Synthesis of 2-ethylhexyl acetate by transesterification of methyl acetate with 2-ethylhexanol

Article abstract of DOI:10.14233/ajchem.2015.18263

In order to explore a new application field of methyl acetate which is of limited industrial importance, one of the possibilities to obtain the desired products would be the transesterification of methyl acetate with 2-ethylhexanol. The choice of catalyst and the determination of the best experimental conditions for the transesterification were investigated in this paper. Strongly acidic cation-exchange resin NKC-9 was chose as the catalyst in this reaction. The reaction time, the effects of the reaction temperature, the catalyst loading and the molar ratio of methyl acetate to 2-ethylhexyl acetate on the conversion of 2-ethylhexyl acetate were discussed. This paper describes an optimization study on the transesterification reaction based on nine well-planned orthogonal experiments. The maximum conversion of 2-ethylhexanol was found at a NKC-9 catalyst loading of 20 wt. %, a molar ratio of methyl acetate to 2-ethylhexanol of 4:1, a reactive time of 3 h and a reaction temperature of 80 °C. The product yield and the conversion of 2-ethylhexanol under optimal conditions reached 90.90 and 79.64 %, respectively. The structure of the product 2-2-ethylhexyl acetate acetate has been conformed by IR and ¹H NMR.

Full text of DOI:10.14233/ajchem.2015.18263

Asian Journal of Chemistry; Vol. 27, No. 8 (2015), 2861-2864
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OURNAL OF HEMISTRY
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http://dx.doi.org/10.14233/ajchem.2015.18263
Synthesis of 2-Ethylhexyl Acetate by Transesterification of Methyl Acetate with 2-Ethylhexanol
*
LINA YIN, DAZHI WANG, FENGZUO QU, LIN JIA and SHAOYIN ZHANG
School of Light Industry and Chemical Engineering, Dalian Polytechnic University, Dalian, Liaoning Province, P.R. China
*Corresponding author: E-mail: wang_dz@dlpu.edu.cn, zhangsy@dlpu.edu.cn, yuanhaowang@126.com
Received: 6 June 2014;
Accepted: 27 August 2014;
Published online: 27 April 2015;
AJC-17150
In order to explore a new application field of methyl acetate which is of limited industrial importance, one of the possibilities to obtain the
desired products would be the transesterification of methyl acetate with 2-ethylhexanol. The choice of catalyst and the determination of
the best experimental conditions for the transesterification were investigated in this paper. Strongly acidic cation-exchange resin NKC-9
was chose as the catalyst in this reaction. The reaction time, the effects of the reaction temperature, the catalyst loading and the molar ratio
of methyl acetate to 2-ethylhexyl acetate on the conversion of 2-ethylhexyl acetate were discussed. This paper describes an optimization
study on the transesterification reaction based on nine well-planned orthogonal experiments. The maximum conversion of 2-ethylhexanol
was found at a NKC-9 catalyst loading of 20 wt. %, a molar ratio of methyl acetate to 2-ethylhexanol of 4:1, a reactive time of 3 h and a
reaction temperature of 80 °C. The product yield and the conversion of 2-ethylhexanol under optimal conditions reached 90.90 and
79.64 %, respectively. The structure of the product 2-2-ethylhexyl acetate acetate has been conformed by IR and 1H NMR.
Keywords: Methyl acetate, Transesterification, NKC-9, Orthogonal experiment.
Many catalysts have been suggested therefore for use in
the transesterification step, the conventional inorganic acid
catalyst used in transesterification is concentrated sulfuric acid.
Xu et al.4 have reported on the advantages of the heterogenerous
catalyst strongly acidic cation-exchange resin NKC-9. Cui
et al.5 reported the kinetic behavior and chemical equilibrium
of the transesterification of methyl acetate with n-butanol cata-
lyzed by an ionic liquid. Hence, these catalysts are considered
good candidates for the transesterification of methyl acetate
with 2-ethylhexanol.
Although there are many studies on transesterification
reactions, any information about the transesterification of
methyl acetate with 2-ethylhexanol has not been found in the
literature. In this paper, a new method for producing 2-ethyl-
hexyl acetate by transesterification of methyl acetate with
2-ethylhexanol was performed. In addition, the most suitable
catalyst was chosen from the concentrated sulfuric acid, ion-
exchange resin NKC-9 and 1-heptyl-3 methyl imidazole acetate.
INTRODUCTION
Methyl acetate is a byproduct during the production of
polyvinyl alcohol. From 1 ton of polyvinyl alcohol, about 1.68
tons of methyl acetate is produced1,2. It is generally hydrolyzed
by a catalyst to obtain acetic acid and methanol, which is the
conventional method of treating methyl acetate in industry.
However, it became not particularly economical since the price
of acetic acid had decreased rapidly in recent years. Further-
more, the hydrolysis of methyl acetate has many disadvantages,
such as the high requirement for the equipment and more energy
extensive in the process. The transesterification of methyl
acetate with 2-ethylhexanol (2-EH) is therefore a sustainable
option of the applications of the methyl acetate. The coproduct
formed, methanol, can undergo alcoholysis reaction once again
to form polyvinyl alcohol and get recycled back for transesteri-
fication, while 2-ethylhexyl acetate (2-EHA) is a high boiling
retarder solvent with limited water solubility, commonly used
to promote flow and retard blushing in formulations such as
lacquers, lacquer emulsions, screen inks, baking enamels and
air-dry enamels. It is also an excellent solvent for nitrocellulose
and widely used in the leather industry3.
EXPERIMENTAL
Methyl acetate (AR grade) and 2-ethylhexanol (AR
grade) were obtained from Tianjin institute of fine chemicals
retrocession. Strong-acid cationic exchange resin NKC-9 was
obtained from Anhui Sanxing Resin Technology Co. Ltd.,
NaOH (AR grade) was obtained from Shenyang Chemical
Reagent No. 3 Factory. n-Heptane (AR grade) was obtained
Reaction equation can be presented as:
O
O
OH
O
+ CH3OH
+
O

2862 Yin et al.
Asian J. Chem.
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30
20
10
0
from Tianjin Kemiou Chemical Reagent Co., Ltd. Other
chemicals are also analytical grade.
NHK-9
1-Heptyl-3-methyl imidazole
H2SO4
Transesterification reaction procedure: All the experi-
ments were conducted in a 4-neck round bottom flask of volume
250 mL equipped with a stirrer, a thermometer, a condenser
pipe and a pressure-equalizing dropping funnel. The 4-neck
round bottom flask was dipped in a constant temperature water
bath which was equipped with a temperature sensor. 2-Ethyl-
hexanol and NKC-9 were put into the 4-neck round bottom
flask. The temperature in the reactor was maintained within
1 °C with respect to the desired temperature. The measured
quantities of 2-ethylhexanol and NKC-9 were charged into
the 4-neck round bottom flask and methyl acetate was charged
to the constant pressure drop funnel. Once the desired tempe-
rature was achieved, the methyl acetate was being dropped
into the reactive mixture over a 2 h period. After the dropping
was finished, the temperature is maintained at the desired
temperature for the fixed time. NKC-9 and the reactive liquid
were separated by vacuum filtration when it cooled down and
the NKC-9 was recycled at the same time. Finally the fraction
between 130 and 140 °C was collected by reduced pressure
distillation and weighed this fraction.
Gas chromatography was applied to study the components
of the reaction mixture. The conversions of 2-ethylhexanol and
the components of all samples were analyzed by gas chroma-
tography (GC7890F) equipped with hydrogen flame ionization
detector (FID). (N2 as carrier gas, a quartz capillary column
packed with PEG-20M 30 m × 0.53 mm × 0.5 µm, oven tempe-
rature 80 °C, injector temperature 220 °C, detector temperature
240 °C, injecting sample volume 0.2 µL; retention times:
methyl acetate 0.9 min, methanol 1.1 min, 2-ethylhexyl acetate
7 min, 2-ethylhexanol 12.5 min).
1
2
3
4
5
Time (h)
Fig. 1. Conversion of 2-ethylhexanol of the three different catalysts
(reaction temperature = 80 °C, methyl acetate/2-ethylhexanol = 3:1)
equipment corrosion and difficult to separate from the reaction
mixtures. Supported on the results above, the concentrated
sulfuric acid is not suitable for industrial production and the
catalytic activity of 1-heptyl-3 methyl imidazole acetate is
lower than others, thus, the strong-acid cationic exchange resin
NKC-9 proved to be the optimal catalyst in the transesterifi-
cation reaction of methyl acetate with 2-ethylhexanol.
Transesterification is a reversible reaction. The reactive
rate of reserve reaction changes with time. Fig. 1 also showed
that when the reaction time was 3 h, NKC-9 obtained the
highest conversion about 57 %. It was determined that 3 h
was chosen as the suitable reactive time.
Therefore, the catalyst used in the following experiments
in this paper was the strong-acid cationic exchange resin
NKC-9 and the reaction time was 3 h.
Product spectroscopic characterization: Infrared spectra
of the reaction product 2-ethylhexyl acetate (KBr pellets) was
recorded on Spectrum One-B (Perkin Elmer®) FT-IR spectro-
meter. 1H NMR spectra was measured in CHCl3-d1 using TMS
as internal standard with aVarian® INOVA spectrometer (400
MHz for 1H).
Optimization of reaction conditions
Effect of the reaction temperature: Temperature has a
significant effect on transesterification. To investigate the effect
of the reaction temperature, operations were carried out at 60,
70, 80, 90 and 100 °C. The initial molar ratio of methyl acetate
and 2-ethylhexanol was 3:1, reactive time was 3 h and the
catalyst loading was 20 wt. % (by mass of methyl acetate). As
shown in Fig. 2, at the beginning, with the increasing of tempe-
rature, the conversion of 2-ethylhexanol increased, because
the increase of temperature led to more successful collisions.
These successful collisions had sufficient energy (activation
energy) to break the bonds and form products and thus resulted
in higher convention of 2-ethylhexanol. However, when the
temperature reached 80 °C, the conversion of 2-ethylhexanol
was the highest point and then decreased with the increase of
temperature. Therefore, 80 °C was chosen as the most fixed
reaction temperature.
RESULTS AND DISCUSSION
Catalyst and reaction time choices: Choice of catalyst
is important and results were obtained with different catalysts
for the transesterification.According to literature, the suitable
catalyst loading of concentrated sulfuric acid was chosen as
2 wt. % (by mass of methyl acetate)6, NKC-9 was 20 wt. %
(by mass of methyl acetate)4, 1-heptyl-3 methyl imidazole
acetate was 5 wt. % (by mass of methyl acetate)7.
The catalytic effect of the three different catalysts is
illustrated in Fig. 1. According to Fig. 1, it can be observed
that the catalytic effect: H2SO4 > NKC-9 > 1-heptyl-3 methyl
imidazole acetate. When acidic catalyst catalyzed, the reaction
mechanism of transesterification is that proton firstly combines
with the carbonyl of methyl acetate to form the intermediate
of carbocation. Then protophilic 2-ethylhexanol combines with
carbocation to form the intermediate. Finally this intermediate
is resolved to 2-ethylhexyl acetate and methanol. As H2SO4 is
stronger acidity than NKC-9, it showed better catalytic result
than NKC-9. But the concentrated sulfuric acid may cause
Effect of catalyst loading: The catalyst loading was
expressed as the weight ratio of the catalyst to the weight of
methyl acetate. The effect of catalyst loading on the conversion
of 2-ethylhexanol was tested varied from 0 to 20 wt % (by
mass of methyl acetate) at reaction temperature of 80 °C,
reactive time of 3 h and methyl acetate to 2-ethylhexanol molar

Vol. 27, No. 8 (2015)
Synthesis of 2-Ethylhexyl Acetate by Transesterification of Methyl Acetate with 2-Ethylhexanol 2863
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60
50
40
30
20
10
0
60
50
40
30
1:1
2:1
3:1
3.5:1
4:1
0
5
10
15
20
Mole ratio of methyl acetate and 2-ethylhexanol
Catalyst loading (%)
Fig. 2. Effect of the initial molar ratio of methyl acetate to 2-ethylhexanol
on the conversion of 2-ethylhexanol (reaction time = 3 h, NKC-9
catalyst loading = 20 wt. %, 80 °C)
Fig. 4. Effect of catalyst loading on conversion of 2-ethylhexanol (reaction
time = 3 h, methyl acetate/2-ethylhexanol = 3:1, NKC-9 catalyst
loading = 20 wt. %, 80 °C)
ratio of 3:1. The effect of catalyst loading on the conversion
rate of 2-ethylhexanol is given in Fig. 3. It can be observed
that the conversion of 2-ethylhexanol increased with the
increase of catalyst loading. It was due to the fact that the
increase of catalyst loading corresponded to more available
active sites for the transesterification reaction, resulting in
higher conversion.
ratio of methyl acetate to 2-ethylhexanol. Transesterification
of methyl acetate with 2-ethylhexanol is an equilibrium
controls the amount of product formed, therefore, the use
of an excess of methyl acetate increased the conversion of
2-ethylhexanol.
Product spectroscopic characterization: The chemical
structure of the product 2-ethylhexyl acetate was characterized
by the combined methods of IR, 1H NMR. The results of the
IR, 1H NMR spectra were consistent well with the proposed
structure.
80
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50
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40
IR spectrum of 2-ethylhexyl acetate: IR spectrum data:
ν(C=O): 1744.69 cm-1, ν(C-O): 1037.07 cm-1, ν(C-H): 2861.33
cm-1, 2930.76 cm-1, 2960.39 cm-1, δ(C-H): 1365.53 cm-1,
1383.61 cm-1, 1463.63 cm-1, ν(C-C): 1235.07 cm-1, γ(C-H):
606.04 cm-1, 728.35 cm-1, 771.74 cm-1.
1H NMR of 2-ethylhexyl acetate: 1H NMR data: δH: 3.96
(d, 2H, OCH2), 2.04 (s, 1H, CH), 2.03 (t, 3H, CH3C=O), 1.25
(m, 8H, CH2CH2CH2), 0.87 (q, 6H, CH3).
Orthogonal experiment: The orthogonal experiment
design may provide a useful guidance to determine design
parameters and improve conversion of 2-ethylhexanol and find
the optimal combination for the demand of wholesale
industrialization. The orthogonal experiment Table L9(3)4 was
selected, which contained four factors three levels and nine
experiments. Four factors are the reaction time, reactive tempe-
rature, catalyst loading and the initial molar ratio of methyl
acetate to 2-ethylhexanol. These are considered as principal
process parameters. It was found that the order of significant
factors for the the conversion of 2-ethylhexanol is reaction
time > catalyst loading > the initial molar ratio of methyl acetate
and 2-ethylhexanol > reactive temperature. Based on the results
of the range analysis, the maximum conversion of 2-ethyl-
hexanol was found at a NKC-9 catalyst loading of 20 wt. %, a
molar ratio of methyl acetate to 2-ethylhexanol of 4:1, a reactive
time of 3 h and a reaction temperature of 80 °C. The product
yield and the conversion of 2-ethylhexanol under optimal
conditions reached 90.90 and 79.64 %, respectively.
60
70
80
90
100
Temperature (°C)
Fig. 3. Effect of reaction temperature on the conversion of 2-ethylhexanol
(reaction time = 3 h, methyl acetate/2-ethylhexanol = 3:1, NKC-9
catalyst loading = 20 wt.%)
Effect of molar ratio of 2-ethylhexanol to methyl acetate:
According to the principle of chemical equilibrium, it is useful
for the forward reaction to increase the amount of reactant.
Therefore, the effect of different initial reactant molar ratio of
methyl acetate to 2-ethylhexanol from 1:1 to 4:1 was deter-
mined at 80 °C, reactive time 3 h and loading catalyst of 20
wt. % (by mass of methyl acetate). Fig. 4 showed that the
conversion of 2-ethylhexanol increased with increasing molar

2864 Yin et al.
Asian J. Chem.
Conclusion
of production and propitious to the demand of wholesale
industrialization.
The transesterification of methyl acetate and 2-ethyl-
hexanol, which is a new highly potential and sustainable method
to treat with the methyl acetate, leading to 2-ethylhexyl acetate
and methanol catalyzed by NKC-9 has been studied experi-
mentally. Strongly acidic cation-exchange resin NKC-9 was
chosen as the most suitable catalyst in this reaction. The reaction
time, the effects of the reaction temperature, the catalyst loading
and the initial molar ratio of methyl acetate to 2-ethylhexanol
on the conversion of 2-ethylhexanol were discussed. The
orthogonal experiment design is adopted to investigate the
optimal combination. Based on the results of the range analysis,
the maximum conversion rate of 2-ethylhexanol was found at
a NKC-9 catalyst loading of 20 wt. %, a initial molar ratio of
methyl acetate to 2-ethylhexanol of 4:1, a reactive time of 3 h
and a reaction temperature of 80 °C. The product yield and
the conversion of 2-ethylhexanol under optimal conditions
reached 90.90 and 79.64 %, respectively. This method possesses
that procedure is simple, less demand for equipment, low cost
ACKNOWLEDGEMENTS
The authors are gratefully thanks for financial support from
Liaoning Province Natural Science Fund Project (201202012)
and the ministry of Housing and Urban-Rural Development
of the People’s Republic of China under Grant [2014-K4-034].
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