Improved synthesis of sucrose fatty acid monoesters under ultrasonic irradiation

Article abstract of DOI:10.1016/j.ultsonch.2009.08.009

Sucrose fatty acid esters were synthesized by the transesterification of sucrose with aliphatic esters under ultrasound irradiation in good yield (≥73%). The optimum reaction conditions for the transesterification reaction include a molar ratio of sucrose to fatty acid ethyl ester of 2:1 and the use of a 13% mol anhydrous K₂CO₃ catalyst. The optimum reaction temperature was set at 70 °C, the optimum reaction time was 2 h, and the optimum reaction pressure was 11 kPa. The reaction had excellent monoester selectivity. The proportion of monoester (6-monoester + 6′-monoester) in the purified products was up to 92-95% via flash column chromatography over silica gel, the ratios of 6-monoester/6′-monoester are 2.1-2.7, and the sucrose monoesters were identified by HPLC-MS, NMR and IR.

Full text of DOI:10.1016/j.ultsonch.2009.08.009

Ultrasonics Sonochemistry 17 (2010) 352–355
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Improved synthesis of sucrose fatty acid monoesters under ultrasonic irradiation
a
a
a
a
a
Dan Huang a,b, , Xue Jiang , Hao Zhu , Xiaorong Fu , Kangrong Zhong , Weidong Gao
*
a Key Laboratory of Eco-Textile (Jiangnan University), Ministry of Education, Wuxi, China
b Department of Chemistry and Chemical Engineering, Nantong University, Nantong, Jiangsu, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Sucrose fatty acid esters were synthesized by the transesterification of sucrose with aliphatic esters
under ultrasound irradiation in good yield (P73%). The optimum reaction conditions for the transesteri-
fication reaction include a molar ratio of sucrose to fatty acid ethyl ester of 2:1 and the use of a 13% mol
anhydrous K2CO3 catalyst. The optimum reaction temperature was set at 70 °C, the optimum reaction
time was 2 h, and the optimum reaction pressure was 11 kPa. The reaction had excellent monoester
selectivity. The proportion of monoester (6-monoester + 60-monoester) in the purified products was up
to 92–95% via flash column chromatography over silica gel, the ratios of 6-monoester/60-monoester
are 2.1–2.7, and the sucrose monoesters were identified by HPLC–MS, NMR and IR.
Received 31 August 2008
Received in revised form 1 August 2009
Accepted 19 August 2009
Available online 23 August 2009
Keywords:
Sucrose monoesters
Synthesis
Transesterification
Ultrasonic irradiation
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
one-pot, regioselective synthesis of 6-acyl esters of sucrose (yield:
47–70%) by means of transforming sucrose into the dibutyltin ace-
Sucrose esters are nonionic surfactants that may be produced
from renewable, economical and readily available resources [1].
The free alcoholic hydroxyl groups of sucrose react with aliphatic
or aromatic acids to produce sucrose esters. They are widely used
in foods, cosmetics, detergents, agriculture, bioengineered en-
zymes and pharmaceuticals [2,3]. Apart from their emulsifying
properties, they are completely biodegradable, harmless to the
environment, nontoxic, skin-compatible, odorless, tasteless, a good
insecticide, and are digested as a blend of sucrose and fatty acids in
the stomach [4].
Although the reactivities of the different primary and secondary
hydroxyl groups vary slightly in sucrose, attempts to acylate su-
crose often involve non-specific reactions leading to mixtures of
compounds differing in their degree of esterification and the posi-
tion of acylation [5]. Even if for many applications these mixtures
of mono-, di-, and triesters are convenient, selective reactions
would be valuable because the hydroxyl groups of sucrose could
be effectively distinguished and sucrose monoesters in a single
procedure could be preferentially produced. Selective acylation of
unprotected sucrose has been accomplished by enzymatic ap-
proaches [6–8]. However, the selective monoacylation of sucrose
is difficult to achieve by chemical approaches due to the similar
reactivity of the eight hydroxyl groups and the existence of intra-
molecular migration processes [9]. Linhardt reported the direct,
tal, enhancing the nucleophilicity at the C-6 oxygen and restricting
the subsequent acylation reaction, but such methods need a long
reaction time (48–96 h) [10]. Plou reported the synthesis of four
sucrose fatty acid esters (caprylate, laurate, myristate, and palmi-
tate) in dimethylsulfoxide by transesterification of sucrose with
the corresponding vinyl esters using disodium hydrogen phos-
phate as catalyst. Since vinyl alcohol formed during the process
tautomerizes to the low-boiling-point acetaldehyde, the equilib-
rium is shifted toward the ester formation, resulting in high yields
(85%), with 2-O-acylsucrose as the major product (60–70%), but a
molar ratio sucrose/vinyl ester (4:1) was high [11]. By employing
alkyl fatty acid esters the transesterification reactions became
reversible, resulting in low yields. Furthermore, none of the current
processes is particularly selective. They all afford mixtures of com-
pounds differing in their degree of esterification [5].
Ultrasonic irradiation is a useful tool for emulsification of
immiscible liquids. The collapse of the cavitation bubbles disrupts
the phase boundary and causes emulsification, by ultrasonic jets
that impinge from one liquid to another [12]. Stavarache and co-
workers reported the transesterification of vegetable oil with
short-chain alcohols for biodiesel fabrication by low frequency
ultrasound [13–15].
Recently, in our study, we found that transesterification of su-
crose with fatty acid esters can be accelerated by ultrasonic irradi-
ation. Here, we reported the preparation of a homologous series of
sucrose monoesters with n-acyl chains of 8, 12, 14, and 16 carbon
atoms under ultrasonic irradiation. Good yield (P73%) and high
percentage of monoesters (P92%) were obtained.
* Corresponding author. Address: Key Laboratory of Eco-Textile (Jiangnan Uni-
versity), Ministry of Education, Wuxi, China. Tel.: +86 510 85987599; fax: +86 510
85705599.
E-mail address: huangdan6@163.com (D. Huang).
1350-4177/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2009.08.009

D. Huang et al. / Ultrasonics Sonochemistry 17 (2010) 352–355
353
and identified by 1H NMR and 13C NMR. Reactions with longer car-
boxylic ester (lauroyl, myristoyl and palmitoyl) were performed
following the same procedure as ethyl octanoate, and the variously
substituted sucrose esters were isolated using the same eluents.
Spectral data for monoesters are given as follows.
2. Experiment
2.1. Apparatus and analysis
A Ultrasonic Cleaner (KQ-100E) operating at a frequency of
40 kHz came from Ultrasonic Cleaner Co. Ltd. of Kun-Shang China;
1H NMR and 13C NMR spectra were recorded on a Varian Mercury
400 MHz spectrometer as solutions in CD3OD. All chemical shifts
are reported in ppm relative to tetramethylsilane. Infrared spectra
were recorded on a Nicolet FT-IR 500 spectrometer using KBr pel-
lets and absorption is reported in wave-numbers (cmꢀ1). Mass
spectrometer analyses were performed at a Waters Synapt MS.
Flash column chromatography was carried out on Merck silica
gel (230–400 mesh). Thin-layer chromatography (TLC) was per-
formed on silica gel 60 F254 plates (Merck) with chloroform/meth-
anol 4:1 (vol/vol) as eluent; spots were detected by dipping the
plates into the solution (1 g carbamide + 4.8 mL 85% phosphoric
acid + 48 mL water saturated 1-butanol solution), drying, and
heating at 80 °C for 30 min. The separation and analysis of the ratio
of sucrose monoesters (regioisomers) were achieved using an
IR spectrum and mass spectrometric data for the monoesters –
mixture of isomers (6 and 60): mono-O-octanoylsucroses: IR(KBr)
(cmꢀ1): 3362 (a strong peak, O–H stretch of free hydroxyl in su-
crose); 2857, 2928, 2945 (C–H stretch of methyl and methylene),
1728 (C@O stretch of ester), 1056, 1107 (C–O stretch of C–O–C),
955 (glycosidic bond stretch of sucrose). HRMS (ES+) m:z requires
491.2105 [M+Na]+, found 491.2214. Mono-O-lauroylsucroses:
IR(KBr) (cmꢀ1): 3383 (a strong peak, O–H stretch of free hydroxyl
in sucrose); 2853, 2924 (C–H stretch of methyl and methylene),
1737 (C@O stretch of ester), 1019, 1109 (C–O stretch of C–O–C),
953 (glycosidic bond stretch of sucrose). HRMS (ES+) m:z requires
547.2731 [M+Na]+, found 547.2952. Mono-O-myristoylsucroses:
IR(KBr) (cmꢀ1): 3331 (a strong peak, O–H stretch of free hydroxyl
in sucrose); 2852, 2923 (C–H stretch of methyl and methylene),
1737 (C@O stretch of ester), 1016, 1108 (C–O stretch of C–O–C),
952 (glycosidic bond stretch of sucrose). HRMS (ES+) m:z requires
575.3044 [M+Na]+, found 575.3224. Mono-O-palmitoylsucroses:
IR(KBr) (cmꢀ1): 3433 (a strong peak, O–H stretch of free hydroxyl
in sucrose); 2850, 2918 (C–H stretch of methyl and methylene),
1740 (C@O stretch of ester), 1061, 1107 (C–O stretch of C–O–C),
995 (glycosidic bond stretch of sucrose). HRMS (ES+) m:z requires
603.3357 [M+Na]+, found 603.3500.
Agilent. The HPLC was equipped with
a Diamonsil column
m C18 and a ELSD detector
(4.6 mm ꢁ 250 mm) packed with 5
l
and with a methanol/water as the mobile phase. The gradient pro-
gram was 85% of solvent A from 0 to 10 min at a flow rate of 1 mL/
min, and 90% solvent A from 10 to 25 min at a flow rate of 1.0 mL/
min.
6-O-Octanoylsucrose: 1H NMR (400 MHz, CD3OD) d(ppm): 0.91
(t, J = 4.8 Hz, 3H), 1.32 (s, 8H), 1.61–1.64 (m, 2H), 2.29 (t,
J = 7.2 Hz, 2H), 3.32 (dd, J = 8.0 Hz and J = 8.4 Hz, H-4) 3.41 (dd,
J = 4.0 Hz and J = 3.2 Hz, H-2), 3.57–3.64 (m, H-10), 3.72 (dd,
J = 8.8 Hz, H-3), 3.78–3.84 (m, H-60), 3.91–3.96 (m, H-50), 3.99 (t,
J = 8.4 Hz, H-40), 4.03–4.10 (m, H-5), 4.16 (d, J = 6.0 Hz, H-30), 4.40
(dd, J = 12, H-6a), 4.60 (dd, J = 12, H-6b), 5.37 (d, J = 2.8, H-1); 13C
NMR (100 MHz, CD3OD) d(ppm): 14.5, 23.4, 25.7, 30.0, 32.4, 34.1
(alkyl), 63.4 (C-10), 63.9 (C-60), 64.6 (C-6), 71.2 (C-4), 71.7 (C-2),
72.8 (C-5), 74.3 (C-3), 75.2 (C-40), 78.7 (C-30), 83.4 (C-50), 92.3 (C-
1), 104.8 (C-20), 175.1 (C@O).
2.2. Reagents and materials
Sucrose, dimethylsulfoxide (DMSO), anhydrous K2CO3, anhy-
drous disodium hydrogen phosphateethyl, PEG-400, ethyl capry-
late, ethyl laurate, ethyl myristate, ethyl palmitate and 1-butanol
were purchased from Sinopharm Chemical Reagent Co. Ltd. and
were used as received.
2.3. Synthesis of sucrose esters
In a dry Erlenmeyer type flask equipped with stopper, milled
sucrose 34 g (100 mmol) and anhydrous K2CO3 0.9 g (6.5 mmol)
were added to 30 mL DMSO. After the sucrose was completely dis-
solved in the DMSO, ethyl octanoate 1 mL was added to the mix-
ture and sonicated for a preset time at 60–80 °C under reduced
pressure. The desired reaction temperature was controlled by set-
ting the ultrasound apparatus and then maintaining temperature
( 3 °C) by use of a circulating water bath. After the complete con-
version of the fatty acid ester, as determined by TLC analysis, the
reaction was stopped and DMSO was evaporated off by vacuum
distillation. The residue was dissolved in 25% aqueous sodium
chloride/1-butanol 1:1 (vol/vol) under stirring, and the mixture
was allowed to separate into two phases. In order to eliminate
the non-reacted sucrose, the organic phases were washed with
fresh aqueous sodium chloride solution. The above process should
be repeated twice. After phases separation, the organic phase was
dried with anhydrous Na2SO4. The solvent was then evaporated off,
and the residue was further purified by the addition of ethyl ace-
tate (preheated to 40 °C) with vigorous stirring until dissolution
was completed. The solution was allowed to stand while cooling.
The precipitated sucrose esters were then filtered off and dried un-
der vacuum at 45 °C to a constant weight. The sucrose ester (a
white amorphous solid) was obtained at a yield of 17.5 g (74.8%,
based on ethyl fatty acid ester as the limiting reagent and assum-
ing that product is entirely monoester). The sucrose monoester
was isolated by thin-layer chromatography (TLC) with chloro-
form/methanol 4:1 (vol/vol) as eluent and characterized by IR
and MS. The isomers of the monoester were separated by HPLC
60-O-Octanoylsucrose. 1H NMR (400 MHz, CD3OD) d(ppm): 0.91
(t, J = 4.8 Hz, 3H), 1.32 (s, 8H), 1.61–1.64 (m, 2H), 2.29 (t,
J = 7.2 Hz, 2H), 3.32 (dd, J = 8.0 Hz and J = 8.4 Hz, H-4), 3.41 (dd,
J = 4.0 Hz and J = 3.2 Hz, H-2), 3.64 (s, H-10), 3.69–3.76 (m, H-3,
H-5, H-6), 3.79–3.84 (m, H-50), 3.96–4.08 (m, H-40), 4.14–4.19 (m,
H-60), 4.40 (d, J = 12, H-30), 5.37 (d, J = 2.8, H-1); 13C NMR
(100 MHz, CD3OD) d(ppm): 14.5, 23.4, 25.7, 30.0, 32.4, 34.1 (alkyl),
62.2 (C-6), 63.1 (C-10), 66.6 (C-60), 71.0 (C-4), 72.9 (C-2), 74.1 (C-3),
74.5 (C-5), 76.5 (C-40), 78.7 (C-30), 80.6 (C-50), 93.3 (C-1), 105.1 (C-
20), 175.4 (C@O).
6-O-Lauroylsucrose. 1H NMR (CD3OD, 400 MHz) d(ppm): 0.89 (t,
J = 5.0 Hz, 3H), 1.28 (s, 16H), 1.60–1.64 (m, 2H), 2.39 (t, J = 6.8 Hz,
2H), 3.31 (dd, J = 8.4 Hz and J = 8.8 Hz, H-4) 3.38 (dd, J = 5.2 Hz
and J = 4.0 Hz, H-2), 3.55–3.66 (m, H-10), 3.72 (dd, J = 7.6 Hz, 3-H),
3.79–3.85 (m, H-60), 3.91–3.96 (m, H-50), 3.99 (t, J = 8.4 Hz, 40-H),
4.01–4.09 (m, H-5), 4.16 (d, J = 6.4 Hz, H-30), 4.42 (dd, J = 12, H-
6a), 4.61 (dd, J = 12, H-6b), 5.38 (d, J = 3.6, H-1); 13C NMR
(100 MHz, CD3OD) d(ppm): 14.5, 23.6, 25.9, 30.1, 30.4, 30.6, 30.7,
33.1, 34.8 (alkyl), 63.5 (C-10), 63.9 (C-60), 64.6 (C-6), 71.4 (C-4),
71.7 (C-2), 73.0 (C-5), 74.3 (C-3), 75.5 (C-40), 78.9 (C-30), 83.6 (C-
50), 92.4 (C-1), 104.9 (C-20), 175.1 (C@O).
60-O-Lauroylsucrose. 1H NMR (400 MHz, CD3OD) d(ppm): 0.89 (t,
J = 5.0 Hz, 3H), 1.28 (s, 16H), 1.60–1.64 (m, 2H), 2.39 (t, J = 6.8 Hz,
2H), 3.30 (dd, J = 8.0 Hz and J = 8.4 Hz, H-4), 3.41 (dd, J = 5.2 Hz and
J = 4.0 Hz, H-2), 3.64 (s, H-10), 3.69–3.76 (m, H-3, H-5, H-6), 3.79–
3.84 (m, H-50), 3.96–4.08 (m, H-40), 4.14–4.19 (m, H-60), 4.40 (d,
J = 12, H-30), 5.37 (d, J = 2.8, H-1); 13C NMR (100 MHz, CD3OD)
d(ppm): 14.5, 23.6, 25.9, 30.1, 30.4, 30.6, 30.7, 33.1, 34.8 (alkyl),

354
D. Huang et al. / Ultrasonics Sonochemistry 17 (2010) 352–355
62.5 (C-6), 64.0 (C-10), 66.6 (C-60), 71.2 (C-4), 73.0 (C-2), 74.1 (C-3),
74.5 (C-5), 76.5 (C-40), 78.9 (C-30), 80.6 (C-50), 93.2 (C-1), 105.2 (C-
20), 175.2 (C@O).
Initially, esterification of sucrose was performed using 10 mmol
sucrose and 5 mmol ethyl caprylate with anhydrous disodium
hydrogen phosphate (Na2HPO4), potassium carbonate (K2CO3)
and K2CO3 + PEG-400, respectively as catalyst at different reduced
pressures. The results are summarized in Table 1. K2CO3 was found
to be the best catalyst with regard to yield and catalytic activity for
the transesterification of sucrose and ethyl caprylate, and the best
yield was obtained when the quantity of catalyst was 13% (mol/
mol) to ethyl caprylate (Table 1, entry 7).
Furthermore, the influence of the molar ratio of sucrose to ethyl
caprylate, reaction time and temperatures were analyzed in the
presence of the optimized anhydrous catalyst K2CO3 (13% mmol).
The results are summarized in Table 2.
6-O-Myristoylsucrose. 1H NMR (400 MHz, CD3OD) d(ppm): 0.90
(t, J = 4.8 Hz, 3H), 1.29 (s, 20H), 1.61–1.64 (m, 2H), 2.29 (t,
J = 7.2 Hz, 2H), 3.32 (dd, J = 8.0 Hz and J = 8.4 Hz, H-4) 3.41 (dd,
J = 4.0 Hz and J = 3.2 Hz, H-2), 3.57–3.64 (m, H-10), 3.72 (dd,
J = 8.8 Hz, H-3), 3.78–3.84 (m, H-60), 3.91–3.96 (m, H-50), 3.99 (t,
J = 8.4 Hz, H-40), 4.03–4.10 (m, H-5), 4.16 (d, J = 6.0 Hz, H-30), 4.40
(dd, J = 12, H-6a), 4.60 (dd, J = 12, H-6b), 5.37 (d, J = 2.8, H-1); 13C
NMR (100 MHz, CD3OD) d(ppm): 14.5, 23.5, 26.0, 30.1, 30.5, 30.6,
30.8, 33.1, 34.8 (alkyl), 63.6 (C-10), 64.0 (C-60), 64.6 (C-6), 71.5 (C-
4), 71.8 (C-2), 73.0 (C-5), 74.4 (C-3), 75.7 (C-40), 79.1 (C-30), 83.7
(C-50), 92.4 (C-1), 105.0 (C-20), 175.1 (C@O).
These results show that as molar ratio was increased from 1:1
to 2:1, the reaction yield increased accordingly, but when the mo-
lar ratio was increased to 2.5:1 the yield decreased gradually. It
was also observed that the yield of reaction increased from 21.5%
to 74.8% when temperature rose from 50 °C to 70 °C, but decreased
60-O-Myristoylsucrose. 1H NMR (400 MHz, CD3OD) d(ppm): 0.90
(t, J = 4.8 Hz, 3H), 1.29 (s, 20H), 1.61–1.64 (m, 2H), 2.29 (t,
J = 7.2 Hz, 2H), 3.32 (dd, J = 8.0 Hz and J = 8.4 Hz, H-4), 3.41 (dd,
J = 4.0 Hz and J = 3.2 Hz, H-2), 3.64 (s, H-10), 3.69–3.76 (m, H-3,
H-5, H-6), 3.79–3.84 (m, H-50), 3.96–4.08 (m, H-40), 4.14–4.19 (m,
H-60), 4.40 (d, J = 12, H-30), 5.37 (d, J = 2.8, H-1); 13C NMR
(100 MHz, CD3OD) d(ppm): 14.5, 23.5, 26.0, 30.1, 30.5, 30.6, 30.8,
33.1, 34.8 (alkyl), 62.2 (C-6), 63.3 (C-10), 66.6 (C-60), 71.0 (C-4),
72.9 (C-2), 74.1 (C-3), 74.6 (C-5), 76.5 (C-40), 78.7 (C-30), 80.6 (C-
50), 93.3 (C-1), 105.1 (C-20), 175.4 (C@O).
Table 1
The choice of catalysts.a
Entry
Catalyst
Mol (%)b
Pressure (kPa)
Time
Yield (%)
1
2
3
4
5
6
7
8
None
0
200
200
10
8
10
13
16
20
10
10
11
100
11
100
11
11
11
11
11
5
4
3
2
2
2
2
2
0
0
2
10.5
63.6
67.7
74.8
68.1
60.4
0
6-O-Palmitoylsucrose. 1H NMR (400 MHz, CD3OD) d(ppm): 0.91
(t, J = 4.8 Hz, 3H), 1.32 (s, 24H), 1.61–1.64 (m, 2H), 2.29 (t,
J = 7.2 Hz, 2H), 3.33 (dd, J = 8.4 Hz and J = 8.8 Hz, H-4) 3.40 (dd,
J = 4.4 Hz and J = 3.6 Hz, H-2), 3.58–3.65 (m, H-10), 3.72 (dd,
J = 8.4 Hz, H-3), 3.78–3.84 (m, H-60), 3.91–3.95 (m, H-50), 3.98 (t,
J = 8.4 Hz, H-40), 4.03–4.11 (m, H-5), 4.16 (d, J = 6.0 Hz, H-30), 4.40
(dd, J = 12, H-6a), 4.60 (dd, J = 12, H-6b), 5.37 (d, J = 3.2, H-1); 13C
NMR (100 MHz, CD3OD) d(ppm): 14.5, 23.5, 26.0, 30.1, 30.5, 30.6,
30.8, 33.1, 34.8 (alkyl), 63.6 (C-10), 64.0 (C-60), 64.6 (C-6), 71.5 (C-
4), 71.8 (C-2), 73.0 (C-5), 74.4 (C-3), 75.7 (C-40), 79.1 (C-30), 83.7
(C-50), 92.4 (C-1), 105.0 (C-20), 175.1 (C@O).
NaH2PO4
NaH2PO4
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3 + PEG-400
K2CO3 + PEG-400
9
10
11
2
3
2.5
100
11
10.1
a
Reactions were carried out with 10 mmol sucrose and 5 mmol ethyl caprylate in
6 mL DMSO at entries 1–9, solution-free at entries 10 and 11 at 70 °C.
b
The quantity of catalyst was mole percentage to ethyl caprylate in reactions 2–9
60-O-Palmitoylsucrose. 1H NMR (400 MHz, CD3OD) d(ppm): 0.91
(t, J = 4.8 Hz, 3H), 1.32 (s, 24H), 1.61–1.64 (m, 2H), 2.29 (t,
J = 7.2 Hz, 2H), 3.32 (dd, J = 8.0 Hz and J = 8.4 Hz, H-4), 3.41 (dd,
J = 4.4 Hz and J = 3.6 Hz, H-2), 3.64 (s, H-10), 3.68–3.76 (m, H-3,
H-5, H-6), 3.79–3.85 (m, H-50), 3.96–4.09 (m, H-40), 4.14–4.18 (m,
H-60), 4.40 (d, J = 12, H-30), 5.37 (d, J = 3.2, H-1); 13C NMR
(100 MHz, CD3OD) d(ppm): 14.5, 23.5, 26.0, 30.1, 30.5, 30.6, 30.8,
33.1, 34.8 (alkyl), 62.3 (C-6), 63.3 (C-10), 66.6 (C-60), 71.0 (C-4),
72.9 (C-2), 74.1 (C-3), 74.6 (C-5), 76.5 (C-40), 78.7 (C-30), 80.6 (C-
50), 93.3 (C-1), 105.1 (C-20), 175.4 (C@O).
and mixture of 10% mmol anhydrous K2CO3 and 3 mL PEG-400 in reactions 10 and
11.
Table 2
The effect of the molar ratio of reactant, temperature and time.*
Entry
Sucrose/ethyl caprylate (mol/mol)
T (°C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
1:1
1.5:1
2:1
2:1
2:1
2:1
2:1
2:1
2:1
2:1
2:1
2.5:1
70
70
50
60
70
70
70
70
70
70
80
70
2
2
2
2
0.5
1
1.5
2
2.5
3
2
55.3
63.1
21.5
49.3
30.1
37.2
56.1
74.8
67.3
63.8
64.8
70.3
3. Results and discussion
9
3.1. The choice of esterification conditions under ultrasonic irradiation
10
11
12
2
Experimental conditions that affect the yield including the type
and concentration of the catalyst, reaction time and system pres-
sure were investigated with ethyl caprylate as the acylating agent
(Scheme 1).
* Reaction was carried out using 13% mmol anhydrous K2CO3 to ethyl caprylate as
catalyst, with dimethylsulfoxide (DMSO) as solvent, in system pressure of 11 kPa
under ultrasonic irradiation.
R1O
O
HO
OH
OH
O
O
OH
OH
O
OEt
O
R
+ diester
cat, solvent
HO
HO
OH
OH
O
O
U. S., T, P
OR2
HO
OH
HO
OH
OH
a: R1=RCO-, R2=H
R: CH3(CH2)nCH2— n= 5, 9, 11, 13
b: R1=H,
R2=RCO-
Scheme 1. Reaction of sucrose with fatty acid esters.

D. Huang et al. / Ultrasonics Sonochemistry 17 (2010) 352–355
355
Table 3
The synthesis of sucrose esters under ultrasonic irradiation.a
O
R1O
HO
OH
OH
O
O
OH
OH
OEt
R
O
O
+ diester
HO
HO
OH
K2CO3, DMSO
U.S., 70°C, 11Kpa
OH
O
O
OR2
OH
HO
HO
OH
OH
a: R1=RCO-, R2=H
b: R1=H, R2=RCO-
R: CH3(CH2)nCH2— n= 5, 9, 11, 13
Entry
Acyl donor
Yieldb (%)
Monoesterc (%) (6-O:60-O)d
1
2
3
4
Ethyl caprylate
Ethyl laurate
Ethyl myristate
Ethyl palmitate
75
78
74
73
92 (2.5:1)
95 (2.7:1)
94 (2.1:1)
92 (2.2:1)
a
b
c
Experiment conditions: 10 mmol sucrose, 5 mmol ethyl fatty acid ester, 11% anhydrous K2CO3, 70 °C, 11 kPa, 6 mL DMSO.
Based on ethyl fatty acid ester as limiting reagent and assuming that product is entirely the monoester.
Referred to the percentage of the monoester fraction, determined by flash column chromatography over silica gel.
Referred to the ratio of 6-O-monoester and 60-O-monoester, as identified by HPLC.
d
when temperature exceeded 70 °C. The reason is that while a high-
er temperature accelerated the reaction, too high of a temperature
caused the caramelization and degradation of sucrose. The obser-
vation also showed that the yield of reaction increased with pro-
longing reaction time within 2 h, but decreased above 2 h. The
best conditions of the reaction were as follows: the molar ratio su-
crose/ethyl caprylate was 2:1, reaction temperature was 70 °C,
reaction time was 2 h, the quantity of catalyst accounted for ethyl
caprylate was 13% mol, the reaction pressure was 11 kPa under
ultrasonic irradiation and the yield was 75% (Table 2, entry 8).
irradiation. Presently the mechanism of the selective monoacyla-
tion of sucrose is still unclear, and further study is in progress.
4. Conclusion
In conclusion, we have found an efficient and convenient proce-
dure for the preparation of sucrose monoesters via sucrose with
fatty acid ethyl ester under ultrasound irradiation. The method
not only shortened the reaction time, reduced the quantity of cat-
alyst and improved quality of product, but also led to a higher
selectivity in the reaction.
3.2. The synthesis of sucrose esters under ultrasonic irradiation
Acknowledgements
After establishing the best reaction conditions (on the basis of
higher conversion to monoester in the shortest time), the transe-
sterification was performed with ethyl caprylate (C8), laurate
(C12), myristate (C14) and palmitate(C16), and sucrose mono-
and diesters were isolated by flash column chromatography over
silica gel. Monoesters were further purified by HPLC, and monoes-
ters were analyzed by electrospray ionization-mass spectrometry
(ESI-MS) and nuclear magnetic resonance. The percentage of each
monoester was identified by HPLC. The results are summarized
in Table 3.
It is easy to see that the reaction of sucrose with ethyl fatty acid
esters was carried out in good yields under ultrasound irradiation.
Although there is similar reactivity between the eight hydroxyl
groups in sucrose and the existence of intramolecular migration
processes can occur in reaction, the products were substantially
monoesters, with a higher monoester/diester ratio and purity.
Identification of each monoester was based on the chemical shifts
The project was supported by the Open Project Program of Key
Laboratory of Eco-Textiles (Jiangnan University), Ministry of Edu-
cation, China (No. KLET0901) and Natural Science Foundation of
Jiangsu Province (KB2005043), China.
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a position next to the acyl-
ated hydroxyl group (ca. +0.5), and, in 13C NMR, the carbon atom
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