Ultrasound-assisted synthesis of aliphatic acid esters at room temperature

Article abstract of DOI:10.1016/j.ultsonch.2011.06.020

This work describes the ultrasound-assisted synthesis of saturated aliphatic esters from synthetic aliphatic acids and either methanol or ethanol. The products were isolated in good yields after short reaction times under mild conditions.

Full text of DOI:10.1016/j.ultsonch.2011.06.020

Ultrasonics Sonochemistry 19 (2012) 387–389
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Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Short Communication
Ultrasound-assisted synthesis of aliphatic acid esters at room temperature
a
a
a
a
a
Cristiane B. Hobuss , Dalila Venzke , Bruna S. Pacheco , Alexander O. Souza , Marco A.Z. Santos ,
b
c
d
d
a,
⇑
Sidnei Moura , Frank H. Quina , Karina G. Fiametti , J. Vladimir Oliveira , Claudio M.P. Pereira
Laboratório de Heterociclos Bioativos e Bioprospecção (LAHBBio), Universidade Federal de Pelotas, Centro de Ciências Químicas, Farmacêuticas e de Alimentos, 96010-900 Pelotas,
RS, Brazil
Universidade de Caxias do Sul, Instituto de Química, 96070-560 Caxias do Sul, RS, Brazil
Universidade de São Paulo, Instituto de Química, 05513-970 São Paulo, SP, Brazil
a
b
c
d
Universidade Regional Integrada URI, RS, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
This work describes the ultrasound-assisted synthesis of saturated aliphatic esters from synthetic ali-
phatic acids and either methanol or ethanol. The products were isolated in good yields after short reac-
tion times under mild conditions.
Received 30 November 2010
Received in revised form 25 April 2011
Accepted 29 June 2011
Ó 2011 Elsevier B.V. All rights reserved.
Available online 13 July 2011
Keywords:
Ultrasound irradiation
Aliphatic esters
Sonochemistry
1
. Introduction
Fatty acid esters and derivatives find widespread applications in
2. Method
2.1. Apparatus and analysis
the food, cosmetics and pharmaceutical industries owing to their
biodegradability and low toxicity [1–3]. Esters of short chain fatty
acids are important flavor and aroma compounds and esters of
long chain fatty acids are being explored for their use as biodiesel
and as waxes in the oleo-chemical industries [3,4]. In general, their
preparation by purely chemical means requires vigorous condi-
tions, acid catalysis, and high temperatures with incomplete con-
versions [5,6]. Free fatty acids are typically esterified by refluxing
in methanol with 10% sulfuric acid [7]. Very long reflux times
All solvents and chemicals were of research grade and were
used as received from Aldrich. The reactions were carried out with
a microtip probe connected to a 500W Sonics Vibracell ultrasonic
processor operating at 20 kHz at 25% of the maximum power out-
put. The progress of the reactions was monitored on a Shimadzu
2010 Gas Chromatograph equipped with a Rtx-Wax polyethylene
glycol capillary column (0.32 mm  30 m). The mass spectra were
obtained on a Hewlett Packard 6890/MSD5973 GC–MS with a
split–splitless injector and equipped with a HP-Innowax capillary
(
up to 6 h), high sulfuric acid concentrations (20%) [8] or high tem-
peratures (170 °C) [9,10] can lead to the formation of colored by-
products and to the destruction of polyenoic fatty acids.
The favorable effects of ultrasonic irradiation are playing an
increasing role in chemical processes, especially in cases where
classical methods require onerous conditions or prolonged reac-
tion times [11]. As part of our continuing work on the use of ultra-
sound irradiation to improve organic reactions [12–18], we report
here a rapid and facile procedure for the synthesis of saturated ali-
phatic acid esters by the ultrasound irradiation induced reaction of
aliphatic acids with methanol or ethanol in acidic media at room
temperature [11].
column (30 m  250
lm); helium was used as the carrier gas
(56 Kpa). The IR spectra were taken on a Shimadzu IR Prestige-21
spectrometer in KBr pellets.
2.2. Synthesis of esters by ultrasound irradiation
In a 25 ml beaker, the fatty acid (4.0 mmol) and sulfuric acid
(2.0 mmol) were mixed with ethanol (27.6 ml) or methanol
(16.8 ml) and sonicated for 15–30 min at room temperature
(25 °C) (Scheme 1). After the time indicated (Table 1), the alcohol
was evaporated under reduced pressure. The solid residue was dis-
solved in water (35 ml), the product was extracted into ethyl ether
(
3 Â 20 ml) and the combined organic fractions were dried
(MgSO ). The solvent was evaporated under vacuum to give the
pure esters.
⇑
Corresponding author. Tel.: +55 13 33629367; fax: +55 13 33629363.
E-mail address: claudio.martin@pq.cnpq.br (C.M.P. Pereira).
4
1
350-4177/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2011.06.020

3
88
C.B. Hobuss et al. / Ultrasonics Sonochemistry 19 (2012) 387–389
À1
24 2
Ethyl decanoate: C12H O , MW: 200.32. IR: m (cm ) 1720–
+
1
760, 1160–1200, 2800–2960; m/z (%) 200(M 1,3), 155(21),
1
43(5), 88(100), 73(19), 55(26), 43(30).
À1
Ethyl dodecanoate: C14
H
28
O
2
, MW: 228.37. IR:
m
(cm ) 1720–
+
1
1
4
760, 1160–1200, 2800–2960; m/z (%) 228(M 1, 7), 183(15),
57(17), 143(8), 129(8), 115(8), 101(54), 88(100), 73(18), 55(27),
3(33).
À1
Ethyl tetradecanoate: C16
H
32
O
2
, MW: 256.42. IR:
m
(cm
)
+
1
720–1760, 1120–1200, 2800–2960; m/z (%) 256 (M 1, 7),
2
11(9), 157(17), 101(60), 88(100), 73(17), 55(26), 43(35).
Scheme 1. Synthesis of aliphatic acid esters.
À1
Ethyl palmitate: C18
H
36
O
2
, MW: 284.48. IR:
m
(cm ) 1720–
+
1
1
760, 1160–1200, 2800–2960; m/z (%) 284(M 1, 9), 241(9),
57(17), 143(9), 101(61), 88(100), 70(17), 55(26), 43(35).
2
.3. Spectral data of products 3–12
À1
Methyl octanoate: C , MW: 158.24. IR:
9
H
18
O
2
m
(cm ) 1720–
3. Results and discussion
+
1
1
760, 1160–1200, 2800–2960; m/z (%) 158 (M 1, 2), 127 (19),
15 (11), 101(10), 87(48), 74(100), 55(27), 43(38).
The direct synthesis of esters from fatty acids and alcohols by an
enzymatic process has been studied [19]. Ionic liquids are also an
attractive alternative, although they have the disadvantage of high
cost [20]. Recently, esterification has been investigated with a vari-
ety of catalysts, but all require very long reaction times [21–27].
In particular, the ultrasound has been employed to improve the
transesterification reaction in two ways: (a) a reduction of reaction
time and (b) an increase in the biodiesel yield. The origin of the
enhancement of transesterification reactions by ultrasound was
studied by Kalva and co-authors and the effect found to be due
to a physical rather than a chemical mechanism [28]. However,
the reaction times required to prepare biodiesel by using ultra-
sound are often similar to those of traditional routes, with little
or no advantages. For instance, the synthesis of isopropyl esters
from palm fatty acids and isopropyl alcohol via sonochemistry re-
ported Deshmane and co-authors [29] required long reaction time
À1
Methyl decanoate: C11
H
22
O
2
, MW: 186.29. IR:
m
(cm ) 1720–
+
1
760, 1120–1200, 2800–2960; m/z (%) 186(M 1, 3), 155 (12), 143
(
26), 101 (9), 87 (55), 74 (100), 55 (26), 43 (34).
Methyl dodecanoate: C13 , MW: 214.34. IR:
720–1760, 1160–1200, 2800–2960; m/z (%) 214 (M 1, 3), 183
À1
H
26
O
2
m (cm )
+
1
(
8), 171(12), 143(17), 87(67), 74(100), 55(28), 43(33).
Methyl tetradecanoate: C15 , MW: 242.40. IR: m (cm )
À1
H
30
O
2
+
1
720–1760, 1160–1200, 2800–2960; m/z (%) 242(M 1, 9), 211(9),
1
99(17), 143(26), 87(70), 74(100), 55(30), 43(35).
À1
Methyl palmitate: C17
H
34
O
2
, MW: 270.45. IR:
m
(cm ) 1720–
+
1
1
760, 1160–1200, 2800–2960; m/z (%) 270(M 1, 10), 239(7),
43(33), 87(74), 74(100), 55(35), 43(43).
À1
Ethyl octanoate: C10
H
20
O
2
, MW: 172.26. IR:
m
(cm ) 1720–
+
1
760, 1160–1200, 2800–2960; m/z (%) 172(M 1, 2), 127 (36), 115
(
11), 101 (40), 88 (100), 73 (20), 57 (40), 41 (31).
Table 1
Ultrasound-assisted ester synthesis.
Product
Sonochemistry
Time (min)
30
Literature
Yield (%)a
93
Time (h)[ref.]
21[22]
Yield (%)[ref.]
73[22]
O
OMe
O
OMe
O
15
15
15
15
15
80
63
77
80
80
48[23]
4,5[24]
48[23]
48[23]
4.5[24]
71[23]
94[24]
79[23]
64[23]
90[24]
OMe
O
OMe
O
OMe
OEt
O
1
1
1
3
5
5
5
0
50
70
78
95
30[25]
6[26]
90[25]
65[26]
86[27]
95[22]
O
OEt
O
OEt
8[27]
O
OEt
3,5[24]
O
OEt
a
Yields of isolated products.

C.B. Hobuss et al. / Ultrasonics Sonochemistry 19 (2012) 387–389
389
(
[
6 h) in acidic medium. Similar conditions were used by Hanh et al.
30,31] to obtain of esters of oleic acid (FFA) with short-chain alco-
Acknowledgements
hols (ethanol, propanol and butanol) under ultrasonic irradiation.
The esterification of oleic acid was investigated over the range
of molar ratios of alcohol to oleic acid of 1:1–10:1, with 0.5–
The authors are grateful to INCT de Estudos do Meio Ambiente
(573.667/2008-0), CEPEMA-USP (Centro de Capacitação e Pesquisa
em Meio Ambiente), CNPq (310472/2007-5, 475575/2008-3), FA-
PERGS and CAPES for financial and fellowship support. FHQ is affil-
iated with the INCT for Catalysis in Molecular and Nanostructures
Systems (INCT-Catalysis).
1
0 wt.% of the acid catalyst (wt. of sulfuric acid/wt. of oleic acid)
and irradiation times of 10 h. The optimized condition for the
esterification process was a molar ratio of alcohol to oleic acid of
3
[
:1 with 5 wt.% of H
30,31].
Stavarache and co-authors recently reported two important
2 4
SO at 60 °C and an irradiation time of 2 h
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required) and the temperature (room temperature) with no sacri-
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[
[
[
[
(
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4
. Conclusion
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method for carrying out esterification reactions of commercial
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conducted at ambient temperature; (iii) the required reaction
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(
[
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(
v) the products are isolated in good yields (50–95%). This mild,
(
convenient and improved protocol for the ultrasound-promoted
preparation of esters can potentially be explored for biodiesel
synthesis.
[