Ultrasound assisted heteropoly acid catalyst SiW12/SiO 2 for synthesis of benzyl acetate

Article abstract of DOI:10.14233/ajchem.2013.11621

Under ultrasonic radiation, benzyl acetate is synthesized from benzyl alcohol and glacial acetic acid in presence of catalyst SiW₁₂/ SiO₂. The catalyst was prepared and characterized by IR, X-ray diffraction and SEM in the experiment. The XRD result indicates that heteropoly acid retains the Keggin-type structure. The kinetic parameters of reaction were, respectively measured at 90, 100 and 110 °C and the kinetic equation was built. Then, the effects of reaction temperature, the amount of catalyst, molar ratio of benzyl alcohol to glacial acetic acid and ultrasonic intensity on the esterification yield were discussed. The results showed that the optimum operating parameters for the present work when 10 kHz ultrasonic frequency and 1.0 W/cm² ultrasonic intensity are as follows: reaction temperature: 110 °C, use amount of catalyst: 1.5 g, molar ratio of benzyl alcohol to glacial acetic acid: 1.5; reaction time: 75 min. Under such conditions, the esterification yield of the reaction reached above 95.3 %.

Full text of DOI:10.14233/ajchem.2013.11621

Asian Journal of Chemistry; Vol. 25, No. 2 (2013), 623-627
http://dx.doi.org/10.14233/ajchem.2013.11621
Ultrasound Assisted Heteropoly Acid Catalyst SiW12/SiO for Synthesis of Benzyl Acetate
2
*
XI CHEN, JUN WANG, YUE HAN, XIAO-PING LU and PING-FANG HAN
Nanjing University of Technology College of Chemistry and Chemical Engineering, Nanjing 210009, Jiangsu, P.R. China
*
Corresponding author: E-mail: chenxi198408@163.com
Received: 3 February 2011;
(
Accepted: 9 August 2012)
AJC-11942
2
Under ultrasonic radiation, benzyl acetate is synthesized from benzyl alcohol and glacial acetic acid in presence of catalyst SiW12/SiO .
The catalyst was prepared and characterized by IR, X-ray diffraction and SEM in the experiment. The XRD result indicates that heteropoly
acid retains the Keggin-type structure. The kinetic parameters of reaction were, respectively measured at 90, 100 and 110 ºC and the
kinetic equation was built. Then, the effects of reaction temperature, the amount of catalyst, molar ratio of benzyl alcohol to glacial acetic
acid and ultrasonic intensity on the esterification yield were discussed. The results showed that the optimum operating parameters for the
2
present work when 10 kHz ultrasonic frequency and 1.0 W/cm ultrasonic intensity are as follows: reaction temperature: 110 ºC, use
amount of catalyst: 1.5 g, molar ratio of benzyl alcohol to glacial acetic acid: 1.5; reaction time: 75 min. Under such conditions, the
esterification yield of the reaction reached above 95.3 %.
Key Words: Benzyl Acetate, Ultrasound, Benzyl alcohol, Glacial acetic acid, Esterification.
6
2
7
, SBA- 5 and
chosen in high surface area materials (SiO
8
MCM-41 ).
INTRODUCTION
Benzyl acetate, a kind of edible spice that can be used
according to the relevant regulations of the state, is widely
used in preparation of apple, banana, papaya and other types
Now, more and more researchers are paying attention to
9,10
ultrasound . It provides the chemical researchers with an
unusual way of making energy introduced into molecule,
optimizing the chemical reaction conditions, avoiding high
temperature and high pressure, shortening reaction time,
1
of fragrance . It is also widely used in textile and dye industry
as solvent. At present, benzyl acetate is synthesized by homo-
geneous catalysis of acetic acid and benzyl butanol in industrial
production, but the oxidizability and dehydration property of
concentrated sulfuric acid leads to so many disadvantages such
as many side reactions, complex post-treatment, large amount
of wastewater, serious corrosion to equipment and great pressure
changing surface features and improving reaction yield and
11,12
selectivity
.
To meet the requirements for green chemistry synthesis
routes, The optimum conditions for the preparation of benzyl
2
acetate with SiW12/SiO catalyst and the kinetics are discussed
2,3
on the environment .
in the paper. The kinetic parameters of reaction were measured
and the kinetic equation was built. The results provided a
reliable theoretical and experimental basis for the further
development of the synthesis process of benzyl acetate.
Heteropoly acid has been widely recognized and applied
as a kind of environmental friendly catalyst. It has many
advantages: for example, it has the structure characteristics of
complexes and metal oxides and it also has strong acidity,
redox property, stable structure, high regeneration speed, high
EXPERIMENTAL
4
activity , low pollution, unique acidic property, pseudo liquid
phase, multi-function (strong acidity, strong oxidizability,
polymerization retardation and photoelectrocatalysis), no
CH
O, C H O
3
COOH, C
8 20 4 7 8 2 6 2
H O Si, HCl, C H O, SiW12, C H O ,
C
2
H
6
2 4 2
and NaOH were procured by Shanghai
5
corrosion to equipment and it can be well modified . There-
Experiment Reagent Co. Ltd. All these reagents were reagent
grade chemicals.
fore, the application of heteropoly acid in chemical reaction
has a good prospect. The problem in traditional bio-reaction
processes, such as complicated separation process and difficult
recycles of catalyst, could be solved well by using supported
heteropoly acid catalysts. In general, the carriers can be
The FT/IR spectra are recorded on a Nicolet Impact 380
infrared spectrophotometer placing the materials in KBr
pellets. The wide angle XRD were recorded by using a Bruker
D8 diffractometer and small angle using a Bruker D8Advance

(3)
2
θ (º)
6
24 Chen et al.
Asian J. Chem.
RESULTS AND DISCUSSION
Characterization of catalyst
XRD diffractometer equipped with a gobel mirror using CuK
α
-
10
radiation (λ = 1.5418 × 10 m), tube voltage 40 kV, tube
current 30 mA, scan scope 5-60º, scan step 0.05º and scan
rate 0.2 s/step. DGC-1200 ultrasonic processor (10 kHz,
IR: Fig. 1 is the infrared spectrums about active compo-
nent SiW , catalyst SiW /SiO and carrier SiO . It was
analyzed by infra-red spectrum with KBr squash method. The
0
-250 V), hydrophone (CS-3) and oscillograph (SR8) were
1
2
12
2
2
also used in the experiments. CS-3 hydrophone (made by
Institute of Acoustics, Chinese Academy of Sciences) was
used to measure and estimate the ultrasonic intensity in the
solution.
-1
spectrum are as follows: In 1000-700 cm fingerprint region,
the synthetic product shows obvious four characteristic
absorption peaks of keggin structure heteropolyanion: 979,
13
-1
9
absorption vibration peak of ν(W=O), ν(Si-O), ν(W-Ob-W)
26, 879 and 783 cm , which, respectively belong to the
2
Preparation of catalyst SiW12/SiO : 34.65 g of TEOS,
2
2
8
0
0.65 g of ethylene glycol and 20 g of ethanol dissolved in a
50 mL beaker; then make the solutions mixed and heated to
0 ºC, followed by the addition of SiW12. After stirring for
.5 h, run the ultrasound and add 60 g ethanol, 15 g distilled
15
and ν(W-Oc-W) . The results imply that the product is intact
keggin structure polyoxometallate.
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water into the solution. The slurry was further heated at 80 ºC
for 8 h so as to obtain a clear jelly. Finally, the product was
left for 24 h at room temperature. The final solid was identified
(
1)
2
as the catalyst SiW12/SiO .
Synthesis of benzyl acetate: The sonochemical reactor
produced by Wuxi Dejia Electronics Co. Ltd., is used for the
experimental setup for the preparation of benzyl acetate.
Ultrasonic horn, the device used for the generation of cavita-
tion, operates at the frequency of 10 kHz (voltage output
(2)
(3)
0-250 V). The diameter of ultrasonic horn with the frequency
of 10 kHz is 2.1 cm. The reactions were carried out in a four
necked bottle of 250 mL capacity where the reaction volume
1100
1000
900
u mb e
800
700
(
ca. 100 mL) was kept constant for all the reactions. The
-
1
–1
w
W
av
a
e
v
n
e
u
n
m
b
r
e
/
r
c
(
m
cm )
thermometer and water separator were installed on the necks.
In a typical procedure, the right amount of catalyst was added
to toluene, which was dissolved in the mixed solvent of the
proper amount of acetic acid and benzyl alcohol. Then the
mixture was heated for 2 h. The magnetic stirrer was provided
to stir the mixtures. The reaction mixture samples were taken
out at each 15 min interval and titrated with 0.4 mol/L NaOH
solution to determine the amount of unconverted acetic acid
in terms of acid value.
Fig. 1. IR of SiW12/SiO
2
catalyst [(1) SiW12 (2) 40 % SiW12/SiO ; (3) SiO
2
2
]
XRD: Fig. 2 is the X-ray diffraction about active compo-
nent the SiW12, catalyst SiW12/SiO and carrier SiO . It showed
that the XRD of carrier SiO didn't show the characteristic peak.
The characteristic peak of active component SiW12 appears at
º. From the Fig. 2, it implied that characteristic peak of catalyst
SiW /SiO was the same with the peak of active component
2
2
2
8
12
2
SiW . It demonstrated that SiW was dispersed on the carrier
12
12
Determination of the esterification yield R was carried
out by following GB 1668-81 acid determination, it was
SiO
on the carrier SiO
intact keggin structure of SiW12/ SiO
2
surface and that part of SiW12 crystals gathered into large
surface. From the XRD of catalyst, the
can be seen at four
2
14
obtained by the following equation :
2
1
6
angles: 10-11, 17-19, 22-30 and 35-38º .

V 
t
R = 1−
×100 %


V

0 
where V
0
(mL) is the volume of sodium hydroxide solution
(mL) is the
(
1)
consumed for titration before reaction while V
t
volume of sodium hydroxide solution consumed for titration
at time t.
(
2)
Infrared spectrum results of benzyl acetate are as follows:
-1
1
745 cm is C=O stretching band. The correlation peak of
CH is C-H asymmetric stretching vibration absorption band
2965 cm ), C-H symmetric stretching vibration absorption
3
-1
(
-1
band (2894 cm ) and C-H in-plane bending vibration absor-
-1
ption peak (1462 and 1367 cm ). The characteristic peak of
-1
-1
C-O-C is 1240 and 1067 cm . 1607, 1498 and 1460 cm are
the C=C stretching vibration band of benzene ring. The results
implied that the product is benzyl acetate.
5
10
15
20
25
30
35
40
o
2
¦È )
(
2 2 2
Fig. 2. XRD of SiW12/SiO catalyst [(1) SiW12; (2) SiW12/SiO ; (3) SiO ]

Vol. 25, No. 2 (2013)
Ultrasound Assisted Heteropoly Acid Catalyst SiW12/SiO
2
for Synthesis of Benzyl Acetate 625
Effect of reaction temperature: The effect of reaction
temperature (90, 100, 110 and 120 ºC) on the esterification of
benzyl acetate was examined. In Fig. 3, it was found that the
esterification yields at the reaction temperature 90 ºC was the
lowest (75 %). Remarkably, the esterification yield increased
with the increase of reaction temperature. A comparison was
made for the reaction at 110 and 120 ºC; the two curves almost
coincide and the esterification yields could all up to 95 % in
+
CH C OH
3
CH OH
2
O
C
O
+
CH3
OH +
A+
A
H
CH
2
CH
2
CH
2
+
O
O
O
-
H
2
O
+
CH C OH
75 min. The optimal reaction temperature was 110 ºC. These
CH C+
CH C OH
3
3
2
3
data implied that esterification was closely related to the
reaction temperature.
O
A
O
A
O
A
8
6
4
2
0
0
0
0
0
A+
O
C
CH2
O
CH
3
+
+
A = acid site on SiO
Scheme-I: Possible reaction mechanism for the esterification of benzyl
alcohol with acetic acid by SiW12/SiO
2
o
0 C
9
2
o
00 C
1
o
10 C
1
Effect of molar ratio: The effect of molar ratio on the
rate of reaction was investigated at four different molar ratios
of benzyl alcohol to acetic acid viz., 1:1, 1.5:1, 2:1 and 2.5:1
under constant reaction temperature (110 ºC) and the
ultrasounic frequency of 10 kHz. The results have been shown
in Fig. 5. We can easily observe from the figure that an initial
increase in the molar ratio from 1:1 to 1.5:1 significantly
increases the extent of equilibrium conversion, but beyond this
optimum molar ratio of 1.5:1, only marginal improvement in
the rate of reaction and equilibrium conversion is observed. It
should be noted here that dependency of the rate of the reaction
on the molar ratio is less significant in the present case as
compared to higher ratio of benzyl alcohol to acetic acid (2:1).
If molar ratio continues to increase to 2.5, the esterification
yield decreased sharply. It implied that the yield may decrease
because the relative concentration of acid and catalyst was
reduced by using the excessive benzyl alcohol.
o
20 C
1
0
15
30
45
60
75
90
105 120
Time (min)
ʱ¼ä /min
Fig. 3. Relationship between esterification yield and reaction temperature.
(n(acid)/n(benzyl alcohol) = 1:1.5, amount of catalyst 1.5 g,
2
ultrasonic frequency: 10 kHz, ultrasonic intensity: 1.0 W/cm )
Effect of amount of catalyst: The effect of catalyst
amount (0.5, 1.0, 1.5 and 2.0 g) on the esterification of benzyl
acetate was examined.As shown in Fig. 6, the effect of catalyst
of 0.5 and 1.0 g were significantly poor. The yields were 80
and 85 %, respectively.A comparison was made for the catalyst
amount of 1.5 and 2.0 g, the esterification of 2.0 g was higher
before 45 min. After 45 min, the esterification at the amount
of catalyst of 1.5 and 2.0 g were almost the same. It is worth
noting that the esterification could up to 95.0 % in 75 min
with the amount of catalyst of 1.5 and 2.0 g. The result implied
us that esterification was closely related to the amount of
catalyst. The esterification reaction takes place between acetic
acid adsorbed on the SiO
2
surface, forming electrophile and
80
benzyl alcohol in the liquid phase (Scheme-I). The optimal
amount of catalyst was 1.5 g.
6
4
2
0
0
0
0
1
: 1
.5 : 1
: 1
.5 : 1
1
100
2
2
80
60
40
20
0
0
15
30
45
60 75
ʱ¼ä /min
90
105 120
Time (min)
0
1
1
2
.5 g
.0 g
.5 g
.0 g
Fig. 5. Relationship between esterification yield and molar ratio
(temperature 110 ºC, amount of catalyst 1.5 g, ultrasonic frequency:
2
10 kHz, ultrasonic intensity: 1.0 W/cm )
Study on kinetics: Since there is no kinetic data on ultra-
sound assisted synthesis of benzyl acetate, a kinetic model for
the esterification reaction was developed. The esterification
reaction between acetic acid and benzyl is a reversible reaction
0
15
30
45
60
75
90
105
120
ʱ¼ä /min
Time (min)
Fig. 4. Relationship between esterification yield and amount of catalyst.
(Temperature 110 ºC, n(acid)/n(benzyl alcohol) = 1:1.5, ultrasonic
2
frequency: 10 kHz ,ultrasonic intensity: 1.0 W/cm )
2
with SiW12/SiO as catalyst. For the reaction equilibrium can

626 Chen et al.
Asian J. Chem.
be moved to the right by removing the water produced in the
esterification process, it can be assumed as a second order and
The kinetic parameters of this reaction under different
reaction temperatures have been estimated by using Origin.
The equilibrium constants at different temperatures have been
all given in Table-1.
17
nonreversible. The related model can be expressed as follows :
dCA
r = −
A
= kC CB
(1)
According to Arrhenius eqn. 5, activation energy and
frequency factor were all showed in Table-2.
dt
where (C
A
) is the concentration of acetic acid, (C
B
) is concen-
Eq
tration of benzyl acetate, k is the second order rate constants
in the reaction.
ln k = −
+ ln A
(5)
RT
IfY = C
B
- C
A
0, then C
B
– C
A
= Y, C
B
=Y + C
A
, the model
0
The kinetics equation of benzyl acetate with SiW12/SiO
2
can be rewritten as:
by ultrasound was calculated as:
d
4
CA




dCA
5.912×10
−
= kC (Y + C )
A
4
A
(2)
−
= 3.863×10 exp−
C C
A
B
dt

dt
RT

The differential eqn. 2 can be solved by Matlab as follows:
Conclusion
1
 Y

kt = ln
+1 + C
The results of present work have showed us that SiW12
/


(3)
Y
CA

Simplifying the eqn. 4 as:

2
SiO catalyst can be effectively used for the esterification
process for synthesis of benzyl acetate. Two conclusions have
been given as follows: The optimum parameters of the esteri-
fication process at ultrasonic frequency of 10 kHz and ultra-
1
 Y
ln

+1 = kt − C


(4)
2
Y
CA
sound intensity of 1.0 W/cm have been found to be reaction


TABLE-1
REACTION RATE CONSTANTS UNDER DIFFERENT TEMPERATURES (90-110 ºC)
1
 Y
ln

-
1
2
R
+1
Temperature (ºC)
Time (min)
C (mol/L)
A
k [L (mol s )]


Y
CA


0
3.773600
3.313221
2.709445
1.950951
1.309439
1.067929
0.924532
0.784909
0.732078
3.773600
3.200013
2.294349
1.381138
0.845286
0.705663
0.633965
0.652833
0.633965
3.773600
3.147182
2.184914
1.233967
0.433964
0.241510
0.177359
0.184906
0.203774
0.16263
0.23159
0.33821
0.51228
0.7236
15
30
45
-
-
-
4
4
4
9
0
60
1.2021 × 10
1.9714 × 10
3.3491 × 10
0.9812
0.9593
0.9559
7
5
0
0.83165
0.90807
0.99484
1.03177
0.16263
0.25001
0.42635
0.69534
0.95557
1.05125
1.10804
1.09249
1.10804
0.16263
0.25884
0.45225
0.75506
1.30892
1.61953
1.78316
1.76107
1.70957
9
1
05
20
0
1
1
5
0
5
3
4
100
60
7
5
0
9
1
05
20
0
1
1
5
0
5
3
4
110
60
7
5
0
9
1
05
20
1
TABLE-2
APPARENT ACTIVATION ENERGY (90-110 ºC)
1
−3
-1
E (kJ mol )
-1
A [L (mol h) ]
T (K)
×10
ln k
lnA
T
363
373
383
2.755
2.681
2.611
-9.02627
-8.5316
4
59.12
10.5551
3.863*10
-8.00165

Vol. 25, No. 2 (2013)
2
Ultrasound Assisted Heteropoly Acid Catalyst SiW12/SiO for Synthesis of Benzyl Acetate 627
6
7
.
.
J. Pozniczek, A. Lubanska, A.D. Micek-Ilnicka, E.L. Mucha and A.
Bielanski, Appl. Catal. A, 298, 217 (2006).
temperature 110 ºC, amount of catalyst 1.5 g and molar ratios
of benzyl alcohol to acetic acid 1.5:1.0. Under these conditions,
the esterification yield of the reaction reached above 95.3 %.
R. Palcheva, A. Spojakina, L. Dimitrov and K. Jiratova, Micropor.
Mesopor. Mater., 122, 128 (2009).
8. G. Karthikeyan and A. Pandurangan, J. Mol. Catal. A, 311, 36 (2009).
The kinetics equation of benzyl acetate with SiW12/SiO
2
by
9
1
.
Y.C. Wang, X.H. Yi and Wen Qin, Asian J. Chem., 24, 217 (2012).
0. X.-C. Yu, D.-L. Sun and X.-S. Li, Asian J. Chem., 24, 217 (2012).
ultrasound was calculated as:
4







dCA
dt
5.912×10
11. J. Mason and E.D. Cordemas, Trans. Ichem. E, 74, 409 (1996).
12. G.D. Vishwanath, R.G. Parag and B.P.Aniruddha, Ultrason. Sonochem.,
4

−
= 3.863×10 exp −
C C
A B
RT
1
6, 345 (2009).
1
1
1
1
1
3. F.M. Zhang, Y.J. Zhong, W.D. Zhu and J. Wang, China Pet. Process.
Petrochem. Technol., 36, 1144 (2007).
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