1 and 1400 cm−1 on
the spectra of the water-washing 30%KOH/Al2O3. The fact showed
e
d
c
b
a
10
20
30
40
50
60
70
80
90
o
2 Theta
(
)
Fig. 1. XRD patterns. (a) ␥-Al2O3; (b) 10%KOH/Al2O3; (c) 20%KOH/Al2O3; (d)
30%KOH/Al2O3; (e) 40%KOH/Al2O3; (f) 30%KOH/Al2O3-U1; (g) 30%KOH/Al2O3-U2;
(h) 30%KOH/Al2O3-U3; (i) 30%KOH/Al2O3-U4; (j) 30%KOH/Al2O3-W.
2−
CO3 has been washed by water.
3.1.3. BET surface area measurement
in the composite [21,27] during the calcination at 500 ◦C for 3 h,
which agreed with low-temperature form of ␣-KAlO2 [29].
The patterns of the used 30%KOH/Al2O3 and water-washing
30%KOH/Al2O3 were shown in Fig. 1. The result showed that XRD
patterns of all the repeated used catalysts had the same XRD pat-
terns as that of the fresh 30%KOH/Al2O3 and the intensities of the
XRD patterns kept well after reusing four times. In other words, the
new phase of Al–O–K groups still remained. The XRD patterns of the
water-washing catalyst agreed well with the fresh 30%KOH/Al2O3.
It was suggested that the new phase of Al–O–K compound could
not react with water and not be destroyed by water.
The BET surface area, average pore size and pore volume of the
supports and catalysts were presented in Table 1. It was found
that the BET surface area and the pore volume of the catalysts
varied in a wide range 284.17 m2/g to 50.59 m2/g, and 0.53 cm3/g
to 0.11 cm3/g, respectively. As listed in Table 1, the BET surface
area and the pore volume of the catalysts decreased sharply with
increasing amount of KOH. This might be due to that some smaller
pores were blocked [27,32]. Meanwhile, the average pore sizes
increased firstly with KOH amount below 20% and then decreased.
The average pore size over the catalysts used for four times became
˚
˚
large from 7.76 A to 9.10 A. This suggested some potassium species
leached away. After washed by water, the catalyst showed differ-
ent textural characteristics from that of Al2O3. Combing with the
results of XRD pattern and the FT-IR, it can be concluded that the
species K2O·CO2 was washed away, while KAlO2 still existed on the
surface.
3.1.2. FT-IR spectroscopy
FT-IR spectroscopy was used to investigate the functional
groups in the catalysts. The results were shown in Fig. 2. There
were two bands in curve at 3440 cm−1 and 1640 cm−1 attributed
to the present of physical adsorbed water [22,30,31]. The two shoul-
ders were assigned to the O–H stretching (3440 cm−1) and the O–H
bending (1640 cm−1) of physical adsorbed water respectively. The
water might come from the reaction of the promoter salt (KOH)
with the ␥-Al2O3 or the atmospheric H2O during the calcination
of the catalyst preparation. By the way, the band at 3440 cm−1
could be partly attributed to the stretching vibrations of Al–O–K
3.1.4. CO2-TPD
The TPD profiles of desorbed CO2 on ␥-Al2O3, KOH/Al2O3, used
30% KOH/Al2O3 and water-washing 30%KOH/Al2O3 were shown
in Fig. 3, and the quantitative results were listed in Table 2.
Fig. 3 showed there were mainly two desorption ranges at ␥-
Al2O3, KOH/Al2O3, used 30% KOH/Al2O3 curves. One was centered
at around 150 ◦C and was assigned to the weak basic sites, and
the second one was assigned to the strong basic sites at around
550 ◦C [37,38]. The basic strength increased after 30%KOH/Al2O3
used, which was related to pore sizes (see Table 1). The water-
washing 30%KOH/Al2O3 catalyst had three peaks at 100 ◦C, 255 ◦C,
and 550 ◦C, which meant the water-washing 30%KOH/Al2O3 exited
weak, intermediate, and strong basic sites [37,38]. As listed in
Table 2, the total base amount of the catalysts changed significantly
in the range of our research. The total base amount of KOH/Al2O3
reached the maximum of 27.28 mmol/g at the KOH loading of 20%,
and then decreased as the loading kept increasing, which was simi-
lar to the solid base MgO/Al2O3 and MgO/ZrO2 reported by D. Jiang
et al. [39,40]. The decrease of the total base amount was possi-
bly related to a low average pore and a small surface area [39,40].
When the KOH loading increased from 10% to 20%, the increase of
total base amount was possibly due to new phases Al–O–K groups
and K2O·CO2 species formed during the calcination (see Fig. 1). As
the KOH loading exceeded 20%, the KOH/Al2O3 had a low average
pore and a small surface area (see Table 1), which were due to the
blockage of some smaller pore pores. The base sites on the surface
were possibly originate from the new phase K2O·CO2 species and
were less with the increase of KOH amount. During the reaction, the
j
i
778
582
h
g
f
e
d
3444
c
b
a
1648
1407
1527
4000 3500 3000 2500 2000 1500 1000
Wavenumber ( cm-1)
500
Fig. 2. FT-IR spectra. (a) ␥-Al2O3; (b) 10% KOH/Al2O3; (c) 20%KOH/Al2O3; (d)
30%KOH/Al2O3; (e) 40%KOH/Al2O3; (f) 30%KOH/Al2O3-U1; (g) 30%KOH/Al2O3-U2;
(h) 30%KOH/Al2O3-U3; (i) 30%KOH/Al2O3-U4; (j) 30%KOH/Al2O3-W.

4
X. Li et al. / Applied Catalysis A: General 455 (2013) 1–7
Table 1
Surface areas, average pore size, and pore volume of the studied fresh and spent KOH on alumina.
Catalyst
Surface area (m2/g)
Average pore size (Å)
Pore volume (cm3/g)
␥-Al2O3
284.17
126.8
58.34
50.59
40.28
52.45
58.64
63.89
68.35
245.08
6.96
9.49
12.87
7.76
6.78
9.46
9.76
9.55
9.10
6.26
0.53
0.32
0.21
0.11
0.10
0.13
0.16
0.17
0.18
0.40
10% KOH/Al2O3
20% KOH/Al2O3
30% KOH/Al2O3
40% KOH/Al2O3
30% KOH/Al2O3-U1
30% KOH/Al2O3-U2
30% KOH/Al2O3-U3
30% KOH/Al2O3-U4
30% KOH/Al2O3-W
Table 2
The surface basicity of the catalyst from CO2-TPD.
Catalysts
Peak temperature (◦C)
Basicityamount(mmol/g)
Ratio basicity of Peak II/Peak I
Total base amount (mmol/g)
Peak I
Peak II
Peak I
Peak II
␥-Al2O3
139
136
147
135
135
171
192
189
514
553
553
553
553
560
552
550
559
530
0.98
9.22
10.78
4.80
3.35
11.33
10.19
10.64
12.45
0.50/7.0
1.12
14.04
16.50
10.43
8.57
25.87
24.23
18.41
21.25
8.39
1.14
1.52
1.53
2.17
2.56
2.28
2.38
1.73
1.71
1.20
2.10
23.25
27.28
15.23
11.92
37.20
34.42
34.35
34.11
15.79
10% KOH/Al2O3
20% KOH/Al2O3
30% KOH/Al2O3
40% KOH/Al2O3
30% KOH/Al2O3-U1
30% KOH/Al2O3-U2
30% KOH/Al2O3-U3
30% KOH/Al2O3-U4
30% KOH/Al2O3-W
182
100/255
K2O·CO2 species were continually released into reaction medium.
After the 30%KOH/Al2O3 were reused, the average pore and sur-
face area became larger (see Table 1), and the total base amount
were more than fresh 30%KOH/Al2O3. Meanwhile, water-washing
30%KOH/Al2O3 exhibited more basicity amount than ␥-Al2O3. It
was deduced that Al–O–K groups existed on the surface, which
agreed with XRD patterns (Fig. 1). It was found that the basicity ratio
of two peaks increased with the increase of KOH loading in Table 2.
The ratio had a decline trend after the catalysts reusing for four
times. The ratio of the water-washing catalyst was closed to that
of ␥-Al2O3. Table 2 showed that the basicity amount and basicity
ratio were responsible for activity during the transesterification.
a
Al O
10% KOH/Al O
20% KOH/Al O
30% KOH/Al O
2
3
200 a.u.
2
3
3
3
3
2
2
40% KOH/Al O
2
3.1.5. X-ray fluorescence (XRF)
100
200
300
400
oC
500
600
XRF was used to determine the potassium content before
and after the reaction of 30%KOH/Al2O3 and water-washing
30%KOH/Al2O3. Table 3 showed that about 3% potassium of
30%KOH/Al2O3 was leached from the surface each test. Correspond-
ing to BET result of the used catalysts, used 30%KOH/Al2O3 had
a higher surface area, average pore size, and pore volume than
that of fresh 30%KOH/Al2O3. This suggested that the part of the
species containing potassium on the catalyst surface was leached
from the surface. Combining with the results of FT-IR, the leached
species were K2O·CO2 species. But the potassium could not be wash
out completely by water based on the result of water-washing
30%KOH/Al2O3, which proved the new phase (Al–O–K) compound
was stabilized during polar solvents, like water.
Temperature
(
)
b
Al O
2 3
30% KOH/Al O
30% KOH/Al O
2 3-U2
30% KOH/Al O
30% KOH/Al O
2 3-U4
30% KOH/Al O
2 3-
2 3-U1
200 a.u.
2 3-U3
W
Table 3
Potassium, aluminum and ratio of aluminum/potassium of the catalysts from XRF
analysis.
100
200
300
Temperature
400
oC
500
600
Catalyst
Al(wt%)
K(wt%)
Al/K
1.63
1.71
1.76
1.95
2.05
(
)
Fresh 30% KOH/Al2O3
30% KOH/Al2O3-U1
30% KOH/Al2O3-U2
30% KOH/Al2O3-U3
30% KOH/Al2O3-U4
30% KOH/Al2O3-W
36.65
37.42
37.60
38.57
38.92
51.12
22.44
21.90
21.40
19.81
19.01
1.27
Fig. 3. CO2-TPD profiles for ␥-Al2O3, fresh KOH/Al2O3, used 30%KOH/Al2O3, and
water-washing 30%KOH/Al2O3.
40.25

X. Li et al. / Applied Catalysis A: General 455 (2013) 1–7
5
Table 4
70
60
Effect of KOH loading on ␥-Al2O3 for transesterification.
Catalyst
Conversion of
Selectivity of cis-3-hexen-1-yl
cis-3-hexen-1-ol (%)
acetate (%)
50
40
30
20
10
0
␥-Al2O3
0.0
8.4
40.5
59.3
59.0
0.0
100
100
100
100
10% KOH/Al2O3
20% KOH/Al2O3
30% KOH/Al2O3
40% KOH/Al2O3
88 oC
80 oC
70 oC
60 oC
Reaction conditions: 0.05 mol cis-3-hexen-1-ol; 0.1 mol ethyl acetate; 5 g catalyst;
reaction temperature, 88 ◦C; reaction time, 120 min; atmospheric pressure.
3.2. Catalytic performance
0
20
40
60
80 100 120 140 160
3.2.1. Effect of KOH loading on Al2O3
Reaction time (min)
To investigate the effect of KOH loading on the activity of
the KOH/␥-Al2O3 catalysts, several KOH/␥-Al2O3 catalysts with
different amounts of KOH were prepared and their catalytic per-
formances were tested. It should be mentioned firstly that two
series of reaction data (conversion and selectivity), which were
calculated on the basis of cis-3-hexen-ol, were given in Table 4.
As listed in Table 4, the selectivity of cis-3-hexen-1-yl acetate was
100% over all catalysts. The cis-3-hexen-1-ol conversion increased
from 8.4% to 59.3%, as the KOH amount increased from 10% to 30%.
However, there was little improvement in the cis-3-hexen-1-yl
acetate after the KOH amount was above 30%. The fresh Al2O3 had
no catalytic activity on the transesterification. Thus the optimum
catalyst was 30%KOH/Al2O3.
Fig. 5. Effect of reaction time and temperature. Reaction conditions: 0.05 mol cis-3-
hexen-1-ol; 0.1 mol ethyl acetate; 0.5 g 30% KOH/Al2O3; atmospheric pressure. All
of cis-3-hexen-1-yl acetate selectivity was 100%.
varied between 60 ◦C and 88 ◦C. As can be seen in Fig. 5, the reaction
equilibrium was affected significantly by the reaction temperature.
At 60 ◦C, the reaction reached equilibrium in 120 min, while the
time was 60 min at 88 ◦C. It can be expected that the reaction could
proceed more rapidly at a temperature higher than 88 ◦C. How-
ever, the reaction mixture (the molar ratio of cis-3-hexen-1-ol to
ethyl acetate was 1:2) cannot be heated to a temperature exceeded
88 ◦C under atmospheric pressure for the low boiling point of ethyl
acetate. The equilibrium conversion of cis-3-hexen-1-ol increased
with the reaction temperature. Therefore, the optimizing reaction
temperature and time were 88 ◦C and 120 min. The reaction time
was 120 min for guaranteeing the reaction reached equilibrium
completely.
The molar ratio of cis-3-hexen-1-ol to ethyl acetate is one
of the important factors that affected the conversion of cis-3-
hexen-1-ol. Stoichiometrically, one mole of cis-3-hexen-1-ol was
required for each mole ethyl acetate. In practice, a higher molar
ratio was employed in order to drive the reaction toward comple-
tion and produced more cis-3-hexen-1-yl acetate as products. As
shown in Fig. 6, when the molar ratio of cis-3-hexen-1-ol to ethyl
acetate was increased, the cis-3-hexen-1-ol conversion increased,
and the highest conversion (59.3%) was obtained at a cis-3-hexen-
1-ol to ethyl acetate molar ratio of 1:2. When further increasing
the molar ratio over 1:2, the conversion decreased significantly.
3.2.2. Effect of reaction parameters over 30% KOH/Al2O3
30%KOH/Al2O3 was selected for further study because of its
excellent performance. The effect of catalyst amount in the range
of 4–12% (relative to weight of cis-3-hexen-1-ol) on the conversion
of cis-3-hexen-1-ol in the transesterification was investigated and
the results were shown in Fig. 4. The results showed that when the
amount of catalysts was not sufficient (10%), the reaction could not
reach equilibrium for 120 min. However, a further increase in the
amount of 30%KOH/Al2O3 from 4% to 10% led to a slow increase
in cis-3-hexen-1-ol conversion. When the amount of catalysts
exceeded 10%, the conversion of cis-3-hexen-1-ol was indepen-
dent of the amount of 30%KOH/Al2O3. Therefore, this indicated
that a chemical equilibrium had been reached due to the reversible
nature of the reaction. 10% was a suitable catalyst amount in this
experimental system.
The effect of reaction temperature on the cis-3-hexen-1-ol con-
version was summarized in Fig. 5. The reaction temperature was
70
70
100
100
60
60
80
60
40
20
0
80
60
40
20
0
50
40
30
20
10
0
50
40
30
20
10
0
4
6
8
10
12
1/6 1/5 1/4 1/3 1/2 1/1 2/1 3/1
Molar ratio (cis-3-hexen-1-ol : ethyl acetate)
Catalyst amount (%)
Fig. 4. Effect of catalyst amount on cis-3-hexen-1-ol conversion and cis-3-hexen-
yl acetate selectivity. Reaction conditions: 0.05 mol cis-3-hexen-1-ol; 0.10 mol
ethyl acetate; catalyst, 30%KOH/Al2O3; reaction temperature, 88 ◦C; reaction time,
120 min; atmospheric pressure.
Fig. 6. Effect of the molar ratio of cis-3-hexen-1-ol/ethyl acetate. Reaction condi-
tions: 0.05 mol cis-3-hexen-1-ol; 0.5 g 30%KOH/Al2O3; reaction temperature, 88 ◦C;
reaction time, 120 min; atmospheric pressure.

6
X. Li et al. / Applied Catalysis A: General 455 (2013) 1–7
3.3. Discussion
80
70
60
50
40
30
20
10
0
the used catalyst calcined
the used catalyst uncalcined
According to corroborating data provided by the characteriza-
tion techniques (XRD, FT-IR, CO2-TPD, BET, and XRF), a catalyst
model and a plausible mechanism for this transesterification
were proposed in Fig. 8. The excellent catalytic performance of
30%KOH/Al2O3 should be originated form the abundant surface
oxygen-containing species. The basicity of oxygen in K2O·CO2
species were stronger than that in Al–O–K groups [32] and Al–O–Al
groups.
Generally, a new phase of K2O and Al–O–K were generated
through the reaction KOH with ␥-Al2O3 [21,27,32]. However, they
have different opinions on the main active sites. D. M. Alonso and
H. B. Ma et al. considered the Al–O–K groups were responsible for
the activity of KOH/Al2O3 [41,42]. While H. Liu and W. Xie et al.
thought K2O species and Al–O–K groups on the surface were prob-
ably the main active sites [21,32]. The Al–O–K groups had lower
catalytic activity and basicity than K2O phase [32]. From Fig. 1,
K2O phase was not observed clearly. These results did not agree
well with the result of KI/Al2O3 and KNO3/Al2O3 reported by W.
1
2
3
4
5
Run
Fig. 7. Reusability of 30% KOH/Al2O3 on the transesterification. Reaction conditions:
0.05 mol cis-3-hexen-1-ol; 0.1 mol ethyl acetate; 0.5 g 30% KOH/Al2O3; reaction
temperature, 88 ◦C; reaction time, 120 min; atmospheric pressure.
2−
Xie et al. [21,22] and KOH/Al2O3 [27]. While the bands of CO3
were observed clearly from Fig. 2. There was a possible reason
for K2O species reacting with CO2 forming a specie like K2CO3.
Because the K2O species had high activity and adsorbed CO2 easily
in air (K2O + CO2 → K2O·CO2). During the reaction process, a part of
K2O·CO2 species was dissolved in the reaction medium and leached
away, which agreed with the result of BET and XRF. The fresh
30% KOH/Al2O3 was washed, the K2O·CO2 species was washed out
(Fig. 2), but the Al–O–K groups still exited (Fig. 1). These results
agreed with that of XRD (Fig. 1) and FT-IR (Fig. 2). The water-
washing 30%KOH/Al2O3 had no activity for transesterification. It
was deducted that the K2O·CO2 species was possibly responsible
for the activity of KOH/Al2O3.
The catalytic activity increased with the increasing of KOH
amount (see Table 4). However, the activity was little improve-
ment after the amount of KOH was above 30%. In addition, the
typical diffraction peaks of ␥-Al2O3 at 2ꢀ value of 37◦ and 46◦
weakened as the amount of KOH was above 20% (see Fig. 1). It was
deducted that Al–O–K groups were firstly formed and few K2O·CO2
species were generated as the increasing of KOH amount from 10%
to 30%. When all Al–O–H groups were transformed into Al–O–K
groups, more K2O·CO2 species were generated. With the amount
of KOH above 30%, the catalyst had smaller surface areas and pore
size (Table 1). Therefore, the activity was little improvement after
the amount of KOH was above 30%. After the used 30%KOH/Al2O3
Therefore, the optimum molar ratio of cis-3-hexen-1-ol to ethyl
acetate to produce cis-3-hexen-1-yl acetate was approximately
1:2.
3.2.3. Reusability of the catalyst
The reusability of the catalyst is very important for its com-
mercial application. Therefore, the recyclability of 30%KOH/Al2O3
was investigated (Fig. 7). After each experiment, the used
30%KOH/Al2O3 catalyst was filtered, dried at 120 ◦C overnight. As
can be seen in Fig. 7, the conversion decreased form 59.3% to
24.8% after five cycles. The recyclability of KOH/Al2O3 was sim-
ilar to KF/Al2O3 [15] and K2CO3/Al2O3 [41]. The activity of the
used 30%KOH/Al2O3 catalyst without calcination decreased due
to the leach out of potassium (see Table 3) and the deactiva-
tion of K2O·CO2 species. While the used 30%KOH/Al2O3 catalyst
was calcined at 500 ◦C for 3 h, the activity of 30%KOH/Al2O3 cat-
alyst was able to largely maintain its overall catalytic activity for
at least five times. When the used 30%KOH/Al2O3 catalyst was
calcined, the active sites were activated again and the catalyst
would have enough number of active sites in successive runs.
This feature made the 30%KOH/Al2O3 more attractive for potential
application in the synthesis of cis-3-hexen-yl acetate in the flavor
industry.
Fig. 8. The catalyst model and a plausible reaction mechanism for transesterification.

X. Li et al. / Applied Catalysis A: General 455 (2013) 1–7
7
was calcined, the K2O·CO2 species was formed again. The water-
References
washing 30%KOH/Al2O3 had no activity for transesterification. It
was possible that K2O·CO2 species were washed out (see Fig. 2) and
the Al–O–K groups still existed on the surface of 30%KOH/Al2O3 (see
Fig. 1). Therefore, K2O·CO2 species might be the major active species
on KOH/Al2O3, and Al–O–K groups was inactive for cis-3-hexen-yl
acetate synthesis.
[1] H.D. Belitz, W. Grosch, P. Schieberle, Food Chemistry, fourth ed., Springer, 2009.
[2] S. Horst, P. Johannes, Common Fragrance and Flavor Materials, fifth ed., Wiley-
VCH, Darmstadt, 2006.
[3] W.D. Chiang, S.-W. Chang, C.-J. Shieh, Process Biochem. 38 (2003) 1193–1199.
[4] K. Nakane, T. Hotta, T. Ogihara, N. Ogata, S. Yamaguchi, J. Appl. Polym. Sci. 106
(2007) 863–867.
[5] M. Liaquat, J. Mol. Catal. B: Enzym. 68 (2011) 59–65.
[6] S. Bourg-Garros, N. Razafindramboa, A.A. Pavia, Biotechnol. Bioeng. 59 (1998)
495–500.
[7] S. Bourg-Garros, N. Razafindramboa, A.A. Pavia, Enzyme Microb. Tech. 22 (1998)
240–245.
[8] S. Bourg-Garros, N. Razafindramboa, A. Pavia, J. Am. Oil Chem. Soc. 74 (1997)
1471–1475.
[9] S. Velusamy, S. Borpuzari, T. Punniyamurthy, Tetrahedron 61 (2005)
2011–2015.
[10] G. Bartoli, M. Bosco, R. Dalpozzo, E. Marcantoni, M. Massaccesi, L. Sambri, Eur.
J. Org. Chem. (2003) 4611–4617.
[11] C.L. Xu, J. Sun, B.B. Zhao, Q.A. Liu, Appl. Catal. B: Environ. 99 (2010) 111–117.
[12] D. Cantrell, L. Gillie, A. Lee, K. Wilson, Appl. Catal. A: Gen. 287 (2005) 183–190.
[13] W. Xie, H. Peng, L. Chen, Appl. Catal. A: Gen. 300 (2006) 67–74.
[14] C. Murugan, H.C. Bajaj, Fuel Process. Technol. 92 (2011) 77–82.
[15] P. Qiu, B. Yang, C. Yi, S. Qi, Catal. Lett. 137 (2010) 232–238.
[16] Y.M. Dong, X.Q. Chen, C.X. Zhao, T.S. Zhao, J. Mol. Catal. A: Chem. 331 (2010)
125–129.
[17] X.Q. Chen, Y.M. Dong, C.X. Zhao, T.S. Zhao, Energy Fuels 22 (2008) 3571–3574.
[18] Y. Feng, N. Yin, Q. Li, J. Wang, M. Kang, X. Wang, Catal. Lett. 121 (2008) 97–102.
[19] H. Kabashima, H. Tsuji, S. Nakata, Y. Tanaka, H. Hattori, Appl. Catal. A: Gen.
194–195 (2000) 227–240.
Therefore, the strong base oxygen from K2O·CO2 species on
the catalyst could make cis-3-hexen-1-ol forming nucleophile
(C6H11O−), and then K2O·CO2 species acquired hydrogen cation
forming H-K2O·CO2 species, which were dissolved in the reaction
medium. The nucleophile attacked the carbonyl group of ethyl
acetate forming the tetrahedral intermediate; then, the ethoxy
departed quickly from the tetrahedral intermediate. The ethoxy
gets hydrogen from H-K2O·CO2 species, while potassium mate-
rial stayed in the reaction medium. Many articles have reported
that alkali and alkali earth species from catalysts containing
alkali and alkali earth dissolved in the reaction medium, and
most of the catalysts were formed homogeneous-heterogeneous
system [32,43–47]. The K2O·CO2 species and Al–O–K groups in
KOH/Al2O3 formed a homogeneous-heterogeneous catalytic sys-
tem. The deactivation of catalysts was for leaching of K2O·CO2
species.
[20] P. Claus, M. Lucas, B. Luecke, T. Berndt, P. Birke, Appl. Catal. A: Gen. 79 (1991)
1–18.
4. Conclusions
[21] W. Xie, H. Peng, L. Chen, Appl. Catal. A: Gen. 300 (2006) 67–74.
[22] W. Xie, H. Li, J. Mol. Catal. A: Chem. 255 (2006) 1–9.
[23] M. Zabeti, W.M.A.W. Daud, M.K. Aroua, Appl. Catal. A: Gen. 366 (2009) 154–159.
[24] N. Boz, N. Degirmenbasi, D.M. Kalyon, Appl. Catal. B: Environ. 89 (2009)
590–596.
[25] C. Xu, J. Sun, B. Zhao, Q. Liu, Appl. Catal. B: Environ. 99 (2010) 111–117.
[26] H. Ma, S. Li, B. Wang, R. Wang, S. Tian, J. Am. Oil Chem. Soc. 85 (2008) 263–270.
[27] K. Noiroj, P. Intarapong, A. Luengnaruemitchai, S. Jai-In, Renew Energ. 34 (2009)
1145–1150.
[28] E. Rashtizadeh, F. Farzaneh, M. Ghandi, Fuel 89 (2010) 3393–3398.
[29] S.L.G. Husheer, J.G. Thompson, A. Melnitchenko, J. Solid State Chem. 147 (1999)
624–630.
[30] C. Murugan, H.C. Bajaj, R.V. Jasra, Catal. Lett. 137 (2010) 224–231.
[31] S.U. Rege, R.T. Yang, Chem. Eng. Sci. 56 (2001) 3781–3796.
[32] H. Liu, L. Su, F. Liu, C. Li, U.U. Solomon, Appl. Catal. B: Environ. 106 (2011)
550–558.
The heterogeneous catalyst KOH/Al2O3 can be used as solid
base catalyst for cis-3-hexen-1-yl acetate via transesterification.
The optimum conditions was 30%KOH/Al2O3, 10% of catalyst, 1:2
cis-3-hexen-1-ol to ethyl acetate molar ratio, reaction time 2 h
and temperature 88 ◦C. At the optimum conditions, the highest
conversion of 59.3% was obtained. According to characteriza-
tion results, KOH on the surface of ␥-Al2O3 transformed into
Al–O–K groups and K2O·CO2 species through reaction with ␥-
Al2O3. Fresh 30%KOH/Al2O3 washed by water without active,
K2O·CO2 disappeared while Al–O–K groups existed on the sur-
face of the catalyst. Therefore, K2O·CO2 species might be the
major active species on KOH/Al2O3, and Al–O–K groups was
inactive for cis-3-hexen-yl acetate synthesis. The leaching of
K2O·CO2 species was the main reason for the deactivation of
catalysts.
[33] B.W. Krupay, Y. Amenomiya, J. Catal. 67 (1981) 362–370.
[34] Y. Amenomiya, G. Pleizier, J. Catal. 76 (1982) 345–353.
[35] Y. Amenomiya, J. Catal. 55 (1978) 205–212.
[36] L. Fernández-Carrasco, E. Vázquez, Fuel 88 (2009) 1533–1538.
[37] P. Sun, D. Yu, K. Fu, M. Gu, Y. Wang, H. Huang, H. Ying, Catal. Commun. 10 (2009)
1345–1349.
[38] Y. Dong, X. Chen, C. Zhao, T. Zhao, J. Mol. Catal. A: Chem. 331 (2010) 125–129.
[39] D. Jiang, G. Pan, B. Zhao, G. Ran, Y. Xie, E. Min, Appl. Catal. A: Gen. 201 (2000)
169–176.
Acknowledgements
[40] D. Jiang, B. Zhao, Y. Xie, G. Pan, G. Ran, E. Min, Appl. Catal. A: Gen. 219 (2001)
69–78.
[41] D.M. Alonso, R. Mariscal, R. Moreno-Tost, M.D.Z. Poves, M.L. Granados, Catal.
Commun. 8 (2007) 2074–2080.
[42] H.B. Ma, S.F. Li, B.Y. Wang, R.H. Wang, S.J. Tian, J. Am. Oil Chem. Soc. 85 (2008)
263–270.
[43] J. Ni, D. Rooney, F.C. Meunier, Appl. Catal. B: Environ. 97 (2010) 269–275.
[44] S.I. Fujita, B.M. Bhanage, D. Aoki, Y. Ochiai, N. Iwasa, M. Arai, Appl. Catal. A: Gen.
313 (2006) 151–159.
Authors thank the financial support from National Key Tech-
nology R&D Program (Grant No. 2012BAD32B08), National Basic
Research Program (Grant No. 2011CB710806), National Natural
Science Foundation of China (Grant No. 20906051), and the Ph.D.
Programs Foundation of Ministry of Education of China (Grant No.
20113221110010).
[45] M.C.G. Albuquerque, I. Jiménez-Urbistondo, J. Santamaría-González, J.M.
Mérida-Robles, R. Moreno-Tost, E. Rodríguez-Castellón, A. Jiménez-López,
D.C.S. Azevedo, C.L. Cavalcante Jr., P. Maireles-Torres, Appl. Catal. A: Gen. 334
(2008) 35–43.
[46] J.P. Tessonnier, B. Louis, S. Rigolet, M.J. Ledoux, C. Pham-Huu, Appl. Catal. A:
Gen. 336 (2008) 79–88.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.apcata.2013.01.015.
[47] H. Sun, K. Hu, H. Lou, X. Zheng, Energy Fuels 22 (2008) 2756–2760.